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The current clinical landscape of personalized cancer vaccines

  • Hajer Fritah
    Affiliations
    Department of Oncology, Centre Hospitalier Universitaire Vaudois (CHUV), Ludwig Institute for Cancer Research, University of Lausanne, CH-1011 Lausanne, Switzerland
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  • Raphaël Rovelli
    Affiliations
    Department of Oncology, Centre Hospitalier Universitaire Vaudois (CHUV), Ludwig Institute for Cancer Research, University of Lausanne, CH-1011 Lausanne, Switzerland
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  • Cheryl Lai-Lai Chiang
    Correspondence
    Corresponding authors at: Department of Oncology, Centre Hospitalier Universitaire Vaudois (CHUV), Ludwig Institute for Cancer Research, University of Lausanne, CH-1011 Lausanne, Switzerland (L.E. Kandalaft).
    Affiliations
    Department of Oncology, Centre Hospitalier Universitaire Vaudois (CHUV), Ludwig Institute for Cancer Research, University of Lausanne, CH-1011 Lausanne, Switzerland
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  • Lana E. Kandalaft
    Correspondence
    Corresponding authors at: Department of Oncology, Centre Hospitalier Universitaire Vaudois (CHUV), Ludwig Institute for Cancer Research, University of Lausanne, CH-1011 Lausanne, Switzerland (L.E. Kandalaft).
    Affiliations
    Department of Oncology, Centre Hospitalier Universitaire Vaudois (CHUV), Ludwig Institute for Cancer Research, University of Lausanne, CH-1011 Lausanne, Switzerland

    Center of Experimental Therapeutics, Department of Oncology, CHUV, CH-1011 Lausanne, Switzerland
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Open AccessPublished:March 24, 2022DOI:https://doi.org/10.1016/j.ctrv.2022.102383

      Highlights

      • Personalized cancer vaccines can trigger a broad-based antitumor response and long-term immunological memory.
      • Use of autologous antigens can elicit antitumor immunity that is beneficial and relevant to individual patients.
      • Preclinical tumor animal models are useful tools for investigating and improving cancer vaccination strategies.

      Abstract

      Due to the intrinsic genetic instability of tumor cells, aberrant and novel tumor antigens can be expressed and serve as potential targets for cancer immunotherapy. This intrinsic feature can be exploited by cancer immunotherapy, particularly with cancer vaccination. Personalized cancer vaccination strategy can be a potent approach to trigger a broad-based antitumor response that is both beneficial and relevant to individual cancer patients. Also, cancer vaccination strategy can be designed to help elicit immunological memory for long-lasting tumor control. In this review, we describe the different types of personalized cancer vaccines and summarize the completed and ongoing cancer vaccination clinical trials in the last 10 years (database from www.clinicaltrials.gov). We also discuss the pros and cons of using different tumor animal models, i.e. syngeneic models, patient-derived xenografts models and genetically engineered mouse models, as tools for investigating cancer vaccination strategies. Finally, we describe preclinical studies that seek to test new emerging vaccination strategies as well as improving existing methods.

      Keywords

      Introduction

      The earliest known form of immunotherapy was performed by the American surgeon William Coley in 1890 who treated cancer patients with streptococcal bacterial cultures (dubbed “Coley’s toxin”) and observed tumor regression in some cases [
      • Parish C.R.
      Cancer immunotherapy: the past, the present and the future.
      ]. Since then, tremendous amount of work has demonstrated that the human immune system can indeed prevent, control and eradicate cancer cells [
      • Parish C.R.
      Cancer immunotherapy: the past, the present and the future.
      ]. Cancer immunotherapy can be classified into two main categories, i.e. passive or active, based on their mode of actions. Passive immunotherapy seeks to enhance existing antitumor responses with therapeutic agents such as targeted antibodies, lymphocytes (e.g. adoptive cell transfer [ACT] of ex vivo propagated tumour-infiltrating lymphocytes or engineered chimeric antigen receptor [CAR] T cells), cytokines, adjuvants and immune checkpoint inhibitors [

      Corthay A. Does the immune system naturally protect against cancer? Front Immunol 2014;5:197. doi: 10.3389/fimmu.2014.00197. eCollection 2014.

      ]. Such therapies have shown clinical efficacies, demonstrated by patients with advanced cancer experiencing durable tumor regression following ACT [
      • Thomas L.
      • Lawrence H.
      Cellular and humoral aspects of the hypersensitive states.
      ]. Immune checkpoint inhibition of T-lymphocyte-associated antigen-4 (CTLA-4), programmed cell death-1 (PD-1), and their ligands (B7 and PDL1/2) on antigen-presenting cells (APCs), stromal and tumor cells [
      • Schreiber R.D.
      • Old L.J.
      • Smyth M.J.
      Cancer immunoediting: integrating immunity’s roles in cancer suppression and promotion.
      ,
      • Dunn G.P.
      • Old L.J.
      • Schreiber R.D.
      The three Es of cancer immunoediting.
      ], has been particularly effective in different cancers including melanoma and lung cancers. Active immunotherapy with cancer vaccines, on the other hand, seeks to stimulate and/or restore the ability of the immune system to recognise and attack cancer cells, and to establish immunological memory for sustained tumor suppression [

      Corthay A. Does the immune system naturally protect against cancer? Front Immunol 2014;5:197. doi: 10.3389/fimmu.2014.00197. eCollection 2014.

      ,
      • Thomas L.
      • Lawrence H.
      Cellular and humoral aspects of the hypersensitive states.
      ]. Different types of therapeutic cancer vaccines have been evaluated in clinical trials and demonstrated some clinical benefits. The effectiveness of therapeutic cancer vaccines can be influenced by several factors including the choice of the target antigen(s), use of adjuvants and the ability of the cancer vaccine to elicit antitumor T cell responses in a highly immunosuppressive tumor microenvironment [
      • Shemesh C.S.
      • Hsu J.C.
      • Hosseini I.
      • Shen B.-Q.
      • Rotte A.
      • Twomey P.
      • et al.
      Personalized Cancer Vaccines: Clinical Landscape, Challenges, and Opportunities.
      ,
      • Castle J.C.
      • Uduman M.
      • Pabla S.
      • Stein R.B.
      • Buell J.S.
      Mutation-Derived Neoantigens for Cancer Immunotherapy.
      ].
      Personalized cancer vaccination is a promising strategy for eliciting a diversified antitumor T cell repertoire that is beneficial and relevant for individual cancer patients. As tumor cells exhibit extensive genetic instability, they could express a variety of abnormal proteins that have limited (e.g. tumour-associated antigens [TAAs]) or no expression (e.g. de novo mutated tumor neoantigens) on normal cells. Such tumor-derived antigens can serve as potential targets for cancer vaccination [

      Corthay A. Does the immune system naturally protect against cancer? Front Immunol 2014;5:197. doi: 10.3389/fimmu.2014.00197. eCollection 2014.

      ]. Personalized cancer vaccines can be prepared from a variety of antigen sources, e.g. from resected tumors, RNA or DNA obtained from autologous tumor cells and autologous tumor neoantigens in the form of synthetic peptides or proteins (Fig. 1). Autologous DCs can also be used to create personalized vaccines (Fig. 2). Although the overall clinical efficacy of therapeutic cancer vaccines is still limited as compared to that of immune-checkpoint inhibition or T cell therapies [
      • Dunn G.P.
      • Old L.J.
      • Schreiber R.D.
      The three Es of cancer immunoediting.
      ], continuous efforts are being made in improving cancer vaccine formulations and preparations. Well-designed personalized cancer vaccines have the potential of engaging both the innate and adaptive immunities to elicit long-lasting immunological memory that is capable of controlling tumor and preventing relapse [
      • Parish C.R.
      Cancer immunotherapy: the past, the present and the future.
      ]. In this review, we describe the different types of personalized cancer vaccines and summarize the clinical trials that evaluated personalized cancer vaccines in the last 10 years using the keywords cancer, vaccine and personalized (www.clinicaltrials.gov) [Table 1a, Table 1b and Table 2a, Table 2b]. Finally, we discuss the use of different tumor animal models as tools for investigating cancer vaccination strategies. As tumor neoantigen vaccines are proving to be a potent strategy, we summarize the different tumor models that are currently being utilized for neoantigen investigation (Table 3).
      Figure thumbnail gr1
      Fig. 1Different types of personalized cancer vaccines can be prepared from autologous tumor cells and tumor-derived cellular products due to the expression of unique (i.e. neoantigens) and shared (i.e. tumor-associated antigens) on individual patient’s tumors. Personalized vaccines created from autologous antigen sources can help to elicit antitumor responses that are relevant and beneficial to the patients. Examples of autologous antigen sources include whole tumor cells and lysates, exosomes derived from tumor or dendritic cells, endogenous cellular products such as heat-shock proteins and nucleic acids (DNA and RNA). The immunogenicity of tumor antigens could be enhance with adjuvant such as Bacillus Calmette-Guérin (BCG). Autologous tumor cells could also be genetically modified to express immunostimulatory molecules such as granulocyte-macrophage colony-stimulating factor (GM-CSF).
      Figure thumbnail gr2
      Fig. 2Personalized and well-designed dendritic cell (DC)-based cancer vaccines has the ability to engage both the innate and adaptive immunities, as well as developing a long-lasting immunological memory against tumor relapse. Autologous DCs can be pulsed with numerous types of tumor antigens including tumor mRNA, neoantigen or TAA-derived synthetic peptides, as well as whole tumor lysates. DCs can also be fused with autologous tumor cells to create DC-tumor fusion vaccine to ensure efficient presentation of tumor antigens by DCs to T cells.
      Table 1aOngoing personalized cancer vaccine clinical trials conducted by research institutes and hospitals from year 2010–2021 (www.clinicaltrials.gov).
      Study (title, clinical trial number and phase)Cancer type(s)Treatment(s)Study evaluations
      Personalized Peptide Vaccine in Treating Patients With Advanced Pancreatic Cancer or Colorectal Cancer

      (NCT02600949, Phase I)

      Start date: September 2015
      Advanced colorectal adenocarcinoma and pancreatic ductal adenocarcinomaSubcutaneous injection of personalized synthetic tumor-associated peptide vaccine in combination with pembrolizumab and topical application of imiquimodAssess incidence of toxicity, progression free survival (PFS), response rate (RR), change in tumor biomarker CA19-9, CEA or circulating free DNA (cfDNA) mutation, and overall survival (OS)
      Personalized and Cell-based Antitumor Immunization MVX-ONCO-1 in Advanced HNSCC

      (NCT02999646, interventional)

      Start date: December 2016
      Head and Neck Squamous Cell Carcinoma (HNSCC)Subcutaneous vaccination with MVX-ONCO-1 that consists of lethally irradiated autologous tumor cells as a source of antigen, and encapsulated allogeneic cell line (MVX-1) that is genetically modified to secrete GM-CSFEvaluate OS at 26 week, time to subsequent therapy, duration of response, adverse events (AEs), PFS and OS
      Personalized Tumor Vaccine Strategy and PD-1 Blockade in Patients With Follicular Lymphoma

      (NCT03121677, Phase I)

      Start date: April 2017
      Follicular LymphomaSubcutaneous injection of personalized peptide vaccine in combination with Poly ICLC, and intravenous administration of 240 mg nivolumab. Patients who demonstrate progression on this regimen will be treated with an anti-CD20 monoclonal antibody such as rituximabAssess feasibility and safety of the peptide vaccine in combination with nivolumab with or without anti-CD20 monoclonal antibody therapy. Assess duration of response. Determine PFS and OS
      Personalized Immunotherapy in Adults With Advanced Cancers

      (NCT03568058, Phase Ib)

      Start date: June 2018
      Incurable solid tumorVaccine will be constructed for each subject that express multiple candidate tumor-derived neoantigens, and concomitant intravenous infusion of 200 mg pembrolizumab every 3 weeks.Determine the number of participants with treatment-related AEs, the overall response, PFS and OS
      Clinical Study of Personalized mRNA Vaccine Encoding Neoantigen in Patients With Advanced Digestive System Neoplasms

      (NCT03468244, Phase I)

      Start date: June 2018
      Advanced esophageal squamous carcinoma, gastric adenocarcinoma, pancreatic adenocarcinoma, colorectal adenocarcinomaSubcutaneous injection of personalized mRNA tumor vaccine encoding patient’s neoantigensDetermine the safety, tolerability and efficacy of the personalized mRNA tumor vaccine.
      Clinical Trial on Personalized Neoantigen Vaccine for Pancreatic Tumor

      (NCT03558945, Phase I)

      Start date: June 2018
      Pancreatic cancerAfter surgery and at least 1 cycle of chemotherapy patients will receive subcutaneous injection of Personalized neoantigen vaccine composed of 0.3 mg peptide, plus 0.5 mg Poly ICLCAssess AEs and safety of the study. Evaluate immune response to neoantigens using ELISPOT
      Testing the Addition of an Individualized Vaccine to Nab-Paclitaxel, Durvalumab and Tremelimumab and Chemotherapy in Patients With Metastatic Triple Negative Breast Cancer

      (NCT03606967, Phase II)

      Start date: July 2018
      Stage IV breast cancer, invasive breast carcinoma, metastatic triple-negative breast carcinoma,1. Patients receive either intravenous injection of Nab-Paclitaxel + Durvalumab (MEDI4736) + Tremelimumab, or 2. receive intravenous injection of Nab-paclitaxel + durvalumab (MEDI4736) + tremelimumab and subcutaneous injection of tumor-specific mutant antigen-based synthetic long peptide vaccine together with Poly ICLC as adjuvantEvaluate PFS, incidences of AEs, clinical RR, OS and immune response
      Personalized Vaccine in Treating Patients With Smoldering Multiple Myeloma (NCT03631043, Phase I)

