HCMV UL8 interaction with ß-catenin and DVL2 regulates viral reactivation in CD34+ hematopoietic progenitor cells.

IMPORTANCE: CD34+ hematopoietic progenitor cells (HPCs) are an important cellular reservoir for latent human cytomegalovirus (HCMV). Several HCMV genes are expressed during latency that are involved with the maintenance of the viral genome in CD34+ HPC. However, little is known about the process of viral reactivation in these cells. Here, we describe a viral protein, pUL8, and its interaction and stabilization with members of the Wnt/ß-catenin pathway as an important component of viral reactivation. We further define that pUL8 and ß-catenin interact with DVL2 via a PDZ-binding domain, and loss of UL8 interaction with ß-catenin-DVL2 restricts viral reactivation. Our findings will be instrumental in understanding the molecular processes involved in HCMV reactivation in order to design new antiviral therapeutics.

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.

Clonal hematopoiesis is associated with risk of severe Covid-19.

Acquired somatic mutations in hematopoietic stem and progenitor cells (clonal hematopoiesis or CH) are associated with advanced age, increased risk of cardiovascular and malignant diseases, and decreased overall survival. These adverse sequelae may be mediated by altered inflammatory profiles observed in patients with CH. A pro-inflammatory immunologic profile is also associated with worse outcomes of certain infections, including SARS-CoV-2 and its associated disease Covid-19. Whether CH predisposes to severe Covid-19 or other infections is unknown. Among 525 individuals with Covid-19 from Memorial Sloan Kettering (MSK) and the Korean Clonal Hematopoiesis (KoCH) consortia, we show that CH is associated with severe Covid-19 outcomes (OR = 1.85, 95%=1.15-2.99, p = 0.01), in particular CH characterized by non-cancer driver mutations (OR = 2.01, 95% CI = 1.15-3.50, p = 0.01). We further explore the relationship between CH and risk of other infections in 14,211 solid tumor patients at MSK. CH is significantly associated with risk of Clostridium Difficile (HR = 2.01, 95% CI: 1.22-3.30, p = 6×10-3) and Streptococcus/Enterococcus infections (HR = 1.56, 95% CI = 1.15-2.13, p = 5×10-3). These findings suggest a relationship between CH and risk of severe infections that warrants further investigation.

Infecting human hematopoietic stem and progenitor cells with SARS-CoV-2.

Determining how hematopoietic stem and progenitor cells (HSPCs) can be infected by viruses is necessary to understand and predict how the immune system will drive the host response. We present here a protocol to analyze the capacity of SARS-CoV-2 to infect different subsets of human HSPCs, inlcuding procedures for SARS-CoV-2 production and titration, isolation of human HSPCs from different sources (bone marrow, umbilical cord, or peripheral blood), and quantification of SARS-Cov-2 infection capacity by RT-qPCR and colony forming unit assay. For complete details on the use and execution of this protocol, please refer to Huerga Encabo et al. (2021).

Colony-forming units optimization and human papillomavirus detection in umbilical cord blood.

INTRODUCTION: Analysis of several parameters is required for adequate quality control in umbilical cord blood units (UCBU) when used for therapeutic purposes. OBJECTIVE: To optimize colony-forming units (CFU) from clonogenic cultures and to detect the human papillomavirus (HPV) genome in UCBU. METHODS: One hundred and forty-one umbilical cord blood (UCB), segment or CFU samples from UCBU clonogenic cultures were included. DNA extraction, quantification and endogenous GAPDH gene PCR amplification were carried out. Subsequently, HPV L1 gene was detected using the MY09/MY11 and GP5/GP6+ oligonucleotides. PCR products were analyzed with electrophoresis in agarose gel. CFU-extracted purified DNA was analyzed by electrophoresis in agarose gel, as well as some DNAs, using the sequence-specific priming technique. RESULTS: CFU-extracted DNA concentration was higher in comparison with that of UCB (p = 0.0041) and that of the segment (p < 0.0001), as well as that of UCB in comparison with that of the segment (p < 0.0001). All samples were positive for GAPDH amplification and negative for MY09/MY/11 and GP5/GP6+. CONCLUSIONS: Cryopreserved UCBUs were HPV-negative. Obtaining CFU DNA from clonogenic cultures with high concentrations and purity is feasible.

