Variable region genes of anti-HIV human monoclonal antibodies: Non-restricted use of the V gene repertoire and extensive somatic mutation

The extent of the expressed human V gene repertoire for the most part has been derived from fetal cDNA libraries, autoantibodies, and myeloma proteins. In order to continue to explore the utilization of the V_H and V_L gene repertoire in response to exogenous viral antigens, the heavy and light chain cDNAs from four human anti-HIV monoclonal antibodies were PCR amplified from human-mouse heterohybridomas, cloned, and nucleotide sequence analysis performed. Of the monoclonals analyzed, three were directed against gp120 and one reacted with gp41. Three of the antibodies were of the IgG₁ λ isotype and one was an IgG₁ κ. Three of the four heavy chains were derived from V_HI gene segments and one V_HII was observed. D segments showed evidence of D-D joining and three J_H4 and one J_H5 gene were utilized. Two V_λII lambda chains and one from the V_λIII gene family were observed and the single kappa chain sequenced was from the V_κIII family. DNA sequence comparison with known germline gene segments identified putative precursor V gene segments for one of the heavy chains and two light chains. Comparison of the expressed amino acid sequences with the predicted germline sequences indicated that changes were clustered in the CDRs and FR3 regions of the V gene segments. We reported previously the nucleotide sequences of five human monoclonal antibodies from HIV-infected individuals, three of which utilized V_HIV, one V_HV and one a V_HI gene segment and also found extensive evidence of somatic mutation. Collectively, our results indicate that an antigen driven response is functioning following HIV infection and, surprisingly, to date we have not encountered a V_HIII gene segment. Since V_HIII is the largest human V_H gene family, it may well be that this under-representation has both functional and clinical implications.