Neoadjuvant chemotherapy (NAC) is the standard of care for muscle-invasive bladder cancer (MIBC), but despite this aggressive care, over half of patients eventually relapse and die from their disease. Several immune checkpoint inhibitors targeting the PD-1/PD-L1 pathway have recently been FDA approved in the treatment of metastatic bladder cancer, and immunotherapy trials and combination chemo-immunotherapy trials are underway. It is therefore critical to identify the potential immunomodulatory effects of chemotherapy to inform the development of chemo-immunotherapy combinations. Our lab (among others) has previously identified two molecular subtypes of high-grade, MIBC, termed “luminal” and “basal.” We have evidence that a subset of luminal tumors, which at baseline have a paucity of inflammation and immune checkpoint expression, become more heavily immune infiltrated after NAC. We hypothesize that NAC is eliciting an antigen-driven immune response and we aim to evaluate the effect of NAC on the intratumoral and peripheral blood T cell receptor (TCR) repertoire. In addition, previous studies have suggested that a subset of luminal tumors may be more sensitive to treatment with immune checkpoint inhibition. We hypothesize that the addition of immunotherapy to NAC will potentiate the antigen-driven immune response in luminal tumors. To answer these questions, we will study the dynamic response of the immune microenvironment and the peripheral blood in a subtype-specific manner after cytotoxic chemotherapy alone and combination chemo-immunotherapy via our ongoing biospecimen acquisition protocol and our UNC-led, multicenter phase II trial of neoadjuvant pembrolizumab, gemcitabine, and cisplatin followed by radical cystectomy in MIBC. These studies will assist the development and optimization of chemo-immunotherapy combinations in MIBC to ultimately improve the cure rate of a deadly disease.