Antibody-dependent cellular cytotoxicity against HIV-1 in sera of immunized chimpanzees

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After immunization of chimpanzees against HIV antigens, antibodies that mediate antibody-dependent cellular cytotoxicity (ADCC) were evaluated and compared with anti-HIV-antibody levels detected by enzyme-linked immunosorbent assay (ELISA) and neutralizing antibody titers. Adult chimpanzees were immunized with different HIV-1 (LAV-BRU) antigen preparations: recombinant vaccinia virus (rVV) expressing gp160, p25 or p27nef; formalin- and β-propiolactone-inactivated whole virus (inHIV); soluble recombinant gp160 either associated or not associated with other HIV proteins; a 25-mer peptide from the V3 region of gp120 coupled with KLH (V3-KLH). Immunization with the various rVV mixtures induced no or borderline ADCC increase above preimmune serum levels. Stronger and more sustained reactivity was elicited by inHIV. Purified HIV antigens elicited ADCC activity when the chimpanzees were naive; ADCC increased or remained at the same level when the animals had been preimmunized with rVV and/or inHIV. This type of reactivity apparently did not depend on whether gp160 alone or mixed with other proteins was used for immunization. The injection of V3-KLH resulted in only little, if any, recall ADCC response. ELISA antibody titers significantly correlated with ADCC and neutralizing antibody titers, but serum ADCC was independent of neutralizing antibody titers, an indication that the two latter serum activities are mediated by independent antibodies. Therefore, ADCC is elicited in the same manner as other antibody activities by the immunization of chimpanzees with inHIV or with purified recombinant HIV antigen preparations. The results obtained from the three chimpanzees of this series, which were subsequently challenged with infectious virus through the intravenous route, suggest that serum ADCC may be considered for vaccination purposes.

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