B-lymphocyte stimulator/a proliferation-inducing ligand heterotrimers are elevated in the sera of patients with autoimmune disease and are neutralized by atacicept and B cell maturation antigen-immunoglobulin

Abstract

IntroductionB-lymphocyte stimulator (BLyS) and a proliferation-inducing ligand (APRIL) are members of the tumor necrosis factor (TNF) family that regulate B-cell maturation, survival, and function. They are overexpressed in a variety of autoimmune diseases and reportedly exist in vivo not only as homotrimers, but also as BLyS/APRIL heterotrimers.MethodsA proprietary N-terminal trimerization domain was used to produce recombinant BLyS/APRIL heterotrimers. Heterotrimer biologic activity was compared with that of BLyS and APRIL in a 4-hour signaling assay by using transmembrane activator and CAML interactor (TACI)-transfected Jurkat cells and in a 4-day primary human B-cell proliferation assay. A bead-based immunoassay was developed to quantify native heterotrimers in human sera from healthy donors (n = 89) and patients with systemic lupus erythematosus (SLE; n = 89) or rheumatoid arthritis (RA; n = 30). Heterotrimer levels were compared with BLyS and APRIL homotrimer levels in a subset of these samples.ResultsThe recombinant heterotrimers consisted mostly of one BLyS and two APRIL molecules. Heterotrimer signaling did not show any significant difference compared with APRIL in the TACI-Jurkat assay. Heterotrimers were less-potent inducers of B-cell proliferation than were homotrimeric BLyS or APRIL (EC50, nMol/L: BLyS, 0.02; APRIL, 0.17; heterotrimers, 4.06). The soluble receptor fusion proteins atacicept and B-cell maturation antigen (BCMA)-immunoglobulin (Ig) neutralized the activity of BLyS, APRIL, and heterotrimers in both cellular assays, whereas B-cell activating factor belonging to the TNF family receptor (BAFF-R)-Ig neutralized only the activity of BLyS. In human sera, significantly more patients with SLE had detectable BLyS (67% versus 18%; P < 0.0001), APRIL (38% versus 3%; P < 0.0002), and heterotrimer (27% versus 8%; P = 0.0013) levels compared with healthy donors. Significantly more patients with RA had detectable APRIL, but not BLyS or heterotrimer, levels compared with healthy donors (83% versus 3%; P < 0.0001). Heterotrimer levels weakly correlated with BLyS, but not APRIL, levels.ConclusionsRecombinant BLyS/APRIL heterotrimers have biologic activity and are inhibited by atacicept and BCMA-Ig, but not by BAFF-R-Ig. A novel immunoassay demonstrated that native BLyS/APRIL heterotrimers, as well as BLyS and APRIL homotrimers, are elevated in patients with autoimmune diseases.

Stoichiometry of Heteromeric BAFF and APRIL Cytokines Dictates Their Receptor Binding and Signaling Properties

“…A previously characterized APRIL 2 BAFF 1 heteromer activated TACI as efficiently as APRIL in an NF-B reporter assay, was less potent than either BAFF or APRIL taken alone in B cell proliferation assays, and could be inhibited by BCMA-Fc and TACI-Fc but not BAFFR-Fc (18). Our data are in line with these findings and extend them to APRIL 1 BAFF 2 .…”

“…Although APRIL is mainly released in a soluble form (15), it can bind to proteoglycans and thus create niches for antibody-secreting cells (16,17). Heteromers of BAFF and APRIL are produced in autoimmune diseases and are sometimes also detected in healthy subjects (18,19). Because of the intrinsic difficulty of producing and purifying BAFF-APRIL heteromers, these ligands have remained incompletely characterized.…”

Antibody-based therapeutics to watch in 2011

“…B cells are thought to play a key role in the pathogenesis of the disease. 74 Atacicept binds to B-lymphocyte stimulator (BLyS) and a proliferation-inducing ligand (APRIL), two members of the tumor necrosis factor superfamily that are overexpressed in the sera of patients with autoimmune disorders, 75 and thus interferes with B-cell signal transduction induced by these two ligands. In Phase 2 studies, the effects of atacicept administration were investigated in patients with multiple sclerosis, optic neuritis and lupus nephritis, but these studies had been terminated as of September 2010.…”

Atacicept in patients with rheumatoid arthritis and an inadequate response to tumor necrosis factor antagonist therapy: Results of a phase II, randomized, placebo-controlled, dose-finding trial

“…BLyS also binds to the BAFF receptor, and APRIL binds to the proteoglycan receptor. Only the TACI and BCMA receptors bind these heterotrimers (17,19). In light of the potential role of BLyS and APRIL in autoimmune diseases, targeting these cytokines is a rational approach to therapy.…”