      Start date: August 2018
      Multiple myeloma6 cycles of subcutaneous injection of vaccine derived from patient’s blood and bone marrow biopsies plus LenalidomideAssess the feasibility, intensity and longevity of antigen-specific T-cell mediated responses. Evaulate time to progression, clinical benefit rate and OS
      Personalized Vaccine Generated by Autologous Dendritic Cells Pulsed With Autologous Whole Tumor Cell Lysate Treat Advanced Solid Tumor Patients With High Tumor Mutation Burden

      (NCT03671720, early Phase I)

      Start date: September 2018
      Advanced or metastatic solid tumors.Intranodal injection of personalized autologous dendritic cells loaded with autologous whole tumor cell lysate in combination with oral cyclophosphamide (50 mg)Evaluate treatment-related AEs, changes in immune-response specific patient-reported outcomes(irPRO) and objective response rate (ORR)
      Personalized Neo-antigen Vaccine in Advanced Solid Tumors (NeoPepVac) (NCT03715985, Phase I-II)

      Start date: October 2018
      Malignant melanoma, metastatic non-small cell lung cancer (NSCLC), metastatic urothelial carcinomaPersonalized neoantigen vaccine containing up to 15 peptides derived from somatic mutation of the individual patient with CAF09b as adjuvant. The neoantigen vaccine will be administered in combination with an approved anti-PD-1 or anti-PD-L1 antibodyDetermine tolerability and safety of the personalized neo-antigen vaccine. Evaluate the immunological impact of the treatment
      NeoVax With Nivolumab in Patients With Ovarian Cancer

      (NCT04024878, Phase I)

      Start date: July 2019
      Ovarian Cancer5 doses of NeoVax will be administered to the patient in combination with intravenous infusion of Nivolumab. NeoVax consists of up to 20 peptides encoded by mutations from patient’s tumors with Poly ICLC as adjuvant.Determine overall incidence of treatment-related Aes, the rates of autoimmune effects, ORR and OS
      A Personalized NeoAntigen Cancer Vaccine Combined With Anti-PD-1 in Melanoma (NCT04072900, Phase I)

      Start date: August 2019
      MelanomaAdministration of a personalized neoantigen cancer vaccine Neo-Vac-Mn (3 mg of neoantigen peptides), 3 mg/kg of Toripalimab, 3 μg/kg of recombinant human GM-CSF, and topical application on injection site of Imiquimod 5% topical creamAssess AEs, complete remission rate, partial response and progressive disease. Monitor cellular immune response
      Breast Cancer Neoantigen Vaccination With Autologous Dendritic Cells

      (NCT04105582, Phase I)

      Start date: September 2019
      Triple-negative breast cancer (TNBC)Patients that finished their conventional treatment (chemotherapy and/or surgery) will receive autologous dendritic cells pulsed with synthetic long peptides encoded by patient’s tumor mutationsAssess AEs and safety of the study. Evaluate neoantigen immunogenicity
      Personalized DC Vaccine for Postoperative Cancer

      (NCT04147078, Phase I)

      Start date: October 2019
      Gastric cancer, hepatocellular carcinoma, NSCLC, colorectal cancerPatients receive between 3 and 5 subcutaneous doses of autologous dendritic cells primed with personalized tumor neoantigensDetermine tolerability and safety of the personalized neo-antigen vaccine, disease-free survival and OS
      Personalized Vaccine With SOC Chemo Followed by Nivo in Pancreatic Cancer (NCT04627246, Phase I)

      Start date: November 2020
      Pancreatic AdenocarcinomaSubcutanous injection of autologous dendritic cell loaded with personalized peptides in combination with intravenous administration of gemcitabine and capecitabine chemotherapy (8 cycles). Patients also receive 3 weeks after the last chemotherapy cycle 240 mg of nivolumabAssess feasibility and AEs of the regimen. Perform gene analysis of immunological response. Evaluation of tumor markers CA19-9 or CEA kinetics, PFS and OS
      Optimizing Cellular and Humoral Immunity by Vaccinating With PCV13 Before and After CAR-T Therapy

      (NCT04745559, Phase II)

      Start date: February 2021
      Diffuse large-cell lymphoma, primary mediastinal large B-cell lymphoma (PMBCL), Transformed follicular lymphoma (TFL), and high-grade B-cell lymphoma (HGBCL)3 times injection of intramuscular of 5 ml Pneumococcal conjugate vaccine (PCV13) prior and after infusion of personalized CD19-targeted CAR T cellsDetermine humoral RR to PCV13 vaccine. Evaluate the RR of CD19-targeted CAR T therapy when combined with PCV13 vaccination. Determine PFS and OS
      Table 1bCompleted and terminated personalized cancer vaccine clinical trials conducted by research institutes and hospitals from year 2010–2021 (www.clinicaltrials.gov).
      Study (title, clinical trial number and phase)Cancer type(s)Treatment(s)Study evaluations and results if available
      A Phase I Study With a Personalized NeoAntigen Cancer Vaccine in Melanoma (NCT01970358, Phase I-II)

      Start date: October 2013
      MelanomaAdministration of NeoVax composed of personalized neoantigen peptides and Poly ICLC as adjuvantAssess AEs, cellular immune responses following administration of NeoVax, and number of participants alive without progression at two years following treatment
      Safety and Immunogenicity of a Personalized Polyepitope DNA Vaccine Strategy in Breast Cancer Patients With Persistent Triple-Negative Disease Following Neoadjuvant Chemotherapy

      (NCT02348320, Phase I)

      Start date: January 2015
      Triple Negative Breast Cancer3 cycles of Intramuscular administration (with TriGrid electroporation device) of 4 mg of a personalized polyepitope DNA plasmid vaccine.Safety and immunogenicity of the personalized polyepitope DNA vaccine strategy
      Neoepitope-based Personalized Vaccine Approach in Patients With Newly Diagnosed Glioblastoma

      (NCT02510950, Phase I)

      Start date: July 2015
      Multiforme glioblastoma and grade IV astrocytomaAministration of long neoantigen peptide vaccine and Poly ICLC as adjuvant during the cycles of chemotherapy (temozolomide)Assess safety and tolerability of the personalized neoantigen peptide vaccine. Evaluate the ability to identify patient tumor-derived candidate neoantigens and generate a tumor-specific vaccine. Determine progression free survival (PFS) and overall survival (OS)
      (Safety and Immunogenicity of Personalized Genomic Vaccine to Treat Malignancies (NCT02721043, Phase I)

      Start date: March 2016
      1. Oral, oropharyngeal, hypopharyngeal or laryngeal squamous cell carcinoma; 2. Non-small cell carcinoma of the bronchus and/or lung; 3. Ductal or lobular carcinoma of the breast; 4. Serous and epithelial carcinomas of the ovary, fallopian tube, or other uterine adnexa; 5.Urothelial cell carcinoma of renal pelvis, ureter, or bladder; 6.Cutaneous squamous cell carcinomaAdministration of Personalized Genome Vaccine 001 (PVG001) constituted of personalized peptide vaccine (100mcg per peptide per dose) based on a patient's own tumor sequence and 1.4 mg of PolyI CLC as adjuvantSafety and dose-limiting toxicities
      Messenger RNA (mRNA)-Based, Personalized Cancer Vaccine Against Neoantigens Expressed by the Autologous Cancer

      (NCT03480152, Phase I-II)

      Start date: March 2019
      Metastatic melanoma, gastrointestinal, genitourinary cancerPredicted mutations of driver genes were concatenated into a single mRNA construct and administered intramuscularly to patients at 2 weeks interval (4 cycles).Evaluate the safety and immunogenicity of the mRNA-based vaccine.

      Results: Vaccine was safe and elicited mutation-specific T cell responses against predicted neoepitopes not detected before vaccination. T cell receptors targeting KRASG12D mutation was isolated and verified. No objective clinical responses was observed in the 4 patients treated in the trial. Reference
      • Cafri G.
      • Gartner J.J.
      • Zaks T.
      • Hopson K.
      • Levin N.
      • Paria B.C.
      • et al.
      mRNA vaccine-induced neoantigen-specific T cell immunity in patients with gastrointestinal cancer.
      .
      Personalized Vaccine for Cancer Immunotherapy

      (NCT04879888, Phase I)

      Start date: May 2021
      Triple-negative breast cancer6 weekly doses of Intradermal vaccination with autologous dendritic cells pulsed with neoantigen peptides derived from patient’s own tumorEvaluation of number and severity of the adverse effects (AEs) in the vaccinated patients
      Table 2aOngoing clinical trials conducted by pharmaceutical companies that evaluate personalized cancer vaccines from year 2010–2021 (www.clinicaltrials.gov).
      Study (title, clinical trial number and phase)Cancer type(s)Treatment(s)Study evaluations
      Phase IIB TL + YCWP + DC in Melanoma

      (NCT02301611, Phase IIb)

      Start date: November 2014
      Melanoma3 monthly intradermal injection of patient’s dendritic cell (DC)-pulsed with autologous tumor lysate loaded into yeast cell wall particles. These particles are naturally and efficiently taken up by patient’s DCsDisease free survival assessment
      Personalized NeoAntigen Cancer Vaccine w RT Plus Pembrolizumab for Patients With Newly Diagnosed GBM (NCT02287428, Phase I)

      Start date: November 2014
      GlioblastomaPatients will first receive 6 weeks of standard radiation therapy. Then patients will receive NeoVax ± Pembrolizumab ± temozolomideAssess adverse events (AEs). Evaluate immune response via IFN-γ T cell response using ELISPOT, progression free survival (PFS) and overall survival (OS).
      NeoVax Plus Ipilimumab in Renal Cell Carcinoma (NCT02950766, Phase I)

      Start date: November 2016
      Renal cell carcinomaPatients will receive NeoVax (personalized neoantigen peptides plus polyICLC as adjuvant) in combination with ipilimumab after respective surgery to remove the primary kidney tumor.Assess the dose-limiting toxicity. Evaluate the immune response induced by the vaccine, especially IFN-γ T-cell responses against the neoepitopes. Determine the number of participants alive at 2 years.
      Safety and Immunogenicity of Personalized Genomic Vaccine and Tumor Treating Fields (TTFields) to Treat Glioblastoma (NCT03223103, Phase Ia-b)

      Start date: July 2017
      GlioblastomaAfter radiation and chemotherapy, patients receive a personalized mutation-derived tumor vaccine in conjunction with tumor-treating (TT) fields and maintenance of temozolomide. The vaccine is composed of several peptides based on each patient's own tumor sequence coadministered with Poly ICLC as adjuvant.Assess AEs and safety of the therapy. Evaluate PFS and OS.
      Atezolizumab Given in Combination With a Personalized Vaccine in Patients With Urothelial Cancer (NCT03359239, Phase I)

      Start date: December 2017
      Urothelial or bladder CancerAtezolizumab is infused intravenously (1200 mg) every 3 weeks in combination with personalized neoantigen vaccine PGV001 (composed of up to 10 synthetic peptides encoded by patient’s mutations). 1.4 mg of Poly ICLC is added as an adjuvantAssess the feasibility and safety of administration of the personalized neoantigen-based vaccine (PGV001) plus atezolizumab. Evaluate the objective response rate (ORR) and OS.
      Neoantigen DNA Vaccine in Combination With Nivolumab/Ipilimumab and PROSTVAC in Metastatic Hormone-Sensitive Prostate Cancer (NCT03532217, Phase I)

      Start date: May 2018
      Metastatic hormone-sensitive prostate cancerA month after the last chemotherapy, patients will receive intramuscular injection of a shared antigen DNA vaccine (PROSTVAC) in combination with intravenous administration of nivolumab and ipilimumab. Each DNA vaccine will be administred using the TriGrid electroporation deviceSafety and tolerability of the regimen. Interrogate immune response with tetramer staining, genomic studies and flow cytometry.
      Safety, Tolerability, Immunogenicity, and Antitumor Activity of GEN-009 Adjuvanted Vaccine (NCT03633110, Phase I-II)

      Start date: August 2018
      Cutaneous melanoma, non-small cell lung cancer (NSCLC), squamous cell carcinoma of the head and neck, urothelial carcinoma and renal cell carcinoma.Identify neoantigens using ATLAS™ (Antigen Lead Acquisition System) developed by Genocea. Then, subcutanous injection of GEN-009 vaccine (synthetic long peptides encoding patient’s private neoantigen) admix with Poly ICLC. Patients with no evidence of disease will receive only the GEN-009 vaccine. Patients with metastatic solid tumors will receive GEN-009 vaccine in combination with nivolumab or pembrolizumabDetermine incidence of treatment-related AEs, T cell responses and antitumor activity to GEN-009 adjuvanted vaccine.
      An Efficacy Study of Adjuvant Treatment With the Personalized Cancer Vaccine mRNA-4157 and Pembrolizumab in Participants With High-Risk Melanoma (KEYNOTE-942) [NCT03897881, Phase II]

      Start date: April 2019
      MelanomaPatients will receive up to 9 doses of mRNA-4157 (a messenger RNA-based personalized vaccine targeting 20 TAAs that are specifically expressed in the patient’s tumor) ± pembrolizumab infused intravenouslyAssess AEs, distant metastasis-free survival (DMFS) using radiological imaging and PFS.
      A Study of a Personalized Cancer Vaccine Targeting Shared Neoantigens (NCT03953235, Phase I)

