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International audience; Generating patient-specific stem cells representing the onset of development has become possible since the discovery of somatic cell reprogramming into induced pluripotent stem cells. However, human pluripotent stem cells are generally cultured in a primed pluripotent state: they are poised for differentiation and represent a stage of development corresponding to post-implantation epiblast. Here, we describe a protocol to reprogram human fibroblasts into naive pluripotent stem cells by overexpressing the transcription factors OCT4, SOX2, KLF4, and c-MYC using Sendai viruses. The resulting cells represent an earlier stage of development that corresponds to pre-implantation epiblast. We also discuss validation methods for human naive pluripotent stem cells.

SUMMARYHuman trophoblast stem cells (hTSC) derived from blastocysts and first-trimester cytotrophoblasts offer an unprecedented opportunity to study the human placenta. However, access to human embryos and first trimester placentas is limited thus preventing the establishment of hTSC from a variety of genetic backgrounds associated with placental disorders. In the present study, we show that hTSC can be generated from numerous genetic backgrounds using post-natal cells via two alternative methods: (I) somatic cell reprogramming of adult fibroblasts using the Yamanaka factors, and (II) cell fate conversion of naive and extended pluripotent stem cells. The resulted induced and converted hTSC (hiTSC/hcTSC) recapitulated hallmarks of hTSC including long-term self-renewal, expression of specific transcription factors, transcriptome-side signature, and the potential to differentiate into syncytiotrophoblast and extravillous trophoblast cells. We also clarified the developmental stage of hTSC and show that these cells resemble post-implantation NR2F2+ cytotrophoblasts (day 8-10). Altogether, hTSC lines of diverse genetics origins open the possibility to model both placental development and diseases in a dish.HighlightsReprogramming of human somatic cells to induced hTSC with OSKMConversion of naive and extended hPSC to hTSCGenetic diversity of hTSC linesDevelopmental matching of hTSC in the peri-implantation human embryo

International audience; Several lines of evidence support a key role for CD8+ T cells in central nervous system tissue damage of patients with multiple sclerosis. However, the precise phenotype of the circulating CD8+ T cells that may be recruited from the peripheral blood to invade the CNS remains largely undefined to date. It has been suggested that IL-17 secreting CD8 (Tc17) T cells may be involved, and in humans these cells are characterized by the expression of CD161. We focused our study on a unique and recently described subset of CD8 T cells characterized by an intermediate expression of CD161 as its role in neuroinflammation has not been investigated to date. The frequency, phenotype, and function of CD8+ T cells with an intermediate CD161 expression level were characterized ex-vivo, in vitro, and in situ using RNAseq, RT-PCR, flow cytometry, TCR sequencing, and immunohistofluorescence of cells derived from healthy volunteers (n = 61), MS subjects (n = 90), as well as inflammatory (n = 15) and non-inflammatory controls (n = 6). We report here that CD8+CD161int T cells present characteristics of effector cells, up-regulate cell-adhesion molecules and have an increased ability to cross the blood-brain barrier and to secrete IL-17, IFNγ, GM-CSF, and IL-22. We further demonstrate that these cells are recruited and enriched in the CNS of MS subjects where they produce IL-17. In the peripheral blood, RNAseq, RT-PCR, high-throughput TCR repertoire analyses, and flow cytometry confirmed an increased effector and transmigration pattern of these cells in MS patients, with the presence of supernumerary clones compared to healthy controls. Our data demonstrate that intermediate levels of CD161 expression identifies activated and effector CD8+ T cells with pathogenic properties that are recruited to MS lesions. This suggests that CD161 may represent a biomarker and a valid target for the treatment of neuroinflammation.

