Mosunetuzumab and Polatuzumab Vedotin for the Treatment of Patients With Relapsed or Refractory Grade 1-3a Follicular Lymphoma

PRIMARY OBJECTIVES: I. Evaluate the safety and tolerability of mosunetuzumab plus polatuzumab vedotin in patients with relapsed/refractory (R/R) follicular lymphoma (FL). (Safety lead-in) II. Estimate the complete response (CR) rate to mosunetuzumab plus polatuzumab vedotin in R/R FL patients. (Phase II) SECONDARY OBJECTIVES: I. Estimate the overall response rate (ORR), time to first CR, time to best response, duration of response (DOR), duration of response among CR (DORC), progression-free survival (PFS), overall survival (OS), and quality of life (QOL) in R/R FL patients treated with mosunetuzumab plus polatuzumab vedotin. II. Evaluate the toxicity of mosunetuzumab plus polatuzumab vedotin for R/R FL. III. Examine the use of tocilizumab for cytokine release syndrome (CRS) in R/R FL patients treated with mosunetuzumab plus polatuzumab vedotin. EXPLORATORY OBJECTIVES: I. Assess baseline and on-treatment biomarkers, and evaluate association with anti-tumor activity and safety. II. Examine the type and incidence of CD20 gene mutations/ downregulation at relapse in R/R FL patients treated with mosunetuzumab plus polatuzumab vedotin. OUTLINE: Patients receive polatuzumab vedotin intravenously (IV) over 30-90 minutes on day 1 of each cycle. Cycles repeat every 21 days for up to 6 cycles in the absence of disease progression or unacceptable toxicity. Patients also receive mosunetuzumab subcutaneously (SC) on days 1, 8 and 15 of cycle 1 and day 1 of remaining cycles. Cycles repeat every 21 days for up to 8-17 cycles in the absence of disease progression or unacceptable toxicity. Additionally, patients undergo blood sample collection and computed tomography (CT), positron emission tomography (PET)/CT, or magnetic resonance imaging (MRI) throughout the study. After completion of study treatment, patients are followed up at 30 days and then for 3 years.