Augmentation of Human Immunodeficiency Virus Type 1 Neutralizing Antibody by Priming with gp160 Recombinant Vaccinia and Boosting with gp160 in Vaccinia-Naive Adults

Twelve vaccinia-naive volunteers were inoculated with recombinant vaccinia virus expressing the human immunodeficiency virus type 1 (HIV-1) strain IIIB (HIV-1IIIB) envelope glycoprotein gp160 and subsequently immunized with 640 mug of recombinant (r) gp160 protein produced in baculovirus. After booster immunization with rgp160, the sera of all vaccinees showed strong antibody responses detected by Western blot and ELISA; 8 had neutralizing activity and 5 had fusion inhibition activity against the homologous strain; 5 blocked binding of CD4 cells to gp120. Cross-reactive neutralization of HIV-1MN was detected in 3 of 8 sera that neutralized HIV-1IIIB. The combination of live recombinant vaccinia followed by subunit booster immunization was more immunogenic than either product alone and represents a promising approach for HIV-I immunoprophylaxis. Further definition of recombinant vaccinia safety and augmentation of immune responses to geographically prevalent HIV-1 strains will be necessary before expanding clinical trials to high-risk groups.