"The elicitation of broadly neutralising antibodies (Nab) remains the primary and most challenging goal in HIV-1 vaccine development. Although a few anti-HIV-1 monoclonal antibodies with broadly neutralising capability have been isolated from infected individuals, none of the immunization strategies thus far explored has proven effective in inducing similar antibodies. Objective of this application is the development of a variety of ‘next-generation’ HIV-1 envelope-based immunogens that in combination with new adjuvant formulations are capable of eliciting high-titer broadly Nab responses. Our strategy will be based on one side on the identification and cloning of envelopes that have successfully elicited broad Nabs in their natural hosts, focusing on HIV-1 strains derived from patients with high-titered broad Nabs in their sera; on the other side, we will introduce rational modifications into these and promising HIV-env based immunogens that are already under development by NGIN’s partners, with the aim of exposing cryptic conserved neutralization epitopes and permitting their efficient presentation to the immune system. HIV-1 envelopes will be expressed in viral vectors or as trimeric (gp150) soluble proteins and screened for their immunogenicity and antigenicity in rabbits. A selection of envelopes with highest antigenicity will be expressed as trimeric envelope-complexes on the surface of virosomes or virus-like particles (VLP), to further improve immunogenicity. New immunogens will be evaluated in prime-boost regimens in rabbits using novel effective adjuvant formulations. Immunogen/adjuvant combinations that prove most effective in eliciting broadly Nabs both systemically and at the mucosal level will be evaluated in non-human primates for their immunogenicity and efficacy upon challenge with live heterologous virus. Finally, formulations that will elicit protective immunity in non-human primates will be forwarded for proof-of-principle testing in humans."