Hematopoietic Stem Cell Markers Research Articles

The effect of plerixafor on autologous stem cell mobilization, cell viability, and apheresis challenges

Abstract Objective The aim of this study was to determine the efficacy of plerixafor for hematopoietic stem cell (HSC) mobilization prior to autologous stem cell transplantation (aSCT) for patients with multiple myeloma (MM) and various lymphomas, using an oncologist-guided HSC collection goal and markers of cell viability. Methods A retrospective chart review of all aSCT patients at Yale New Haven Hospital between 2017 and 2021 who met diagnostic criteria for MM, non-Hodgkin, or Hodgkin lymphoma (n = 382) was undertaken. Logistic regression evaluated plerixafor’s effect on meeting the individual’s HSC goal. The use of t-tests determined plerixafor’s relationship to HSC yield and analysis of variance testing assessed its effect on cell viability. Results Mobilization with granulocyte colony–stimulating factor (G-CSF) and plerixafor (odds ratio [OR] = 0.08; P < .05) relative to G-CSF alone was negatively associated with meeting the individual’s HSC goal. Diffuse large B-cell lymphoma in patients mobilized with plerixafor yielded fewer HSCs than those without plerixafor (t = –2.78; P = .03). Mobilization regimen (P = .13) had no association with HSC viability. Mobilization failure with plerixafor was rare but occurred in patients with multiple risk factors, including exposure to several rounds of HSC-affecting chemotherapy. Conclusion Plerixafor is effective across multiple diagnoses using an oncologist-driven HSC collection endpoint. Its association with mobilization failure is likely attributable to its use in patients predicted to be poor mobilizers.

Mesenchymal stem cells derived from hard palate: Anattractive alternative for regenerative medicine.

The palatal mucosa exhibits a notable ability to regenerate without causing scarring during the process of wound healing, rendering it a highly valuable reservoir of mesenchymal stem cells (MSCs). The aim of this review is to summarize the different sources of MSCs derived from hard palatal (PMSCs), thereby presenting a promising avenue for the utilization of regenerative medicine. Pertinent literatures focused on the sources, identification methods, and advantageous characteristics of PMSCs are obtained from PubMed and Web of Science. PMSCs, originating from the hard palate periosteum, subepithelial adipose tissue, and lamina propria, have been successfully isolated and characterized, with positive markers for MSCs and negative markers for hematopoietic stem cells. Moreover, PMSCs demonstrate resistance to inflammatory stimuli, enabling uninterrupted osteogenesis in the presence of inflammation. Additionally, PMSCs possess a notable migratory capacity, facilitating prompt arrival at the site of injury. Furthermore, PMSCs exhibit various advantageous inherent in stem cells, including clonogenicity, self-renewal capability, and pluripotent differentiation potential. PMSCs have stem cell-related properties and can be used for regenerative medicine of cells and tissues in the future.

Urine-Derived Stem Cells Reverse Bleomycin‑Induced Experimental Pulmonary Fibrosis by Inhibition of the TGF-β1-Smad2/3 Pathway

BackgroundIdiopathic pulmonary fibrosis (IPF) is characterized by progressive lung interstitial lesions with the disease pathophysiology incompletely understood, which is a serious and fatal disorder with limited treatment options. Mesenchymal stem cells (MSCs) have exhibited promising therapeutic capability for IPF. While most types of MSCs are obtained invasively, urine-derived stem cells (USCs) can be gained in a safe, noninvasive, and inexpensive procedure, which are readily available and reported to exhibit no risk of teratoma formation or oncogenic potential in vivo, sounding alternative to other MSCs. This study aims to investigate the therapeutic effect and mechanism of USCs on IPF, using a bleomycin (BLM)-induced IPF model in mice. MethodsCell surface marker examination by flow cytometry analysis and cell differentiation culture were used to characterize USCs obtained from healthy individuals. BLM was instilled endotracheally in adult C57BL/6 mice, followed by USCs or human bone marrow-derived mesenchymal stem cells (BMSCs) treatment by tail vein injection on day 14. Mice were euthanized on day 14 before administration or day 21 for the evaluation of pulmonary histopathology and hydroxyproline (HYP) content. Inflammatory factors of the lung, including transforming growth factor (TGF)-β1, TNF-α, IL-6, MMP2 were analyzed by quantitative real-time PCR (qRT-PCR). Additionally, immunohistochemistry (IHC) and western blotting (WB) were applied to evaluate the expression of α-SMA and activation of TGF-β1-Smad2/3 in lung. ResultsUSCs highly expressed CD29 and CD90, showing negative expression of hematopoietic stem cell markers (CD45, CD34) and could differentiate into, at least, bone and fat in vitro. In mice challenged with BLM, septal thickening and prominent fibrosis were observed on day 14, with higher HYP content and mRNA levels of TGF-β1, TNF-α and IL-6 exhibited, compared to untreated mice. USCs could migrate to lung and accumulate there in mouse model after intravenous injection. Transplantation of USCs into BLM-induced mice improved their pulmonary histopathology, decreasing Ashcroft score, Szapiel score, HYP content and mRNA levels of TGF-β1 and MMP2 of lung, similar to the effects of BMSCs. IHC and WB further revealed that USCs could inhibit activation of the TGF‑β1-Smad2/3 pathway of lung in vivo. ConclusionsTransplantation of USCs effectively reverses pulmonary fibrotic phenotype in an experimental IPF model, inhibiting the TGF-β1-Smad2/3 pathway, a key driver of fibrosis. These results suggest the therapeutic application of USCs for IPF, instead of other types of MSCs obtained invasively.

Biodistribution and Safety of Human Multi-Chimeric Cells After Systemic Intraosseous and Intravenous Administration in the Experimental Mouse Model.