INTRODUCCIÓN: Se requiere analizar diversos parámetros para el control de calidad adecuado de las unidades de sangre de cordón umbilical (USCU) cuando se utilizan con fines terapéuticos. OBJETIVO: Optimizar las unidades formadoras de colonias (UFC) de cultivos clonogénicos y detectar el genoma del virus del papiloma humano (VPH) en USCU. MÉTODOS: Se incluyeron 141 muestras de sangre de cordón umbilical (SCU), de segmento y de UFC de cultivos clonogénicos de USCU. Se realizó extracción de ADN, cuantificación y amplificación por PCR del gen endógeno GAPDH. Se detectó el gen L1 del VPH con los oligonucleótidos MY09/MY11 y GP5/GP6+; los productos de PCR se migraron en electroforesis de agarosa. El ADN purificado de las UFC se analizó mediante electroforesis de agarosa y algunos ADN, con la técnica sequence specific priming. RESULTADOS: La concentración de ADN extraído de UFC fue superior comparada con la de SCU (p = 0.0041) y la de segmento (p < 0.0001); así como la de SCU comparada con la de segmento (p < 0.0001). Todas las muestras fueron positivas para la amplificación de GAPDH y negativas para MY09/MY11 y GP5/GP6+. CONCLUSIONES: Las USCU criopreservadas fueron VPH netativas; además, es factible obtener ADN en altas concentraciones y con alta pureza a partir de UFC de los cultivos clonogénicos.

Protocol to produce high-titer retrovirus for transduction of mouse bone marrow cells.

Regulating gene expression through retroviral infection has been widely used in mouse bone marrow transplantation (BMT) to test the capacity of self-renewal, as well as multi-lineage differentiation of hematopoietic stem and progenitor cells (HSPCs). However, it remains challenging to achieve high transduction efficiency in bone marrow cells as transduction of these cells subsequently leads to transplantation failure. Here, we present a modified protocol to overcome this issue, enabling reproducible and high-efficient retroviral transduction of HSPCs for BMT. For complete details on the use and execution of this protocol, please refer to Yang et al. (2019).

Syngeneic leukemia models using lentiviral transgenics.

Animal models are necessary to study cancer and develop treatments. After decades of intensive research, effective treatments are available for only a few types of leukemia, while others are currently incurable. Our goal was to generate novel leukemia models in immunocompetent mice. We had achieved abilities for overexpression of multiple driving oncogenes simultaneously in normal primary cells, which can be transplanted and followed in vivo. Our experiments demonstrated the induction of primary malignant growth. Leukemia lines that model various types of leukemia, such as acute myeloid leukemia (AML) or chronic lymphocytic leukemia (CLL), were passaged robustly in congenic wild-type immunocompetent mice. These novel leukemia lines, which may complement previous models, offer the flexibility to generate tailored models of defined oncogenes of interest. The characterization of our leukemia models in immunocompetent animals can uncover the mechanisms of malignancy progression and offer a unique opportunity to stringently test anti-cancer chemotherapies.

P2Y14 Receptor as a Target for Neutrophilia Attenuation in Severe COVID-19 Cases: From Hematopoietic Stem Cell Recruitment and Chemotaxis to Thrombo-inflammation.