      Start date: May 2019
      Microsatellite-stable colorectal cancer, NSCLC, pancreatic ductal adenocarcinoma, and solid tumor with disease progressionA shared neoantigen cancer vaccine prime and boost with nivolumab and ipilimumabEvaluate incidence of AEs and dose limiting toxicities. Measure the immune response to the neoantigens.
      Neoantigen-based Personalized DNA Vaccine in Patients With Newly Diagnosed, Unmethylated Glioblastoma (NCT04015700, Phase I)

      Start date: July 2019
      GlioblastomaVaccination with DNA plasmid vector expressing tumor-specific antigens and plasmid encoding IL-12 (INO-9012)Evaluate the safety, feasibility, and immunogenicity of the personalized neoantigen DNA vaccine.
      Phase I Study of Individualized Neoantigen Peptides in the Treatment of EGFR Mutant Non-small Cell Lung Cancer (NCT04397926, Phase I)

      Start date: May 2020
      NSCLCSubcutaneous injection of individualized neoantigen peptides vaccineSafety of the neoantigen vaccine treatment
      Clinical Study of Neoantigen Vaccine Combined With Targeted Drugs in the Treatment of Non-small Cell Lung Cancer (NCT04487093, Phase I)

      Start date: July 2020
      EGFR-mutant NSCLCSubcutaneous injection of individualized neoantigen vaccines at a dose of 200 µg per peptide once a week for 5 weeks combined with anti-angiogenesis drug therapy (EGFR-TKI)Evaluate the safety and immune response of the neoantigen vaccine treatment.
      Clinical Study of a Personalized Neoantigen Cancer Vaccine Combined With Anti-PD-1 and RFA in Patients With Solid Tumors (NCT04864379, Phase I)

      Start date: April 2021
      Advanced malignant solid tumorsRadiofrequency ablation and follow by intravenous injection of anti-PD-1 (200 mg), neoantigen peptides (iNeo-Vac-P01; 300mcg) and GM-CSF (40mcg).Safety, tolerability and immunogenicity of iNeo-Vac-P01 in combination with anti-PD-1 antibody and radiofrequency ablation
      Table 2bCompleted and terminated clinical trials conducted by pharmaceutical companies that evaluated personalized cancer vaccines from year 2010–2021 (www.clinicaltrials.gov).
      Study (title, clinical trial number and phase)Cancer type(s)Treatment(s)Study evaluations
      Trial to Compare the Routes of Administration of an Investigational, Personalized, Therapeutic Cancer Vaccine Oncophage (HSPPC-96) in Patients With Metastatic Renal Cell Carcinoma (NCT00082459, Phase II)

      Start date: May 2004
      Renal Cell Carcinoma (RCC)Kidney ablation by surgery, and follow by subcutaneous injection or intradermal injection of autologous heat-shock protein peptide complex-96 (HSPPC-96; an immunotherapeutic agent made from individual patient's tumor).Determine the safety of HSPPC-96 and the route of administration for a better response with the vaccine.
      Clinical Trial Studying a Personalized Cancer Vaccine in Patients With Non-metastatic Kidney Cancer

      (NCT00126178, Phase III)

      Start date: August 2005
      RCCInjections of autologous HSPPC-96Characterize the safety profile of HSPPC-96, and evaluate recurrence free survival and overall survival (OS).
      Phase I/II Study of a Therapeutic Cancer Vacccine Created In-situ in Patients With Refractory or Metastatic Cancer

      (NCT00861107, Phase I-II)

      Start date: March 2009
      Metastatic cancers that are refractory to standard of care therapies - breast, colorectal, non-small cell lung, ovarian, gynecological cancer, prostate, pancreatic, gastrointestinal cancer, melanoma, head or neck cancer, lymphoma, plasmacytoma.Minimally invasive percutaneous tumor cryoablation plus AlloStim (vaccine is composed of CD4 + memory Th1-like T-cells plus Dynabeads® ClinExVivo™ CD3/CD28) infusion in the ablated tumor region.Evaluation of drug-related toxicity and antitumor effects of AlloStim administration
      Safety and Tolerability Study of AlloVax(TM) in Patients With Metastatic or Recurrent Cancer of the Head and Neck

      (NCT01998542, Phase II)

      Start date: November 2013
      Squamous cell carcinoma of the head and neckPatients will first receive a priming dose of intradermal AlloStim injection followed by intradermal priming with AlloVax (personalized cancer vaccine combining CRCL as a source of antigen from patient's tumor) and intravenous infusion of AlloStim as adjuvantEvaluate tumor response using imaging tools. Assess antitumor immune response by monitoring changes in tumor pathology and immune cell infiltration.
      IVAC MUTANOME Phase I Clinical Trial (NCT02035956, Phase I)

      Start date: January 2014
      MelanomaIntranodal injection of IVAC MUTANOME vaccine composed of poly-neoepitopic coding RNA targeting the unique mutation signature of a patient’s tumor. In addition, depending on the tumor positivity to 2 melanoma TAAs, patients will receive or not RBL001/RBL002 vaccines prior to IVAC MUTANOME vaccination.Clinical first-in-human study evaluating the safety, tolerability and immunogenicity of intra-nodal administration of IVAC MUTANOME vaccine with or without initial treatment with RBL001/RBL002 vaccine
      GAPVAC Phase I Trial in Newly Diagnosed Glioblastoma Patients

      (NCT02149225, Phase I)

      Start date: May 2014
      GlioblastomaIntradermal injection of APVAC1 vaccine (composed of 5 to 10 peptides) in combination of subcutaneous injection of Poly ICLC (1.5 mg) and intradermal injection of GM-CSF (75 μg)Evaluate the safety and tolerability, feasibility and immunogenicity of APVAC1 vaccine
      AlloStim® Immunotherapy Dosing Alone or in Combination With Cryoablation in Metastatic Colorectal Cancer

      (NCT02380443, Phase II)

      Start date: March 2015
      Metastatic colorectal cancerFirst, cryoablation of a selected metastatic region. Then, intra-lesional injection of bioengineered allogeneic immune cells AlloStim.Determine the safety of increased dose frequency of CryoVax. Evaluate the antitumor effect of AlloStim combined with cryoablation and OS.
      An Individualized Anti-Cancer Vaccine in Advanced Hepatocellular Carcinoma Subjects (NCT02409524, Phase IIa)

      Start date: April 2015
      Advanced hepatocellular carcinomaFirst, priming by interdermal injection of AlloStim and chaperone rich cell lysate (CRCL; an autologous tumor-derived chaperone protein mixture). Then, immune activation by intravenous infusion of AlloStim. Finally, boosting with intradermal injection of CRCL alone.Investigate the safety and efficacy the CRCL-AlloVax in advanced HCC patients, as well as OS.
      Neoantigen-based Personalized Vaccine Combined With Immune Checkpoint Blockade Therapy in Patients With Newly Diagnosed, Unmethylated Glioblastoma (NCT03422094, Phase I)

      Start date: February 2018
      GlioblastomaSubcutaneous injection of maximum 20 synthetic long peptides coadministered with 1.5 mg of Poly ICLC. Intravenous injection of 480 mg of nivolumab is also given.Evaluate the safety, feasibility and immunogenicity of the personalized neoantigen-based vaccine
      Table 3Tumor neoantigen evaluation in syngeneic tumor mouse models.
      StudyMouse strainCancer typeNeoantigen identification methodNumbers of non-synonymous mutations identifiedNumber of neoantigens evaluated in vivoResults of in vivo validationReference
      1C57/BL64T1 breast cancer cell lineFrameshift Peptide Arrays20010Reduction of primary tumor burden and lung metastasis. Vaccine induced neoantigen specific T-cell responses. 70% survival for vaccinated mice compared to 20% for the control.
      • Peterson M.
      • Murphy S.N.
      • Lainson J.
      • Zhang J.
      • Shen L.
      • Diehnelt C.W.
      • et al.
      Comparison of personal and shared frameshift neoantigen vaccines in a mouse mammary cancer model.
      2C57BL/6, BALB/cB16F10 melanoma cell lineNext generation sequencing (Illumina HiSeq2000), Immune Epitope Database (IEDB)30812T cells for each single epitope were elicited and able to target tumor lesions. Also they reshaped the cellular composition of the tumor microenvironment and controlled tumor growth in vivo.
      • Kreiter S.
      • Vormehr M.
      • van de Roemer N.
      • Diken M.
      • Löwer M.
      • Diekmann J.
      • et al.
      Mutant MHC class II epitopes drive therapeutic immune responses to cancer.
      C57BL/6, BALB/cCT26 colon carcinoma cell line19221
      C57BL/6, BALB/c4T1-Luc breast cancer cell line87217
      3C57BL/6B16F10 melanoma cell lineNext generation sequencing (Illumina HiSeq2000), Immune Epitope Database (IEDB)96250Among the selected neoantigens, 16 were able to induce a T cell response in vivo. Tumor-bearing mice vaccinated with the 2 most immunogenic peptides had reduced tumor size and increased survival.
      • Castle J.C.
      • Kreiter S.
      • Diekmann J.
      • Löwer M.
      • van de Roemer N.
      • de Graaf J.
      • et al.
      Exploiting the mutanome for tumor vaccination.
      4BALB/c4T1 breast cancer cell lineMass spectrometry-based immunopeptidomics and whole exome sequencing (Illumina HiSeq 4000), NetMHCpan V.4.12714 in the 4T1 cell line and 5077 in tumor grown in vivo4Sixty percent of vaccinated tumor-bearing mice reached a survival of 66 days compared to control mice which were all sacrificed at day 40. Also, vaccination reduced MDSCs and increased IFN-γ and TNF-α production by T cells in the tumor microenvironments.
      • Mohsen M.O.
      • Speiser D.E.
      • Michaux J.
      • Pak HuiSong
      • Stevenson B.J.
      • Vogel M.
      • et al.
      Bedside formulation of a personalized multi-neoantigen vaccine against mammary carcinoma.
      5C57BL/6MC38 colon adenocarcinoma cell lineMass spectrometry, NetMHCpan V3.412907Tumor-bearing mice vaccinated with immunogenic peptide had lower tumor volume compared to control. Vaccination reduced the frequency of TIM-3+ PD-1+ T CD8+ T cells in the tumor microenvironment and increased the frequency of IFNg secreting CD8+ T cells.
      • Yadav M.
      • Jhunjhunwala S.
      • Phung Q.T.
      • Lupardus P.
      • Tanguay J.
      • Bumbaca S.
      • et al.
      Predicting immunogenic tumour mutations by combining mass spectrometry and exome sequencing.
      6NOD SCID gamma (NSG)Advanced breast cancer xenograft WHIM30next-generation sequencing (n Illumina HiSeq2000), NetMHC v3.220912Adoptive transfer of neoantigen-stimulated PBMCs limited tumor growth below 100 mm2 as opposed to pdx models treated with PBMCs pulsed with control peptide who reached tumor sizes of 200–300 mm2.
      • Zhang X.
      • Kim S.
      • Hundal J.
      • Herndon J.M.
      • Li S.
      • Petti A.A.
      • et al.
      Breast Cancer Neoantigens Can Induce CD8(+) T-Cell Responses and Antitumor Immunity.
      Advanced breast cancer xenograft WHIM353541
      Advanced breast cancer xenograft WHIM372351
      7C57BL/6MC38 colon adenocarcinoma cell linehigh-throughput sequencing, NetMHC 3.45013When combined with IL15 superagonist fusion protein N-803, immunocytokine NHS-IL12 and PD-L1 MAb, neoepitope vaccine was able to induce significant tumor regression in animals. This was correlated with increased CD8+ T cell infiltration in tumors.
      • Lee K.L.
      • Benz S.C.
      • Hicks K.C.
      • Nguyen A.
      • Gameiro S.R.
      • Palena C.
      • et al.
      Efficient tumor clearance and diversified immunity through neoepitope vaccines and combinatorial immunotherapy.