Cellular therapies provide promising options for inducing tolerance in transplantation of solid organs, bone marrow, and vascularized composite allografts. However, novel tolerance-inducing protocols remain limited, despite extensive research. We previously introduced and characterized a human multi-chimeric cell (HMCC) line, created through ex vivo fusion of human umbilical cord blood (UCB) cells derived from three unrelated donors. In this study, we assessed in vivo biodistribution and safety of HMCCs in the NOD.Cg-PrkdcscidIl2rgtm1Wjl/SzJ NOD scid gamma (NSG) mouse model. Twenty-four NSG mice were randomly assigned to four groups (n = 6/group) and received intraosseous (IO.) or intravenous (IV.) injections of 0.6 × 106 donor UCB cells or fused HMCC: Group 1-UCB (IO.), Group 2-UCB (IV.), Group 3-HMCC (IO.), and Group 4-HMCC (IV.). Hematopoietic phenotype maintenance and presence of human leukocyte antigens (HLA), class I antigens, in the selected lymphoid and nonlymphoid organs were assessed by flow cytometry. Weekly evaluation and magnetic resonance imaging (MRI) assessed HMCC safety. Comparative analysis of delivery routes revealed significant differences in HLA class I percentages for IO.: 1.83% ± 0.79%, versus IV. delivery: 0.04% ± 0.01%, P < 0.01, and hematopoietic stem cell marker percentages of CD3 (IO.: 1.41% ± 0.04%, vs. IV.: 0.07% ± 0.01%, P < 0.05) and CD4 (IO.: 2.74% ± 0.31%, vs. IV.: 0.59% ± 0.11%, P < 0.01). Biodistribution analysis after IO. delivery confirmed HMCC presence in lymphoid organs and negligible presence in nonlymphoid organs, except for lung (IO.: 0.19% ± 0.06%, vs. IV.: 6.33% ± 0.56%, P < 0.0001). No evidence of tumorigenesis was observed by MRI at 90 days following IO. and IV. administration of HMCC. This study confirmed biodistribution and safety of HMCC therapy in the NSG mouse model, both following IO. and IV. administration. However, IO. delivery route confirmed higher efficacy of engraftment and safety profile, introducing HMCCs as a novel cell-based therapeutic approach with promising clinical applications in solid organ, bone marrow, and vascularized composite allotransplantation transplantation.

Investigation of the Presence of Stem Cells in Rat Uterus Tissue in Postnatal Development Periods

Uterine tissue is an organ with a high proliferation capacity where regeneration, differentiation and shedding are seen. Although this tissue is regenerated every month, the source of it hasn’t been determined yet. Studies are carried out on stem cells being a source that can provide regeneration of the endometrium and the markers expressed by these cells. The purpose of this study was to examine the immunreactivity of CD9 and CD13 expressed by essential population of uterus and CD34, marker of hematopoietic stem cells, at various stages of the postnatal developing pro- cess. In this study, was used 42 female Wistar-albino rats split into six groups; Group I; newborn (2-days), Group II; pubertal (38-days), and Group III: fertile group (12 weeks), by identifying the stages of the estrous cycle in rats a) pro- estrus, b) estrus, c) metestrus, d) diestrus. The expression of CD9, CD13, and CD34 in uterine tissues excised from rats was investigated. In the groups of 38-days and 12-weeks, CD34-expressing cells were present in the stroma of the endometrium next to the myometrium, but such cells were absent in the 2-days group. All groups' uterine epithelium displayed CD9 expression, except for group 2-days. Endometrial stromal cells that expressed CD13 showed only little immureactivity in groups 2 and 38-days, while CD13 expression is noticeable in group 12-weeks. It was thought that the uterine endometrium could be regenerated in puberty and adulthood with the contribution of bone marrow-derived stem cells and uterine-derived epithelial and stromal cells.

The Bone Marrow-Targeted Conditioning Stress Test Demonstrates Vertebrae Niche Being More Radio-Tolerant Than Femur, Indicating Skeleton Resilience and Global Heterogeneity

Introduction: Myeloablative conditioning prior to Hematopoietic cell transplant, the curative treatment for several hematopoietic disorders, is essential for successful donor cell homing and engraftment. Despite the anatomical classifications, it has been challenging to grasp the complexity of large skeletal systems' global and local bone marrow (BM) environments, which may play a crucial role in donor homing, engraftment, and treatment response. Moreover, due to a lack of comprehensive in vivo studies, there is sparse information about radio-sensitivity on BM niches in local (i.e, endosteal and sinusoidal) and regional skeletal systems (femur, spine etc.,). This may be due to a lack of technology to deliver targeted radiation and therefore using systemic whole-body radiation which resulted in lethality at higher doses due to the composite effect of hematopoietic failure and organ toxicity. Hence, we developed a preclinical image-guided total marrow irradiation (TMI) model, which allows BM specific increase in radiation dose while sculping dose to vital organs, therefore providing an opportunity to evaluate the radio-sensitivity of the BM niche. Here, using TMI dose escalation, we determined the radiation sensitivity of BM niches and its effect on donor homing. Methods: TMI treatment delivery was developed as described previously (Zuro et al., 2022). Different radiation doses (12, 16, 20 and 24 Gy) were delivered to the host (CD45.1 B6 mouse) skeleton in two fractions and was transplanted with 10 million Donor BM cells (CD45.2 B6). The femur and L Spine were harvested for these treated mice at 20+ h, post BMT. The central marrow (CM) cells were harvested by flushing/gently crushing the bone with Collagenase I and Dispase I enzymatic solution, while endosteal marrow (EM) was harvested by digesting the bone fragments with Collagenase IV enzyme, for 30 minutes at 150-200 rpm at 37° C. The isolated cells from endosteal and Central marrow were stained with standard verified markers for Hematopoietic stem cells, Mesenchymal Stem cells and Endothelial cells (18 antibody Panel) and data was acquired in Aurora spectral flow cytometer (Cytek) and was analyzed using FloJo software. Results: The CM cells were more sensitive to radiation, ~≤10% cell survived compared to untreated controls (20h post BMT) while EM cells were more radio tolerant both in Femur (~≥30% survived) and L spine (≥80% survived), however the endosteal cells from l-spine were more radio tolerant than Femur (~≥ 80% vs 16-28%) ( Fig 1 A-B). Further, in femur it was dose dependent i.e., cell number reduced with increasing doses (~28% (12 Gy) to ~16% (24 Gy), unlike l-spine where cell numbers were similar across treated doses. Also, in femur, the Donor cells preferred EM niche over CM, however at higher dose (24 Gy) this spatial preference was lost ( Fig 1C), unlike l-spine which was similar in CM and EM at all doses. The Sca1 + MSC was significantly higher in EM than CM both in the femur and l-spine, however it decreased in femur at higher doses (24 Gy), while remained unchanged in l-Spine ( Fig 1D-E). The arteriolar endothelial cells (AECs) were predominantly present in the EM both in femur and spine, and while sinusoidal endothelial cells (SEC) were higher in EM than CM in Femur, however Spine did not show this pattern. Although, at higher doses (24 Gy), the AECs were significantly reduced even in the EM but were still higher than CM ( Fig 1F). The donor HSPCs (Lineage- cKit+ cells) were significantly higher in the central marrow while the HSCs (Lineage-, cKit+ Sca1+, CD150+) were higher in endosteal marrow. Only in femur, at higher doses AECs, SECs, and Sca1+ MSCs were reduced, resulting in lower CD150+ HSC homing, which was not affected in the l-spine ( Fig 1G-H). Conclusion: In summary, skeletal niche tolerates much higher radiation than previously performed using conventional myeloablative studies and support donor homing. Increasing radiation doses reduced the BM niche constituent cells like AECs, SECs and Sca1+ MSCs, preferentially in femur and reducing homing, surprisingly though the spine BM was more resistant and did not show any reduction in above mentioned cellular composition. This preferential radiotolerance between skeletal regions warrants more studies to understand the' BM stromal cells radio sensitivity with respect to regional and spatial skeletal niche.

