Human T, B, natural killer, and dendritic cells arise from a common bone marrow progenitor cell subset

A single cell framework identifies functionally and molecularly distinct multipotent progenitors in adult human hematopoiesis

Hematopoietic multipotent progenitors (MPPs) regulate blood cell production to appropriately meet the biological demands of the human body. Human MPPs remain ill-defined whereas mouse MPPs have been well characterized with distinct immunophenotypes and lineage potencies. Using multiomic single cell analyses and complementary functional assays, we identified new human MPPs and oligopotent progenitor populations within Lin-CD34+CD38dim/lo adult bone marrow with distinct biomolecular and functional properties. These populations were prospectively isolated based on expression of CD69, CLL1, and CD2 in addition to classical markers like CD90 and CD45RA. We show that within the canonical Lin-CD34+CD38dim/loCD90CD45RA-MPP population, there is a CD69+ MPP with long-term engraftment and multilineage differentiation potential, a CLL1+ myeloid-biased MPP, and a CLL1-CD69-erythroid-biased MPP. We also show that the canonical Lin-CD34+CD38dim/loCD90-CD45RA+ LMPP population can be separated into a CD2+ LMPP with lymphoid and myeloid potential, a CD2-LMPP with high lymphoid potential, and a CLL1+ GMP with minimal lymphoid potential. We used these new HSPC profiles to study human and mouse bone marrow cells and observe limited cell type specific homology between humans and mice and cell type specific changes associated with aging. By identifying and functionally characterizing new adult MPP sub-populations, we provide an updated reference and framework for future studies in human hematopoiesis.

Preclinical characterization of a novel investigational monoclonal antibody CM313 with potent CD38-positive cell killing activity

Introduction

CM313 is currently under clinical investigation for treatments of multiple myeloma, systemic lupus erythematosus, and immune thrombocytopenia. We aimed to report the preclinical profile of the novel therapeutic anti-CD38 monoclonal antibody (mAb) CM313, with an emphasis on the difference with other CD38-targeting mAb.

Methods

The binding of CM313 to CD38 recombinant protein across species was assessed using ELISA. The binding of CM313 to CD38-positive (CD38+) cells was detected using flow cytometry assays. CM313-induced complement-dependent cytotoxicity (CDC), antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP) and apoptosis on different CD38+ cells were assessed by LDH release assays or flow cytometry assays. The effect of CM313 on CD38 enzymatic activity was measured using fluorescence spectroscopy. CM313 immunotoxicity in human blood was assessed using flow cytometry assays, ELISA, and LDH release assays. Anti-tumor activity of CM313 was assessed in multiple mouse xenograft models. Safety profile of CM313 were evaluated in cynomolgus monkeys and human CD38 transgenic (B-hCD38) mice.

Results

There exist unique sequences at complementarity-determining regions (CDR) of CM313, which facilitates its affinity to CD38 is consistently higher across a spectrum of CD38+ cell lines than daratumumab. In vitro studies showed that CM313 induces comparable killing activity than daratumumab, including ADCC, CDC, ADCP, apoptosis induced by Fc-mediated cross-linking, and effectively inhibited the enzymatic activity of CD38. However, CM313 showed more potent CDC than isatuximab. In vivo, CM313 dose-dependently inhibited xenograft tumor growth, both as a monotherapy and in combination with dexamethasone or lenalidomide. Furthermore, CM313 was well tolerated with no drug-related clinical signs or off-target risks, as evidenced by 4-week repeat-dose toxicology studies in cynomolgus monkeys and B-hCD38 mice, with the later study showing no observed adverse effect level (NOAEL) of 300mg/kg once weekly.

Discussion

CM313 is a novel investigational humanized mAb with a distinct CDR sequence, showing comparable killing effects with daratumumab and stronger CDC activity than isatuximab, which supports its clinical development.

Generation of complex bone marrow organoids from human induced pluripotent stem cells

The human bone marrow (BM) niche sustains hematopoiesis throughout life. We present a method for generating complex BM-like organoids (BMOs) from human induced pluripotent stem cells (iPSCs). BMOs consist of key cell types that self-organize into spatially defined three-dimensional structures mimicking cellular, structural and molecular characteristics of the hematopoietic microenvironment. Functional properties of BMOs include the presence of an in vivo-like vascular network, the presence of multipotent mesenchymal stem/progenitor cells, the support of neutrophil differentiation and responsiveness to inflammatory stimuli. Single-cell RNA sequencing revealed a heterocellular composition including the presence of a hematopoietic stem/progenitor (HSPC) cluster expressing genes of fetal HSCs. BMO-derived HSPCs also exhibited lymphoid potential and a subset demonstrated transient engraftment potential upon xenotransplantation in mice. We show that the BMOs could enable the modeling of hematopoietic developmental aspects and inborn errors of hematopoiesis, as shown for human VPS45 deficiency. Thus, iPSC-derived BMOs serve as a physiologically relevant in vitro model of the human BM microenvironment to study hematopoietic development and BM diseases.

Marmosets as models of infectious diseases

Animal models of infectious disease often serve a crucial purpose in obtaining licensure of therapeutics and medical countermeasures, particularly in situations where human trials are not feasible, i.e., for those diseases that occur infrequently in the human population. The common marmoset (Callithrix jacchus), a Neotropical new-world (platyrrhines) non-human primate, has gained increasing attention as an animal model for a number of diseases given its small size, availability and evolutionary proximity to humans. This review aims to (i) discuss the pros and cons of the common marmoset as an animal model by providing a brief snapshot of how marmosets are currently utilized in biomedical research, (ii) summarize and evaluate relevant aspects of the marmoset immune system to the study of infectious diseases, (iii) provide a historical backdrop, outlining the significance of infectious diseases and the importance of developing reliable animal models to test novel therapeutics, and (iv) provide a summary of infectious diseases for which a marmoset model exists, followed by an in-depth discussion of the marmoset models of two studied bacterial infectious diseases (tularemia and melioidosis) and one viral infectious disease (viral hepatitis C).

Deciphering the localization and trajectory of human natural killer cell development

Innate immune cells represent the first line of cellular immunity, comprised of both circulating and tissue-resident natural killer cells and innate lymphoid cells. These innate lymphocytes arise from a common CD34+ progenitor that differentiates into mature natural killer cells and innate lymphoid cells. The successive stages in natural killer cell maturation are characterized by increased lineage restriction and changes to phenotype and function. Mechanisms of human natural killer cell development have not been fully elucidated, especially the role of signals that drive the spatial localization and maturation of natural killer cells. Cytokines, extracellular matrix components, and chemokines provide maturation signals and influence the trafficking of natural killer cell progenitors to peripheral sites of differentiation. Here we present the latest advances in our understanding of natural killer and innate lymphoid cell development in peripheral sites, including secondary lymphoid tissues (i.e. tonsil). Recent work in the field has provided a model for the spatial distribution of natural killer cell and innate lymphoid cell developmental intermediates in tissue and generated further insights into the developmental niche. In support of this model, future studies using multifaceted approaches seek to fully map the developmental trajectory of human natural killer cells and innate lymphoid cells in secondary lymphoid tissues.