Understanding lineage specification during human pre-implantation development is a gateway to improving assisted reproductive technologies and stem cell research. Here we employ pseudotime analysis of single-cell RNA sequencing (scRNA-seq) data to reconstruct early mouse and human embryo development. Using time-lapse imaging of annotated embryos, we provide an integrated, ordered, and continuous analysis of transcriptomics changes throughout human development. We reveal that human trophectoderm/inner cell mass transcriptomes diverge at the transition from the B2 to the B3 blastocyst stage, just before blastocyst expansion. We explore the dynamics of the fate markers IFI16 and GATA4 and show that they gradually become mutually exclusive upon establishment of epiblast and primitive endoderm fates, respectively. We also provide evidence that NR2F2 marks trophectoderm maturation, initiating from the polar side, and subsequently spreads to all cells after implantation. Our study pinpoints the precise timing of lineage specification events in the human embryo and identifies transcriptomics hallmarks and cell fate markers.

Recent technological advances such as single-cell RNAseq1-3and CRISPR-CAS9-mediated knock-out4have allowed an unprecedented access into processes orchestrating human preimplantation development5. However, the sequence of events which occur during human preimplantation development are still unknown. In particular, timing of first human lineage specification, the process by which the morula cells acquire a specific fate, remains elusive. Here, we present a human preimplantation development model based on transcriptomic pseudotime modelling of scRNAseq biologically validated by spatial information and precise time-lapse staging. In contrast to mouse, we show that trophectoderm (TE) / inner cell mass (ICM) lineage specification in human is only detectable at the transcriptomic level at the blastocyst stage, just prior to expansion. We validated the expression profile of novel markers enabling precise staging of human preimplantation embryos, such as IFI16 which highlights establishment of epiblast (EPI) and NR2F2 which appears at the transition from specified to mature TE. Strikingly, mature TE cells arise from the polar side, just after specification, supporting a model of polar TE cells driving TE maturation. Altogether, our study unravels the first lineage specification event in the human embryo and provides a browsable resource for mapping spatio-temporal events underlying human lineage specification.

Recent technological advances such as single-cell (sc) RNAseq and CRISPR-CAS9-mediated knock-out have allowed an unprecedented access to processes orchestrating human preimplantation development. However, the sequence of events which occur during human preimplantation development are still unknown. In particular, the timing of the first human lineage specification, the process by which the morula cells acquire a specific fate, remains elusive. Here, we present a mouse and human preimplantation development model based on transcriptomic pseudotime modelling of scRNAseq biologically validated by spatial information and precise time-lapse staging. We show that in human, trophectoderm (TE) and inner cell mass (ICM) specification in not complete until the B3 blastocyst stage. This reveals a delay with the mouse first specification. We identified novel markers enabling precise staging of human preimplantation embryos: IFI16, associated to the developed epiblast (EPI) and NR2F2, associated with TE development. Strikingly, NR2F2 positive TE cells arise from the polar side, shortly after specification, supporting a model of faster polar TE development leading to polar implantation in the endometrium. Altogether, our study unravels preimplantation lineage specification in human embryos and provides a browsable resource for mapping spatio-temporal events orchestrating human preimplantation development.

Several lines of evidence support a key role for CD8

Rat and human CD4(+) and CD8(+) Tregs expressing low levels of CD45RC have strong immunoregulatory properties. We describe here that human CD45 isoforms are nonredundant and identify distinct subsets of cells. We show that CD45RC is not expressed by CD4(+) and CD8(+) Foxp3(+) Tregs, while CD45RA/RB/RO are. Transient administration of a monoclonal antibody (mAb) targeting CD45RC in a rat cardiac allotransplantation model induced transplant tolerance associated with inhibition of allogeneic humoral responses but maintained primary and memory responses against cognate antigens. Anti-CD45RC mAb induced rapid death of CD45RC(high) T cells through intrinsic cell signaling but preserved and potentiated CD4(+) and CD8(+) CD45RC(low/-) Tregs, which are able to adoptively transfer donor-specific tolerance to grafted recipients. Anti-CD45RC treatment results in distinct transcriptional signature of CD4(+) and CD8(+) CD45RC(low/-) Tregs. Finally, we demonstrate that anti-human CD45RC treatment inhibited graft-versus-host disease (GVHD) in immune-humanized NSG mice. Thus, short-term anti-CD45RC is a potent therapeutic candidate to induce transplantation tolerance in human.