Rh autoantigen presentation to helper T cells in chronic lymphocytic leukemia by malignant B cells

Chronic lymphocytic leukemia (CLL) is frequently associated with autoimmune diseases directed against constituents of the blood, including hemolytic anemia (AIHA). We hypothesized that CLL cells predispose to hematologic autoimmunity by acting as aberrant antigen-presenting cells (APCs). Initially, it was confirmed that all studied patients with AIHA secondary to CLL harbored activated helper T (T(H)) cells specific for epitopes on the dominant red blood cell (RBC) autoantigens in primary AIHA, the Rh proteins. Rh-specific T(H) cells were also detected in a number of patients with CLL who, although they did not have AIHA, had low levels of anti-RBC antibody in their sera. Fractionation of putative APC populations from the peripheral blood of patients by negative selection showed that CD5+ CLL cells are the most effective cell type in processing and presenting purified Rh protein to autoreactive T(H) cells. This ability was confirmed using positively selected CD5+ CLL cells. Thus, our study provides the first evidence for malignant cells driving an autoimmune response by acting as aberrant APCs.