In vitro generation of T lymphocytes from embryonic stem cell-derived prehematopoietic progenitors

Generation and clinical potential of functional T lymphocytes from gene-edited pluripotent stem cells

Engineered T cells have been shown to be highly effective in cancer immunotherapy, although T cell exhaustion presents a challenge for their long-term function. Additional T-cell sources must be exploited to broaden the application of engineered T cells for immune defense and reconstitution. Unlimited sources of pluripotent stem cells (PSCs) have provided a potential opportunity to generate precise-engineered therapeutic induced T (iT) cells. Single-cell transcriptome analysis of PSC-derived induced hematopoietic stem and progenitor cells (iHSPC)/iT identified the developmental pathways and possibilities of generating functional T cell from PSCs. To date, the PSC-to-iT platforms encounter several problems, including low efficiency of conventional T subset specification, limited functional potential, and restrictions on large-scale application, because of the absence of a thymus-like organized microenvironment. The updated PSC-to-iT platforms, such as the three-dimensional (3D) artificial thymic organoid (ATO) co-culture system and Runx1/Hoxa9-enforced iT lymphopoiesis, provide fresh perspectives for coordinating culture conditions and transcription factors, which may greatly improve the efficiency of T-cell generation greatly. In addition, the improved PSC-to-iT platform coordinating gene editing technologies will provide various functional engineered unconventional or conventional T cells. Furthermore, the clinical applications of PSC-derived immune cells are accelerating from bench to bedside.

Close Quarters Can Be a Good Fit for Stem Cells to Become T Cells

Human pluripotent stem cells (PSCs) could potentially provide a potentially unlimited supply of T cells. In this issue of Cell Stem Cell, Montel-Hagen et al. (2019) take advantage of a three-dimensional mouse stromal cell-based system that combines mesoderm specification with organoid-induced hematopoietic differentiation to enable commitment, selection, and maturation of conventional human T cells.

The potential of non-myeloablative heterochronous autologous hematopoietic stem cell transplantation for extending a healthy life span

Aging is a complex multifactorial process, a prominent component being the senescence of the immune system. Consequently, immune-related diseases develop, including atherosclerosis, cancer, and life-threatening infections, which impact on health and longevity. Rejuvenating the aged immune system could mitigate these diseases, thereby contributing to longevity and health. Currently, an appealing option for rejuvenating the immune system is heterochronous autologous hematopoietic stem cell transplantation (haHSCT), where healthy autologous bone marrow/peripheral blood stem cells are collected during the youth of an individual, cryopreserved, and re-infused when he or she has reached an older age. After infusion, young hematopoietic stem cells can reconstitute the compromised immune system and improve immune function. Several studies using animal models have achieved substantial extension of the life span of animals treated with haHSCT. Therefore, haHSCT could be regarded as a potential procedure for preventing age-related immune defects and extending healthy longevity. In this review, the pros, cons, and future feasibility of this approach are discussed.

Embryonic Stem Cells in Development and Regenerative Medicine

After progressive improvement in embryonic stem (ES) cell field, several studies have been conducted to explore the usage of ES cells in regenerative medicine. Unlimited self renewal and pluripoteny properties, combined with encouraging preclinical trials, remark that ES cell technology might be promising for clinical practice. ES cells, which can form three germ layers in vitro, are potential candidates to study development at the cellular and molecular level. Understanding the cell fate decision and differentiation processes during development might enable generating functional progenitor cells for tissue restoration. Progression in gene modifications and tissue engineering technology has facilitated the derivation of desired cells for therapy. Success in differentiation protocols and identification the regulatory pathways simplify the research for clinical applications. Although there are established protocols for cell differentiation in vitro and promising preclinical studies in vivo, many challenges need to be adressed before clinical translation. In this review, ES cells are discussed as a model of development in vitro and as a potential candidate for regenerative medicine. This review also dissusses current challenges for ES cell based therapy.

Engineering approaches for regeneration of T lymphopoiesis

T cells play a central role in immune-homeostasis; specifically in the induction of antigen-specific adaptive immunity against pathogens and mutated self with immunological memory. The thymus is the unique organ where T cells are generated. In this review, first the complex structures and functions of various thymic microcompartments are briefly discussed to identify critical engineering targets for regeneration of thymic functions in vitro and in vivo. Then the biomimetic regenerative engineering approaches are reviewed in three categories: 1) reconstruction of 3-D thymic architecture, 2) cellular engineering, and 3) biomaterials-based artificial presentation of critical biomolecules. For each engineering approach, remaining challenges and clinical opportunities are also identified and discussed.

Advances in cellular technology in the hematology field: What have we learned so far?

Despite the advances in the hematology field, blood transfusion-related iatrogenesis is still a major issue to be considered during such procedures due to blood antigenic incompatibility. This places pluripotent stem cells as a possible ally in the production of more suitable blood products. The present review article aims to provide a comprehensive summary of the state-of-the-art concerning the differentiation of both embryonic stem cells and induced pluripotent stem cells to hematopoietic cell lines. Here, we review the most recently published protocols to achieve the production of blood cells for future application in hemotherapy, cancer therapy and basic research.

Invariant natural killer T cells generated from human adult hematopoietic stem-progenitor cells are poly-functional

Invariant natural killer T (iNKT) cells constitute an important subset of T cells that can both directly and indirectly mediate anti-tumor immunity. However, cancer patients have a reduction in both iNKT cell number and function, and these deficits limit the potential clinical application of iNKT cells for cancer therapy. To overcome the problem of limited iNKT cell numbers, we investigated whether iNKT cells can be generated in vitro from bone marrow-derived adult hematopoietic stem-progenitor cells (HSPC). Our data demonstrate that co-culture of HSPC with OP9-DL1 stromal cells, results in a functional CD3(+) T cell population. These T cells can be further differentiated into iNKT cells by secondary culture with CD1d-Ig-based artificial antigen-presenting cells (aAPC). Importantly, these in vitro-generated iNKT cells are functional, as demonstrated by their ability to proliferate and secrete IFN-γ and GM-CSF following stimulation.

