Abstract 3444: Administration of anti-CD40 enhances local and systemic antitumor efficacy of radiotherapy in allograft tumor model of a check-point blockade resistant melanoma

Abstract

Abstract Resistance to immune checkpoint therapy develops in a subset of patients after initial response. Therefore, we hypothesized that defective antigen presentation contributes to immune resistance, and a sequential therapy comprising of ablative radiation therapy (RT) and agonist αCD40 antibody can reprogram the tumor-infiltrating myeloid and dendritic cells for effective in-situ tumor antigen presentation and activation of T cells. Palpable B16-F10-Res499 tumors in C57BL/6 mice, resistant to the systemic effects of RT and αCTLA-4 blockade, were treated with 3 fractions of 20Gy (RT) followed by agonist αCD40 antibody (3x100μg). Tumor growth, survival, and anti-tumoral immune memory after rechallenge was monitored. Mice were sacrificed on Day 16 post-RT, and immune cells from irradiated tumors and draining lymph nodes (DLN) were analyzed using flow cytometry. There was complete tumor regression and enhanced anti-tumoral immune memory in RT+αCD40-treated animals. In a dual tumor model, combination therapy significantly delayed abscopal tumor growth by 64% on D30 (p<0.0001). When compared to unirradiated or tumors treated with RT alone, there was a significant increase in cell surface expression of co-stimulatory molecules (CD80, CD86, CD40 and 4-1BBL) and TNF-α, and iNOS in the CD103+ DCs and myeloid cells (p<0.05) indicating a reprogramming of antigen presentation and co-stimulatory function in MDSCs. There was an increase in CD8+ T cells with reduced CD4/CD8 ratio (p<0.01) in abscopal tumors and DLN in the RT+αCD40 group. Combination treatment enhanced the frequency of proliferating Ki67+ (p<0.001) and IFNγ+ (p<0.01) CD8 T cells and an increase in the Ki67+ high GRZ+ (granzyme secreting) population in the pool of early exhausted cells (PD1intEOMESlow). Interestingly CD8 depletion by anti-CD8 only partially reversed the effect of the combination group. Furthermore, αCD40 showed an increase in the CD11b+Ly6C population in the tumors. Also, Ly6C depletion completely reversed the effect of the IR+anti-CD40 treatment. Conclusion: Combination of ablative RT, followed by αCD40 therapy, overcame immune resistance in murine melanoma by enhancing systemic anti-tumoral immunity, abscopal effects, survival, and anti-tumoral immune memory. The immunomodulatory effects of αCD40 are dependent upon Ly6C+ cells and partially on CD8+ T cells. Citation Format: Sanjay Pandey, Claudia G. Chavez, Indranil Basu, Andy Minn, Chandan Guha. Administration of anti-CD40 enhances local and systemic antitumor efficacy of radiotherapy in allograft tumor model of a check-point blockade resistant melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3444.