Abstract
Personalized neoantigen-targeting vaccines have demonstrated great promise; however, improved immunogenicity is still needed. Since antigen availability and effective T cell priming are critical for maximal immunogenicity, we tested a synthetic long peptide vaccine formulated with Montanide, poly-ICLC, and locally administered ipilimumab in addition to systemic nivolumab in 10 patients with melanoma. These personalized vaccines generated de novo ex vivo T cell responses against the majority of immunizing neoepitopes in all 9 fully vaccinated patients and ex vivo CD8+ T cell responses in 6 of 9. Vaccination induced hundreds of circulating and intratumoral T cell receptor (TCR) clonotypes that were distinct from those arising after PD-1 inhibition. By linking the vaccine neoantigen specificity of T cell clonotypes with single-cell phenotypes in tumors, we demonstrate remodeling of the intratumoral T cell repertoire following vaccination. These observations show that multi-pronged immune adjuvanticity can boost T cell responses to neoantigen-targeting vaccines.