Cancer Cell Resistance to IFNg Can Occur via Enhanced Double-Strand Break Repair Pathway Activity

The pleiotropic cytokine interferon-gamma (IFNy) is associ-ated with cytostatic, antiproliferation, and proapoptotic func-tions in cancer cells. However, resistance to IFNy occurs in many cancer cells, and the underlying mechanism is not fully under-stood. To investigate potential IFNy-resistance mechanisms, we performed IFNy-sensitivity screens in more than 40 cancer cell lines and characterized the sensitive and resistant cell lines. By applying CRISPR screening and transcriptomic profiling in both IFNy-sensitive and IFNy-resistant cells, we discovered that activation of double-strand break (DSB) repair genes could result in IFNy resistance in cancer cells. Suppression of single-strand break (SSB) repair genes increased the dependency on DSB repair genes after IFNy treatment. Furthermore, inhibition of the DSB repair pathway exhibited a synergistic effect with IFNy treatment both in vitro and in vivo. The relationship between the activation of DSB repair genes and IFNy resistance was further confirmed in clinical tumor profiles from The Cancer Genome Atlas (TCGA) and immune checkpoint blockade (ICB) cohorts. Our study provides comprehensive resources and evidence to elucidate a mechanism of IFNy resistance in cancer and has the potential to inform combination therapies to overcome immu-notherapy resistance.