Background: Belimumab, the first biological drug approved for the treatment of patients with Systemic Lupus Erythematosus (SLE), is a fully human IgG1λ monoclonal antibody directed against BlyS (B Lymphocyte Stimulator). BLyS inhibition is associated with a reduction in circulating B subsets and short-lived plasmacells

Objectives: The aim of this study was to characterize the B cell phenotype in SLE patients at baseline and after B-cell targeted therapy with Belimumab in a cohort of active SLE patients.

Methods: Fifty-four SLE patients diagnosed according to the 2012 SLICC criteria (49 females, mean age 40.6±13.2 years, disease duration 12.3±9.0 years, SLEDAI-2K 6.6±3.1) who received belimumab were enrolled. Phenotyping of peripheral blood (PB)- derived B lymphocytes (using as phenotypic markers IgD, CD27 and CD38) was performed at six (T6) and twelve (T12) months in 38 SLE patients, together with the expression of BAFF and BAFF- R by flow cytometry.

Results: In the whole SLE cohort, a reduction over time was observed in the percentage of CD19 ^pos [T0:11.1±6.1% vs T6:6.4±3.4%,p<0.01;T12:4.2±3.4%,p<0.01] and naïve B cells (IgD ^pos CD27 ^neg ) [T0:55.8±28.7% vs T6:34.9±22.2%,p<0.01;T12:30.0±19.4%;p=0.04] and an increase of switched memory B cells (IgD ^neg CD27 ^pos )[T0:21.0±20.2% vs T6:37.5±21.4%,p<0.01;T12:42.2±21.%7,p=0.02] after B-cell targeted therapy with anti-BLyS. Moreover, a reduction of IgD ^neg CD27 ^neg memory B cells at T6(p=0.01) was observed. Conversely, BAFF and BAFFR expression in peripheral blood-derived CD19 ^pos cells remained unchanged during therapy with anti-BLyS. Stratifying SLE patients based on severe (renal and/or neurological) and mild (articular and/or cutaneous) organ involvement, a significant reduction of CD19 ^pos percentage[T0:10.7±4.6% vs 6:6.8±2.4%,p=0.03;T12:4.5±3.5%,p=0.03] and naïve B cells[T0:61.0±24.6% vs T6:38.9±17.5%,p<0.01;T12:36.9±16.0%,p=0.03] was found in SLE patients with mild organ involvement and a significant increase of switched memory B cell subsets in both subgroups [(severe T0:24.1±25.0% vs T6:44.9±27.4%,p=0.01) (mild T0:18.9±18.3 vs T6:31.2±12.7%,p<0.01)]. Evaluating the B cell subsets regarding the response to treatment (based on the reduction of the SLEDAI-2K), a significant reduction of naïve B cells was observed at T6 in both SLE group,[(responders T0:55.4±29.3 vs T6:32.3±19.9,p<0.01)(no responders T0:63.1±41.3% vs T6:41.4±33.5%,p=0.05)] and switched memory B cells[(responders T0:22.4±21.2% vs T6:39.6±19.4%,p<0.01)(no responders T0:20.6±26.1% vs T6:38.6±35.3%,p<0.05)], with a significant higher percentage at baseline of switched memory B cells in responder SLE than in no-responder SLE group (22.4±21.2% vs 20.6±26.1%,p=0.02). ROC curve analysis of IgD ^neg CD27 ^pos subset [AUC(95% CIs):0.761:(0.566-0.957)p=0.023] identified a cut-off of 9.94% associated with response at 6 months. Moreover, having a IgD ^neg CD27 ^pos rate ≥9.94% [OR:4.5(95% CIs:0.9-17.2)]; and the presence of anti-dsDNA antibodies at baseline[OR:5.2(95%CIs:1.2-22.1)], identified SLE patients who achieved early response within 6 months from belimumab therapy initiation.

Conclusion: Anti BLyS therapy significantly impacts on the composition of peripheral blood B-cell subpopulations in SLE patients in relation with the distinct organ involvement. Moreover, baseline immunological features and IgD ^neg CD27 ^pos B cell subset rate are novel putative biomarkers of response to anti-BLyS therapy in SLE patients.

REFERENCES:

[1]D. Ramsköld et al. B cell alterations during BAFF inhibition with belimumab in SLE. EBioMedicine. 2019 Feb;40:517-527.

[2]S. Piantoni et al. Characterization of B- and T-cell compartment and B-cell related factors belonging to the TNF/TNFr superfamily in patients with clinically active systemic lupus erythematosus: baseline BAFF serum levels are the strongest predictor of response to belimumab after twelve months of therapy. Front Pharmacol. 2021 May 21;12:666971.

Disclosure of Interests: None declared