Cross-protection in NYVAC-HIV-1-immunized/HIV-2-challenged but not in NYVAC-HIV-2-immunized/SHIV-challenged rhesus macaques

Objectives: Immunization with attenuated poxvirus-HIV-1 recombinants follow ed by protein boosting had protected four of eight rhesus macaques from HIV -2(SBL6669) challenge. The present study was designed to confirm this resul t and to conduct the reciprocal cross-protection experiment. Methods: Twenty-four macaques were primed with NYVAC (a genetically attenua ted Copenhagen vaccinia strain) recombinants with HIV-1 and HIV-2 env and g ag-pol or NYVAC vector alone and boosted with homologous, oligomeric gp160 proteins or adjuvant only. Binding and neutralizing antibodies, cytotoxic T -lymphocytes (CTL) and CD8 T cell antiviral activity (CD8AA) were evaluated . One half of each immunization and control group were intravenously challe nged with SHIVHXB2 the other half was challenged with HIV-2(SBL6669), Prote ctive outcome was assessed by monitoring virus isolation, proviral DNA and plasma viral RNA. Results: Both immunization groups developed homologous binding antibodies; however, homologous neutralizing antibodies were only observed in NYVAC-HIV -2-immunized macaques. While no cross-reactive neutralizing antibodies were detected, both immunization groups displayed cross-reactive CTL. Significa nt CD8AA was observed for only one NYVAC-HIV-2-immunized macaque. Virologic al assessments verified that both NYVAC-HIV-1 and NYVAC-HIV-2 immunization significantly reduced viral burdens and partially protected against HIV-2 c hallenge, although cross-protection was not at the level that had been prev iously reported. Humoral antibody and/or CTL and CD8AA were associated with protection against homologous HIV-2 challenge, while cellular immune respo nses seemed more important for cross-protection. No significant protection was observed in the SHIV-challenged macaques, although NYVAC-HIV-1 immuniza tion resulted in significantly lower viral burdens compared with controls. Conclusions: Further delineation of cross-reactive mechanisms may aid in th e development of a broadly protective vaccine. (C) 2000 Lippincott Williams & Wilkins.