Short exposure to Notch ligand Delta-4 is sufficient to induce T-cell differentiation program and to increase the T cell potential of primary human CD34+ cells

In Vitro Human Haematopoietic Stem Cell Expansion and Differentiation

The haematopoietic system plays an essential role in our health and survival. It is comprised of a range of mature blood and immune cell types, including oxygen-carrying erythrocytes, platelet-producing megakaryocytes and infection-fighting myeloid and lymphoid cells. Self-renewing multipotent haematopoietic stem cells (HSCs) and a range of intermediate haematopoietic progenitor cell types differentiate into these mature cell types to continuously support haematopoietic system homeostasis throughout life. This process of haematopoiesis is tightly regulated in vivo and primarily takes place in the bone marrow. Over the years, a range of in vitro culture systems have been developed, either to expand haematopoietic stem and progenitor cells or to differentiate them into the various haematopoietic lineages, based on the use of recombinant cytokines, co-culture systems and/or small molecules. These approaches provide important tractable models to study human haematopoiesis in vitro. Additionally, haematopoietic cell culture systems are being developed and clinical tested as a source of cell products for transplantation and transfusion medicine. This review discusses the in vitro culture protocols for human HSC expansion and differentiation, and summarises the key factors involved in these biological processes.

Development of γδ T cells in the thymus - A human perspective

γδ T cells are increasingly emerging as crucial immune regulators that can take on innate and adaptive roles in the defence against pathogens. Although they arise within the thymus from the same hematopoietic precursors as conventional αβ T cells, the development of γδ T cells is less well understood. In this review, we focus on summarising the current state of knowledge about the cellular and molecular processes involved in the generation of γδ T cells in human.

Baboon envelope LVs efficiently transduced human adult, fetal, and progenitor T cells and corrected SCID-X1 T-cell deficiency

T cells represent a valuable tool for treating cancers and infectious and inherited diseases; however, they are mainly short-lived in vivo. T-cell therapies would strongly benefit from gene transfer into long-lived persisting naive T cells or T-cell progenitors. Here we demonstrate that baboon envelope glycoprotein pseudotyped lentiviral vectors (BaEV-LVs) far outperformed other LV pseudotypes for transduction of naive adult and fetal interleukin-7-stimulated T cells. Remarkably, BaEV-LVs efficiently transduced thymocytes and T-cell progenitors generated by culture of CD34⁺ cells on Delta-like ligand 4 (Dll4). Upon NOD/SCIDγC^-/- engraftment, high transduction levels (80%-90%) were maintained in all T-cell subpopulations. Moreover, T-cell lineage reconstitution was accelerated in NOD/SCIDγC^-/- recipients after T-cell progenitor injection compared with hematopoietic stem cell transplantation. Furthermore, γC-encoding BaEV-LVs very efficiently transduced Dll4-generated T-cell precursors from a patient with X-linked severe combined immunodeficiency (SCID-X1), which fully rescued T-cell development in vitro. These results indicate that BaEV-LVs are valuable tools for the genetic modification of naive T cells, which are important targets for gene therapy. Moreover, they allowed for the generation of gene-corrected T-cell progenitors that rescued SCID-X1 T-cell development in vitro. Ultimately, the coinjection of LV-corrected T-cell progenitors and hematopoietic stem cells might accelerate T-cell reconstitution in immunodeficient patients.

Metcalf Lecture Award: Applying niche biology to engineer T-cell regenerative therapies

The processes generating cells of adaptive immunity render them less amenable to the single cytokine signals used so effectively to regenerate myeloid cells. T-cell neogenesis begins in the bone marrow, where specific sets of late osteolineage cells govern the specification of hematopoietic cells capable of migrating to the thymus where differentiation is completed. Osteocalcin-expressing bone marrow stromal cells producing Dll4 serve as a progenitor niche enabling this T-competent cell production. Biocompatible alginate-based cryogels containing bone morphogenetic proteins (BMP-2) and the Notch ligand Dll4 were engineered to recapitulate the endogenous niche. These cryogels are highly pliable and can be injected under the skin of animals undergoing bone marrow transplantation. The result in mice is an ectopic niche fostering T-competent progenitor generation that results in improved T-cell numbers and receptor diversity. The recipients can generate neoantigen vaccine responses while having improved tolerance manifest by reduced graft-versus-host disease upon allogeneic transplant. Through emerging details of niches in the bone marrow, therapeutics more complex than those necessary for myeloid reconstitution are possible. Niche biology-guided bioengineered design offers the possibility of regenerative therapies for T lymphoid cells.

