A pilot study of anti-CD5 ricin A chain immunoconjugate in systemic lupus erythematosus.

Abstract

To determine the safety and clinical and biological effects of a murine monoclonal anti-CD5 ricin A chain immunoconjugate (CD5 Plus) in patients with systemic lupus erythematosus (SLE). An open label phase I study of CD5 Plus. A dose of 0.1 mg/kg was administered intravenously on 5 consecutive days. A second course of immunoconjugate was given to patients who failed to show any clinical response one to 2 months later. Six patients (4 with glomerulonephritis and 2 with thrombocytopenia) were studied. Improvement was documented in 2 patients with nephritis; no effect on thrombocytopenia was observed. Adverse effects were mild and transient. Relative to pretreatment lymphocyte counts, the mean reduction in CD3+ T cell count was 69% at 2 weeks, 32% at one month, and 34% at 6 months following initial treatment. A comparable decrease in all subpopulations of mature T cells was noted, using a variety of surface markers, including CD4 and CD8. The mean percentage of T cells expressing the activation markers HLA-DR and interleukin 2R (IL-2R) was high before treatment, and remained so. There was a transient decrease in CD5+ B cells, but no persistent depletion of total B cell numbers. There was no consistent change in natural killer cell populations. Anti-CD5 ricin A chain immunoconjugate is well tolerated in patients with SLE, causes modest T cell depletion which may persist for months, and may have some clinical efficacy in lupus nephritis.