Epo-IGF1R cross talk expands stress-specific progenitors in regenerative erythropoiesis and myeloproliferative neoplasm.

We found that in regenerative erythropoiesis, the erythroid progenitor landscape is reshaped, and a previously undescribed progenitor population with colony-forming unit-erythroid (CFU-E) activity (stress CFU-E [sCFU-E]) is expanded markedly to restore the erythron. sCFU-E cells are targets of erythropoietin (Epo), and sCFU-E expansion requires signaling from the Epo receptor (EpoR) cytoplasmic tyrosines. Molecularly, Epo promotes sCFU-E expansion via JAK2- and STAT5-dependent expression of IRS2, thus engaging the progrowth signaling from the IGF1 receptor (IGF1R). Inhibition of IGF1R and IRS2 signaling impairs sCFU-E cell growth, whereas exogenous IRS2 expression rescues cell growth in sCFU-E expressing truncated EpoR-lacking cytoplasmic tyrosines. This sCFU-E pathway is the major pathway involved in erythrocytosis driven by the oncogenic JAK2 mutant JAK2(V617F) in myeloproliferative neoplasm. Inability to expand sCFU-E cells by truncated EpoR protects against JAK2(V617F)-driven erythrocytosis. In samples from patients with myeloproliferative neoplasm, the number of sCFU-E-like cells increases, and inhibition of IGR1R and IRS2 signaling blocks Epo-hypersensitive erythroid cell colony formation. In summary, we identified a new stress-specific erythroid progenitor cell population that links regenerative erythropoiesis to pathogenic erythrocytosis.

Multiplex Fragment Analysis for Flexible Detection of All SARS-CoV-2 Variants of Concern.

BACKGROUND: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants continue to emerge, and effective tracking requires rapid return of results. Surveillance of variants is typically performed by whole genome sequencing (WGS), which can be financially prohibitive and requires specialized equipment and bioinformatic expertise. Genotyping approaches are rapid methods for monitoring SARS-CoV-2 variants but require continuous adaptation. Fragment analysis may represent an approach for improved SARS-CoV-2 variant detection. METHODS: A multiplex fragment analysis approach (CoVarScan) was validated using PCR targeting variants by size and fluorescent color. Eight SARS-CoV-2 mutational hot spots in variants of concern (VOCs) were targeted. Three primer pairs (recurrently deleted region [RDR] 1, RDR2, and RDR3-4) flank RDRs in the S-gene. Three allele-specific primers target recurrent spike receptor binding domain mutants. Lastly, 2 primer pairs target recurrent deletions or insertions in ORF1A and ORF8. Fragments were resolved and analyzed by capillary electrophoresis (ABI 3730XL), and mutational signatures were compared to WGS results. RESULTS: We validated CoVarScan using 3544 clinical respiratory specimens. The assay exhibited 96% sensitivity and 99% specificity compared to WGS. The limit of detection for the core targets (RDR1, RDR2, and ORF1A) was 5 copies/reaction. Variants were identified in 95% of samples with cycle threshold (CT) <30 and 75% of samples with a CT 34 to 35. Assay design was frozen April 2021, but all subsequent VOCs have been detected including Delta (n = 2820), Mu, (n = 6), Lambda (n = 6), and Omicron (n = 309). Genotyping results are available in as little as 4 h. CONCLUSIONS: Multiplex fragment analysis is adaptable and rapid and has similar accuracy to WGS to classify SARS-CoV-2 variants.

Defective erythroid differentiation in miR-451 mutant mice mediated by 14-3-3zeta.

Erythrocyte formation occurs throughout life in response to cytokine signaling. We show that microRNA-451 (miR-451) regulates erythropoiesis in vivo. Mice lacking miR-451 display a reduction in hematrocrit, an erythroid differentiation defect, and ineffective erythropoiesis in response to oxidative stress. 14-3-3zeta, an intracellular regulator of cytokine signaling that is repressed by miR-451, is up-regulated in miR-451(-/-) erythroblasts, and inhibition of 14-3-3zeta rescues their differentiation defect. These findings reveal an essential role of 14-3-3zeta as a mediator of the proerythroid differentiation actions of miR-451, and highlight the therapeutic potential of miR-451 inhibitors.

Cbl ubiquitination of p85 is essential for Epo-induced EpoR endocytosis.

