Abstract 3917: A CXCR4 partial agonist TFF2-MSA improves anti-PD-1 immunotherapy in advanced gastric cancer by selectively targeting PMN-MDSC

Abstract Introduction: Advanced gastric cancer poses a challenge for PD-1 immunotherapy due in part to the prevalence of polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs). PMN-MDSCs are mostly immature granulocytes but coexist with mature neutrophils, complicating their precise targeting. While PMN-MDSCs highly express CXCR4, recent clinical trials suggest that CXCR4 antagonists may provide limited additive efficacy to PD-1 blockade. This study explored the efficacy of a secreted CXCR4 partial agonist, trefoil factor family 2 (TFF2), in the context of anti-PD-1 refractory gastric cancer. Methods: We fused mouse TFF2 with murine serum albumin to generate a novel TFF2-MSA peptide with extended half-life, and evaluated its therapeutic effects with or without anti-PD-1 antibody. As histidine decarboxylase (HDC) is expressed in immature neutrophils, we used the HDC-GFP transgene to track PMN-MDSC in vivo. The HDC-GFP mice received subcutaneous or orthotopic implantation of murine syngeneic gastric cancer cells and subsequent treatments. Additionally, human blood was assessed for both serum TFF2 and immune profiles. Results: The combination of TFF2-MSA plus anti-PD-1 antibody displayed remarkable synergy, boosting intratumoral cytotoxic CD8 T cells by 50-fold, leading to tumor regression or eradication, 80% reduction of distant metastasis and 2-fold extension of mouse survival. The immunosuppressive HDC-GFP+ PMN-MDSCs expressed the highest level of CXCR4 among immune cells, and TFF2-MSA treatment systematically reduced HDC-GFP+ PMN-MDSCs in the tumor, blood, spleen and their myeloid progenitors in the bone marrow. In contrast, CXCR4 antagonist AMD3100 in combination with anti-PD-1 failed to restrict tumor growth or PMN-MDSCs. Further single-cell RNA-seq and functional assays revealed that combination of TFF2-MSA plus anti-PD-1 induced a skewing of remaining tumor HDC-GFP+PMN-MDSC compositions from highly immature CD300ld+ subsets to less immature subsets expressing interferon-stimulated genes, accompanied by reduced immunosuppression and increased antigen presentation functions. Rather than local reprogramming, this compositional shift stemmed from an IRF1-driven interferon response in splenic HDC-GFP+ PMN-MDSCs. In human, PMN-MDSCs marked by LOX1 significantly expanded in the blood of gastric cancer patients compared to healthy donors. Human LOX1+ PMN-MDSCs showed an inverse correlation with T cell number, activation, proliferation and the serum TFF2 level. Conclusions: TFF2-MSA synergizes with PD-1 blockade by selectively targeting CXCR4high PMN-MDSCs. This study provides a rational for a novel combination therapy of the CXCR4 partial agonist, TFF2-MSA, rather than CXCR4 antagonists, plus PD-1 blockade for treatment of advanced gastric cancer. Citation Format: Jin Qian, Chenkai Ma, Quin T. Waterbury, Christine S. Moon, Xiaofei Zhi, Feijing Wu, Ruhong Tu, Biyun Zheng, Hiroki Kobayashi, Leah B. Zamechek, Ryan H. Moy, Arnold Han, Bruce Daugherty, Seth Lederman, Timothy C. Wang. A CXCR4 partial agonist TFF2-MSA improves anti-PD-1 immunotherapy in advanced gastric cancer by selectively targeting PMN-MDSC [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 3917.