The global SARS-CoV-2 pandemic starting in 2019 has already reached more than 2.3 million deaths. Despite the scientific community's efforts to investigate the COVID-19 disease, a drug for effectively treating or curing patients yet needs to be discovered. Hematopoietic stem cells (HSC) differentiating into immune cells for defense express COVID-19 entry receptors, and COVID-19 infection hinders their differentiation. The importance of purinergic signaling in HSC differentiation and innate immunity has been recognized. The metabotropic P2Y14 receptor subtype, activated by UDP-glucose, controls HSC differentiation and mobilization. Thereon, the exacerbated activation of blood immune cells amplifies the inflammatory state observed in COVID-19 patients, specially through the continuous release of reactive oxygen species and extracellular neutrophil traps (NETs). Further, the P2Y14 subtype, robustly inhibits the infiltration of neutrophils into various epithelial tissues, including lungs and kidneys. Here we discuss findings suggesting that antagonism of the P2Y14 receptor could prevent the progression of COVID-19-induced systemic inflammation, which often leads to severe illness and death cases. Considering the modulation of neutrophil recruitment of extreme relevance for respiratory distress and lung failure prevention, we propose that P2Y14 receptor inhibition by its selective antagonist PPTN could limit neutrophil recruitment and NETosis, hence limiting excessive formation of oxygen reactive species and proteolytic activation of the kallikrein-kinin system and subsequent bradykinin storm in the alveolar septa of COVID-19 patients.

Optimización de unidades formadoras de colonias y detección del virus de papiloma humano en sangre de cordón umbilical / Colony-forming units optimization and human papillomavirus detection in umbilical cord blood

Resumen Introducción: Se requiere analizar diversos parámetros para el control de calidad adecuado de las unidades de sangre de cordón umbilical (USCU) cuando se utilizan con fines terapéuticos. Objetivo: Optimizar las unidades formadoras de colonias (UFC) de cultivos clonogénicos y detectar el genoma del virus del papiloma humano (VPH) en USCU. Métodos: Se incluyeron 141 muestras de sangre de cordón umbilical (SCU), de segmento y de UFC de cultivos clonogénicos de USCU. Se realizó extracción de ADN, cuantificación y amplificación por PCR del gen endógeno GAPDH. Se detectó el gen L1 del VPH con los oligonucleótidos MY09/MY11 y GP5/GP6+; los productos de PCR se migraron en electroforesis de agarosa. El ADN purificado de las UFC se analizó mediante electroforesis de agarosa y algunos ADN, con la técnica sequence specific priming. Resultados: La concentración de ADN extraído de UFC fue superior comparada con la de SCU (p = 0.0041) y la de segmento (p < 0.0001); así como la de SCU comparada con la de segmento (p < 0.0001). Todas las muestras fueron positivas para la amplificación de GAPDH y negativas para MY09/MY11 y GP5/GP6+. Conclusiones: Las USCU criopreservadas fueron VPH netativas; además, es factible obtener ADN en altas concentraciones y con alta pureza a partir de UFC de los cultivos clonogénicos.

Abstract Introduction: Analysis of several markers is required for adequate quality control in umbilical cord blood units (UCBU) when are used for therapeutic purposes. Objective: To optimize colony-forming units (CFU) from clonogenic cultures and to detect the human papillomavirus (HPV) genome in UCBU. Methods: One hundred and forty-one umbilical cord blood (UCB), segment or CFU samples from UCBU clonogenic cultures were included. DNA extraction, quantification and endogenous GAPDH gene PCR amplification were carried out. Subsequently, HPV L1 gene was detected using the MY09/MY11 and GP5/GP6+ oligonucleotides. PCR products were analyzed with electrophoresis in agarose gel. CFU-extracted purified DNA was analyzed by electrophoresis in agarose gel, as well as some DNAs, using the SSP technique. Results: CFU-extracted DNA concentration was higher in comparison with that of UCB (p = 0.0041) and that of the segment (p < 0.0001), as well as that of UCB in comparison with that of the segment (p < 0.0001). All samples were positive for GAPDH amplification and negative for MY09/MY11 and GP5/GP6+. Conclusions: Cryopreserved UCBUs were HPV-negative. Obtaining CFU DNA from clonogenic cultures with high concentrations and purity is feasible.