Erythropoietin (Epo) binding to the Epo receptor (EpoR) elicits downstream signaling that is essential for red blood cell production. One important negative regulatory mechanism to terminate Epo signaling is Epo-induced EpoR endocytosis and degradation. Defects in this mechanism play a key role in the overproduction of erythrocytes in primary familial and congenital polycythemia (PFCP). Here we have identified a novel mechanism mediating Epo-dependent EpoR internalization. Epo induces Cbl-dependent ubiquitination of the p85 regulatory subunit of PI3K, which binds to phosphotyrosines on EpoR. Ubiquitination allows p85 to interact with the endocytic protein epsin-1, thereby driving EpoR endocytosis. Knockdown of Cbl, expression of its dominant negative forms, or expression of an epsin-1 mutant devoid of ubiquitin-interacting motifs all compromise Epo-induced EpoR internalization. Mutated EpoRs mimicking those from PFCP patients cannot bind p85, co-localize with epsin-1, or internalize on Epo stimulation and exhibit Epo hypersensitivity. Similarly, knockdown of Cbl also causes Epo hypersensitivity in primary erythroid progenitors. Restoring p85 binding to PFCP receptors rescues Epo-induced epsin-1 co-localization and EpoR internalization and normalizes Epo hypersensitivity. Our results uncover a novel Cbl/p85/epsin-1 pathway in EpoR endocytosis and show that defects in this pathway contribute to excessive Epo signaling and erythroid hyperproliferation in PFCP.

CCR7 guides migration of mesenchymal stem cell to secondary lymphoid organs: a novel approach to separate GvHD from GvL effect.

Inefficient homing of systemically infused mesenchymal stem cells (MSCs) limits the efficacy of existing MSC-based clinical graft-versus-host disease (GvHD) therapies. Secondary lymphoid organs (SLOs) are the major niches for generating immune responses or tolerance. MSCs home to a wide range of organs, but rarely to SLOs after intravenous infusion. Thus, we hypothesized that targeted migration of MSCs into SLOs may significantly improve their immunomodulatory effect. Here, chemokine receptor 7 (CCR7) gene, encoding a receptor that specifically guides migration of immune cells into SLOs, was engineered into a murine MSC line C3H10T1/2 by retrovirus transfection system (MSCs/CCR7). We found that infusion of MSCs/CCR7 potently prolonged the survival of GvHD mouse model. The infused MSCs/CCR7 migrate to SLOs, relocate in proximity with T lymphocytes, therefore, potently inhibited their proliferation, activation, and cytotoxicity. Natural killer (NK) cells contribute to the early control of leukemia relapse. Although MSCs/CCR7 inhibited NK cell activity in vitro coculture, they did not impact on the proportion and cytotoxic capacities of NK cells in the peripheral blood of GvHD mice. In an EL4 leukemia cell loaded GvHD model, MSCs/CCR7 infusion preserved the graft-versus-leukemia (GvL) effect. In conclusion, this study demonstrates that CCR7 guides migration of MSCs to SLOs and thus highly intensify their in vivo immunomodulatory effect while preserving the GvL activity. This exciting therapeutic strategy may improve the clinical efficacy of MSC based therapy for immune diseases.

Effect of bone mass density and alveolar bone resorption on stress in implant restoration of free-end edentulous posterior mandible: Finite element analysis of double-factor sensitivity.

