Project Summary Pregnant women are highly vulnerable to influenza A virus (IAV) and are at increased risk for maternal death, preterm birth and stillbirth. Universal influenza vaccines (UFV) are thought to be possible if conserved regions of influenza virus are targeted and appropriate immune responses generated. However, relevant animal models are lacking in which to test such a vaccine, particularly for pregnant women. This proposal is focused on investigating maternal and placental immune responses to IAV in a pregnant nonhuman primate (NHP) model to understand the viral-host factors driving enhanced maternal disease. Our central hypothesis is that an aberrant Th17 response during an acute IAV infection leads to a broadly dysfunctional innate and adaptive immune response that prevents viral clearance and enhances risk for maternal death and stillbirth. Th17 cells produce high levels of the inflammatory cytokines IL-17 and IL-2218,19 with early Th17 polarization considered to be critical for IAV resolution; aberrant and/or late activation of the Th17 pathway by IL-23 in murine models is thought to impair viral clearance and promote lung injury.20,21 Our preliminary data in a pregnant NHP model of an acute IAV H1N1 infection demonstrates pneumonia in all animals by Day 5 post-IAV inoculation. In pregnant NHP, influenza disease scores were higher than non-pregnant animals with notable extra-pulmonary organ injury (myocarditis, white matter injury). Pregnant NHP demonstrated a nearly absent early Th17 CD4+ T cell response in whole blood and PBMC coupled with a marked increase in Th17 cells in the lung at peak immunopathology compared to non-pregnant animals. Inflammatory cytokines and chemokines in the lungs and bronchoalveolar lavage fluid (BAL) were also greater in pregnant versus non-pregnant animals. In Aim 1, non-pregnant and pregnant pigtail macaques will be challenged with either IAV H1N1 A/CA/04/09 or H3N2 A/Texas/71/2017 (N=8, each group) and undergo blood and BAL sampling until necropsy at Day 5 (peak immunopathology). In Aims 1A and 1B, we will determine pregnancy- specific immune correlates of IAV disease by evaluating the frequency of Th17 CD4+ T cells and a broad spectrum of innate/adaptive immune responses (i.e. immune cell subsets, cytokines/chemokines, Type I/III interferons) in the blood, BAL and lung. In Aim 1C, we will evaluate antiviral responses in the placenta linked to adverse pregnancy outcomes (e.g. cytokines/chemokines, NLRP3 inflammasome activation, CD8+ T cells). In Aim 2, we will use bulk and single cell RNA-sequencing to define changes in the transcriptome within PBMC, BAL, lung and placenta with a focus on Th17 transcriptional networks and antiviral innate immune pathways. In summary, the preliminary data indicates an aberrant Th17 response in pregnant animals, which is critical to promoting viral clearance and preventing lung injury. These studies will be the first to comprehensively analyze innate/adaptive immune ...