Expanded potential stem cell media as a tool to study human developmental hematopoiesis in vitro.

Pluripotent stem cell (PSC) differentiation in vitro represents a powerful and tractable model to study mammalian development and an unlimited source of cells for regenerative medicine. Within hematology, in vitro PSC hematopoiesis affords novel insights into blood formation and represents an exciting potential approach to generate hematopoietic and immune cell types for transplantation and transfusion. Most studies to date have focused on in vitro hematopoiesis from mouse PSCs and human PSCs. However, differences in mouse and human PSC culture protocols have complicated the translation of discoveries between these systems. We recently developed a novel chemical media formulation, expanded potential stem cell medium (EPSCM), that maintains mouse PSCs in a unique cellular state and extraembryonic differentiation capacity. Herein, we describe how EPSCM can be directly used to stably maintain human PSCs. We further demonstrate that human PSCs maintained in EPSCM can spontaneously form embryoid bodies and undergo in vitro hematopoiesis using a simple differentiation protocol, similar to mouse PSC differentiation. EPSCM-maintained human PSCs generated at least two hematopoietic cell populations, which displayed distinct transcriptional profiles by RNA-sequencing (RNA-seq) analysis. EPSCM also supports gene targeting using homologous recombination, affording generation of an SPI1 (PU.1) reporter PSC line to study and track in vitro hematopoiesis. EPSCM therefore provides a useful tool not only to study pluripotency but also hematopoietic cell specification and developmental-lineage commitment.

Establishment of mouse expanded potential stem cells.

Mouse embryonic stem cells derived from the epiblast contribute to the somatic lineages and the germline but are excluded from the extra-embryonic tissues that are derived from the trophectoderm and the primitive endoderm upon reintroduction to the blastocyst. Here we report that cultures of expanded potential stem cells can be established from individual eight-cell blastomeres, and by direct conversion of mouse embryonic stem cells and induced pluripotent stem cells. Remarkably, a single expanded potential stem cell can contribute both to the embryo proper and to the trophectoderm lineages in a chimaera assay. Bona fide trophoblast stem cell lines and extra-embryonic endoderm stem cells can be directly derived from expanded potential stem cells in vitro. Molecular analyses of the epigenome and single-cell transcriptome reveal enrichment for blastomere-specific signature and a dynamic DNA methylome in expanded potential stem cells. The generation of mouse expanded potential stem cells highlights the feasibility of establishing expanded potential stem cells for other mammalian species.

Single-cell RNA-seq identifies a PD-1hi ILC progenitor and defines its development pathway.

Innate lymphoid cells (ILCs) functionally resemble T lymphocytes in cytotoxicity and cytokine production but lack antigen-specific receptors, and they are important regulators of immune responses and tissue homeostasis. ILCs are generated from common lymphoid progenitors, which are subsequently committed to innate lymphoid lineages in the α-lymphoid progenitor, early innate lymphoid progenitor, common helper innate lymphoid progenitor and innate lymphoid cell progenitor compartments. ILCs consist of conventional natural killer cells and helper-like cells (ILC1, ILC2 and ILC3). Despite recent advances, the cellular heterogeneity, developmental trajectory and signalling dependence of ILC progenitors are not fully understood. Here, using single-cell RNA-sequencing (scRNA-seq) of mouse bone marrow progenitors, we reveal ILC precursor subsets, delineate distinct ILC development stages and pathways, and report that high expression of programmed death 1 (PD-1hi) marked a committed ILC progenitor that was essentially identical to an innate lymphoid cell progenitor. Our data defined PD-1hiIL-25Rhi as an early checkpoint in ILC2 development, which was abolished by deficiency in the zinc-finger protein Bcl11b but restored by IL-25R overexpression. Similar to T lymphocytes, PD-1 was upregulated on activated ILCs. Administration of a PD-1 antibody depleted PD-1hi ILCs and reduced cytokine levels in an influenza infection model in mice, and blocked papain-induced acute lung inflammation. These results provide a perspective for exploring PD-1 and its ligand (PD-L1) in immunotherapy, and allow effective manipulation of the immune system for disease prevention and therapy.

The transcription factor Bcl11b is specifically expressed in group 2 innate lymphoid cells and is essential for their development.

Group 2 innate lymphoid cells (ILCs), or ILC2s, are a subset of recently identified ILCs, which play important roles in innate immunity by producing type 2 effector cytokines. Several transcription factors have been found to have critical functions in the development of both ILC2s and T cells. We report here that Bcl11b, a transcription factor essential in T cell lineage commitment and maintenance, is specifically expressed in progenitors committed to the ILC2 lineage and is required for ILC2 development. The Bcl11b gene is expressed in ∼28% of ILC progenitors (ILCPs; common helper innate lymphoid progenitors or ILCPs expressing either ID2 or promyelocytic leukemia zinc finger, respectively). Both in vitro and in vivo, these Bcl11b-expressing early ILCPs generate only ILC2s. Inactivation of Bcl11b causes a complete loss of ILC2 development from hematopoietic progenitors, which is confirmed upon immune challenge with either papain administration or influenza virus infection.