Human Cytomegalovirus UL7, miR-US5-1, and miR-UL112-3p Inactivation of FOXO3a Protects CD34+ Hematopoietic Progenitor Cells from Apoptosis.

Human cytomegalovirus (HCMV) infection of myeloid lineage cells, such as CD34+ hematopoietic progenitor cells (HPCs) or monocytes, results in the upregulation of antiapoptotic cellular proteins that protect the newly infected cells from programmed cell death. The mechanisms used by HCMV to regulate proapoptotic cellular proteins upon infection of CD34+ HPCs have not been fully explored. Here, we show that HCMV utilizes pUL7, a secreted protein that signals through the FLT3 receptor, and miR-US5-1 and miR-UL112-3p to reduce the abundance and activity of the proapoptotic transcription factor FOXO3a at early times after infection of CD34+ HPCs. Regulation of FOXO3a by pUL7, miR-US5-1, and miR-UL112 results in reduced expression of the proapoptotic BCL2L11 transcript and protection of CD34+ HPCs from virus-induced apoptosis. These data highlight the importance of both viral proteins and microRNAs (miRNAs) in protecting CD34+ HPCs from apoptosis at early times postinfection, allowing for the establishment of latency and maintenance of viral genome-containing cells.IMPORTANCE Human cytomegalovirus (HCMV) causes serious disease in immunocompromised individuals and is a significant problem during transplantation. The virus can establish a latent infection in CD34+ hematopoietic progenitor cells (HPCs) and periodically reactivate to cause disease in the absence of an intact immune system. What viral gene products are required for successful establishment of latency is still not fully understood. Here, we show that both a viral protein and viral miRNAs are required to prevent apoptosis after infection of CD34+ HPCs. HCMV pUL7 and miRNAs miR-US5-1 and miR-UL112-3p act to limit the expression and activation of the transcription factor FOXO3a, which in turn reduces expression of proapoptotic gene BCL2L11 and prevents virus-induced apoptosis in CD34+ HPCs.

Hematopoietic cell-mediated dissemination of murine cytomegalovirus is regulated by NK cells and immune evasion.

Cytomegalovirus (CMV) causes clinically important diseases in immune compromised and immune immature individuals. Based largely on work in the mouse model of murine (M)CMV, there is a consensus that myeloid cells are important for disseminating CMV from the site of infection. In theory, such dissemination should expose CMV to cell-mediated immunity and thus necessitate evasion of T cells and NK cells. However, this hypothesis remains untested. We constructed a recombinant MCMV encoding target sites for the hematopoietic specific miRNA miR-142-3p in the essential viral gene IE3. This virus disseminated poorly to the salivary gland following intranasal or footpad infections but not following intraperitoneal infection in C57BL/6 mice, demonstrating that dissemination by hematopoietic cells is essential for specific routes of infection. Remarkably, depletion of NK cells or T cells restored dissemination of this virus in C57BL/6 mice after intranasal infection, while dissemination occurred normally in BALB/c mice, which lack strong NK cell control of MCMV. These data show that cell-mediated immunity is responsible for restricting MCMV to hematopoietic cell-mediated dissemination. Infected hematopoietic cells avoided cell-mediated immunity via three immune evasion genes that modulate class I MHC and NKG2D ligands (m04, m06 and m152). MCMV lacking these 3 genes spread poorly to the salivary gland unless NK cells were depleted, but also failed to replicate persistently in either the nasal mucosa or salivary gland unless CD8+ T cells were depleted. Surprisingly, CD8+ T cells primed after intranasal infection required CD4+ T cell help to expand and become functional. Together, our data suggest that MCMV can use both hematopoietic cell-dependent and -independent means of dissemination after intranasal infection and that cell mediated immune responses restrict dissemination to infected hematopoietic cells, which are protected from NK cells during dissemination by viral immune evasion. In contrast, viral replication within mucosal tissues depends on evasion of T cells.

