CFU-S assay: a historical single-cell assay that offers modern insight into clonal hematopoiesis.

Hematopoietic stem cells (HSCs) have been studied extensively since their initial functional description in 1961 when Dr. James Till and Dr. Ernest McCulloch developed the first in vivo clonal strategy, termed the spleen colony-forming unit (CFU-S) assay, to assess the functional capacity of bone marrow-derived hematopoietic progenitors at the single-cell level. Through transplantation of bone marrow cells and analysis of the resulting cellular nodules in the spleen, the CFU-S assay revealed both the self-renewal and clonal differentiation capacity of hematopoietic progenitors. Further development and use of this assay have identified highly proliferative, self-renewing, and differentiating HSCs that possess clonal, multilineage differentiation. The CFU-S strategy has also been adapted to interrogating single purified hematopoietic stem and progenitor cell populations, advancing our knowledge of the hematopoietic hierarchy. In this review, we explore the major discoveries made with the CFU-S assay, consider its modern use and recent improvements, and compare it with commonly used long-term transplantation assays to determine the continued value of the CFU-S assay for understanding HSC biology and hematopoiesis.

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).

Circulating Endothelial Progenitor Cells in Patients with Heart Failure with Preserved versus Reduced Ejection Fraction.

BACKGROUND: Heart failure with preserved ejection fraction (HFpEF) is a common clinical entity, with a mechanism that appears to involve endothelial dysfunction of the cardiac microcirculation. Endothelial progenitor cells (EPC) are bone marrow derived cells that are able to differentiate into functional endothelial cells and participate in endothelial surface repair. OBJECTIVES: To compare the level and function of EPCs in patients with HFpEF compared with heart failure with reduced ejection fraction (HFrEF) and control subjects. METHODS: We enrolled 21 patients with HFpEF (LVEF ≥ 50%, age 74.5 ± 9.9 years, 43% men, 48% diabetes), 20 patients with HFrEF (LVEF < 40%, age 70 ± 11.5 years, 90% men, 60% diabetes), and 11 control subjects with cardiovascular risk factors (age 53.3 ± 6.1years, 90% men, 64% diabetes). Circulating EPC levels were evaluated by expression of vascular endothelial growth factor receptor-2 (VEGFR-2), CD34, and CD133 by flow-cytometry. EPCs colony forming units (CFUs) were quantified after 7 days in culture. RESULTS: The proportion of cells that co-expressed VEGFR-2 and CD34 or VEGFR-2 and CD133 was similar among the HFpEF and HFrEF groups, and significantly lower than in the control group. The number of EPC-CFUs was also similar among the two heart failure groups and significantly lower than the control group. CONCLUSIONS: Patients with HFpEF, like HFrEF, have significant reduction in EPC level and function.

Pretomanid dose selection for pulmonary tuberculosis: An application of multi-objective optimization to dosage regimen design.

Clinical development of combination chemotherapies for tuberculosis (TB) is complicated by partial or restricted phase II dose-finding. Barriers include a propensity for drug resistance with monotherapy, practical limits on numbers of treatment arms for component dose combinations, and limited application of current dose selection methods to multidrug regimens. A multi-objective optimization approach to dose selection was developed as a conceptual and computational framework for currently evolving approaches to clinical testing of novel TB regimens. Pharmacokinetic-pharmacodynamic (PK-PD) modeling was combined with an evolutionary algorithm to identify dosage regimens that yield optimal trade-offs between multiple conflicting therapeutic objectives. The phase IIa studies for pretomanid, a newly approved nitroimidazole for specific cases of highly drug-resistant pulmonary TB, were used to demonstrate the approach with Pareto optimized dosing that best minimized sputum bacillary load and the probability of drug-related adverse events. Results include a population-typical characterization of the recommended 200 mg once daily dosage, the optimality of time-dependent dosing, examples of individualized therapy, and the determination of optimal loading doses. The approach generalizes conventional PK-PD target attainment to a design problem that scales to drug combinations, and provides a benefit-risk context for clinical testing of complex drug regimens.

Bone Marrow Stromal Cell Assays: In Vitro and In Vivo.