Multimodal cartography of human lymphopoiesis reveals B and T/NK/ILC lineages are subjected to differential regulation

The developmental cartography of human lymphopoiesis remains incompletely understood. Here, we establish a multimodal map demonstrating that lymphoid specification follows independent direct or stepwise hierarchic routes converging toward the emergence of newly characterized CD117lo multi-lymphoid progenitors (MLPs) that undergo a proliferation arrest before entering the CD127- (NK/ILC/T) or CD127+ (B) lymphoid pathways. While the differentiation of CD127- early lymphoid progenitors is mainly driven by Flt3 signaling, emergence of their CD127+ counterparts is regulated cell-intrinsically and depends exclusively on the divisional history of their upstream precursors, including hematopoietic stem cells. Further, transcriptional mapping of differentiation trajectories reveals that whereas myeloid granulomonocytic lineages follow continuous differentiation pathways, lymphoid trajectories are intrinsically discontinuous and characterized by sequential waves of cell proliferation allowing pre-commitment amplification of lymphoid progenitor pools. Besides identifying new lymphoid specification pathways and regulatory checkpoints, our results demonstrate that NK/ILC/T and B lineages are under fundamentally distinct modes of regulation. (149 words).

Single-cell multiomics of human fetal hematopoiesis define a developmental-specific population and a fetal signature

Knowledge of human fetal blood development and how it differs from adult blood is highly relevant to our understanding of congenital blood and immune disorders and childhood leukemia, of which the latter can originate in utero. Blood formation occurs in waves that overlap in time and space, adding to heterogeneity, which necessitates single-cell approaches. Here, a combined single-cell immunophenotypic and transcriptional map of first trimester primitive blood development is presented. Using CITE-seq (cellular indexing of transcriptomes and epitopes by sequencing), the molecular profile of established immunophenotype-gated progenitors was analyzed in the fetal liver (FL). Classical markers for hematopoietic stem cells (HSCs), such as CD90 and CD49F, were largely preserved, whereas CD135 (FLT3) and CD123 (IL3R) had a ubiquitous expression pattern capturing heterogenous populations. Direct molecular comparison with an adult bone marrow data set revealed that the HSC state was less frequent in FL, whereas cells with a lymphomyeloid signature were more abundant. An erythromyeloid-primed multipotent progenitor cluster was identified, potentially representing a transient, fetal-specific population. Furthermore, differentially expressed genes between fetal and adult counterparts were specifically analyzed, and a fetal core signature was identified. The core gene set could separate subgroups of acute lymphoblastic leukemia by age, suggesting that a fetal program may be partially retained in specific subgroups of pediatric leukemia. Our detailed single-cell map presented herein emphasizes molecular and immunophenotypic differences between fetal and adult blood cells, which are of significance for future studies of pediatric leukemia and blood development in general.

Distinct subsets of multi-lymphoid progenitors support ontogeny-related changes in human lymphopoiesis

Changes in lymphocyte production patterns occurring across human ontogeny remain poorly defined. In this study, we demonstrate that human lymphopoiesis is supported by three waves of embryonic, fetal, and postnatal multi-lymphoid progenitors (MLPs) differing in CD7 and CD10 expression and their output of CD127-/+ early lymphoid progenitors (ELPs). In addition, our results reveal that, like the fetal-to-adult switch in erythropoiesis, transition to postnatal life coincides with a shift from multilineage to B lineage-biased lymphopoiesis and an increase in production of CD127+ ELPs, which persists until puberty. A further developmental transition is observed in elderly individuals whereby B cell differentiation bypasses the CD127+ compartment and branches directly from CD10+ MLPs. Functional analyses indicate that these changes are determined at the level of hematopoietic stem cells. These findings provide insights for understanding identity and function of human MLPs and the establishment and maintenance of adaptative immunity.

Dynamics of Human Hematopoietic Stem and Progenitor Cell Differentiation to the Erythroid Lineage

Erythropoiesis, the development of erythrocytes from hematopoietic stem cells, occurs through four phases: erythroid progenitor development, early erythropoiesis, terminal erythroid differentiation (TED), and maturation. According to the classical model that is based on immunophenotypic profiles of cell populations, each of these phases comprises multiple differentiation states that arise in a hierarchical manner. After segregation of lymphoid potential, erythroid priming begins during progenitor development and progresses through progenitor cell types that have multilineage potential. Complete separation of the erythroid lineage is achieved during early erythropoiesis with the formation of unipotent erythroid progenitors: burst forming unit-erythroid and colony forming unit-erythroid. These erythroid committed progenitors undergo TED and maturation, which involves expulsion of the nucleus and remodeling to form functional biconcave, hemoglobin-filled erythrocytes. In the last decade or so, many studies employing advanced techniques such as single cell RNA-sequencing (scRNA-seq) as well as the conventional methods, including colony forming cell assays and immunophenotyping, have revealed heterogeneity within the stem, progenitor, and erythroblast stages, and uncovered alternate paths for segregation of erythroid lineage potential. In this review, we provide an in-depth account of immunophenotypic profiles of all cell types within erythropoiesis, highlight studies that demonstrate heterogeneous erythroid stages, and describe deviations to the classical model of erythropoiesis. Overall, although scRNA-seq approaches have provided new insights, flow cytometry remains relevant and is the primary method for validation of novel immunophenotypes.

Natural killer cells and type 1 innate lymphoid cells in cancer

Innate lymphoid cells (ILCs) are a group of innate lymphocytes that do not express RAG-dependent rearranged antigen-specific cell surface receptors. ILCs are classified into five groups according to their developmental trajectory and cytokine production profile. They encompass NK cells, which are cytotoxic, helper-like ILCs 1-3, which functionally mirror CD4⁺ T helper (Th) type 1, Th2 and Th17 cells respectively, and lymphoid tissue inducer (LTi) cells. NK cell development depends on Eomes (eomesodermin), whereas the ILC1 program is regulated principally by the transcription factor T-bet (T-box transcription factor Tbx21), that of ILC2 is regulated by GATA3 (GATA-binding protein 3) and that of ILC3 is regulated by RORγt (RAR-related orphan receptor γ). NK cells were discovered close to fifty years ago, but ILC1s were first described only about fifteen years ago. Within the ILC family, NK and ILC1s share many similarities, as witnessed by their cell surface phenotype which largely overlap. NK cells and ILC1s have been reported to respond to tissue inflammation and intracellular pathogens. Several studies have reported an antitumorigenic role for NK cells in both humans and mice, but data for ILC1s are both scarce and contradictory. In this review, we will first describe the different NK cell and ILC1 subsets, their effector functions and development. We will then discuss their role in cancer and the effects of the tumor microenvironment on their metabolism.

