Systemic Virus Infections Differentially Modulate Cell Cycle State and Functionality of Long-Term Hematopoietic Stem Cells In Vivo

IFN alpha signaling drives hematopoietic stem cells malfunction under acute inflammation

Inflammation stimulation regulates the activity of hematopoietic stem cells (HSCs) through direct-sensing and cytokine-mediation. It is known that HSCs directly sense lipopolysaccharide (LPS), a classical infection-related inflammatory signal, via toll like receptor 4 (TLR4) and subsequently become active. However, the mechanism underlying the activity change of HSCs induced by LPS remains incompletely disclosed. Here we explored that under LPS stimulation, the activation of interferon alpha (IFNα) signal pathway resulted in the activation and exhaustion of HSCs in vitro, indicating HSCs directly responded to LPS through the downstream IFNα signal pathway. We also discovered the increased production of IFNα in mice bone marrow and expression of interferon-α/β receptor (IFNAR) on mice HSCs after LPS stimulation. Creatine, an IFNα inhibitor, could reverse the activation and prevent the exhaustion of HSCs caused by LPS by suppressing the expressions of genes associated with the IFNα signal pathway both in vitro and in vivo. Furthermore, we found that the IFNAR deficiency in mice effectively protected HSCs from activation, elevated apoptosis and impaired reconstitution ability under LPS stimulation in vivo. This finding further supports the notion that LPS activates and injures HSCs indirectly via promoting IFNα secretion in the bone marrow environment. Overall, our findings reveal that LPS causes the injury to HSCs either through direct or cytokine-mediated indirect activation of the IFNα signal pathway.

Spinal cord injury enhances lung inflammation and exacerbates immune response following exposure to LPS

Introduction

The severity of spinal cord injury (SCI) is closely tied to pulmonary function, especially in cases of higher SCI levels. Despite this connection, the underlying pathological mechanisms in the lungs post-SCI are not well understood. Previous research has established a connection between disrupted sympathetic regulation and splenocyte apoptosis in high thoracic SCI, leading to pulmonary dysfunction. The aim of this study was to investigate whether mice with low-level SCI exhibit increased susceptibility to acute lung injury by eliciting systemic inflammatory responses that operate independently of the sympathetic nervous system.

Methods

Here, we employed T9 contusion SCI and exposed mice to aerosolized lipopolysaccharide (LPS) to simulate lung inflammation associated with acute respiratory distress syndrome (ARDS). Twenty-four hours post-LPS exposure, lung tissues and bronchoalveolar lavage (BAL) fluid were analyzed.

Results

LPS markedly induced proinflammatory gene expression (SAA3, IRG1, NLRP3, IL-1beta, MCP-1) and cytokine release (IL-1beta, IL-6, MCP-1) in SCI mice compared to controls, indicating an exaggerated inflammatory response. Infiltration of Ly6G/C positive neutrophils and macrophages was significantly higher in SCI mice lungs post-LPS exposure. Interestingly, spleen size and weight did not differ between control and SCI mice, suggesting that T9 SCI alone does not cause spleen atrophy. Notably, bone-marrow-derived macrophages (BMDMs) from SCI mice exhibited hyper-responsiveness to LPS.

Discussions

This study demonstrated an increase in lung inflammation and immune responses subsequent to low-level T9 SCI, underscoring the widespread influence of systemic inflammation post-SCI, especially pronounced in specific organs like the lungs.

Immune surveillance of cytomegalovirus in tissues

Cytomegalovirus (CMV), a representative member of the Betaherpesvirinae subfamily of herpesviruses, is common in the human population, but immunocompetent individuals are generally asymptomatic when infected with this virus. However, in immunocompromised individuals and immunologically immature fetuses and newborns, CMV can cause a wide range of often long-lasting morbidities and even death. CMV is not only widespread throughout the population but it is also widespread in its hosts, infecting and establishing latency in nearly all tissues and organs. Thus, understanding the pathogenesis of and immune responses to this virus is a prerequisite for developing effective prevention and treatment strategies. Multiple arms of the immune system are engaged to contain the infection, and general concepts of immune control of CMV are now reasonably well understood. Nonetheless, in recent years, tissue-specific immune responses have emerged as an essential factor for resolving CMV infection. As tissues differ in biology and function, so do immune responses to CMV and pathological processes during infection. This review discusses state-of-the-art knowledge of the immune response to CMV infection in tissues, with particular emphasis on several well-studied and most commonly affected organs.

Severe morbidity and hospital-based mortality from Rift Valley fever disease between November 2017 and March 2020 among humans in Uganda

BACKGROUND

Rift Valley fever (RVF) is a zoonotic viral disease of increasing intensity among humans in Africa and the Arabian Peninsula. In Uganda, cases reported prior to 2016 were mild or not fully documented. We report in this paper on the severe morbidity and hospital-based mortality of human cases in Uganda.

METHODS

Between November 2017 and March 2020 human cases reported to the Uganda Virus Research Institute (UVRI) were confirmed by polymerase chain reaction (PCR). Ethical and regulatory approvals were obtained to enrol survivors into a one-year follow-up study. Data were collected on socio-demographics, medical history, laboratory tests, potential risk factors, and analysed using Stata software.

RESULTS

Overall, 40 cases were confirmed with acute RVF during this period. Cases were not geographically clustered and nearly all were male (39/40; 98%), median age 32 (range 11-63). The median definitive diagnosis time was 7 days and a delay of three days between presumptive and definitive diagnosis. Most patients (31/40; 78%) presented with fever and bleeding at case detection. Twenty-eight (70%) cases were hospitalised, out of whom 18 (64%) died. Mortality was highest among admissions in regional referral (11/16; 69%) and district (4/5; 80%) hospitals, hospitalized patients with bleeding at case detection (17/27; 63%), and patients older than 44 years (9/9; 100%). Survivors mostly manifested a mild gastro-intestinal syndrome with nausea (83%), anorexia (75%), vomiting (75%), abdominal pain (50%), and diarrhoea (42%), and prolonged symptoms of severe disease including jaundice (67%), visual difficulties (67%), epistaxis (50%), haemoptysis (42%), and dysentery (25%). Symptom duration varied between two to 120 days.

CONCLUSION

RVF is associated with high hospital-based mortality, severe and prolonged morbidity among humans that present to the health care system and are confirmed by PCR. One-health composite interventions should be developed to improve environmental and livestock surveillance, prevent infections, promptly detect outbreaks, and improve patient outcomes.

