Description

Agonist Anti-CD40 Antibody Treatment Reinvigorates Neoantigen-Specific CD8 T-cells and Induces Regression of Established Tumors

Jeffrey Ward¹, E Alspach², D Runci², T Noguchi², M Gubin², C Arthur², E Mardis,³ M Artyomov², and RD Schreiber²

¹Divison of Oncology, Department of Medicine, ²Department of Pathology & Immunology and ³McDonnell Genome Institute, Washington University School of Medicine, St. Louis, Missouri, USA

Work by several groups including ours has demonstrated that tumor specific mutant antigens (neoantigens) that elicit CD8+ and CD4+ T-cell responses serve as targets for both spontaneous and therapeutic anti-tumor immunity. Using our established immunogenomics approach, we identified a missense mutation in Pex14 expressed by the edited, checkpoint blockade sensitive MCA-induced sarcoma line F244 that induces CD8+ T-cells detectable by MHC Class I tetramers infiltrating tumors by day +8 post tumor challenge. However, an mPex14 neoantigen vaccine was ineffective at inducing regression of F244. This result contrasts with our previous report that focused on the unrelated T3 sarcoma that expresses the neoantigens mLama4 and mAlg8. As effective CD4+ T-cell help is required to drive CD8+ T-cells to become functional cytotoxic effectors, we formed the hypothesis that F244 expressed weak or limited numbers of MHC II neoantigens. To test this possibility, we enforced expression of CIITA in F244 that drove constitutive expression of MHC II on these tumor cells. No F244-specific response was identifiable in F244 CD4+ TIL. In contrast, T3 tumor cells engineered for CIITA expression induced a strong CD4+ T-cell help response. Since it was known that agonist anti-CD40 could circumvent the lack of CD4+ T-cell help, we asked whether F244 rejection could be induced in tumor bearing mice treated with agonistic anti-CD40 antibody. Whereas treatment with agonistic anti-CD40 at early times following tumor challenge (days 3-5) had no effect on tumor outgrowth, a single dose administered on day +8 rapidly induced tumor regression. The therapeutic effects of the anti-CD40 were abolished if tumor bearing mice were treated with monoclonal antibodies that depleted CD4+ or CD8+ T cells or neutralized IFN- or IL-12. We analyzed the cell populations infiltrating F244 tumors in the presence or absence of anti-CD40 therapy and noted that CD103⁺ XCR1⁺ DC could be identified in F244 tumors as early as five days after tumor implantation and expressed CD40 by day 8 in a CD4+ T-cell dependent manner. CD103+ DC in the tumor environment rapidly upregulated CD80 and CD86 within 8 hr of anti-CD40 treatment. Moreover, mPex14-specific CD8+ T-cells constitute an abundant component of TIL as the tumor is destroyed. Thus agonistic anti-CD40 mAb can drive primed tumor-specific CD8⁺ T-cells to become cytotoxic effectors capable of mediating tumor regression. Current work is focused on determining whether CD103⁺ DC are specific targets of agonistic anti-CD40 and elucidating the mechanisms by which anti-CD40 promotes immune elimination of established tumors.