Abstract 6597: CD40 agonism induces CD4 T cell mediated rejection of major histocompatibility complex class I deficient pancreatic tumors
Authors: Haerr Margaret E. , Kim Samuel I. , Arora Charu , Gribbin Kyle P. , Vonderheide Robert H. , Byrne Katelyn T. 
Published: March 2024

Abstract
Cytotoxic CD8 T cells are the canonical mediators of tumor clearance by the adaptive immune system. As such, current immunotherapies, including immune checkpoint blockade (ICB), target exhausted CD8 T cells with the hope of reinvigorating the CD8 T cells to drive tumor clearance. However, many tumors, including pancreatic ductal adenocarcinoma (PDAC), can evade CD8 T cell detection via downregulation of the antigen presentation molecule, major histocompatibility complex I (MHC I) as either primary or acquired resistance to immunotherapy. We have previously reported that agonistic CD40 antibody (αCD40), which promotes the maturation and licensing of dendritic cells to drive T cell priming, synergizes with ICB to induce tumor rejection dependent on both CD4 and CD8 T cells in mouse models of PDAC. Given the potential mechanisms of resistance to CD8 T cell immunity, we hypothesized that interrogation of the mechanisms underlying αCD40-induced CD4 T cell rejection of PDAC will reveal targets for improving CD4 T cell-directed immunotherapies. Here, we show that implantation of an MHC I deficient PDAC cell line derived from the genetically engineered KrasG12DTrp53R172HPdx1-Cre (KPC) mouse model results in normal tumor establishment and progression. Upon treatment with combined αCD40 and ICB, tumor growth was significantly decreased in a CD4, but not CD8, T cell-dependent manner. Using genetic knockout mice, we determined that tumor regression was perforin-independent and identified host expression of IFNγ as requisite for therapeutic efficacy. To identify the cellular subset mediating CD4 T cell-rejection of the tumor, we assessed the major histocompatibility complex II (MHC II) positive cells in the tumor microenvironment (TME), which possess the ability to directly synapse with CD4 T cells to drive anti-tumorigenic T cell programs. We determined that macrophage and myeloid cells were dispensable for treatment efficacy, however non-immune cells in the TME can also interact with CD4 T cells through expression of MHC II. Interrogation of stromal cells reveals an increase in the proportion of MHC II+ subsets after combined αCD40/ICB treatment, with a concomitant decrease in the proportion of MHC II+ tumor cells. These data support the notion that CD4 T cell control of tumors may be mediated by both direct and indirect mechanisms of tumor killing. Findings from this work will elucidate non-canonical mechanisms of CD4 T cell-mediated rejection of tumors and may be leveraged to discover novel translational targets for immunotherapy.
Citation Format: Margaret E. Haerr, Samuel I. Kim, Charu Arora, Kyle P. Gribbin, Robert H. Vonderheide, Katelyn T. Byrne. CD40 agonism induces CD4 T cell mediated rejection of major histocompatibility complex class I deficient pancreatic tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6597.