BACKGROUND: Osseous condition of the mandible was regarded as a key factor influencing stability of implants in the early stage. Finite element analysis was used to assess the effect of bone mass density and alveolar bone resorption (double factors) on stress in a four-unit implant restoration of a free-end edentulous posterior mandible. METHODS: A 3D finite element model was constructed for a single-sided free-end edentulous mandible (from mandibular first premolar to mandibular second molar) containing threaded dental implants. Mandible sensitivity modes were constructed with different alveolar bone resorption levels for normal conditions as well as mild, moderate and severe periodontitis, respectively. Based on the mass density of cancellous bone for four types of bones as the sensitivity parameter, two implant design modes were constructed: Model A (four-unit fixed bridge supported by three implants, implant positions were 34, 36 and 37) and model B: 34 × 36, 37 (37: a single implant crown) (34 × 36: three-unit fixed bridge supported by two implants, implant positions were 34 and 36). A total of 32 sensitivity-based finite element models, grouped in two groups, were constructed. Stress distribution and maximum von Mises stress on cortical bone and cancellous bone around the implant, as well as the surface of implant were investigated by using ABAQUS when vertical loading and 45° oblique loading were applied, respectively. RESULTS: When vertical loading was applied on the implant, maximum von Mises stress on the cortical bone around the implant was assessed to be 4.726 MPa - 13.15 MPa and 6.254 MPa - 13.79 MPa for groups A and B, respectively; maximum stress on the cancellous bone around the implant was 2.641 MPa - 3.773 MPa and 2.864 MPa - 4.605 MPa, respectively; maximum stress on the surface of implant was 14.7 MPa - 21.17 MPa and 21.64 MPa - 30.70 MPa, respectively. When 45° oblique loading was applied on the implant restoration, maximum von Mises stress on the cortical bone around the implant was assessed to be 42.08 MPa - 92.71 MPa and 50.84 MPa - 102.5 MPa for groups A and B, respectively; maximum stress on the cancellous bone around the implant was 4.88 MPa - 25.95 MPa and 5.227 MPa - 28.43 MPa, respectively; maximum stress on the surface of implant was 77.91 MPa - 124.8 MPa and 109.2 MPa - 150.7 MPa, respectively. Stress peak on the cortical bone and that on cancellous bone around the implant increased and decreased with the decrease in bone mass density, respectively. Stress peak on alveolar bone increased with alveolar bone resorption when oblique loading was applied. CONCLUSION: 1. Both alveolar bone resorption and bone mass density (double factors) are critical to implant restoration. Bone mass density may exhibit a more pronounced impact than alveolar bone resorption. 2. From the biomechanical perspective, types I and II bones are preferred for implant restoration, while implantation should be considered carefully in the case of type III bones, or those with less bone mass density accompanied by moderate to severe alveolar bone loss. 3. Splinting crowns restoration is biomechanically superior to single crown restoration.

Migration of dorsal aorta mesenchymal stem cells induced by mouse embryonic circulation.

Mesenchymal stem cells (MSCs) represent powerful tools for regenerative medicine for their differentiation and migration capacity. However, ontogeny and migration of MSCs in mammalian mid-gestation conceptus is poorly understood. We identified canonical MSCs in the mouse embryonic day (E) 11.5 dorsal aorta (DA). They possessed homogenous immunophenotype (CD45(-)CD31(-)Flk-1(-)CD44(+)CD29(+)), expressed perivascular markers (α-SMA(+)NG2(+)PDGFRß(+)PDGFRα(+)), and had tri-lineage differentiation potential (osteoblasts, adipocytes, and chondrocytes). Of interest, MSCs were also detected in E12.5-E13.5 embryonic circulation, 24 hr later than in DA, suggesting migration like hematopoietic stem cells. Functionally, E12.5 embryonic blood could trigger efficient migration of DA-MSCs through platelet-derived growth factor (PDGF) receptor-, transforming growth factor-beta receptor-, but not basic fibroblast growth factor receptor-mediated signaling. Moreover, downstream JNK and AKT signaling pathway played important roles in embryonic blood- or PDGF-mediated migration of DA-derived MSCs. Taken together, these results revealed that clonal MSCs developed in the mouse DA. More importantly, the embryonic circulation, in addition to its conventional transporting roles, could modulate migration of MSC during early embryogenesis.

Digital Droplet PCR for SARS-CoV-2 Resolves Borderline Cases.

OBJECTIVES: The Bio-Rad SARS-CoV-2 ddPCR Kit (Bio-Rad Laboratories) was the first droplet digital polymerase chain reaction (ddPCR) assay to receive Food and Drug Administration (FDA) Emergency Use Authorization approval, but it has not been evaluated clinically. We describe the performance of ddPCR-in particular, its ability to confirm weak-positive severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) results. METHODS: We clinically validated the Bio-Rad Triplex Probe ddPCR Assay. The limit of detection was determined by using serial dilutions of SARS-CoV-2 RNA in an artificial viral envelope. The ddPCR assay was performed according to the manufacturer's specifications on specimens confirmed to be positive (n = 48) or negative (n = 30) by an FDA-validated reverse transcription-polymerase chain reaction assay on the m2000 RealTime system (Abbott). Ten borderline positive cases were also evaluated. RESULTS: The limit of detection was 50 copies/mL (19 of 20 positive). Forty-seven specimens spanning a range of quantification cycles (2.9-25.9 cycle numbers) were positive by this assay (47 of 48; 97.9% positive precent agreement), and 30 negative samples were confirmed as negative (30 of 30; 100% negative percent agreement). Nine of 10 borderline cases were positive when tested in triplicate. CONCLUSIONS: The ddPCR of SARS-CoV-2 is an accurate method, with superior sensitivity for viral RNA detection. It could provide definitive evaluation of borderline positive cases or suspected false-negative cases.

