INDUCTION OF CYTOLYTIC T-LYMPHOCYTES DIRECTED TOWARDS THE V3 LOOP OF THE HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 EXTERNAL GLYCOPROTEIN-GP120 BYP55(GAG) V3 CHIMERIC VACCINIA VIRUSES/

T cell-mediated cytotoxicity may play an important role in controlling infection by human immunodeficiency virus (HIV). In order to study th e ability of rationally designed antigens to induce cytolytic T lympho cytes (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 p55gag precursor by the third variable doma in (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 investi gate class I major histocompatibility complex (MHC)-restricted present ation of antigenic V3 peptides. Immunoprecipitation and Western blot a nalysis of the group-specific antigen (p55gag)/V3 chimeric proteins de monstrated significant differences in the accessibility of the V3 doma in for a monoclonal antibody or polyclonal V3-specific antisera, depen ding on the position of the V3 loop within the p55gag carrier protein. Immunization of BALB/c mice with three variants of p55gag/V3 recombin ant 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 p55gag/V3 chimeras, did not demonstrate a significant effect on V3-spe cific lysis of the target cells when compared to the authentic gp120 e nvelope 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 epitope s (V3) with immunologically relevant complex carrier proteins (p55gag) can be accomplished without the loss of biological activity.