A Notch positive feedback in the intestinal stem cell niche is essential for stem cell self-renewal

The intestinal epithelium is the fastest regenerative tissue in the body, fueled by fast‐cycling stem cells. The number and identity of these dividing and migrating stem cells are maintained by a mosaic pattern at the base of the crypt. How the underlying regulatory scheme manages this dynamic stem cell niche is not entirely clear. We stimulated intestinal organoids with Notch ligands and inhibitors and discovered that intestinal stem cells employ a positive feedback mechanism via direct Notch binding to the second intron of the Notch1 gene. Inactivation of the positive feedback by CRISPR/Cas9 mutation of the binding sequence alters the mosaic stem cell niche pattern and hinders regeneration in organoids. Dynamical system analysis and agent‐based multiscale stochastic modeling suggest that the positive feedback enhances the robustness of Notch‐mediated niche patterning. This study highlights the importance of feedback mechanisms in spatiotemporal control of the stem cell niche.

P2X7 Receptor Inhibition Improves CD34 T-Cell Differentiation in HIV-Infected Immunological Nonresponders on c-ART

Peripheral CD4+ T-cell levels are not fully restored in a significant proportion of HIV+ individuals displaying long-term viral suppression on c-ART. These immunological nonresponders (INRs) have a higher risk of developing AIDS and non-AIDS events and a lower life expectancy than the general population, but the underlying mechanisms are not fully understood. We used an in vitro system to analyze the T- and B-cell potential of CD34+ hematopoietic progenitor cells. Comparisons of INRs with matched HIV+ patients with high CD4+ T-cell counts (immune responders (IRs)) revealed an impairment of the generation of T-cell progenitors, but not of B-cell progenitors, in INRs. This impairment resulted in the presence of smaller numbers of recent thymic emigrants (RTE) in the blood and lower peripheral CD4+ T-cell counts. We investigated the molecular pathways involved in lymphopoiesis, focusing particularly on T-cell fate specification (Notch pathway), survival (IL7R-IL7 axis) and death (Fas, P2X7, CD39/CD73). P2X7 expression was abnormally strong and there was no CD73 mRNA in the CD34+ cells of INRs, highlighting a role for the ATP pathway. This was confirmed by the demonstration that in vitro inhibition of the P2X7-mediated pathway restored the T-cell potential of CD34+ cells from INRs. Moreover, transcriptomic analysis revealed major differences in cell survival and death pathways between CD34+ cells from INRs and those from IRs. These findings pave the way for the use of complementary immunotherapies, such as P2X7 antagonists, to restore T-cell lymphopoiesis in INRs.

Pleiotropic roles of Notch signaling in normal, malignant, and developmental hematopoiesis in the human

The Notch signaling pathway is evolutionarily conserved across species and plays an important role in regulating cell differentiation, proliferation, and survival. It has been implicated in several different hematopoietic processes including early hematopoietic development as well as adult hematological malignancies in humans. This review focuses on recent developments in understanding the role of Notch signaling in the human hematopoietic system with an emphasis on hematopoietic initiation from human pluripotent stem cells and regulation within the bone marrow. Based on recent insights, we summarize potential strategies for treatment of human hematological malignancies toward the concept of targeting Notch signaling for fate regulation.

Technical advance: ascorbic acid induces development of double-positive T cells from human hematopoietic stem cells in the absence of stromal cells

The efficacy of donor HSCT is partly reduced as a result of slow post-transplantation immune recovery. In particular, T cell regeneration is generally delayed, resulting in high infection-related mortality in the first years post-transplantation. Adoptive transfer of in vitro-generated human T cell progenitors seems a promising approach to accelerate T cell recovery in immunocompromised patients. AA may enhance T cell proliferation and differentiation in a controlled, feeder-free environment containing Notch ligands and defined growth factors. Our experiments show a pivotal role for AA during human in vitro T cell development. The blocking of NOS diminished this effect, indicating a role for the citrulline/NO cycle. AA promotes the transition of proT1 to proT2 cells and of preT to DP T cells. Furthermore, the addition of AA to feeder cocultures resulted in development of DP and SP T cells, whereas without AA, a preT cell-stage arrest occurred. We conclude that neither DLL4-expressing feeder cells nor feeder cell conditioned media are required for generating DP T cells from CB and G-CSF-mobilized HSCs and that generation and proliferation of proT and DP T cells are greatly improved by AA. This technology could potentially be used to generate T cell progenitors for adoptive therapy.

