Antibodies cloned from a patient with Idiopathic CD4 Lymphopenia induce potent anti-T and B cell complement-dependent lysis 2304145

Abstract Introduction Idiopathic CD4 Lymphopenia (ICL) is a rare immunodeficiency disorder characterized by an unexplained CD4+ T-cell lymphopenia. Often, these patients harbor additional deficiencies in CD8, B, and/or NK cells and, therefore, may suffer from opportunistic infections. We previously found that half of patients with ICL possess auto-antibodies-(Ab) against a broad spectrum of molecules, including those expressed on the membranes of B and T-cells, suggesting a potential role of these anti-lymphocyte Ab (ALAb) in their lymphopenia/s. We focused here on a patient (ICL-9) whose IgM ALAb induced complement dependent cytotoxicity (CDC) against healthy donor’s (HD) lymphocytes and against B-cell lymphoma cell lines. Methods We performed single-cell B-cell receptor (BCR) sequencing of sorted ICL-9’s B cells, cloned 21 IgM BCR sequences, and screened them for specificity against B/T lymphocytes and Raji B-cell line. The positive reactive clones were further tested for CDC of their cellular targets. Results The cloned ALAb belonged to the previously described autoreactive VH4-34 family. Ten of the auto-Ab recognized B and/or T cells, with three of them inducing lysis of their targets by CDC. A particularly potent clone, named Aliron, induced CDC of 50% of B lymphocytes at 0.01 nM concentration, showing a 100-fold higher CDC potency than anti-CD20 Ab Rituximab. At higher concentrations, Aliron was also able to kill T-cells by CDC. Further, Aliron induced CDC of all seven B-cell lymphoma lines tested. We are currently analyzing the in vivo activity of these IgM monoclonal Abs in humanized mouse models. Conclusion From a single patient with ICL we cloned and characterized IgM Abs that recognized membrane targets on T and B lymphocytes and induce CDC. The discovery of these ALAb support their possible pathogenic role on ICL and they might develop into potential future clinical applications. Funding Source NIAID, NIH Topic Categories Immune Mechanisms of Human Disease (HUM)