Disease-associated mutations in topoisomerase IIß result in defective NK cells.

BACKGROUND: Hoffman syndrome is a syndromic, inborn error of immunity due to autosomal-dominant mutations in TOP2B, an essential gene required to alleviate topological stress during DNA replication and gene transcription. Although mutations identified in patients lead to a block in B-cell development and the absence of circulating B cells, an effect on natural killer (NK) cells was not previously examined. OBJECTIVE: We sought to determine whether disease-associated mutations in TOP2B impact NK-cell development and function. METHODS: Using a knockin murine model and patient-derived induced pluripotent stem cells (iPSCs), we investigated NK-cell development in mouse bone marrow and spleen, and performed immunophenotyping by flow cytometry, gene expression, and functional assessment of cytotoxic activity in murine NK cells, and human IPSC-derived NK cells. RESULTS: Mature NK cells were reduced in the periphery of TOP2B knockin mice consistent with patient reports, with reduced cytotoxicity toward target cell lines. IPSCs were successfully derived from patients with Hoffman syndrome, but under optimal conditions showed reduced cytotoxicity compared with iPSC-derived NK cells from healthy controls. CONCLUSIONS: Hoffman syndrome-associated mutations in TOP2B impact NK-cell development and function in murine and human models.

Pluripotent stem cell-derived NK cells with high-affinity noncleavable CD16a mediate improved antitumor activity.

Antibody-dependent cellular cytotoxicity (ADCC) is a key effector mechanism of natural killer (NK) cells that is mediated by therapeutic monoclonal antibodies (mAbs). This process is facilitated by the Fc receptor CD16a on human NK cells. CD16a appears to be the only activating receptor on NK cells that is cleaved by the metalloprotease a disintegrin and metalloproteinase-17 upon stimulation. We previously demonstrated that a point mutation of CD16a prevents this activation-induced surface cleavage. This noncleavable CD16a variant is now further modified to include the high-affinity noncleavable variant of CD16a (hnCD16) and was engineered into human induced pluripotent stem cells (iPSCs) to create a renewable source for human induced pluripotent stem cell-derived NK (hnCD16-iNK) cells. Compared with unmodified iNK cells and peripheral blood-derived NK (PB-NK) cells, hnCD16-iNK cells proved to be highly resistant to activation-induced cleavage of CD16a. We found that hnCD16-iNK cells were functionally mature and exhibited enhanced ADCC against multiple tumor targets. In vivo xenograft studies using a human B-cell lymphoma demonstrated that treatment with hnCD16-iNK cells and anti-CD20 mAb led to significantly improved regression of B-cell lymphoma compared with treatment utilizing anti-CD20 mAb with PB-NK cells or unmodified iNK cells. hnCD16-iNK cells, combined with anti-HER2 mAb, also mediated improved survival in an ovarian cancer xenograft model. Together, these findings show that hnCD16-iNK cells combined with mAbs are highly effective against hematologic malignancies and solid tumors that are typically resistant to NK cell-mediated killing, demonstrating the feasibility of producing a standardized off-the-shelf engineered NK cell therapy with improved ADCC properties to treat malignancies that are otherwise refractory.

Human induced pluripotent stem cell-derived macrophages ameliorate liver fibrosis.

With an increasing number of patients with degenerative hepatic diseases, such as liver fibrosis, and a limited supply of donor organs, there is an unmet need for therapies that can repair or regenerate damaged liver tissue. Treatment with macrophages that are capable of phagocytosis and anti-inflammatory activities such as secretion of matrix metalloproteinases (MMPs) provide an attractive cellular therapy approach. Human induced pluripotent stem cells (iPSCs) are capable of efficiently generating a large-scale, homogenous population of human macrophages using fully defined feeder- and serum-free differentiation protocol. Human iPSC-macrophages exhibit classical surface cell markers and phagocytic activity similar to peripheral blood-derived macrophages. Moreover, gene and cytokine expression analysis reveal that these macrophages can be efficiently polarized to pro-inflammatory M1 or anti-inflammatory M2 phenotypes in presence of LPS + IFN-γ and IL-4 + IL-13, respectively. M1 macrophages express high level of CD80, TNF-α, and IL-6 while M2 macrophages show elevated expression of CD206, CCL17, and CCL22. Here, we demonstrate that treatment of liver fibrosis with both human iPSC-derived macrophage populations and especially M2 subtype significantly reduces fibrogenic gene expression and disease associated histological markers including Sirius Red, αSMA and desmin in immunodeficient Rag2-/- γc-/- mice model, making this approach a promising cell-based avenue to ameliorate fibrosis.

Lineage-specific differentiation of osteogenic progenitors from pluripotent stem cells reveals the FGF1-RUNX2 association in neural crest-derived osteoprogenitors.

