Certain infections during pregnancy are linked to developmental and behavioral abnormalities in the offspring. Whether overt inflammatory responses in the mother can have a lasting impact on the development of immune system of the offspring is unknown. This gap in knowledge is directly linked to a lack of detailed insights into how lymphocytes normally develop in the fetus. How animals generate multiple immunocyte subtypes from fetal to aged stages remains an active area of research with many unresolved fundamental questions. In particular, it is unknown whether the immune system is a) one dimensional, a collective of diverse cell types generated from a single stem cell or is b) multi-layered, with each layer made of functionally specialized cell systems tailored to the distinct developmental age of an animal. We discovered that skin lymphocytes (immune sentinels) essential to prevent dermatitis originate from progenitors with dedicated gene programs that only develop in embryos. Importantly, data further suggest that the unique genetic networks of immune sentinels are active in fetal tissues prior to the emergence of a single hematopoietic stem cell (HSC) in the fetal liver. It has been assumed that fetal HSCs are the primary stem cell for all lymphocytes. Our results thus suggest the existence of undiscovered embryonic innate lymphoid progenitors (eILPs) distinct from classical HSCs or their immediate daughter cells primed toward the lymphoid lineage. We plan to identify and characterize eILP subtypes by employing a spectrum of molecular beacons, each embedded in the genome and reporting the activity of predicted gene network hubs of eILPs. Rare cells in the fetus with a specified combination of beacons will be captured and these candidate eILPs will be analyzed molecularly at a single cell level and transplanted into animals to determine their generative potential. Candidate eILPs are predicted to preferentially generate mucosal immune sentinels in fetal and neonatal animals, and once these sentinels are made they persist long term, well into adulthood. Absence or alterations of these innate sentinels results in aberrant tissue homeostasis and inflammatory disorders. Once the embryonic hematopoietic lineage tree is constructed how immune perturbations in pregnancy impact the development of innate lymphocytes can be systematically assessed.
Immune cell activation and overt inflammation during pregnancy are linked to developmental and behavioral abnormalities in the offspring. How these perturbations affect immune system development in the fetus and neonates is unknown. This gap in knowledge is directly linked to a lack of detailed insights into how immunocytes develop in the fetus. It is assumed that the hematopoietic stem cell (HSC) is responsible for generating all blood cells in adult animals. This project will identify new types of lymphoid progenitors arising from hemogenic endothelial cells, which are produced only during fetal development. These embryonic innate lymphoid progenitors (eILPs) are postulated to generate mucosal immune sentinels or innate lymphoid cells that are most prevalent in neonates and provide immediate responses to infectious agents at the site of pathogen entry and maintain tissue homeostasis. Once eILP subtypes are identified their developmental processes and intermediates will be incorporated into the overall embryonic hematopoiesis. This mapping will require high-resolution single cell transcriptomic analyses to establish age-resolved cellular and molecular heterogeneity of hematopoietic progenitors in embryonic hematopoietic tissues. The project has three major human health relevance. First, animals lacking dermal IL-17 producing innate T cells suffer from spontaneous skin inflammatory disorders closely resembling human atopic dermatitis. Thus, understanding how mucosal sentinels are made and how their generation is impacted by immune perturbations during pregnancy will provide new insights into why these diseases arise and how to treat them using new modalities targeting the pathways dedicated to innate lymphocyte development. Second, given the awareness that several conditions with an immunological component could arise before birth, it is imperative to dissect the developmental steps that could be targeted early in life. Understanding how innate immune sentinels are made in the fetus and how the process can be aborted or aberrant will provide new insights into why certain immune diseases arise in neonates. Third, patients undergoing bone marrow cell transplant post radiation or chemotherapy are predicted to not effectively replenish mucosal innate lymphocytes since they originate from non- bone marrow cells of fetal origin. To optimally protect these patients from infections at the mucosal barrier patient-specific innate lymphocytes can be generated from eILPs and transplanted along with bone marrow cells. To perform such interventions will require detailed understanding of how mucosal-resident innate lymphoid sentinels are made.