      Autologous whole tumor cell vaccines admixed with adjuvant

      Autologous whole tumor cell vaccines that are prepared from patients’ own tumor cells are one of the first personalized vaccines to be tested in clinics [
      • Hanna M.
      • Peters L.
      Immunotherapy of established micrometastases with Bacillus Calmette-Guerin tumor cell vaccine.
      ]. The main advantage of this approach is that it can provide a large repertoire of patient-specific tumor antigens, i.e. TAAs and private neoantigens, for stimulating a broad tumour-specific response to avoid tumor escape. The effectiveness of such autologous cell vaccines has been evaluated in several phase I and II clinical trials, including in advanced metastatic prostate [
      • Berger M.
      • Kreutz F.T.
      • Horst J.L.
      • Baldi A.C.
      • Koff W.J.
      Phase I study with an autologous tumor cell vaccine for locally advanced or metastatic prostate cancer.
      ], lung [
      • Nemunaitis J.
      • Nemunaitis J.
      Granulocyte-Macrophage Colony-Stimulating Factor Gene-Transfected Autologous Tumor Cell Vaccine: Focus on Non–Small-Cell Lung Cancer.
      ,
      • Schulof R.
      • Mai D.
      • Nelson M.
      • Paxton H.
      • Cox Jr, J.
      • Turner M.
      • et al.
      Active specific immunotherapy with an autologous tumor cell vaccine in patients with resected non-small cell lung cancer.
      ], colorectal [
      • de Weger V.A.
      • Turksma A.W.
      • Voorham Q.J.M.
      • Euler Z.
      • Bril H.
      • van den Eertwegh A.J.
      • et al.
      Clinical effects of adjuvant active specific immunotherapy differ between patients with microsatellite-stable and microsatellite-instable colon cancer.
      ], melanoma [
      • Berd D.
      • Maguire Jr, H.C.
      • McCue P.
      • Mastrangelo M.J.
      Treatment of metastatic melanoma with an autologous tumor-cell vaccine: clinical and immunologic results in 64 patients.
      ,
      • Baars A.
      • van Riel J.
      • Cuesta M.
      • Jaspars E.
      • Pinedo H.
      • van den Eertwegh A.
      Metastasectomy and active specific immunotherapy for a large single melanoma metastasis.
      ] and renal cell carcinoma (RCC) [
      • Fishman M.
      • Hunter T.B.
      • Soliman H.
      • Thompson P.
      • Dunn M.
      • Smilee R.
      • et al.
      Phase II trial of B7–1 (CD-86) transduced, cultured autologous tumor cell vaccine plus subcutaneous interleukin-2 for treatment of stage IV renal cell carcinoma.
      ,
      • Antonia S.J.
      • Seigne JOHN
      • Diaz JOSE
      • Muro-cacho CARLOS
      • Extermann MARTINE
      • Farmelo M.J.
      • et al.
      Phase I trial of a B7–1 (CD80) gene modified autologous tumor cell vaccine in combination with systemic interleukin-2 in patients with metastatic renal cell carcinoma.
      ], and showed good safety profiles and therapeutic immune responses. For example, the autologous tumor cell lysate vaccine Reniale has demonstrated effectiveness in treating non-metastatic RCC [
      • Van Poppel H.
      • Joniau S.
      • Van Gool S.W.
      Vaccine therapy in patients with renal cell carcinoma.
      ]. When administered after nephrectomy, Reniale improved the 5-year progression-free-survival (PFS) of high-risk non-metastatic RCC patients at all tumor stages (77.4%) when compared to the control group (67.8%) [
      • Van Poppel H.
      • Joniau S.
      • Van Gool S.W.
      Vaccine therapy in patients with renal cell carcinoma.
      ,
      • Jocham D.
      • Richter A.
      • Hoffmann L.
      • Iwig K.
      • Fahlenkamp D.
      • Zakrzewski G.
      • et al.
      Adjuvant autologous renal tumour cell vaccine and risk of tumour progression in patients with renal-cell carcinoma after radical nephrectomy: phase III, randomised controlled trial.
      ]. Autologous tumor cell vaccines can be rendered more immunogenic by admix with immunomodulatory adjuvants. In a phase III/b clinical trial with stage II and II colon cancer patients, OncoVax (irradiated autologous colon tumor cells admixed with Bacillus Calmette-Guérin [BCG]) significantly improved the overall survival (OS) and PFS in patients with stage-II cancer (p = 0·011) [
      • Vermorken J.B.
      • Claessen A.ME.
      • van Tinteren H.
      • Gall H.E.
      • Ezinga R.
      • Meijer S.
      • et al.
      Active specific immunotherapy for stage II and stage III human colon cancer: a randomised trial.
      ,
      • Khan S.T.
      • Montroy J.
      • Forbes N.
      • Bastin D.
      • Kennedy M.A.
      • Diallo J.-S.
      • et al.
      Safety and efficacy of autologous tumour cell vaccines as a cancer therapeutic to treat solid tumours and haematological malignancies: a meta-analysis protocol for two systematic reviews.
      ]. Furthermore, over a median follow-up period of 5.3 years, a 44% risk reduction for recurrence was observed in all the patients treated with OncoVAX (p = 0.023) [
      • Vermorken J.B.
      • Claessen A.ME.
      • van Tinteren H.
      • Gall H.E.
      • Ezinga R.
      • Meijer S.
      • et al.
      Active specific immunotherapy for stage II and stage III human colon cancer: a randomised trial.
      ,
      • Khan S.T.
      • Montroy J.
      • Forbes N.
      • Bastin D.
      • Kennedy M.A.
      • Diallo J.-S.
      • et al.
      Safety and efficacy of autologous tumour cell vaccines as a cancer therapeutic to treat solid tumours and haematological malignancies: a meta-analysis protocol for two systematic reviews.
      ]. Other autologous tumor cell vaccines that were prepared with BCG as an adjuvant also demonstrated the ability to improve overall survival in advanced metastatic prostate cancer and stage-III/IV melanoma [
      • Berger M.
      • Kreutz F.T.
      • Horst J.L.
      • Baldi A.C.
      • Koff W.J.
      Phase I study with an autologous tumor cell vaccine for locally advanced or metastatic prostate cancer.
      ,
      • Baars A.
      • Claessen A.M.E.
      • van den Eertwegh A.J.M.
      • Gall H.E.
      • Stam A.G.M.
      • Meijer S.
      • et al.
      Skin tests predict survival after autologous tumor cell vaccination in metastatic melanoma: experience in 81 patients.
      ]. As BCG could induce side effects such as ulcerations [
      • Koster B.D.
      • Santegoets S.J.A.M.
      • Harting J.
      • Baars A.
      • van Ham S.M.
      • Scheper R.J.
      • et al.
      Autologous tumor cell vaccination combined with systemic CpG-B and IFN-α promotes immune activation and induces clinical responses in patients with metastatic renal cell carcinoma: a phase II trial.
      ], other immune adjuvants including unmethylated cytosine-phosphate-guanine oligodeoxynucleotides (CpG-ODN) that forms the active elements of bacterial DNA and interferon (IFN)-α that has antiviral and antitumor effects have been investigated. In a phase II clinical trial, the coinjection of CpG-ODN and IFN-α with autologous tumor cell lysate in patients with metastatic RCC (mRCC) was well tolerated, immunogenic and elicited antitumor responses [
      • Koster B.D.
      • Santegoets S.J.A.M.
      • Harting J.
      • Baars A.
      • van Ham S.M.
      • Scheper R.J.
      • et al.
      Autologous tumor cell vaccination combined with systemic CpG-B and IFN-α promotes immune activation and induces clinical responses in patients with metastatic renal cell carcinoma: a phase II trial.
      ].

      Genetically modified autologous tumor cells as vaccines

      Autologous tumor cells can be genetically engineered to express immunostimulatory molecules to enhance their immunogenicity. In a phase I clinical study of mRCC, patients were vaccinated with autologous tumor cells expressing the costimulatory B7-1 (CD80) molecule in combination with systemic interleukin (IL)-12 [
      • Antonia S.J.
      • Seigne JOHN
      • Diaz JOSE
      • Muro-cacho CARLOS
      • Extermann MARTINE
      • Farmelo M.J.
      • et al.
      Phase I trial of a B7–1 (CD80) gene modified autologous tumor cell vaccine in combination with systemic interleukin-2 in patients with metastatic renal cell carcinoma.
      ]. Two out of the 15 treated patients showed partial responses (PR), while another 2 patients had stable diseases (SD) [
      • Antonia S.J.
      • Seigne JOHN
      • Diaz JOSE
      • Muro-cacho CARLOS
      • Extermann MARTINE
      • Farmelo M.J.
      • et al.
      Phase I trial of a B7–1 (CD80) gene modified autologous tumor cell vaccine in combination with systemic interleukin-2 in patients with metastatic renal cell carcinoma.
      ]. Autologous tumor cells modified to express granulocyte-macrophage colony-stimulating factor (GM-CSF) [also known as GVAX] have been studied extensively in preclinical and clinical settings; they were effective in recruiting and maturing dendritic cells (DCs) for tumor antigen-presentation and priming of cytotoxic CD8+ T cells [
      • Mach N.
      • Gillessen S.
      • Wilson S.B.
      • Sheehan C.
      • Mihm M.
      • Dranoff G.
      Differences in dendritic cells stimulated in vivo by tumors engineered to secrete granulocyte-macrophage colony-stimulating factor or Flt3-ligand.
      ,
      • Wu A.A.
      • Bever K.M.
      • Ho W.J.
      • Fertig E.J.
      • Niu N.
      • Zheng L.
      • et al.
      A Phase II Study of Allogeneic GM-CSF–Transfected Pancreatic Tumor Vaccine (GVAX) with Ipilimumab as Maintenance Treatment for Metastatic Pancreatic Cancer.
      ]. Vigil vaccine (Gradalis®), an autologous ovarian cancer (OC) cell vaccine engineered to express GM-CSF and a knock-down of endogenous transforming growth factor (TGF)-β, was effective in patients with advanced OC by inducing a prolonged PFS (604 days vs. 377 days in control group; p = 0.033) [
      • Oh J.
      • Barve M.
      • Matthews C.M.
      • Koon E.C.
      • Heffernan T.P.
      • Fine B.
      • et al.
      Phase II study of Vigil® DNA engineered immunotherapy as maintenance in advanced stage ovarian cancer.
      ]. Based on these promising phase II data, a phase III randomized OC clinical trials of the Vigil vaccine is underway [

      Rocconi RP, Ghamande SA, Barve MA, Stevens EE, Aaron P, Stanbery L, et al. Maintenance vigil immunotherapy in newly diagnosed advanced ovarian cancer: Efficacy assessment of homologous recombination proficient (HRP) patients in the phase IIb VITAL trial. J Clin Oncol. 2021 39:15_suppl, 5502-5502.

      ]. The MVX-ONCO-1 vaccine, which comprises of lethally irradiated autologous tumor cells and allogenic tumor cell line engineered to release GM-CSF, was investigated in two open-label, single-arm clinical trials (NCT02193503 and NCT02999646) for treating advanced head and neck squamous cell carcinoma [
      • Fernandez E.
      • Vernet R.
      • Charrier E.
      • Migliorini D.
      • Joerger M.
      • Belkouch M.-C.
      • et al.
      MVX-ONCO-1 in advanced refractory cancers: Safety, feasibility, and preliminary efficacy results from all HNSCC patients treated in two ongoing clinical trials.
      ]. Of the 11 patients who were evaluable, 2 demonstrated complete responses (CRs), 4 had SDs and 2 showed PRs [
      • Fernandez E.
      • Vernet R.
      • Charrier E.
      • Migliorini D.
      • Joerger M.
      • Belkouch M.-C.
      • et al.
      MVX-ONCO-1 in advanced refractory cancers: Safety, feasibility, and preliminary efficacy results from all HNSCC patients treated in two ongoing clinical trials.
      ].

      Autologous cell-derived exosomes as vaccines

      Exosomes are extracellular membrane vesicles released from cells, including from normal cells, tumor cells and DCs, and are involved in cell-cell interaction, communication and transmission of macromolecules. Exosomes derived from tumor cells are highly enriched in tumor antigens, major histocompatibility complex (MHC) molecules, heat-shock proteins (HSPs) and inducible costimulatory molecules [
      • Xu H.Y.
      • Li N.
      • Yao N.
      • Xu X.F.
      • Wang H.X.
      • Liu X.Y.
      • et al.
      CD8+ T cells stimulated by exosomes derived from RenCa cells mediate specific immune responses through the FasL/Fas signaling pathway and combined with GM-CSF and IL-12, enhance the anti-renal cortical adenocarcinoma effect.
      ]. Studies have demonstrated the ability of tumour-derived exosomes in triggering potent CD8+ T cell antitumor responses when combined with appropriate immunostimulatory agents [
      • Xu H.Y.
      • Li N.
      • Yao N.
      • Xu X.F.
      • Wang H.X.
      • Liu X.Y.
      • et al.
      CD8+ T cells stimulated by exosomes derived from RenCa cells mediate specific immune responses through the FasL/Fas signaling pathway and combined with GM-CSF and IL-12, enhance the anti-renal cortical adenocarcinoma effect.
      ]. In a phase I study of advanced colorectal cancer, 40 patients were vaccinated subcutaneously once a week with autologous ascites-derived exosomes (Aex) and GM-CSF for a total of four weeks [
      • Dai S.
      • Wei D.
      • Wu Z.
      • Zhou X.
      • Wei X.
      • Huang H.
      • et al.
      Phase I clinical trial of autologous ascites-derived exosomes combined with GM-CSF for colorectal cancer.
      ]. The vaccine was safe, and the patients developed beneficial tumour-specific cytotoxic T lymphocyte (CTL) responses [
      • Dai S.
      • Wei D.
      • Wu Z.
      • Zhou X.
      • Wei X.
      • Huang H.
      • et al.
      Phase I clinical trial of autologous ascites-derived exosomes combined with GM-CSF for colorectal cancer.
      ]. Another phase I study evaluated the use of autologous DC-derived exosomes (DEX) that were pulsed with MAGE-3 peptides for vaccinating stage III/IV melanoma patients [
      • Escudier B.
      • Dorval T.
      • Chaput N.
      • André F.
      • Caby M.P.
      • Novault S.
      • et al.
      Vaccination of metastatic melanoma patients with autologous dendritic cell (DC) derived-exosomes: results of thefirst phase I clinical trial.
      ]. The patients received four exosome vaccinations with had only grade 1 adverse effects. Of the 15 patients treated, 2 had SDs and 1 had PR [
      • Escudier B.
      • Dorval T.
      • Chaput N.
      • André F.
      • Caby M.P.
      • Novault S.
      • et al.
      Vaccination of metastatic melanoma patients with autologous dendritic cell (DC) derived-exosomes: results of thefirst phase I clinical trial.
      ]. In a phase I non-small cell lung cancer (NSCLC) study, 13 stage-III/IV patients were vaccinated with 4 weekly doses of DEX pulsed with MAGE-A3, -A4, -A10, and MAGE-3DPO4 peptides [
      • Morse M.A.
      • Garst J.
      • Osada T.
      • Khan S.
      • Hobeika A.
      • Clay T.M.
      • et al.
      A phase I study of dexosome immunotherapy in patients with advanced non-small cell lung cancer.
      ]. MAGE-specific T cell and natural killer (NK) cell activities were detected, and the OS ranged from 52 to >665 days post-treatment [
      • Morse M.A.
      • Garst J.
      • Osada T.
      • Khan S.
      • Hobeika A.
      • Clay T.M.
      • et al.
      A phase I study of dexosome immunotherapy in patients with advanced non-small cell lung cancer.
      ]. In a further phase II NSCLC study, exosomes derived from IFN-γ-maturated DC (IFN-γ-DEXs) and loaded with MHC class I- and II-restricted cancer antigens were evaluated as a maintenance therapy [
      • Besse B.
      • Charrier M.
      • Lapierre V.
      • Dansin E.
      • Lantz O.
      • Planchard D.
      • et al.
      Dendritic cell-derived exosomes as maintenance immunotherapy after first line chemotherapy in NSCLC.
      ]. The median OS was 15 months, and 7 out of 22 patients had disease stabilisation of >4 months. Increased NK cell activities were also detected [
      • Besse B.
      • Charrier M.
      • Lapierre V.
      • Dansin E.
      • Lantz O.
      • Planchard D.
      • et al.
      Dendritic cell-derived exosomes as maintenance immunotherapy after first line chemotherapy in NSCLC.
      ].

