Definitive haematopoiesis in the fetal liver supports self-renewal and differentiation of haematopoietic stem cells/multipotent progenitors (HSC/MPPs) but remains poorly defined in humans. Using single cell transcriptome profiling of ~140,000 liver and ~74,000 skin, kidney and yolk sac cells, we identify the repertoire of human blood and immune cells during development. We infer differentiation trajectories from HSC/MPPs and evaluate the impact of tissue microenvironment on blood and immune cell development. We reveal physiological erythropoiesis in fetal skin and the presence of mast cells, NK and ILC precursors in the yolk sac. We demonstrate a shift in fetal liver haematopoietic composition during gestation away from being erythroid-predominant, accompanied by a parallel change in HSC/MPP differentiation potential, which we functionally validate. Our integrated map of fetal liver haematopoiesis provides a blueprint for the study of paediatric blood and immune disorders, and a valuable reference for harnessing the therapeutic potential of HSC/MPPs.

The skin confers biophysical and immunological protection through a complex cellular network established early in embryonic development. We profiled the transcriptomes of more than 500,000 single cells from developing human fetal skin, healthy adult skin, and adult skin with atopic dermatitis and psoriasis. We leveraged these datasets to compare cell states across development, homeostasis, and disease. Our analysis revealed an enrichment of innate immune cells in skin during the first trimester and clonal expansion of disease-associated lymphocytes in atopic dermatitis and psoriasis. We uncovered and validated in situ a reemergence of prenatal vascular endothelial cell and macrophage cellular programs in atopic dermatitis and psoriasis lesional skin. These data illustrate the dynamism of cutaneous immunity and provide opportunities for targeting pathological developmental programs in inflammatory skin diseases.

SummaryDendritic cells (DCs), monocytes, and macrophages are leukocytes with critical roles in immunity and tolerance. The DC network is evolutionarily conserved; the homologs of human tissue CD141hiXCR1+CLEC9A+ DCs and CD1c+ DCs are murine CD103+ DCs and CD64−CD11b+ DCs. In addition, human tissues also contain CD14+ cells, currently designated as DCs, with an as-yet unknown murine counterpart. Here we have demonstrated that human dermal CD14+ cells are a tissue-resident population of monocyte-derived macrophages with a short half-life of <6 days. The decline and reconstitution kinetics of human blood CD14+ monocytes and dermal CD14+ cells in vivo supported their precursor-progeny relationship. The murine homologs of human dermal CD14+ cells are CD11b+CD64+ monocyte-derived macrophages. Human and mouse monocytes and macrophages were defined by highly conserved gene transcripts, which were distinct from DCs. The demonstration of monocyte-derived macrophages in the steady state in human tissue supports a conserved organization of human and mouse mononuclear phagocyte system.

Haematopoiesis in the bone marrow (BM) maintains blood and immune cell production throughout postnatal life. Haematopoiesis first emerges in human BM at 11-12 post conception weeks 1,2 , yet almost nothing is known about how fetal BM (FBM) evolves to meet the highly specialised needs of the fetus and newborn. Here, we detail the development of FBM, including stroma, using multi-omic assessment of mRNA and multiplexed protein epitope expression. We find that the full blood and immune cell repertoire is established in FBM in a short time window of 6-7 weeks early in the second trimester. FBM promotes rapid and extensive diversification of myeloid cells, with granulocytes, eosinophils and dendritic cell subsets emerging for the first time. Substantial B-lymphocyte expansion in FBM contrasts with FL at the same gestational age. Haematopoietic progenitors from FL, FBM and cord blood (CB) exhibit transcriptional and functional differences that contribute to tissue-specific identity and cellular diversification. Endothelial cell types form distinct vascular structures that we demonstrate are regionally compartmentalized within FBM. Finally, we reveal selective disruption of B-lymphocyte, erythroid and myeloid development due to cell-intrinsic differentiation bias as well as extrinsic regulation through an altered microenvironment in Down syndrome (trisomy 21).

The aim of this study was to assess the efficacy and tolerability of paclitaxel and carboplatin (TC) in the treatment of patients with advanced or recurrent endometrial cancer. Patients eligible for this retrospective analysis had endometrial cancer with either advanced or recurrent measurable disease (untreated primary stage III/IV or stage III/IV patients with persistent, measurable disease [> or =2 cm] after surgery), Eastern Cooperative Oncology Group (ECOG) performance status > or =3, and received at least one cycle of TC. Response rates were determined using Response Evaluation Criteria in Solid Tumors criteria. Institutional Review Board approval was obtained prior to the initiation of this study. Eighty-five eligible patients, with a median age of 62 years (range 36-80) were identified. Fifty-seven (67%) of patients were treated at the time of recurrence. Prior radiation therapy had been used in the treatment of 36 (42%) patients, while 13 (15%) patients had received prior chemotherapy. Median follow-up time was 11.7 months (range 1.1-96.7 months), and the median number of cycles of therapy received was six (range 1-18). The overall response rate (ORR) was 43%, with a complete response rate of 5% and a partial response rate of 38%. Chemotherapy-naive patients had an ORR of 47%. Only seven (8%) patients had to discontinue therapy due to toxicity. Median progression-free survival was 5.3 months (95% CI, 4.6-7.4), with a median overall survival of 13.2 months (95% CI, 11.7-18.2). We conclude that TC is an active and tolerable regimen in the treatment of patients with advanced or recurrent endometrial cancer.

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In the original publication of this article, the name of an author was inadvertently misspelled. The corrected author name is Diego Miranda-Saavedra. The spelling is now correct in the online version of the study. The authors apologize for the inconvenience.

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