Inherited Primary Immunodeficiency (PID) disorders are associated with increased risk ofmalignancy that may relate to impaired antitumor immune responses or a direct role for PIDgermline mutations in tumorigenesis. We recently identified germline loss of function mutations inJanus Associated Kinase 1 (JAK1) causing primary immunodeficiency characterised by infectionsand associated with early onset, fatal high-grade bladder carcinoma. Somatic mutations in JAK1,required for immune cell signalling in response to interferon gamma (IFNγ), have been associatedwith several non-hematopoietic and hematopoietic cancer cell types but pathogenic mechanismsremain largely unexplored. Here we demonstrate that JAK1 is required for the intrinsic IFNγresponse of urothelial cells impacting immunogenicity and cell survival. Specifically, JAK1-deficient urothelial cells showed reduced surface expression of major histocompatibility complexclass II (MHC II), intercellular adhesion molecule-1 (ICAM-1) and programmed death-ligand-1(PD-L1) after IFNγ stimulation and were resistant to IFNγ-induced apoptosis and lymphocytemediatedkilling. In addition, we identify a previously unknown role for IFNγ signalling inmodulating urothelial differentiation. Together, our findings support a role for urothelial cell JAK1in immune surveillance and development of bladder cancer. Our results have implications forpatients with rare JAK1 PID and, more broadly, inform development of biomarker and targetedtherapies for urothelial carcinoma.