The Effect of SCD-1 Inhibition on Human Hematopoietic Stem Cell Mitochondrial Metabolism, Cell Proliferation, and Differentiation Potential

Hematopoietic stem cells (HSC) give rise to all blood lineages and sustain the production of blood cells throughout life. Due to their inherently high regenerative potential, HSC are used in a variety of clinical settings, including bone marrow transplantation (BMT) directly to cure a variety of hematologic and oncologic disorders often with gene therapy. During regeneration, HSC are activated into cycle. For this, HSC undergo drastic mitochondrial and metabolic remodeling to meet the bioenergetic and biosynthetic needs of activated HSC. A growing body of evidence indicates that HSC sustain injury during activation. This remodeling is important for optimal HSC function but is permanently changed after HSC activating stress. It is thus important to identify the metabolic needs of activated HSC to improve HSC functions for therapeutic purposes. In both murine and human HSC, numerous metabolic enzymes get upregulated during activation, including those involved in de novo lipid synthesis. This metabolism is poorly understood in human HSC. Our overarching question is to understand the metabolic needs of HSC within the human system. Stearoyl-co-A-desaturase 1 (SCD-1), an enzyme responsible for conversion of stearic to oleic acid within the de novo lipid synthesis pathway, is suspected to play a role in metabolic reprogramming after stress. Using CD34+ mobilized human peripheral blood, we analyzed the effect of SCD-1 inhibition on HSC and progenitor proliferation, mitochondrial metabolism, and lineage differentiation potential. Cells were cultured either in vehicle control conditions or with SCD-1 inhibitor (SCDi). Subsequently, cells were counted and analyzed by flow cytometry on Days 4-5 and 10-15. More primitive or stem cell markers were utilized on Days 0 and 5 whereas differentiation markers were utilized on Day 10-15. Both tetramethylrhodamine-ethyl ester dye (TMRE) and MitoSOX reagents were used to assess mitochondrial membrane potential and mitochondrial ROS, respectively. Our results demonstrate that the size of the HSC population generated by SCDi-treated CD34+ cells within 5 days of culture was similar to vehicle treated cells and was composed of similar proportion of CD34+CD38+, CD34+CD38-, and CD38+CD34- cells, indicating that SCD-1 inhibition does not alter HSC expansion under these culture conditions. However, TMRE levels were lower in all HSC populations whereas mitoSOX levels were unchanged by SCD-1 inhibition compared to vehicle. In differentiation conditions, SCDi cultures were composed of a larger proportion of myeloid progenitors and a smaller proportion of erythroid cells after 10-15 days, compared to vehicle-treated cultures. These findings suggest that de novo lipid synthesis is necessary for HSC differentiation but dispensable for proliferation/expansion in vitro. We then used a xenotransplant model to assess the effect of SCDi on HSC regenerative potential in vivo. CD34+ mobilized human peripheral blood cells were cultured for 3 days under conditions that maintain HSC functions in vitro and transplanted into immunodeficient, sublethally irradiated NSG mice. Peripheral blood of xenotransplanted mice was analyzed monthly for human cell chimerism and mature blood lineage potential from 1 to 6 months post-transplant. Bone marrow analysis was performed at the 6 month time point as well, assessing for both HSC markers and lineage markers. Mice that received SCDi-treated cells exhibited human cell chimerism at a level similar to mice that were transplanted with vehicle treated cells, at about 3 to 30%. However, SCDi-treated cells gave rise to a lymphoid-biased graft, in particular T cells, both in the peripheral blood and in the bone marrow of xenotransplanted mice, compared to a more balanced myeloid-lymphoid graft from vehicle treated cells. In conclusion, these findings suggest that de novo lipid synthesis is critically important for HSC lineage fate and balanced differentiation in vitro and in vivo. This is especially clinically relevant as this work may implicate a possible therapeutic target as improving de novo lipid synthesis may aid in patients who suffer from persistent cytopenias after BMT and graft failure.

