Abstract Immune checkpoint blockade (ICB) therapy revolutionized cancer treatment, but many patients with impaired MHC-I expression remain refractory. Here, we combined FACS-based genome-wide CRISPR screens with a data-mining approach to identify drugs that can upregulate MHC-I without inducing PD-L1. CRISPR screening identified TRAF3, a critical suppressor of the NF-κB pathway, as a negative regulator of MHC-I but not PD-L1. The Traf3-knockout (Traf3-KO) gene expression signature is associated with better survival in ICB-naive cancer patients and better ICB response. We then screened for drugs with similar transcriptional effects as this signature and identified SMAC mimetics. We experimentally validated that the SMAC mimetic birinapant upregulates MHC-I, sensitizes cancer cells to T-cell-dependent killing, and synergizes with ICB. Our findings provide preclinical rationale for treating tumors expressing low MHC-I expression with SMAC mimetics to enhance sensitivity to immunotherapy. The approach used in this study can be generalized to identify other drugs that enhance immunotherapy efficacy. Citation Format: Shengqing Gu, Wubing Zhang, Xiaoqing Wang, Peng Jiang, Nicole Traugh, Ziyi Li, Clifford Meyer, Blair Stewig, Yingtian Xie, Xia Bu, Michael Manos, Alba Font-Tello, Evisa Gjini, Ana Lako, Klothilda Lim, Jake Conway, Alok Tewari, Zexian Zeng, Avinash Das Sahu, Collin Tokheim, Jason L. Weirather, Jingxin Fu, Yi Zhang, Benjamin Kroger, Jin Hua Liang, Paloma Cejas, Gordon J. Freeman, Scott J. Rodig, Henry Long, Benjamin E. Gewurz, F. Stephen Hodi, Myles Brown, X. Shirley Liu. Therapeutically increasing MHC-I expression potentiates immune checkpoint blockade abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 65.