To understand the effects of prolonged BLyS inhibition in human SLE.
17 SLE patients enrolled in a clinical trial of belimumab, a BLyS-specific inhibitor, plus standard of care therapy were studied. Phenotypic analysis of lymphocytes was performed using flow cytometry. Circulating antibody-secreting cells were enumerated using ELISpot assay. Serum was analyzed by ELISA using an antibody that recognizes products of the VH4-34 gene. Lymphocyte counts, Ig levels and anti-dsDNA antibody levels were available as part of the clinical trial analyses.
Samples were collected at days 0, 84, 168, 365, 532 and >730. The total B cell number decreased from baseline starting between days 84–168. This was due to a decrease in naïve and transitional B cells. CD27+/IgD+memory B cells and plasmablasts decreased only after 532 days, whereas CD27+/IgD− memory B cells were not affected, and there were no changes in T cells. Serum IgM levels began to decline between days 84–168, but there were no changes in serum levels of IgG, IgG anti-DNA antibodies or VH4-34 antibodies during the study. SLE patients had more IgM-, IgG-, and autoantibody-producing B cells than normal controls at Day 0. There was only a modest decrease in the frequency of total IgM-producing but not IgG-producing cells at Days 365 and 532, consistent with the phenotypic and serologic data.
Our data confirm the dependence of newly formed B cells on BLyS for survival in humans. In contrast, memory B cells and plasma cells are less susceptible to selective BLyS inhibition.