Background: There is no established neoadjuvant therapy (NAT) for patients (pt) with muscle invasive bladder cancer (MIBC) ineligible for cisplatin-based chemotherapy preceding radical cystectomy. Encouraging prospective data indicate PD-1/PD-L1 inhibitors, including pembrolizumab and atezolizumab, are safe and active as NAT for MIBC. Durvalumab (D), a PD-L1 inhibitor, is FDA approved for treating locally advanced or metastatic urothelial carcinoma following platinum-based chemotherapy. The safety and activity of D as NAT in MIBC have not been reported. Methods: We are conducting a single-center sequential multicohort trial (NCT03773666) of D alone (Cohort 1, N=10) and D plus the CD73 inhibitor oleclumab (Cohort 2, N=10) in cT2-T4aN0M0 MIBC pts who are RC candidates and are ineligible for or declined cisplatin-based chemotherapy. The primary endpoint is feasibility, defined as ≥7 of 10 pts receiving at least 1 dose of D followed by radical cystectomy without dose limiting toxicity (DLT) up to 12 wks post-RC. In Cohort 1, D is administered at 750mg IV Q2W for 3 cycles followed by RC 2-4 weeks after the last dose. Baseline and RC tissue and baseline and on-study blood are collected for correlative studies, including immunohistochemistry, genomics, transcriptomics, and metabolomics. Results: Cohort 1 has completed enrollment; ten pts were enrolled between Feb 2019 to Sept 2019. Median age was 67 (Range: 53-85) and 8 (80%) were men. All 10 pts completed 3 durvalumab doses. Eight pts completed planned RC with at least 12wk follow-up post-op to date. No DLTs were observed. One Grade 3 treatment-related adverse event (trAE) was reported (anemia), with no Grade 4 or higher trAE. Pathologic response (<pT2N0) was seen in 2 of 8 (25%) pts with pathologic complete response (pT0) in 1 (12.5%) pts. Updated safety and efficacy data from Cohort 1 will be presented. Conclusions: D appears to be feasible as NAT in MIBC with preliminary evidence for antitumor activity. Toxicities are consistent with data from other PD-1/PD-L1 inhibitor trials. Future cohorts will examine D-containing combination NAT strategies. Analysis of tissue and blood-based predictive biomarkers are ongoing. Clinical trial information: NCT03773666