Identification of Nonhuman Primate Hematopoietic Stem and Progenitor Cells

The preclinical development of hematopoietic stem cell (HSC) gene therapy/editing and transplantation protocols is frequently performed in large animal models such as nonhuman primates (NHPs). Similarity in physiology, size, and life expectation as well as cross-reactivity of most reagents and medications allows for the development of treatment strategies with rapid translation to clinical applications. Especially after the adverse events of HSC gene therapy observed in the late 1990s, the ability to perform autologous transplants and follow the animals long-term make the NHP a very attractive model to test the efficiency, feasibility, and safety of new HSC-mediated gene-transfer/editing and transplantation approaches.This protocol describes a method to phenotypically characterize functionally distinct NHP HSPC subsets within specimens or stem cell products from three different NHP species. Procedures are based on the flow-cytometric assessment of cell surface markers that are cross-reactive in between human and NHP to allow for immediate clinical translation. This protocol has been successfully used for the quality control of enriched, cultured, and gene-modified NHP CD34+ hematopoietic stem and progenitor cells (HSPCs) as well as sort-purified CD34 subsets for transplantation in the pig-tailed, cynomolgus, and rhesus macaque. It further allows the longitudinal assessment of primary specimens taken during the long-term follow-up post-transplantation in order to monitor homing, engraftment, and reconstitution of the bone marrow stem cell compartment.

Waves of layered immunity over innate lymphoid cells

Innate lymphoid cells (ILCs) harbor tissue-resident properties in border zones, such as the mucosal membranes and the skin. ILCs exert a wide range of biological functions, including inflammatory response, maintenance of tissue homeostasis, and metabolism. Since its discovery, tremendous effort has been made to clarify the nature of ILCs, and scientific progress revealed that progenitor cells of ILC can produce ILC subsets that are functionally reminiscent of T-cell subsets such as Th1, Th2, and Th17. Thus, now it comes to the notion that ILC progenitors are considered an innate version of naïve T cells. Another important discovery was that ILC progenitors in the different tissues undergo different modes of differentiation pathways. Furthermore, during the embryonic phase, progenitor cells in different developmental chronologies give rise to the unique spectra of immune cells and cause a wave to replenish the immune cells in tissues. This observation leads to the concept of layered immunity, which explains the ontology of some cell populations, such as B-1a cells, γδ T cells, and tissue-resident macrophages. Thus, recent reports in ILC biology posed a possibility that the concept of layered immunity might disentangle the complexity of ILC heterogeneity. In this review, we compare ILC ontogeny in the bone marrow with those of embryonic tissues, such as the fetal liver and embryonic thymus, to disentangle ILC heterogeneity in light of layered immunity.

A bifurcation concept for B-lymphoid/plasmacytoid dendritic cells with largely fluctuating transcriptome dynamics

Hematopoiesis was considered a hierarchical stepwise process but was revised to a continuous process following single-cell RNA sequencing. However, the uncertainty or fluctuation of single-cell transcriptome dynamics during differentiation was not considered, and the dendritic cell (DC) pathway in the lymphoid context remains unclear. Here, we identify human B-plasmacytoid DC (pDC) bifurcation as large fluctuating transcriptome dynamics in the putative B/NK progenitor region by dry and wet methods. By converting splicing kinetics into diffusion dynamics in a deep generative model, our original computational methodology reveals strong fluctuation at B/pDC bifurcation in IL-7Rα⁺ regions, and LFA-1 fluctuates positively in the pDC direction at the bifurcation. These expectancies are validated by the presence of B/pDC progenitors in the IL-7Rα⁺ fraction and preferential expression of LFA-1 in pDC-biased progenitors with a niche-like culture system. We provide a model of fluctuation-based differentiation, which reconciles continuous and discrete models and is applicable to other developmental systems.

Targeting NK Cells for HIV-1 Treatment and Reservoir Clearance

Combined antiretroviral therapy (cART) can inhibit the replication of human immunodeficiency virus type 1 (HIV-1) and reduce viral loads in the peripheral blood to undetectable levels. However, the presence of latent HIV-1 reservoirs prevents complete HIV-1 eradication. Several drugs and strategies targeting T cells are now in clinical trials, but their effectiveness in reducing viral reservoirs has been mixed. Interestingly, innate immune natural killer (NK) cells, which are promising targets for cancer therapy, also play an important role in HIV-1 infection. NK cells are a unique innate cell population with features of adaptive immunity that can regulate adaptive and innate immune cell populations; therefore, they can be exploited for HIV-1 immunotherapy and reservoir eradication. In this review, we highlight immunotherapy strategies for HIV infection that utilize the beneficial properties of NK cells.

Innate Lymphoid Cells: Emerging Players in Pancreatic Disease

Common pancreatic diseases have caused significant economic and social burdens worldwide. The interstitial microenvironment is involved in and plays a crucial part in the occurrence and progression of pancreatic diseases. Innate lymphoid cells (ILCs), an innate population of immune cells which have only gradually entered our visual field in the last 10 years, play an important role in maintaining tissue homeostasis, regulating metabolism, and participating in regeneration and repair. Recent evidence indicates that ILCs in the pancreas, as well as in other tissues, are also key players in pancreatic disease and health. Herein, we examined the possible functions of different ILC subsets in common pancreatic diseases, including diabetes mellitus, pancreatitis and pancreatic cancer, and discussed the potential practical implications of the relevant findings for future further treatment of these pancreatic diseases.

Innate Lymphoid Cells in Autoimmune Diseases

Innate lymphoid cells (ILC) are a heterogeneous group of immune cells characterized by lymphoid morphology and cytokine profile similar to T cells but which do not express clonally distributed diverse antigen receptors. These particular cells express transcription factors and cytokines reflecting their similarities to T helper (Th)1, Th2, and Th17 cells and are therefore referred to as ILC1, ILC2, and ILC3. Other members of the ILC subsets include lymphoid tissue inducer (LTi) and regulatory ILC (ILCreg). Natural killer (NK) cells share a common progenitor with ILC and also exhibit a lymphoid phenotype without antigen specificity. ILC are found in low numbers in peripheral blood but are much more abundant at barrier sites such as the skin, liver, airways, lymph nodes, and the gastrointestinal tract. They play an important role in innate immunity due to their capacity to respond rapidly to pathogens through the production of cytokines. Recent evidence has shown that ILC also play a key role in autoimmunity, as alterations in their number or function have been identified in systemic lupus erythematosus, systemic sclerosis, and rheumatoid arthritis. Here, we review recent advances in the understanding of the role of ILC in the pathogenesis of autoimmune diseases, with particular emphasis on their role as a potential diagnostic biomarker and as therapeutic targets.