Derivation of T cells in vitro from mouse embryonic stem cells

The OP9/OP9-DL1 co-culture system has become a well-established method for deriving differentiated blood cell types from embryonic and hematopoietic progenitors of both mouse and human origin. It is now used to address a growing variety of complex genetic, cellular and molecular questions related to hematopoiesis, and is at the cutting edge of efforts to translate these basic findings to therapeutic applications. The procedures are straightforward and routinely yield robust results. However, achieving successful hematopoietic differentiation in vitro requires special attention to the details of reagent and cell culture maintenance. Furthermore, the protocol features technique sensitive steps that, while not difficult, take care and practice to master. Here we focus on the procedures for differentiation of T lymphocytes from mouse embryonic stem cells (mESC). We provide a detailed protocol with discussions of the critical steps and parameters that enable reproducibly robust cellular differentiation in vitro. It is in the interest of the field to consider wider adoption of this technology, as it has the potential to reduce animal use, lower the cost and shorten the timelines of both basic and translational experimentation.

Mesodermal and hematopoietic differentiation from ES and iPS cells

Embryonic stem (ES) and induced pluripotent stem (iPS) cells can differentiate into any type of tissue when grown in a suitable culture environment and are considered valuable tools for regenerative medicine. In the field of hematology, generation of hematopoietic stem cells (HSCs) and mature hematopoietic cells (HCs) from ES and iPS cells through mesodermal cells, the ancestors of HCs, can facilitate transplantation and transfusion therapy. Several studies report generation of functional HCs from both mouse and human ES and iPS cells. This approach will likely be applied to individual patient-derived iPS cells for regenerative medicine approaches and drug screening in the future. Here, we summarize current studies of HC-generation from ES and iPS cells.

Reversing T cell immunosenescence: why, who, and how

Immunosenescence is the term commonly used to describe the multifaceted phenomenon encompassing all changes occurring in the immune system during aging. It contributes to render older adults more prone to develop infectious disease and main age-related diseases. While age clearly imposes drastic changes in immune physiology, older adults have heterogeneous health and immune phenotypes. This confronts scientists and researcher to develop more age-specific interventions rather than simply adopting intervention regimes used in younger people and this in order to maintain immune protection in older adults. Thus, this review provides evidences of the central role played by cell-mediated immunity in the immunosenescence process and explores the means by which senescent state of the cell-mediated immune function could be identified and predicted using biomarkers. Furthermore considerations are given to recent advances made in the field of age-specific immune interventions that could contribute to maintain immune protection, to improve quality of life, and/or to promote healthy aging of the growing part of the population.

Composition and characteristics of distinct macrophage subpopulations in the mouse thymus

The aim of the present study was to investigate the composition, morphology, characteristics, distribution and function of distinct macrophage subpopulations in the mouse thymus. Apoptosis of mouse thymocytes was induced by glucocorticoids and three monoclonal antibodies against Mac-2, F4/80 and ED1 were used for immunofluorescence staining and immunohistochemical analysis. The morphology of thymic macrophages was examined by transmission electron microscopy. Four subpopulations of mouse thymic macrophages were identified. Dendritic macrophages were identified using anti-Mac-2 and anti-F4/80 antibodies, and were demonstrated to be distributed in the entire thymus. Phagocytes were also observed. In addition, plate-shaped macrophages, identified using the anti-F4/80 antibody, were distributed under the thymic cortex capsule. Small oval macrophages, identified using the anti-Mac-2 antibody, were distributed in the thymic medulla and corticomedullary region (CMR), while phagocytes were not observed in these types of cell. ED1+ thymic macrophages with irregular forms were distributed in the CMR. All of the four subpopulations of mouse thymic macrophages described above exhibited acid phosphate activity. This study indicated the existence of macrophage subpopulations with different shapes, distribution and functions in the mouse thymus.

Antibacterial capacity of differentiated murine embryonic stem cells during defined in vitro inflammatory conditions

Embryonic stem (ES) cells are a powerful model for the development of cells responsible for the cellular immune response. Therefore, we analyzed the defense and phagocytic capacity of embryoid bodies (EBs) derived from ES cells using in the vitro inflammatory conditions caused by Escherichia coli. Further, we used this phagocytic activity to purify activated immune cells. Our data show that spontaneously differentiated 18-day-old EBs of the cell line CGR8 contained immune cells, which were positive for CD45, CD68, CD11b, F4/80, and CD19. Exposure of these EBs to E. coli with defined infection doses of bacterial colony-forming units (CFUs) led to a significant time-dependent reduction of CFUs, indicating the immune responses exerted by EBs. This was paralleled by an upregulation of inflammatory cytokines, that is, IL-1β and TNF-α. Western blot analysis of infected EBs indicated an upregulation of CD14 and cytochrome b-245 heavy chain (NOX2). Silencing of NOX2 significantly reduced the antibacterial capacity of EBs, which was partially explained by reduction of F4/80-positive cells. To identify, isolate, and further cultivate phagocytic active cells from differentiated EBs, a cocultivation assay of differentiated ES cells with green fluorescent protein (GFP)-labeled E. coli was established. Colocalization of GFP-labeled E. coli with cells positive for CD45, CD68, and F4/80 revealed time-dependent phagocytotic uptake, which was underlined by colocalization with the LysoTracker-Red(®) dye as well as preincubation with cytochalasin D. In conclusion, a primitive immune response with efficient phagocytosis was responsible for the antibacterial capacity of differentiated EBs.

