Inhibitory human anti-chimeric antibodies to rituximab in a pemphigus patient.

Luisa Lunardon and Aimee S. Payne.

To the Editor

Rituximab is a chimeric mouse-human IgG1 monoclonal antibody that targets CD20, a transmembrane protein expressed on B cells. It has demonstrated success in two prospective case series in pemphigus, a potentially fatal blistering disease caused by autoantibodies to desmoglein skin adhesion proteins. The production of human anti-chimeric antibodies (HACA) to the murine fragments of rituximab has previously been described in pemphigus and other autoimmune disease patients, although a direct functional effect of these HACA has not been reported. Here we describe a pemphigus patient treated with rituximab who developed inhibitory IgG HACA associated with infusion reactions and lack of therapeutic response (i.e. complete or partial remission of disease).