Enhanced immunity to human immunodeficiency virus (HIV) envelope elicited by a combined vaccine regimen consisting of priming with a vaccinia recombinant expressing HIV envelope and boosting with gp160 protein

Transmission studies have suggested that an optimal human immunodeficiency virus type 1 (HIV-1) vaccine should induce both neutralizing antibodies and cytolytic T cells to eliminate free virus and infected cells. A phase I trial in healthy HIV-1-seronegative persons was conducted with a combination HIV-1 vaccine regimen (strain IIIB) consisting of priming with a recombinant vaccinia (vac/env) virus expressing HIV-1 envelope and boosting with a gp160 glycoprotein derived from a recombinant baculovirus (rgp160). T-cell and antibody responses detected after immunization with either vac/env alone or rgp160 alone were generally of low magnitude and transient, and no subject developed neutralizing antibodies. In contrast, recipients of the combination regimen demonstrated in vitro T-cell proliferative responses to homologous HIV-1 antigens that were 3- to 10-fold higher than responses with either vaccine alone, and these responses were sustained for >18 months in 75% of recipients. Moreover, both CD8⁺ and CD4⁺ cytolytic T cells were detected. Antibody responses (titer, 1:800 to 1:102,400) to homologous HIV envelope developed in all recipients of the combination regimen, and neutralizing antibodies were detected in 7 of 13. Thus, immunization with a live virus vaccine followed by boosting with a soluble protein offers promise for inducing the broad immunity needed in an HIV vaccine.