Introduction of Rituximab

Rituximab is a genetically engineered chimeric murine/human monoclonal antibody targeting CD20 antigen, which is primarily found on the surface of immune system B cells. This drug is an IgG1 kappa immunoglobulin antibody containing murine light and heavy-chain variable region sequences and human constant region sequences. Rituximab is used for the treatment of diseases which are characterized by having too many B cells, overactive B cells, or dysfunctional B cells as it could bind to CD20 on normal or malignant B cells. The diseases that rituximab can treat include Non–Hodgkin’s Lymphoma (NHL), Chronic Lymphocytic Leukemia (CLL), Rheumatoid Arthritis (RA) in combination with methotrexate in adult patients with moderately-to severely-active RA, Granulomatosis with Polyangiitis (GPA) (Wegener’s Granulomatosis), and Microscopic Polyangiitis (MPA).

Mechanism of Action of Rituximab

Rituximab is an antibody drug that targets the CD20 antigen, which was expressed in 90% of B lymphoma cells and normal B lymphoid cells, but not in hematopoietic stem cells, primary B lymphoid cells, normal blood cells and other normal tissues.

Rituximab consists of a murine variable region (Fab region) and a human constant region (Fc region). The Fab region has variable sections that define a specific target antigen, which allows the antibody to secure its binding to exclusive antigen. The Fc region is the tail end of the antibody that binds to cell surface receptors to induce sequence events including the depletion of circulating B lymphocytes by complement-dependent cell lysis, antibody-dependent cellular cytotoxicity (ADCC), as well as apoptosis, activating the immune system. When rituximab binding to CD20, the body's natural immune defenses are recruited to attack and kill the marked B-cells, leading to B-cell lysis. Stem cells do not have the CD20 antigen, and thus, healthy B-cells can regenerate after treatment.

Fig.1 Mechanism of action of Rituximab

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