A substantial part of rheumatoid arthritis (RA) patients is chronically treated with adalimumab. Some of these patients produce antibodies against adalimumab, which correlate with lower serum drug levels and reduced clinical response. Long term exposure to antigens may result in antigen specific IgG4 production as was demonstrated in studies on prolonged exposure to antigens such as different allergens, Factor VIII and IFN-β. Here, we investigate whether long term treatment of RA patients with the therapeutic monoclonal antibody adalimumab leads to the production of specific IgG4 antibodies.

We developed radio immunoassays to detect total IgG or IgG4 against adalimumab and applied these in a cohort of 271 consecutive RA patients during 3 years of adalimumab treatment.

In 32 % of the 271 patients antibodies against adalimumab were detectable. IgG4 antibodies were detected in 29 % of the patients. The proportion IgG4 of total IgG against adalimumab varies widely between patients, and IgG4 was found to contribute significantly to the anti drug antibody (ADA) response in some patients.

In the immune response against adalimumab in adalimumab-treated RA patients a considerable part of the ADA is IgG4. Although IgG4 is often considered to be harmless due to its lack of effector function, neutralization of adalimumab by IgG4 antibodies will lead to a reduced clinical response.