Biochemical, structural, and immunization experiments to evaluate new immunogens designed and selected to induce broadly neutralizing antibodies will require expression and purification of large numbers of proteins, including HIV envelope proteins and antibodies. The Protein Expression Core will provide purified proteins for this program project, which will facilitate the goals of identifying immunogens and defining immunization strategies that elicit a strong and targeted immune response. Antibodies isolated from immunized mice (Project 1) will be expressed and purified for binding and biochemical characterization as well as for structural studies (Project 2). Env proteins, both monomeric gp120s and native-like Env gp140 trimers (SOSIP.664 constructs), will be expressed for immunizations in Project 1, binding studies in Projects 1 and 2, and structural/biochemical analyses in Project 2. Core B will use various expression systems to produce Env proteins with different glycosylation to determine the effects of glycosylation form on the generated immune response. The large number of different antibodies and HIV proteins to be expressed and purified for this program requires a dedicated protein expression core.