Interleukin-3 promotes hemangioblast development in mouse aorta-gonad-mesonephros region.

BACKGROUND: The hemangioblast is a bi-potential precursor cell with the capacity to differentiate into hematopoietic and vascular cells. In mouse E7.0-7.5 embryos, the hemangioblast can be identified by a clonal blast colony-forming cell (BL-CFC) assay or single cell OP9 co-culture. However, the ontogeny of the hemangioblast in mid-gestation embryos is poorly defined. DESIGN AND METHODS: The BL-CFC assay and the OP9 system were combined to illustrate the hemangioblast with lymphomyeloid and vascular potential in the mouse aorta-gonad-mesonephros region. The colony-forming assay, reverse transcriptase polymerase chain reaction analysis, immunostaining and flow cytometry were used to identify the hematopoietic potential, and Matrigel- or OP9-based methods were employed to evaluate endothelial progenitor activity. RESULTS: Functionally, the aorta-gonad-mesonephros-derived BL-CFC produced erythroid/myeloid progenitors, CD19(+) B lymphocytes, and CD3(+)TCRbeta(+) T lymphocytes. Meanwhile, the BL-CFC-derived adherent cells generated CD31(+) tube-like structures on OP9 stromal cells, validating the endothelial progenitor potential. The aorta-gonad-mesonephros-derived hemangioblast was greatly enriched in CD31(+), endomucin(+) and CD105(+) subpopulations, which collectively pinpoints the endothelial layer as the main location. Interestingly, the BL-CFC was not detected in yolk sac, placenta, fetal liver or embryonic circulation. Screening of candidate cytokines revealed that interleukin-3 was remarkable in expanding the BL-CFC in a dose-dependent manner through the JAK2/STAT5 and MAPK/ERK pathways. Neutralizing interleukin-3 in the aorta-gonad-mesonephros region resulted in reduced numbers of BL-CFC, indicating the physiological requirement for this cytokine. Both hematopoietic and endothelial differentiation potential were significantly increased in interleukin-3-treated BL-CFC, suggesting a persistent positive influence. Intriguingly, interleukin-3 markedly amplified primitive erythroid and macrophage precursors in E7.5 embryos. Quantitative polymerase chain reaction analysis demonstrated declined Flk-1 and elevated Scl and von Willebrand factor transcription upon interleukin-3 stimulation, indicating accelerated hemangiopoiesis. CONCLUSIONS: The hemangioblast with lymphomyeloid potential is one of the precursors of definitive hematopoiesis in the mouse aorta-gonad-mesonephros region. Interleukin-3 has a regulatory role with regards to both the number and capacity of the dual-potential hemangioblast.

Essential role of endothelial Smad4 in vascular remodeling and integrity.

New blood vessels are formed through the assembly or sprouting of endothelial cells (ECs) and become stabilized by the formation of perivascular matrix and the association with supporting mural cells. To investigate the role of endothelial Smad4 in vascular development, we deleted the Smad4 gene specifically in ECs using the Cre-LoxP system. EC-specific Smad4 mutant mice died at embryonic day 10.5 due to cardiovascular defects, including attenuated vessels sprouting and remodeling, collapsed dorsal aortas, enlarged hearts with reduced trabeculae, and failed endocardial cushion formation. Noticeably, Smad4-deficient ECs demonstrated an intrinsic defect in tube formation in vitro. Furthermore, the mutant vascular ECs dissociated away from the surrounding cells and suffered from impaired development of vascular smooth muscle cells. The disturbed vascular integrity and maturation was associated with aberrant expression of angiopoietins and a gap junction component, connexin43. Collectively, we have provided direct functional evidence that Smad4 activity in the developing ECs is essential for blood vessel remodeling, maturation, and integrity.

Installation of a cancer promoting WNT/SIX1 signaling axis by the oncofusion protein MLL-AF9.

