Purpose Belimumab (BEL), a recombinant human monoclonal antibody directed against B-cell activating factor (BAFF), is the first approved biological agent for patients with systemic lupus erythematosus (SLE) and a high level of disease activity or lupus nephritis (LN). BEL inhibits primary humoral immune responses by depleting naive B-cells that are dependent on BAFF for their survival while secondary humoral immune responses by memory B cells (MBCs) remain intact. Indeed, some studies reported an increase of circulating MBCs following neutralization of BAFF1,2. So far these effects of BEL on the MBC compartment in SLE patients have not been investigated. This study aimed to establish the dynamics of circulating MBCs in patients with SLE treated with BEL and to perform an in-depth analysis of the impact of BEL on the MBC compartment.

Methods First, extensive B cell subset phenotyping was performed prospectively by employing high-sensitivity flow cytometry (HSFC) based on EuroFlow protocols3 in severe SLE/LN patients treated with BEL4. Additionally, in-depth characterisation of surging MBCs in circulation was performed by single-cell RNA sequencing (scRNA-seq).

Results HSFC established that the increase in MBCs was non-specific and observed in a broad range of MBC immunoglobulin subclasses peaking as early as 2 weeks after BEL initiation. Subsequent scRNA-seq analysis of the emerging MBCs revealed a non-proliferating phenotype with a prominent decrease in activation status. In these circulating MBCs, a large amount of migration and adhesion genes were downregulated suggesting that the accumulation of MBCs following BEL treatment was related to their impaired cell-cell adhesion, disrupting cell-trafficking and preventing extravasation.

Conclusions After initiation of BEL treatment, a substantial increase of circulating MBCs was firmly established in patients with SLE/LN. The surge of circulating MBCs appeared to be associated with disrupted lymphocyte trafficking of MBCs, thereby suggesting a new potential therapeutic mechanism of BEL on MBCs in SLE. These findings have important implications to our understanding and consequent improvement of B-cell targeted treatment strategies in patients with active SLE and LN as MBC accumulation in circulation might allow for more efficient targeting of the B-cell compartment.

References

1. Furie R et al. A phase III, randomized, placebo-controlled study of belimumab, a monoclonal antibody that inhibits B lymphocyte stimulator, in patients with systemic lupus erythematosus. Arthritis Rheum 2011;63(12):3918–3930.

2. Stohl W et al. Belimumab reduces autoantibodies, normalizes low complement levels, and reduces select B cell populations in patients with systemic lupus erythematosus. Arthritis Rheum 2012;64(7):2328–2337.

3. ClinicalTrials.gov[Internet] Bethesda(MD): National Library of Medicine(US) 2000 Feb29 Identifier NCT03747159, Synergetic B-cell Immunomodulation in SLE-2nd Study(SynBioSe-2) 2018 Nov 20 https://clinicaltrials.gov/ct2/show/NCT03747159

4. Blanco E et al. Age-associated distribution of normal B-cell and plasma cell subsets in peripheral blood. J Allergy Clin Immunol 2018;141(6):2208–2219.