Rituximab, an anti-CD20 monoclonal antibody, does NOT affect plasma cells in multiple myeloma because:

• A Plasma cells are located in the bone marrow, preventing rituximab access
• B Plasma cells express high levels of complement decay-accelerating factor (DAF/CD55)
• C CD20 is not expressed on terminally differentiated plasma cells ✓
• D Plasma cells rapidly downregulate CD20 in response to rituximab binding

Explanation

CD20 is a B-cell surface antigen expressed from pre-B cells through mature B cells but is downregulated upon terminal differentiation into antibody-secreting plasma cells. This is why rituximab is effective in B-cell lymphomas (which express CD20) but has no direct activity against plasma cell myeloma (which lacks CD20 expression). Anti-myeloma therapy instead targets CD38 (daratumumab) or SLAMF7 (elotuzumab).

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.