8th International AIDS Conference Amsterdam, Netherlands — July 19-24, 1992

Int Conf AIDS 1992 Jul 19-24; 8:We52 (abstract no. WeD 1039)
Sia C, Matthews T, Chong P, Bolognesi D, Klein M; Connaught Centre for Biotechnology Research, Willowdale, Ont., Canada.

OBJECTIVE: To construct synthetic HIV vaccine candidates using defined T-and B-cell epitopes of the HIV structural proteins.

METHODS: Two pairs of chimeric peptides were synthesized. The first pair, CLTB-28 and CLTB-32 contained two contiguous neutralizing epitopes mapped by human monoclonal antibodies (residues 307-320) of the V3(MN) loop linked to the C- or N-terminus of a defined p24(MN) T-cell epitope, p24E (residues 291-305), respectively. In the second pair of peptides, CLTB-36 and CLTB-37, an extended V3(MN) sequence comprising of the two neutralizing epitopes (residues 305-325) was linked to the C- and N-terminus of the T-cell epitope, respectively. The immunogenicity of the tandem epitopes was tested in Balb/c (H-2d) mice. Anti-envelope antibody levels were measured by peptide-specific Enzyme Immunoassays, and the biological properties of the antibodies assessed by an in-vitro syncytia-formation blocking assay.

RESULTS: The free envelope peptides emulsified in Freund's adjuvant were poorly immunogenic. However, their immunogenicity was markedly enhanced when linked to the C- but not the N-terminus of p24E as judged by the substantially higher titres of the anti-envelope peptide antibodies measured in the anti-CLTB-28 and anti-CLTB-36 antisera as compared to those detected in the anti-CLTB-32 and anti-CLTB37 antisera, respectively. Both antisera raised against the immunogenic peptides, CLTB-28 and CLTB-36 strongly cross-reacted with synthetic peptides of the V3 loops of several other HIV-1 isolates that shared the amino acid sequence IHIGPGRAF with the V3(MN) loop. Analysis of the functional properties of these antisera revealed that only the anti-CLTB-36 antiserum, but not the anti-CLTB-28 antiserum, displayed potent syncytia-formation blocking activity.

CONCLUSION: Epitope-polarity and amino acid residues adjacent to the neutralizing determinant(s) in the V3(MN) loop critically influence the immunogenicity of tandem epitopes and likely modulate their configuration and/or processing, thus influencing the nature of the antibody response.

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