Background: Checkpoint inhibitors can achieve durable responses in cis-ineligible 1L mUC. However, use is restricted to patients whose tumors are PD-L1 high. Approximately 70% of cis-ineligible patients have tumors with low PD-L1 expression, leaving a significant proportion of 1L mUC patients in need of new treatment options. Bempegaldesleukin (BEMPEG; NKTR-214) is a CD122-preferential IL-2 pathway agonist designed to provide sustained signaling through the IL-2 βγ receptor. NIVO is an anti-PD-1 antibody that is approved for treatment in several types of cancers, including 2L mUC after treatment with a platinum agent. Early BEMPEG plus NIVO data in 1L mUC (cis-eligible and -ineligible) patients found an objective response rate (ORR) of 48% (13/27) in the efficacy evaluable population (defined as having undergone at least one post-baseline scan) and a CR rate of 19%, prompting this further exploration of BEMPEG plus NIVO in a phase 2 study (Siefker-Radke, 2019). Methods: This Phase 2 multi-national trial evaluates BEMPEG plus NIVO in previously untreated patients with cis-ineligible mUC. Eligibility also requires tumor tissue be analyzed by central laboratory to document PD-L1 status. Approximately 205 patients will be enrolled. BEMPEG (0.006 mg/kg) and NIVO (360 mg) are given intravenously (IV) on Day 1 of each 3-week cycle. The primary endpoint is ORR assessed per RECIST 1.1 by blinded independent central review (BICR) in patients with low PD-L1 expression (defined as Combined Positive Score [CPS] < 10). Secondary endpoints include ORR and duration of response in all treated patients, safety, and tolerability. Tumor and blood samples will be collected for biomarker analyses. Enrollment is ongoing. Clinical trial information: NCT03785925