CBD1 peptide (
SLEQIWNNMTWMQWDK), corresponding to the consensus
caveolin-1 binding domain in HIV-1 envelope
glycoprotein gp41, elicits the production of
antibodies that inhibit
infection of primary CD4(+) T lymphocytes by various primary HIV-1 isolates. Here the immunogenicity of the
CBD1 peptide was investigated in cynomolgus macaques using adjuvants that are acceptable for human use. In the first set of studies, macaques were immunized with the
CBD1 peptide in association with
muramyl dipeptide derivative
MDP-Lys(L18) combined with the oil-in-water
emulsion, MF-59. After five immunizations at 4 weeks interval, the antibody titer against the
CBD1 peptide was found to be either medium, poor, weak or none, thus suggesting that the CBD1 immune response might be restricted by the major histocompatibility complex (
MHC) class II molecules. In the second set of studies therefore, macaques were immunized with the
CBD1 peptide in association with the 'promiscuous'
T cell epitope from the
tetanus toxin, either as free
peptides or covalently linked with the
dilysine linker using
CpG ODN and
Montanide ISA 51 as adjuvants. This latter immunization procedure boosted markedly the anti-CBD1 antibody response, since even the non-responders generated high-titered
peptide-specific
antibodies. Moreover, co-immunization of the CBD1 and the T helper
epitope as free
peptides seemed to be favorable for the production of
neutralizing antibodies, with 50% inhibition of HIV-1
infection occurring at 300-400-fold dilution of the
immune sera. Finally, neutralizing and non-neutralizing immune macaque sera could be differentiated by the profile of cross-reactivity with overlapping CBD1-related
peptides in ELISA. Taken together, our results demonstrate that the
CBD1 peptide is immunogenic in macaques and that an eventual MHC-restriction could be overcome by the administration with an appropriate T helper
epitope.