A Study Evaluating the Safety, Efficacy, and Pharmacokinetics of Mosunetuzumab and a Combined Regimen of Mosunetuzumab and Venetoclax in Participants With Relapsed or Refractory Chronic Lymphocytic Leukemia

This study will assess the safety, tolerability, pharmaokinetics, and preliminary efficacy of mosunetuzumab (Lunsumio) monotherapy in participants with relapsed or refractory (R/R) chronic lymphocytic leukemia (CLL) or small lymphocytic lymphoma (SLL). This study will also allow participants who are currently progressing on a Bruton tyrosine kinase inhibitor (BTKi) and requiring salvage therapy as assessed by the treating physician to continue their BTKi throughout the screening period and for the first three cycles of mosunetuzumab. An additional arm (open to non-US participants only) has been added to assess the safety, tolerability, pharmacokinetics, and preliminary efficacy of mosunetuzumab in combination with venetoclax, a B-cell lymphoma 2 (BCL2) inhibitor, compared to standard-of-care rituximab plus venetoclax.