Human pluripotent stem cells (hPSCs) can provide a platform to model bone organogenesis and disease. To reflect the developmental process of the human skeleton, hPSC differentiation methods should include osteogenic progenitors (OPs) arising from three distinct embryonic lineages: the paraxial mesoderm, lateral plate mesoderm, and neural crest. Although OP differentiation protocols have been developed, the lineage from which they are derived, as well as characterization of their genetic and molecular differences, has not been well reported. Therefore, to generate lineage-specific OPs from human embryonic stem cells and human induced pluripotent stem cells, we employed stepwise differentiation of paraxial mesoderm-like cells, lateral plate mesoderm-like cells, and neural crest-like cells toward their respective OP subpopulation. Successful differentiation, confirmed through gene expression and in vivo assays, permitted the identification of transcriptomic signatures of all three cell populations. We also report, for the first time, high FGF1 levels in neural crest-derived OPs-a notable finding given the critical role of fibroblast growth factors (FGFs) in osteogenesis and mineral homeostasis. Our results indicate that FGF1 influences RUNX2 levels, with concomitant changes in ERK1/2 signaling. Overall, our study further validates hPSCs' power to model bone development and disease and reveals new, potentially important pathways influencing these processes.

Aryl hydrocarbon receptor inhibition promotes hematolymphoid development from human pluripotent stem cells.

The aryl hydrocarbon receptor (AHR) plays an important physiological role in hematopoiesis. AHR is highly expressed in hematopoietic stem and progenitor cells (HSPCs) and inhibition of AHR results in a marked expansion of human umbilical cord blood-derived HSPCs following cytokine stimulation. It is unknown whether AHR also contributes earlier in human hematopoietic development. To model hematopoiesis, human embryonic stem cells (hESCs) were allowed to differentiate in defined conditions in the presence of the AHR antagonist StemReginin-1 (SR-1) or the AHR agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). We demonstrate a significant increase in CD34+CD31+ hematoendothelial cells in SR-1-treated hESCs, as well as a twofold expansion of CD34+CD45+ hematopoietic progenitor cells. Hematopoietic progenitor cells were also significantly increased by SR-1 as quantified by standard hematopoietic colony-forming assays. Using a clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9)-engineered hESC-RUNX1c-tdTomato reporter cell line with AHR deletion, we further demonstrate a marked enhancement of hematopoietic differentiation relative to wild-type hESCs. We also evaluated whether AHR antagonism could promote innate lymphoid cell differentiation from hESCs. SR-1 increased conventional natural killer (cNK) cell differentiation, whereas TCDD treatment blocked cNK development and supported group 3 innate lymphoid cell (ILC3) differentiation. Collectively, these results demonstrate that AHR regulates early human hematolymphoid cell development and may be targeted to enhance production of specific cell populations derived from human pluripotent stem cells.

Concise Review: Human Pluripotent Stem Cells to Produce Cell-Based Cancer Immunotherapy.

Human pluripotent stem cells (PSCs) provide a promising resource to produce immune cells for adoptive cellular immunotherapy to better treat and potentially cure otherwise lethal cancers. Cytotoxic T cells and natural killer (NK) cells can now be routinely produced from human PSCs. These PSC-derived lymphocytes have phenotype and function similar to primary lymphocytes isolated from peripheral blood. PSC-derived T and NK cells have advantages compared with primary immune cells, as they can be precisely engineered to introduce improved anti-tumor activity and produced in essentially unlimited numbers. Stem Cells 2018;36:134-145.

Single Cell Resolution of Human Hematoendothelial Cells Defines Transcriptional Signatures of Hemogenic Endothelium.

Endothelial-to-hematopoietic transition (EHT) is an important stage in definitive hematopoietic development. However, the genetic mechanisms underlying human EHT remain poorly characterized. We performed single cell RNA-seq using 55 hemogenic endothelial cells (HECs: CD31+ CD144+ CD41- CD43- CD45- CD73- RUNX1c+ ), 47 vascular endothelial cells without hematopoietic potential (non-HE: CD31+ CD144+ CD41- CD43- CD45- CD73- RUNX1c- ), and 35 hematopoietic progenitor cells (HPCs: CD34+ CD43+ RUNX1c+ ) derived from human embryonic stem cells (hESCs). HE and HP were enriched in genes implicated in hemogenic endothelial transcriptional networks, such as ERG, GATA2, and FLI. We found transcriptional overlap between individual HECs and HPCs; however, these populations were distinct from non-HE. Further analysis revealed novel biomarkers for human HEC/HPCs, including TIMP3, ESAM, RHOJ, and DLL4. Collectively, we demonstrate that hESC-derived HE and HP share a common developmental pathway, while non-HE are more heterogeneous and transcriptionally distinct. Our findings provide a novel strategy to test new genetic targets and optimize the production of definitive hematopoietic cells from human pluripotent stem cells. Stem Cells 2018;36:206-217.

Advances in the role of the aryl hydrocarbon receptor to regulate early hematopoietic development.