Schistosome Infection Impacts Hematopoiesis

Helminth infections are common in animals. However, the impact of a helminth infection on the function of hematopoietic stem cells (HSCs) and other hematopoietic cells has not been comprehensively defined. In this article, we describe the hematopoietic response to infection of mice with Schistosoma mansoni, a parasitic flatworm that causes schistosomiasis. We analyzed the frequency or number of hematopoietic cell types in the bone marrow, spleen, liver, thymus, and blood and observed multiple hematopoietic changes caused by infection. Schistosome infection impaired bone marrow HSC function after serial transplantation. Functional HSCs were present in the infected liver. Infection blocked bone marrow erythropoiesis and augmented spleen erythropoiesis, observations consistent with the anemia and splenomegaly prevalent in schistosomiasis patients. This work defines the hematopoietic response to schistosomiasis, a debilitating disease afflicting more than 200 million people, and identifies impairments in HSC function and erythropoiesis.

Perinatal murine cytomegalovirus infection reshapes the transcriptional profile and functionality of NK cells

Infections in early life can elicit substantially different immune responses and pathogenesis than infections in adulthood. Here, we investigate the consequences of murine cytomegalovirus infection in newborn mice on NK cells. We show that infection severely compromised NK cell maturation and functionality in newborns. This effect was not due to compromised virus control. Inflammatory responses to infection dysregulated the expression of major transcription factors governing NK cell fate, such as Eomes, resulting in impaired NK cell function. Most prominently, NK cells from perinatally infected mice have a diminished ability to produce IFN-γ due to the downregulation of long non-coding RNA Ifng-as1 expression. Moreover, the bone marrow's capacity to efficiently generate new NK cells is reduced, explaining the prolonged negative effects of perinatal infection on NK cells. This study demonstrates that viral infections in early life can profoundly impact NK cell biology, including long-lasting impairment in NK cell functionality.

Spotlight on the impact of viral infections on Hematopoietic Stem Cells (HSCs) with a focus on COVID-19 effects

Hematopoietic stem cells (HSCs) are known for their significant capability to reconstitute and preserve a functional hematopoietic system in long-term periods after transplantation into conditioned hosts. HSCs are thus crucial cellular targets for the continual repair of inherited hematologic, metabolic, and immunologic disorders. In addition, HSCs can undergo various fates, such as apoptosis, quiescence, migration, differentiation, and self-renewal. Viruses continuously pose a remarkable health risk and request an appropriate, balanced reaction from our immune system, which as well as affects the bone marrow (BM). Therefore, disruption of the hematopoietic system due to viral infection is essential. In addition, patients for whom the risk-to-benefit ratio of HSC transplantation (HSCT) is acceptable have seen an increase in the use of HSCT in recent years. Hematopoietic suppression, BM failure, and HSC exhaustion are all linked to chronic viral infections. Virus infections continue to be a leading cause of morbidity and mortality in HSCT recipients, despite recent advancements in the field. Furthermore, whereas COVID-19 manifests initially as an infection of the respiratory tract, it is now understood to be a systemic illness that significantly impacts the hematological system. Patients with advanced COVID-19 often have thrombocytopenia and blood hypercoagulability. In the era of COVID-19, Hematological manifestations of COVID-19 (i.e., thrombocytopenia and lymphopenia), the immune response, and HSCT may all be affected by the SARS-CoV-2 virus in various ways. Therefore, it is important to determine whether exposure to viral infections may affect HSCs used for HSCT, as this, in turn, may affect engraftment efficiency. In this article, we reviewed the features of HSCs, and the effects of viral infections on HSCs and HSCT, such as SARS-CoV-2, HIV, cytomegalovirus, Epstein-Barr virus, HIV, etc. Video Abstract.

Inflammatory abrasion of hematopoietic stem cells: a candidate clue for the post-CAR-T hematotoxicity?

Chimeric antigen receptor T-cell (CAR-T) therapy has shown remarkable effects in treating various hematological malignancies. However, hematotoxicity, specifically neutropenia, thrombocytopenia, and anemia, poses a serious threat to patient prognosis and remains a less focused adverse effect of CAR-T therapy. The mechanism underlying lasting or recurring late-phase hematotoxicity, long after the influence of lymphodepletion therapy and cytokine release syndrome (CRS), remains elusive. In this review, we summarize the current clinical studies on CAR-T late hematotoxicity to clarify its definition, incidence, characteristics, risk factors, and interventions. Owing to the effectiveness of transfusing hematopoietic stem cells (HSCs) in rescuing severe CAR-T late hematotoxicity and the unignorable role of inflammation in CAR-T therapy, this review also discusses possible mechanisms of the harmful influence of inflammation on HSCs, including inflammatory abrasion of the number and the function of HSCs. We also discuss chronic and acute inflammation. Cytokines, cellular immunity, and niche factors likely to be disturbed in CAR-T therapy are highlighted factors with possible contributions to post-CAR-T hematotoxicity.

Characterization of murine lymphocyte activation and exhaustion markers by a 14-color flow cytometry panel

Previously designed flow cytometry panels have provided a framework to analyze T-cell activation; however, few provide an extensive view of lymphocyte populations, and none are optimized for murine models. This article describes a panel designed specifically to assess the expression of activation and exhaustion markers in expanding lymphocyte populations in tumor-bearing mice across two distinct genetic backgrounds: BALB/c and C57BL/6. This comprehensive panel enables the assessment of multiple functional states and immune checkpoint markers across cytotoxic CD8⁺ T cells, helper and regulatory CD4⁺ T cells and NK cells in murine whole blood, lymph nodes and tumor.

Recent advances in understanding the impact of infection and inflammation on hematopoietic stem and progenitor cells

Just over one decade ago, it was discovered that hematopoietic stem cells (HSCs) could directly respond to inflammatory cytokines by mounting a proliferative response thought to mediate the emergency production of mature blood cells. In the intervening years, we have gained mechanistic insight into this so-called activation process and have started to learn such a response may come at a cost in terms of ultimately resulting in HSC exhaustion and hematologic dysfunction. In this review article, we report the progress we have made in understanding the interplay between infection, inflammation and HSCs during the funding period of the Collaborative Research Center 873 "Maintenance and Differentiation of Stem Cells in Development and Disease", and place this work within the context of recent output by others working within this field.

Helminth infection impacts hematopoiesis

Helminth infections are common in animals. However, the impact of a helminth infection on the function of hematopoietic stem cells (HSCs) and other hematopoietic cells has not been comprehensively defined. Here we describe the hematopoietic response to infection of mice with Schistosoma mansoni, a parasitic flatworm which causes schistosomiasis. We analyzed the frequency or number of hematopoietic cell types in the bone marrow, spleen, liver, thymus, and blood, and observed multiple hematopoietic changes caused by infection. Schistosome infection impaired bone marrow HSC function after serial transplantation. Functional HSCs were present in the infected liver. Infection blocked bone marrow erythropoiesis and augmented spleen erythropoiesis, observations consistent with the anemia and splenomegaly prevalent in schistosomiasis patients. This work defines the hematopoietic response to schistosomiasis, a debilitating disease afflicting more than 200 million people, and identifies impairments in HSC function and erythropoiesis.

