How rituximab works
LEMS is an autoimmune condition in which the immune cells (T and B-cells) mistakenly attack the neuromuscular junction — the point where nerve cells meet muscles. The attack blocks the communication between nerve cells and muscles, causing the symptoms of LEMS.
Rituximab is a monoclonal antibody that binds to a specific protein — CD20– present on the surface of B-cells. This binding triggers the lysis (disintegration) of B-cells, thereby decreasing their number in the blood and dampening their attack on the neuromuscular junction.
As a therapy for autoimmune conditions like LEMS, rituximab may have another mechanism of action. One of the functions of B-cells is to introduce the T-cells to their target to prime them for an immune attack. By reducing the level of B-cells, rituximab also may disrupt this function and prevent T- cells from attacking the target, which in the case of LEMS is the neuromuscular junction.
Rituximab is prescribed for LEMS treatment based on its function to suppress the growth of B-cells. However, it has not been assessed in clinical trials involving LEMS patients, but its effectiveness has been described in LEMS patients who were prescribed rituximab by their healthcare team.
A reassessment of medical data from LEMS patients who were treated with rituximab highlighted its effectiveness as a therapeutic option for LEMS. In this study, researchers from the U.K. collected data from 10 patients with myasthenia gravis, a neuromuscular condition related to LEMS, and two patients with LEMS who underwent rituximab treatment. In 18 months, three patients (25%) achieved remission, while five (42%) showed clinically relevant improvements. Rituximab treatment alleviated symptoms in both LEMS patients, and both showed improvement during follow-up.
A case report of a 61-year-old man with LEMS who lacked muscle coordination, causing walking difficulty (gait ataxia), speech difficulty (dysarthria), and swallowing problems (dysphagia), was published in the journal Muscle & Nerve. Standard immunosuppressive treatment with azathioprine did not improve his condition, so doctors switched to rituximab, administered twice with a two-week interval between each infusion. Rituximab treatment led to a marked decrease in B-cell counts and an alleviation of symptoms after two courses of treatment. After 12 months, the B-cells increased in number again, but when the patient was given two more doses of rituximab at two-week intervals, this led to the depletion of B-cells and clinically relevant improvement in his condition. Rituximab’s effect was maintained even at the five-year follow-up.
Rituximab was initially developed as a cancer therapy. It is now a treatment approved by the U.S. Food and Drug Administration (FDA) under the brand name Rituxan for six conditions. These include two types of cancer (non-Hodgkin’s lymphoma and chronic lymphocytic leukemia), two inflammatory conditions (granulomatosis with polyangiitis and microscopic polyangiitis), and two autoimmune disorders (rheumatoid arthritis and pemphigus vulgaris).
Last updated: July 24, 2019
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