Abstract 3926: ARF6-dependent endocytic trafficking of the interferon-gamma receptor drives adaptive immune resistance and response to immune checkpoint blockade

Abstract Interferon-gamma (IFNγ) -driven adaptive immune resistance (AIR) in cancer begins at the plasma membrane where cytokine signaling is initiated. Cytotoxic CD8+ T cells secrete IFNγ, eliciting tumor-intrinsic IFNγ signaling and expression of immunosuppressive genes, which are critical for effective therapeutic response to anti-PD-1 and anti-CTLA-4 immune checkpoint blockade (ICB). Although the IFNγ receptor (IFNγR) is expressed in all cell types, its surface density can determine a cell’s responsiveness to ligand. Mechanistic control over this process remains a mystery. Herein we report that the endocytic trafficking protein ADP-Ribosylation Factor 6 (ARF6) is critical for IFNγ-driven AIR during primary tumor progression and in the setting of ICB therapy. The IFNγR1 subunit of the receptor is constitutively internalized in a ligand-independent manner. ARF6 is necessary for endocytic recycling of IFNγR1 and determines the steady-state surface density of the receptor. Loss of ARF6 results in lysosomal degradation of the receptor and controls IFNγR1 protein levels in melanoma, non-small cell lung cancer, colorectal cancer, and triple-negative breast cancer. IFNγ activates ARF6 in parallel with JAK1-STAT1 signaling, suggesting a positive feedback loop that allows tumor cells to dynamically respond to immune attack. Silencing ARF6 reduces tumor intrinsic IFNγ signaling and downstream expression of immunosuppressive genes. In murine melanoma, loss of ARF6 causes resistance to systemic ICB therapy. Likewise, low expression of ARF6 in patient tumors correlates with inferior outcomes with ICB. Our data provide new mechanistic insights into tumor immune escape, defined by ARF6-dependent adaptive immunity, and support that ARF6-dependent endomembrane trafficking of the IFNγ receptor shapes clinical outcomes of ICB therapy. Private Information Citation Format: Yinshen Wee, Junhua Wang, Emily C. Wilson, Coulson P. Rich, Aaron Rogers, Zhongzong Tong, Evelyn DeGroot, Y. N. Vashisht Gopal, Michael Davies, Huseyin Atakan Ekiz, Joshua K. H. Tay, Chris Stubben, Kenneth M. Boucher, Juan M. Oviedo, Keke C. Fairfax, Matthew A. Williams, Sheri L. Holmen, Roger K. Wolff, Allie H. Grossmann. ARF6-dependent endocytic trafficking of the interferon-gamma receptor drives adaptive immune resistance and response to immune checkpoint blockade abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 3926.