Production of Long-Lived Neutralizing Antibodies to HIV-1 IIIB in Mice with a Vaccinia Recombinant Virus-Infected Cell Vaccine Expressing gp160

Abstract

A formaldehyde-fixed cell vaccine in adjuvant (syngeneic cells infected with a vaccinia virus recombinant expressing gp160: vacc-gp160) stimulated only nonneutralizing antibody when used on its own in four strains of mice, but a similar nonfixed cell vaccine stimulated neutralizing antibodies up to a titer of 1/320 in C57BL/6 (H-2 ^b ) mice previously infected with live vacc-gp160. Synthesis of ELISA antibodies to rgp120 or rgp160 did not correspond closely to the synthesis of neutralizing antibodies and should not therefore be used to monitor the production of neutralizing antibody. The ELISA antibody response produced by boosting with the cell vaccine made with the vaccinia virus expressing gp160 under the control of a T7 promoter (vacc-gp160-PT7) was as high as that in mice given an approximately 10-fold higher dose of purified rgp160. The ELISA antibody response to the cell vaccine made with vacc-gp160-PT7 was better than that in which gp160 was expressed under the vaccinia early/late promoter (vacc-gp160-P7.5). Nearly all mice (92%; 11 of 12) primed by infection with vacc-gp160 produced comparable levels of neutralizing antibodies after a single boost with rgp160, vacc-gp160-PT7-infected cells, or vacc-gp160-P7.5-infected cells. Neutralization titers peaked at around day 22 after boost, and declined by day 29. A second boost with the same vacc-gp160-infected cells gave increased neutralizing titers in all (eight of eight) mice. The cell vaccine expressing gp160 under the control of the T7 promoter gave superior neutralizing antibody to the cell vaccine with the P7.5 promoter and, importantly, these antibodies were the more stable in the mouse. In fact, significant neutralizing activity was still present in all mice in this group 8.5 months after the second and last boost. Immunogens compounded with aluminum hydroxide [Al(OH)₃], a clinically relevant adjuvant, and Freund's incomplete adjuvant stimulated comparable levels of neutralizing antibody, although Al(OH)₃ was clearly superior by ELISA.