Belimumab, a biologic targeting B lymphocyte stimulator (BLyS), shows therapeutic promise in SLE, but its effects on pediatric patients remain unclear.<h4>Methods</h4>This study used CyTOF to analyze immunophenotypic changes before and after belimumab treatment and investigate immune features in refractory SLE.<h4>Results</h4>Results showed that belimumab treatment primarily reduced transitional and naïve B cells, and also decreased age-associated B cells (ABCs), a subset implicated in autoimmunity or chronic inflammation. Here, TNFSF13B is linked to systemic lupus erythematosus.