MOLECULAR CHARACTERIZATION OF 5 NEUTRALIZING ANTI-HIV TYPE-1 ANTIBODIES - IDENTIFICATION OF NONCONVENTIONAL D-SEGMENTS IN THE HUMAN MONOCLONAL-ANTIBODIES 2G12 AND 2F5

We have stabilized a panel of 33 hybridomas producing human monoclonal antibodies (MAbs) against HIV-1 gp160 and p24. Five of these antibodi es were able to neutralize different HIV-1 isolates, and two of them ( 2F5 and 2G12) revealed remarkable potential to neutralize primary viru s isolates of different clades in several in vitro tests. To determine whether a structural basis for neutralization could be identified, we analyzed the antibodies at the molecular level. This study reports th e primary nucleotide and deduced amino acid sequences of the rearrange d heavy and light chain V segments (VH, V kappa) Of the neutralizing M Abs (1B1, 1F7, 2F5, 2G12, and 3D5) and the nonneutralizing anti-gp41 M Ab 3D6. Aligning the V segments with the nearest related germline gene s illustrated the occurrence of somatic mutations. The neutralizing MA bs show mutational rates comparable to those of antibodies that appear in patients in whom the immune system is under constant antigenic pre ssure over a long period of time. In contrast, 3D6, which recognizes t he immunodominant region on gp41, displays homologies as high as 97 an d 98% compared with its VH and V kappa germline genes. The diversity s egments [D(H)] of 1B1, 1F7, 3D5, and 3D6 were assigned to single D(H) segments on the chromosomal D(H) locus. 2F5 presents a D(H) segment 52 nucleotides in length, which could be explained by fusion of two segm ents on the immunoglobulin heavy chain locus that have not yet been de scribed as rearranged regions. 2G12 D(H) shows best homologies to a D( H) segment between D3-22 and D4-23. This D(H) segment could be the rea son for the rare occurrence of antibodies competing with 2G12. Since t his nearest related chromosomal region on the D(H) locus does not disp lay recombination signals at the flanking regions, this segment is nor mally not taken into consideration as a site for immunoglobulin heavy chain rearrangement.