T Cells Development Is Different between Thymus from Normal and Intrauterine Growth Restricted Pig Fetus at Different Gestational Stage

This experiment was conducted to evaluate the development of T cells in intrauterine growth retarded (IUGR) piglets at different gestational stages, and tentatively explore the relationship between T cells development and the Notch signaling pathway. A total of 18 crossbred (Landrace×Large white) primiparous sows were mated at similar weights and estruses and euthanized at d 60, 90 and 110 of gestation with six replicates for each time point. One IUGR and one normal fetus were picked from each litter. The T-cell subsets, mRNA expression of Delta-like1, Delta-like4, Jagged1, and Notch2 genes in the thymus were investigated. Compared to normal piglets, CD3⁺CD4⁻CD8⁺ cells in IUGR fetuses at d 90 was 0.13% lower (p<0.05). At d 110 of gestation CD8⁺ T cells in IUGR fetuses was 0.19% lower (p<0.05). The percentage of CD8⁺ T cells was 3.14% lower (p<0.05) of the total T cells in IUGR pigs at d 60. The abundance of Notch2 and Delta-like4 mRNA at d 110 was 20.93% higher and 0.77% (p<0.05) lower, and Delta-like1 mRNA at d 90 was 0.19% (p<0.05) higher compared to normal pigs. These results suggested that normal fetuses had a greater proportion of T-cell subsets at earlier gestation periods, and the Notch signaling pathway was likely partially responsible for these differences to some degree.

Human T-lymphoid progenitors generated in a feeder-cell-free Delta-like-4 culture system promote T-cell reconstitution in NOD/SCID/γc(-/-) mice

Slow T-cell reconstitution is a major clinical concern after transplantation of cord blood (CB)-derived hematopoietic stem cells. Adoptive transfer of in vitro-generated T-cell progenitors has emerged as a promising strategy for promoting de novo thymopoiesis and thus accelerating T-cell reconstitution. Here, we describe the development of a new culture system based on the immobilized Notch ligand Delta-like-4 (DL-4). Culture of human CD34⁺ CB cells in this new DL-4 system enabled the in vitro generation of large amounts of T-cell progenitor cells that (a) displayed the phenotypic and molecular signatures of early thymic progenitors and (b) had high T lymphopoietic potential. When transferred into NOD/SCID/γc^−/− (NSG) mice, DL-4 primed T-cell progenitors migrated to the thymus and developed into functional, mature, polyclonal αβ T cells that subsequently left the thymus and accelerated T-cell reconstitution. T-cell reconstitution was even faster and more robust when ex vivo-manipulated and nonmanipulated CB samples were simultaneously injected into NSG mice (i.e., a situation reminiscent of the double CB transplant setting). This work provides further evidence of the ability of in vitro-generated human T-cell progenitors to accelerate T-cell reconstitution and also introduces a feeder-cell-free culture technique with the potential for rapid, safe transfer to a clinical setting.

Manipulation of human early T lymphopoiesis by coculture on human bone marrow stromal cells: potential utility for adoptive immunotherapy