Populations of bone marrow stromal cells (BMSCs, also known as bone marrow-derived "mesenchymal stem cells") contain a subset of cells that are able to recapitulate the formation of a bone/marrow organ (skeletal stem cells, SSCs). It is now apparent that cells with similar but not identical properties can be isolated from other skeletal compartments (growth plate, periosteum). The biological properties of BMSCs, and these related stem/progenitor cells, are assessed by a variety of assays, both in vitro and in vivo. Application of these assays in an appropriate fashion provide a great deal of information on the role of BMSCs, and the subset of SSCs, in health and in disease.

Cryopreserved bone marrow aspirate concentrate as a cell source for the colony-forming unit fibroblast assay.

PURPOSE: The prevalence of connective tissue progenitor cells within a cell-based therapy is often quantified using the colony-forming unit fibroblast (CFU-F) assay. The present study investigates the feasibility of using cryopreserved bone marrow aspirate concentrate (BMAC) as an alternative cell source to fresh BMAC for CFU-F quantification. METHODS: Freshly prepared and corresponding cryopreserved BMAC samples from patients receiving autologous cell therapy (n = 98) were analyzed using the CFU-F assay for comparison. Cultures were established by directly plating BMAC at low cell densities and maintained for a 2-week growth period. Colonies were enumerated to determine CFU-F frequency, and a subset of cultures was imaged and analyzed to quantify colony area and density. RESULTS: A nonlinear relationship was observed between plating density and CFU-F frequency over a wide range in plating densities (~30-fold). Cryopreserved BMAC yielded recoverable (77 ± 23%) and viable (73 ± 9%) nucleated cells upon thawing. After cryopreservation, CFU-F frequencies were found to be significantly lower (56.6 ± 34.8 vs. 50.3 ± 31.7 colonies per million nucleated cells). Yet the number of CFU-F in fresh and cryopreserved BMAC were strongly correlated (r = 0.87) and had similar area and densities. Further, moderate correlations were observed between the number of CFU-F and nucleated cells, and both the mean colony area and density were negatively correlated with patient age. Notably, no relationship was found between CFU-F frequency and age, regardless of whether fresh or cryopreserved BMAC was used. CONCLUSIONS: Freshly prepared and cryopreserved BMAC yielded correlated results when analyzed using the CFU-F assay. Our findings support the cryogenic storage of patient BMAC samples for retrospective CFU-F analyses, offering a potential alternative for characterizing BMAC and furthering our understanding of progenitor cells in relation to clinical outcome.

Generation of hematopoietic cells from mouse pluripotent stem cells in a 3D culture system of self-assembling peptide hydrogel.

In vitro generation of hematopoietic stem cells from pluripotent stem cells (PSCs) can be regarded as novel therapeutic approaches for replacing bone marrow transplantation without immune rejection or graft versus host disease. To date, many different approaches have been evaluated in terms of directing PSCs toward different hematopoietic cell types, yet, low efficiency and no function restrict the further hematopoietic differentiation study, our research aims to develop a three dimension (3D) hematopoietic differentiation approach that serves as recapitulation of embryonic development in vitro to a degree of complexity not achievable in a two dimension culture system. We first found that mouse PSCs could be efficiently induced to hematopoietic differentiation with an expression of hematopoietic makers, such as c-kit, CD41, and CD45 within self-assembling peptide hydrogel. Colony-forming cells assay results suggested mouse PSCs (mPSCs) could be differentiated into multipotential progenitor cells and 3D induction system derived hematopoietic colonies owned potential of differentiating into lymphocyte cells. In addition, in vivo animal transplantation experiment showed that mPSCs (CD45.2) could be embedded into nonobese diabetic/severe combined immunodeficiency mice (CD45.1) with about 3% engraftment efficiency after 3 weeks transplantation. This study demonstrated that we developed the 3D induction approach that could efficiently promote the hematopoietic differentiation of mPSCs in vitro and obtained the multipotential progenitors that possessed the short-term engraftment potential.

Clonogenic Culture of Mouse Thymic Epithelial Cells.