N-3 Polyunsaturated Fatty Acid (N-3 PUFA) Derived Lipid Mediators Increase Hematopoiesis during Zebrafish Embryogenesis

Polyunsaturated fatty acids (PUFAs), which include n-3 PUFAs and n-6 PUFAs, are essential fatty acids that we can only get from diet. The richest source of PUFAs is fish oil. N-3 PUFAs have been used in the prevention and treatment of coronary artery disease, diabetes, hypertension, arthritis, cancer, and other inflammatory and autoimmune disorders in humans. Lipid mediators derived from n-3 PUFAs are implicated in mediating the resolution of inflammation. However, their effect on hematopoietic stem and progenitor cell (HSPC) proliferation and differentiation and on hematopoiesis has not been studied. Therefore, in this project, we investigated the pro-hematopoietic effects of n-3 PUFA-derived lipid mediators. We exposed wild-type zebrafish embryos to different n-3 PUFA-derived lipid mediators. After fixation, we performed whole mount in situ hybridization (WISH) using antisense RNA probes such as c-myb (hematopoietic stem cell marker), gata1 (erythroid progenitor cell marker), hbbe1 (erythrocyte marker), l-plastin (macrophage and neutrophil cell marker ), mpx (neutrophil cell marker), lyz (neutrophil cell marker), and rag1 (immature lymphocyte marker); reverse transcription-quantitative polymerase chain reaction (RT-qPCR); and fluorescence-activated cell sorting (FACS) to understand the effect of lipid mediator exposure on the proliferation of HSPCs, erythroid progenitor cells, erythrocytes, granulocytic cells, neutrophils, macrophages, and T lymphocytes in different development stages during vertebrate hematopoiesis. In addition, we also used o-dianisidine staining to study red blood cell (RBC) formation and transgenic zebrafish to observe different blood lineages including HSPCs, neutrophils, macrophages, erythroid progenitors, and erythrocytes with fluorescent microscopy. We identified two novel lipid mediators which promote HSPC proliferation, enhance erythroid progenitor cell and erythrocyte production, and increase neutrophil cell number. These two molecules could be applied as novel therapeutics for blood disorders and blood cancers such as anemia and leukemia in humans. These two compounds can be intensely investigated to become candidate supplements to enhance HSPC amplification before HSPC transplantation for leukemia patients.

Single Cell Analysis Identifies Expression of PD-L2 on Human Bone Marrow Hematopoietic Stem Cells

The identification of specific and reliable markers for human hematopoietic stem cells (HSCs) is crucial to enable their prospective isolation allowing the investigation of unique physiological HSC functions within the blood cell hierarchy. Despite significant advancements in identification of surface markers for human bone marrow HSC isolation, the enriched populations remain heterogeneous. Here we applied single cell CITE-Seq (cellular indexing of transcriptomes and epitopes) of FACS-enriched hematopoietic stem and progenitor cells (HSPCs) to decipher differentiation hierarchies and to identify markers of most immature populations. We FACS-isolated over 60.000 high-quality human bone marrow HSPCs by sorting CD34 + and CD34 +CD38 - cells from 15 different healthy donors. These were subjected to scCITE-Seq using the BD Rhapsody system with a targeted gene panel comprising 600 most relevant genes of early HSC differentiation and 50 antibodies. To validate differentially expressed surface marker genes, we performed extensive in vitro and in vivo studies of FACS-purified subpopulations of human bone marrow and mobilized peripheral blood samples (mPB) from healthy donors. Our multi-omics based single HSPC profiling indicated Programmed death ligand 2 (PD-L2 / CD273) as a surface marker expressed on the most immature HSCs within the hematopoietic compartment defined as CD34 +CD38 -CD45RA -CD90 +. Prospective FACS-based isolation allowed a deeper understanding of transcriptomic differences depending on PD-L2 positivity. A transcriptomic principal component analysis of CD273 hi and CD273 low expressing HSCs isolated pairwise from four healthy donors proved distinct clustering accompanied by discriminative molecular signatures. Stem cell genes as HOPX, MLLT3 and MPL were enriched in CD273 hi HSCs, and CDK6 was downregulated, further validating our single-cell analysis. The differential expression of stem cell genes was validated at protein level. Single cell tracking using video-microscopy confirmed a delayed entry into cell cycle in CD273 hi HSCs, suggesting deeper quiescence of these cells. Furthermore, their mitochondrial potential was reduced. In vivo transplantations of both populations in immunocompromised NSGs are ongoing and will reveal the long-term repopulation potential of CD273 hi HSCs. Multiple in vitro differentiation assays demonstrated CD273 positivity to be associated with an increased stem cell phenotype with higher expression of EPCR (CD201) and CD90 in liquid culture, a delayed differentiation and high capability of generating multipotent colonies. Interestingly, CD273 surface expression was strongly upregulated in HSCs upon in vitro culture. Since PD-L2 is known as a ligand for the Programmed death receptor 1 (PD1), we investigated the immunomodulating function of PD-L2 expressing HSPCs by establishing an allogeneic lymphocyte reaction assay. In addition to their stem cell-like characteristics, PD-L2 expressing HSPCs mediated diminished T cell proliferation in allogeneic co-culture settings. Furthermore, cytokine profiling of co-culture supernatants indicated increased secretion of anti-inflammatory cytokines (IL-10 and TGF-β1), accompanied by reduced secretion of pro-inflammatory cytokines (IL-17A) and a diminished expression of the pro-inflammatory receptor CD69 on CD8 + T cells. These findings showed that CD34 + cells isolated from mobilized peripheral blood of healthy donors possess immunomodulating capabilities, and that PD-L2 expression indicates an immunocompromising HSC phenotype. In conclusion, this study demonstrates differential surface expression of PD-L2 within the most immature human HSCs. PD-L2 expression is associated with HSC quiescence and delayed in vitro differentiation. Furthermore, these results provide valuable insights into the immunomodulating features of HSCs expressing PD-L2.