      DNA and RNA-based vaccines derived from autologous tumor cells

      Nucleic acid vaccine is an attractive platform for delivering multiple tumor antigens in one immunization. It is also capable of inducing both humoral and cellular antitumor immune responses [
      • McNamara M.A.
      • Nair S.K.
      • Holl E.K.
      RNA-Based Vaccines in Cancer Immunotherapy.
      ,
      • Gurunathan S.
      • Klinman D.M.
      • Seder R.A.
      DNA vaccines: immunology, application, and optimization*.
      ], and proven to be clinically safe [
      • Ulmer J.B.
      • Mason P.W.
      • Geall A.
      • Mandl C.W.
      RNA-based vaccines.
      ]. DNA vaccines can be generated by inserting gene(s) of interest into bacterial plasmids that serve as the gene delivery system [
      • McNamara M.A.
      • Nair S.K.
      • Holl E.K.
      RNA-Based Vaccines in Cancer Immunotherapy.
      ]. They can be manufactured in a cost-effective manner and store without the need of strict cold-chain procedures [
      • Gurunathan S.
      • Klinman D.M.
      • Seder R.A.
      DNA vaccines: immunology, application, and optimization*.
      ]. Currently, there are more than 200 cancer clinical trials evaluating DNA vaccines (www.clinicaltrials.gov) and some are summarized in Table 1a, Table 1b and Table 2a, Table 2b. Although DNA vaccines are capable of eliciting immune responses, the magnitude of these responses remain limited as compared to cell-based cancer vaccines. This could be explained in part by the suboptimal delivery of DNA plasmids into the target cell nuclei and/or inadequate stimulation of immune responses by DNA vaccine [
      • Ulmer J.B.
      • Mason P.W.
      • Geall A.
      • Mandl C.W.
      RNA-based vaccines.
      ].
      RNA vaccines are readily translated within the host cytoplasm. Hence, there is no risk of oncogene activation as the RNA cannot integrate into the host genome [
      • McNamara M.A.
      • Nair S.K.
      • Holl E.K.
      RNA-Based Vaccines in Cancer Immunotherapy.
      ]. RNA can be readily amplified with polymerase chain reaction to a large amount from limited tumor biopsies or tumor stroma [
      • Kandalaft L.E.
      • Motz G.T.
      • Busch J.
      • Coukos G.
      Angiogenesis and the tumor vasculature as antitumor immune modulators: the role of vascular endothelial growth factor and endothelin.
      ]. As RNA is less stable than DNA, careful handling of the initial biopsy excision is required [
      • McNamara M.A.
      • Nair S.K.
      • Holl E.K.
      RNA-Based Vaccines in Cancer Immunotherapy.
      ,
      • Chiang C.L.
      • Benencia F.
      • Coukos G.
      Whole tumor antigen vaccines.
      ]. RNA vaccines have been evaluated in multiple clinical trials for treating melanoma, prostate and RCC [
      • Su Z.
      • Dannull J.
      • Heiser A.
      • Yancey D.
      • Pruitt S.
      • Madden J.
      • et al.
      Immunological and clinical responses in metastatic renal cancer patients vaccinated with tumor RNA-transfected dendritic cells.
      ]. A first-in-human phase I study of RNA-based vaccine was performed in melanoma to mobilize immunity against patients’ neoantigen mutations [
      • Sahin U.
      • Derhovanessian E.
      • Miller M.
      • Kloke B.-P.
      • Simon P.
      • Löwer M.
      • et al.
      Personalized RNA mutanome vaccines mobilize poly-specific therapeutic immunity against cancer.
      ]. The vaccine was composed of two engineered synthetic RNAs with each encoding for five linker-connected long synthetic peptides. All the patients developed T cell responses against multiple neoepitopes encoded by the vaccine [
      • Sahin U.
      • Derhovanessian E.
      • Miller M.
      • Kloke B.-P.
      • Simon P.
      • Löwer M.
      • et al.
      Personalized RNA mutanome vaccines mobilize poly-specific therapeutic immunity against cancer.
      ]. Neoepitope-specific killing of autologous tumor cells was also demonstrated [
      • Sahin U.
      • Derhovanessian E.
      • Miller M.
      • Kloke B.-P.
      • Simon P.
      • Löwer M.
      • et al.
      Personalized RNA mutanome vaccines mobilize poly-specific therapeutic immunity against cancer.
      ]. Eleven of the 13 treated patients remained disease-free for up to 26 months post-treatment and one patient whose cancer relapsed became tumor-free after receiving anti-PD-1 antibody as a combination therapy [
      • Sahin U.
      • Derhovanessian E.
      • Miller M.
      • Kloke B.-P.
      • Simon P.
      • Löwer M.
      • et al.
      Personalized RNA mutanome vaccines mobilize poly-specific therapeutic immunity against cancer.
      ]. Currently, ModernaTX Inc. is conducting a phase II study to evaluate a RNA vaccine encoding for 20 neoantigens (mRNA-4157) in melanoma patients (https://www.modernatx.com/pipeline/therapeutic-areas/mrna-personalized-cancer-vaccines-and-immuno-oncology) [Table 2a].

      Tumor neoantigen peptides

      As described earlier, genetic instability of tumor cells can lead to the expression of neoantigens [
      • Greenman C.
      • Stephens P.
      • Smith R.
      • Dalgliesh G.L.
      • Hunter C.
      • Bignell G.
      • et al.
      Patterns of somatic mutation in human cancer genomes.
      ]. Tumor antigens, unlike self-TAAs, are expressed solely on tumor cells [
      • Blass E.
      • Ott P.A.
      Advances in the development of personalized neoantigen-based therapeutic cancer vaccines.
      ]. They are also capable of eliciting high-avidity T cells as they are not subjected to thymic selection and central tolerance. The neoantigen candidates can be screened with predictive algorithms and state-of-the-art technologies such as mass spectrometry to determine the most suitable neoantigens for personalized vaccination [
      • Aldous A.R.
      • Dong J.Z.
      Personalized neoantigen vaccines: a new approach to cancer immunotherapy.
      ]. Seminal work from Wu and colleagues demonstrated that the use of synthetic long peptides in clinical trials was safe and produced clinical benefits [
      • Hacohen N.
      • Fritsch E.F.
      • Carter T.A.
      • Lander E.S.
      • Wu C.J.
      Getting personal with neoantigen-based therapeutic cancer vaccines.
      ,
      • Fritsch E.F.
      • Hacohen N.
      • Wu C.J.
      Personal neoantigen cancer vaccines: the momentum builds.
      ,
      • Fritsch E.F.
      • Burkhardt U.E.
      • Hacohen N.
      • Wu C.J.
      Personal neoantigen cancer vaccines: a road not fully paved.
      ]. In a phase I clinical trial, 4 out of 6 melanoma patients treated with NeoVax (composed of up to 20 long synthetic personalized neoantigen peptides admixed with polyinosinic-polycytidylic acid, and poly-L-lysine [Poly IC:LC] as adjuvant) had no recurrence at 25 months post-treatment [
      • Ott P.A.
      • Hu Z.
      • Keskin D.B.
      • Shukla S.A.
      • Sun J.
      • Bozym D.J.
      • et al.
      An immunogenic personal neoantigen vaccine for patients with melanoma.
      ]. Two patients had complete tumor regression after additional anti-PD-1 antibody therapy [
      • Ott P.A.
      • Hu Z.
      • Keskin D.B.
      • Shukla S.A.
      • Sun J.
      • Bozym D.J.
      • et al.
      An immunogenic personal neoantigen vaccine for patients with melanoma.
      ]. NeoVax is currently being evaluated in different cancers in combination with immune checkpoint inhibitors (Table 2a). As neoantigen-based cancer vaccines is gaining traction in the pharmaceutical industry, a number of companies are assessing several neoantigen-based vaccines in clinical trials (Table 2a, Table 2b). Neon Therapeutics launched a phase I clinical trial in melanoma, NSCLC and bladder cancer by using synthetic personalized peptides (at least 20 peptides per vaccine) together with nivolumab [
      • Mullard A.
      The cancer vaccine resurgence.
      ]. Agenus Inc. launched a phase I clinical trial to use AutoSynVax (ASV®) AGEN2017 vaccine for treating advanced cancers refractory to standard therapies (NCT03673020). AutoSynVax (ASV®) is made by combining synthetic peptides of patient’s cancer neoantigens and HSP70 to improve antigen-processing and recognition by the immune system (NCT02992977) [
      • Aldous A.R.
      • Dong J.Z.
      Personalized neoantigen vaccines: a new approach to cancer immunotherapy.
      ].

