GSE122846
Single cell profiling of CD4+ T cells from human fetal intestine
The fetus is thought to be protected from exposure to foreign antigens, yet CD45RO+ T-cells reside in the fetal intestine. We combined functional assays with mass cytometry, single-cell RNA-sequencing, and high-throughput TCR-sequencing to characterize the fetal intestinal CD4+ T-cell compartment. We identified 22 CD4+ T-cell clusters, including naive-like, regulatory-like, and memory-like subpopulations, which were confirmed and further characterized at the transcriptional level. Memory-like cells expressed high levels of Ki-67, indicating cell division, and CD5, a surrogate marker of TCR-avidity, and produced IFN-? and IL-2. Pathway analysis revealed a differentiation trajectory associated with cellular activation and proinflammatory effector functions, and TCR-repertoire analysis demonstrated clonal expansions, distinct repertoire characteristics, and interconnections between subpopulations of memory-like CD4+ T-cells. Imaging-mass cytometry further showed that memory-like CD4+ T-cells colocalized with antigen-presenting cells. Collectively, these results provided evidence for the generation of memory-like CD4+ T-cells in the human fetal intestine, consistent with exposure to foreign antigens. Overall design: Single, live, CD3+CD8a–TCR?d–CD4+/– T-cells from one human fetal  intestines were processed on the Chromium 3' single cell platform (10x Genomics) and sequenced on an Illumina HiSeq 4000.