Can neoantigen vaccines treat patients safely and durably?

How safe are neoantigen vaccines?

Across all 11 clinical trials reviewed, neoantigen vaccines were consistently well-tolerated, with no severe vaccine-related adverse events reported. The most common side effects were mild injection-site reactions, fatigue, and fever, typically grade 1 [1][3][4][5][6][8][9]. For example, in a phase 1 trial of 38 patients with non-small cell lung cancer, no treatment-related serious adverse events were observed [8]. In a trial of 10 patients with hepatocellular carcinoma, no obvious adverse events occurred during vaccination [4]. Even in a study combining the vaccine with an immune checkpoint inhibitor (atezolizumab) in urothelial cancer, only one patient developed grade 3 immune-related hepatitis, and the most common side effects remained mild injection-site reactions and fatigue [3][7]. These findings are consistent across different cancer types and vaccine platforms (mRNA, long peptides, DNA), indicating a strong safety profile.

Does the vaccine produce durable immune responses?

Yes, neoantigen vaccines can generate durable, long-lasting T-cell responses. In a landmark phase 1 trial for pancreatic cancer, 8 of 16 patients developed de novo neoantigen-specific T cells after vaccination, with some T cells comprising up to 10% of all blood T cells and persisting as long-lived polyfunctional effector CD8+ T cells [1]. In a trial for lymphoplasmacytic lymphoma, vaccine therapy activated and expanded bone marrow T-cell clonotypes, and functional neoantigen-specific responses were detected as a secondary endpoint [5]. In urothelial cancer, all evaluated patients demonstrated the emergence of ex vivo T-cell responses, including circulating multi-functional CD4+ and CD8+ neoantigen-specific T cells [3][7]. In advanced pancreatic cancer, one patient had a 21-month overall survival associated with vaccine treatment, and the abundance of antigen-specific T-cell receptor clones increased from 0% to nearly 100% [9]. These data show that the vaccines can induce strong, persistent, and functional T-cell immunity.

Does this translate into clinical benefit?

Yes, several trials show that patients who mount a vaccine-induced immune response have significantly better outcomes. In pancreatic cancer, patients with vaccine-expanded T cells had a median recurrence-free survival not reached at 18 months, compared to 13.4 months for non-responders (p=0.003) [1]. In hepatocellular carcinoma, patients who demonstrated neoantigen-induced T-cell responses had significantly longer recurrence-free survival after radical surgery than those without responsive neoantigens (p=0.035) [4]. In microsatellite-stable colorectal cancer, 4 of 6 patients remained progression-free up to the end of the trial, with a median progression-free survival of 19 months in responders versus 11 months in non-responders [6]. In lymphoplasmacytic lymphoma, all 9 patients achieved stable disease or better, with a median time to progression of over 72 months [5]. In urothelial cancer, 3 of 4 adjuvant patients were free of recurrence at a median follow-up of 39 months, and 2 of 5 metastatic patients achieved an objective response [7]. These results, from multiple independent trials, demonstrate that neoantigen vaccines can provide meaningful clinical benefit.

What are the limitations and challenges?

Despite promising results, several challenges remain. First, not all patients respond: in the pancreatic cancer trial, only 8 of 16 patients (50%) developed vaccine-induced T cells [1]. In a broader analysis of 352 patients, only 10-20% of selected neoantigen peptides actually induced immune responses, highlighting the need for better prediction methods [2]. Second, vaccine production time can be a barrier: in the urothelial cancer trial, the median time from consent to vaccine preparation was 20.3 weeks, which may be too slow for some patients with rapidly progressing disease [7]. Third, resistance mechanisms can emerge: in lymphoplasmacytic lymphoma, some tumor cells downregulated HLA class II molecules and upregulated insulin-like growth factor signaling, suggesting escape pathways [5]. Finally, most trials are small phase 1 studies, and larger randomized controlled trials are needed to confirm efficacy. The evidence is strongest for safety and immunogenicity; the durability of clinical benefit is encouraging but still preliminary.

About These Sources

This answer is built on 9 peer-reviewed studies — published from 2021 to 2026, 4 from 2024 or later, 9 in Q1 journals, collectively cited 1,551 times — selected as the most relevant from 11 studies that passed quality screening, drawn from 57 papers retrieved from a database of over 500 million.

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