Impact Of Gemcitabine Plus Cisplatin Plus Ipilimumab On Circulating Immune Cells In Patients (Pts) With Metastatic Urothelial Cancer (Muc).

4586 Background: Immune checkpoint blockade may play a role in the treatment of mUC. However, the role of CTLA4 blockade, the impact of chemotherapy on immune cell populations, and the optimal approach to combination regimens in pts with mUC remains poorly defined. An increase in tumor infiltrating and circulating CD4+ICOS+ cells after ipilimumab has been shown in pts with localized UC and correlated with improved outcomes in ipilimumab-treated melanoma pts (Carthon, Clin Can Res, 2010). Methods: Pts with mUC were enrolled on a phase 2 trial of chemotherapy + CTLA4 blockade. Patients received 2 cycles of gemcitabine + cisplatin (GC) followed by 4 cycles of GC + ipilimumab (GCI). Flow cytometry was performed on peripheral blood mononuclear cells at baseline, after GC, and after GCI to determine the impact of treatment on the frequency and phenotype of CD4+ and CD8+ T cells, regulatory T cells (CD4+CD25+CD127-CD45RA- Tregs), and myeloid-derived suppressor cells (CD13+CD14+CD11b+HLA-DR- MDSCs). Comparisons b...