The display of proteins in dense, repetitive arrays in known to result in strong humoral immune responses, as exemplified by the virus-like particle (VLP) vaccine for human papillomavirus. This concept has relevance to HIV-1 vaccine development, because recent structural studies of HIV-1 virions have shown that the envelope spikes on the virus surface are sparse and irregularly distributed. This may contribute to low spike immunogenicity, and complicate the generation of broadly neutralizing antibodies. [unreadable] [unreadable] This proposal will test the hypothesis that the immunogenicity of HIV-1 envelope spikes is limited, in part, as a result of their sparse and irregular distribution on the virion surface. To do this, HIV-1 envelope spikes will be displayed at high density on a repetitively ordered scaffold (provided by the bacteriophage lambda capsid). Env display will be acheived using a simple in vitro complementation system, to "decorate" phage particles with soluble Env oligomers, produced in mammalian cells. In the R21 (feasibility) phase of this proposal, experiments will be conducted to generate lambda phage particles that display well-characterized, oligomeric envelope spikes on their surface at both high and low density. The immunogenicity of these phage particles will then be assessed in a small animal model, to determine if ordered, high density display of envelope spikes results in a measurable increase in the magnitude or quality of Env-specific antibody responses (including virus-neutralizing antibodies). [unreadable] [unreadable] If quantifiable milestones are met, the project will progress to the R33 (development) phase. This phase focus on the evaluation of methods intended to further improve the quality and magnitude of the humoral immune response elicited by lambda phage particles displaying HIV-1 Env. The focus will be on the evaluation of practical, translationally-relevant strategies that can be readily applied to enhance humoral immune responses to the phage-displayed envelope spikes. The studies will culminate in a proof-of- concept immunogenicity study in non-human primates, in which the immune response to phage-displayed envelope spikes will compared to that elicited by a soluble oligomeric envelope preparation. [unreadable] [unreadable] Collectively, these experiments are expected to provide a comprehensive proof-of-concept evaluation of our hypothesis that ordered, dense display of HIV-1 envelope spikes on the lambda phage scaffold will allow for the generation of improved antibody responses to HIV-1 Env. [unreadable] [unreadable] [unreadable]