BACKGROUND: Chromosomal translocation-induced expression of the chromatin modifying oncofusion protein MLL-AF9 promotes acute myelocytic leukemia (AML). Whereas WNT/ß-catenin signaling has previously been shown to support MLL-AF9-driven leukemogenesis, the mechanism underlying this relationship remains unclear. METHODS: We used two novel small molecules targeting WNT signaling as well as a genetically modified mouse model that allow targeted deletion of the WNT protein chaperone Wntless (WLS) to evaluate the role of WNT signaling in AML progression. ATAC-seq and transcriptome profiling were deployed to understand the cellular consequences of disrupting a WNT signaling in leukemic initiating cells (LICs). FINDINGS: We identified Six1 to be a WNT-controlled target gene in MLL-AF9-transformed leukemic initiating cells (LICs). MLL-AF9 alters the accessibility of Six1 DNA to the transcriptional effector TCF7L2, a transducer of WNT/ß-catenin gene expression changes. Disruption of WNT/SIX1 signaling using inhibitors of the Wnt signaling delays the development of AML. INTERPRETATION: By rendering TCF/LEF-binding elements controlling Six1 accessible to TCF7L2, MLL-AF9 promotes WNT/ß-catenin-dependent growth of LICs. Small molecules disrupting WNT/ß-catenin signaling block Six1 expression thereby disrupting leukemia driven by MLL fusion proteins.

Cytokine Receptor Endocytosis: New Kinase Activity-Dependent and -Independent Roles of PI3K.

Type I and II cytokine receptors are cell surface sensors that bind cytokines in the extracellular environment and initiate intracellular signaling to control processes such as hematopoiesis, immune function, and cellular growth and development. One key mechanism that regulates signaling from cytokine receptors is through receptor endocytosis. In this mini-review, we describe recent advances in endocytic regulations of cytokine receptors, focusing on new paradigms by which PI3K controls receptor endocytosis through both kinase activity-dependent and -independent mechanisms. These advances underscore the notion that the p85 regulatory subunit of PI3K has functions beyond regulating PI3K kinase activity, and that PI3K plays both positive and negative roles in receptor signaling. On the one hand, the PI3K/Akt pathway controls various aspects downstream of cytokine receptors. On the other hand, it stimulates receptor endocytosis and downregulation, thus contributing to signaling attenuation.

Dynamic Change of Transcription Pausing through Modulating NELF Protein Stability Regulates Granulocytic Differentiation.

The NELF complex is a metazoan-specific factor essential for establishing transcription pausing. Although NELF has been implicated in cell fate regulation, the cellular regulation of NELF and its intrinsic role in specific lineage differentiation remains largely unknown. Using mammalian hematopoietic differentiation as a model system, here we identified a dynamic change of NELF-mediated transcription pausing as a novel mechanism regulating hematopoietic differentiation. We found a sharp decrease of NELF protein abundance upon granulocytic differentiation and a subsequent genome-wide reduction of transcription pausing. This loss of pausing coincides with activation of granulocyte-affiliated genes and diminished expression of progenitor markers. Functional studies revealed that sustained expression of NELF inhibits granulocytic differentiation, whereas NELF depletion in progenitor cells leads to premature differentiation towards the granulocytic lineage. Our results thus uncover a previously unrecognized regulation of transcription pausing by modulating NELF protein abundance to control cellular differentiation.

[RUNX1 regulates transcription activity of WNT5A in mouse bone marrow derived mesenchymal stem cells].

This study was purposed to investigate the effect of RUNX1 on transcription activity of WNT5A promoter in mouse bone marrow derived mesenchymal stem cells (MSC), and to explore the mechanism by which bone marrow environments regulate MSC. RT-PCR was used to detect the expression of RUNX1 in MSC isolated from mouse bone marrow and cultured in vitro; the chromatin immunoprecipitation (ChIP) was used to investigate the direct in vivo interaction between the RUNX1 and WNT5A promoter; retrovirus system was utilized to introduce the RUNX1 gene into MSC to detect the regulation of RUNX1 on the transcription activity of WNT5A promoter. The results showed that mouse bone marrow derived MSC was positive for Oil Red O, van Kossa and toluidine blue staining respectively and RUNX1 expressed in MSC. WNT5A promoter could be bound by RUNX1, and the expression level of WNT5A was enhanced with the increase of RUNX1. It is concluded that RUNX1 expresses in mouse bone marrow derived MSC, WNT5A is a direct target gene of RUNX1 and its transcriptional activity is regulated by RUNX1.

[Effect of endothelium-specific deletion of PTEN on hemangioblast development in mouse embryo AGM region].

