The Hippo Pathway Is Dysregulated in Cancer-Associated Fibroblasts in Anti–PD-L1–Resistant Cancer

The use of immunotherapy in solid tumors has significantly improved the outcomes and quality of life for patients with cancer. However, a substantial fraction of patients remains unresponsive, highlighting the urgent need to identify mechanisms of resistance to enhance immune-centric, chemo-free treatment regimens. In this study, we investigated associations with immunotherapy resistance by integrating RNA sequencing data from 2,800 patients with bladder cancer enrolled in the IMvigor trials, focusing on resistance to the anti–PD-L1 therapy atezolizumab, along with single-cell data from 200 patient samples and healthy donors. To expand the analysis to a massive collection of more than 100 million cells from hundreds of diverse single-cell studies, Firmament was developed as a method to efficiently identify cell populations that show enrichment for expression of gene signatures. These analyses identified the Hippo pathway as critically associated with immunotherapy resistance in bladder cancer and other solid tumors. Notably, Hippo dysregulation in stromal cells, rather than cancer cells, drove the high YAP/TAZ signal in these tumors, and Hippo signaling was specifically dysregulated in cancer-associated fibroblasts (CAF) compared with healthy donor fibroblasts. Inhibition of YAP signaling with a pan-TEAD inhibitor reduced expression of a myofibroblast gene program and decreased contractility of CAFs. Overall, this study provides insights that could aid in developing therapeutic combinations to improve outcomes for patients with solid tumors treated with immune checkpoint inhibitors.