Antigen presentation safeguards the integrity of the hematopoietic stem cell pool

Hematopoietic stem and progenitor cells (HSPCs) are responsible for the production of blood and immune cells. Throughout life, HSPCs acquire oncogenic aberrations that can cause hematological cancers. Although molecular programs maintaining stem cell integrity have been identified, safety mechanisms eliminating malignant HSPCs from the stem cell pool remain poorly characterized. Here, we show that HSPCs constitutively present antigens via major histocompatibility complex class II. The presentation of immunogenic antigens, as occurring during malignant transformation, triggers bidirectional interactions between HSPCs and antigen-specific CD4+ T cells, causing stem cell proliferation, differentiation, and specific exhaustion of aberrant HSPCs. This immunosurveillance mechanism effectively eliminates transformed HSPCs from the hematopoietic system, thereby preventing leukemia onset. Together, our data reveal a bidirectional interaction between HSPCs and CD4+ T cells, demonstrating that HSPCs are not only passive receivers of immunological signals but also actively engage in adaptive immune responses to safeguard the integrity of the stem cell pool.

A complex proinflammatory cascade mediates the activation of HSCs upon LPS exposure in vivo

HSCs are transiently activated by acute LPS challenge via direct and indirect mechanisms, including CD115⁺ monocytic cells in BM.

The combined action of IFNα, IFNγ, TNFα, IL-1α, IL-1β, and other cytokines is required to mediate HSC activation in response to LPS in vivo.

Infections are a key source of stress to the hematopoietic system. While infections consume short-lived innate immune cells, their recovery depends on quiescent hematopoietic stem cells (HSCs) with long-term self-renewal capacity. Both chronic inflammatory stress and bacterial infections compromise competitive HSC capacity and cause bone marrow (BM) failure. However, our understanding of how HSCs act during acute and contained infections remains incomplete. Here, we used advanced chimeric and genetic mouse models in combination with pharmacological interventions to dissect the complex nature of the acute systemic response of HSCs to lipopolysaccharide (LPS), a well-established model for inducing inflammatory stress. Acute LPS challenge transiently induced proliferation of quiescent HSCs in vivo. This response was not only mediated via direct LPS-TLR4 conjugation on HSCs but also involved indirect TLR4 signaling in CD115⁺ monocytic cells, inducing a complex proinflammatory cytokine cascade in BM. Downstream of LPS-TLR4 signaling, the combined action of proinflammatory cytokines such as interferon (IFN)α, IFNγ, tumor necrosis factor-α, interleukin (IL)-1α, IL-1β, and many others is required to mediate full HSC activation in vivo. Together, our study reveals detailed mechanistic insights into the interplay of proinflammatory cytokine-induced molecular pathways and cell types that jointly orchestrate the complex process of emergency hematopoiesis and HSC activation upon LPS exposure in vivo.

Persistent Cutaneous Leishmania major Infection Promotes Infection-Adapted Myelopoiesis

Hematopoietic stem/progenitor cells (HSPC) are responsible for the generation of most immune cells throughout the lifespan of the organism. Inflammation can activate bone marrow HSPCs, leading to enhanced myelopoiesis to replace cells, such as neutrophils, which are attracted to inflamed tissues. We have previously shown that HSPC activation promotes parasite persistence and expansion in experimental visceral leishmaniasis through the increased production of permissive monocytes. However, it is not clear if the presence of the parasite in the bone marrow was required for infection-adapted myelopoiesis. We therefore hypothesized that persistent forms of Leishmania major (cutaneous leishmaniasis) could also activate HSPCs and myeloid precursors in the C57Bl/6 mouse model of intradermal infection in the ear. The accrued influx of myeloid cells to the lesion site corresponded to an increase in myeloid-biased HSPCs in the bone marrow and spleen in mice infected with a persistent strain of L. major, together with an increase in monocytes and monocyte-derived myeloid cells in the spleen. Analysis of the bone marrow cytokine and chemokine environment revealed an attenuated type I and type II interferon response in the mice infected with the persistent strain compared to the self-healing strain, while both strains induced a rapid upregulation of myelopoietic cytokines, such as IL-1β and GM-CSF. These results demonstrate that an active infection in the bone marrow is not necessary for the induction of infection-adapted myelopoiesis, and underline the importance of considering alterations to the bone marrow output when analyzing in vivo host-pathogen interactions.

Chronic viral infections persistently alter marrow stroma and impair hematopoietic stem cell fitness

Chronic viral infections are associated with hematopoietic suppression, bone marrow (BM) failure, and hematopoietic stem cell (HSC) exhaustion. However, how persistent viral challenge and inflammatory responses target BM tissues and perturb hematopoietic competence remains poorly understood. Here, we combine functional analyses with advanced 3D microscopy to demonstrate that chronic infection with lymphocytic choriomeningitis virus leads to (1) long-lasting decimation of the BM stromal network of mesenchymal CXCL12-abundant reticular cells, (2) proinflammatory transcriptional remodeling of remaining components of this key niche subset, and (3) durable functional defects and decreased competitive fitness in HSCs. Mechanistically, BM immunopathology is elicited by virus-specific, activated CD8 T cells, which accumulate in the BM via interferon-dependent mechanisms. Combined antibody-mediated inhibition of type I and II IFN pathways completely preempts degeneration of CARc and protects HSCs from chronic dysfunction. Hence, viral infections and ensuing immune reactions durably impact BM homeostasis by persistently decreasing the competitive fitness of HSCs and disrupting essential stromal-derived, hematopoietic-supporting cues.

Remodeling of the Bone Marrow Stromal Microenvironment During Pathogenic Infections

The bone marrow (BM) is the primary hematopoietic organ and a hub in which organismal demands for blood cellular output are systematically monitored. BM tissues are additionally home to a plethora of mature immune cell types, providing functional environments for the activation of immune responses and acting as preferred anatomical reservoirs for cells involved in immunological memory. Stromal cells of the BM microenvironment crucially govern different aspects of organ function, by structuring tissue microanatomy and by directly providing essential regulatory cues to hematopoietic and immune components in distinct niches. Emerging evidence demonstrates that stromal networks are endowed with remarkable functional and structural plasticity. Stress-induced adaptations of stromal cells translate into demand-driven hematopoiesis. Furthermore, aberrations of stromal integrity arising from pathological conditions critically contribute to the dysregulation of BM function. Here, we summarize our current understanding of the alterations that pathogenic infections and ensuing inflammatory conditions elicit on the global topography of the BM microenvironment, the integrity of anatomical niches and cellular interactions, and ultimately, on the regulatory function of diverse stromal subsets.

