Immunization with an inactivated whole-virus
vaccine is highly effective in preventing
lentivirus infection. The
viral protein(s) essential to the induction of protective responses, however, have not been identified. To define the role of virion components in the induction of protective immunity, we evaluated the efficacy of
glycoprotein-enriched and
glycoprotein-depleted simian immunodeficiency virus (SIV)
subunit vaccines prepared by
lentil-lectin affinity chromatography of gradient-purified virions using the immunization and challenge regimen previously found successful with an inactivated whole-virus
vaccine.
Infection was determined by successful recovery of virus, the induction of SIV-specific antibody responses, and
infection of naive recipients by inoculation with lymph-node-derived lymphocytes from the vaccinates. Immunization with the
glycoprotein-enriched preparation prevented
infection in two out of four monkeys, whereas the
glycoprotein-depleted
vaccine failed to prevent
infection in all four vaccinates tested. However, the
glycoprotein-depleted
vaccine appeared to moderate the progression of SIV-induced disease compared with non-immunized infected control monkeys inoculated with the same challenge dose. These data suggest that
subunit vaccines containing sufficient quantities of viral
glycoproteins can protect against SIV
infection, whereas
subunit vaccines composed predominantly of
viral core proteins cannot. The development of effective
vaccines against
HIV infection should include studies on the optimum presentation of the
viral envelope glycoproteins to produce long-term broadly protective immune responses.