Immune Evasion Mechanism and AXL

Extensive interest in cancer immunotherapy is reported according to the clinical importance of CTLA-4 and (PD-1/PD-L1) [programmed death (PD) and programmed death-ligand (PD-L1)] in immune checkpoint therapies. AXL is a receptor tyrosine kinase expressed in different types of cancer and in relation to resistance against various anticancer therapeutics due to poor clinical prognosis. AXL and its ligand, i.e., growth arrest-specific 6 (GAS6) proteins, are expressed on many cancer cells, and the GAS6/AXL pathway is reported to promote cancer cell proliferation, survival, migration, invasion, angiogenesis, and immune evasion. AXL is an attractive and novel therapeutic target for impairing tumor progression from immune cell contracts in the tumor microenvironment. The GAS6/AXL pathway is also of interest immunologically because it targets fewer antitumor immune responses. In effect, several targeted therapies are selective and nonselective for AXL, which are in preclinical and clinical development in multiple cancer types. Therefore, this review focuses on the role of the GAS6/AXL signaling pathway in triggering the immunosuppressive tumor microenvironment as immune evasion. This includes regulating its composition and activating T-cell exclusion with the immune-suppressive activity of regulatory T cells, which is related to one of the hallmarks of cancer survival. Finally, this article discusses the GAS6/AXL signaling pathway in the context of several immune responses such as NK cell activation, apoptosis, and tumor-specific immunity, especially PD-1/PDL-1 signaling.

An in vitro platform supports generation of human innate lymphoid cells from CD34+ hematopoietic progenitors that recapitulate ex vivo identity

Innate lymphoid cells (ILCs) are critical effectors of innate immunity and inflammation, whose development and activation pathways make for attractive therapeutic targets. However, human ILC generation has not been systematically explored, and previous in vitro investigations relied on the analysis of few markers or cytokines, which are suboptimal to assign lineage identity. Here, we developed a platform that reliably generated human ILC lineages from CD34⁺ hematopoietic progenitors derived from cord blood and bone marrow. We showed that one culture condition is insufficient to generate all ILC subsets, and instead, distinct combination of cytokines and Notch signaling are essential. The identity of natural killer (NK)/ILC1s, ILC2s, and ILC3s generated in vitro was validated by protein expression, functional assays, and both global and single-cell transcriptome analysis, recapitulating the signatures and functions of their ex vivo ILC counterparts. These data represent a resource to aid in clarifying ILC biology and differentiation.

Delineating spatiotemporal and hierarchical development of human fetal innate lymphoid cells

Whereas the critical roles of innate lymphoid cells (ILCs) in adult are increasingly appreciated, their developmental hierarchy in early human fetus remains largely elusive. In this study, we sorted human hematopoietic stem/progenitor cells, lymphoid progenitors, putative ILC progenitor/precursors and mature ILCs in the fetal hematopoietic, lymphoid and non-lymphoid tissues, from 8 to 12 post-conception weeks, for single-cell RNA-sequencing, followed by computational analysis and functional validation at bulk and single-cell levels. We delineated the early phase of ILC lineage commitment from hematopoietic stem/progenitor cells, which mainly occurred in fetal liver and intestine. We further unveiled interleukin-3 receptor as a surface marker for the lymphoid progenitors in fetal liver with T, B, ILC and myeloid potentials, while IL-3RA- lymphoid progenitors were predominantly B-lineage committed. Notably, we determined the heterogeneity and tissue distribution of each ILC subpopulation, revealing the proliferating characteristics shared by the precursors of each ILC subtype. Additionally, a novel unconventional ILC2 subpopulation (CRTH2- CCR9+ ILC2) was identified in fetal thymus. Taken together, our study illuminates the precise cellular and molecular features underlying the stepwise formation of human fetal ILC hierarchy with remarkable spatiotemporal heterogeneity.

Role of Toll-like receptors in natural killer cell function in acute lymphoblastic leukemia

Natural killer (NK) cells are specialized lymphocytes primarily involved in the response to infection and tumors. NK cells are characterized by the presence of specific surface molecules, as well as a wide repertoire of receptors that impart microenvironment-dependent effector functions. Among these receptors, Toll-like receptors (TLRs) can be activated to condition the NK response to either a cytotoxic or immunoregulatory phenotype. However, cellular function is frequently impaired during disorders such as cancer. In the last decade, it has become increasingly evident that the stimulation of NK cells is a requirement for their increased cytotoxic activity. TLR activation has been suggested as an alternative route for reestablishing the antitumor activity of NK cells. The present review summarizes the characteristics of NK cells, their receptors, the expression and function of NK cell TLRs, and their functional status in cancer, primarily acute lymphoblastic leukemia.

Human NK Cells in Autologous Hematopoietic Stem Cell Transplantation for Cancer Treatment

Simple Summary

Natural killer (NK) cells are key elements of the innate immune system that have the ability to kill transformed (tumor and virus-infected) cells without prior sensitization. Hematopoietic stem cell transplantation (HSCT) is a medical procedure used in the treatment of a variety of cancers. The early reconstitution of NK cells after HSCT and their functions support the therapeutic potential of these cells in allogenic HSCT. However, the role of NK cells in autologous HSCT is less clear. In this review, we have summarized general aspects of NK cell biology. In addition, we have also reviewed factors that affect autologous HSCT outcome, with particular attention to the role played by NK cells.

Abstract

Natural killer (NK) cells are phenotypically and functionally diverse lymphocytes with the ability to recognize and kill malignant cells without prior sensitization, and therefore, they have a relevant role in tumor immunosurveillance. NK cells constitute the main lymphocyte subset in peripheral blood in the first week after hematopoietic stem cell transplantation (HSCT). Although the role that NK cells play in allogenic HSCT settings has been documented for years, their significance and beneficial effects associated with the outcome after autologous HSCT are less recognized. In this review, we have summarized fundamental aspects of NK cell biology, such as, NK cell subset diversity, their effector functions, and differentiation. Moreover, we have reviewed the factors that affect autologous HSCT outcome, with particular attention to the role played by NK cells and their receptor repertoire in this regard.

son is necessary for proper vertebrate blood development

The gene SON is on human chromosome 21 (21q22.11) and is thought to be associated with hematopoietic disorders that accompany Down syndrome. Additionally, SON is an RNA splicing factor that plays a role in the transcription of leukemia-associated genes. Previously, we showed that mutations in SON cause malformations in human and zebrafish spines and brains during early embryonic development. To examine the role of SON in normal hematopoiesis, we reduced expression of the zebrafish homolog of SON in zebrafish at the single-cell developmental stage with specific morpholinos. In addition to the brain and spinal malformations we also observed abnormal blood cell levels upon son knockdown. We then investigated how blood production was altered when levels of son were reduced. Decreased levels of son resulted in lower amounts of red blood cells when visualized with lcr:GFP transgenic fish. There were also reduced thrombocytes seen with cd41:GFP fish, and myeloid cells when mpx:GFP fish were examined. We also observed a significant decrease in the quantity of T cells, visualized with lck:GFP fish. However, when we examined their hematopoietic stem and progenitor cells (HSPCs), we saw no difference in colony-forming capability. These studies indicate that son is essential for the proper differentiation of the innate and adaptive immune system, and further investigation determining the molecular pathways involved during blood development should elucidate important information about vertebrate HSPC generation, proliferation, and differentiation.

