PROJECT SUMMARY The goal of this Mentored Clinical Scientist Research Career Development Award is to provide the necessary training and skills to develop into a physician scientist who successfully runs an independent research program focused on reproductive immunology. Dr. Kristen Noble is an Instructor in the Division of Neonatology at Vanderbilt University Medical Center. Her career goal is to study the host response to infection during pregnancy to develop novel diagnostic and therapeutic strategies to improve maternal-fetal health. With the strong mentorship of Dr. C. Henrique Serezani, Dr. David Aronoff, and a multidisciplinary Faculty Oversight Committee, Dr. Noble will master skills in systems biology (including next generation sequencing and ultra-high level multiplex immunofluorescence), modeling of infection during pregnancy, and techniques in reproductive immunology. Vanderbilt provides a rich environment for scientific discovery and collaboration with unique career development opportunities, shared resources, and facilities with cutting-edge technology to support early career physician-scientists on their path to independence. This proposal tests the central hypothesis that the natural evolution of the immune system during pregnancy dictates gestation-dependent pregnancy outcomes to Group B Streptococcal (GBS) infection, including differential maternal and fetal immune responses in the gestational tissues. To test this hypothesis, Aim 1 will define dynamic genetic programs at the single cell level that are activated in response to GBS infection as a function of gestational age. The intrauterine gestational tissues have unique and dynamic immune compositions throughout pregnancy. Therefore, we will also use ultra-high level multiplex immunofluorescence to provide spatial context to key GBS-induced immune responses. The innate immune system is essential for the protection against pathogens. The intrauterine niche is uniquely composed of both maternal- and fetal- derived innate immune cells, including macrophages. Aim 2 will use unique mouse models to define the differential maternal and fetal macrophage contributions to immunity against GBS and to pregnancy outcomes after infection. Completion of these aims will close substantial knowledge gaps regarding the dynamic nature of local intrauterine immunity protecting against bacterial infection during pregnancy. This is critical for the discovery of early diagnostic indicators of infection of which there are none, and necessary to identify potential therapeutic mechanisms for decreasing poor pregnancy outcomes after GBS infection.