V-H GENE USE BY HIV TYPE 1-ASSOCIATED LYMPHOPROLIFERATIONS

The pathogenesis of polyclonal HIV-associated lymphomas lacking tradit ional B cell cofactors (i.e., Epstein-Barr virus [EBV] infection, c-my c 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 domi nant malignant clone. Chronically present antigens have been proposed as a likely stimulus for polyclonal B cell proliferation; if so, polyc lonal lymphoma-associated immunoglobulins (Igs) should have molecular evidence of somatic hypermutation, a process by which antibody affinit y maturation in response to chronic antigenic stimulation occurs. Mole cular 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 gener ated from RT-PCR yielded 15 unique V-H sequences, all of which were mo st homologous to only three previously identified germline V(H)1 genes . Two sets of clones (consisting of three and two clones, respectively ) had identical V-H gene sequences, and one pair of clones had identic al third complementarity determining regions (CDR3s) but different V-H gene sequences; eight clones were <95% homologous to their most relat ed germline V(H)1 genes. We compared these results with Ig V(H)1 gene use by B cells present in a reactive hyperplastic lymph node obtained from an HIV-1-infected individual. Fifteen clones randomly selected fr om RT-PCRs yielded 15 unique V(H)1 sequences, all of which were most h omologous to 5 previously identified germline V(H)1 genes; 10 clones w ere <95% homologous to their most related germline gene. Binomial prob ability analysis revealed that only 1 of the 15 unique V(H)1 sequences derived from the polyclonal lymphoma (i.e., 7%), as compared with 5 o f 15 unique V(H)1 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-as sociated polyclonal lymphoma, demonstrate a qualitative difference in somatic hypermutations of Ig V-H genes associated with malignant versu s reactive B cell lymphoproliferations, and support an antigen-mediate d multistep pathogenesis model of HIV-1-associated lymphomagenesis.