Abstract 1297: Chemotherapy-induced senescence activates robust, parallel programs of immune checkpoint expression that can be targeted with immunotherapy

Abstract We and others have previously shown that the breast cancers most difficult to eradicate with chemotherapy are TP53 wild-type, and these are among the most lethal breast cancers. For instance, chemotherapy-treated TNBC patients with TP53 wild-type tumors have a median overall survival of 45 months, vs 263 months for TP53 mutant tumors. Treatments fail to eradicate these cancers for two reasons: the tumor cells 1) avoid intrinsic cell death, and 2) escape immune clearance. We have shown that p53 drives a program of senescence that arrests the cell cycle to prevent intrinsic modes of cell death such as mitotic catastrophe, apoptosis and nutrient deprivation. However, it is not currently understood how breast cancer cells that enter senescence to survive chemotherapy escape immune clearance. Here, we show tumor cells from mice and human patients that survive chemotherapy activate complex programs of immune modulation. Surprisingly, the surviving, senescent tumor cells are highly enriched for many antigen presentation genes and positive regulators of T cell activation, suggesting they have switched from immunologically “cold” to “hot”. Unfortunately, these senescent tumors concurrently upregulate redundant expression of many T cell inhibitory checkpoint genes, including CD80 and PD-L1. scRNA-seq and cell imaging revealed that CD80 and PD-L1 each mark unique populations of cells in the treated tumor, typified by p53 signaling or interferon signaling, respectively. In p53 wild-type, syngeneic, orthotopic mouse mammary tumor models that recapitulate human breast cancer response to chemotherapy, treatment of tumors with chemotherapy followed by targeting of the PD-L1 and/or CD80 axes improved response, including complete eradication in some instances. Unfortunately, however, even combination strategies failed to elicit a cure in the majority of cases. Our findings reveal the formidable challenge of eliminating residual disease populated by senescent cells that express multiple redundant immune inhibitory pathways and suggest rational strategies are needed based on the specific checkpoint pathways expressed in residual disease. Citation Format: Ashkan Shahbandi, Fang-Yen Chiu, Nathan A. Ungerleider, Ashlyn Y. Anderson, Heather L. Machado, Zachary F. Pursell, Raegan Kvadas, Sonia G. Rao, James G. Jackson. Chemotherapy-induced senescence activates robust, parallel programs of immune checkpoint expression that can be targeted with immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1297.