The thymus plays an essential role in the development and selection of T cells by providing a unique microenvironment that is mainly composed of thymic epithelial cells (TECs). We previously identified stem cells of medullary TECs (mTECs) that are crucial for central tolerance induction using a novel clonogenic culture system. We also found that medullary thymic epithelial stem cells (mTESCs) maintain life-long mTECs regeneration and central T cell self-tolerance in mouse models. The clonogenic efficiency of TECs in vitro is highly correlated to the TEC reconstitution activity in vivo. Here, we describe the clonogenic culture system to evaluate the self-renewing activity of TESCs. The colonies are derived from TESCs, are visualized and quantified by rhodamine-B staining on a feeder layer, and can be passaged in vitro. Thus, our system enables quantitative evaluation of TESC activity and is useful for dissecting the mechanisms that regulate TESC activity in physiological aging as well as in various clinical settings.

Isolation and Characterization of Colony-Forming Progenitor Cells from Adult Pancreas.

Obtaining, growing, and analysis of pancreatic progenitor cells. Adult stem and progenitor cells have been successfully used for cell-based therapies such as transplantation of hematopoietic stem cells for various diseases. Whether stem and progenitor cells in the adult pancreas can be identified and used for replacement therapy has been a highly controversial topic. To address this controversy, our laboratory has developed in vitro colony assays to detect and characterize individual pancreatic stem and progenitor-like cells. We found that a subpopulation of ductal cells in the adult murine pancreas has the abilities to self-renew and differentiate into multiple pancreatic lineages in three-dimensional space in methylcellulose-containing semisolid media. This protocol details the techniques used for culturing and characterizing these pancreatic stem and progenitor-like cells, which we have named pancreatic colony-forming units (PCFUs), as well as their progenies (colonies). The techniques presented here include dissociation of pancreases, sorting antibody-stained cells with a fluorescence-activated cell sorter, viral transduction of dissociated pancreatic cells, growth of PCFUs in semi-solid media, whole-mount immunostaining and Western blot analysis for proteins expressed in colonies, and kidney capsule transplantation of colonies for in vivo functional analysis.

Validation of a semi automatic device to standardize quantification of Colony-Forming Unit (CFU) on hematopoietic stem cell products.

Accurate characterization of hematopoietic stem cells (HSC) products is needed to better anticipate the hematopoietic reconstitution and the outcome in patients. Although CD34+ viable cells enumeration is a key predictor of time to correction of aplasia, it does not fully inform about functionality of cells contained in the graft. CFU assay is the gold standard in vitro potency assay to assess clonogenicity of HSC and consists on the count and identification of colonies several days after culture in a semi solid media. Manual count of colonies with optic microscope is the most commonly used method but its important variability and subjectivity hinders the universal implementation of this potency assay. The aim of this study is to validate a standardized method using the STEMvision™ system, the first semi-automated instrument for imaging and scoring hematopoietic colonies, according to French and European recommendations. Results obtained highlight better performance criteria with STEMvision™ system than the manual method. This semi-automatic device tends to reduce the coefficients of variation of repeatability, inter-operator variability and intermediate precision. This newly available platform could represent an interesting option, significantly improving performances of CFU assays used for the characterization of hematopoietic progenitors.

Colony Formation: An Assay of Hematopoietic Progenitor Cells.

The colony-forming cell (CFC) assay is used to study the proliferation and differentiation pattern of each input hematopoietic progenitors by their ability to form colonies in a semisolid medium. The resulting colonies are consisting of more differentiated cells, and the number and the morphology of the colonies provide preliminary information about the ability of progenitors to differentiate and proliferate. To allow colonies to grow to a size which facilitates accurate counting and identification, about 14 days of culture is sufficient. In certain situations also shorter periods may be used.

The protective effects of 1,2-propanediol against radiation-induced hematopoietic injury in mice.

Agents that provide protection against irradiation-induced hematopoietic injury are urgently needed for radiotherapy. We examined the effects of the small molecule, 1,2-propanediol (PPD), on total body irradiation (TBI)-induced hematopoietic injury in C57BL/6 mice. PPD administration 1 h before TBI significantly increased hematopoietic parameters such as white blood cell, platelet, red blood cell, and lymphocyte counts in vivo and enhanced the survival of mice exposed to TBI (7.0 and 7.5 Gy). PPD administration 1 h before TBI improved bone marrow (BM) and spleen recovery after TBI, with increases in both BM cellularity and spleen index. The number of colony-forming-units in bone marrow mononuclear cells (BMNCs) in vitro also increased significantly. PPD pretreatment increased the numbers of hematopoietic stem cells and hematopoietic progenitor cells in BM. Importantly, PPD also maintained endogenous antioxidant status by decreasing levels of malondialdehyde and increasing the expression of reduced glutathione, superoxide dismutase and catalase in the serum of irradiated mice. PPD alleviated the levels of apoptosis in HSCs induced by TBI, thus increasing the proportion of dividing BMNCs. These results suggest that PPD protects against TBI-induced hematopoietic injury through the increased activities of antioxidant enzymes and the inhibition of apoptosis in HSCs. PPD increased the serum levels of granulocyte-colony stimulating factor and interleukin-6 irrespective of TBI. In conclusion, these data suggest that PPD acts as a radioprotector against radiation-induced hematopoietic injury.

