PROJECT SUMMARY/ABSTRACT Relative to the general population, HIV-infected individuals have a 60–200-fold higher relative risk to develop Non-Hodgkin's Lymphomas, including plasmablastic lymphoma, primary central nervous system lymphoma, primary effusion lymphoma and diffuse large B-cell lymphoma. They also have an 8–10-fold higher relative risk to develop Hodgkin's Lymphoma compared to uninfected individuals. Many of these malignancies are driven by Epstein-Barr virus (EBV) and result from poor immune control of the virus driven by HIV- dependent immune dysfunction. Thus, a safe and effective vaccine that prevents EBV infection and eliminates the EBV-associated component of risk could have a significant clinical benefit in resource-poor areas where HIV-1 is endemic. The correlate of protection for most successful viral vaccines is neutralizing antibodies. Previously, our lab isolated the first anti-EBV mAb that could potently neutralize infection of both B cells and epithelial cells. We further demonstrated that passive transfer of AMMO1 protected both humanized mice and rhesus macaques from experimental EBV infection. These results strongly suggest that antibodies are important for, if not sufficient to protect against EBV infection, and that a prophylactic vaccine should seek to elicit high titers of AMMO1-like antibodies. To this end, we developed and tested several gH/gL vaccines. All gH/gL vaccines were strongly immunogenic, but they only showed partial protection against experimental EBV infection in humanized mice and macaques. Epitope mapping studies revealed that vaccine-elicited gH/gL antibodies targeting the AMMO1 epitope were subdominant and rare, while antibodies targeting other non- neutralizing epitopes on gH/gL were immunodominant. The goal of this proposal is to obtain a high-resolution antigenic landscape of the gH/gL glycoprotein to define the most critical sites of vulnerability. We will then use this this information to employ structure guided EBV vaccine design intended to immunofocus the antibody response onto protective epitopes like the one targeted by AMMO1, and evaluate their ability to protect against EBV challenge in humanized mice and macaques.