B-cell monitoring predicts infection risk in childhood SLE patients on belimumab

OBJECTIVES: Belimumab improves outcomes in childhood-onset SLE (cSLE) but raises infection risks due to B-cell modulation. We aimed to evaluate dynamic B-cell and IgG monitoring for predicting infection risk. METHODS: In this historical cohort study, cSLE patients initiating belimumab were followed for 12 months. The primary outcome was a clinically significant infection requiring antimicrobials. CD19+ B-cell counts and IgG levels were measured at baseline, 3 and 6 months. Logistic regression identified risk factors, and a predictive nomogram was developed. RESULTS: Among the 78 patients, 19 (24.4%) developed infections. The infection group had significantly lower B-cell counts at 3 months (median 12 vs 25 cells/μl, P < 0.001) and a greater decline in IgG from baseline (-28.5% vs -12.1%, P < 0.001). Multivariate analysis identified three independent predictors: CD19+ count <15 cells/μl at 3 months (OR 5.82, 95% CI 2.11-16.03), IgG <600 mg/dl at 3 months (OR 4.55, 95% CI 1.63-12.71) and baseline prednisone >0.5 mg/kg/day (OR 3.98, 95% CI 1.40-11.31). The nomogram showed good accuracy (AUC 0.876, 95% CI 0.791-0.961). CONCLUSION: Early, profound B-cell depletion and IgG reduction are key predictors of infection in belimumab-treated cSLE. Our nomogram provides a practical tool for risk stratification and personalized monitoring.