Directed differentiation of embryonic stem cells to the T-lymphocyte lineage

Hematopoiesis is the highly regulated and complex process by which blood cells are formed. Hematopoiesis can be achieved in vitro by the differentiation of embryonic stem cells (ESCs) into hematopoietic lineage cells. Differentiation of ESCs initially gives rise to mesoderm colonies that go on to form hemangioblast cells, which possess endothelial and hematopoietic lineage potential. While the differentiation of several hematopoietic lineages from ESCs, such as erythrocytes and macrophages, can be easily recapitulated in vitro, T-cell differentiation requires additional Notch-dependent signals for their generation. Keeping with this, ESCs induced to differentiate with OP-9 cells, a bone marrow-derived stromal cell line, give rise to erythro-myeloid cells and B lymphocytes, while the expression of an appropriate Notch ligand, such as Delta-like 1, on OP-9 cells (OP9-DL1) is required to support the generation of T-cells in vitro. Here, we describe an updated and streamlined protocol for the generation of T-lineage cells from mouse ESCs cultured on OP9-DL1 cells. This approach can facilitate studies aimed to assess the effects of environmental and genetic manipulations at various stages of T-cell development.

Connecting the dots: artificial antigen presenting cell-mediated modulation of natural killer T cells

Natural killer T (NKT) cells constitute an important subset of T cells that can both directly and indirectly mediate antitumor immunity. However, we and others have reported that cancer patients have a reduction in both NKT cell number and function. NKT cells can be stimulated and expanded with α-GalCer and cytokines and these expanded NKT cells retain their phenotype, remain responsive to antigenic stimulation, and display cytotoxic function against tumor cell lines. These data strongly favor the use of ex vivo expanded NKT cells in adoptive immunotherapy. NKT cell based-immunotherapy has been limited by the use of autologous antigen-presenting cells, which can vary substantially in their quantity and quality. A standardized system that relies on artificial antigen-presenting cells (aAPCs) could produce the stimulating effects of dendritic cell (DC) without the pitfalls of allo- or xenogeneic cells. In this review, we discuss the progress that has been made using CD1d-based aAPC and how this acellular antigen presenting system can be used in the future to enhance our understanding of NKT cell biology and to develop NKT cell-specific adoptive immunotherapeutic strategies.

Control of leucocyte differentiation from embryonic stem cells upon vasculogenesis and confrontation with tumour tissue

Embryonic stem (ES) cells spontaneously differentiate capillary-like structures as well as leucocytes such as monocytes/macrophages, neutrophils, natural killer (NK) cells and cytototoxic T lymphocytes. The interplay between vasculogenesis and leucocyte differentiation as well as the population of tumour tissues with ES cell-derived leucocytes and endothelial cells is, however, not sufficiently specified. In the present study, gene expression of the cell surface markers CD68 and CD14 (expressed on monocytes and macrophages), Mac-1 (CD11b) (expressed on granulocytes, monocytes and NK cells) and CD16 (expressed on neutrophils) was investigated in murine CGR8 ES cells in relation to the endothelial cell markers CD31 and vascular endothelial (VE)-cadherin. Expression of leucocyte markers increased from day 7–8 of cell culture on. Furthermore, addition of macrophage colony-stimulating factor to the cell culture medium resulted in a threefold increase in the number of CD68⁺ monocytes/macrophages. Treatment of embryoid bodies with lipopolysaccharide (LPS) up-regulated CD14 thus suggesting functionality of the CD14 LPS receptor. Differentiation of vascular structures positive for CD31 and VE-cadherin preceded leucocyte differentiation by 2 days (i.e. from day 5–6 on) suggesting that vasculogenesis may be a determinant of leucocyte differentiation. Consequently the Flk-1 antagonist SU5416 which inhibits vasculogenesis of ES cells significantly blunted leucocyte differentiation. Confrontation culture of embryoid bodies with multicellular breast tumour spheroids initiated significant increase of leucocyte cell numbers and invasion of leucocytes into the tumour tissue. In summary our data demonstrate that during ES cell differentiation vasculogenesis precedes leucocyte differentiation, and point towards the direction that leucocyte cell invasion into tumour tissue may initiate the pro-inflammatory microenvironment necessary for tumour vascularization.

Immunity of embryonic stem cell-derived hematopoietic progenitor cells

A number of medical conditions including hematopoietic stem cell malignancies, immunodeficiencies, and autoimmune diseases can be treated using bone marrow cells. However, the major hindrance to the routine use of bone marrow cells is their unparalleled immunogenicity, requiring the use of harsh and toxic preconditioning regimens that can be fatal. Thus, identification of a safer alternative source of hematopoietic stem cells that can be broadly used in such therapies is highly desirable. Despite the current limited number of human ES cell lines, we believe that the newer technology of reprogramming adult somatic cells into pluripotent cells will eventually lead to greater availability of stem cell lines. Even more compelling is the possibility to directly reprogram a somatic cell into another adult cell type of a different tissue without the need for generating pluripotent cells. Here, I will discuss the immunological properties of mouse ES cell-derived hematopoietic progenitor cells. These progenitor cells poorly express MHC class I antigens but are responsive to stimulation by IFN-γ and other cytokines. However, despite upregulating MHC class I antigens after stimulation, they do not express class II molecules, a consequence of their lack of expression of the critical class II transcription factor CIITA. In this overview, I will discuss some of the published data on antigenicity and immunogenicity of ES cell-derived tissues. As more cells and tissues derived from ES cells become available for transplantation, we will gain more insight and into their abilities to interact with immune cells.

Hematopoiesis from pluripotent stem cell lines

Embryonic stem cells (ESCs) can differentiate into various types of hematopoietic cells (HPCs) when placed in an appropriate environment. Various methods for the differentiation of ESCs into specific HPC lineages have been developed using mouse ESCs. These ESC-differentiation methods have been utilized also as an in vitro model to investigate hematopoiesis in embryos and they provided critical perceptions into it. These methods have been adapted for use with human ESCs, which have the possibility of being employed in regenerative medicine; further improvement of these methods may lead to the efficient production of HPCs for use in transfusions. The generation of transplantable hematopoietic stem cells is a medical goal that is still difficult to achieve. Recently, induced pluripotent stem (iPS) cells have been established from differentiated cells. Thereby, iPS cells have expanded further possibilities of the use of pluripotent stem cell lines in clinical application. Indeed, iPS cells have been established from cells with disease genes and those which have undergone reprogramming and targeting have generated phenotypically normal HPCs. Here, we mainly summarize the recent progress in research on hematopoiesis conducted with ESCs and iPS cells.

