Epitope mapping, V-region DNA sequence, and neutralizing Fab fragments of two monoclonal antibodies against the HIV-1 V3 loop (original) (raw)

Backgroutd Experimental evidence suggests that neutralizing antibodies could constitute an important factor in the control of AIDS progression and that the V3 loop of gpl20 constitutes the main target for such purposes. We have previously developed two neutralizing murine monoclonal antibodies (Mabs) against the V3 region of the HIV-l MN strain. Objecrives: To characterize those Mabs in terms of fine specificity and DNA sequence of their V regions and to study if Fab fragments retain their neutralizing potential in vitro. Study design: A set of 1Zmer alanine substituted peptides were employed for epitope mapping using two ELBA procedures: (1) indirect, with each peptide bound to polystyrene plates, and (2) competitive, with co-incubation of peptides and Mabs in solution. The V regions of both Mabs were PCR amplified from cDNA and their nucleotide sequences were determined. Finally, Fab fragments of Mab 1OFlO were generated and their neutralizing capacity against the MN isolated was assessed. Resulfs: We first restricted the minimal length of the epitopes recognized by 2C4 and 1OFlO to the 12-mer peptide KRIHIGPGRAFY. The core of the epitopes recognized by Mabs 2C4 and 1OFlO were IHIGP-R and IHIG-R, respectively. While substitution of proline in position 7 completely abolished the binding of 2C4, it only reduced that of 1OFlO by 50%. Finally, Fab fragments of Mab 1OFlO were still able to neutralize the HIV-l MN strain in vitro. Conclusion: This subtle distinction in the tine mapping of the epitope recognized by Mabs 2C4 and 1OFlO should correspond to three amino acid differences that we found in the heavy chain V-regions. The Fab fragments of Mab 1OFlO retained the neutralizing capacity. This indicates that HIV neutralization by anti V3 Mabs is an Fc independent process.