mosunetuzumab — Drug Monograph
Brand names: Lunsumio
Drug class: Monoclonal Antibody
Mechanism of Action
Mosunetuzumab is a full-length IgG1 bispecific T-cell engager that simultaneously binds CD20 on B-cell tumor cells and CD3ε on T lymphocytes, forming an immune synapse that redirects cytotoxic T cells to lyse CD20-expressing malignant cells. Unlike CD19-targeted BiTEs, the IgG1 Fc region confers a longer half-life allowing intermittent (rather than continuous) dosing. Crosslinking of CD3 leads to T-cell activation, proliferation, and release of cytotoxic granules containing perforin and granzymes. Serial killing of antigen-positive tumor cells can occur with a single activated T cell.
FDA Indications
- Relapsed or refractory follicular lymphoma after ≥2 prior lines of therapy in adults (December 2022; GO29781 pivotal trial)
Common Side Effects
- CRS (~39%, mostly Grade 1–2)
- Fatigue (~36%)
- Rash (~29%)
- Pyrexia (~27%)
- Headache (~24%)
- Constipation (~22%)
- Neutropenia (~22%)
- Hypophosphatemia (~19%)
- Nausea (~18%)
- Diarrhea (~16%)
- Cough (~15%)
- Edema (~13%)
- Hypotension (~11%)
Clinical Pearl
Mosunetuzumab is notable as the first bispecific T-cell engager approved for a B-cell lymphoma as a fixed-duration, outpatient regimen, distinguishing it from continuous-infusion BiTEs. The step-up dosing strategy in Cycle 1 (1 mg → 2 mg → 60 mg) substantially reduces Grade ≥2 CRS without compromising efficacy. Patients achieving complete response by end of treatment tend to have durable remissions, making early PET-CT assessment valuable for counseling. Given the risk of…
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