Aberrant chromatin landscape following loss of the H3.3 chaperone Daxx in haematopoietic precursors leads to Pu.1-mediated neutrophilia and inflammation

Defective silencing of retrotransposable elements has been linked to inflammageing, cancer and autoimmune diseases. However, the underlying mechanisms are only partially understood. Here we implicate the histone H3.3 chaperone Daxx, a retrotransposable element repressor inactivated in myeloid leukaemia and other neoplasms, in protection from inflammatory disease. Loss of Daxx alters the chromatin landscape, H3.3 distribution and histone marks of haematopoietic progenitors, leading to engagement of a Pu.1-dependent transcriptional programme for myelopoiesis at the expense of B-cell differentiation. This causes neutrophilia and inflammation, predisposing mice to develop an autoinflammatory skin disease. While these molecular and phenotypic perturbations are in part reverted in animals lacking both Pu.1 and Daxx, haematopoietic progenitors in these mice show unique chromatin and transcriptome alterations, suggesting an interaction between these two pathways. Overall, our findings implicate retrotransposable element silencing in haematopoiesis and suggest a cross-talk between the H3.3 loading machinery and the pioneer transcription factor Pu.1.

Hematopoietic Dysfunction during Graft-Versus-Host Disease: A Self-Destructive Process?

Graft-versus-host disease (GvHD) is a major complication of allogeneic hematopoietic (stem) cell transplantation (HCT). Clinically, GvHD is associated with severe and long-lasting hematopoietic dysfunction, which may contribute to the high mortality of GvHD after HCT. During GvHD, excessive immune activation damages both hematopoietic stem and progenitor cells and their surrounding bone marrow niche, leading to a reduction in cell number and functionality of both compartments. Hematopoietic dysfunction can be further aggravated by the occurrence—and treatment—of HCT-associated complications. These include immune suppressive therapy, coinciding infections and their treatment, and changes in the microbiome. In this review, we provide a structured overview of GvHD-mediated hematopoietic dysfunction, including the targets in the bone marrow, the mechanisms of action and the effect of GvHD-related complications and their treatment. This information may aid in the identification of treatment options to improve hematopoietic function in patients, during and after GvHD.

The Hematopoietic Bone Marrow Niche Ecosystem

The bone marrow (BM) microenvironment, also called the BM niche, is essential for the maintenance of fully functional blood cell formation (hematopoiesis) throughout life. Under physiologic conditions the niche protects hematopoietic stem cells (HSCs) from sustained or overstimulation. Acute or chronic stress deregulates hematopoiesis and some of these alterations occur indirectly via the niche. Effects on niche cells include skewing of its cellular composition, specific localization and molecular signals that differentially regulate the function of HSCs and their progeny. Importantly, while acute insults display only transient effects, repeated or chronic insults lead to sustained alterations of the niche, resulting in HSC deregulation. We here describe how changes in BM niche composition (ecosystem) and structure (remodeling) modulate activation of HSCs in situ. Current knowledge has revealed that upon chronic stimulation, BM remodeling is more extensive and otherwise quiescent HSCs may be lost due to diminished cellular maintenance processes, such as autophagy, ER stress response, and DNA repair. Features of aging in the BM ecology may be the consequence of intermittent stress responses, ultimately resulting in the degeneration of the supportive stem cell microenvironment. Both chronic stress and aging impair the functionality of HSCs and increase the overall susceptibility to development of diseases, including malignant transformation. To understand functional degeneration, an important prerequisite is to define distinguishing features of unperturbed niche homeostasis in different settings. A unique setting in this respect is xenotransplantation, in which human cells depend on niche factors produced by other species, some of which we will review. These insights should help to assess deviations from the steady state to actively protect and improve recovery of the niche ecosystem in situ to optimally sustain healthy hematopoiesis in experimental and clinical settings.

NLRP1 in Bone Marrow Microenvironment Controls Hematopoietic Reconstitution After Transplantation

Pretreatment before transplantation initiates an inflammatory response. Inflammasomes are key regulators of immune and inflammatory responses, but their role in regulating hematopoiesis is unclear. Our study intended to assess the role and mechanism of nucleotide-binding domain and leucine-rich repeat pyrin-domain containing protein 1 (NLRP1) in the bone marrow microenvironment on hematopoiesis regulation. To explore the effects of an absence of NLRP1 on hematopoietic reconstitution, we established a hematopoietic cell transplantation model by infusing bone marrow mononuclear cells of wild-type C57BL/6 mice into either NLRP1 knockout (NLRP1-KO) or wild-type C57BL/6 mice. Using the transplantation model, the role of NLRP1 in the bone marrow microenvironment was determined by flow cytometry, hemacytometry, and hematoxylin and eosin staining. As the major component of the bone marrow microenvironment, mesenchymal stem cells (MSCs) were isolated to analyze the effects of NLRP1 on them by osteogenic and adipogenic induction. Endothelial cells (ECs) were isolated and sorted by magnetic beads. The expression of adhesion molecules and their relationship with nuclear factor kappa B (NF-κB) were measured by immunofluorescence, enzyme-linked immunosorbent assay, and western blot. Finally, the effect of NLRP1-deleted MSCs or ECs on hematopoietic stem and progenitor cells (HSPCs) was examined by establishing co-culture models. Compared with C57BL/6 recipients, reduced inflammatory cell infiltration, decreased levels of proinflammatory cytokines interleukin (IL)-18, IL-1β, IL-6, tumor necrosis factor alpha (TNF-α), and interferon gamma (IFN-γ), together with reduced pathological injury of bone marrow, were observed in NLRP1-KO recipients after transplantation. However, increased HSPC engraftment and hematopoietic reconstitution were detected in NLRP1-KO recipients after transplantation. Furthermore, MSCs isolated from NLRP1-KO mice had decreased osteogenic and adipogenic differentiation and increased proliferation and differentiation of HSPCs. The expression of adhesion molecules in ECs from NLRP1-KO mice was increased due to the promotion of nuclear translocation of NF-κB; these adhesion molecules are critical for hematopoietic stem cell homing. Knockout of NLRP1 in the bone marrow microenvironment could significantly relieve bone marrow inflammatory response and promote hematopoietic reconstitution, perhaps by regulating MSCs and ECs, indicating that NLRP1 might be a target for the treatment of delayed hematopoietic and immune recovery in patients after hematopoietic stem cell transplantation.

Inflammation as a regulator of hematopoietic stem cell function in disease, aging, and clonal selection

Inflammation is an evolutionarily selected defense response to infection or tissue damage that involves activation and consumption of immune cells in order to reestablish and maintain organismal integrity. In this process, hematopoietic stem cells (HSCs) are themselves exposed to inflammatory cues and via proliferation and differentiation, replace mature immune cells in a demand-adapted fashion. Here, we review how major sources of systemic inflammation act on and subsequently shape HSC fate and function. We highlight how lifelong inflammatory exposure contributes to HSC inflamm-aging and selection of premalignant HSC clones. Finally, we explore emerging areas of interest and open questions remaining in the field.

