AIDSVAX (R) (MN) in Bangkok injecting drug users: A report on safety and immunogenicity, including macrophage-tropic virus neutralization

A randomized, double-blind, placebo-controlled phase I/II study of AIDSVAX( R) (MN) was conducted among injecting drug users in Bangkok, Thailand. Four doses of vaccine (300 mu g of MN-rgp120 in alum) or placebo (alum) were gi ven at study entry and at 1, 6, and 12 months. The objectives of the study were to evaluate (1) the feasibility of conducting vaccine trials in this p opulation; (2) the safety of this candidate AIDS vaccine; and (3) the immun ogenicity of this vaccine. Thirty-three volunteers (22 vaccine and 11 place bo recipients) were recruited. None were lost to follow-up during the 18-mo nth study. Mild reactogenicity was noted, which was similar in both vaccine and placebo recipients. The vaccine induced anti-HIV-l antibody in all vac cine recipients. Maximal titers of binding antibodies of MN-rgp120 and the V3 domain of MN-rgp120 mere induced after the third (6 month) dose while ma ximal neutralizing antibodies followed the fourth (12 month) dose. The vacc ine-induced antibodies from several volunteers were capable of neutralizing macrophage-tropic, subtype B viruses (301660 and JRCSF) detected in a PBMC -based assay. Binding and neutralizing antibodies declined about Ill-fold i n the 6 months after the last boost. Two vaccinees became infected during t he trial, both with subtype E viruses. A phase III efficacy trial, using a bivalent gp120 vaccine containing antigens from a subtype B virus (MN) and a subtype virus (A244), was initiated in March 1999 in injecting drug users in Bangkok.