Background T-cell targeting of tumor-specific non-synonymous mutations has been demonstrated to drive antitumor responses. Developing therapies against such neoantigens as monotherapy or in combination with a checkpoint inhibitor (CPI) may elicit antitumor immune responses, resulting in clinical benefit. The combination of the novel INT mRNA-4157 (V940) and pembrolizumab improved recurrence-free survival and demonstrated a manageable safety profile when compared with pembrolizumab monotherapy in patients with resected high-risk stage III/IV cutaneous melanoma in the randomized phase 2 mRNA-4157-P201/KEYNOTE-942 study (NCT03897881). Here, we report results from the first-in-human phase 1 study (NCT03313778) of mRNA-4157 ± pembrolizumab to characterize the mechanism of action in patients with resected cutaneous melanoma or non-small cell lung cancer (NSCLC).

Methods Baseline tumor core biopsies and matched whole blood from patients with resected NSCLC (cohort A, 1 mg mRNA-4157, n=4) and resected cutaneous melanoma (cohort D, 1 mg mRNA-4157 and 200 mg pembrolizumab, n=12) underwent whole exome sequencing (WES). The immune response to mRNA-4157 was assessed via antigen-specific T-cell assays in peripheral blood mononuclear cells (PBMCs). T-cell responses to INT neoantigen pools or to individual neoantigens were analyzed directly ex vivo using interferon-gamma enzyme-linked ImmunoSpot (ELISpot) assays at longitudinal study timepoints. Neoantigen-specific CD4 and/or CD8 T-cell responses were characterized through restimulation of expanded cells followed by intracellular cytokine staining. Direct ex vivo immunophenotyping was performed by flow cytometry.

Results T-cell immunogenicity analysis was assessed in available samples from cohorts A (n=3) and D (n=7) across multiple timepoints during the course of treatment. Neoantigen-specific T cells were induced in all patients tested. There was consistent induction of de novo T-cell responses in both cohorts and longitudinal immunogenicity analyses showed sustained T-cell responses to targeted neoantigens, including in blood samples collected at 30 weeks and beyond post start of treatment. Increases in pre-existing neoantigen responses that were present at baseline (endogenous) or after pembrolizumab run-in were observed following mRNA-4157 therapy. Combination of therapy drove expansion of effector CD4 and CD8 T cells with cytotoxic potential.

Conclusions In this phase 1 first-in-human study, mRNA-4157 as a monotherapy or in combination with pembrolizumab showed immunogenicity in patients with resected NSCLC or melanoma. These data demonstrate the ability of the algorithm to select neoantigens with tumor-infiltrating lymphocyte reactivities, support the mechanism of action hypothesized for mRNA-4157, and underscore the potential clinical benefit of an INT approach.

Acknowledgements Medical writing and editorial assistance were provided by Caudex, a division of IPG Health Medical Communications, New York, NY, USA in accordance with Good Publication Practice 2022 guidelines, funded by Moderna Inc., and under the direction of the authors. Funding for this research was provided by Moderna Inc., in collaboration with Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA.

Trial Registration ClinicalTrials.gov; NCT03313778

Ethics Approval The study protocol was approved by the institutional review board or ethics committee of each participating site. All patients provided written informed consent prior to study participation.