SARS-CoV-2 Entry Receptor ACE2 Is Expressed on Very Small CD45- Precursors of Hematopoietic and Endothelial Cells and in Response to Virus Spike Protein Activates the Nlrp3 Inflammasome.

Angiotensin-converting enzyme 2 (ACE2) plays an important role as a member of the renin-angiotensin-aldosterone system (RAAS) in regulating the conversion of angiotensin II (Ang II) into angiotensin (1-7) (Ang [1-7]). But at the same time, while expressed on the surface of human cells, ACE2 is the entry receptor for SARS-CoV-2. Expression of this receptor has been described in several types of cells, including hematopoietic stem cells (HSCs) and endothelial progenitor cells (EPCs), which raises a concern that the virus may infect and damage the stem cell compartment. We demonstrate for the first time that ACE2 and the entry-facilitating transmembrane protease TMPRSS2 are expressed on very small CD133+CD34+Lin-CD45- cells in human umbilical cord blood (UCB), which can be specified into functional HSCs and EPCs. The existence of these cells known as very small embryonic-like stem cells (VSELs) has been confirmed by several laboratories, and some of them may correspond to putative postnatal hemangioblasts. Moreover, we demonstrate for the first time that, in human VSELs and HSCs, the interaction of the ACE2 receptor with the SARS-CoV-2 spike protein activates the Nlrp3 inflammasome, which if hyperactivated may lead to cell death by pyroptosis. Based on this finding, there is a possibility that human VSELs residing in adult tissues could be damaged by SARS-CoV-2, with remote effects on tissue/organ regeneration. We also report that ACE2 is expressed on the surface of murine bone marrow-derived VSELs and HSCs, although it is known that murine cells are not infected by SARS-CoV-2. Finally, human and murine VSELs express several RAAS genes, which sheds new light on the role of these genes in the specification of early-development stem cells. Graphical Abstract •Human VSELs and HSCs express ACE2 receptor for SARS-CoV2 entry. •Interaction of viral spike protein with ACE2 receptor may hyperactivate Nlrp3 inflammasome which induces cell death by pyroptosis. •SARS-CoV2 may also enter cells and eliminate them by cell lysis. •What is not shown since these cells express also Ang II receptor they may hyperactivate Nlrp3 inflammasome in response to Ang II which may induce pyroptosis. Our data indicates that Ang 1-7 may have a protective effect.

CD34+ Hematopoietic Progenitor Cell Subsets Exhibit Differential Ability To Maintain Human Cytomegalovirus Latency and Persistence.

In human cytomegalovirus (HCMV)-seropositive patients, CD34+ hematopoietic progenitor cells (HPCs) provide an important source of latent virus that reactivates following cellular differentiation into tissue macrophages. Multiple groups have used primary CD34+ HPCs to investigate mechanisms of viral latency. However, analyses of mechanisms of HCMV latency have been hampered by the genetic variability of CD34+ HPCs from different donors, availability of cells, and low frequency of reactivation. In addition, multiple progenitor cell types express surface CD34, and the frequencies of these populations differ depending on the tissue source of the cells and culture conditions in vitro In this study, we generated CD34+ progenitor cells from two different embryonic stem cell (ESC) lines, WA01 and WA09, to circumvent limitations associated with primary CD34+ HPCs. HCMV infection of CD34+ HPCs derived from either WA01 or WA09 ESCs supported HCMV latency and induced myelosuppression similar to infection of primary CD34+ HPCs. Analysis of HCMV-infected primary or ESC-derived CD34+ HPC subpopulations indicated that HCMV was able to establish latency and reactivate in CD38+ CD90+ and CD38+/low CD90- HPCs but persistently infected CD38- CD90+ cells to produce infectious virus. These results indicate that ESC-derived CD34+ HPCs can be used as a model for HCMV latency and that the virus either latently or persistently infects specific subpopulations of CD34+ cells.IMPORTANCE Human cytomegalovirus infection is associated with severe disease in transplant patients and understanding how latency and reactivation occur in stem cell populations is essential to understand disease. CD34+ hematopoietic progenitor cells (HPCs) are a critical viral reservoir; however, these cells are a heterogeneous pool with donor-to-donor variation in functional, genetic, and phenotypic characteristics. We generated a novel system using embryonic stem cell lines to model HCMV latency and reactivation in HPCs with a consistent cellular background. Our study defined three key stem cell subsets with differentially regulated latent and replicative states, which provide cellular candidates for isolation and treatment of transplant-mediated disease. This work provides a direction toward developing strategies to control the switch between latency and reactivation.

