The project is focused on progressing BiTar-s3, a vaccine adjuvant agent. The project will develop a vaccine that targets HA stem epitopes shared across many flu-A strains, thereby addressing the difficulty of eliciting heterosubtypic neutralizing antibodies (nAb) against influenza. Specifically, the project’s aims are constructing immunogens fused to the BiTar-s3 adjuvant, to select a lead vaccine candidate; test safety and immunogenicity of the s3-adjuvanted candidate in mice; and test safety and immunogenicity of the s3-adjuvanted and unadjuvanted vaccine candidate in aged rhesus macaques. Methods will include testing expression and immunoreactivity with anti-HA antibodies of targeted candidate immunogens, engineering the selected immunogen into a high-capacity adenovector, testing the ability of s3 to drive anti-HA stem Tfh and antibody responses, testing safety of the s3-adjuvanted and unadjuvanted vaccines in aged rhesus macaques, evaluating adaptive immune responses, and examining the mechanisms of s3 adjuvant activity in germinal centers.