CUX1 Levels Control Hematopoietic Stem Cell Fate and Plasticity

Hematopoietic stem cells (HSCs) sustain lifelong, multipotent output, however, the molecular mechanisms governing HSC homeostasis remain unclear. Elucidating this process is key to understanding the imbalanced differentiation and self-renewal evident in myeloid malignancies. CUX1 is a transcription factor that is monoallelically mutated or deleted in high-risk myeloid malignancies. We previously reported that CUX1 has critical, dose-dependent roles in hematopoiesis and myeloid neoplasia. The haploinsufficient nature of CUX1 in myeloid neoplasia and the broad dose-dependent requirement of CUX1 in hematopoiesis led us investigate the role of CUX1 in earliest stages of hematopoiesis. We generated a CUX1 reporter mouse in which mCherry is fused in-frame with the C-terminus of CUX1 to study how the level of CUX1 in HSCs affects their behavior. Overall, we find that CUX1 protein levels within the HSC compartment delineates stem cell activity. Stringently defined immunophenotypic HSCs with low CUX1 levels (CUX1 Dim) are phenotypically dormant, as assessed by transcriptional profiling and proliferation assays, as opposed to CUX1 Bright HSCs which have greater cell cycle participation. In transplantation assays, CUX1 Dim HSCs are initially platelet-biased but give rise to long-term, multilineage reconstitution. CUX1 Bright HSCs are initially erythroid-biased but lack long-term HSC activity and the capacity for self-renewal. In other words, despite immunophenotypic HSC markers, CUX1 Bright HSCs are not, by definition, HSCs. By most metrics, CUX1 Intermediate HSCs exhibit a distinct, albeit intermediate, phenotype. Therefore, along a continuous gradient of CUX1 expression, HSCs gradually lose the ability to self-renew as CUX1 expression increases. Remarkably, knockdown of CUX1 in CUX1 Bright HSCs re-endows these cells with the capacity for long-term multilineage chimerism, suggesting low levels of CUX1 are required for stem cell activity in HSCs. Inversely, overexpression of CUX1 in HSCs promotes their expansion and ultimate exhaustion, further demonstrating that the level of CUX1 controls HSC fate. Altogether, we report that low CUX1 levels are required for HSC self-renewal and implicate CUX1 as a molecular rheostat for HSC behaviors such as cell division and differentiation. Further, we describe an unprecedented capacity for cells without demonstrated HSC activity to acquire HSC capacity and a novel role for CUX1 in preventing this plasticity.

CD34+ Megakaryocytes Associate with Myelodysplastic Syndromes and Related Cytogenetic Abnormalities, but Not Other Hematological Disorders

Background: CD34 is a transmembrane phosphoglycoprotein that is a marker of hematopoietic stem cells and is used clinically to aid in enumeration of blast cells for identification of advanced myeloid neoplasms. Megakaryocytes are differentiated cells from the myeloid lineage that reside in the bone marrow and generally stain negative for CD34 (CD34-). However, CD34 positive (CD34+) megakaryocytes have been observed in hematological disorders such as myelodysplastic syndrome, myeloproliferative neoplasms, and acute leukemias. CD34+ megakaryocytes are proposed to be relatively specific for malignant hematologic conditions and have been reported to associate with a worse prognosis. However, the general clinical, biochemical, and cytogenic characteristics for bone marrow cases of CD34+ megakaryocytes versus CD34- megakaryocytes remains unclear. Objective: We sought to determine the clinical, biochemical, and cytogenetic characteristics associated with finding CD34+ megakaryocytes on bone marrow biopsies. Methods: We identified 281 independent, index bone marrow biopsy cases between 2011-01-01 and 2017-12-31 from Vancouver General Hospital, Canada that underwent CD34 immunohistochemistry at clinical request. The clinical, biochemical, and cytogenetic characteristics of patients were compared based on megakaryocytes being CD34+ vs CD34- on immunohistochemistry. Cases of CD34+ megakaryocytes were defined as having &amp;gt;5% of megakaryocytes staining CD34+, but sensitivity analyses were performed using different percentage cut-offs of 10, 30, and 50%. Results: Out of 281 cases, 134 had CD34+ megakaryocytes (58.2% male sex; mean age = 64.1 years [SD = 15.2 years]) and 147 had CD34- megakaryocytes (57.1% male sex; mean age = 60.0 years [SD = 16.6 years]). There was a significant difference in the distribution of diagnostic categories observed between cases of CD34+ versus CD34- megakaryocytes: myelodysplastic syndromes 35.1% (n=47) versus 21.8% (n=32), acute myeloid leukemias 20.9% (n=28) versus 21.1% (n=31), non-diagnostic etiology 17.9% (n=24) versus 14.3% (n=21), and myeloproliferative neoplasms 10.4% (n=14) versus 19.7% (n=29) (Figure A; Chi-square p-value=0.0004). Sensitivity analyses using different percentage cut-offs to define cases of CD34+ from CD34- megakaryocytes yielded similar results. The differences in biochemical characteristics between cases of CD34+ versus CD34- megakaryocytes were generally unremarkable. The median (IQR) for biochemical parameters between cases of CD34+ and CD34- megakaryocytes were hemoglobin 99 (28) versus 100 (34) g/L, mean corpuscular volume 94 (14) versus 93 (10) fL, neutrophil count 2.20 (3.68) versus 2.46 (3.63) x10 9/L, platelet count 98 (158) versus 112 (194) x10 9/L, and bone marrow blasts 7 (4) versus 3 (14)%. Lastly, there were notable trends in cytogenetic results associated with 90 cases with CD34+ versus 84 cases with CD34- megakaryocytes including: complex karyotypes for 15.6% (n=14) versus 6.0% (n=5), isolated deletion 5q for 7.8% (n=7) versus 1.2% (n=1), and/or isolated trisomy 8 for 5.6% (n=5) versus 2.4% (n=2). Similar cytogenetic results were observed when cases were restricted to only cases of CD34+ versus CD34- megakaryocytes with a diagnosis of myelodysplastic syndrome (Figure B). Conclusion: The presence of CD34+ megakaryocytes is more common in cases of myelodysplastic syndrome relative to other neoplastic hematologic disorders, but does not appear to help with discriminating between neoplastic and non-neoplastic hematological disorders ( e.g. non-diagnostic etiology). Cases with CD34+ megakaryocytes tend to associate with complex karyotype and deletion 5q abnormalities relative to cases with CD34- megakaryocytes.