      Autologous dendritic cell-based immunotherapy

      Loading DCs with autologous whole tumor lysate, mRNA or neoantigen peptides

      DC pulsed with autologous whole tumor lysate (WTL) have been extensively investigated in different cancers (Table 1a, Table 1b and Table 2a, Table 2b). Previously, we treated ovarian cancer (OC) patients with autologous DCs pulsed with hypochlorous acid (HOCl)-oxidized autologous WTL. This vaccine was able to elicit “de novo” T cell responses against previously unrecognized private tumor neoantigens in some patients [
      • Tanyi J.L.
      • Bobisse S.
      • Ophir E.
      • Tuyaerts S.
      • Roberti A.
      • Genolet R.
      • et al.
      Personalized cancer vaccine effectively mobilizes antitumor T cell immunity in ovarian cancer.
      ]. Vaccine-induced T cell responses were also associated with significantly prolonged PFS in the patients [
      • Tanyi J.L.
      • Bobisse S.
      • Ophir E.
      • Tuyaerts S.
      • Roberti A.
      • Genolet R.
      • et al.
      Personalized cancer vaccine effectively mobilizes antitumor T cell immunity in ovarian cancer.
      ]. Recently, we demonstrated that the effectiveness of this DC vaccine could be enhanced with anti-VEGF, cyclophosphamide, acetylsalicylic acid and low-dose IL-2 [
      • Tanyi J.L.
      • Chiang C.-L.
      • Chiffelle J.
      • Thierry A.-C.
      • Baumgartener P.
      • Huber F.
      • et al.
      Personalized cancer vaccine strategy elicits polyfunctional T cells and demonstrates clinical benefits in ovarian cancer.
      ]. Such therapeutic combination was safe, and induced increased OS that was associated with increased polyfunctionality of the vaccine-elicited T cells in the OC patients [
      • Tanyi J.L.
      • Chiang C.-L.
      • Chiffelle J.
      • Thierry A.-C.
      • Baumgartener P.
      • Huber F.
      • et al.
      Personalized cancer vaccine strategy elicits polyfunctional T cells and demonstrates clinical benefits in ovarian cancer.
      ]. In a phase I/II study, 37 patients with metastatic or recurrent sarcomas were treated with autologous DCs pulsed with WTL [
      • Miwa S.
      • Nishida H.
      • Tanzawa Y.
      • Takeuchi A.
      • Hayashi K.
      • Yamamoto N.
      • et al.
      Phase 1/2 study of immunotherapy with dendritic cells pulsed with autologous tumor lysate in patients with refractory bone and soft tissue sarcoma.
      ]. Six patients had SD, and 1 patient had PR after vaccination. Increased sera IFN-γ and IL-12 levels were observed a month after vaccination [
      • Miwa S.
      • Nishida H.
      • Tanzawa Y.
      • Takeuchi A.
      • Hayashi K.
      • Yamamoto N.
      • et al.
      Phase 1/2 study of immunotherapy with dendritic cells pulsed with autologous tumor lysate in patients with refractory bone and soft tissue sarcoma.
      ]. In a phase I study, autologous DC pulsed with WTL was evaluated in patients with high-grade gliomas [
      • Rudnick J.D.
      • Sarmiento J.M.
      • Uy B.
      • Nuno M.
      • Wheeler C.J.
      • Mazer M.J.
      • et al.
      A phase I trial of surgical resection with Gliadel Wafer placement followed by vaccination with dendritic cells pulsed with tumor lysate for patients with malignant glioma.
      ]. Five out of the 20 evaluable patients showed elevated IFN-γ T cell responses and OS of 16.9 months [
      • Rudnick J.D.
      • Sarmiento J.M.
      • Uy B.
      • Nuno M.
      • Wheeler C.J.
      • Mazer M.J.
      • et al.
      A phase I trial of surgical resection with Gliadel Wafer placement followed by vaccination with dendritic cells pulsed with tumor lysate for patients with malignant glioma.
      ]. Although the majority of the trials using DCs loaded with WTL showed modest clinical results, several ongoing clinical trials seek to enhance the efficacy of DC-WTL vaccines in combination with other immunomodulatory agents (Table 1a, Table 1b and Table 2a, Table 2b).
      DCs could be transfected with whole tumor cell mRNA. In a phase I/II trial, 9 out of the 29 melanoma patients receiving autologous DC vaccine transfected with tumor mRNA developed vaccine-specific responses as demonstrated by T cell proliferation and ELISPOT assays [
      • Kyte J.A.
      • Mu L.
      • Aamdal S.
      • Kvalheim G.
      • Dueland S.
      • Hauser M.
      • et al.
      Phase I/II trial of melanoma therapy with dendritic cells transfected with autologous tumor-mRNA.
      ]. DCs could also be electroporated with tumor mRNA to ensure efficient delivery into the cell cytoplasm. In a phase I//II study, it was demonstrated that DCs electroporated with mRNA encoding for gp100 or tyrosinase were able to migrate from the injection site to T cell areas in resected lymph nodes and elicited anti-specific CD8+ T cell responses in the treated patients [
      • Schuurhuis D.H.
      • Verdijk P.
      • Schreibelt G.
      • Aarntzen E.H.J.G.
      • Scharenborg N.
      • de Boer A.
      • et al.
      In situ expression of tumor antigens by messenger RNA-electroporated dendritic cells in lymph nodes of melanoma patients.
      ]. In another clinical trial, 14 patients with metastatic uveal melanoma were vaccinated with DCs pulsed with peptides (gp100 and tyrosinase) or mRNA expressing these TAAs [
      • Bol K.F.
      • Mensink H.W.
      • Aarntzen E.H.J.G.
      • Schreibelt G.
      • Keunen J.E.E.
      • Coulie P.G.
      • et al.
      Long overall survival after dendritic cell vaccination in metastatic uveal melanoma patients.
      ]. Four out of 14 patients (29%) showed prolonged median OS of 19.2 months as compared to historical controls [
      • Bol K.F.
      • Mensink H.W.
      • Aarntzen E.H.J.G.
      • Schreibelt G.
      • Keunen J.E.E.
      • Coulie P.G.
      • et al.
      Long overall survival after dendritic cell vaccination in metastatic uveal melanoma patients.
      ]. Several other clinical studies also showed promising results of tumor mRNA transfected autologous DCs in late-stage melanoma [
      • Kyte J.A.
      • Mu L.
      • Aamdal S.
      • Kvalheim G.
      • Dueland S.
      • Hauser M.
      • et al.
      Phase I/II trial of melanoma therapy with dendritic cells transfected with autologous tumor-mRNA.
      ,
      • Schuurhuis D.H.
      • Verdijk P.
      • Schreibelt G.
      • Aarntzen E.H.J.G.
      • Scharenborg N.
      • de Boer A.
      • et al.
      In situ expression of tumor antigens by messenger RNA-electroporated dendritic cells in lymph nodes of melanoma patients.
      ,
      • Bol K.F.
      • Mensink H.W.
      • Aarntzen E.H.J.G.
      • Schreibelt G.
      • Keunen J.E.E.
      • Coulie P.G.
      • et al.
      Long overall survival after dendritic cell vaccination in metastatic uveal melanoma patients.
      ,
      • Bol K.F.
      • Figdor C.G.
      • Aarntzen E.H.
      • Welzen M.EB.
      • van Rossum M.M.
      • Blokx W.AM.
      • et al.
      Intranodal vaccination with mRNA-optimized dendritic cells in metastatic melanoma patients.
      ,
      • Aarntzen E.H.J.G.
      • Schreibelt G.
      • Bol K.
      • Lesterhuis W.J.
      • Croockewit A.J.
      • de Wilt J.H.W.
      • et al.
      Vaccination with mRNA-electroporated dendritic cells induces robust tumor antigen-specific CD4+ and CD8+ T cells responses in stage III and IV melanoma patients.
      ,
      • Wilgenhof S.
      • Van Nuffel A.M.T.
      • Corthals J.
      • Heirman C.
      • Tuyaerts S.
      • Benteyn D.
      • et al.
      Therapeutic vaccination with an autologous mRNA electroporated dendritic cell vaccine in patients with advanced melanoma.
      ], advanced uterine and OC [
      • Hernando J.J.
      • Park T.W.
      • Fischer H.P.
      • Zivanovic O.
      • Braun M.
      • Pölcher M.
      • et al.
      Vaccination with dendritic cells transfected with mRNA-encoded folate-receptor-alpha for relapsed metastatic ovarian cancer.
      ,
      • Coosemans A.
      • Vanderstraeten A.
      • Tuyaerts S.
      • Verschuere T.
      • Moerman P.
      • Berneman Z.N.
      • et al.
      Wilms' Tumor Gene 1 (WT1)–loaded dendritic cell immunotherapy in patients with uterine tumors: a phase I/II clinical trial.
      ,
      • Coosemans A.
      • Vanderstraeten A.
      • Tuyaerts S.
      • Verschuere T.
      • Moerman P.
      • Berneman Z.
      • et al.
      Immunological response after WT1 mRNA-loaded dendritic cell immunotherapy in ovarian carcinoma and carcinosarcoma.
      ], stage III/IV RCC [
      • Su Z.
      • Dannull J.
      • Heiser A.
      • Yancey D.
      • Pruitt S.
      • Madden J.
      • et al.
      Immunological and clinical responses in metastatic renal cancer patients vaccinated with tumor RNA-transfected dendritic cells.
      ], prostate cancer [
      • Heiser A.
      • Coleman D.
      • Dannull J.
      • Yancey D.
      • Maurice M.A.
      • Lallas C.D.
      • et al.
      Autologous dendritic cells transfected with prostate-specific antigen RNA stimulate CTL responses against metastatic prostate tumors.
      ], pancreatic adenocarcinoma [
      • Morse M.A.
      • Nair S.K.
      • Boczkowski D.
      • Tyler D.
      • Hurwitz H.I.
      • Proia A.
      • et al.
      The feasibility and safety of immunotherapy with dendritic cells loaded with CEA mRNA following neoadjuvant chemoradiotherapy and resection of pancreatic cancer.
      ], colorectal cancer [
      • Rains N.
      • Cannan R.J.
      • Chen W.
      • Stubbs R.S.
      Development of a dendritic cell (DC)-based vaccine for patients with advanced colorectal cancer.
      ], multiple myeloma and acute myeloid leukemia [
      • Hobo W.
      • Strobbe L.
      • Maas F.
      • Fredrix H.
      • Greupink-Draaisma A.
      • Esendam B.
      • et al.
      Immunogenicity of dendritic cells pulsed with MAGE3, Survivin and B-cell maturation antigen mRNA for vaccination of multiple myeloma patients.
      ,
      • Anguille S.
      • Van de Velde A.L.
      • Smits E.L.
      • Van Tendeloo V.F.
      • Juliusson G.
      • Cools N.
      • et al.
      Dendritic cell vaccination as postremission treatment to prevent or delay relapse in acute myeloid leukemia.
      ].
      DCs pulsed with specific neoantigen peptides have been investigated in several clinical trials including in melanoma [
      • Carreno B.M.
      • Magrini V.
      • Becker-Hapak M.
      • Kaabinejadian S.
      • Hundal J.
      • Petti A.A.
      • et al.
      Cancer immunotherapy. A dendritic cell vaccine increases the breadth and diversity of melanoma neoantigen-specific T cells.
      ], NSLC [
      • Ding Z.
      • Li Q.
      • Zhang R.
      • Xie L.i.
      • Shu Y.
      • Gao S.
      • et al.
      Personalized neoantigen pulsed dendritic cell vaccine for advanced lung cancer.
      ] and ovarian cancer [
      • Sarivalasis A.
      • Boudousquié C.
      • Balint K.
      • Stevenson B.J.
      • Gannon P.O.
      • Iancu E.M.
      • et al.
      A Phase I/II trial comparing autologous dendritic cell vaccine pulsed either with personalized peptides (PEP-DC) or with tumor lysate (OC-DC) in patients with advanced high-grade ovarian serous carcinoma.
      ] . In a phase I trial, stage-III melanoma patients treated with ex vivo generated DCs pulsed with synthetic long peptides encoding tumor-neoantigens with Poly(I:C) as an adjuvant demonstrated a significant increase in the breadth and diversity of melanoma neoantigen-specific T cells [
      • Carreno B.M.
      • Magrini V.
      • Becker-Hapak M.
      • Kaabinejadian S.
      • Hundal J.
      • Petti A.A.
      • et al.
      Cancer immunotherapy. A dendritic cell vaccine increases the breadth and diversity of melanoma neoantigen-specific T cells.
      ]. In another trial, 12 late-stage NSCLC patients vaccinated with neoantigen peptide-pulsed DCs demonstrated a 25% objective response rate [
      • Ding Z.
      • Li Q.
      • Zhang R.
      • Xie L.i.
      • Shu Y.
      • Gao S.
      • et al.
      Personalized neoantigen pulsed dendritic cell vaccine for advanced lung cancer.
      ]. One patient with advanced body disseminated metastasis had a 29% reduction in overall tumor lesions following 5 doses of the personalized DC vaccine. Finally, the vaccine induced low to no side effects [
      • Ding Z.
      • Li Q.
      • Zhang R.
      • Xie L.i.
      • Shu Y.
      • Gao S.
      • et al.
      Personalized neoantigen pulsed dendritic cell vaccine for advanced lung cancer.
      ]. Our group is currently conducting a series of phase I/II clinical trials to test the effectiveness of personalized tumor noenatigen peptides-pulsed DCs in OC [
      • Sarivalasis A.
      • Boudousquié C.
      • Balint K.
      • Stevenson B.J.
      • Gannon P.O.
      • Iancu E.M.
      • et al.
      A Phase I/II trial comparing autologous dendritic cell vaccine pulsed either with personalized peptides (PEP-DC) or with tumor lysate (OC-DC) in patients with advanced high-grade ovarian serous carcinoma.
      ], lung and pancreatic cancers. The aims of the OC study are to determine the efficacy and tolerability of DC vaccine, as well as to evaluate the PFS and OS for up to 36 months [
      • Sarivalasis A.
      • Boudousquié C.
      • Balint K.
      • Stevenson B.J.
      • Gannon P.O.
      • Iancu E.M.
      • et al.
      A Phase I/II trial comparing autologous dendritic cell vaccine pulsed either with personalized peptides (PEP-DC) or with tumor lysate (OC-DC) in patients with advanced high-grade ovarian serous carcinoma.
      ]. In the lung cancer trial, patients with advanced or recurrent metastatic NSCLC will receive the DC vaccine in combination with low dose cyclophosphamide as standard-of-care therapy (SOC) [NCT05195619]. In the pancreatic cancer study, patients with non-metastatic surgically resected pancreatic adenocarcinoma will be treated with the DC vaccine, SOC adjuvant chemotherapy and follow by nivolumab (NCT04627246).

      DC-tumor cell fusion vaccine

      Gong and colleagues were the first to demonstrate the feasibility of using fusions of autologous DCs and autologous whole tumor cells as cancer vaccines [
      • Gong J.
      • Koido S.
      • Calderwood S.K.
      Cell fusion: from hybridoma to dendritic cell-based vaccine.
      ]. This method involves the fusion of cytoplasm of both cell types without nucleic fusion, thus allowing the maintenance of the cellular function of these cells [
      • Dendritic-Tumor K.S.
      • Vaccines F.-B.
      ]. With such fusion vaccine, a large spectrum of known and unknown tumor antigens can be expressed and processed endogenously by the DCs [
      • Koido S.
      • Hara E.
      • Homma S.
      • Fujise K.
      • Gong J.
      • Tajiri H.
      Dendritic/tumor fusion cell-based vaccination against cancer.
      ]. The addition of adjuvants such as IL-12 [
      • Gong J.
      • Koido S.
      • Chen D.
      • Tanaka Y.
      • Huang L.
      • Avigan D.
      • et al.
      Immunization against murine multiple myeloma with fusions of dendritic and plasmacytoma cells is potentiated by interleukin 12.
      ], IL-4 [
      • Liu Y.
      • Zhang W.
      • Chan T.
      • Saxena A.
      • Xiang J.
      Engineered fusion hybrid vaccine of IL-4 gene-modified myeloma and relative mature dendritic cells enhances antitumor immunity.
      ], CpG [
      • Hiraoka K.
      • Yamamoto S.
      • Otsuru S.
      • Nakai S.
      • Tamai K.
      • Morishita R.
      • et al.
      Enhanced tumor-specific long-term immunity of hemagglutinating [correction of hemaggluttinating] virus of Japan-mediated dendritic cell-tumor fused cell vaccination by coadministration with CpG oligodeoxynucleotides.
      ] or GM-CSF [
      • Cao X.
      • Zhang W.
      • Wang J.
      • Zhang M.
      • Huang X.
      • Hamada H.
      • et al.
      Therapy of established tumour with a hybrid cellular vaccine generated by using granulocyte-macrophage colony-stimulating factor genetically modified dendritic cells.
      ] could significantly enhanced the potency of DC-tumor cell fusion vaccines. DC-tumor cell fusion vaccines have been investigated in melanoma, renal and breast cancers, and multiple myeloma [
      • Browning M.J.
      Antigen presenting cell/ tumor cell fusion vaccines for cancer immunotherapy.
      ] with some successes. Avigan and colleagues treated 23 patients with metastatic breast or renal cancer and demonstrated disease regression in 2 breast cancer patients, and SDs in 1 breast and 5 renal cancer patients [
      • Browning M.J.
      Antigen presenting cell/ tumor cell fusion vaccines for cancer immunotherapy.
      ,
      • Avigan D.
      • Vasir B.
      • Gong J.
      • Borges V.
      • Wu Z.
      • Uhl L.
      • et al.
      Fusion cell vaccination of patients with metastatic breast and renal cancer induces immunological and clinical responses.
      ]. A subset of the vaccinated patients experienced increased IFN-γ-producing CD4+ and CD8+ T cells responding to tumorl ysates, indicating that tumour-specific immune responses were elicited [
      • Avigan D.
      • Vasir B.
      • Gong J.
      • Borges V.
      • Wu Z.
      • Uhl L.
      • et al.
      Fusion cell vaccination of patients with metastatic breast and renal cancer induces immunological and clinical responses.
      ]. In another study, 17 multiple myeloma patients vaccinated with autologous DCs-tumor cell fusion vaccine had SDs of up to 41 months [
      • Browning M.J.
      Antigen presenting cell/ tumor cell fusion vaccines for cancer immunotherapy.
      ,
      • Rosenblatt J.
      • Vasir B.
      • Uhl L.
      • Blotta S.
      • MacNamara C.
      • Somaiya P.
      • et al.
      Vaccination with dendritic cell/tumor fusion cells results in cellular and humoral antitumor immune responses in patients with multiple myeloma.
      ].