Generation of functional NKT cells in vitro from embryonic stem cells bearing rearranged invariant Vα14-Jα18 TCRα gene

Establishment of a system with efficient generation of natural killer T (NKT) cells from embryonic stem (ES) cells would enable us to identify the cells with NKT-cell potential and obtain NKT cells with desired function. Here, using cloned ES (NKT-ES) cells generated by the transfer of nuclei from mature NKT cells, we have established a culture system that preferentially developed functional NKT cells and also identified early NKT progenitors, which first appeared on day 11 as a c-kit+ population in the cocultures on OP9 cells with expression of Notch ligand, delta-like1 (OP9/Dll-1) and became c-kitlo/− on day 14. Interestingly, in the presence of Notch signals, NKT-ES cells differentiated only to thymic CD44lo CD24hi NKT cells producing mainly interleukin-4 (IL-4), whereas NKT cells resembling CD44hi CD24lo liver NKT cells producing mainly interferon γ (IFN-γ) and exhibiting strong adjuvant activity in vivo were developed in the switch culture starting at day 14 in the absence of Notch. The cloned ES culture system offers a new opportunity for the elucidation of the molecular events on NKT-cell development and for the establishment of NKT-cell therapy.

Engineering lymphocyte subsets: tools, trials and tribulations

Cell-based therapies with various lymphocyte subsets hold promise for the treatment of several diseases, including cancer and disease resulting from inflammation and infection. The ability to genetically engineer lymphocyte subsets has the potential to improve the natural immune response and correct impaired immunity. In this Review we focus on the lymphocyte subsets that have been modified genetically or by other means for therapeutic benefit, on the technologies used to engineer lymphocytes and on the latest progress and hurdles in translating these technologies to the clinic.

Autologous blood cell therapies from pluripotent stem cells

The discovery of human embryonic stem cells (hESCs) raised promises for a universal resource for cell based therapies in regenerative medicine. Recently, fast-paced progress has been made towards the generation of pluripotent stem cells (PSCs) amenable for clinical applications, culminating in reprogramming of adult somatic cells to autologous PSCs that can be indefinitely expanded in vitro. However, besides the efficient generation of bona fide, clinically safe PSCs (e.g., without the use of oncoproteins and gene transfer based on viruses inserting randomly into the genome), a major challenge in the field remains how to efficiently differentiate PSCs to specific lineages and how to select cells that will function normally upon transplantation in adults. In this review, we analyse the in vitro differentiation potential of PSCs to the hematopoietic lineage by discussing blood cell types that can be currently obtained, limitations in derivation of adult-type HSCs and prospects for clinical application of PSCs-derived blood cells.

Ontogeny of haematopoiesis: recent advances and open questions

Unravelling the embryonic origins of the haematopoietic system has been the subject of sustained research for more than a century. Nevertheless, many important questions are still either unanswered or remain a matter of intense debate. Recent progress in mouse and embryonic stem cell model systems as well as imaging and post-genomic technologies has provided new insights into many of these open questions. Here we place into context recent reports on the anatomical site of blood stem cell emergence and, using red blood cells as an example, illustrate how the development of stem cells and the other blood lineages is both temporally and spatially decoupled. In addition, we outline how embryonic stem cell assays are increasingly used as a powerful surrogate for studying lineage relationships and developmental potential of early embryonic blood progenitors. Finally, we review how recent progress in the reconstruction of transcriptional regulatory networks is beginning to define the connectivity between key regulators that control early blood development. In light of these rapid recent advances, research into the embryonic origins of the haematopoietic system should remain one of the most vibrant disciplines within the wider field of haematology for the foreseeable future.

Toward clinical therapies using hematopoietic cells derived from human pluripotent stem cells

Human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) provide remarkable cellular platforms to better understand human hematopoiesis and to develop clinically applicable hematopoietic cell-based therapies. Over the past decade, hESCs have been used to characterize molecular and cellular mechanisms underpinning the differentiation of hematopoietic progenitors and mature, functional hematopoietic cells. These advances are now poised to lead to clinical translation of hESC- and iPSC-derived hematopoietic cells for novel therapies in the next few years. On the basis of areas of recent success, initial clinical use of hematopoietic cells derived from human pluripotent stem cells will probably be in the areas of transfusion therapies (erythrocytes and platelets) and immune therapies (natural killer cells). In contrast, efficient development and isolation of hematopoietic stem cells capable of long-term, multilineage engraftment still remains a significant challenge. Technical, safety, and regulatory concerns related to clinical applications of human PSCs must be appropriately addressed. However, proper consideration of these issues should facilitate and not inhibit clinical translation of new therapies. This review outlines the current status of hematopoietic cell development and what obstacles must be surmounted to bring hematopoietic cell therapies from human PSCs from "bench to bedside."

Hematopoiesis from Human Embryonic Stem Cells: Overcoming the Immune Barrier in Stem Cell Therapies

The multipotency and proliferative capacity of human embryonic stem cells (hESCs) make them a promising source of stem cells for transplant therapies and of vital importance given the shortage in organ donation. Recent studies suggest some immune privilege associated with hESC-derived tissues. However, the adaptability of the immune system makes it unlikely that fully differentiated tissues will permanently evade immune rejection. One promising solution is to induce a state of immune tolerance to a hESC line using tolerogenic hematopoietic cells derived from it. This could provide acceptance of other differentiated tissues from the same line. However, this approach will require efficient multilineage hematopoiesis from hESCs. This review proposes that more efficient differentiation of hESCs to the tolerogenic cell types required is most likely to occur through applying knowledge gained of the ontogeny of complex regulatory signals used by the embryo for definitive hematopoietic development in vivo. Stepwise formation of mesoderm, induction of definitive hematopoietic stem cells, and the application of factors key to their self-renewal may improve in vitro production both quantitatively and qualitatively.