The Origin of B-cells: Human Fetal B Cell Development and Implications for the Pathogenesis of Childhood Acute Lymphoblastic Leukemia

Human B-lymphopoiesis is a dynamic life-long process that starts in utero by around six post-conception weeks. A detailed understanding of human fetal B-lymphopoiesis and how it changes in postnatal life is vital for building a complete picture of normal B-lymphoid development through ontogeny, and its relevance in disease. B-cell acute lymphoblastic leukemia (B-ALL) is one of the most common cancers in children, with many of the leukemia-initiating events originating in utero. It is likely that the biology of B-ALL, including leukemia initiation, maintenance and progression depends on the developmental stage and type of B-lymphoid cell in which it originates. This is particularly important for early life leukemias, where specific characteristics of fetal B-cells might be key to determining how the disease behaves, including response to treatment. These cellular, molecular and/or epigenetic features are likely to change with age in a cell intrinsic and/or microenvironment directed manner. Most of our understanding of fetal B-lymphopoiesis has been based on murine data, but many recent studies have focussed on characterizing human fetal B-cell development, including functional and molecular assays at a single cell level. In this mini-review we will give a short overview of the recent advances in the understanding of human fetal B-lymphopoiesis, including its relevance to infant/childhood leukemia, and highlight future questions in the field.

Genetic models of human and mouse dendritic cell development and function

Dendritic cells (DCs) develop in the bone marrow from haematopoietic progenitors that have numerous shared characteristics between mice and humans. Human counterparts of mouse DC progenitors have been identified by their shared transcriptional signatures and developmental potential. New findings continue to revise models of DC ontogeny but it is well accepted that DCs can be divided into two main functional groups. Classical DCs include type 1 and type 2 subsets, which can detect different pathogens, produce specific cytokines and present antigens to polarize mainly naive CD8+ or CD4+ T cells, respectively. By contrast, the function of plasmacytoid DCs is largely innate and restricted to the detection of viral infections and the production of type I interferon. Here, we discuss genetic models of mouse DC development and function that have aided in correlating ontogeny with function, as well as how these findings can be translated to human DCs and their progenitors.

Cytokines and signaling pathways involved in differentiation potential of hematopoietic stem cells towards natural killer cells

NK cells are innate immune cells derived from common lymphoid progenitor and are developed primarily in the bone marrow. These cells respond to stress signals, inflammatory cytokines, and cancerous cells through the secretion of active immune mediators. Previous studies revealed that NK cells can be used as an essential cell in the defense against cancers. According to the literature, a set of cytokines and factors play a crucial role during differentiation of NK cells. In other words, developmental events of NK cells are regulated through multiple critical cytokines, including interleukins (ILs), kit ligand, fms-like tyrosine kinase three ligand, transforming growth factor-β, and typical γ chain family of cytokines. Among previously investigated ILs, IL-2, IL-3, IL-7, and IL-15 are the most important. In addition to ILs, transcription factors and MicroRNAs are involved in NK cell development. In this review study, after presenting a brief description of developmental stages and production of the NK cells, the factors and signaling pathways involved in differentiation of NK cells were discussed.

Characterization and generation of human definitive multipotent hematopoietic stem/progenitor cells

Definitive hematopoiesis generates hematopoietic stem/progenitor cells (HSPCs) that give rise to all mature blood and immune cells, but remains poorly defined in human. Here, we resolve human hematopoietic populations at the earliest hematopoiesis stage by single-cell RNA-seq. We characterize the distinct molecular profiling between early primitive and definitive hematopoiesis in both human embryonic stem cell (hESC) differentiation and early embryonic development. We identify CD44 to specifically discriminate definitive hematopoiesis and generate definitive HSPCs from hESCs. The multipotency of hESCs-derived HSPCs for various blood and immune cells is validated by single-cell clonal assay. Strikingly, these hESCs-derived HSPCs give rise to blood and lymphoid lineages in vivo. Lastly, we characterize gene-expression dynamics in definitive and primitive hematopoiesis and reveal an unreported role of ROCK-inhibition in enhancing human definitive hematopoiesis. Our study provides a prospect for understanding human early hematopoiesis and a firm basis for generating blood and immune cells for clinical purposes.

Hypoxia Regulates Lymphoid Development of Human Hematopoietic Progenitors

Hypoxia plays a major role in the physiology of hematopoietic and immune niches. Important clues from works in mouse have paved the way to investigate the role of low O₂ levels in hematopoiesis. However, whether hypoxia impacts the initial steps of human lymphopoiesis remains unexplored. Here, we show that hypoxia regulates cellular and metabolic profiles of umbilical cord blood (UCB)-derived hematopoietic progenitor cells. Hypoxia more specifically enhances in vitro lymphoid differentiation potentials of lymphoid-primed multipotent progenitors (LMPPs) and pro-T/natural killer (NK) cells and in vivo B cell potential of LMPPs. In accordance, hypoxia exacerbates the lymphoid gene expression profile through hypoxia-inducible factor (HIF)-1α (for LMPPs) and HIF-2α (for pro-T/NK). Moreover, loss of HIF-1/2α expression seriously impedes NK and B cell production from LMPPs and pro-T/NK. Our study describes how hypoxia contributes to the lymphoid development of human progenitors and reveals the implication of the HIF pathway in LMPPs and pro-T/NK-cell lymphoid identities.

Immune Cells in the Placental Villi Contribute to Intra-amniotic Inflammation

Intra-amniotic (IA) inflammation is associated with significant morbidities for both the mother and the fetus. Prior studies have illustrated many of the effects of IA inflammation on the uterine lining (decidua) and membranous layers of the placenta at the fetal–maternal interface. However, much less is known about the immunological response occurring within the villous placenta. Using a rhesus macaque model of lipopolysaccharide (LPS)-induced IA inflammation, we showed that pregnancy-matched choriodecidua and villi have distinct immunological profiles in rhesus pregnancies. In the choriodecidua, we show that the abundance of neutrophils, multiple populations of antigen-presenting cells, and two populations of natural killer (NK) cells changes with prenatal IA LPS exposure. In contrast, in immune cells within the villous placenta we observed alterations in the abundance of B cells, monocytes, and CD8 T cells. Prior work has illustrated that IA inflammation leads to an increase in tumor necrosis factor alpha (TNFα) at the fetal–maternal interface. In this study, pretreatment with a TNFα blockade partially reversed inflammation in the placental villi. Furthermore, we report that immune cells in the villous placenta sensed LPS during our experimental window, and subsequently activated T cells to produce proinflammatory cytokines. Moreover, this study is the first report of memory T cells in third-trimester non-human primate placental villi and provides evidence that manipulation of immune cells in the villi at the fetal–maternal interface should be considered as a potential therapeutic target for IA inflammation.

