Background: The advent of proteasome inhibitors and immunomodulatory drugs (IMiDs) have significantly improved outcomes in MM, and the first monoclonal antibodies for MM have been recently approved (daratumumab, elotuzumab). Despite novel therapies and improved disease management, MM is still considered incurable and most pts relapse, confirming the need for additional treatment options. MM cells express PD-L1, with higher levels observed after relapse and with advanced disease. Additionally, PD-L1–expressing immune cells in the microenvironment promote MM cell survival and potential immune escape. However, anti–PD-1 monotherapy did not result in objective responses in the MM cohort of a Ph I study, suggesting that MM pts need combination therapy. Daratumumab has activity as a single agent, as well as in combination with IMiDs plus dexamethasone and bortezomib plus dexamethasone in R/R MM. Immunomodulatory activity for daratumumab has also been reported. Thus, disruption of the PD-L1/PD-1 pathway may be additive or synergistic. The safety and efficacy of atezo (anti–PD-L1) alone or with lenalidomide or pomalidomide and/or daratumumab will be evaluated in a Ph Ib study of MM pts. NCT02431208. Methods: R/R MM pts with ≤ 3 prior therapies will be enrolled in Cohorts A (atezo), B (atezo + lenalidomide), D (atezo + daratumumab) and E (atezo + daratumumab + lenalidomide); MM pts with measurable disease after ASCT (Cohort C: atezo) or ≥ 3 prior therapies (Cohort F: atezo + daratumumab + pomalidomide) will also be enrolled. Cohorts B, D, E and F include a safety run-in (D) or dose escalation phase (B, E, F) and an expansion. Lenalidomide and pomalidomide will be dose escalated and the MTD evaluated in expansion phases. Atezo will be given at 1200 mg IV (A, B, C) or 840 mg IV (D, E, F); pts will get daratumumab at 16 mg/kg IV (D, E, F). All pts will be ECOG PS ≤ 2. Primary endpoints are ORR and the RP2D of lenalidomide and pomalidomide with atezo and daratumumab and the RP2D of lenalidomide with atezo. DOR and PFS are secondary endpoints; safety, PK and the relationship between biomarkers and other endpoints, including efficacy, will be assessed. Pts will be enrolled at 19 US sites. Clinical trial information: NCT02431208