Abstract 5308: Ifngr1 signaling on tumor-specific CD4 T cells is required to mitigate Treg differentiation during CD40 agonist and anti-PD-L1 immunotherapy in pancreatic ductal adenocarcinoma

Abstract Pancreatic ductal adenocarcinoma (PDA) is a particularly lethal malignancy that lacks effective therapeutic strategies. A promising therapeutic modality that can elicit transient antitumor responses in a subset of metastatic PDAs is chemotherapy + CD40 agonist +/- anti-PD-1. A deeper understanding of the cellular mechanisms that mediate the initial responses will inform new strategies to enhance the durability of this therapy. Our prior studies demonstrated that tumor-specific CD4 T cells are critical for mitigating tumor growth in a syngeneic KPC orthotopic tumor model of PDA that expresses a model neoantigen, click beetle red luciferase (CBR). CD4 T cells direct tumor antigen recognition by tumor-associated macrophages and host interferon-gamma receptor (Ifngr1) signaling. Here, we demonstrate that CD4 T cells are required for the antitumor effects of anti-CD40 agonist indicating that this therapy fails to compensate for a lack of CD4 T cell help. We sought to test the hypothesis that host Ifngr1 signaling acts in a CD4 T cell intrinsic manner to promote antitumor responses. As such, we develop and validate a novel MHC class II tetramer (CBR54-62: I-Ab) to track the fate of endogenous CD4 T cells during tumor growth. We demonstrate that tumor-specific CD4 T cell abundance and Th1 polarization is decreased in orthotopic tumors, particularly between day 14 and day 21 post tumor implantation. Combination agonistic anti-CD40 + anti-PD-L1 maintained tumor-specific CD4 T cell numbers in the spleen and pancreas-draining lymph nodes of tumor-bearing mice. Intriguingly, Th1 polarized tumor-infiltrating CD4 T cells were decreased by aPD-L1, but were restored by anti-CD40, a finding further corroborated by single-cell RNA sequencing. Further, agonistic anti-CD40 + anti-PD-L1 alone or in combination robustly decreased Treg polarized tumor-specific CD4 T cells. Using a mixed bone marrow chimeric approach, we show immunotherapy’s Treg-depletion effect is dependent on Ifngr1 on antigen-specific CD4 T cells. In contrast, Ifngr1 signaling on tumor-specific CD8 T cells appeared inconsequential to CD8 T cell fate following immunotherapy. To our knowledge, this is the first study to interrogate tumor-specific CD4 T cells in PDA and uncover novel interplay between CD4 T cells, CD8 T cells, and myeloid cells that are critical for immunotherapy response. Citation Format: Eduardo Cruz-Hinojoza, Adam Burrack, Zoe Schmiechen, Cara-Lin Lonetree, Ebony A. Miller, Michael Patterson, Jesse Williams, Thamotharampillai Dileepan, Ingunn Stromnes. Ifngr1 signaling on tumor-specific CD4 T cells is required to mitigate Treg differentiation during CD40 agonist and anti-PD-L1 immunotherapy in pancreatic ductal adenocarcinoma 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 (6Suppl): Abstract nr 5308.