Potently Cytotoxic Natural Killer Cells Initially Emerge from Erythro-Myeloid Progenitors during Mammalian Development

Natural killer (NK) cells are a critical component of the innate immune system. However, their ontogenic origin has remained unclear. Here, we report that NK cell potential first arises from Hoxaneg/low Kit+CD41+CD16/32+ hematopoietic-stem-cell (HSC)-independent erythro-myeloid progenitors (EMPs) present in the murine yolk sac. EMP-derived NK cells and primary fetal NK cells, unlike their adult counterparts, exhibit robust degranulation in response to stimulation. Parallel studies using human pluripotent stem cells (hPSCs) revealed that HOXAneg/low CD34+ progenitors give rise to NK cells that, similar to murine EMP-derived NK cells, harbor a potent cytotoxic degranulation bias. In contrast, hPSC-derived HOXA+ CD34+ progenitors, as well as human cord blood CD34+ cells, give rise to NK cells that exhibit an attenuated degranulation response but robustly produce inflammatory cytokines. Collectively, our studies identify an extra-embryonic origin of potently cytotoxic NK cells, suggesting that ontogenic origin is a relevant factor in designing hPSC-derived adoptive immunotherapies.

Integrated scRNA-Seq Identifies Human Postnatal Thymus Seeding Progenitors and Regulatory Dynamics of Differentiating Immature Thymocytes

During postnatal life, thymopoiesis depends on the continuous colonization of the thymus by bone-marrow-derived hematopoietic progenitors that migrate through the bloodstream. The current understanding of the nature of thymic immigrants is largely based on data from pre-clinical models. Here, we employed single-cell RNA sequencing (scRNA-seq) to examine the immature postnatal thymocyte population in humans. Integration of bone marrow and peripheral blood precursor datasets identified two putative thymus seeding progenitors that varied in expression of CD7; CD10; and the homing receptors CCR7, CCR9, and ITGB7. Whereas both precursors supported T cell development, only one contributed to intrathymic dendritic cell (DC) differentiation, predominantly of plasmacytoid dendritic cells. Trajectory inference delineated the transcriptional dynamics underlying early human T lineage development, enabling prediction of transcription factor (TF) modules that drive stage-specific steps of human T cell development. This comprehensive dataset defines the expression signature of immature human thymocytes and provides a resource for the further study of human thymopoiesis.

Helper-like Innate Lymphoid Cells in Humans and Mice

The innate lymphoid cell (ILC) family consists of natural killer (NK) cells, helper-like lymphoid cells (ILC1s, ILC2s, and ILC3s), and lymphoid tissue inducer (LTi) cells. Helper-like ILCs are considered the innate counterpart of T-helper cells because of similarities in their cytokine output and expression of key transcription factors. ILCs provide and regulate innate immune functions before the development of adaptive immunity. They are involved in host defense against pathogens, inflammation, tissue repair, and metabolic homeostasis. However, they can also be involved in inflammatory disorders and carcinogenesis. In this review, we summarize the latest research on ILC development and plasticity in humans and mice, focusing on the pathogenic role of helper-like ILCs in inflammatory disorders, such as asthma, Crohn's disease (CD), and rheumatoid arthritis (RA).

The ontogenetic path of human dendritic cells

Dendritic cells (DCs) orchestrate adaptive immune responses. In healthy individuals, DCs are drivers and fine-tuners of T cell responses directed against invading pathogens or cancer cells. In parallel, DCs control autoreactive T cells, thereby maintaining T cell tolerance. Under various disease conditions, a disruption of this delicate balance can lead to chronic infections, tumor evasion, or autoimmunity. While great efforts have been made to unravel the origin and development of this powerful cell type in mice, only little is known about the ontogeny of human DCs. Here, we summarize the current understanding of the developmental path of DCs from hematopoietic stem cells to fully functional DCs in their local tissue environment and provide a template for the identification of DCs across various tissues.

Human NK Cell Development: One Road or Many?

CD3⁻CD56⁺ NK cells develop from CD34⁺ hematopoietic progenitors (HPCs) in vivo, and this process can be recapitulated in vitro. The prevailing model is that human NK cell development occurs along a continuum whereby common lymphocyte progenitors (CLPs) gradually downregulate CD34 and upregulate CD56. Acquisition of CD94 marks commitment to the CD56^bright stage, and CD56^bright NK cells subsequently differentiate into CD56^dim NK cells that upregulate CD16 and killer immunoglobulin-like receptors (KIR). Support for this linear model comes from analyses of cell populations in secondary lymphoid tissues and in vitro studies of NK cell development from HPCs. However, several lines of evidence challenge this linear model and suggest a more branched model whereby different precursor populations may independently develop into distinct subsets of mature NK cells. A more definitive understanding of human NK cell development is needed to inform in vitro differentiation strategies designed to generate NK cells for immunotherapy. In this review, we summarize current evidence supporting the linear and branched models of human NK cell development and the challenges associated with reaching definitive conclusions.

NK Cell Precursors in Human Bone Marrow in Health and Inflammation

NK cells are generated from hematopoietic stem cells (HSC) residing in the bone marrow (BM), similar to other blood cells. Development toward mature NK cells occurs largely outside the BM through travel of CD34+ and other progenitor intermediates toward secondary lymphoid organs. The BM harbors multipotent CD34+ common lymphoid progenitors (CLPs) that generate T, B, NK, and Dendritic Cells and are devoid of erythroid, myeloid, and megakaryocytic potential. Over recent years, there has been a quest for single-lineage progenitors predominantly with the objective of manipulation and intervention in mind, which has led to the identification of unipotent NK cell progenitors devoid of other lymphoid lineage potential. Research efforts for the study of lymphopoiesis have almost exclusively concentrated on healthy donor tissues and on repopulation/transplant models. This has led to the widely accepted assumption that lymphopoiesis during disease states reflects the findings of these models. However, compelling evidences in animal models show that inflammation plays a fundamental role in the regulation of HSC maturation and release in the BM niches through several mechanisms including modulation of the CXCL12-CXCR4 expression. Indeed, recent findings during systemic inflammation in patients provide evidence that a so-far overlooked CLP exists in the BM (Lin⁻CD34⁺DNAM-1^brightCXCR4⁺) and that it overwhelmingly exits the BM during systemic inflammation. These “inflammatory” precursors have a developmental trajectory toward surprisingly functional NK and T cells as reviewed here and mirror the steady state maintenance of the NK cell pool by CD34⁺DNAM-1⁻CXCR4⁻ precursors. Our understanding of NK cell precursor development may benefit from including a distinct “inflammatory” progenitor modeling of lymphoid precursors, allowing rapid deployment of specialized Lin⁻CD34⁺DNAM-1^brightCXCR4⁺ -derived resources from the BM.

