Personalized Peptide Cancer Vaccines: Neoantigen Targeting in 31 Active Clinical Trials

As of November 2024, ClinicalTrials.gov lists 78 registered personalized cancer vaccine trials spanning multiple delivery platforms. Among these, peptide-based vaccines constitute the single largest category with 31 active trials, followed by dendritic cell vaccines (15 trials) and RNA-based platforms (13 trials). The dominance of peptide vaccines is consistent with earlier analyses indicating that peptide delivery accounts for approximately 64.8% of all neoantigen-specific vaccine trials, reflecting the platform's established immunogenicity profile, favorable safety data, and relatively straightforward manufacturing workflow compared to viral vector or cell-based approaches.

Geographically, the United States hosts approximately 44% of all registered personalized cancer vaccine trials, with China contributing 24%. Over 90% of these studies remain in Phase I, underscoring the early but rapidly expanding nature of this field. Solid tumors — including melanoma, pancreatic, renal, breast, and hepatocellular carcinoma — represent the primary indications under investigation, though hematologic malignancies are increasingly included in multi-tumor platform trials.

Neoantigen peptide vaccines are constructed from tumor-specific mutant peptide sequences identified through whole-exome sequencing (WES) and RNA sequencing of patient tumor tissue relative to matched normal DNA. Computational pipelines — including NetMHCpan for MHC binding prediction, variant calling algorithms, and expression-level filtering — rank candidate neoantigens by predicted immunogenicity. Selected peptides are typically 15-30 amino acid residues in length (long peptides), enabling both MHC class I and class II presentation and thereby engaging CD8+ cytotoxic and CD4+ helper T-cell responses simultaneously.

Adjuvant selection is critical to peptide vaccine immunogenicity. Commonly employed adjuvants in current trials include poly-ICLC (a synthetic double-stranded RNA analog that activates TLR3 and MDA5), GM-CSF (granulocyte-macrophage colony-stimulating factor for dendritic cell recruitment), and plasmid-encoded IL-12 for enhanced Th1 polarization. The choice of adjuvant platform directly influences the magnitude and quality of the resulting T-cell response.

A landmark Phase I trial (NCT02950766), published in Nature in February 2025, tested a personalized neoantigen-targeting peptide vaccine in nine patients with high-risk, fully resected stage III or IV clear cell renal cell carcinoma (ccRCC). At a median follow-up of 40.2 months after surgery, none of the nine vaccinated participants experienced disease recurrence — a striking observation given the historically high recurrence rate in this population.

All nine patients generated polyfunctional T-cell immune responses against vaccine-encoded neoantigens, including responses targeting key RCC driver mutations in VHL, PBRM1, BAP1, KDM5C, and PIK3CA. T-cell reactivity against autologous tumors was confirmed in seven of nine patients. Peripheral T-cell clone expansion was durable, persisting well beyond the vaccination period. No dose-limiting toxicities were observed. These data are particularly noteworthy because ccRCC is characterized by a relatively low tumor mutational burden, suggesting that neoantigen-targeting peptide vaccines may be effective even in tumors with limited neoantigen repertoires.

A Phase 1/2 trial (NCT04251117), published in Nature Medicine in April 2024, evaluated a DNA plasmid personalized therapeutic cancer vaccine (GNOS-PV02) encoding up to 40 patient-specific neoantigens, co-administered with plasmid-encoded interleukin-12 and the PD-1 inhibitor pembrolizumab, in 36 patients with advanced hepatocellular carcinoma (HCC) previously treated with a multityrosine kinase inhibitor.

Safety was favorable: the most common treatment-related adverse events were injection-site reactions (41.6% of patients), with no dose-limiting toxicities and no treatment-related grade 3 or higher events. Efficacy signals were substantial for this difficult-to-treat indication: the objective response rate was 30.6% per RECIST 1.1 criteria, with a complete response rate of 8.3% (3 of 36 patients). Neoantigen-specific T-cell responses were confirmed in 86.4% (19/22) of evaluable patients via ELISpot assays, with multiparametric profiling revealing active, proliferative, and cytolytic vaccine-specific CD4+ and CD8+ effector T cells. Clinical responses correlated with the number of neoantigens encoded in the vaccine construct.

The PNeoVCA trial (NCT05269381), led by investigators at Mayo Clinic, is a single-arm Phase I study evaluating a personalized neoantigen peptide-based vaccine in combination with pembrolizumab in patients with advanced solid tumors that have progressed on at least one prior line of systemic therapy. The vaccine consists of up to 20 synthetic long peptides (15-30 residues) comprising patient-specific neoantigens identified through the REAL-neo computational pipeline, delivered subcutaneously with GM-CSF as adjuvant.

The vaccination schedule includes priming doses on days 1, 4, 8, 15, and 21, with a booster phase added for the second enrollment cohort at weeks 5 and 8. Cohort 1 was completed without dose-limiting toxicity, and enrollment in Cohort 2 commenced in January 2024. Primary endpoints include safety and feasibility assessment, with secondary endpoints evaluating objective response rate per RECIST criteria. This trial is significant as it directly tests whether personalized peptide neoantigen vaccination can enhance PD-1 blockade efficacy in treatment-refractory solid malignancies.

