The vaccine Env 2-3 is created from one of the viral proteins that make up HIV called envelope glycoprotein gp120. A problem with many immunogens, including candidate HIV vaccines, is that they may evoke relatively weak immune responses, particularly in humans and in nonhuman primates. Thus, there is considerable interest in the development of "adjuvants" (substances that augment immune responses to vaccines). MTP-PE/MF59 is an adjuvant that appears to be particularly promising, and is selected for the studies with this HIV vaccine candidate.

This study is being conducted in two parts: Part A examines the safety of the adjuvant MTP-PE/MF59 alone; Part B examines the safety and immunogenicity of Env 2-3 in combination with MTP-PE/MF59. In Part A, three volunteers receive MTP-PE/MF59, and one volunteer receives emulsion alone at each dose level. Initiation of each dose level is separated by at least 72 hours. Doses of adjuvant emulsion are administered at day 0 and day 30 for the highest tolerated dose. If significant reactions are encountered, additional subjects may be studied at lower doses. In Part B, six doses of MTP-PE adjuvant (0, 5, 10, 25, 50, or 100 mcg) in the MF59 emulsion are studied. Six volunteers receive Env 2-3/MTP-PE/MF59 and two receive MTP-PE/MF59 alone at each dose level. There is a minimum 1-week interval between dose escalations. Per amendment, volunteers may receive an additional dose of Env 2-3 or placebo in MF59 emulsion only, administered 12-18 months post initial inoculation.