Cystectomy is a standard treatment for muscle-invasive bladder cancer (MIBC), but it is life-altering. We initiated a phase 2 study in which patients with MIBC received four cycles of gemcitabine, cisplatin, plus nivolumab followed by clinical restaging. Patients achieving a clinical complete response (cCR) could proceed without cystectomy. The co-primary objectives were to assess the cCR rate and the positive predictive value of cCR for a composite outcome: 2-year metastasis-free survival in patients forgoing immediate cystectomy or ATM, RB1, FANCC and ERCC2) or increased tumor mutational burden did not improve the positive predictive value of cCR. Exploratory analyses of peripheral blood mass cytometry and soluble protein analytes demonstrated an association between the baseline and on-treatment immune contexture with clinical outcomes. Stringently defined cCR after gemcitabine, cisplatin, plus nivolumab facilitated bladder sparing and warrants further study. ClinicalTrials.gov identifier: NCT03451331.