The PGV001 platform (NCT02721043), developed at the Icahn School of Medicine at Mount Sinai and published in Cancer Discovery in May 2025, represents a multi-peptide personalized neoantigen vaccine tested in the adjuvant setting across patients with both solid and hematologic malignancies at high risk of recurrence. The vaccine targeted up to 10 computationally predicted neoantigens per patient using the open-source OpenVax bioinformatics pipeline, administered with poly-ICLC adjuvant.

Of 14 enrolled patients, 13 received the vaccine and 11 completed the full treatment course. Immunogenicity was remarkable: 100% of vaccinated patients developed measurable neoantigen-specific T-cell and B-cell responses. At five-year follow-up, 6 of 13 treated patients survived, with 3 of the surviving patients remaining tumor-free. The OpenVax pipeline demonstrated the ability to predict immunogenic neoantigens across tumors with widely varying mutational burdens, supporting the feasibility of peptide neoantigen vaccination as a platform-agnostic approach applicable to diverse cancer types.

The mechanistic rationale for combining neoantigen peptide vaccines with immune checkpoint inhibitors (ICIs) rests on complementary modes of action. Peptide vaccines prime and expand tumor-specific T-cell populations by presenting mutant epitopes in an immunogenic context with appropriate adjuvant co-stimulation. Checkpoint inhibitors — particularly anti-PD-1 (pembrolizumab, nivolumab) and anti-CTLA-4 (ipilimumab) antibodies — release the brakes on these primed T cells by blocking inhibitory receptor signaling in the tumor microenvironment.

Across the trials reviewed, tumor-specific T-cell activation rates approach 80% in patients with treatment-refractory cancers when peptide vaccination is combined with checkpoint blockade. The HCC trial demonstrated that vaccine-induced T-cell clones actively infiltrate tumors post-vaccination, with TCR-beta sequencing confirming clonal expansion and tumor homing of vaccine-specific T cells. The RCC data further showed that vaccine-induced responses target driver mutations in tumor suppressor genes, suggesting functional relevance beyond mere immunologic detection. These findings collectively indicate a synergistic interaction: vaccination generates the effector T-cell repertoire while checkpoint blockade sustains its antitumor activity within the immunosuppressive tumor microenvironment.

• Peptide vaccines generate de novo T-cell responses against tumor-specific mutant epitopes
• Anti-PD-1 therapy prevents T-cell exhaustion and maintains effector function in the tumor microenvironment
• Anti-CTLA-4 enhances T-cell priming and broadens the neoantigen-specific repertoire during the vaccine priming phase
• Combination approaches show higher response rates than either modality alone in early-phase data
• T-cell receptor sequencing confirms that vaccine-induced clones actively traffic to and infiltrate tumor tissue

Despite promising clinical data, personalized peptide neoantigen vaccines face substantial manufacturing and scalability challenges that currently limit their broader clinical deployment. The end-to-end manufacturing timeline — from tumor biopsy through sequencing, neoantigen prediction, peptide synthesis, quality control, and GMP release — typically spans 8 to 16 weeks. This timeline constraint is particularly relevant for patients with rapidly progressive disease who may not have the luxury of waiting for vaccine availability.

Each vaccine is a unique product, requiring individualized synthesis of 10 to 40 distinct peptide sequences per patient. GMP-grade synthesis of long peptides (20-30 residues) with acceptable purity (typically greater than 95%) and endotoxin levels demands specialized facilities and rigorous quality control. Cost per patient remains high, with estimates ranging from $50,000 to $100,000 for the vaccine manufacturing component alone, exclusive of clinical administration and monitoring costs. Emerging strategies to address these constraints include shared (off-the-shelf) neoantigen libraries targeting recurrent hotspot mutations, automated peptide synthesis platforms, and hybrid approaches combining personalized peptides with shared tumor-associated antigens.

A comprehensive review published in Cell Reports Medicine in February 2026, authored by investigators from Mount Sinai's Tisch Cancer Center and the Parker Institute for Cancer Immunotherapy, maps the trajectory from early failures to the current clinical pipeline. The review identifies several convergent factors driving the field forward: improved neoantigen prediction algorithms with higher positive predictive value, recognition that combination with checkpoint inhibitors substantially amplifies vaccine efficacy, and growing evidence from adjuvant settings suggesting that vaccination in minimal residual disease states may offer the highest probability of durable responses.

Key unresolved questions include optimal patient selection biomarkers, the minimum number of targetable neoantigens required for clinical benefit, the relative merits of peptide versus mRNA versus DNA delivery platforms, and the durability of vaccine-induced immune memory beyond current follow-up periods. The field is also beginning to address whether personalized vaccines can be combined with additional modalities — including radiation therapy, bispecific antibodies, and adoptive cell transfer — to further enhance antitumor immunity.

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