T cell precursors are an attractive target for adoptive immunotherapy. We examined the regulation of human early T lymphopoiesis by human bone marrow stromal cells to explore in vitro manipulation of human T cell precursors in a human-only coculture system. The generation of CD7(+)CD56(-)cyCD3(-) proT cells from human hematopoietic progenitors on telomerized human bone marrow stromal cells was enhanced by stem cell factor, flt3 ligand, and thrombopoietin, but these stimulatory effects were suppressed by interleukin 3. Expression of Notch ligands Delta-1 and -4 on stromal cells additively promoted T cell differentiation into the CD7(+)cyCD3(+) pre-T cell stage, while cell growth was strongly inhibited. By combining these coculture systems, we found that initial coculture with telomerized stromal cells in the presence of stem cell factor, flt3 ligand, and thrombopoietin, followed by coculture on Delta-1- and -4-coexpressing stromal cells led to a higher percentage and number of pre-T cells. Adoptive immunotherapy using peripheral blood T cells transduced with a tumor antigen-specific T cell receptor (TCR) is a promising strategy but has several limitations, such as the risk of forming a chimeric TCR with the endogenous TCR. We demonstrated that incubation of TCR-transduced hematopoietic progenitors with the combination of coculture systems gave rise to CD7(+)TCR(+)CD3(+)CD1a(-) T cell precursors that rapidly proliferated and differentiated under the culture condition to induce mature T cell differentiation. These data show the regulatory mechanism of early T lymphopoiesis on human stromal cells and the potential utility of engineered human stromal cells to manipulate early T cell development for clinical application.

Notch activation on effector T cells increases their sensitivity to Treg cell-mediated suppression through upregulation of TGF-βRII expression

Notch proteins play an important role in embryonic development and cell-fate decisions. Notch influences also the activation and differentiation of peripheral T cells. Here, we investigated whether Notch signaling modulates the response of effector T cells to regulatory T (Treg) cells. Pre-exposure of CD4(+) CD25(-) effector T cells to the Notch ligands Delta-4 and Jagged-1, but not Delta-1, increases significantly effector T-cell sensitivity to Treg cell-mediated suppression through upregulation of TGF-βRII expression and increased levels of the phosphorylated form of the Smad 3 protein. This effect is relieved by anti-TGF-β Abs. We demonstrate that HES (hairy and enhancer of split), the main transcription factor downstream of Notch, induces strong transactivation of TGF-ßRII by binding the TGF-βRII promoter through its DNA-binding domain. Thus, the crosstalk between Notch and the TGF-β pathway leads to potentiation of the suppressive effect of Treg cells.

Notch signaling during human T cell development

Notch signaling is critical during multiple stages of T cell development in both mouse and human. Evidence has emerged in recent years that this pathway might regulate T-lineage differentiation differently between both species. Here, we review our current understanding of how Notch signaling is activated and used during human T cell development. First, we set the stage by describing the developmental steps that make up human T cell development before describing the expression profiles of Notch receptors, ligands, and target genes during this process. To delineate stage-specific roles for Notch signaling during human T cell development, we subsequently try to interpret the functional Notch studies that have been performed in light of these expression profiles and compare this to its suggested role in the mouse.

Advances in adoptive immunotherapy to accelerate T-cellular immune reconstitution after HLA-incompatible hematopoietic stem cell transplantation

Although partially HLA-mismatched hematopoietic stem cell transplantation (HSCT) has become an important therapeutic option for children with primary immunodeficiencies, delayed reconstitution of the T-cell compartment remains a major clinical concern. Adoptive immunotherapies to provide recipients with a protective and diverse T-cell repertoire in the months following HSCT are warranted. In order to improve T-cell reconstitution after T-cell-depleted HSCT, different strategies are currently being studied. Some are based on administration of modified mature T cells (e.g., allodepleted T cells or pathogen-specific T cells). Others aim at accelerating de novo thymopoiesis from donor-derived hematopoietic stem cells in vivo via the administration of thymopoietic agents or the transfer of large numbers of T-cell precursors generated ex vivo. The present article will provide a brief summary of recent advances in the field of allodepletion and adoptive transfer of pathogen-specific T cells and a detailed discussion of strategies for enhancing thymopoiesis in vivo.

Induction of notch signaling by immobilization of jagged-1 on self-assembled monolayers

