Induction of cytolytic T lymphocytes directed towards the V3 loop of the human immunodeficiency virus type 1 external glycoprotein gp120 by p55gag/V3 chimeric vaccinia viruses

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Abstract
T cell-mediated cytotoxicity may play an important role in controlling infection by human immunodeficiency virus (HIV). In order to study the ability of rationally designed antigens to induce cytolytic T lymphocytes (CTLs) we replaced stretches of 30 to 50 amino acids at the p17-MA/p24-CA cleavage site, within the p24-CA moiety and within the p6-LI portion of the HIV type 1 p55 gag precursor by the third variable domain (V3) of the external glycoprotein gp120. This site is known to be a target for CTL attack in mice and humans. The chimeric antigens were recombined into highly attenuated vaccinia viruses in order to investigate class I major histocompatibility complex (MHC)-restricted presentation of antigenic V3 peptides. Immunoprecipitation and Western blot analysis of the group-specific antigen (p55 gag )/V3 chimeric proteins demonstrated significant differences in the accessibility of the V3 domain for a monoclonal antibody or polyclonal V3-specific antisera, depending on the position of the V3 loop within the p55 gag carrier protein. Immunization of BALB/c mice with three variants of p55 gag /V3 recombinant vaccinia virus, however, resulted in a comparable priming of CD4- CD8+ CTLs in vivo irrelevant of the position of the V3 loop within p55 gag . Local conformational changes, including the V3 domain within the p55 gag /V3 chimeras, did not demonstrate a significant effect on V3-specific lysis of the target cells when compared to the authentic gp120 envelope protein. Class I MHC-restricted CTLs induced by a V3 consensus sequence cross-reacted perfectly with the LAI strain-derived V3 loop sequence. These data indicate that the combination of selected epitopes (V3) with immunologically relevant complex carrier proteins (p55 gag ) can be accomplished without the loss of biological activity.

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