Type I IFNs and CD8 T cells increase intestinal barrier permeability after chronic viral infection.

Intestinal barrier leakage constitutes a potential therapeutic target for many inflammatory diseases and represents a disease progression marker during chronic viral infections. However, the causes of altered gut barrier remain mostly unknown. Using murine infection with lymphocytic choriomeningitis virus, we demonstrate that, in contrast to an acute viral strain, a persistent viral isolate leads to long-term viral replication in hematopoietic and mesenchymal cells, but not epithelial cells (IECs), in the intestine. Viral persistence drove sustained intestinal epithelial barrier leakage, which was characterized by increased paracellular flux of small molecules and was associated with enhanced colitis susceptibility. Type I IFN signaling caused tight junction dysregulation in IECs, promoted gut microbiome shifts and enhanced intestinal CD8 T cell responses. Notably, both type I IFN receptor blockade and CD8 T cell depletion prevented infection-induced barrier leakage. Our study demonstrates that infection with a virus that persistently replicates in the intestinal mucosa increases epithelial barrier permeability and reveals type I IFNs and CD8 T cells as causative factors of intestinal leakage during chronic infections.

Human umbilical cord-derived mesenchymal stem cell therapy in patients with COVID-19: a phase 1 clinical trial.

No effective drug treatments are available for coronavirus disease 2019 (COVID-19). Host-directed therapies targeting the underlying aberrant immune responses leading to pulmonary tissue damage, death, or long-term functional disability in survivors require clinical evaluation. We performed a parallel assigned controlled, non-randomized, phase 1 clinical trial to evaluate the safety of human umbilical cord-derived mesenchymal stem cells (UC-MSCs) infusions in the treatment of patients with moderate and severe COVID-19 pulmonary disease. The study enrolled 18 hospitalized patients with COVID-19 (n = 9 for each group). The treatment group received three cycles of intravenous infusion of UC-MSCs (3 × 107 cells per infusion) on days 0, 3, and 6. Both groups received standard COVID-treatment regimens. Adverse events, duration of clinical symptoms, laboratory parameters, length of hospitalization, serial chest computed tomography (CT) images, the PaO2/FiO2 ratio, dynamics of cytokines, and IgG and IgM anti-SARS-CoV-2 antibodies were analyzed. No serious UC-MSCs infusion-associated adverse events were observed. Two patients receiving UC-MSCs developed transient facial flushing and fever, and one patient developed transient hypoxia at 12 h post UC-MSCs transfusion. Mechanical ventilation was required in one patient in the treatment group compared with four in the control group. All patients recovered and were discharged. Our data show that intravenous UC-MSCs infusion in patients with moderate and severe COVID-19 is safe and well tolerated. Phase 2/3 randomized, controlled, double-blinded trials with long-term follow-up are needed to evaluate the therapeutic use of UC-MSCs to reduce deaths and improve long-term treatment outcomes in patients with serious COVID-19.

A novel approach to genetic engineering of T-cell subsets by hematopoietic stem cell infection with a bicistronic lentivirus.

