Biased IGH VDJ gene repertoire and clonal expansions in B cells of chronically hepatitis C virus–infected individuals

Abstract

Patients chronically infected with hepatitis C virus (HCV) frequently develop mixed cryoglobulinemia (MC), a monoclonal expansion of immunoglobulin M (IgM)1 autoreactive B cells, and also have an increased B-cell lymphoma risk. Whether HCV infection also impacts the B-cell compartment and the B-cell receptor repertoire in patients not affected by MC or lymphomas is poorly understood. Flow cytometric analysis of peripheral blood B cells of 30 MC-negative HCV-infected patients and 15 healthy controls revealed that frequencies of class-switched memory B cells were increased in the patients, whereas frequencies of transitional and naive B cells were decreased. For 22 HCV1 patients and 7 healthy controls, we performed high-throughput sequencing of immunoglobulin heavy chain VDJ rearrangements of naive, mature CD51, IgM1 memory, and class-switched memory B cells. An increased usage of several IGHV genes, including IGHV1-69 and IGHV4-59, which are closely linked to MC and HCV-associated lymphomas, was specifically seen among IgM1 memory B cells of the patients. Moreover, many, and partly very large, expanded clones were seen predominantly among IgM1 memory B cells of all HCV-infected patients analyzed. Thus, chronic HCV infection massively disturbs the B-cell compartment even in patients without clinically detectable B-cell lymphoproliferation and generates many large B-cell clones, especially among non–class-switched memory B cells. Because B-cell clones in MC and lymphomas derive from this B-cell subset, this establishes IgM1 memory B cells as a general target of lymphoproliferation in HCV1 patients, affecting apparently all patients.