Evaluation of GBT021601 As a Therapeutic Agent to Restore Bone Marrow Health and Effective Erythropoiesis in a Sickle Mouse Model

Introduction: Hypoxia-mediated damage resulting from vaso-occlusion in sickle cell disease (SCD) leads to abnormal angiogenesis, such as occurs with moyamoya disease and proliferative retinopathy. Abnormal angiogenesis in mouse models of SCD has been observed to impact the bone marrow niche, resulting in a structurally abnormal vascular network. A dysfunctional bone marrow environment results in ineffective erythropoiesis and can damage hematopoietic stem cells (HSCs). Healthy HSCs are essential to the maintenance of hemoglobin (Hb) levels regardless of the rapid turnover of red cells and because of their potential as material for gene therapy. Recently, red cell transfusions were shown to reverse pathogenic angiogenesis in a sickle cell mouse model. However, chronic red cell transfusions are difficult to sustain in individuals with SCD due to complications including iron overload, risk of alloimmunization, and the time and cost involved. GBT021601 is a potent sickle Hb polymerization inhibitor that improves the rheology of red blood cells (RBCs) and has been shown to increase total Hb by as much as 3 g/dL. Here, we explore the effectiveness of GBT021601 for restoring bone marrow health and decreasing proangiogenic factors while maintaining the stemness of marrow cells to preserve erythrocyte maturation. Understanding the impact of GBT021601 on aberrant angiogenesis and the function of HSCs will indicate if it has a role in improving the bone marrow niche and HSC fitness in an era of expanded cell-based therapies for SCD. Methods: Nine-week-old, humanized Townes HbSS SCD mice were split into 3 cohorts (n=8 per group: 4 male, 4 female) and for 12 weeks were fed either standard chow (control) or chow containing 0.1% or 0.2% of GBT021601. After 12 weeks, the mice were phlebotomized and euthanized. Spleens were collected and weighed. Whole bone marrow was collected via centrifugation from both tibias and one femur; the other femur was saved for subsequent 3D confocal microscopy. Bone marrow was analyzed using flow cytometry to measure erythroid cell maturation (Annexin V, TER119, and CD44) and HSC markers (Lin, Sca-1, c-kit). Immunoblot analysis was performed on peripheral plasma to measure hypoxia-induced signaling and markers of angiogenesis (VCAM-1, VEGF-A, ANG-1, and -2). Results: Hb increased by 3 g/dL on average with administration of GBT021601, and spleen weights were significantly reduced ( P=0.0023 and P=0.0015 for control vs 0.1% and 0.2%, respectively). Flow cytometry of the extracted bone marrow revealed a significant increase in mature RBCs and a decrease in erythroid progenitors at all stages ( P&amp;lt;0.001 for RBCs and basophils; P=0.04, P=0.002, and P=0.001 for pro-, poly-, and ortho-chromatic erythroblasts, respectively) (Figure 1). HSCs, defined as Lin-Sca-1 +c-kit +, were not significantly different between groups (control vs 0.1%, control vs 0.2%, and for 0.1% vs 0.2%). Immunoblot analysis revealed a reduction in VCAM-1 and ANG-1 markers with administration of GBT021601 relative to control. However, no difference between ANG-2 and VEGF-A markers was observed between treated and control mice (Figure 2). Conclusions: Treatment with GBT021601 was effective at reducing extramedullary hematopoiesis as determined by the reduction in spleen size compared with control mice. VCAM-1 and ANG-1 are increased in HbSS compared with HbAA mice; treatment with GBT021601 reduced factors that contribute to pathogenic angiogenesis. Treatment with GBT021601 did not change ANG-2 and VEGF-A expression; notably, VEGF-A levels are similar between HbSS and HbAA mice. Our findings support GBT021601 as a sustainable treatment to reduce ineffective erythropoiesis and abnormal angiogenesis-which can otherwise damage the bone marrow niche-thereby suggesting a potential benefit for individuals with SCD participating in future cell-based therapies with curative intent and improved outcomes. More work is planned to examine the ability of GBT021601 to normalize the bone marrow environment and reduce the risk of deleterious effects on allogenic or autologous edited HSCs.

FLT3-Ligand Alone Enables the Identification and Maintenance in Vitro of Viable Quiescent Human Fetal Liver Hematopoietic Stem Cells with Maintenance of Their Function

Cells with sustained multi-lineage blood cell regenerative potential are referred to as hematopoietic stem cells (HSCs). Current findings indicate that they are responsible for lifelong blood production, are first detected within the first month of development in humans and are largely created prior to birth after which they expand their numbers in response to physiological demands for normal or enhanced blood cell output requirements. Interestingly, a number of the intrinsically determined functional properties of HSCs also change after birth. These include an apparent decline in their self-renewal potential. Thus, for example, in humans as in mice, cells with long-term (&amp;gt;6 month) HSC regenerative properties present in the developing fetal liver (FL) are a source of HSCs that possess a much higher in vivo regenerative capability than those from older donor sources, such as adult bone marrow or even cord blood (CB). Accordingly, it has been of longstanding interest to better understand the molecular regulation of this high regenerative capacity prevalent in fetal HSCs for potential future therapeutic as well as scientific exploitation. Here, we describe the results of experiments designed to answer the hypothesis that human FL HSCs with human-relevant self-renewal properties can be isolated as a quiescent CD49f+ subset of the GPI80+CD90+CD38-CD45RA-CD34+CD45+ population following their incubation in standard serum-free culture medium supplemented with FLT3-ligand (FLT3-L) alone. Initial experiments showed expression of the CD49f integrin on first trimester hFL cells selectively depleted cells able to produce colonies of granulocytes, macrophages or erythroid cells in standard 2-week methylcellulose cultures containing SCF, GM-CSF, IL6, IL3 and EPO. Conversely, expression of the CD49f integrin selectively enriched for cells with 12-week output capabilities in both growth factor (GF)-supplemented stromal co-cultures and in sublethally irradiated, transplanted immunodeficient NOD-Rag1 -/-IL2Rγc -/- W 41/41 (NRG-W) mice. Initial experiments designed to test the effect of multiple GF and small molecule additives on the maintenance over a 7-day period of this in vivo regenerative ability of the input FL HSC confirmed GPI80 expression to be a continuing positive selective phenotype. In addition, the result of transplant experiments showed that a 2-day incubation in FLT3-L alone maintained the 12-week serially transplantable activity of the HSCs (12-weeks/cycle) as fully equivalent to the unmanipulated input cells and significantly superior (P&amp;lt;0.05) to FLT3-L+IL3+SF (3GF) with or without addition of UM171, stemregenin, or eltrombopag. Interestingly, in vitro monitoring of GPI80+ cells showed FLT3-L alone maintained the survival of only 20% of the input GPI80+ cells compared to any of the 3GF-based conditions. In addition, the time to complete a first division and subsequent divisions of the input cells was delayed and prolonged, respectively, in the FLT3-L versus the 3GF conditions. Subsequent 7-day suspension cultures and 6-week GF-supplemented stromal co-cultures experiments have confirmed the existence of a G0 population within the HSC-enriched subset of human FL cells that best maintains their growth potential in FLT3-L alone. Together, these results demonstrate CD49f expression to be a pervasive marker of human HSCs throughout development and reveal the importance of different GF conditions to support the maintenance of viability and retention of self-renewal capability of human fetal HSCs in contrast to those required to activate/support a rapid initiation of cell division. These findings set the stage for future development of strategies to exploit human FL cells therapeutically and may also be critical to designing conditions that will best support the ex vivo maintenance of HSCs at and after birth.