To portray clonal evolution in blood cancer, count your stem cells

Clonal evolution, the process of expansion and diversification of mutated cells, plays an important role in cancer development, resistance, and relapse. Although clonal evolution is most often conceived of as driven by natural selection, recent studies uncovered that neutral evolution shapes clonal evolution in a significant proportion of solid cancers. In hematological malignancies, the interplay between neutral evolution and natural selection is also disputed. Because natural selection selects cells with a greater fitness, providing a growth advantage to some cells relative to others, the architecture of clonal evolution serves as indirect evidence to distinguish natural selection from neutral evolution and has been associated with different prognoses for the patient. Linear architecture, when the new mutant clone grows within the previous one, is characteristic of hematological malignancies and is typically interpreted as being driven by natural selection. Here, we discuss the role of natural selection and neutral evolution in the production of linear clonal architectures in hematological malignancies. Although it is tempting to attribute linear evolution to natural selection, we argue that a lower number of contributing stem cells accompanied by genetic drift can also result in a linear pattern of evolution, as illustrated by simulations of clonal evolution in hematopoietic stem cells. The number of stem cells contributing to long-term clonal evolution is not known in the pathological context, and we advocate that estimating these numbers in the context of cancer and aging is crucial to parsing out neutral evolution from natural selection, 2 processes that require different therapeutic strategies.

Yin and Yang: The dual effects of interferons on hematopoiesis

Interferons are an ancient and well-conserved group of inflammatory cytokines most famous for their role in viral immunity. A decade ago, we discovered that interferons also play an important role in the biology of hematopoietic stem cells (HSCs), which are responsible for lifelong blood production. Though we have learned a great deal about the role of interferons on HSC quiescence, differentiation, and self-renewal, there remains some controversy regarding how interferons impact these stem cells, with differing conclusions depending on experimental models and clinical context. Here, we review the contradictory roles of Type 1 and 2 interferons in hematopoiesis. Specifically, we highlight the roles of interferons in embryonic and adult hematopoiesis, along with short-term and long-term adaptive and maladaptive responses to inflammation. We discuss experimental challenges in the study of these powerful yet short-lived cytokines and strategies to address those challenges. We further review the contribution by interferons to disease states including bone marrow failure and aplastic anemia as well as their therapeutic use to treat myeloproliferative neoplasms and viral infections, including SARS-CoV2. Understanding the opposing effects of interferons on hematopoiesis will elucidate immune responses and bone marrow failure syndromes, and future therapeutic approaches for patients undergoing HSC transplantation or fighting infectious diseases and cancer.

Antiviral immunity and nucleic acid sensing in haematopoietic stem cell gene engineering

The low gene manipulation efficiency of human hematopoietic stem and progenitor cells (HSPC) remains a major hurdle for sustainable and broad clinical application of innovative therapies for a wide range of disorders. Given that all current and emerging gene transfer and editing technologies are bound to expose HSPC to exogenous nucleic acids and most often also to viral vectors, we reason that host antiviral factors and nucleic acid sensors play a pivotal role in the efficacy of HSPC genetic manipulation. Here, we review recent progress in our understanding of vector-host interactions and innate immunity in HSPC upon gene engineering and discuss how dissecting this crosstalk can guide the development of more stealth and efficient gene therapy approaches in the future.

Fate of Hematopoiesis During Aging. What Do We Really Know, and What are its Implications?

There is an ongoing shift in demographics such that older persons will outnumber young persons in the coming years, and with it age-associated tissue attrition and increased diseases and disorders. There has been increased information on the association of the aging process with dysregulation of hematopoietic stem (HSC) and progenitor (HPC) cells, and hematopoiesis. This review provides an extensive up-to date summary on the literature of aged hematopoiesis and HSCs placed in context of potential artifacts of the collection and processing procedure, that may not be totally representative of the status of HSCs in their in vivo bone marrow microenvironment, and what the implications of this are for understanding aged hematopoiesis. This review covers a number of interactive areas, many of which have not been adequately explored. There are still many unknowns and mechanistic insights to be elucidated to better understand effects of aging on the hematopoietic system, efforts that will take multidisciplinary approaches, and that could lead to means to ameliorate at least some of the dysregulation of HSCs and HPCs associated with the aging process. Graphical Abstract.

The Transition from Quiescent to Activated States in Human Hematopoietic Stem Cells Is Governed by Dynamic 3D Genome Reorganization

Lifelong blood production requires long-term hematopoietic stem cells (LT-HSCs), marked by stemness states involving quiescence and self-renewal, to transition into activated short-term HSCs (ST-HSCs) with reduced stemness. As few transcriptional changes underlie this transition, we used single-cell and bulk assay for transposase-accessible chromatin sequencing (ATAC-seq) on human HSCs and hematopoietic stem and progenitor cell (HSPC) subsets to uncover chromatin accessibility signatures, one including LT-HSCs (LT/HSPC signature) and another excluding LT-HSCs (activated HSPC [Act/HSPC] signature). These signatures inversely correlated during early hematopoietic commitment and differentiation. The Act/HSPC signature contains CCCTC-binding factor (CTCF) binding sites mediating 351 chromatin interactions engaged in ST-HSCs, but not LT-HSCs, enclosing multiple stemness pathway genes active in LT-HSCs and repressed in ST-HSCs. CTCF silencing derepressed stemness genes, restraining quiescent LT-HSCs from transitioning to activated ST-HSCs. Hence, 3D chromatin interactions centrally mediated by CTCF endow a gatekeeper function that governs the earliest fate transitions HSCs make by coordinating disparate stemness pathways linked to quiescence and self-renewal.

The early life education of the immune system: Moms, microbes and (missed) opportunities

The early life immune system is characterized by unique developmental milestones. Functionally diverse immune cells arise from distinct waves of hematopoietic stem cells, a phenomenon referred to as 'layered' immunity. This stratified development of immune cells extends to lineages of both innate and adaptive cells. The defined time window for the development of these immune cells lends itself to the influence of specific exposures typical of the early life period. The perinatal immune system develops in a relatively sterile fetal environment but emerges into one filled with a multitude of antigenic encounters. A major burden of this comes in the form of the microbiota that is being newly established at mucosal surfaces of the newborn. Accumulating evidence suggests that early life microbial exposures, including those arising in utero, can imprint long-lasting changes in the offspring's immune system and determine disease risk throughout life. In this review, I highlight unique features of early life immunity and explore the role of intestinal bacteria in educating the developing immune system.

The role of the stem cell epigenome in normal aging and rejuvenative therapy

Adult stem cells are ultimately responsible for the lifelong maintenance of regenerating of tissues during both homeostasis and following injury. Hence, the functional attrition of adult stem cells is thought to be an important driving factor behind the progressive functional decline of tissues and organs that is observed during aging. The mechanistic cause underlying this age-associated exhaustion of functional stem cells is likely to be complex and multifactorial. However, it is clear that progressive remodeling of the epigenome and the resulting deregulation of gene expression programs can be considered a hallmark of aging, and is likely a key factor in mediating altered biological function of aged stem cells. In this review, we outline cell intrinsic and extrinsic mediators of epigenome remodeling during aging; discuss how such changes can impact on stem cell function; and describe how resetting the aged epigenome may rejuvenate some of the biological characteristics of stem cells.

