Project Summary Respiratory syncytial virus (RSV) is a leading cause of serious lower respiratory tract disease in infants and young children worldwide. Since infection induces only partial protection, it causes repeat infection and disease throughout life. Though a high priority for vaccine development no vaccine is yet available. The lack of success in developing a vaccine suggests novel strategies are needed to achieve success. Most of the focus for RSV subunit vaccines has been on the RSV F protein. The G protein of RSV: 1) causes inflammation that increases RSV disease and 2) provides binding to primary human airway epithelial cells to infect the cells at the primary site of infection in humans. Blocking G with antibodies prevents these effects in mice. Accordingly, inducing anti- G antibodies with a G immunogen in a vaccine, should improve both safety and efficacy. This proposal is designed to identify the optimal G protein construct to use with a pre-fusion stabilized F protein in an RSV vaccine for adults. This approach takes advantage of the pre-fusion F’s ability to induce highly levels of broadly neutralizing antibodies and the G protein’s ability to induce antibodies that both neutralize the virus and block RSV-induced host responses that cause disease. This proposal is built on the principal investigator’s (PI’s) work that 1) helped elucidate the disease caused by G, especially the central conserved domain of G (CCD-G), and 2) developed an RSV-based virus-like particle (VLP) platform for RSV vaccines. The RSV VLP platform should ~maintain the native structures of F and G to induce optimal immune responses. We propose to make and evaluate RSV VLPs with prefusion stabilized F plus different constructs of a group A, G protein or G protein peptides and a group B G protein or peptides with different adjuvants. We use the PI’s mouse model of RSV disease to determine which VLP/adjuvant is most effective at inducing F and G neutralizing antibodies, preventing virus replication and disease in RSV-challenged mice, and fails to cause enhanced disease. These studies will identify the optimal F plus G vaccine to move toward licensure. This vaccine promises to be safer and more effective than existing RSV vaccines.