A cord-blood specific subset of human gamma-delta T cells with distinct functional features - Infants are especially susceptible to intracellular pathogens because their immune system is not fully equipped to fight against these microorganisms. As a result, infant infections are a leading cause of mortality, with >1.5 million children dying of infections before 5 years of age in 2022 alone. The current consensus is that before birth, conventional T cells are skewed in favor of T regulatory or T helper (Th) 2 responses, leaving neonates and infants more vulnerable to pathogens cleared by Th1 immunity. Therefore, Vγ9Vδ2 (or simply Vδ 2) T cells, are particularly important in early life, because they are poised to secrete Th1 cytokines even before birth and acquire potent cytotoxic function shortly after birth. Despite their protective role against pathogens, human Vδ2 cells, which are absent in mice, are not well studied in neonates and infants. Our long-term goal is to elucidate their functional heterogeneity because understanding their features in the first few months of life will allow us to harness their properties to protect infants from infections. This task is challenging for many reasons, including the difficulty in obtaining samples from the infants at highest risk of early infections, such as premature babies. Our recent observations, obtained using spectral flow cytometry (SFC) and single cell RNA-seq, converge to show phenotypic and functional heterogeneity of cord blood (CB) Vδ2 cells, with heightened stemness compared to their adult counterpart and a cluster of PD1-hi cells (absent in adults) that may follow a distinct functional program specific for the early life stage. We posit that differences in Vδ2 cell cluster composition at birth have functional consequences and result in improved or decreased antimicrobial activity depending on the composition. The resulting overarching hypothesis is that human neonatal V δ2 lymphocytes exist in heterogenous functional/differentiation states impacting host immune competence in the critical early life window. As a multidisciplinary team of immunologists and computational biologists, we propose to characterize cord blood Vδ2 cells in existing specimens, including samples of premature babies, using state of the art techniques –Cellular Indexing of Transcriptomes and Epitopes by sequencing (CITE- seq) and SFC- with the following aims. Aim 1. Evaluate the phenotypic and functional heterogeneity of Vδ2 T cells at birth and in early life in relation to age, with a focus on a unique subset of PD1-hi cells present in cord blood. Aim 2: Assess how the composition of Vδ2 T cells at birth impacts function of these cells at the population level, combining CITE-seq analysis with depletion and transduction experiments. The goal of this proposal is to develop a robust molecular and functional map of a critical subset of innate-like T cells, which will provide a valuable reference for the cellular heterogeneity in the neonatal human immune system and a foundation for future proposals aimed at understanding Vδ2 cell biology in early life.
