BCG therapy downregulates HLA-I on malignant cells to subvert antitumor immune responses in bladder cancer [RNA-seq]

Patients with high-risk non-muscle-invasive bladder carcinoma (NMIBC) frequently relapse after standard BCG immunotherapy and have a dismal outcome after progression to muscle-invasive bladder carcinoma (MIBC). Although BCG induces potent inflammatory responses upon intravesical instillations, the mechanisms of tumor resistance to such immunotherapy remain elusive. We performed a longitudinal immune profiling of a cohort of MIBC pre- and post BCG therapy with gene and protein expression analysis to establish correlations with 5 year clinical follow up. Here, we demonstrate two distinct patterns of BCG-induced immunosubversion, which include acquired immune resistance and tumor-cell intrinsic resistance. Firstly, intracellular BCG infection of a subset of urothelial carcinoma cells downregulated HLA-I expression and induced epithelial to mesenchymal transition (EMT) characteristics. BCG treated tumors exhibiting such HLA class I loss displayed an immune desert tumor microenvironment dominated by myeloid immunosuppressive cells. Such patients presented with early cancer relapses and a bad outcome. Conversely, BCG-treated tumors which did not lose HLA class I antigens at relapse displayed an immune escape mechanism dominated by a Th1 pattern with high expression of inhibitory checkpoints and exhaustion markers. Such patients had a favorable outcome upon second surgery. We surmise that HLA class I expression does not result from immunoediting but rather from an EMT process associated to myeloid immunosuppression that predicts dismal prognosis. RNA-seq profile of non-muscle-invasive bladder carcinoma.