Notch signaling is a key mechanism during mammal development and stem cell regulation. This study aims to target and control Notch signaling by ligands immobilization using self-assembled monolayers (SAMs) as model surfaces. Non-fouling substrates were prepared by immersion of gold substrates in (1-Mercapto-11-undecyl)tetra(ethylene glycol) thiol solutions. These surfaces were activated with N,N'-carbonyldiimidazole (CDI) at different concentrations (0, 0.03, 0.3, 3 and 30 mg/ml) and an anti-human IgG, Fc specific fragment antibody (Ab) was covalently bound to EG4-SAMs to guarantee the correct exposure of the Notch ligand Jagged-1/Fc chimera (Jag-1). The presence of Ab and Jag-1 was confirmed by radiolabeling, X-ray photoelectron spectroscopy (XPS), ellipsometry and ELISA. The biological activity of Jag-1-Ab-SAMs was assessed by real-time PCR for Hes-1 family gene expression, a Notch pathway target gene, in HL-60 cell line. Results have shown an increase of the amount of immobilized Ab with increasing surface activator concentrations. Jag-1 concentration also increases with Ab concentration. Interestingly, a higher Jagged-1 exposure and fold increase in Hes-1 expression were obtained for surfaces activated with the lowest concentration of CDI (0.03 mg/ml). These results illustrate the great importance of ligands orientation and exposure, when compared with density. This investigation brings new insights into Notch signaling mechanisms. In particular, Jag-1-Ab-SAMs have shown to be adequate model surfaces to study Notch pathway activation and may provide a basis to develop new interfaces in biomaterials to control Notch mechanism in different cell systems.

Immune reconstitution after haematopoietic stem cell transplantation: obstacles and anticipated progress

Improvement of immune reconstitution after haematopoietic stem cell transplantation (HSCT) is a key issue determining the clinical outcome of this widely used therapeutic approach. To this end, new strategies have been prompted by recent discoveries in immunology. In the setting of human leukocyte antigen (HLA) geno(pheno)identical HSCT, better prevention and treatment of acute and chronic graft-versus-host disease (GvHD) could significantly attenuate the thymic epithelium damage responsible for delayed and incomplete T-cell reconstitution. In a haploidentical setting, methods that would significantly accelerate neothymopoiesis in the months following injection of highly purified CD34+ cells are warranted. If these objectives could be achieved, the haploidentical procedure would become more readily available to patients affected by acquired or inherited disorders of the haematopoietic system.

Shortening the immunodeficient period after hematopoietic stem cell transplantation

The delayed reconstitution of the T-lymphoid compartment represents a major clinical challenge after HLA-mismatched hematopoietic stem cell transplantation. The generation of new T lymphocytes deriving from transplanted hematopoietic stem cells requires several months, a period associated with an increased risk of opportunistic infections and relapses. Recently, the early steps of human lymphopoiesis and the nature of the thymus-seeding progenitors were described. Moreover several scientific groups succeeded to generate T-cell precursors from murine and human hematopoietic stem cells in vitro by transitory exposition to Notch-ligands. Here we summarize and discuss these results and their possible usage in the development of new cell therapies to shorten the immunodeficient period following hematopoietic stem cell transplantation.

Notch ligands potentiate IL-7-driven proliferation and survival of human thymocyte precursors

Notch and IL-7 are both well-characterized factors involved in T-cell development. In contrast to the mouse model, their precise requirements in the differentiation and/or proliferation of various stages of human thymic development have not been fully explored. Here, we demonstrate that IL-7 alone is sufficient to induce the differentiation of ex vivo purified CD34(+) triple negative (TN) surface (s) CD3(-) CD4(-)CD8(-) (CD3(-)CD4(-)CD8(-)), CD4 immature single positive (ISP) (sCD3(-)CD4(+)CD8(-)) and double positive (DP) (sCD3(-)CD4(+)CD8(+)) human thymic precursors to mature DP expressing sCD3 (sCD3(+)CD4(+)CD8(+)). We show that activation of Notch signaling by its ligands Delta-1 or Delta-4 potentiates IL-7-driven proliferation and survival of CD34(+) TN and to a lesser extent of CD4(+) ISP precursors. This effect of Notch is related to a sustained induction of IL-7 receptor alpha chain expression on thymocytes through a decreased methylation of its gene promoter. Thus, we show here that proliferation and differentiation of T-cell precursors are differentially modulated by IL-7 depending on the presence or absence of external signals. These results may have important implications for the clinical use of this cytokine as a strategy aimed at improving immune restoration.

