Identification of Covariates Modulating B-Cell Repopulation Kinetics in Subjects Receiving Rituximab Treatment

Objective: B-cell depletion using the anti-CD20 monoclonal antibody rituximab is a cornerstone in the therapeutic concept of multiple autoimmune diseases. B-cell depletion is associated with a higher risk for severe infections, and the time span of B-cell repopulation differs greatly between individuals. Data on factors influencing B-cell repopulation kinetics are limited. This study aims to identify patient-specific and therapy-associated covariates that modulate B-cell repopulation.

Methods: This single-center retrospective observational study presents data of 839 subjects receiving 2,017 courses of rituximab for autoimmune diseases. Assessed covariates are patient-specific factors (sex, age, kidney function, and underlying disease) and co-immunosuppression with common agents (azathioprine, cyclosporine A, cyclophosphamide, hydroxychloroquine, methotrexate, mycophenolate mofetil, tacrolimus, and corticosteroids). The primary end point is the time to B-cell repopulation (≥5/μl). The secondary end point is the time to B-cell reconstitution (≥50/μl). Multivariate time-to-event analysis and logistic regression models were applied to estimate the influence of covariates.

Results: Age over 60 years (hazard ratio [HR] 0.71 for repopulation, P = 0.008), impaired kidney function (HR 0.72, P = 0.001), antineutrophil cytoplasmic antibody-associated vasculitis (HR 0.61, P < 0.001), solid organ transplantation (HR 0.4, P < 0.001), and co-immunosuppression with corticosteroids (HR 0.64, P < 0.001) or azathioprine (HR 0.49, P < 0.001) were associated with impaired B-cell repopulation and reconstitution. Effects of corticosteroids (P = 0.043) and azathioprine (P = 0.025) were dose dependent.

Conclusion: Prolonged rituximab dosing intervals may be effective to achieve B-cell depletion and reduce risk of infection in advanced age or patients with impaired kidney function. Co-medication with corticosteroids or azathioprine prolongs B-cell recovery, which may increase therapeutic effects but also the rate of adverse events.