Development of CD4+CD25+FoxP3+ regulatory T cells from cord blood hematopoietic progenitor cells

Adult stem cells are capable of generating all of the cells of the hematopoietic system, and this process is orchestrated in part by the interactions between these cells and the stroma. T cell progenitors emerge from the stem cell compartment and migrate to the thymus, where their terminal differentiation and maturation occur, and it is during this phase that selection shapes the immune repertoire. Notch ligands, including Delta-like 1 (DL1), play a critical role in this lymphoid differentiation. To mimic this in vitro, stroma-expressing DL1 have been used to generate CD4(+)CD8(+) double-positive and single-positive T cells from hematopoietic stem/progenitor cells. This system provides a robust tool to investigate thymopoiesis; however, its capacity to generate regulatory T cells (Tregs) has yet to be reported. Natural Tregs (nTregs) develop in the thymus and help maintain immune homeostasis and have potential clinical use as a cell therapy for modulation of autoimmune disease or for transplant tolerization. Here, we describe for the first time the development of a population of CD4(+)CD25(+) CD127(lo)FoxP3(+) cells that emerge in coculture of cord blood (CB) CD34(+) progenitors on OP9-DL1 stroma. These hematopoietic progenitor-derived CD4(+)CD25(+) Tregs have comparable suppressor function with CB nTregs in vitro. The addition of IL-2 to the coculture enhanced the expansion and survival of this population significantly. This manipulable culture system, therefore, generates functional Tregs and provides a system to elucidate the mechanism of Treg development.

Both primitive and definitive blood cells are derived from Flk-1+ mesoderm

Emerging evidence suggests that all hematopoietic and endothelial cells originate from Flk-1(+) mesoderm in the mouse. However, this concept has not been completely proven, especially for the origin of blood cells. Using either Flk1(+/Cre);Rosa26R-EYFP or Flk1(+/Cre);Rosa26R-LacZ mice, we permanently marked Flk-1(+) cells and their progenies to determine the relationship between hematopoietic tissues and cells that express Flk-1. In embryos, all blood cells within the yolk sac and aorta were of Flk-1(+) origin. In addition, nearly all CD45(+) cells in bone marrow and circulating blood in adults were of Flk-1(+) origin. These results provide clear evidence that all blood cells, primitive and definitive, in mice are derived from Flk-1(+) mesodermal cells.

Human intrathymic development: a selective approach

Human T lymphocytes can be generated from CD34 progenitor cells from different sources. This can be obtained in an in vivo model wherein human thymic tissue and fetal liver is transplanted in an immunodeficient mouse. However, human T cells are also generated in immunodeficient mice without co-transplantation of human thymus or in in vitro hybrid human-mouse fetal thymus organ culture. This shows that xenogeneic mouse thymus tissue supports human T cell differentiation. Finally, human T cells are generated on co-culture with murine stromal cells that express the Delta-like1 ligand for the Notch receptor. How these different environments influence the human T cell repertoire is reviewed and discussed.

Nuclear proteomics and directed differentiation of embryonic stem cells

During the past decade, regenerative medicine has been the subject of intense interest due, in large part, to our growing knowledge of embryonic stem (ES) cell biology. ES cells give rise to cell lineages from the three primordial germ layers--endoderm, mesoderm, and ectoderm. This process needs to be channeled if these cells are to be differentiated efficiently and used subsequently for therapeutic purposes. Indeed, an important area of investigation involves directed differentiation to influence the lineage commitment of these pluripotent cells in vitro. Various strategies involving timely growth factor supplementation, cell co-cultures, and gene transfection are used to drive lineage specific emergence. The underlying goal is to control directly the center of gene expression and cellular programming--the nucleus. Gene expression is enabled, managed, and sustained by the collective actions and interactions of proteins found in the nucleus--the nuclear proteome--in response to extracellular signaling. Nuclear proteomics can inventory these nuclear proteins in differentiating cells and decipher their dynamics during cellular phenotypic commitment. This review details what is currently known about nuclear effectors of stem cell differentiation and describes emerging techniques in the discovery of nuclear proteomics that will illuminate new transcription factors and modulators of gene expression.

Hematopoietic development of human embryonic stem cells in culture

The successful isolation and characterization of human embryonic stem cells (hESCs) provides a powerful tool to study the cellular and genetic mechanisms that mediate cell-fate decisions toward distinct developmental lineages. hESC-derived cells may also be suitable for novel cellular therapies. Significant progress in hematopoietic development of hESCs has demonstrated production of many types of blood cells from hESCs including myeloid, erythroid and lymphoid lineage cells, and possibly hematopoietic stem cells. Current established approaches to generate specific hematopoietic lineages are based on the initial pre-differentiation of hESCs into a heterogeneous mixture of cell populations. In this chapter, we describe two methods that have been successfully used in our laboratory: (1) co-culture with stromal cells derived from hematopoietic microenvironments and (2) x embryoid body (EB) formation. Subsequent to this early differentiation step, distinct progenitor cell populations can be derived, sorted, and utilized for further lineage-specific developmental studies.

Embryonic stem-cell culture as a tool for developmental cell biology

The cell biology of the early processes of mammalian embryogenesis, such as germ-layer formation, has been technically challenging to study owing to the size and accessibility of mammalian embryos. Embryonic stem cells, which can generate the three germ layers in vitro, are useful for studying embryogenesis at the cellular level. So, how can the study of embryonic stem cells and their differentiation provide a deeper understanding of the cell biology of early development?

T-cell potential and development in vitro: the OP9-DL1 approach

In vivo, T cells develop in the thymus from bone marrow-derived hematopoietic progenitors. Similarly, T cells can develop in vitro in model systems that mimic thymic function. The recent development of the OP9-DL1 cell culture system, a two-dimensional T-inductive environment, has provided greater access to the processes of commitment and development in T lymphocytes.