      Pros and cons of different tumor mouse models for evaluating cancer vaccines

      Syngeneic tumor models

      Syngeneic mouse models are the most frequently used tumor mouse models. They are generated by inoculating in vitro cultured tumor cell lines [
      • Talmadge J.E.
      • Singh R.K.
      • Fidler I.J.
      • Raz A.
      Murine models to evaluate novel and conventional therapeutic strategies for cancer.
      ] that are derived from common inbred mouse strains such as C57BL/6, BALB/c or FVB mice [
      • DeVita Jr., V.T.
      • Chu E.
      A history of cancer chemotherapy.
      ]. The tumor cells can be inoculated subcutaneously, intraperitoneally, intravenously or orthotopically in specific organs depending on the desired tumor model. Due to the ease of generating syngeneic tumor mouse models, large number of replicates and test groups can be used for robust statistical analysis. Moreover, the use of syngeneic tumor mouse models can ensure a highly similar disease development in the tumor-inoculated mice. Importantly, an intact immune system in syngeneic mouse models allows for immunotherapy evaluation [
      • DeVita Jr., V.T.
      • Chu E.
      A history of cancer chemotherapy.
      ]. The major limitation of syngeneic mouse models is that the inoculated tumor cell line may not contain all the relevant or specific gene mutations of a given cancer [
      • Hanahan D.
      • Weinberg R.A.
      Hallmarks of cancer: the next generation.
      ]. In addition, the growth kinetic of tumor resulting from tumor cell implantation does not reflect the reality of the spontaneous apparition of the disease. The fast tumor cell expansion from implantation could lead to unwanted side effects such as tumor necrosis and inflammation that could influence the immune response [
      • Yu J.W.
      • Bhattacharya S.
      • Yanamandra N.
      • Kilian D.
      • Shi H.
      • Yadavilli S.
      • et al.
      Tumor-immune profiling of murine syngeneic tumor models as a framework to guide mechanistic studies and predict therapy response in distinct tumor microenvironments.
      ]. Furthermore, the route of tumor implantation may not reflect the real disease and could cause unwanted consequences such as uncommon metastasis sites or no metastasis [
      • Talmadge J.E.
      • Singh R.K.
      • Fidler I.J.
      • Raz A.
      Murine models to evaluate novel and conventional therapeutic strategies for cancer.
      ,
      • Fidler I.J.
      • Hart I.R.
      Biological diversity in metastatic neoplasms: origins and implications.
      ]. To date, only a small fraction of syngeneic tumor mouse models used orthotopic implantation to closely model organ-specific cancer development. As metastasis is the principal cause of cancer death in patients, using tumor mouse models that can closely mimic relevant cancer metastatic events is highly useful [
      • Dillekås H.
      • Rogers M.S.
      • Straume O.
      Are 90% of deaths from cancer caused by metastases?.
      ]. Lastly, it has been shown that even inbred strains can be subjected to a certain variation due to genetic drift, husbandry conditions or immune infiltration differences [
      • Zeldovich L.
      Genetic drift: the ghost in the genome.
      ,
      • Parks C.
      • Giorgianni F.
      • Jones B.C.
      • Beranova-Giorgianni S.
      • Moore II B.M.
      • Mulligan M.K.
      Comparison and functional genetic analysis of striatal protein expression among diverse inbred mouse strains.
      ,
      • Bleul T.
      • Zhuang X.
      • Hildebrand A.
      • Lange C.
      • Böhringer D.
      • Schlunck G.
      • et al.
      Different innate immune responses in BALB/c and C57BL/6 strains following corneal transplantation.
      ]. Hence, this suggests tumor cell clonal selection and long-term passage in vitro could result in homogeneous cancer cell populations adapting to cell culture conditions that altered from the original parent tumor cells derived from patients. Although there are disadvantages associated with using syngeneic tumor models, they have provided invaluable insight into the complex interactions between cancer and the intact immune system to facilitate systematic immunotherapy evaluations.

      Patient-derived xenografts tumor models

      Patient-derived xenografts (PDXs) tumor models are generated by implanting surgically removed tumor fragments from patients into immunocompromised animals. Three main mice strains are used – i) athymic nude mice lacking thymus and hence no adaptive immunity, ii) severe combined immunodeficiency (SCID) mice lacking adaptive immunity and NK cells, and iii) NOD/SCID IL2rγ chain knockout (NSG) mice derived from SCID mice that are also knockout of the IL2rγ gene to give a strong immunodeficiency [
      • Hasgur S.
      • Aryee K.E.
      • Shultz L.D.
      • Greiner D.L.
      • Brehm M.A.
      Generation of immunodeficient mice bearing human immune systems by the engraftment of hematopoietic stem cells.
      ]. NSG mice are used for primary human tumor engraftment, whereas athymic nude and SCID mice are mainly used for human cell line engraftments [
      • Walsh N.C.
      • Kenney L.L.
      • Jangalwe S.
      • Aryee K.-E.
      • Greiner D.L.
      • Brehm M.A.
      • et al.
      Humanized mouse models of clinical disease.
      ]. The main advantage of grafting patient tumor samples is that it is possible to transfer the patient disease in its real state, i.e. in terms of cancer heterogeneity that reflect the original malignancy and its tumor microenvironment, to an animal model [
      • Reyal F.
      • Guyader C.
      • Decraene C.
      • Lucchesi C.
      • Auger N.
      • Assayag F.
      • et al.
      Molecular profiling of patient-derived breast cancer xenografts.
      ,
      • Evans K.W.
      • Yuca E.
      • Akcakanat A.
      • Scott S.M.
      • Arango N.P.
      • Zheng X.
      • et al.
      A Population of Heterogeneous Breast Cancer Patient-Derived Xenografts Demonstrate Broad Activity of PARP Inhibitor in BRCA1/2 Wild-Type Tumors.
      ]. This allows for the evaluation of treatment efficiency in real time following the evolution of the disease in the patient [
      • Ben-David U.
      • Ha G.
      • Tseng Y.-Y.
      • Greenwald N.F.
      • Oh C.
      • Shih J.
      • et al.
      Patient-derived xenografts undergo mouse-specific tumor evolution.
      ]. Also, PDX models provide an opportunity to study biomarkers and chemosensitivity [
      • Rivera M.
      • Fichtner I.
      • Wulf-Goldenberg A.
      • Sers C.
      • Merk J.
      • Patone G.
      • et al.
      Patient-derived xenograft (PDX) models of colorectal carcinoma (CRC) as a platform for chemosensitivity and biomarker analysis in personalized medicine.
      ]. However, as with syngeneic models, subcutaneously implanted PDX models may not reflect the real disease as observed in the patients [
      • Julien S.
      • Merino-Trigo A.
      • Lacroix L.
      • Pocard M.
      • Goéré D.
      • Mariani P.
      • et al.
      Characterization of a large panel of patient-derived tumor xenografts representing the clinical heterogeneity of human colorectal cancer.
      ]. To address this concern, PDX models with orthotopic implantation could be used [
      • Hoffman R.M.
      Patient-Derived Orthotopic Xenograft (PDOX) Models of Melanoma.
      ,
      • Fu X.
      • Guadagni F.
      • Hoffman R.M.
      A metastatic nude-mouse model of human pancreatic cancer constructed orthotopically with histologically intact patient specimens.
      ]. Another concern of PDX models is the progressive replacement of human intratumoural fibroblasts by mouse fibroblasts. This is particularly relevant as tumor-associated fibroblasts are shown to be important mediators of treatment resistance [
      • Ben-David U.
      • Ha G.
      • Tseng Y.-Y.
      • Greenwald N.F.
      • Oh C.
      • Shih J.
      • et al.
      Patient-derived xenografts undergo mouse-specific tumor evolution.
      ,
      • Junttila M.R.
      • de Sauvage F.J.
      Influence of tumour micro-environment heterogeneity on therapeutic response.
      ]. Finally, PDX models are unsuitable for evaluating immunotherapies due to their deficient intrinsic immune systems. Hence, there is an increasing interest in developing humanized PDX models with an immune system that is autologous to the implanted tumour. A study showed that allogeneic umbilical cord CD34+ hematopoietic stem cells (HSC) were used to recreate an immune system in NSG mice, and led to the regression of the engrafted tumors [
      • Wang M.
      • Yao L.-C.
      • Cheng M.
      • Cai D.
      • Martinek J.
      • Pan C.-X.
      • et al.
      Humanized mice in studying efficacy and mechanisms of PD-1-targeted cancer immunotherapy.
      ]. The therapeutic response was correlated with the presence of CD8+ lymphocytes, and could be further enhanced with anti-programmed death-ligand 1 (PD-L1) therapy [
      • Wang M.
      • Yao L.-C.
      • Cheng M.
      • Cai D.
      • Martinek J.
      • Pan C.-X.
      • et al.
      Humanized mice in studying efficacy and mechanisms of PD-1-targeted cancer immunotherapy.
      ]. However, it is important to note that that the immune response could be due to graft-versus-host disease (GVDH) instead of from the recognition of TAA(s). A solution could be to generate a mouse model with a human immune system. For example, the NSG-SGM3 BLT mice express human stem cell factor, GM-CSF and IL-3 can allow for the reconstitution of a human immune system after the engraftment of human hematopoietic stem cells, autologous fetal liver or thymic tissues [
      • Jangalwe S.
      • Shultz L.D.
      • Mathew A.
      • Brehm M.A.
      Improved B cell development in humanized NOD-scid IL2Rγ(null) mice transgenically expressing human stem cell factor, granulocyte-macrophage colony-stimulating factor and interleukin-3.
      ]. The NSG-SGM3 BLT mice are capable of producing human T and B lymphocytes, as well as human myeloid cells [
      • Jangalwe S.
      • Shultz L.D.
      • Mathew A.
      • Brehm M.A.
      Improved B cell development in humanized NOD-scid IL2Rγ(null) mice transgenically expressing human stem cell factor, granulocyte-macrophage colony-stimulating factor and interleukin-3.
      ]. As the development of such humanized mouse models improved, they can serve as useful tools for evaluating cancer vaccination strategies.

      Genetically engineered mouse models

      Genetically engineered mouse models (GEMMs) could serve as a realistic model for understanding human tumor development that is still difficult to model with syngeneic and PDX mouse models. Our increasing knowledge on oncogenes such as c-myc [
      • Stewart T.A.
      • Pattengale P.K.
      • Leder P.
      Spontaneous mammary adenocarcinomas in transgenic mice that carry and express MTV/myc fusion genes.
      ], k-ras [
      • Quaife C.J.
      • Pinkert C.A.
      • Ornitz D.M.
      • Palmiter R.D.
      • Brinster R.L.
      Pancreatic neoplasia induced by ras expression in acinar cells of transgenic mice.
      ] or p53 [
      • Jacks T.
      • Remington L.
      • Williams B.O.
      • Schmitt E.M.
      • Halachmi S.
      • Bronson R.T.
      • et al.
      Tumor spectrum analysis in p53-mutant mice.
      ] and genetic engineering allowed us to develop animal models with inducible overexpression or knockout of gene(s) [
      • Van Dyke T.
      • Jacks T.
      Cancer modeling in the modern era: progress and challenges.
      ]. With the advances made in the field, it is possible to administer a single compound (e.g. tamoxifen) to the mice to alter a gene not only in the desired tissue but also conditionally at a particular developmental stage [
      • Rubera I.
      • Poujeol C.
      • Bertin G.
      • Hasseine L.
      • Counillon L.
      • Poujeol P.
      • et al.
      Specific Cre/Lox recombination in the mouse proximal tubule.
      ]. As GEMMs allow the spontaneous development of the disease in an immunocompetent host, this help to preserve the evolution of a native tumor microenvironment that is more representative of the real disease. This is particularly important as the tumor microenvironment has a noticeable impact on immunotherapies [
      • Gajewski T.F.
      • Woo S.-R.
      • Zha Y.
      • Spaapen R.
      • Zheng Y.
      • Corrales L.
      • et al.
      Cancer immunotherapy strategies based on overcoming barriers within the tumor microenvironment.
      ]. Other notable use of GEMMs is the discovery of the fact that mammalian cell proliferation does not always rely on the activity of cyclin-dependent kinase 2 (CDK2), which is a key mediator in cell cycle G1/S transition [
      • Ortega S.
      • Prieto I.
      • Odajima J.
      • Martín A.
      • Dubus P.
      • Sotillo R.
      • et al.
      Cyclin-dependent kinase 2 is essential for meiosis but not for mitotic cell division in mice.
      ,
      • Berthet C.
      • Aleem E.
      • Coppola V.
      • Tessarollo L.
      • Kaldis P.
      Cdk2 knockout mice are viable.
      ]. Moreover, the inherent slow tumor development in GEMMs offers an opportunity to monitor the long-term evolution of the disease. GEMMs could be used to model after clinical situations in patients who undergo long-term chemo-, radio- and/or chemotherapy, and determining if the patients’ tumors will develop treatment resistance or responsive to immunotherapy. GEMMs are good tools for studying cancer treatment toxicity, for example, by generating specific gene knockout(s) for drug evaluation [
      • Maggi A.
      • Ciana P.
      Reporter mice and drug discovery and development.
      ]. GEMMs have limitations as it is still complex to develop models that can accurately recapitulate the human disease. Also, the latency and penetrance of the disease can be relatively variable between mice in the same experiment that can complicate experimental design. Another major hurdle for the use of GEMMs is that most of the transgenic mice technologies are under patents [
      • Marshall E.
      Intellectual property. DuPont ups ante on use of Harvard's OncoMouse.
      ] that can add to the cost of the experiments in terms of license and set up.