Single-cell and spatial transcriptomics approaches of the bone marrow microenvironment

PURPOSE OF REVIEW

The bone marrow is home to hematopoietic stem cells responsible for lifelong blood production, alongside mesenchymal stem cells required for skeletal regeneration. In the bone marrow, a unique combination of signals derived from a multitude of cell types results in the establishment of so-called niches that regulate stem-cell maintenance and differentiation. Recently, single-cell and spatially resolved transcriptomics technologies have been utilized to characterize the murine bone marrow microenvironment during homeostasis, stress and upon cancer-induced remodeling. In this review, we summarize the major findings of these studies.

RECENT FINDINGS

Single-cell technologies applied to bone marrow provided the first systematic and label-free identification of bone marrow cell types, enabled their molecular and spatial characterization, and clarified the cellular sources of key prohematopoietic factors. Large transcriptional heterogeneity and novel subpopulations were observed in compartments previously thought to be homogenous. For example, Lepr Cxcl12-abundant reticular cells were shown to constitute the major source of prohematopoietic factors, but consist of subpopulations differing in their adipogenic versus osteogenic priming, morphology and localization. These subpopulations were suggested to act as professional cytokine secreting cells, thereby establishing distinct bone marrow niches.

SUMMARY

Single-cell and spatially resolved transcriptomics approaches have clarified the molecular identity and localization of bone marrow-resident cell types, paving the road for a deeper exploration of bone marrow niches in the mouse and humans.

Common Sources of Inflammation and Their Impact on Hematopoietic Stem Cell Biology

Purpose of Review

Inflammatory signals have emerged as critical regulators of hematopoietic stem cell (HSC) function. Specifically, HSCs are highly responsive to acute changes in systemic inflammation and this influences not only their division rate but also their lineage fate. Identifying how inflammation regulates HSCs and shapes the blood system is crucial to understanding the mechanisms underpinning these processes, as well as potential links between them.

Recent Findings

A widening array of physiologic and pathologic processes involving heightened inflammation are now recognized to critically affect HSC biology and blood lineage production. Conditions documented to affect HSC function include not only acute and chronic infections but also autoinflammatory conditions, irradiation injury, and physiologic states such as aging and obesity.

Summary

Recognizing the contexts during which inflammation affects primitive hematopoiesis is essential to improving our understanding of HSC biology and informing new therapeutic interventions against maladaptive hematopoiesis that occurs during inflammatory diseases, infections, and cancer-related disorders.

Lineage commitment of hematopoietic stem cells and progenitors: insights from recent single cell and lineage tracing technologies

Blood production is essential to maintain human health, and even small perturbations in hematopoiesis can cause disease. Hematopoiesis has therefore been the focus of much research for many years. Experiments determining the lineage potentials of hematopoietic stem and progenitor cells (HSPCs) in vitro and after transplantation revealed a hierarchy of progenitor cell states, where differentiating cells undergo lineage commitment-a series of irreversible changes that progressively restrict their potential. New technologies have recently been developed that allow for a more detailed analysis of the molecular states and fates of differentiating HSPCs. Proteomic and lineage-tracing approaches, alongside single-cell transcriptomic analyses, have recently helped to reveal the biological complexity underlying lineage commitment during hematopoiesis. Recent insights from these new technologies were presented by Dr. Marjorie Brand and Dr. Allon Klein in the Summer 2019 ISEH Webinar, and are discussed in this Perspective.

The mechanisms of pathological extramedullary hematopoiesis in diseases

Extramedullary hematopoiesis (EMH) is the expansion and differentiation of hematopoietic stem and progenitor cells outside of the bone marrow. In postnatal life, as a compensatory mechanism for ineffective hematopoiesis of the bone marrow, pathological EMH is triggered by hematopoietic disorders, insufficient hematopoietic compensation, and other pathological stress conditions, such as infection, advanced tumors, anemia, and metabolic stress. Pathological EMH has been reported in many organs, and the sites of pathological EMH may be related to reactivation of the embryonic hematopoietic structure in these organs. As a double-edged sword (blood and immune cell supplementation as well as clinical complications), pathological EMH has been widely studied in recent years. In particular, pathological EMH induced by late-stage tumors contributes to tumor immunosuppression. Thus, a deeper understanding of the mechanism of pathological EMH may be conducive to the development of therapies against the pathological processes that induce EMH. This article reviews the recent progress of research on the cellular and molecular mechanisms of pathological EMH in specific diseases.

The bone marrow hematopoietic niche and its adaptation to infection

Hematopoiesis is responsible for the formation of all blood cells from hematopoietic stem cells (HSC) in the bone marrow (BM). It is a highly regulated process, in order to adapt its cellular output to changing body requirements. Specific microenvironmental conditions within the BM must exist in order to maintain HSC pluripotency and self-renewal, as well as to ensure appropriate differentiation of progenitor cells towards each hematopoietic lineage. Those conditions were coined "the hematopoietic niche" and their identity in terms of cell types, location and soluble molecular components has been the subject of intense research in the last decades. Infections are one of the environmental challenges to which hematopoiesis must respond, to feed the immune system with functional cell components and compensate for cellular losses. However, how infections impact the bone marrow hematopoietic niche(s) remains elusive and most of the mechanisms involved are still largely unknown. Here, we review the most recent advances on our knowledge on the hematopoietic niche composition and regulation during homeostasis and also on how the niche responds to infectious stress.

Myeloid Cells Restrict MCMV and Drive Stress-Induced Extramedullary Hematopoiesis through STAT1

Cytomegalovirus (CMV) has a high prevalence worldwide, is often fatal for immunocompromised patients, and causes bone marrow suppression. Deficiency of signal transducer and activator of transcription 1 (STAT1) results in severely impaired antiviral immunity. We have used cell-type restricted deletion of Stat1 to determine the importance of myeloid cell activity for the defense against murine CMV (MCMV). We show that myeloid STAT1 limits MCMV burden and infection-associated pathology in the spleen but does not affect ultimate clearance of infection. Unexpectedly, we found an essential role of myeloid STAT1 in the induction of extramedullary hematopoiesis (EMH). The EMH-promoting function of STAT1 was not restricted to MCMV infection but was also observed during CpG oligodeoxynucleotide-induced sterile inflammation. Collectively, we provide genetic evidence that signaling through STAT1 in myeloid cells is required to restrict MCMV at early time points post-infection and to induce compensatory hematopoiesis in the spleen.

