Core A, the Immunogens and Formulations Core, will provide materials and expertise to all Projects in this grant. It will be responsible for obtaining making Gag proteins and native, glycosylated Envelope protein trimers to be used as boosting agents in rabbit and macaque experiments. These reagents are critical to the activities of all three Project teams. The Core has two Aims: 1) Express and purifiy Gag p24 proteins from patients in the study using E. coli expression systems. 2) Express and purify trimeric gp140 immunogens for vaccine studies in rabbits and macaques using mammalian cell expression systems (early and late proteins from up to six subjects). The proteins expressed in Aim 1will be used in proliferation assay in Project 2 to measure relative ability of patients to mount T helper responses to autologous Gag proteins in vitro. Glycoprotein Envelope trimers expressed in Aim 2 will serve as recombinant antigens for antibody assays in Projects 1 and 3, for T and B cell assays in Project 2, boosting agents for the DMAvaccines in rabbits (Project 3) and macaques (Project 3 and Core B). RELEVANCE (See instructions): HIV vaccines that are effective in eliciting neutralizing antibodies are critically needed. This core will provide recombinant proteins to use in vaccine research.