Early Molecular Steps in Human Bone Marrow Stem Cell Differentiation Trajectories

Understanding the molecular signatures of human hematopoietic stem/progenitor cells (HSCPs) and gene network changes leading to differentiation induction are of utmost importance to achieve therapeutic hematopoietic stem cell (HSC) expansion. The identification of surface markers has improved the prospective isolation of human bone marrow HSCs over the last decades, but the isolated population still remains very heterogeneous. Single cell sequencing approaches have the potential to unbiased assort stem cells along their differentiation stages and trajectories, and to decipher molecular markers in differentiation hierarchies. However, whole transcriptome single cell sequencing often suffers from inadequate detection of low-expressed genes with increased drop-outs. To address this limitation and to provide sensitive mRNA quantification in human HSPCs, we developed a selected targeted gene panel (600 genes) in combination with 50 protein markers to cover most relevant genes/proteins of early HSPC differentiation and cell cycle status. We employed single cell CITE-Seq (cellular indexing of transcriptomes and epitopes by sequencing) based multi-omic profiling to &amp;gt;60.000 high-quality FACS-enriched human bone marrow HSPCs (CD34 + and CD34 +CD38 - cells) from 15 healthy donors representing young, mid and old age groups. Here, we demonstrate the most comprehensive molecular map of early human HSC differentiation and provide evidence of early branching points into lineage trajectories across different age groups using Slingshot pseudotime analysis. Our data demonstrate that the HSC branched into two main lineages, with the first branching point giving rise to megakaryocytic and erythroid progenitors (MKP/ERP), followed by lymphoid and myeloid progenitors (LMP/MDP). As expected, the most immature HSCs were defined by high expression of CD34, CD90, CRHBP, HOPX, HLF, MLLT3. However, we observed a number of hitherto undescribed HSC markers. The MKP/ERP lineage was defined by GATA1, TFRC, CD36, MPL and VWF expression. Furthermore, we found CD274, the Programmed Cell Death receptor ligand 1, to be selectively expressed in the MKP cluster. Re-clustering and trajectory analysis of the most immature CD34 +CD38 -/low cells confirmed early lineage commitment, suggesting that an MKP/ERP development does not include myeloid or lymphoid progenitors. A similar pattern was observed for all age groups. Interestingly, we observed increased expression of novel marker genes ( HLA-E, DLK1, ADGRG6, ADGRG1, MMRN1) and proteins (CD137 and CD273) in the most immature HSCs. Besides a gradual upregulation of CD38 along differentiation, differentiated cells showed lower CD45 levels. Furthermore, MKP/ERP committed cells showed a downregulation of SPINK2. TradeSeq analysis defined the continuous single cell expression changes in genes and markers upon early differentiation and lineage commitment, allowing the detection of decision-making gene networks. Our data adds further evidence to the revised model of hematopoiesis that challenges the dogma of a common myeloid progenitor giving rise to erythroid, megakaryocytic and myeloid cells. Furthermore, we see a structured hierarchical organization with a sequential loss of lineage potential and not an early commitment of uni-lineage restricted precursors. We report on the upregulation of ADGRG6, ADGRG1, DLK1, HLA-E, MMRN1 CD137 and CD273 in the most immature HSCs. Molecular and functional characterization of CD273 hi and low HSCs are presented in an adjacent report by our group at this meeting (Schmachtel et al.). In conclusion, we provide a valuable resource for the continuous regulation of genes and surface proteins along early differentiation of very immature human HSCs.

Identification of Acute Myeloid Leukemia Cell Surface Therapeutic Targets Using Single Cell RNA Sequencing Supported By Surface Proteomics

Background: Acute myeloid leukemia (AML) comprises diverse genomic subgroups and remains hard to treat in most patients. Despite breakthroughs in the therapeutic arsenal in recent years, clinical usage of therapeutic antibodies or chimeric antigen receptor T (CAR-T) cells has been lagging in contrast to other hematological malignancies. In fact, CD33 represents the only antibody-based strategy approved for this disease to date, highlighting the need to identify new promising targets. AML cells span a wide range of aberrant myeloid differentiation programs, complexifying the identification, by bulk genomics, of targets expressed in the most immature leukemic cells. Aims and Methods: To identify the expression landscape of surface proteins in immature leukemic cells, we performed single-cell RNA sequencing (scRNA-seq, 10x 3' Reagent Kits) of primary human AML cells from 20 specimens of the Leucegene cohort enriched in intermediate and adverse genetic backgrounds ( KMT2A-rearranged n=5, chromosome 5 and/or 7 deletions (abn5/7, n=5) complex karyotype (n=4), NPM1/DNMT3A/FLT3-ITD triple-mutant (n=3) and others (n=3)). A Random Forest classifier was developed to unbiasedly classify AML cells into distinct differentiation stages using normal bone marrow-derived scRNA-seq data from the Human Cell Atlas (HCA) consortium. Genes were scored based on their probability of coding for proteins expressed at the cell surface using the SPAT algorithm developed by our group (https://doi.org/10.1101/2023.07.07.547075), retaining high score ones. To validate surface expression, we concomitantly analyzed the surface proteome (hereafter named surfaceome) of 100 primary human AML samples from the Leucegene cohort, including all 20 samples profiled by scRNA-seq. Results: After quality control, we profiled and characterized 103 690 high quality cells (mean of 5185 cells/sample). We trained a Random Forest classifier to annotate cells in a two step process, first identifying plasma cells based on a restricted list of genes abundantly expressed in these cells and subsequently assigning the remaining cells to one of 33 cell types. We performed a five-fold cross validation of the model and subsequently determined the accuracy of our classifier to be 92% on the test subset of the HCA data. Applied to our AML cell collection, a total of 35 053 cells (34%) were unbiasedly classified as Hematopoietic Stem Cell (HSC)-like, corresponding to the most phenotypically immature leukemic cells in each patient sample (ranging from 4 to 74 %). Accordingly, HSC-like AML cells preferentially express genes associated with normal HSCs, such as CD34, FAM30A, and SPINK2, and globally lack expression of mature lineages defining genes, further validating our classifier. The proportion of HSC-like cells varied among AML subgroups, and was lowest in KMT2A-r AML (median 19%) and highest in abn5/7 samples (46%). Integration of our AML atlas using Harmony algorithm preserved differentiation hierarchies across samples, with most cell types, including HSC-like cells, occupying a defined area in the low dimensional embedding. To identify new surface antigens specifically expressed in immature leukemic cells, we compared the high (≥8) SPAT score gene expression profile of AML HSC-like cells with that of normal HSC cells (HCA), and identified 60 genes significantly overexpressed in AML immature cells. Of those, 39 genes were also detected at the protein level by the surfaceome analysis, supporting their predicted expression at the cell surface in AML samples. 59% of these 39 genes (n=23) were detected in over 80% of the specimens analyzed by the surfaceome, and thus are nearly universally expressed in our AML cohort. To identify targets of therapies that could be repurposed, we next evaluated the relevance of our findings by querying the Thera-SAbDab database. Most interestingly, 8 of the 39 AML specific HSC markers are targeted by therapeutic antibodies FDA-approved or in clinical trials for the treatment of AML (n=4, IL3RA, FLT3, CD37 and TNFRSF10B) or other indications (n = 4). Conclusion Our genetically diverse AML single-cell atlas, supported by mass spectrometry, enables the identification of both subset-specific and pan-AML surface protein genes. These represent potential targets for antibody based strategy development or therapy repurposing in AML.