A Bump in the Road: How the Hostile AML Microenvironment Affects CAR T Cell Therapy

Chimeric antigen receptor (CAR) T cells targeting CD19 have been successful treating patients with relapsed/refractory B cell acute lymphoblastic leukemia (ALL) and B cell lymphomas. However, relapse after CAR T cell therapy is still a challenge. In addition, preclinical and early clinical studies targeting acute myeloid leukemia (AML) have not been as successful. This can be attributed in part to the presence of an AML microenvironment that has a dampening effect on the antitumor activity of CAR T cells. The AML microenvironment includes cellular interactions, soluble environmental factors, and structural components. Suppressive immune cells including myeloid derived suppressor cells and regulatory T cells are known to inhibit T cell function. Environmental factors contributing to T cell exhaustion, including immune checkpoints, anti-inflammatory cytokines, chemokines, and metabolic alterations, impact T cell activity, persistence, and localization. Lastly, structural factors of the bone marrow niche, secondary lymphoid organs, and extramedullary sites provide opportunities for CAR T cell evasion by AML blasts, contributing to treatment resistance and relapse. In this review we discuss the effect of the AML microenvironment on CAR T cell function. We highlight opportunities to enhance CAR T cell efficacy for AML through manipulating, targeting, and evading the anti-inflammatory leukemic microenvironment.

Hypercholesterolemia Accelerates the Aging Phenotypes of Hematopoietic Stem Cells by a Tet1-Dependent Pathway

Hypercholesterolemia accelerates the phenotypes of aging in hematopoietic stem cells (HSCs). As yet, little is known about the underlying mechanism. We found that hypercholesterolemia downregulates Ten eleven translocation 1 (Tet1) in HSCs. The total HSC population was increased, while the long-term (LT) population, side population and reconstitution capacity of HSCs were significantly decreased in Tet1^−/− mice. Expression of the Tet1 catalytic domain in HSCs effectively restored the LT population and reconstitution capacity of HSCs isolated from Tet1^−/− mice. While Tet1 deficiency upregulated the expression of p19 and p21 in HSCs by decreasing the H3K27me3 modification, the restoration of Tet1 activity reduced the expression of p19, p21 and p27 by restoring the H3K27me3 and H3K36me3 modifications on these genes. These results indicate that Tet1 plays a critical role in maintaining the quiescence and reconstitution capacity of HSCs and that hypercholesterolemia accelerates HSC aging phenotypes by decreasing Tet1 expression in HSCs.

Training the Fetal Immune System Through Maternal Inflammation-A Layered Hygiene Hypothesis

Over the last century, the alarming surge in allergy and autoimmune disease has led to the hypothesis that decreasing exposure to microbes, which has accompanied industrialization and modern life in the Western world, has fundamentally altered the immune response. In its current iteration, the “hygiene hypothesis” suggests that reduced microbial exposures during early life restricts the production and differentiation of immune cells suited for immune regulation. Although it is now well-appreciated that the increase in hypersensitivity disorders represents a “perfect storm” of many contributing factors, we argue here that two important considerations have rarely been explored. First, the window of microbial exposure that impacts immune development is not limited to early childhood, but likely extends into the womb. Second, restricted microbial interactions by an expectant mother will bias the fetal immune system toward hypersensitivity. Here, we extend this discussion to hypothesize that the cell types sensing microbial exposures include fetal hematopoietic stem cells, which drive long-lasting changes to immunity.

Cyclosporine H Improves the Multi-Vector Lentiviral Transduction of Murine Haematopoietic Progenitors and Stem Cells

Haematopoietic stem cells (HSCs) have the potential for lifetime production of blood and immune cells. The introduction of transgenes into HSCs is important for basic research, as well as for multiple clinical applications, because HSC transplantation is an already established procedure. Recently, a major advancement has been reported in the use of cyclosporine H (CsH), which can significantly enhance the lentivirus (LV) transduction of human haematopoietic stem and progenitor cells (HSPCs). In this study, we employed CsH for LV transduction of murine HSCs and defined haematopoietic progenitors, confirming previous findings in more specific subsets of primitive haematopoietic cells. Our data confirm increased efficiencies, in agreement with the published data. We further experimented with the transduction with the simultaneous use of several vectors. The use of CsH yielded an even more robust increase in rates of multi-vector infection than the increase for a single-vector. CsH was reported to reduce the innate resistance mechanism against LV infection. We indeed found that additional pretreatment could increase the efficiency of transduction, in agreement with the originally reported results. Our data also suggest that CsH does not reduce the efficiency of transplantation into immune-competent hosts or the differentiation of HSCs while enhancing stable long-term expression in vivo. This new additive will surely help many studies in animal models and might be very useful for the development of novel HSC gene therapy approaches.

STAT5A and STAT5B-Twins with Different Personalities in Hematopoiesis and Leukemia

The transcription factors STAT5A and STAT5B have essential roles in survival and proliferation of hematopoietic cells-which have been considered largely redundant. Mutations of upstream kinases, copy number gains, or activating mutations in STAT5A, or more frequently in STAT5B, cause altered hematopoiesis and cancer. Interfering with their activity by pharmacological intervention is an up-and-coming therapeutic avenue. Precision medicine requests detailed knowledge of STAT5A's and STAT5B's individual functions. Recent evidence highlights the privileged role for STAT5B over STAT5A in normal and malignant hematopoiesis. Here, we provide an overview on their individual functions within the hematopoietic system.

Updates on the hematologic tumor microenvironment and its therapeutic targeting

In this review article, we present recent updates on the hematologic tumor microenvironment following the 3rd Scientific Workshop on the Haematological Tumour Microenvironment and its Therapeutic Targeting organized by the European School of Hematology, which took place at the Francis Crick Institute in London in February 2019. This review article is focused on recent scientific advances highlighted in the invited presentations at the meeting, which encompassed the normal and malignant niches supporting hematopoietic stem cells and their progeny. Given the precise focus, it does not discuss other relevant contributions in this field, which have been the scope of other recent reviews. The content covers basic research and possible clinical applications with the major therapeutic angle of utilizing basic knowledge to devise new strategies to target the tumor microenvironment in hematologic cancers. The review is structured in the following sections: (i) regulation of normal hematopoietic stem cell niches during development, adulthood and aging; (ii) metabolic adaptation and reprogramming in the tumor microenvironment; (iii) the key role of inflammation in reshaping the normal microenvironment and driving hematopoietic stem cell proliferation; (iv) current understanding of the tumor microenvironment in different malignancies, such as chronic lymphocytic leukemia, multiple myeloma, acute myeloid leukemia and myelodysplastic syndromes; and (v) the effects of therapies on the microenvironment and some opportunities to target the niche directly in order to improve current treatments.

Causes and Consequences of Hematopoietic Stem Cell Heterogeneity

Blood and immune cells derive from multipotent hematopoietic stem cells (HSCs). Classically, stem and progenitor populations have been considered discrete homogeneous populations. However, recent technological advances have revealed significant HSC heterogeneity, with evidence for early HSC lineage segregation and the presence of lineage-biased HSCs and lineage-restricted progenitors within the HSC compartment. These and other findings challenge many aspects of the classical view of HSC biology. We review the most recent findings regarding the causes and consequences of HSC heterogeneity, discuss their far-reaching implications, and suggest that so-called continuum-based models may help consolidate apparently divergent experimental observations in this field.

