| Therapeutic blockade of the CTLA4 and/or PD1 immune checkpoint pathways has resulted in significant anti-tumor responses in broad variety of cancer types, but resistance is common. Using mouse models of metastatic melanoma and breast cancer in combination with CRISPR/Cas9 to selectively delete genes in our tumor cells, we demonstrate that prolonged interferon signaling orchestrates PDL1-dependent and PDL1-independent resistance to immune checkpoint blockade (ICB), and to combinations such as radiation plus anti-CTLA4. Furthermore, we show that this interferon driven resistance mechanism primarily occurs in ICB resistant tumors and not in ICB responsive tumors. Persistent type II interferon signaling allows tumors to acquire STAT1-related epigenomic changes and augments expression of interferon-stimulated genes and ligands for multiple T cell inhibitory receptors. Both type I and II interferons maintain this resistance program. Crippling the program genetically or pharmacologically interferes with multiple inhibitory pathways, and expands distinct T cell populations with improved anti-tumor functions despite expressing markers of severe exhaustion. Consequently, tumors resistant to multi-agent ICB are rendered responsive to ICB monotherapy. Finally, we observe that biomarkers for interferon-driven resistance associate with clinical progression after anti-PD1 therapy. Thus, the duration of tumor interferon signaling augments adaptive resistance and inhibition of the interferon response bypasses requirements for combinatorial ICB therapies. |
