A Synthetic DNA, Multi-Neoantigen Vaccine Drives Predominately MHC Class I CD8+ T-cell Responses, Impacting Tumor Challenge

T-cell recognition of cancer neoantigens is important for effective immune-checkpoint blockade therapy, and an increasing interest exists in developing personalized tumor neoantigen vaccines. Previous studies utilizing RNA and long-peptide neoantigen vaccines in preclinical and early-phase clinical studies have shown immune responses predominantly driven by MHC class II CD4+ T cells. Here, we report on a preclinical study utilizing a DNA vaccine platform to target tumor neoantigens. We showed that optimized strings of tumor neoantigens, when delivered by potent electroporation-mediated DNA delivery, were immunogenic and generated predominantly MHC class I–restricted, CD8+ T-cell responses. High MHC class I affinity was associated specifically with immunogenic CD8+ T-cell epitopes. These DNA neoantigen vaccines induced a therapeutic antitumor response in vivo, and neoantigen-specific T cells expanded from immunized mice directly killed tumor cells ex vivo. These data illustrate a unique advantage of this DNA platform to drive CD8+ T-cell immunity for neoantigen immunotherapy.