IFN Signaling in Inflammation and Viral Infections: New Insights from Fish Models

The overarching structure of the type I interferon (IFN) system is conserved across vertebrates. However, the variable numbers of whole genome duplication events during fish evolution offer opportunities for the expansion, diversification, and new functionalization of the genes that are involved in antiviral immunity. In this review, we examine how fish models provide new insights about the implication of virus-driven inflammation in immunity and hematopoiesis. Mechanisms that have been discovered in fish, such as the strong adjuvant effect of type I IFN that is used with DNA vaccination, constitute good models to understand how virus-induced inflammatory mechanisms can interfere with adaptive responses. We also comment on new discoveries regarding the role of pathogen-induced inflammation in the development and guidance of hematopoietic stem cells in zebrafish. These findings raise issues about the potential interferences of viral infections with the establishment of the immune system. Finally, the recent development of genome editing provides new opportunities to dissect the roles of the key players involved in the antiviral response in fish, hence enhancing the power of comparative approaches.

Antigen-specific CD8 T cells in cell cycle circulate in the blood after vaccination

Although clonal expansion is a hallmark of adaptive immunity, the location(s) where antigen‐responding T cells enter cell cycle and complete it have been poorly explored. This lack of knowledge stems partially from the limited experimental approaches available. By using Ki67 plus DNA staining and a novel strategy for flow cytometry analysis, we distinguished antigen‐specific CD8 T cells in G₀, in G₁ and in S‐G₂/M phases of cell cycle after intramuscular vaccination of BALB/c mice with antigen‐expressing viral vectors. Antigen‐specific cells in S‐G₂/M were present at early times after vaccination in lymph nodes (LNs), spleen and, surprisingly, also in the blood, which is an unexpected site for cycling of normal non‐leukaemic cells. Most proliferating cells had high scatter profile and were undetected by current criteria of analysis, which under‐estimated up to 6 times antigen‐specific cell frequency in LNs. Our discovery of cycling antigen‐specific CD8 T cells in the blood opens promising translational perspectives.

Hematopoietic Stem Cell Heterogeneity

Hematopoietic stem cells (HSCs) maintain lifelong production of mature blood cells and regenerate the hematopoietic system after cytotoxic injury. Use of expanding cell surface marker panels and advanced functional analyses have revealed the presence of several immunophenotypically different HSC subsets with distinct self-renewal and repopulating capacity and bias toward selective lineage differentiation. This chapter summarizes current understanding of the phenotypic and functional heterogeneity within the HSC pool, with emphasis on the immunophenotypes and functional features of several known HSC subsets, and their roles in steady-state and emergency hematopoiesis, and in aging. The chapter also highlights some of the future research directions to elucidate further the biology and function of different HSC subsets in health and disease states.

The Impact of Integrin β2 on Granulocyte/Macrophage Progenitor Proliferation

Previously, we reported that although the HSPC frequency in bone marrow cells (BMC) was comparable between β2-/- and β2+/+ mice, transplantation of β2-/- BMC into lethally irradiated CD45.1 recipient resulted in more myeloid cell production than β2+/+ BMC. The objective of this study is to address if integrin β2 deficiency skews granulocyte/macrophage progenitor (GMP) proliferation. FACS analysis demonstrated that GMP frequency and cell number were higher and megakaryocyte/erythrocyte progenitor frequency and cell number were lower in β2-/- mice than β2+/+ mice. However, the common myeloid progenitors (CMP) frequency and cell number were similar between the two groups. The increased GMP number was due to GMP proliferation as evidenced by the percentage of BrdU-incorporating GMP. Whole genome transcriptome analysis identified increased FcεRIα expression in β2-/- CMP compared to β2+/+ CMP. FcεRIα expression on β2-/- GMP was detected increased in β2-/- mice by qRT-PCR and FACS. Although transplantation of FcεRIα^hi GMP or FcεRIα^lo GMP into lethally irradiated CD45.1 recipient resulted in comparable myeloid cell production, transplantation of β2 deficient FcεRIα^hi GMP generated more myeloid cells than β2+/+ FcεRIα^hi GMP. GATA2 expression was increased in β2-/- GMP. Using a luciferase reporter assay, we demonstrated that mutation of the GATA2 binding site in the FcεRIα promoter region diminished FcεRIα transcription. In vitro, the addition of IgE, the ligand of FcεRIα, promoted GMP expansion, which was abrogated by inhibition of JNK phosphorylation. Integrin β2 deficiency promoted GMP proliferation and myeloid cell production, which was mediated via FcεRIα/IgE-induced JNK phosphorylation in GMP. Stem Cells 2019;37:430-440.

Cyclosporine H Overcomes Innate Immune Restrictions to Improve Lentiviral Transduction and Gene Editing In Human Hematopoietic Stem Cells

Innate immune factors may restrict hematopoietic stem cell (HSC) genetic engineering and contribute to broad individual variability in gene therapy outcomes. Here, we show that HSCs harbor an early, constitutively active innate immune block to lentiviral transduction that can be efficiently overcome by cyclosporine H (CsH). CsH potently enhances gene transfer and editing in human long-term repopulating HSCs by inhibiting interferon-induced transmembrane protein 3 (IFITM3), which potently restricts VSV glycoprotein-mediated vector entry. Importantly, individual variability in endogenous IFITM3 levels correlated with permissiveness of HSCs to lentiviral transduction, suggesting that CsH treatment will be useful for improving ex vivo gene therapy and standardizing HSC transduction across patients. Overall, our work unravels the involvement of innate pathogen recognition molecules in immune blocks to gene correction in primary human HSCs and highlights how these roadblocks can be overcome to develop innovative cell and gene therapies.

Laboratory diagnostics of murine blood for detection of mouse cytomegalovirus (MCMV)-induced hepatitis

Mouse models are important and versatile tools to study mechanisms and novel therapies of human disease in vivo. Both, the number and the complexity of murine models are constantly increasing and modification of genes of interest as well as any exogenous challenge may lead to unanticipated biological effects. Laboratory diagnostics of blood samples provide a comprehensive and rapid screening for multiple organ function and are fundamental to detect human disease. Here, we adapt an array of laboratory medicine-based tests commonly used in humans to establish a platform for standardized, multi-parametric, and quality-controlled diagnostics of murine blood samples. We determined sex-dependent reference intervals of 51 commonly used laboratory medicine tests for samples obtained from the C57BL/6J mouse strain. As a proof of principle, we applied these diagnostic tests in a mouse cytomegalovirus (MCMV) infection model to screen for organ damage. Consistent with histopathological findings, plasma concentrations of liver-specific enzymes were elevated, supporting the diagnosis of a virus-induced hepatitis. Plasma activities of aminotransferases correlated with viral loads in livers at various days after MCMV infection and discriminated infected from non-infected animals. This study provides murine blood reference intervals of common laboratory medicine parameters and illustrates the use of these tests for diagnosis of infectious disease in experimental animals.