From Discrete to Continuous Modeling of Lymphocyte Development and Plasticity in Chronic Diseases

The molecular events leading to differentiation, development, and plasticity of lymphoid cells have been subject of intense research due to their key roles in multiple pathologies, such as lymphoproliferative disorders, tumor growth maintenance and chronic diseases. The emergent roles of lymphoid cells and the use of high-throughput technologies have led to an extensive accumulation of experimental data allowing the reconstruction of gene regulatory networks (GRN) by integrating biochemical signals provided by the microenvironment with transcriptional modules of lineage-specific genes. Computational modeling of GRN has been useful for the identification of molecular switches involved in lymphoid specification, prediction of microenvironment-dependent cell plasticity, and analyses of signaling events occurring downstream the activation of antigen recognition receptors. Among most common modeling strategies to analyze the dynamical behavior of GRN, discrete dynamic models are widely used for their capacity to capture molecular interactions when a limited knowledge of kinetic parameters is present. However, they are less powerful when modeling complex systems sensitive to biochemical gradients. To compensate it, discrete models may be transformed into regulatory networks that includes state variables and parameters varying within a continuous range. This approach is based on a system of differential equations dynamics with regulatory interactions described by fuzzy logic propositions. Here, we discuss the applicability of this method on modeling of development and plasticity processes of adaptive lymphocytes, and its potential implications in the study of pathological landscapes associated to chronic diseases.

Automated flow cytometry enables high performance point-of-care analysis of leukocyte phenotypes

INTRODUCTION

Phagocytes such as granulocytes and monocytes are fundamental players in the innate immune system. Activation of these cells can be quantified by the measurement of activation marker expression using flow cytometry. Analysis of receptor expression on inflammatory cells facilitates the diagnosis of inflammatory diseases and can be used to determine the extent of inflammation. However, several major limitations of this analysis precludes application of inflammation monitoring in clinical practice. Fast and automated analysis would minimalize ex vivo manipulation and allow reproducible processing. The aim of this study was to evaluate a fully automated "load & go" flow cytometer for analyzing activation of granulocytes and monocytes in a clinically applicable setting.

METHODS

Blood samples were obtained from 10 anonymous and healthy volunteers between the age of 18 and 65 years. Granulocyte and monocyte activation was determined by the use of the markers CD35, CD11b and CD10 measured in the automated AQUIOS CL® "load & go" flow cytometer. This machine is able to pierce the tube caps, add antibodies, lyse and measure the sample within 20 min after vena puncture. Reproducibility tests were performed to test the stability of activation marker expression on phagocytes. The expression of activation markers was measured at different time points after blood drawing to analyze the effect of bench time on granulocyte and monocyte activation.

RESULTS

The duplicate experiments demonstrate a high reproducibility of the measurements of the activation state of phagocytes. Healthy controls showed a very homogenous expression of activation markers at T = 0 (immediately after vena puncture). Activation markers on neutrophils were already significantly increased after 1 h (T = 1) depicted as means (95%Cl) CD35: 2.2× (1.5×-2.5×) p = .028, CD11b: 2.5× (1.7×-3.1×) p = .023, CD10: 2.5× (2.1×-2.7×) p = .009) and a further increase in activation markers was observed after 2 and 3 h. Monocytes also showed a increase in activation markers in 1 h (mean (95%Cl) CD35: 1.8× (1.3×-2.2×) p = .058, CD11b: 2.13× (1.6×-2.4×) p = .025) and also a further significant increase in 2 and 3 h was observed.

CONCLUSION

This study showed that bench time of one hour already leads to a significant upregulation and bigger variance in activation markers of granulocytes and monocytes. In addition, it is likely that automated flow cytometry reduces intra-assay variability in the analysis of activation markers on inflammatory cells. Therefore, we found that it is of utmost importance to perform immune activation analysis as fast as possible to prevent drawing wrong conclusions. Automated flow cytometry is able to reduce this analysis from 2 h to only 15-20 min without the need of dedicated personnel and in a point-of-care context. This now allows fast and automated inflammation monitoring in blood samples obtained from a variety of patient groups. FUND: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Prognostic Impact of Natural Killer Cell Count in Follicular Lymphoma and Diffuse Large B-cell Lymphoma Patients Treated with Immunochemotherapy

PURPOSE

Natural killer (NK) cells are key effector cells for anti-CD20 monoclonal antibodies (mAb), such as obinutuzumab and rituximab. We assessed whether low pretreatment NK-cell count (NKCC) in peripheral blood or tumor tissue was associated with worse outcome in patients receiving antibody-based therapy.

PATIENTS AND METHODS

Baseline peripheral blood NKCC was assessed by flow cytometry (CD3^-CD56⁺ and/or CD16⁺ cells) in 1,064 of 1,202 patients with follicular lymphoma treated with obinutuzumab or rituximab plus chemotherapy in the phase III GALLIUM trial (NCT01332968) and 1,287 of 1,418 patients with diffuse large B-cell lymphoma (DLBCL) treated with obinutuzumab or rituximab plus cyclophosphamide, doxorubicin, vincristine, and prednisone (G-CHOP or R-CHOP) in the phase III GOYA trial (NCT01287741). The prognostic value of tumor NK-cell gene expression, as assessed by whole-transcriptome gene expression using TruSeq RNA sequencing, was also analyzed. The association of baseline variables, such as treatment arm, was evaluated using multivariate Cox regression models using a stepwise approach.

RESULTS

In this exploratory analysis, low baseline peripheral blood NKCC was associated with shorter progression-free survival (PFS) in both follicular lymphoma [hazard ratio (HR), 1.48; 95% confidence interval (CI), 1.02-2.14; P = 0.04] and DLBCL (HR, 1.36; 95% CI, 1.01-1.83; P = 0.04), and overall survival in follicular lymphoma (HR, 2.20; 95% CI, 1.26-3.86; P = 0.0058). Low tumor NK-cell gene expression was associated with shorter PFS in G-CHOP-treated patients with DLBCL (HR, 1.95; 95% CI, 1.22-3.15; P < 0.01).

CONCLUSIONS

These findings indicate that the number of NK cells in peripheral blood may affect the outcome of patients with B-cell non-Hodgkin lymphoma receiving anti-CD20-based immunochemotherapy.