Differential requirements for hematopoietic commitment between human and rhesus embryonic stem cells

Progress toward clinical application of ESC-derived hematopoietic cellular transplantation will require rigorous evaluation in a large animal allogeneic model. However, in contrast to human ESCs (hESCs), efforts to induce conclusive hematopoietic differentiation from rhesus macaque ESCs (rESCs) have been unsuccessful. Characterizing these poorly understood functional differences will facilitate progress in this area and likely clarify the critical steps involved in the hematopoietic differentiation of ESCs. To accomplish this goal, we compared the hematopoietic differentiation of hESCs with that of rESCs in both EB culture and stroma coculture. Initially, undifferentiated rESCs and hESCs were adapted to growth on Matrigel without a change in their phenotype or karyotype. Subsequent differentiation of rESCs in OP9 stroma led to the development of CD34(+)CD45(-) cells that gave rise to endothelial cell networks in methylcellulose culture. In the same conditions, hESCs exhibited convincing hematopoietic differentiation. In cytokine-supplemented EB culture, rESCs demonstrated improved hematopoietic differentiation with higher levels of CD34(+) and detectable levels of CD45(+) cells. However, these levels remained dramatically lower than those for hESCs in identical culture conditions. Subsequent plating of cytokine-supplemented rhesus EBs in methylcellulose culture led to the formation of mixed colonies of erythroid, myeloid, and endothelial cells, confirming the existence of bipotential hematoendothelial progenitors in the cytokine-supplemented EB cultures. Evaluation of four different rESC lines confirmed the validity of these disparities. Although rESCs have the potential for hematopoietic differentiation, they exhibit a pause at the hemangioblast stage of hematopoietic development in culture conditions developed for hESCs.

Characterization of developmental pathway of natural killer cells from embryonic stem cells in vitro

In vitro differentiation of embryonic stem (ES) cells is often used to study hematopoiesis. However, the differentiation pathway of lymphocytes, in particular natural killer (NK) cells, from ES cells is still unclear. Here, we used a multi-step in vitro ES cell differentiation system to study lymphocyte development from ES cells, and to characterize NK developmental intermediates. We generated embryoid bodies (EBs) from ES cells, isolated CD34(+) EB cells and cultured them on OP9 stroma with a cocktail of cytokines to generate cells we termed ES-derived hematopoietic progenitors (ES-HPs). EB cell subsets, as well as ES-HPs derived from EBs, were tested for NK, T, B and myeloid lineage potentials using lineage specific cultures. ES-HPs derived from CD34(+) EBs differentiated into NK cells when cultured on OP9 stroma with IL-2 and IL-15, and into T cells on Delta-like 1-transduced OP9 (OP9-DL1) with IL-7 and Flt3-L. Among CD34(+) EB cells, NK and T cell potentials were detected in a CD45(-) subset, whereas CD45(+) EB cells had myeloid but not lymphoid potentials. Limiting dilution analysis of ES-HPs generated from CD34(+)CD45(-) EB cells showed that CD45(+)Mac-1(-)Ter119(-) ES-HPs are highly enriched for NK progenitors, but they also have T, B and myeloid potentials. We concluded that CD45(-)CD34(+) EB cells have lymphoid potential, and they differentiate into more mature CD45(+)Lin(-) hematopoietic progenitors that have lymphoid and myeloid potential. NK progenitors among ES-HPs are CD122(-) and they rapidly acquire CD122 as they differentiate along the NK lineage.

Generation of immunocompetent T cells from embryonic stem cells

Mature hematopoietic cells, like all other terminally differentiated lineages, arise during ontogeny via a series of increasingly restricted intermediates. Hematopoietic progenitors derive from the mesoderm, which gives rise to hemangioblasts that can differentiate into endothelial or endocardial precursors, or hematopoietic stem cells (HSCs). These HSCs, in turn, may either self-renew or differentiate into lineage-restricted progenitors, and ultimately mature effector cells. The ability to generate most hematopoietic lineages in a two-dimensional in vitro environment has facilitated our study of this complex process. Until recently, T lymphocytes were the exception, and appeared to require the specific three-dimensional microenvironment of the thymus to develop. However, here we describe a protocol for the generation of immunocompetent T lymphocytes from embryonic stem cells (ESCs) in vitro, within the two-dimensional microenvironment provided by OP9 bone marrow stromal cells that have been transduced to express the Notch ligand Delta-like-1. This procedure will facilitate further study of T lymphocytes by providing a model system in which the effects of genetic and environmental manipulations of ESC-derived progenitors can be examined, and the mechanisms of tolerance potentially dissected, in vitro.

Promotion of haematopoietic activity in embryonic stem cells by the aorta-gonad-mesonephros microenvironment

We investigated whether the in vitro differentiation of ES cells into haematopoietic progenitors could be enhanced by exposure to the aorta-gonadal-mesonephros (AGM) microenvironment that is involved in the generation of haematopoietic stem cells (HSC) during embryonic development. We established a co-culture system that combines the requirements for primary organ culture and differentiating ES cells and showed that exposure of differentiating ES cells to the primary AGM region results in a significant increase in the number of ES-derived haematopoietic progenitors. Co-culture of ES cells on the AM20-1B4 stromal cell line derived from the AGM region also increases haematopoietic activity. We conclude that factors promoting the haematopoietic activity of differentiating ES cells present in primary AGM explants are partially retained in the AM20.1B4 stromal cell line and that these factors are likely to be different to those required for adult HSC maintenance.

T lineage differentiation from human embryonic stem cells

Harnessing the ability of genetically manipulated human embryonic stem cells (hESC) to differentiate into appropriate lineages could revolutionize medical practice. These cells have the theoretical potential to develop into all mature cell types; however, the actual ability to develop into all hematopoietic lineages has not been demonstrated. Using sequential in vitro coculture on murine bone marrow stromal cells, and engraftment into human thymic tissues in immunodeficient mice, we demonstrate that hESC can differentiate through the T lymphoid lineage. Stable transgene expression was maintained at high levels throughout differentiation, suggesting that genetically manipulated hESC hold potential to treat several T cell disorders.