      Using preclinical tumor models to improve cancer vaccination strategies

      Liposome- and nanoparticle-based delivery platforms

      Syngeneic mouse tumor models offer a straightforward platform for developing and evaluating cancer vaccines. Due to the challenges present in PDX and GEMs tumor models, we focused on promising cancer vaccination strategies in syngeneic tumor models such as 4T1 breast, B16 melanoma, ID8 ovarian and CT26 colorectal. Preclinical tumor models offer the opportunity to investigate cutting-edge methodologies, as well as improving cancer vaccination strategies. An area of interest in cancer vaccination is to improve the delivery of tumor antigens to the host for efficient antitumor priming. In a study that seek to increase the efficiency of protein delivery into the cytosol of APCs, a nanovaccine comprised of fluoropolymer and tumor cell membrane has been used and showed the ability to impair tumor recurrence and metastasis in several tumor models including B16-OVA-expressing melanoma [
      • Zhang Z.
      • Shen W.
      • Ling J.
      • Yan Y.
      • Hu J.
      • Cheng Y.
      The fluorination effect of fluoroamphiphiles in cytosolic protein delivery.
      ,
      • Xu J.
      • Lv J.
      • Zhuang Q.i.
      • Yang Z.
      • Cao Z.
      • Xu L.
      • et al.
      A general strategy towards personalized nanovaccines based on fluoropolymers for post-surgical cancer immunotherapy.
      ]. Liposome- and nanoparticle-based drug delivery systems are also being actively investigated [
      • Liu J.
      • Miao L.
      • Sui J.
      • Hao Y.
      • Huang G.
      Nanoparticle cancer vaccines: Design considerations and recent advances.
      ,
      • Anselmo A.C.
      • Mitragotri S.
      Nanoparticles in the clinic: an update.
      ]. Examples of marketed liposome-based vaccine preparations such as Epaxal® (hepatitis A virus vaccine) [
      • Lim J.
      • Song Y.-J.
      • Park W.-S.
      • Sohn H.
      • Lee M.-S.
      • Shin D.-H.
      • et al.
      The immunogenicity of a single dose of hepatitis A virus vaccines (Havrix® and Epaxal®) in Korean young adults.
      ] and Inflexal® (influenza vaccine) [
      • Herzog C.
      • Hartmann K.
      • Künzi V.
      • Kürsteiner O.
      • Mischler R.
      • Lazar H.
      • et al.
      Eleven years of Inflexal V-a virosomal adjuvanted influenza vaccine.
      ] have demonstrated that liposomes are safe. A variety of polymer-based nanoparticles including poly (lactide-o-glycolic) acid [PLGA], polyethylene glycol and chitosan have been approved by the Food and Drug Administration (FDA) in USA for clinical use due to their biocompatible and nontoxic characteristics [
      • Anselmo A.C.
      • Mitragotri S.
      Nanoparticles in the clinic: an update.
      ]. Preclinical study with WTL encapsulated with chitosan nanoparticles (CTS-NPs) in B16 melanoma model demonstrated that CTS-NPs were able to delay tumor growth in the animals [
      • Shi G.-N.
      • Zhang C.-N.
      • Xu R.
      • Niu J.-F.
      • Song H.-J.
      • Zhang X.-Y.
      • et al.
      Enhanced antitumor immunity by targeting dendritic cells with tumor cell lysate-loaded chitosan nanoparticles vaccine.
      ]. The injected CTS-NPs were phagocytosed by endogenous DCs and elicited a systemic effect (increased sera IFN-γ and IL-4 levels) and CTL responses against the tumor [
      • Shi G.-N.
      • Zhang C.-N.
      • Xu R.
      • Niu J.-F.
      • Song H.-J.
      • Zhang X.-Y.
      • et al.
      Enhanced antitumor immunity by targeting dendritic cells with tumor cell lysate-loaded chitosan nanoparticles vaccine.
      ].

      Improving (neo)peptide-based vaccination

      Syngeneic tumor models can be used to evaluate the effectiveness of candidate synthetic peptides, including tumor neoantigens. For example, KRAS mutations are frequently present in different malignancies including pancreatic, colorectal and lung cancer [
      • Mann K.M.
      • Ying H.
      • Juan J.
      • Jenkins N.A.
      • Copeland N.G.
      KRAS-related proteins in pancreatic cancer.
      ,
      • Cox A.D.
      • Fesik S.W.
      • Kimmelman A.C.
      • Luo J.
      • Der C.J.
      Drugging the undruggable RAS: Mission possible?.
      ]. The infusion of tumor-infiltrating lymphocyes specific to the KRAS G12D mutations led to significant metastatic regression in a patient with such mutation [
      • Tran E.
      • Robbins P.F.
      • Lu Y.-C.
      • Prickett T.D.
      • Gartner J.J.
      • Jia L.i.
      • et al.
      T-Cell Transfer Therapy Targeting Mutant KRAS in Cancer.
      ]. So far, cancer vaccine based on KRAS mutation has shown modest clinical benefits [
      • Palmer D.H.
      • Valle J.W.
      • Ma Y.T.
      • Faluyi O.
      • Neoptolemos J.P.
      • Jensen Gjertsen T.
      • et al.
      TG01/GM-CSF and adjuvant gemcitabine in patients with resected RAS-mutant adenocarcinoma of the pancreas (CT TG01-01): a single-arm, phase 1/2 trial.
      ]. To create a more immunogenic KRAS-based vaccine, Wan et al. fused the KRAS peptide to a C-terminal of the translocation domain of the diphtheria toxin. Treatment of CT26 tumor-bearing mice with this vaccine led to increase CD8+ T cells and a reduction of T regulatory cells [
      • Wan Y.
      • Zhang Y.
      • Wang G.
      • Mwangi P.M.
      • Cai H.
      • Li R.
      Recombinant KRAS G12D protein vaccines elicit significant anti-tumor effects in mouse CT26 tumor models.
      ]. Another methodology to enhance immunogenicity of a peptide vaccine is by using mesoporous silicas micro-rod (MSR) adsorbed with polyethyleneimine (PEI). Such particles can be used to adsorb peptide antigens. Preclinical studies with this vaccine formulated with B16.F10 and CT26 neoantigens demonstrated the ability to eradicate established lung metastasis in tumor-bearing mice when used in combination with anti-CTLA-4 antibody therapy [
      • Li A.W.
      • Sobral M.C.
      • Badrinath S.
      • Choi Y.
      • Graveline A.
      • Stafford A.G.
      • et al.
      A facile approach to enhance antigen response for personalized cancer vaccination.
      ]. Neoantigen-targeting is becoming increasing important in the context of eliciting high-avidity antitumor T cell responses. For this purpose, syngeneic tumor models are useful tools for evaluating the different methodologies to predict efficacious neoantigen candidates for vaccination. Table 3 summarised a number of preclinical studies that have demonstrated the feasibility of neoantigen vaccination.

      Improving nucleic acid- and exosome-based vaccination

      DNA and RNA vaccines have been evaluated but yet to show significant clinical benefit against cancer [
      • Jahanafrooz Z.
      • Baradaran B.
      • Mosafer J.
      • Hashemzaei M.
      • Rezaei T.
      • Mokhtarzadeh A.
      • et al.
      Comparison of DNA and mRNA vaccines against cancer.
      ]. To improve their efficacy, various methods have been tested. Li et al. developed a polyepitope neoantigen-based DNA vaccine to achieve a similar efficacy as in peptide vaccination in animals bearing breast tumor E0771 or 4T1 [
      • Li L.
      • Zhang X.
      • Wang X.
      • Kim S.W.
      • Herndon J.M.
      • Becker-Hapak M.K.
      • et al.
      Optimized polyepitope neoantigen DNA vaccines elicit neoantigen-specific immune responses in preclinical models and in clinical translation.
      ]. Besides targeting tumors, DNA vaccine can be used to target cancer-associated fibroblasts in the tumor microenvironment to help recruit antitumor effector T cells [
      • Geng F.
      • Guo J.
      • Guo Q.-Q.
      • Xie Y.u.
      • Dong L.
      • Zhou Y.i.
      • et al.
      A DNA vaccine expressing an optimized secreted FAPα induces enhanced anti-tumor activity by altering the tumor microenvironment in a murine model of breast cancer.
      ]. This DNA vaccine can be further enhanced with doxorubicin administration [
      • Geng F.
      • Bao X.
      • Dong L.
      • Guo Q.-Q.
      • Guo J.
      • Xie Y.u.
      • et al.
      Doxorubicin pretreatment enhances FAPα/survivin co-targeting DNA vaccine anti-tumor activity primarily through decreasing peripheral MDSCs in the 4T1 murine breast cancer model.
      ]. Various ways to improve the delivery of mRNA to DCs exist, including lipid/calcium/phosphate nanoparticles; such method was able to achieve a strong CTL response on triple-negative 4T1 breast tumor cells [
      • Liu L.
      • Wang Y.
      • Miao L.
      • Liu Q.i.
      • Musetti S.
      • Li J.
      • et al.
      Combination Immunotherapy of MUC1 mRNA Nano-vaccine and CTLA-4 Blockade Effectively Inhibits Growth of Triple Negative Breast Cancer.
      ]. Liposomes [
      • Salomon N.
      • Vascotto F.
      • Selmi A.
      • Vormehr M.
      • Quinkhardt J.
      • Bukur T.
      • et al.
      A liposomal RNA vaccine inducing neoantigen-specific CD4(+) T cells augments the antitumor activity of local radiotherapy in mice.
      ] and lipid nanoparticles [
      • Zhang H.
      • You X.
      • Wang X.
      • Cui L.
      • Wang Z.
      • Xu F.
      • et al.
      Delivery of mRNA vaccine with a lipid-like material potentiates antitumor efficacy through Toll-like receptor 4 signaling.
      ] can also be used for preparing such mRNA vaccines. Finally, alternative tumor cell-derived antigens, i.e. microRNA-enriched exosomes vaccine have shown promising results against CT26 colorectal tumor-bearing mice [
      • Rezaei R.
      • Baghaei K.
      • Hashemi S.M.
      • Zali M.R.
      • Ghanbarian H.
      • Amani D.
      Tumor-Derived Exosomes Enriched by miRNA-124 Promote Anti-tumor Immune Response in CT-26 Tumor-Bearing Mice.
      ]. Although syngeneic tumor models have been criticized for their simplistic representation of diseases, nonetheless they play an important role in the preclinical development of cancer vaccines.

      Conclusion

      Personalized cancer vaccines are a promising strategy for eliciting a diversified antitumor T cell repertoire that is beneficial and relevant for individual cancer patients. Although the efficacy and success of personalized cancer vaccines are still less dramatic as those seen with immune checkpoint inhibitors and T cell therapy, tremendous effects are continuing to improve cancer vaccine formulations and preparations. Preclinical tumor animal models offer the opportunity to investigate cutting-edge methodologies such as nanoparticle-based antigen delivery system and tumor neoantigen vaccination, as well as improving cancer vaccination strategies. Preclinical tumor models can serve as useful tools to aid future cancer vaccine trial design.

      Funding

      This work is supported by funding from Ludwig Institute for Cancer Research.

      Institutional Review Board Statement

      Not applicable.

      Informed Consent Statement

      Not applicable.

      Data Availability Statement

      Not applicable.

      CRediT authorship contribution statement

      Hajer Fritah: Data curation, Writing – original draft. Raphaël Rovelli: Data curation, Writing – original draft. Cheryl Lai-Lai Chiang: Conceptualization, Data curation, Writing – original draft, Writing - review & editing. Lana E. Kandalaft: Conceptualization, Writing - review & editing.

      Declaration of Competing Interest

      The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

      Acknowledgement

      Fig. 1, Fig. 2 are adapted from “Types of Influenza Vaccines”, by BioRender.com (2022). Retrieved from https://app.biorender.com/biorender-templates.

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