Background/Purpose: Incomplete B-cell and plasmablast depletion, as measured using highly sensitive flow cytometry (HSFC), is associated with lower response rates following rituximab in SLE [1]. Enhanced B-cell depletion with the type II anti-CD20 monoclonal antibody obinutuzumab resulted in increased renal responses in proliferative lupus nephritis (LN) in the NOBILITY trial (NCT02550652) and will be further evaluated in the Phase 3 REGENCY trial (NCT04221477). The objective of this analysis was to measure peripheral B-cells, B-cell subsets (naïve, memory and plasmablast) and B-cell activating factor (BAFF) levels and to assess associations between B-cell depletion and renal response in LN patients in a clinical trial of obinutuzumab.

Methods: 126 patients with active Class III/IV LN were randomized to obinutuzumab or placebo infusions in combination with mycophenolate and glucocorticoids. Peripheral B-cells were measured using a HSFC method with a lower limit of quantitation of 0.441 cells/μL. Serum levels of BAFF were evaluated using ELISA. Sustained depletion was defined by total B-cells below the limit of detection at both weeks 24 and 52. Renal response definitions from Phase 2 NOBILITY and Phase 3 REGENCY trials were used.

Results: Obinutuzumab resulted in rapid depletion of total B-cells, memory and naïve B-cells, and plasmablasts from peripheral blood, with 88% of obinutuzumab patients depleted to < 0.441 total B-cells/μL at week 2 (Figure). Mean serum BAFF increased from 4,585 pg/mL at baseline to 14,601 pg/mL at week 52 in the obinutuzumab group. Sustained B-cell depletion was achieved in 32/52 (62%) of patients with complete data and was associated with a higher renal response rate at week 76 (Table), although patients who achieved sustained depletion also had lower baseline proteinuria and serum creatinine.

Conclusion: Obinutuzumab, a type II anti-CD20 mAb, mediated rapid, complete and sustained depletion of peripheral B-cells and plasmablasts and large increases in serum BAFF. Similar to previous reports, sustained B-cell depletion was associated with increased renal response though there may have been confounding factors. REGENCY is being conducted to further evaluate the therapeutic hypothesis with obinutuzumab in LN.

References:

1. Md Yusof MY et al. Ann Rheum Dis. 2017;76:1829-36.

Figure. Mean levels of selected biomarkers over time by treatment group.

Table. Data from NOBILITY at week 76 by depletion status at weeks 24 and 52.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/biomarkers-of-b-cell-depletion-and-response-in-a-randomized-controlled-trial-of-obinutuzumab-for-proliferative-lupus-nephritis/