Effective neoantigen vaccination correlates with generation of antigen-specific CX3CR1+CD8+ T cells mediated by CD40 and CD80/86 signaling in cDC1s

Background The use of tumor mutation-derived neoantigen represents a promising approach for cancer vaccines. Preclinical and early-phase human clinical studies have shown the successful induction of tumor neoepitope-directed responses; however, overall clinical efficacy of neoantigen vaccines has been limited. One major limitation of this strategy is the lack of a reliable blood-based surrogate marker for clinical response. Here, we investigated a role of CX3C chemokine receptor 1 (CX3CR1), a marker of T-cell differentiation in predicting response to neoantigen vaccination in a preclinical model. Methods Mice bearing MC38 colon adenocarcinoma cells that harbor a single-epitope mutation within the Adpgk protein were treated with mutant Adpgk peptide (AdpgkMut) in combination with toll-like receptor 3 (TLR3) agonist poly(I:C) and/or anti-CD40 antibody (Ab). Antitumor efficacy of neoantigen vaccination and the frequency of peripheral blood AdpgkMut-specific CX3CR1+CD8+ T cells were assessed. Mechanisms underlying the generation of CX3CR1+CD8+ T cells were examined using knockout and bone marrow chimeric mice. Results We found that CD40 stimulation significantly enhanced antitumor efficacy of neoantigen and TLR3 agonist vaccination, which was associated with an increased frequency of circulating AdpgkMut-specific effector CX3CR1+CD8+ T cells. Generation of neoantigen-specific CX3CR1+CD8+ T cells by AdpgkMut/CD40/TLR3 stimulation was dependent on CD40 and Batf3 in bone marrow-derived cells. Further mechanistic studies using mixed bone marrow chimeras identified key roles for CD40 and CD80/86, but not CD70 signaling in Batf3-dependent conventional type 1 dendritic cells (cDC1s) for generation of neoantigen-specific cytotoxic CX3CR1+CD8+ T cells and therapeutic efficacy of neoantigen vaccine. Conclusions Taken together, our results underscore critical roles of cDC1s and an implication of dual CD40/TLR3 stimulation in neoantigen-based therapeutic vaccines, and demonstrate the potential utility of CX3CR1 as a circulating predictive T-cell biomarker in vaccine clinical trials.