An objective flow cytometry method to rapidly determine cord blood potency in cryopreserved units.

BACKGROUND: Cord blood banks have to determine the regenerative potential of cord blood units (CBUs) on a representative sample of the cryopreserved product before release to the transplant center. Potency can be measured by using a colony-forming unit (CFU) method, which delays the release of CBU by 7 to 14 days. To accelerate CBU qualification, we have developed a rapid method to assess the response of CD34 cells to interleukin (IL)-3. Flow cytometry was used to measure IL-3-induced STAT5 phosphorylation within CD34-cells. This IL-3 test was compared to the CFU method, as well as the aldehyde dehydrogenase (ALDH) enzyme-based assay. STUDY DESIGN AND METHODS: Ten cryopreserved CBUs were analyzed for their contents in CD34 and CD45 viable cells, total CFUs, ADLHbright cells, and IL-3-responsive CD34+ cells. Extreme and mild warming event scenarios were simulated on CBUs and used as poor-quality samples. Segments, tubes, and bags from five CBUs were compared for their potency using IL-3 and CFU methods. RESULTS: The IL-3 test was accurate in identifying the samples handled following standard operating procedures and those subjected to extreme warming events. Based on these results, a threshold of 55% of IL-3-responsive CD34 cells was established to identify good-quality samples. The IL-3 test was also the most sensitive to detect samples subjected to milder warming events. CONCLUSIONS: Our new method for determining CBU functionality is rapid, unbiased, and robust. The IL-3 test described herein fulfills the requirements for validation, and we intend to implement this method in our cord blood bank facility.

Cell type-specific differences in redox regulation and proliferation after low UVA doses.

Ultraviolet A (UVA) radiation is harmful for living organisms but in low doses may stimulate cell proliferation. Our aim was to examine the relationships between exposure to different low UVA doses, cellular proliferation, and changes in cellular reactive oxygen species levels. In human colon cancer (HCT116) and melanoma (Me45) cells exposed to UVA doses comparable to environmental, the highest doses (30-50 kJ/m2) reduced clonogenic potential but some lower doses (1 and 10 kJ/m2) induced proliferation. This effect was cell type and dose specific. In both cell lines the levels of reactive oxygen species and nitric oxide fluctuated with dynamics which were influenced differently by UVA; in Me45 cells decreased proliferation accompanied the changes in the dynamics of H2O2 while in HCT116 cells those of superoxide. Genes coding for proteins engaged in redox systems were expressed differently in each cell line; transcripts for thioredoxin, peroxiredoxin and glutathione peroxidase showed higher expression in HCT116 cells whereas those for glutathione transferases and copper chaperone were more abundant in Me45 cells. We conclude that these two cell types utilize different pathways for regulating their redox status. Many mechanisms engaged in maintaining cellular redox balance have been described. Here we show that the different cellular responses to a stimulus such as a specific dose of UVA may be consequences of the use of different redox control pathways. Assays of superoxide and hydrogen peroxide level changes after exposure to UVA may clarify mechanisms of cellular redox regulation and help in understanding responses to stressing factors.

[Evaluation of the Cytotoxicity of Commercially Available Nail Adhesives].

