Idiopathic CD4 lymphopenia (ICL) is characterized by persistent low CD4 counts, frequently in combination with CD8, natural killer, or B cell lymphopenia. It is considered a heterogeneous disorder with manifestations that can include autoimmunity, invasive fungal infections or infections with human papillomavirus, and malignancies typically related to infections. The exact etiology of ICL remains unclear and there is no specific treatment.
Recent data from our group revealed a high prevalence of antilymphocyte antibodies in many of the ICL patients evaluated. The targets of these antibodies remain unknown and are being investigated. On some occasions, these antibodies have the ability to cause antibody-dependent cytotoxicity or complement activation, both mechanisms that can cause cell death. Although it is unclear if these antibodies are the cause (or perhaps more likely the effect) of lymphopenia, it is plausible they play a significant pathogenic role and at a minimum may be hampering lymphocyte compensatory mechanisms for expansion and improved survival.
The immune deficiency and the unclear role of autoantibodies preclude aggressive immunosuppressive treatment (eg, corticosteroids) for ICL. Therefore, a rational approach to treatment is belimumab, a monoclonal antibody that targets Blys (also call BAFF for B-cell activating factor), expressed on activated B cells and plasma cells. Belimumab is approved by the United States Food and Drug Administration (FDA) for patients with systemic lupus erythematosus (SLE) who have evidence of autoantibodies and has shown efficacy in both reducing symptoms and leading to a modest decrease in autoantibodies.
In this open-label prospective single-arm study, ICL patients with laboratory evidence of antilymphocyte antibodies will be recruited. Belimumab will be administered by intravenous infusion for 6 months with an extended follow-up of an additional 6 months. Administration of the study drug will follow the SLE scheme of 10 mg/kg at study entry, 2 weeks, 4 weeks, and monthly thereafter (8 doses total). Three additional visits approximately every 2 months will complete the 52-week study. Clinical safety evaluations with immunologic and serologic testing will be performed at all study visits.
This protocol will assess the safety of belimumab in ICL and also help in better understanding the role of autoantibodies in ICL pathogenesis. This knowledge could substantially improve rationale and design of novel therapeutic interventions in ICL.