Notch Signaling Requires GATA-2 to Inhibit Myelopoiesis from Embryonic Stem Cells and Primary Hemopoietic Progenitors

The bone marrow and thymus, although both hemopoietic environments, induce very distinct differentiation outcomes. The former supports hemopoietic stem cell self-renewal and multiple hemopoietic lineages, while the latter supports T lymphopoiesis almost exclusively. This distinction suggests that the thymic environment acts to restrict the hemopoietic fates available to thymic immigrants. In this study, we demonstrate that the addition of the Notch ligand Delta-like-1 (Dll-1) to an in vitro system that otherwise supports myelopoiesis, greatly reduces the myelopoietic potential of stem cells or uncommitted progenitors. In contrast, committed myeloid progenitors mature regardless of the presence of Dll-1. The block in myelopoiesis is the direct result of Notch signaling within the hemopoietic progenitor, and Dll-1-induced signals cause a rapid increase in the expression of the zinc finger transcription factor GATA-2. Importantly, in the absence of GATA-2, Dll-1-induced signals fail to inhibit commitment to the myeloid fate. Taken together, our results support a role for GATA-2 in allowing Dll-1 to restrict non-T cell lineage differentiation outcomes.

Three-dimensional architecture of the thymus is required to maintain delta-like expression necessary for inducing T cell development

The three-dimensional microarchitecture of the thymus plays a unique role in directing T cell lineage commitment and development. This is supported by the fact that, in contrast to fetal thymic organ cultures, thymic stromal cell monolayer cultures (TSMC) fail to support T lymphopoiesis. Nevertheless, OP9-DL1 cell monolayer cultures induce T lineage commitment and differentiation. Thus, the inability of TSMC to support T lymphopoiesis may be due to a loss of Notch ligand expression and/or function during culture. In this study, we report that, in contrast to fetal thymic organ cultures, TSMC fail to maintain expression of the Notch ligands, Delta-like (Dll) 1 and Dll4, and concomitantly lose the ability to support T lymphopoiesis. Importantly, ectopic re-expression of Dll1 or Dll4 is sufficient to restore the ability of TSMC to support T lymphopoiesis. These findings demonstrate that maintenance of endogenous Dll1 or Dll4 expression by thymic stromal cells is required for the commitment and differentiation of T cells in the absence of a three-dimensional microenvironment.

Hematopoietic Cells

Murine embryonic stem cells (mESC) readily form embryoid bodies (EBs) that exhibit hematopoietic differentiation. Methods based on EB formation or ESC coculture with murine bone marrow stromal cell lines have revealed pathways of both primitive and definitive hematopoietic differentiation progressing from primitive mesoderm via hemangioblasts to endothelium and hematopoietic stem and progenitor cells. The addition of specific hematopoietic growth factors and morphogens to these cultures enhances the generation of neutrophils, macrophages, megakaryocyte/platelets, and hemoglobinized mature red cells. In addition, selective culture systems have been developed to support differentiation into mature T lymphocytes, natural killer cells, B cells, and dendritic cells. In most cases, culture systems have been developed that support equivalent differentiation of various human ESC (hESC). The major obstacle to translation of ESC hematopoietic cultures to clinical relevance has been the general inability to produce hematopoietic stem cells (HSC) that can engraft adult, irradiated recipients. In this context, the pattern of ES hematopoietic development mirrors the yolk sac phase of hematopoiesis that precedes the appearance of engraftable HSC in the aorta-gonad-mesonephros region. Genetic manipulation of mESC hematopoietic progeny by upregulation of HOXB4 or STAT5 has led to greatly enhanced long- or short-term multilineage hematopoietic engraftment, suggesting that genetic or epigenetic manipulation of these pathways may lead to functional HSC generation from hESC.

Propensity of adult lymphoid progenitors to progress to DN2/3 stage thymocytes with Notch receptor ligation

Notch family receptors control critical events in the production and replenishment of specialized cells in the immune system. However, it is unclear whether Notch signaling regulates abrupt binary lineage choices in homogeneous progenitors or has more gradual influence over multiple aspects of the process. A recently developed coculture system with Delta 1-transduced stromal cells is being extensively used to address such fundamental questions. Different from fetal progenitors, multiple types of adult marrow cells expanded indefinitely in murine Delta-like 1-transduced OP9 cell cocultures, progressed to a DN2/DN3 thymocyte stage, and slowly produced TCR(+) and NK cells. Long-term cultured cells of this kind retained some potential for T lymphopoiesis in vivo. Adult marrow progressed through double-positive and single-positive stages only when IL-7 concentrations were low and passages were infrequent. Lin(-)c-Kit(low)GFP(+)IL-7Ralpha(+/-) prolymphocytes were the most efficient of adult bone marrow cells in short-term cultures, but the assay does not necessarily reflect cells normally responsible for replenishing the adult thymus. Although marrow-derived progenitors with Ig D(H)-J(H) rearrangements acquired T lineage characteristics in this model, that was not the case for more B committed cells with V(H)-D(H)J(H) rearrangement products.

Designer blood: creating hematopoietic lineages from embryonic stem cells

Embryonic stem (ES) cells exhibit the remarkable capacity to become virtually any differentiated tissue upon appropriate manipulation in culture, a property that has been beneficial for studies of hematopoiesis. Until recently, the majority of this work used murine ES cells for basic research to elucidate fundamental properties of blood-cell development and establish methods to derive specific mature lineages. Now, the advent of human ES cells sets the stage for more applied pursuits to generate transplantable cells for treating blood disorders. Current efforts are directed toward adapting in vitro hematopoietic differentiation methods developed for murine ES cells to human lines, identifying the key interspecies differences in biologic properties of ES cells, and generating ES cell-derived hematopoietic stem cells that are competent to repopulate adult hosts. The ultimate medical goal is to create patient-specific and generic ES cell lines that can be expanded in vitro, genetically altered, and differentiated into cell types that can be used to treat hematopoietic diseases.

