#1133 Kidney characteristics of belimumab-treated patients with SLE pre-lupus nephritis indication: identifying data for future comparative research

Abstract Background and Aims Lupus nephritis (LN) is a severe, renal manifestation occurring in approximately 40% of patients with the chronic autoimmune disease systemic lupus erythematosus (SLE) [1]. Belimumab (BEL), a human immunoglobulin G1λ monoclonal antibody that binds to and inhibits soluble B-lymphocyte stimulator, was indicated for SLE in 2011 and LN in 2020 by the US Food and Drug Administration [2]. BEL has proven efficacy for SLE and LN [2], but there are limited data regarding the effectiveness of BEL to delay LN onset due to lack of sufficient follow-up time. Evaluating the demographic, clinical and kidney characteristics of patients treated with BEL before its regulatory approval for LN allows for a longer follow-up period. This study describes the kidney characteristics of patients with SLE treated with BEL and/or standard therapy (ST) pre-LN indication. The objective was to evaluate whether there are sufficient data from BEL-treated patients with kidney impairment and available laboratory measurements for use in future comparative research regarding effectiveness of BEL to delay LN onset. Method This retrospective, real-world study (GSK Study 217532) used electronic health record (EHR) data to assess adult patients with SLE. Eligible patients received BEL with or without ST (BEL cohort) or ST only (ST cohort) during the study identification period (1 January 2017 to 31 December 2020) and had activity in the EHR 12 months pre-index (baseline period); the index date was the first prescription of BEL or ST. A diagnosis of SLE was defined as presence of International Classification of Diseases, 10th Revision, Clinical Modification codes (M32.1x, M32.8, M32.9) based on either ≥ 2 outpatient medical claims or ≥ 1 inpatient/emergency department claim during the baseline period (or index date). Patients were excluded if they received BEL during the baseline period. LN- and kidney-related characteristics were measured during the baseline period and after 36 months of follow-up. Results This study identified 32 017 patients with SLE: 1318 in the BEL cohort and 30 699 in the ST cohort. The mean (standard deviation) age of the BEL and ST cohorts was 43.9 (12.7) and 51.9 (15.2) years, respectively. Most patients were White (BEL: n = 804 [61.0%]; ST: n = 19,812 [64.5%]) and female (BEL: n = 1247 [94.6%], ST: n = 27 826 [90.6%]). At baseline, 13.1% of the BEL cohort and 10.0% of the ST cohort had an LN diagnosis; chronic kidney disease (CKD) was reported in 22.1% of the BEL cohort and 27.7% of the ST cohort (Table 1). End-stage kidney disease (ESKD) was observed at baseline in 1.0% of the BEL cohort and 4.0% of the ST cohort. Dialysis rate at baseline was 0.7% in the BEL cohort and 3.5% in the ST cohort. A smaller proportion of the BEL cohort had kidney impairment than the ST cohort. Overall, 32.1% of the BEL cohort (n = 423) and 46.1% of the ST cohort (n = 14,162) had 36 months of valid follow-up. The proportion of patients with available kidney laboratory characteristics was generally similar between baseline and 36 months follow-up, and between BEL and ST cohorts (Table 2). However, the proportion of the BEL cohort at baseline and at 36 months’ follow-up with a proteinuria laboratory measurement was >2-fold that of the ST cohort (baseline: BEL = 30.5%, ST = 12.9%; follow-up: BEL = 42.1%, ST = 20.2%). Conclusion This study demonstrates that there are adequate kidney value measurements for BEL and ST patients available to assess kidney outcomes over time in patients with SLE pre-LN indication of BEL. Observationally, the ST cohort displayed more impairment than the BEL cohort, which could indicate more advanced disease in this slightly older cohort. However, future studies should account for baseline differences between ST and BEL cohorts to assess kidney impairment–related outcome measures, by using matching and weighting procedures. Funding GSK.