Nail tips are nail art materials that can be attached to the nail with adhesives. Recently, nail/finger injuries related to nail tips have been reported and one of the causes is considered to be the adhesives used for attaching nail tips. The components of nail adhesives are mostly cyanoacrylate, which is also used as an industrial instant adhesive. During curing, cyanoacrylate adhesives release formaldehyde through hydrolysis. When it is marketed as a nail adhesive, there is no regulation regarding its formaldehyde amount nor obligation to indicate its ingredients in Japan. Additionally, a biological safety test is not required for nail adhesives. Thus, because the safety of nail adhesives is inadequately confirmed, it is necessary to investigate their biological safety. Therefore, we purchased 5 commercially available nail adhesives and 1 medical adhesive and examined their formaldehyde content and cytotoxicity. We examined the cytotoxicity of the adhesives in V79 cells by a colony forming assay. In this test, 5 nail adhesives showed higher toxicity than 1 medical adhesive. Formaldehyde concentrations in the extract of adhesives were as follows: 17.5 to 24.2 µg/mL for nail adhesives and 7.4 µg/mL for medical adhesives. Cyanoacetate did not elicit cytotoxicity at the final concentration up to 1000 µM. However, formaldehyde showed cytotoxicity, with an IC50 of 79 µM (2.4 µg/mL). Taken together, the cytotoxicity of nail adhesives could be due to the formaldehyde generated by the hydrolysis of cyanoacrylate. It seems important that nail adhesives will be regulated by obligation and enhanced safety in the future.

Aptima Trichomonas vaginalis assay elucidates significant underdiagnosis of trichomoniasis among women in Brazil according to an observational study.

OBJECTIVES: Trichomonas vaginalis (TV) infection is the most common non-viral STI globally and can result in adverse pregnancy outcomes and exacerbated HIV acquisition/transmission. Nucleic acid amplification tests (NAATs) are the most sensitive diagnostic tests, with high specificity, but TV NAATs are rarely used in Brazil. We investigated the TV prevalence and compared the performance of the US Food and Drug Association-cleared Aptima TV assay with microscopy (wet mount and Gram-stained) and culture for TV detection in women in Pelotas, Brazil in an observational study. METHODS: From August 2015 to December 2016, 499 consecutive asymptomatic and symptomatic sexually active women attending a Gynaecology and Obstetrics Outpatient Clinic were enrolled. Vaginal fluid and swab specimens were collected and wet mount microscopy, Gram-stained microscopy, culture and the Aptima TV assay performed. RESULTS: The median age of enrolled women was 36.5 years (range: 15-77). The majority were white, had a steady sexual partner and low levels of education. The TV detection rate was 4.2%, 2.4%, 1.2% and 0% using the Aptima TV assay, culture, wet mount microscopy and Gram-stained microscopy, respectively. The sensitivity of culture and wet mount microscopy was only 57.1% (95% CI 36.5 to 75.5) and 28.6% (95% CI 13.8 to 50.0), respectively. CONCLUSIONS: A 4.2% positivity rate of T. vaginalis was found among women in Pelotas, Brazil and the routine diagnostic test (wet mount microscopy) and culture had low sensitivities. More sensitive diagnostic tests (NAATs) and enhanced testing of symptomatic and asymptomatic at-risk women are crucial to mitigate the transmission of TV infection, TV-associated sequelae and enhanced HIV acquisition and transmission.

In Vitro Approaches for Assessing the Genotoxicity of Nanomaterials.

Genotoxicity is associated with serious health effects and includes different types of DNA lesions, gene mutations, structural chromosome aberrations involving breakage and/or rearrangements of chromosomes (referred to as clastogenicity) and numerical chromosome aberrations (referred to as aneuploidy). Assessing the potential genotoxic properties of chemicals, including nanomaterials (NMs), is a key element in regulatory safety assessment. State-of-the-art genotoxicity testing includes a battery of assays covering gene mutations, structural and numerical chromosome aberrations. Typically various in vitro assays are performed in the first tier. It is not very likely that NMs may induce as yet unknown types of genotoxic damage beyond what is already known for chemicals. Thus, principles of genotoxicity testing as established for chemicals should be applicable to NMs as well. However, established test guidelines (i.e., OECD TG) may require adaptations for NM testing, as currently under discussion at the OECD. This chapter gives an overview of genotoxicity testing of NMs in vitro based on experiences from various research projects. We recommend a combination of a mammalian gene mutation assay (at either Tk or HPRT locus), the in vitro comet assay, and the cytokinesis-block micronucleus assay, which are discussed in detail here. In addition we also include the Cell Transformation Assay (CTA) as a promising novel test for predicting NM-induced cell transformation in vitro.