Embryonic stem cells and islet replacement in diabetes mellitus

Transplantation of functional islets of Langerhans may emerge as a useful therapy for some patients with type 1 diabetes mellitus (DM), but donor islet shortages motivate the search for new sources of transplantable islets. Pluripotent embryonic stem (ES) cells are expandable in culture and have the potential to give rise to all cell types in the body. The recent isolation of pluripotent ES cells from humans has generated excitement over the possibility of engineering glucose-responsive islet replacement tissue from these cells in large quantities. In this study, we review the recent advances in generating insulin-producing cells (IPC) from mouse and human ES (hES) cells.

Effect of VEGF on Mouse Thymocyte Proliferation and Apoptosis In Vitro

Vascular endothelial growth factor is not only angiogenic, but also immunoregulatory factor. For evaluation of the possibility of its direct interaction with mouse thymocytes we studied the effect of vascular endothelial growth factor on proliferation and apoptosis of thymocytes and expression of genes for the corresponding receptor on these cells. Vascular endothelial growth factor modulated mitogen-induced proliferation of thymocytes and stimulated spontaneous apoptosis in intact thymus cells. Thymocytes express mRNA of type 2, but not type 1 vascular endothelial growth factor receptors.

The expression and cellular localization of phosphorylated VEGFR2 in lymphoma and non-neoplastic lymphadenopathy: an immunohistochemical study

AIMS

To study the expression of phosphorylated vascular endothelial growth factor receptor 2 (VEGFR2), a membrane-bound tyrosine kinase receptor to vascular endothelial growth factor, in lymphoma and non-neoplastic lymphadenopathy.

METHODS AND RESULTS

Archival cases (89 cases of lymphoma and 17 cases of non-neoplastic lymphadenopathy) were studied immunohistochemically with three monoclonal antibodies to the different autophosphorylation sites in the cytoplasmic tail of the receptor. There was increased expression of this receptor in lymphoma and particularly in all cases of peripheral T-cell lymphoma. In this category, there was nuclear re-location of this receptor.

CONCLUSIONS

This very interesting finding raises the possibility that VEGFR2 may be involved in the transcriptional regulation of this disease. Small molecule inhibitors to this receptor may therefore be a useful adjunct in the therapy of this disease.

The earliest subpopulation of mouse thymocytes contains potent T, significant macrophage, and natural killer cell but no B-lymphocyte potential

The B-lymphocyte potential of progenitor thymocytes and whether the thymus is colonized by common lymphocyte progenitor cells have been subjects of considerable debate. Herein, we have used limiting dilution analysis to determine the lineage potential of phenotypically defined subpopulations of CD4–CD8– double-negative thymocytes. Culture systems used showed single-hit kinetics and had a high plating efficiency for B-, myeloid, and natural killer cell development. The T-cell potential of sorted cells was confirmed by transferring cells to fetal thymus organ cultures. Our results indicate that the earliest population of CD117+ double-negative cells, although containing potent T-cell developmental potential and significant myeloid and natural killer potential, does not have any residual B-cell potential. Gene transcription analysis also indicated that these double-negative cells contained abundant T and myeloid, but not B cell–specific transcripts. The implications of these results within the context of current models of thymocyte development are discussed.

Directed differentiation and mass cultivation of pure erythroid progenitors from mouse embryonic stem cells

Differentiating embryonic stem (ES) cells are an increasingly important source of hematopoietic progenitors, useful for both basic research and clinical applications. Besides their characterization in colony assays, protocols exist for the cultivation of lymphoid, myeloid, and erythroid cells. With the possible exception of mast cells, however, long-term expansion of pure hematopoietic progenitors from ES cells has not been possible without immortalization caused by overexpression of exogenous genes. Here, we describe for the first time an efficient yet easy strategy to generate mass cultures of pure, immature erythroid progenitors from mouse ES cells (ES-EPs), using serum-free medium plus recombinant cytokines and hormones. ES-EPs represent long-lived, adult, definitive erythroid progenitors that resemble immature erythroid cells expanding in vivo during stress erythropoiesis. When exposed to terminal differentiation conditions, ES-EPs differentiated into mature, enucleated erythrocytes. Importantly, ES-EPs injected into mice did not exhibit tumorigenic potential but differentiated into normal erythrocytes. Both the virtually unlimited supply of cells and the defined culture conditions render our system a valuable tool for the analysis of factors influencing proliferation and maturation of erythroid progenitors. In addition, the system allows detailed characterization of processes during erythroid proliferation and differentiation using wild-type (wt) and genetically modified ES cells.

Embryonic stem cells as an alternate marrow donor source: engraftment without graft-versus-host disease

A single embryonic stem cell (ESC) line can be repetitively cryopreserved, thawed, expanded, and differentiated into various cellular components serving as a potentially renewable and well-characterized stem cell source. Therefore, we determined whether ESCs could be used to reconstitute marrow and blood in major histocompatibility complex (MHC)-mismatched mice. To induce differentiation toward hematopoietic stem cells (HSCs) in vitro, ESCs were cultured in methylcellulose with stem cell factor, interleukin (IL)-3, and IL-6. ESC-derived, cytokine-induced HSCs (c-kit⁺/CD45⁺) were isolated by flow cytometry and injected either intra bone marrow or intravenously into lethally irradiated MHC-mismatched recipient mice. From 2 wk to 6 mo after injection, the peripheral blood demonstrated increasing ESC-derived mononuclear cells that included donor-derived T and B lymphocytes, monocytes, and granulocytes without clinical or histologic evidence of graft-versus-host disease (GVHD). Mixed lymphocyte culture assays demonstrated T cell tolerance to both recipient and donor but intact third party proliferative responses and interferon γ production. ESCs might be used as a renewable alternate marrow donor source that reconstitutes hematopoiesis with intact immune responsiveness without GVHD despite crossing MHC barriers.