A topological view of human CD34+ cell state trajectories from integrated single-cell output and proteomic data

Recent advances in single-cell molecular analytical methods and clonal growth assays are enabling more refined models of human hematopoietic lineage restriction processes to be conceptualized. Here, we report the results of integrating single-cell proteome measurements with clonally determined lymphoid, neutrophilic/monocytic, and/or erythroid progeny outputs from >1000 index-sorted CD34⁺ human cord blood cells in short-term cultures with and without stromal cells. Surface phenotypes of functionally examined cells were individually mapped onto a molecular landscape of the entire CD34⁺ compartment constructed from single-cell mass cytometric measurements of 14 cell surface markers, 20 signaling/cell cycle proteins, and 6 transcription factors in ∼300 000 cells. This analysis showed that conventionally defined subsets of CD34⁺ cord blood cells are heterogeneous in their functional properties, transcription factor content, and signaling activities. Importantly, this molecular heterogeneity was reduced but not eliminated in phenotypes that were found to display highly restricted lineage outputs. Integration of the complete proteomic and functional data sets obtained revealed a continuous probabilistic topology of change that includes a multiplicity of lineage restriction trajectories. Each of these reflects progressive but variable changes in the levels of specific signaling intermediates and transcription factors but shared features of decreasing quiescence. Taken together, our results suggest a model in which increasingly narrowed hematopoietic output capabilities in neonatal CD34⁺ cord blood cells are determined by a history of external stimulation in combination with innately programmed cell state changes.

From pluripotent stem cells to T cells

The generation of T cells from human pluripotent stem cells (PSCs) opens a valuable experimental window into developmental hematopoiesis and raises the possibility of a new therapeutic approach for T-cell immunotherapy. After directing PSCs through mesoderm and early hematopoietic developmental stages, commitment to the T-cell lineage has been achieved by several groups using coculture with stromal cells that express a notch ligand, recapitulating the critical signals that initiate the first stages of normal T-cell differentiation in the thymus. However, positive selection and the production of mature T cells from human PSCs have been limited to date. Nonetheless, T-lineage cells have been generated from PSCs with tumor antigen specificity either through a prearranged clonal T-cell receptor (TCR) or lentiviral-mediated expression of chimeric antigen receptors. The recent development of a 3D artificial organoid model has demonstrated that PSCs can generate mature conventional T cells that are fully functional and express a diverse TCR repertoire. Introduction of a transgenic TCR at the PSC stage allows for the production of tumor-antigen-specific, mature conventional T cells. The tools of gene editing in PSCs are ideally suited to produce off-the-shelf universal products for T-cell immunotherapy. In this review, we describe the studies that have led to this exciting moment in PSC biology and discuss translation to clinical applications.

Cellular pathways in the development of human and murine innate lymphoid cells

Innate lymphoid cells (ILCs) are critical to effective immune surveillance against pathogens, have malignant counterparts, and contribute to disease. Thus, it is important to understand ILC development. All ILCs are derived from the common lymphoid progenitor cell; however, the exact mechanisms and signals that initiate their divergence from T cells, B cells and one and other are incompletely understood. Evidence now supports a stepwise developmental process that includes distinct cellular intermediates, progressively narrowed differentiation, and some plasticity. While the current models of human and murine ILC development share many similarities, they also include some distinct differences. Together these findings have established a working dynamic model of ILC development.

CD7 CAR T Cells for the Therapy of Acute Myeloid Leukemia

Chimeric antigen receptor (CAR) T cell therapy for the treatment of acute myeloid leukemia (AML) has the risk of toxicity to normal myeloid cells. CD7 is expressed by the leukemic blasts and malignant progenitor cells of approximately 30% of AML patients but is absent on normal myeloid and erythroid cells. Since CD7 expression by malignant blasts is also linked with chemoresistance and poor outcomes, targeting this antigen may be beneficial for this subset of AML patients. Here, we show that expression of a CD7-directed CAR in CD7 gene-edited (CD7^KO) T cells effectively eliminates CD7⁺ AML cell lines, primary CD7⁺ AML, and colony-forming cells but spares myeloid and erythroid progenitor cells and their progeny. In a xenograft model, CD7 CAR T cells protect mice against systemic leukemia, prolonging survival. Our results support the feasibility of using CD7^KO CD7 CAR T cells for the non-myeloablative treatment of CD7⁺ AML.

[Bipartite organization of human lymphopoiesis]

Due to difficulties to access primary bone marrow samples, human hematopoiesis has long remained far less characterized than in the mouse. Using an in vivo modeling approach of fetal hematopoiesis in humanized mice, we recently showed that human lymphoid cells stem from two functionally specialized populations of CD127^- and CD127⁺ early lymphoid progenitors (ELP) that differentiate independently, respond differently to growth factors, undergo divergent modes of lineage restriction and generate distinct lymphoid populations. Our results demonstrate that, conversely to the mouse, human lymphopoiesis displays a bipartite developmental architecture.

Immune cell subset differentiation and tissue inflammation

Immune cells were traditionally considered as major pro-inflammatory contributors. Recent advances in molecular immunology prove that immune cell lineages are composed of different subsets capable of a vast array of specialized functions. These immune cell subsets share distinct duties in regulating innate and adaptive immune functions and contribute to both immune activation and immune suppression responses in peripheral tissue. Here, we summarized current understanding of the different subsets of major immune cells, including T cells, B cells, dendritic cells, monocytes, and macrophages. We highlighted molecular characterization, frequency, and tissue distribution of these immune cell subsets in human and mice. In addition, we described specific cytokine production, molecular signaling, biological functions, and tissue population changes of these immune cell subsets in both cardiovascular diseases and cancers. Finally, we presented a working model of the differentiation of inflammatory mononuclear cells, their interaction with endothelial cells, and their contribution to tissue inflammation. In summary, this review offers an updated and comprehensive guideline for immune cell development and subset differentiation, including subset characterization, signaling, modulation, and disease associations. We propose that immune cell subset differentiation and its complex interaction within the internal biological milieu compose a “pathophysiological network,” an interactive cross-talking complex, which plays a critical role in the development of inflammatory diseases and cancers.

Elderly human hematopoietic progenitor cells express cellular senescence markers and are more susceptible to pyroptosis

The maintenance of effective immunity over time is dependent on the capacity of hematopoietic stem cells (HSCs) to sustain the pool of immunocompetent mature cells. Decline of immune competence with old age may stem from HSC defects, including reduced self-renewal potential and impaired lymphopoiesis, as suggested in murine models. To obtain further insights into aging-related alteration of hematopoiesis, we performed a comprehensive study of blood hematopoietic progenitor cells (HPCs) from older humans. In the elderly, HPCs present active oxidative phosphorylation and are pressed to enter cell cycling. However, p53-p21 and p15 cell senescence pathways, associated with telomerase activity deficiency, strong telomere attrition, and oxidative stress, are engaged, thus limiting cell cycling. Moreover, survival of old HPCs is impacted by pyroptosis, an inflammatory form of programmed cell death. Lastly, telomerase activity deficiency and telomere length attrition of old HPCs may be passed on to progeny cells such as naive T lymphocytes, further highlighting the poor hematopoietic potential of the elderly. This pre-senescent profile is characteristic of the multiple intrinsic and extrinsic factors affecting HPCs in elderly individuals and represents a major obstacle in terms of immune reconstitution and efficacy with advanced age.