Single-cell analysis reveals the origins and intrahepatic development of liver-resident IFN-γ-producing γδ T cells

γδ T cells are heterogeneous lymphocytes located in various tissues.However,a systematic and comprehensive understanding of the origins of γδ T cell heterogeneity and the extrathymic developmental pathway associated with liver γδ T cells remain largely unsolved.In this study,we performed single-cell RNA sequencing(scRNA-seq)to comprehensively catalog the heterogeneity of γδ T cells derived from murine liver and thymus samples.We revealed the developmental trajectory of γδ T cells and found that the liver contains γδ T cell precursors(pre-γδ T cells).The developmental potential of hepatic γδ T precursor cells was confirmed through in vitro coculture experiments and in vivo adoptive transfer experiments.The adoptive transfer of hematopoietic progenitor Lin^(-)Sca-1^(+)Mac-1^(+)(LSM)cells from fetal or adult liver samples to sublethally irradiated recipients resulted in the differentiation of liver LSM cells into pre-γδ T cells and interferon-gamma^(+)(IFN-γ^(+))but not interleukin-17a^(+)(IL-17a^(+))γδ T cells in the liver.Importantly,thymectomized mouse models showed that IFN-γ-producing γδ T cells could originate from liver LSM cells in a thymus-independent manner.These results suggested that liver hematopoietic progenitor LSM cells were able to differentiate into pre-γδ T cells and functionally mature γδ T cells,which implied that these cells are involved in a distinct developmental pathway independent of thymus-derived γδ T cells.