With over 2.5 million new HIV infections per year, the majority in resource-poor countries with limited access to antiretroviral therapy, an effective HIV vaccine continues to remain among the most promising and safe strategies for preventing infection and reducing the burden of AIDS. While designing an effective HIV vaccine is a daunting goal, the modest efficacy of the RV144 Thai trial indicates that it is possible to prevent HIV infection in humans by vaccination, and that long-lasting antibody contributes significantly for this protection. Because vaccine-elicited CD4 T follicular helper cells (TFH) are essential for establishing long-lived antibody, harnessing TFH help is vital for an effective HIV vaccine. My proposal is focused on achieving this goal using a recombinant DNA-prime, modified vaccinia Ankara (MVA)-boost vaccine platform in path for clinical development. My preliminary data show that generation of TFH cells expressing the chemokine receptor CXCR3 correlates strongly with multiple attributes of protective humoral immunity. Furthermore, CXCR3+ TFH cells express higher levels of B cell helper factors relative to CXCR3- TFH cells. Based on these data, I hypothesize that an HIV vaccine designed to induce high magnitude CXCR3+ TFH cells increases antibody persistence, which will enhance protection against a mucosal simian(S)HIV challenge. In Aim 1 of this research project, I will design a novel molecularly adjuvanted DNA vaccine to investigate pivotal cues contributing to heterogeneity in vaccine-elicited TFH responses and how this differs across two clinically relevant adjuvant platforms. In Aim 2, I will study the impact of increasing CXCR3+ TFH cells on quantitative and qualitative aspects of the antibody response in systemic and mucosal compartments. Aim 3 will evaluate the efficacy of this novel vaccine platform in mucosal protection against a SHIV challenge. Together, these studies will provide the most comprehensive characterization of CD4 TFH cells in a rhesus model of HIV vaccines to date, and will provide a blueprint for an efficacious vaccine candidate. Furthermore, my studies will compare two well-defined, highly clinically relevant adjuvant systems and the resulting findings will provide crucial information for advancing HIV vaccines. My goal is to become an independently funded investigator studying effective immunological measures to combat HIV. A K01 award will accelerate this goal by facilitating extraordinary mentorship from the world's leading experts in vaccine design, Dr. Rama Amara; rhesus models of HIV, Dr. Guido Silvestri, and HIV clinical trials, Dr. Nicole Frahm. The K01 mechanism will critically develop my skills in vaccine-design and clinical vaccinology through planned experiments, attending focused conferences, and coursework. In addition, my mentoring team and I have assembled a panel of Advisory Committee members, each experts in HIV and HIV models, Drs. Eric Hunter, Genoveffa Franchini, and Susan Buchbinder. Moreover, through this K01 mechanism I will initiate and sustain collaborations with a wide scientific network in academia and industry. Thus, the strong and complementary skill sets of my mentors, advisors, and collaborators will critically contribute to my training and acquisition of skills necessary to succeed in combating HIV. Furthermore, the exceptional institutional environment at the Yerkes National Primate Research Center will foster my training by providing institutional programs, facilities, and opportunities for collaboration. This K01 award mechanism will enable me to establish my independent research program by providing necessary funds to generate preliminary data for independent R01 funding applications.