Abstract 1211: Sexual dimorphism in macrophage phagocytosis limits immune checkpoint inhibitor efficacy in pancreatic ductal adenocarcinoma

Abstract Despite significant advancements in understanding the pancreatic ductal adenocarcinoma (PDAC) tumor microenvironment (TME) through single-cell RNA sequencing (scRNAseq) and the development of novel therapeutic combinations, PDAC remains one of the deadliest cancers, with a five-year survival rate of ∼3%. Notably, survival outcomes are particularly worse in males compared to females. The limited efficacy of immune checkpoint inhibitors (ICI), such as anti-CTLA-4 and anti-PD-1/PD-L1 therapies, in PDAC has been attributed to a profoundly immunosuppressive TME driven by M2-like tumor-associated macrophages (TAM). Our translational studies demonstrated that dual blockade of PD-1 and VPAC stimulates CD8+ T cell activity and eradicates tumors in ∼50% of mice across various PDAC models. We hypothesized that a combinatorial ICI strategy is targeting TAM-driven immunosuppression in the TME and could enhance T cell-mediated anti-tumor immunity in PDAC. To test this hypothesis, we performed in vivo tumor growth and survival experiments in syngeneic PDAC models. We also conducted RNA sequencing (RNAseq) of bone marrow-derived macrophages (BMDM) polarized to M1/M2 phenotypes to investigate immune checkpoint expressions, supplemented by scRNAseq analysis of TAM from PDAC patients using public datasets. Using VIP-knockout mice, we explored the mechanisms underlying VPAC blockade-mediated tumor control. As anticipated, syngeneic PDAC tumors (e.g., KPC-luc and MT5) grew significantly slower in VIP-knockout mice compared to wildtype controls. Notably, the anti-tumor response was markedly superior in female VIP-knockout mice compared to males. To dissect the cellular basis of this sexual dimorphism, we depleted specific immune subsets, including T cells and TAM. Phagocytic TAM depletion accelerated tumor growth in females but had no effect on males, while the depletion of other immune subsets increased tumor growth in both sexes. In vitro, androgen receptor (AR) inhibition (mimicking the female phenotype) reversed the suppressive state of BMDM, marked by reduced Arg1, CD206, and PD-L1 expression. In vivo, AR inhibition or PD-L1 loss significantly enhanced the anti-tumor efficacy of VIP blockade in male mice. Mechanistically, RNAseq and Western blotting revealed increased VPAC1 expression on IC21 and BMDM cells following AR inhibition, reflecting the female-like phenotype. These findings suggest that androgen and VIP pathways mediate sexual dimorphism in TAM phagocytosis, which limits ICI efficacy in PDAC. VPAC1 and PD-L1 are identified as potential sex-specific phagocytosis checkpoints, providing promising therapeutic targets to overcome sex-based differences in PDAC immunotherapy outcomes. Citation Format: Zihan Chen, Tenzin Passang, Fanyuan Zeng, Yuou Wang, JianMing Li, Cynthia Giver, Kiranj Chaudagar, Edmund Waller. Sexual dimorphism in macrophage phagocytosis limits immune checkpoint inhibitor efficacy in pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 1211.