Background/Purpose: B-Lymphocyte (B-Ly) depletion therapy with the monoclonal anti-CD20 antibody rituximab (RTX) is widely used in a variety of autoimmune (AI) diseases. The risk of severe infection related to RTX use in this population is estimated to be 5-14.1/100 patient-years. Additional risk factors for severe infection, such as low IgG levels, age, and concomitant immunosuppressive therapy, have been recognized.

In practice, many clinicians are reluctant to use RTX if B-Ly levels are decreased. Our aim was to examine whether B-Ly counts, the direct target of RTX, are associated with an increased risk of infection in patients with AI diseases.

Methods:  We conducted an observational cohort study of all 161 patients treated with RTX between 2002 and 2012 in the Rheumatology and Immunology Divisions of the Geneva University Hospital. Primary outcome was severe (iv antibiotics, hospitalization, related death) and non-severe infection (requiring antibiotics). Primary predictor of interest was absolute B-Ly count, assessed by flow cytometry before RTX treatment. Time-to-infection was analyzed by Cox proportional hazard model, adjusting for potential confounders (glucocorticoid and other immunosuppressants use, diabetes and other chronic comorbidities, RA versus other AI diseases, age and sex).

Results:  A total of 161 patients were included and followed for a mean period of 2.4 years; 85 (53%) had RA, and the remaining 76 (47%) mainly connective tissue disorders and vasculitides. During follow-up, 63 severe and 111 non-severe incident infections were observed. The incidence rate of severe infection was 15 /100 patients-years in non-RA patients compared to 3.5 in RA patients (p<0.001). The most recent B-Ly level before RTX treatment was not associated with subsequent infections (HR 0.999, p=0.78). Significant predictors of infection were an AI condition other than RA (HR 3.4, p<0.001), age (HR 1.03, p=0.03) and low IgG levels (HR 0.91, p=0.02).

Conclusion:  In this population treated with RTX for AI diseases, B-Ly counts before RTX infusion were not associated with incidence of infections. This data does not support the common concern of infection with low B-Ly counts, and does not encourage assessing B-Ly before RTX treatment. We confirm the higher risk of infection conferred by low IgG levels, older age and AI disease other than RA.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/b-lymphocyte-count-is-not-associated-with-an-increased-risk-of-infection-in-patients-treated-with-rituximab-for-auto-immune-diseases/