Lentiviral modification of hematopoietic stem cells (HSCs) paved the way for in vivo experimentation and therapeutic approaches in patients with genetic disease. A disadvantage of this method is the use of a ubiquitous promoter leads not only to genetic modification of the leukocyte subset of interest e.g. T-cells, but also all other subsequent leukocyte progeny of the parent HSCs. To overcome this limitation we tested a bicistronic lentivirus, enabling subset specific modifications. Designed novel lentiviral constructs harbor a global promoter (mPGK) regulating mCherry for HSCs selection and a T-cell specific promoter upstream of eGFP. Two T-cell specific promoters were assessed: the distal Lck-(dLck) and the CD3δ-promoter. Transduced HSCs were FACS sorted by mCherry expression and transferred into sublethally irradiated C57/BL6 mice. Successful transplantation and T-cell specific expression of eGFP was monitored by peripheral blood assessment. Furthermore, recruitment response of lentiviral engineered leukocytes to the site of inflammation was tested in a peritonitis model without functional impairment. Our constructed lentivirus enables fast generation of subset specific leukocyte transgenesis as shown in T-cells in vivo and opens new opportunities to modify other HSCs derived subsets in the future.

Single-cell lineage tracing approaches in hematology research: technical considerations.

The coordinated differentiation of hematopoietic stem and progenitor cells (HSPCs) into the various mature blood cell types is responsible for sustaining blood and immune system homeostasis. The cell fate decisions underlying this important biological process are made at the level of single cells. Methods to trace the fate of single cells are therefore essential for understanding hematopoietic system activity in health and disease and have had a major impact on how we understand and represent hematopoiesis. Here, we discuss the basic methodologies and technical considerations for three important clonal assays: single-cell transplantation, lentiviral barcoding, and Sleeping Beauty barcoding. This perspective is a synthesis of presentations and discussions from the 2019 International Society for Experimental Hematology (ISEH) Annual Meeting New Investigator Technology Session and the 2019 ISEH Winter Webinar.

SARS-CoV-2 infection and overactivation of Nlrp3 inflammasome as a trigger of cytokine "storm" and risk factor for damage of hematopoietic stem cells.

The scientific community faces an unexpected and urgent challenge related to the SARS-CoV-2 pandemic and is investigating the role of receptors involved in entry of this virus into cells as well as pathomechanisms leading to a cytokine "storm," which in many cases ends in severe acute respiratory syndrome, fulminant myocarditis and kidney injury. An important question is if it may also damage hematopoietic stem progenitor cells?

Adeno-Associated Virus and Hematopoietic Stem Cells: The Potential of Adeno-Associated Virus Hematopoietic Stem Cells in Genetic Medicines.

Adeno-associated virus (AAV)-based vectors have transformed into powerful elements of genetic medicine with proven therapeutic efficacy and a good safety profile. Over the years, efforts to transduce hematopoietic stem cells (HSCs) with AAV2 vectors have, however, been challenging. While there was evidence that AAV2 delivered vector genomes to primitive, quiescent, multipotential, self-renewing, in vivo engrafting HSCs, transgene expression was elusive. In this study, we review the evolution of AAV transduction of HSC, starting with AAV2 vectors leading to the isolation of a family of naturally occurring AAVs from human CD34+ HSC, the AAVHSC. The stem cell-derived AAVHSCs have turned out to have remarkable potentials for genetic therapies well beyond the hematopoietic system. AAVHSCs have tropism for a wide variety of peripheral tissues, including the liver, muscle, and the retina. They cross the blood-brain barrier and transduce cells of the central nervous system. Preclinical gene therapy studies underway using AAVHSC vectors are discussed. We review the notable ability of AAVHSCs to mediate efficient, seamless homologous recombination in the absence of exogenous nuclease activity and discuss the therapeutic implications. We also discuss early results from an AAVHSC-based clinical gene therapy trial that is underway for the treatment of phenylketonuria. Thus, the stem cell-derived AAVHSC, offer a multifaceted platform for in vivo gene therapy and genome editing for the treatment of inherited diseases.