IMMUNOGENICITY OF A PEPTIDE FROM A MAJOR NEUTRALIZING DETERMINANT OF THE FELINE IMMUNODEFICIENCY VIRUS SURFACE GLYCOPROTEIN

The third variable region (V3) of the feline immunodeficiency virus (F IV) surface glycoprotein is predicted to have similar physical propert ies to that of HIV and has been shown to contain immunodominant and ne utralizing epitopes. Immunological characteristics of this region were investigated further using a peptide corresponding to the middle of t he putative FIV V3 loop. The peptide was recognized in ELISA by sera f rom the majority of naturally FIV-infected cars, and absorbed a signif icant fraction of the virus neutralizing activity front a pool of sera of cats naturally infected with FIV, confirming the immunogenic natur e of this region. A sheep immunized with an octameric form of the pept ide (multiple antigenic peptide, MAP) in Freund's complete adjuvant ge nerated neutralizing antibody to a higher titre than infected cats. Ho wever, immunization of cats with the same MAP in an acceptable adjuvan t formulation (Quil A) induced antibody and cytotoxic T-cell responses to the immunizing peptides but only minimal neutralizing activity. Th ese responses did not significantly alter the kinetics of infection or the proviral load after challenge with a homologous strain of FIV, co mpared with naive controls. While the potential efficacy of peptide va ccines to lentiviruses remains to be determined, this study shows that the immune response evoked may be highly dependent on the delivery an d adjuvant regime used. Copyright (C) 1996 Elsevier Science Ltd.