BCL11A is a triple-negative breast cancer gene with critical functions in stem and progenitor cells.

Triple-negative breast cancer (TNBC) has poor prognostic outcome compared with other types of breast cancer. The molecular and cellular mechanisms underlying TNBC pathology are not fully understood. Here, we report that the transcription factor BCL11A is overexpressed in TNBC including basal-like breast cancer (BLBC) and that its genomic locus is amplified in up to 38% of BLBC tumours. Exogenous BCL11A overexpression promotes tumour formation, whereas its knockdown in TNBC cell lines suppresses their tumourigenic potential in xenograft models. In the DMBA-induced tumour model, Bcl11a deletion substantially decreases tumour formation, even in p53-null cells and inactivation of Bcl11a in established tumours causes their regression. At the cellular level, Bcl11a deletion causes a reduction in the number of mammary epithelial stem and progenitor cells. Thus, BCL11A has an important role in TNBC and normal mammary epithelial cells. This study highlights the importance of further investigation of BCL11A in TNBC-targeted therapies.

Polygenic in vivo validation of cancer mutations using transposons.

The in vivo validation of cancer mutations and genes identified in cancer genomics is resource-intensive because of the low throughput of animal experiments. We describe a mouse model that allows multiple cancer mutations to be validated in each animal line. Animal lines are generated with multiple candidate cancer mutations using transposons. The candidate cancer genes are tagged and randomly expressed in somatic cells, allowing easy identification of the cancer genes involved in the generated tumours. This system presents a useful, generalised and efficient means for animal validation of cancer genes.

Bcl11a is essential for lymphoid development and negatively regulates p53.

Transcription factors play important roles in lymphopoiesis. We have previously demonstrated that Bcl11a is essential for normal lymphocyte development in the mouse embryo. We report here that, in the adult mouse, Bcl11a is expressed in most hematopoietic cells and is highly enriched in B cells, early T cell progenitors, common lymphoid progenitors (CLPs), and hematopoietic stem cells (HSCs). In the adult mouse, Bcl11a deletion causes apoptosis in early B cells and CLPs and completely abolishes the lymphoid development potential of HSCs to B, T, and NK cells. Myeloid development, in contrast, is not obviously affected by the loss of Bcl11a. Bcl11a regulates expression of Bcl2, Bcl2-xL, and Mdm2, which inhibits p53 activities. Overexpression of Bcl2 and Mdm2, or p53 deficiency, rescues both lethality and proliferative defects in Bcl11a-deficient early B cells and enables the mutant CLPs to differentiate to lymphocytes. Bcl11a is therefore essential for lymphopoiesis and negatively regulates p53 activities. Deletion of Bcl11a may represent a new approach for generating a mouse model that completely lacks an adaptive immune system.

Reprogramming of T cells to natural killer-like cells upon Bcl11b deletion.

T cells develop in the thymus and are critical for adaptive immunity. Natural killer (NK) lymphocytes constitute an essential component of the innate immune system in tumor surveillance, reproduction, and defense against microbes and viruses. Here, we show that the transcription factor Bcl11b was expressed in all T cell compartments and was indispensable for T lineage development. When Bcl11b was deleted, T cells from all developmental stages acquired NK cell properties and concomitantly lost or decreased T cell-associated gene expression. These induced T-to-natural killer (ITNK) cells, which were morphologically and genetically similar to conventional NK cells, killed tumor cells in vitro, and effectively prevented tumor metastasis in vivo. Therefore, ITNKs may represent a new cell source for cell-based therapies.

Genome-wide screening of yeast metal homeostasis genes involved in mitochondrial functions.

Metal ions are essential for mitochondria to execute their roles. Yeast mutants that are sensitive to metals (either excess or deficiency) on non-fermentable media but not on fermentable media may carry mutations in genes that participate in metal homeostasis involving mitochondrial functions. A collection of approximately 4,800 haploid yeast deletion mutants was screened for metal ion homeostasis genes linked to mitochondrial respiration. In addition to several well-characterized metal homeostasis genes, 45 new mutants, impaired in various molecular functions, were identified on non-fermentable media that were sensitive to adscititious metals or metal deficiency. While 35 of these mutants displayed metal-sensitivity only on non-fermentable media, the remaining 10 also exhibited metal sensitivity on fermentable media, suggesting metal-sensitivity of the latter is not due to mitochondrial dysfunction. Inductively coupled plasma optical emission spectrometry (ICP-OES) was conducted for 12 mutants that were sensitive to metal excess to analyze their metal contents. Among these 12 mutants 7 were sensitive to metal excess on non-fermentable but not on fermentable media. All the seven respiration-dependent mutants displayed abnormal levels of metal ions inside mitochondria, indicative of disrupted mitochondrial metal homeostasis. This study therefore effectively identified multiple new genes involved in metal homeostasis pathways possibly pertinent to mitochondrial functions, and should be helpful for future studies to further understand their molecular roles.