Introduction/Objectives Belimumab combined with mycophenolate mofetil has been proven to be effective for treating systemic lupus erythematosus (SLE) in several randomized controlled trials. Calcineurin inhibitors are also useful in con- trolling the activity of SLE. However, the safety and effectiveness of belimumab-calcineurin inhibitor combination therapy have not been addressed. Therefore, the current single-center retrospective study aimed to analyze the safety/efficacy profile of belimumab-tacrolimus (B-T) combination therapy in patients with SLE.

Method Patients with SLE administered tacrolimus and belimumab during treatment were included in the study. Samples were analyzed for the drug retention rate, SLE flare rate, infection incidence rate, and glucocorticoid-sparing effect of the B-T combination therapy.

Results Thirty-three patients with SLE were treated with B-T combination therapy at our institution. Four patients dis- continued treatment due to insufficient response or adverse events. The drug retention rate was over 90% at week 52 and approximately 80% at day 1000. Only one patient developed serious infection. The lupus low disease activity state (LLDAS) achievement ratio was 9.1% on the day of initiation and improved to 64.0% at 52 weeks after initiation. SLE flares were observed in three patients (9.1%) in the first 52 weeks after initiation, and in five patients (15.2%) throughout the study period. A glucocorticoid-reducing effect was also observed in patients treated with B-T combination therapy.

Conclusions In most patients with SLE, B-T combination therapy is well tolerated with a good efficacy profile and glucocorticoid-reducing effect. Thus, B-T combination therapy represents a feasible option for patients with refractory lupus.