Reduced B lymphocyte and immunoglobulin levels after atacicept treatment in patients with systemic lupus erythematosus: Results of a multicenter, phase ib, double‐blind, placebo‐controlled, dose‐escalating trial

Abstract Objective To assess the safety and tolerability of atacicept in patients with systemic lupus erythematosus (SLE) and the biologic effect of atacicept on B lymphocyte and immunoglobulin levels. Atacicept is a TACI‐Ig fusion protein that inhibits B cell stimulation by binding to B lymphocyte stimulator and a proliferation‐inducing ligand. Methods This phase Ib, double‐blind, placebo‐controlled, dose‐escalating trial comprised 6 cohorts of patients treated with atacicept or placebo in a 3:1 ratio of active drug to placebo (n = 8 per group; n = 7 in cohort 5). Cohorts 1–4 received a single subcutaneous dose of placebo or either 0.3 mg/kg, 1 mg/kg, 3 mg/kg, or 9 mg/kg of atacicept. Cohorts 5 and 6 received weekly doses of placebo or either 1 mg/kg or 3 mg/kg of atacicept for 4 weeks. Patients were followed up for 6 weeks (cohorts 1–4) or 9 weeks (cohorts 5 and 6). Patients with mild‐to‐moderate SLE were enrolled. Results Biologic activity of atacicept was demonstrated by dose‐dependent reductions in immunoglobulin levels and in mature and total B cell numbers. This effect was most pronounced in the repeated‐dose cohorts and was sustained throughout the followup period. There were no changes in the numbers of T cells, natural killer cells, or monocytes. Mild injection‐site reactions occurred more frequently among the atacicept group than the placebo group. There were no differences in the frequency or type of adverse events and no severe or serious adverse events in patients treated with atacicept. Conclusion Atacicept administered subcutaneously was well tolerated and demonstrated biologic activity consistent with the proposed mechanism of action.