LAUSR

Agonistic CD40 antibodies have shown promise when used in combination with checkpoint inhibitors in clinical trials for the treatment of malignancies. However, the mechanisms driving antitumor immune responses in patients are not well understood. The aim of this study was to use a preclinical melanoma model to evaluate the impact of intratumoral anti-CD40 administration on treatment efficacy and the tumor immune landscape in the context of systemic anti-PD1 therapy. Mice bearing 8-day established B16 melanoma tumors were injected with CD40 agonist intratumorally, either alone or in combination with anti-PD1 Ab, every 3 days for a total 4 doses. All mice treated with the combination therapy exhibited tumor growth arrest while progressive tumor growth was observed in control mice and mice treated with anti-PD1 alone. At day 15, tumor weights were 7- and 3-fold reduced in mice treated with the combination therapy as compared to control IgG or PD1 monotherapy, respectively. CyTOF analysis showed a 4-fold increase in the frequency of tumor-infiltrating immune cells in mice treated with either CD40 agonist alone or the combination therapy. Interestingly, CD40 agonistic Ab selectively expanded CD8+ T cells and the combination therapy exhibited a more pronounced effect compared to treatment with anti-PD1 Ab alone. Moreover, CD39+ CD8 T cells, representing tumor antigen-specific cytotoxic T cells, were 14- and 3-fold higher in tumors from mice treated with the combination therapy as compared to control or PD1-treated mice, respectively. This effect correlated with increases in the frequency of antigen-presenting cells, including cDC1 (6-fold) and B cells expressing CD40 (3-fold) in response to the combination therapy. In addition, the combination therapy significantly decreased myeloid cell population resulting in an 8-fold reduction in the ratio of myeloid cells to T cells. Amongst myeloid cells, the density of the monocytic population was diminished, with a selective 10-fold reduction of CD206+ M2-macrophages in tumors from mice treated with both Abs. Our findings provide evidence that combining systemic anti-PD1 therapy with intratumoral CD40 agonist enhanced antitumor immune responses by selectively expanding tumor antigen-specific effector CD8+ T cells, which was associated with increased infiltration of antigen-presenting cells and attenuation of immunosuppressive myeloid cells. Citation Format: Barbara Pazdrak, Heather M. Sonnemann, Salah-Eddine Bentebibel, Barbara M. Nassif, Greg Lizee, Adi Diab. Intratumoral CD40 agonist enhances the antitumor effect of anti-PD1 immunotherapy by activation of antigen-presenting cells and selective expansion of effector CD8+ T cells. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5079.