Utility of SHIV for testing HIV-1 vaccine candidates in macaques

Intravenous injection of SHIV (simian/human immunodeficiency virus, chimeric virus) into rhesus macaques resulted in a viremia in peripheral blood lymphocytes (PBL) and the generation of anti-HIV-1 (human immuno-deficiency virus type 1) envelope immune responses. A challenge stock of a SHIV containing HIV-1 HXBc2 envelope glycoproteins was prepared from infected rhesus monkey peripheral blood mononuclear cells (PBMC). The minimum animal infectious dose of the SHIV stock was determined and used in a challenge experiment to test protection. The vaccination of two rhesus monkeys with whole inactivated HIV-1 plus polydicarboxylatophenoxy phosphazene (PCPP) as the adjuvant protected the animals from becoming infected by a SHIV challenge. This experiment demonstrated for the first time that monkeys immunized with HIV-1 antigens can be protected against an HIV-1 envelope-containing virus. As the challenge virus was prepared from monkey PBMC, human antigens were unlikely to be involved in the protection. Protection of rhesus monkeys from SHIV challenge may help define protective immune responses stimulated by HIV-1 vaccine candidates.