Chronic Lymphocytic Leukemia with Stereotyped IGHV4-59/IGKV3-20 B Cell Receptors: Another Manifestation of Hepatitis C Virus-Associated B Cell Lymphoproliferation?.

Abstract 2331

Poster Board II-308

The hepatitis C virus (HCV) has been implicated in the development of B-cell lymphoproliferative disorders, including type II mixed cryoglobulinemia (MC-II) and B-cell lymphoma. MC-II is characterized by the presence of monoclonal IgM autoantibodies with rheumatoid factor (RF) activity. The monoclonal IgMs typically form immune complexes by binding polyclonal IgGs that exhibit anti-HCV reactivity. In a series of 6,196 patients affected by chronic lymphocytic leukemia (CLL), we have identified a subset of 12 cases sharing stereotyped mutated IGHV4-59/IGKV3-20 B cell receptors (BCRs) of the MD isotype (subset #13). Comparison of subset #13 heavy chain sequences to a comprehensive dataset of relevant public-database sequences revealed identical gene usage and remarkable junctional homology with the Ig sequence GenBank/U85234, the heavy chain of a RF detected in a healthy donor, as well as the sequence GenBank/AF303916, the clonotypic heavy chain from a CLL case with a history of HCV-associated MC-II. In addition, the light chain IGKV3-20/IGKJ1 stereotyped rearrangements in subset #13 were closely similar if not identical to the rearrangements expressed by clonally expanded IgM+κ+CD27+ B cells in HCV-associated MC-II. For both heavy and light chains, sequence similarities extended beyond junctional regions to shared, “stereotyped” somatic hypermutations across the entire IGHV and IGKV domain, respectively. We established viable and antibody-secreting heterohybridomas from the leukemic cells of a subset #13 case and confirmed the identity of the produced soluble antibody to the IG expressed by the CLL clone. ELISA tests against various antigens revealed that the soluble stereotyped IGHV4-59/IGKV3-20 antibody exhibited RF activity in vitro, while it was not reactive against HCV antigens. In conclusion, the present study for the first time provides evidence for the potential implication of HCV in the pathogenesis of at least a subset of CLL cases with distinctive stereotyped BCRs. The elucidation of the underlying immune mechanisms may pave the way for tailored anti-viral/anti-leukemic therapy for selected cohorts of patients that can be easily identified by molecular techniques during the diagnostic work-up.