V H Gene Use by HIV Type 1-Associated Lymphoproliferations

Abstract

The pathogenesis of polyclonal HIV-associated lymphomas lacking traditional B cell cofactors (i.e., Epstein-Barr virus [EBV] infection, c-myc translocations) is poorly understood. A multistep pathogenesis model has been proposed in which polyclonal lymphomas represent an earlier stage in HIV-associated lymphomagenesis before the emergence of a dominant malignant clone. Chronically present antigens have been proposed as a likely stimulus for polyclonal B cell proliferation; if so, polyclonal lymphoma--associated immunoglobulins (Igs) should have molecular evidence of somatic hypermutation, a process by which antibody affinity maturation in response to chronic antigenic stimulation occurs. Molecular analyses of Ig heavy chain variable (V_H) gene use by B cells in a polyclonal HIV-associated large cell lymphoma lacking EBV and c-myc rearrangement was undertaken. Eighteen randomly selected clones generated from RT-PCR yielded 15 unique V_H sequences, all of which were most homologous to only three previously identified germline V_H1 genes. Two sets of clones (consisting of three and two clones, respectively) had identical V_H gene sequences, and one pair of clones had identical third complementarity determining regions (CDR3s) but different V_H gene sequences; eight clones were <95% homologous to their most related germline V_H1 genes. We compared these results with Ig V_H1 gene use by B cells present in a reactive hyperplastic lymph node obtained from an HIV-1-infected individual. Fifteen clones randomly selected from RT-PCRs yielded 15 unique V_H1 sequences, all of which were most homologous to 5 previously identified germline V_H1 genes; 10 clones were <95% homologous to their most related germline gene. Binomial probability analysis revealed that only 1 of the 15 unique V_H1 sequences derived from the polyclonal lymphoma (i.e., 7%), as compared with 5 of 15 unique V_H1 sequences derived from the reactive lymph node (i.e., 33%), had a low probability of occurrence by random chance (p <0.05). These data provide molecular evidence of polyclonality in an HIV-associated polyclonal lymphoma, demonstrate a qualitative difference in somatic hypermutations of Ig V_H genes associated with malignant versus reactive B cell lymphoproliferations, and support an antigen-mediated multistep pathogenesis model of HIV-1-associated lymphomagenesis.