Computational models of the Notch network elucidate mechanisms of context-dependent signaling

The Notch signaling pathway controls numerous cell fate decisions during development and adulthood through diverse mechanisms. Thus, whereas it functions as an oscillator during somitogenesis, it can mediate an all-or-none cell fate switch to influence pattern formation in various tissues during development. Furthermore, while in some contexts continuous Notch signaling is required, in others a transient Notch signal is sufficient to influence cell fate decisions. However, the signaling mechanisms that underlie these diverse behaviors in different cellular contexts have not been understood. Notch1 along with two downstream transcription factors hes1 and RBP-Jk forms an intricate network of positive and negative feedback loops, and we have implemented a systems biology approach to computationally study this gene regulation network. Our results indicate that the system exhibits bistability and is capable of switching states at a critical level of Notch signaling initiated by its ligand Delta in a particular range of parameter values. In this mode, transient activation of Delta is also capable of inducing prolonged high expression of Hes1, mimicking the “ON” state depending on the intensity and duration of the signal. Furthermore, this system is highly sensitive to certain model parameters and can transition from functioning as a bistable switch to an oscillator by tuning a single parameter value. This parameter, the transcriptional repression constant of hes1, can thus qualitatively govern the behavior of the signaling network. In addition, we find that the system is able to dampen and reduce the effects of biological noise that arise from stochastic effects in gene expression for systems that respond quickly to Notch signaling.

This work thus helps our understanding of an important cell fate control system and begins to elucidate how this context dependent signaling system can be modulated in different cellular settings to exhibit entirely different behaviors.

The Notch signaling pathway is an evolutionarily conserved signaling system that is involved in various cell fate decisions, both during development of an organism and during adulthood. While the same core circuit functions in various different cellular contexts, it has experimentally been shown to elicit varied behaviors and responses. On the one hand, it functions as a cellular oscillator critical for somitogenesis, whereas in other situations, it can function as a cell fate switch to pattern developing tissue, for example in the Drosophila eye. Furthermore, malfunctioning of Notch signaling is implicated in various cancers. To better understand the underlying mechanisms that allow the network to function distinctly in different contexts, we have mathematically modeled the behavior of the Notch network, encompassing the Notch gene along with two of its downstream effector transcription factors, which together form a network of positive and negative feedback loops. Our results indicate that the qualitative and quantitative behavior of the system can readily be tuned based on key parameters to reflect its multiple roles. Furthermore, our results provide insights into alterations in the signaling system that lead to malfunction and hence disease, which could be used to identify potential drug targets for therapy.

HIV-1 Nef protein expression in human CD34+ progenitors impairs the differentiation of an early T/NK cell precursor

HIV-1 impairs the production of T cells, through mechanisms that are still unknown. Here, we investigated the effect of the expression of HIV-1 Nef on the T-cell potential of human hematopoietic CD34(+) precursors. Those progenitors were transduced by using lentiviral vectors expressing Nef and cultured on OP9-DL1 cells allowing the differentiation of T cell from human hematopoietic precursors. We demonstrate that Nef impairs the generation of a CD3epsilon(+)CD5(+) CD1a(+) precursor stage that has initiated a D-J rearrangement of the TCRbeta locus. Onward stages of T-cell development were also affected with a quantitative reduction of CD4(+) intraCD3epsilon(+) Immature single positive cells (ISP), Double Positive (DP) CD4(+)CD8(+) TCRalphabeta T cells and CD56(+) NK cells. But B cell production was not affected. Limiting dilution analyses demonstrated a significant reduction in the frequency of T/NK progenitors among Nef-expressing CD34(+) cells. Altogether, these data demonstrate that Nef interferes with the differentiation of a primitive lymphoid human precursor with a T/NK potential.

Launching the T-cell-lineage developmental programme

Multipotent blood progenitor cells enter the thymus and begin a protracted differentiation process in which they gradually acquire T-cell characteristics while shedding their legacy of developmental plasticity. Notch signalling and basic helix-loop-helix E-protein transcription factors collaborate repeatedly to trigger and sustain this process throughout the period leading up to T-cell lineage commitment. Nevertheless, the process is discontinuous with separately regulated steps that demand roles for additional collaborating factors. This Review discusses new evidence on the coordination of specification and commitment in the early T-cell pathway; effects of microenvironmental signals; the inheritance of stem-cell regulatory factors; and the ensemble of transcription factors that modulate the effects of Notch and E proteins, to distinguish individual stages and to polarize T-cell-lineage fate determination.

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.