Project 2: Summary While traditionally regarded as a generalized tolerogenic state, emerging data suggest that pregnancy is far from a simple anti-inflammatory shift but is characterized by dramatic shifts from inflammation to tolerance over the course of pregnancy, to accommodate changes in the fetus. These dramatic shifts in the immune response are under exquisite chronological control and are accompanied by significant changes in ex vivo cellular responsiveness. However, how these immunological dynamics control the systemic immune response remains incompletely understood. Accumulating data point to immune vulnerabilities during pregnancy, with enhanced susceptibility to respiratory viral infectious including influenza and SARS-CoV-2 as well as dampened vaccine induced immunity. However, how the evolving immune response over gestation affects the overall response to vaccination, how it influences the quality of antibody transfer to infant, as well as how these changes may influence durability of protection after birth remains incompletely understood. Yet, we are at a unique moment in history, where a number of novel vaccine platforms are being rolled out to pregnant women in the battle against SARS-CoV-2. In addition to the currently EUA approved vaccines, additional vaccines will emerge, enabling the comparison of mRNA, adenoviral vectors, and adjuvanted protein platform comparisons, all of which will be recommended throughout pregnancy to drive immunity in largely naïve pregnant women and their infants. However, the ability of vaccines to boost immunity in previous infected mothers as well as to boost immunity in the future in previously immunized mothers using heterologous prime/boosting strategies will provide a unique opportunity to begin to define the vaccine strategies able to maximally drive immunity over gestation. Moreover, linked to recommended booster vaccines to Influenza and Pertussis, this consortium will have a rare opportunity to contrast immune responses induced by recall/de novo, homologous/heterologous, and distinct vaccine platforms across the 4 trimesters of pregnancy, providing an opportunity to generate the foundational data on immune programming of T and B cell immunity. Using both proprietary and established systems immunology profiling tools, the consortium will focus in Project 2 on mapping the broad antibody-OME and vaccine induced humoral immune responses as well as to profile the SARS-CoV-2-, Influenza- and Pertussis-specific B and T cell transcriptome. These data will form the basis of the first pregnant Vaccine-OME to guide next generation vaccine and therapeutic design to selectively leverage and maximize protection across the maternal:fetal dyad.