Percentage of residual B cells after 2 weeks of rituximab treatment predicts the improvement of systemic sclerosis‐associated interstitial lung disease

The benefit of rituximab (RTX) for systemic sclerosis-associated interstitial lung disease (SSc-ILD) has been shown in previous clinical trials. However, predictors of RTX efficacy have not been clarified. We investigated whether B-cell responsiveness to RTX is related to therapeutic effect. Ten SSc-ILD patients treated with RTX in an independent clinical trial (Japan Registry of Clinical Trials, jRCTs031180373) were included in this analysis. Peripheral B-cell counts were examined retrospectively before RTX administration (baseline) and at 2, 4, 12, and 24 weeks after the first RTX administration, along with percent-predicted forced vital capacity (%FVC) before and 24 weeks after RTX treatment. Relative to baseline, the percentage of residual peripheral blood B cells at 2 weeks after RTX was negatively correlated with the %FVC improvement at the 24-week assessment (r = -0.41, p = 0.04). In the subgroup with less than 5% B-cell persistence at week 2, %FVC at the 24-week assessment was significantly improved compared to baseline (p = 0.02). In another subgroup with more than 5% residual B cells, %FVC was not significantly different after 24 weeks compared to baseline (p = 0.41). In conclusion, the removal rate of B cells after 2 weeks of RTX treatment may be a useful surrogate marker of subsequent SSc-ILD improvement.