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

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

Combination of CD49b and CD229 Reveals a Subset of Multipotent Progenitors With Short-Term Activity Within the Hematopoietic Stem Cell Compartment.

Hematopoiesis is maintained by hematopoietic stem cells (HSCs) that replenish all blood lineages throughout life. It is well-established that the HSC pool is functionally heterogeneous consisting of cells differing in longevity, self-renewal ability, cell proliferation, and lineage differentiation. Although HSCs can be identified through the Lineage-Sca-1+c-Kit+CD48-CD34-CD150+ immunophenotype, the cell surface marker combination does not permit absolute purification of functional HSCs with long-term reconstituting ability. Therefore, prospective isolation of long-term HSCs is crucial for mechanistic understanding of the biological functions of HSCs and for resolving functional heterogeneity within the HSC population. Here, we show that the combination of CD229 and CD49b cell surface markers within the phenotypic HSC compartment identifies a subset of multipotent progenitor (MPP) cells with high proliferative activity and short-term reconstituting ability. Thus, the addition of CD229 and CD49b to conventional HSC markers permits prospective isolation of functional HSCs by distinguishing MPPs in the HSC compartment.

CD34 Protein: Its expression and function in inflammation.

CD34 has spear-headed the field of basic research and clinical transplantation since the first reports of its expression on hematopoietic stem cells (HSCs). Expressed in mice, humans, rats and other species, CD34 has been used for more than 40years as a hematopoietic stem and progenitor cell marker. It was later found that muscle satellite cells and epidermal precursors can also be identified with the aid of CD34. Despite the usefulness of CD34 as a marker of HSCs, its overall purpose in animal physiology has remained unclear. This review recaptures CD34 structure, evolutionary conservation, proposed functions, and role in lung inflammation, to describe current research findings and to provide guidance for future studies on CD34.

Equivalents of the neutrophil-to-lymphocyte ratio of circulating pool of stem and immature hematopoietic cells for assessing liver transplant status

Objective: to study the applicability of the neutrophil-to-lymphocyte ratio (NLR) for monitoring recipient status and for possible minimization of maintenance immunosuppression in the long-term period after liver transplantation (LT).Materials and methods. Blood samples of 19 recipients with satisfactory graft function were examined by flow cytofluorometry at various time periods after LT using hematopoietic stem cell markers CD133, their CD31 derivatives, and alpha-fetoprotein (AFP), compared with the conventional NLR.Results. The use of NLR equivalents with CD133 and CD31 to assess liver transplant status is due to their high representation in liver tissue. Their values change in the long-term posttransplant period (from 1.5 to 6–7 years following LT) ≈20-fold and in different directions, but only when measuring their commissural to the liver cell fractions bearing the AFP marker.Conclusion. In contrast to the conventional NLR, maintenance of the lowest level of CD31 AFP, an NLR «equivalent», achieved at 1.5 years after LT, can be considered a criterion for the success of immunosuppressive therapy in the long-term post-LT period. The developed technique can be used to decide on whether to reduce or discontinue medication-assisted prophylaxis of graft rejection.

Stem cell decoupling underlies impaired lymphoid development during aging

Mammalian aging is associated with multiple defects of hematopoiesis, most prominently with the impaired development of T and B lymphocytes. This defect is thought to originate in hematopoietic stem cells (HSCs) of the bone marrow, specifically due to the age-dependent accumulation of HSCs with preferential megakaryocytic and/or myeloid potential ("myeloid bias"). Here, we tested this notion using inducible genetic labeling and tracing of HSCs in unmanipulated animals. We found that the endogenous HSC population in old mice shows reduced differentiation into all lineages including lymphoid, myeloid, and megakaryocytic. Single-cell RNA sequencing and immunophenotyping (CITE-Seq) showed that HSC progeny in old animals comprised balanced lineage spectrum including lymphoid progenitors. Lineage tracing using the aging-induced HSC marker Aldh1a1 confirmed the low contribution of old HSCs across all lineages. Competitive transplantations of total bone marrow cells with genetically marked HSCs revealed that the contribution of old HSCs was reduced, but compensated by other donor cells in myeloid cells but not in lymphocytes. Thus, the HSC population in old animals becomes globally decoupled from hematopoiesis, which cannot be compensated in lymphoid lineages. We propose that this partially compensated decoupling, rather than myeloid bias, is the primary cause of the selective impairment of lymphopoiesis in older mice.