Abstract A012: IFNγ-induced antigen loss in chimeric antigen receptor (CAR)-T cell therapy

Abstract FDA-approved chimeric antigen receptor (CAR)-T cell therapies (CARTs) have reshaped the treatment of hematological malignancies. However, no CARTs to-date have been successful in treating solid tumors. Colorectal cancer (CRC) is the 2nd leading cause of cancer-related death in the USA, and its incidence is rapidly rising among younger adults. Currently, CRC immunotherapies are limited to a small percentage of patients with mismatch repair deficiency or microsatellite instability. To overcome such a limitation, we investigated guanylyl cyclase C (GUCY2C)-directed CART (GucyCART) for CRC. GUCY2C is a membrane receptor expressed by nearly all CRCs, and its expression is retained in metastatic disease. While preclinical GucyCART models demonstrated robust therapeutic efficacy in some CRC models, further investigation demonstrated limited in vivo efficacy in models with lower antigen expression. In in vivo models, we observed antigen reduction when CRCs were co-cultured with GucyCART, suggesting that antigen escape may be a potential barrier to therapeutic efficacy. Further mechanistic studies uncovered a novel antigen loss mechanism in which IFNγ secreted by activated CART cells in the tumor immune microenvironment (TIME) drives bystander cancer cells to lose GUCY2C. This previously unexplored antigen loss mechanism is mediated through IFNγR (receptor), janus-associated kinase, and cellular stress signaling pathways, rather than genetic GUCY2C loss. Moreover, this mechanism of antigen loss can be rescued by the IFNγ-neutralizing antibody, ruxolitinib (a JAK inhibitor) or 4-phenylbutyrate (an endoplasmic reticulum stress reliever). Additionally, we observed the loss of HER2 and CDH17 induced by IFNγ, suggesting a broader relevance beyond GUCY2C. While IFNγ has well-established positive effects and is considered essential for CART targeting of solid tumors by inducing intracellular adhesion molecule (ICAM)-1 upregulation, our study revealed a previously undiscovered and unanticipated negative effect of IFNγ, driving non-genetic antigen loss in bystander cancer cells. Citation Format: Miao Cao, Jasmine Alvarez, Michael Xu, Zhengyang Sun, Oluwatobiloba Taylor, Allison Doermann, Ross Staudt, Scott A. Waldman, Adam E. Snook. IFNγ-induced antigen loss in chimeric antigen receptor (CAR)-T cell therapy abstract. In: Proceedings of the AACR Immuno-Oncology Conference (AACR IO): Discovery and Innovation in Cancer Immunology: Revolutionizing Treatment through Immunotherapy; 2026 Feb 18-21; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Immunol Res 2026;14(2 Suppl):Abstract nr A012.