ABSTRACT-Project 3: Immunology Syphilis is a sexually transmitted infection caused by Treponema pallidum that remains a significant public health threat. Despite effective testing and treatment algorithms, the rate of syphilis infections is increasing in the US, especially among economically disadvantaged persons. Development of a vaccine will speed elimination of this disease and reduce the burden of syphilis complications including congenital disease. This overall goal of this program is to develop syphilis vaccine candidates, and this project is designed to characterize the immunological factors associated with protection. This project will isolate, characterize, and test monoclonal antibodies against syphilis derived from clinical samples obtained by our collaborators as well as antibodies that are developed in vitro using phage display techniques. The outcome of this work will be a new set of vaccine candidates that can be advanced to clinical trials.