The molecular and phenotypic makeup of fetal human skin T lymphocytes

Abstract

The adult human skin contains a vast number of T cells that are essential for skin homeostasis and pathogen defense. T cells are first observed in the skin at the early stages of gestation, however, our understanding of their contribution to early immunity has been limited by their low abundance and lack of comprehensive methodologies for their assessment. Here, we describe a new workflow for isolating and expanding significant amounts of T cells from fetal human skin. Using multiparametric flow cytometry and in situ immunofluorescence we found a large population with a naive and small populations with a memory and regulatory phenotype. Their molecular state was characterized using single-cell transcriptomics and TCR repertoire profiling. Importantly, culture of total fetal skin biopsies facilitated T cell expansion without a substantial impact on their phenotype, a major prerequisite for subsequent functional assays. Collectively, our experimental approaches and data advance the understanding of fetal skin immunity and potential use in future therapeutic interventions.

Functional heterogeneity of human skin‐resident memory T cells in health and disease

“…This is readily explained by sparsity in foreign antigen load in utero 9 . Despite this, small populations of CLA + T cells are found in fetal skin and one fourth of skin T cells expresses CD45RO (the remainder being largely naive and regulatory T cells) 5,10 . In human fetal skin, αβ‐TCR + T cells predominate with some γδ‐TCR + T cells 7 .…”

“… 9 Despite this, small populations of CLA + T cells are found in fetal skin and one fourth of skin T cells expresses CD45RO (the remainder being largely naive and regulatory T cells). 5 , 10 In human fetal skin, αβ‐TCR + T cells predominate with some γδ‐TCR + T cells. 7 Memory T cells in fetal skin display a TCR of high diversity comparable to adult skin, 3 but their antigen specificities remain to be studied.…”

Single‐cell transcriptomics in human skin research: available technologies, technical considerations and disease applications

“…The second trimester was identified as a critical time point where most of skin immune cells differentiate to a mature state, a process accompanied by metabolic reprogramming and involvement of cell type‐specific transcription factors 39 40,41 . By integrating scRNA‐seq with flow cytometry, in situ immunofluorescence and TCR repertoire profiling, they provided a comprehensive atlas of T cells during development 41 .…”

“…Two manuscripts by Reitermeier et al characterized foetal skin T lymphocytes, revealing a previously undescribed double‐positive αβγδ functional T‐cell subset with a potential role in protecting from intrauterine infections 40,41 . By integrating scRNA‐seq with flow cytometry, in situ immunofluorescence and TCR repertoire profiling, they provided a comprehensive atlas of T cells during development 41 . Finally, Belote et al performed targeted scRNA‐seq to comprehensively characterize melanocytes across different anatomical sites, skin tones, sexes and developmental stages and defined transcriptional programs and gene expression signatures that could be applied in melanoma prognosis 42 …”

“…The second trimester was identified as a critical time point where most of skin immune cells differentiate to a mature state, a process accompanied by metabolic reprogramming and involvement of cell type-specific transcription factors 39. Two manuscripts by Reitermeier et al characterized foetal skin T lymphocytes, revealing a previously undescribed double-positive αβγδ functional T-cell subset with a potential role in protecting from intrauterine infections 40,41. By integrating scRNA-seq with flow cytometry, in situ immunofluorescence and TCR repertoire profiling, they provided a comprehensive atlas of T cells during development 41.…”