This study was aimed to investigate whether endothelium-specific deletion of PTEN can affect hemangioblast development in the AGM region of mouse embryos. Based on Cre/loxP system, the Tie2CrePten(loxp/loxp) and Tie2CrePten(loxp/wt) mouse embryos were obtained. The genotype was identified by PCR. After treated with type I collagenase, the AGM region was dispersed into single-cell suspension, and then was cultured in blast colony-forming cell (BL-CFC) media. The number of BL-CFC was counted 4 or 5 days later. The hematopoietic capacity of BL-CFC was detected in methylcellulose culture system and the endothelial potential was assessed by tube-like structure formation on Matrigel. The results showed that the number of BL-CFC in AGM region of Tie2CrePten(loxp/loxp) mouse embryo decreased as compared with Tie2CrePten(loxp/wt) embryo. Whereas the hematopoietic capacity of mutant BL-CFC was enhanced, the endothelial potential, as evaluated by tube-like structure formation in vitro, was significantly reduced. It is concluded that the endothelial PTEN is capable of exerting regulatory functions on both the numbers and the dual potential of hemangioblast in mouse AGM region.

Increased expression of annexin A3 is a mechanism of platinum resistance in ovarian cancer.

Resistance to platinum drugs has emerged as a major obstacle in the treatment of ovarian cancers. Through proteomic analysis, we have found that the expression of annexin A3, a member of the Ca(2+) and phospholipid-binding annexin family, is significantly increased in platinum-resistant ovarian cell lines. Anti-annexin A3 immunostaining indicated that cancers from platinum-resistant patients also possess higher levels of annexin A3 than those from platinum-sensitive patients. Although expression of annexin A3 made susceptible ovarian cancer cells more resistant to platinum, expression of antisense annexin A3 downregulated its expression and rendered the resistant cells more sensitive to platinum. In athymic mice, the growth of tumors from inoculated SKOV3 cells was inhibited by the administration of platinum, whereas tumors from annexin A3-expressing SKOV3/Ann were resistant to platinum treatment. Interestingly, the intracellular platinum concentration and platinum-DNA binding are significantly lower in annexin A3-overexpressing cells than those in parental cells. The lower cisplatin concentration was also accompanied by reduced induction of p53, which could be restored by downregulation of annexin A3. These results indicate that increased expression of annexin A3 is a mechanism of platinum resistance in ovarian cancer. It seems to act by preventing uptake or accumulation of platinum in cells. Therefore, it is conceivable that annexin A3 could be a target for therapeutic intervention and may also serve as a biomarker for drug resistance in ovarian cancer patients.

A protocol for isolation and culture of mesenchymal stem cells from mouse compact bone.

Unlike humans, mouse bone marrow-derived mesenchymal stem cells (MSCs) cannot be easily harvested by adherence to plastic owing to the contamination of cultures by hematopoietic cells. The design of the protocol described here is based on the phenomenon that compact bones abound in MSCs and hematopoietic cells exist in the marrow cavities and the inner interfaces of the bones. The procedure includes flushing bone marrow out of the long bones, digesting the bone chips with collagenase type II, deprivation of the released cells and culturing the digested bone fragments, out of which fibroblast-like cells migrate and grow in the defined medium. The entire technique requires 5 d before the adherent cells are readily passaged. Further identification assays confirm that these cells are MSCs. We provide an easy and reproducible method to harvest mouse MSCs that does not require depletion of hematopoietic cells by sorting or immunomagnetic techniques.

Transplanted mesenchymal stem cells can inhibit the three developmental stages of murine acute graft-versus-host disease.

BACKGROUND: Recent data have demonstrated that mesenchymal stem cells (MSCs) have potent immune regulation capacity in vitro, enhancing their therapeutic appeal for their utilisation in the management of acute graft-versus-host disease (aGvHD). However, their immunoregulatory activity in vivo is largely unknown. MATERIALS AND METHODS: Using murine compact bone-derived MSCs in an aGvHD model, the phenotypic status of splenocytes of aGvHD and aGvHD+MSC groups of mice were examined by flow cytometry. RESULTS: MSC infusion decreased the expression of MHC-II and CD69 molecules on splenic CD11b+ cells of aGvHD mice, which resulted in decreased maturation of antigen-presenting cells. Moreover, the down-regulated ratio of CD3+CD69+ to CD3+ cells, leading to restrained early activation and effector T-cell formation, resulted in the enhancement of the absolute and relative number of splenic CD3+ cells by MSCs co-transfer. CONCLUSION: This study demonstrated that MSCs can inhibit the three developmental stages of aGvHD.