Stem cell enriched-epithelial spheroid cultures for rapidly assaying small intestinal radioprotectors and radiosensitizers in vitro.

Radiation therapy is one of the main treatment options for many cancer patients. Although high doses of radiation may maximize tumor cell killing, dose escalation is limited by toxicity to neighboring normal tissues. This limitation applies particularly to the small intestine, the second most radiosensitive organ in the body. Identifying small intestinal (SI) radioprotectors could enable dose escalation in the treatment of abdominopelvic malignancies. However, the only assay currently available to identify effects of radiomodulating drugs on the regenerating capacity of SI stem cells is the Withers-Elkind microcolony assay, which requires large numbers of mice, making it a costly and low throughput method. Here, we describe a novel spheroid formation assay (SFA) that utilizes SI stem cell-enriched three-dimensional epithelial spheroid cultures to identify gastrointestinal radiomodulators ex vivo. The SFA is scalable for high throughput screening and can be used to identify both radioprotectors and radiosensitizers.

Reserve stem cell population in intestinal crypts found to be consistently small by analysis of in vivo clonogenic assays with a biomathematical dynamic model.

BACKGROUND AND PURPOSE: The high plasticity of the intestinal epithelium is maintained by a resilient reserve stem cell population, whose extent and biology are a matter of ongoing debate. The in vivo clonogenic assay (IVCA), presents a well established and efficient analysis of radiation insult to the intestinal crypts. However, we found that inadequate mathematical analysis over the last four decades led to systematic errors and contradictory results in estimates of radio-sensitivity and size of the reserve stem cell pool. MATERIAL AND METHODS: We devised a refinement of the IVCA via development of a biomathematical model that delivers a full statistical dynamic description of epithelial radiation injury and subsequent regeneration. We validated the model against cellular and crypt distribution statistics obtained from IVCA experiments and through systematic re-analysis of experimental data from 27 publications. RESULTS: A full dynamic description of the evolution of stem cell niche population statistics is obtained. A systematic re-analysis reveals a consistent clonogenic content of the crypt of 31±6 cells. The stem cell reserve manifests to be, contrary to prior predictions, radio-resistant: α=(0.22±0.04) Gy-1. CONCLUSION: We established a precision tool for the quantitative analysis of radiation insult to the intestinal crypts, which we employ to show that the reserve stem cell population is small, radio-resistant, and remarkably immutable against a large variety of interventions. The increased resolution of the model allows not only a reduction of the number of animals by about 75%, but also to quantify experimentally the influence of additional agents on damage and on regeneration of the stem cell niche.

Generation of CD34 Fluorescent Reporter Human Induced Pluripotent Stem Cells for Monitoring Hematopoietic Differentiation.

Hematopoietic stem and progenitor cells (HSPCs) derived from human induced pluripotent stem cells (hiPSCs) hold great promise for disease modeling, drug screens, and eventually cell therapy approaches. During in vitro differentiation of hiPSCs into hematoendothelial progenitors, the emergence of CD34-positive cells indicates a critical step of lineage specification. To facilitate the monitoring of hematopoietic differentiation of hiPSCs, we established fluorescent reporter cells for the stem and progenitor cell marker CD34. An IRES-GFP (internal ribosome entry site green fluorescent protein) construct was introduced by CRISPR/Cas9 into the 3' untranslated region of one endogenous CD34 allele. Single-cell clones were generated after excision of the floxed puromycin resistance cassette by Cre recombination and correct insertion was confirmed by genotyping polymerase chain reaction and Southern blot. To validate their functionality, the reporter hiPSCs were in vitro differentiated toward CD34+ cells using the STEMdiff Hematopoietic Kit combined with short-term inhibition of GSK3 (glycogen synthase kinase 3). All cells expressing nuclear GFP were positive for cell surface CD34, thus allowing the direct monitoring of the differentiation of hiPSCs into CD34+ cells either by flow cytometry or confocal microscopy. After fluorescence-activated cell sorting, cells displaying high GFP expression exhibited increased colony-forming potential in the MethoCult colony-forming unit assays as compared with CD34+ cells obtained by magnetic-activated cell sorting. In summary, we have generated functional CD34 GFP reporter hiPSCs, which not only permit label-free separation of HSPCs, but also tracing of the emergence and fate of CD34+ progenitors at the single-cell level.