PURPOSE OF REVIEW: We summarize current advances to define the role the aryl hydrocarbon receptor (AHR) plays in mammalian hematopoiesis. We emphasize approaches to modulate AHR throughout human hematopoietic development in vitro to support the production of clinically relevant blood products suitable for patient care. RECENT FINDINGS: Initial data demonstrate that both pharmacologic AHR inhibition and genetic deletion from human pluripotent stem cells provide useful strategies to enhance the yield of hematopoietic stem and progenitor cells. AHR hyperactivation following the induction of CD34 megakaryocyte-erythroid progenitors skews developed toward erythroid lineages, whereas AHR inhibition supports platelet production. At the level of lymphoid specification, AHR inhibition enhances the proliferation and differentiation of functional human natural killer cells, whereas hyperactivation leads to production of Group 3 innate lymphoid cells and provides a novel platform for studying human innate lymphoid cell development. SUMMARY: Modulation of AHR in human hematopoietic cells in vitro is a promising tool to mediate development of terminal hematopoietic cell populations with significant clinical implications to generate cells suitable for antitumor immunotherapy and bone marrow transplantation.

Fibrinogen Induces RUNX2 Activity and Osteogenic Development from Human Pluripotent Stem Cells.

Pluripotent stem cells, both human embryonic stem cells (hESC) and induced pluripotent stem cells (iPSC), provide an important resource to produce specialized cells such as osteogenic cells for therapeutic applications such as repair or replacement of injured, diseased or damaged bone. hESCs and iPSCs can also be used to better define basic cellular and genetic mechanisms that regulate the earliest stages of human bone development. However, current strategies to mediate osteogenic differentiation of hESC and iPSC are typically limited by the use of xenogeneic components such as fetal bovine serum (FBS) that make defining specific agents that mediate human osteogenesis difficult. Runt-related transcription factor 2 (RUNX2) is a key regulator required for osteogenic differentiation. Here, we used a RUNX2-YFP reporter system to characterize the novel ability of fibrinogen to mediate human osteogenic development from hESC and iPSC in defined (serum-free) conditions. These studies demonstrate that fibrinogen mediates significant osteo-induction potential. Specifically, fibrinogen binds to the surface integrin (α9ß1) to mediate RUNX2 gene expression through the SMAD1/5/8 signaling pathway. Additional studies characterize the fibrinogen-induced hESC/iPSC-derived osteogenic cells to demonstrate these osteogenic cells retain the capacity to express typical mature osteoblastic markers. Together, these studies define a novel fibrinogen-α9ß1-SMAD1/5/8-RUNX2 signaling axis can efficiently induce osteogenic differentiation from hESCs and iPSCs. Stem Cells 2016;34:2079-2089.

Induced Pluripotent Stem Cell-Derived Natural Killer Cells for Treatment of Ovarian Cancer.

Natural killer (NK) cells can provide effective immunotherapy for ovarian cancer. Here, we evaluated the ability of NK cells isolated from peripheral blood (PB) and NK cells derived from induced pluripotent stem cell (iPSC) to mediate killing of ovarian cancer cells in a mouse xenograft model. A mouse xenograft model was used to evaluate the intraperitoneal delivery of three different NK cell populations: iPSC-derived NK cells, PB-NK cells that had been activated and expanded in long-term culture, and overnight activated PB-NK cells that were isolated through CD3/CD19 depletion of PB B and T cells. Bioluminescent imaging was used to monitor tumor burden of luciferase expressing tumor lines. Tumors were allowed to establish prior to administering NK cells via intraperitoneal injection. These studies demonstrate a single dose of any of the three NK cell populations significantly reduced tumor burden. When mice were given three doses of either iPSC-NK cells or expanded PB-NK cells, the median survival improved from 73 days in mice untreated to 98 and 97 days for treated mice, respectively. From these studies, we conclude iPSC-derived NK cells mediate antiovarian cancer killing at least as well as PB-NK cells, making these cells a viable resource for immunotherapy for ovarian cancer. Due to their ability to be easily differentiated into NK cells and their long-term expansion potential, iPSCs can be used to produce large numbers of well-defined NK cells that can be banked and used to treat a large number of patients including treatment with multiple doses if necessary.

Silent IL2RG Gene Editing in Human Pluripotent Stem Cells.

Many applications of pluripotent stem cells (PSCs) require efficient editing of silent chromosomal genes. Here, we show that a major limitation in isolating edited clones is silencing of the selectable marker cassette after homologous recombination and that this can be overcome by using a ubiquitous chromatin opening element (UCOE) promoter-driven transgene. We use this strategy to edit the silent IL2RG locus in human PSCs with a recombinant adeno-associated virus (rAAV)-targeting vector in the absence of potentially genotoxic, site-specific nucleases and show that IL2RG is required for natural killer and T-cell differentiation of human PSCs. Insertion of an active UCOE promoter into a silent locus altered the histone modification and cytosine methylation pattern of surrounding chromatin, but these changes resolved when the UCOE promoter was removed. This same approach could be used to correct IL2RG mutations in X-linked severe combined immunodeficiency patient-derived induced PSCs (iPSCs), to prevent graft versus host disease in regenerative medicine applications, or to edit other silent genes.

The RUNX1 +24 enhancer and P1 promoter identify a unique subpopulation of hematopoietic progenitor cells derived from human pluripotent stem cells.

Derivation of hematopoietic stem cells (HSCs) from human pluripotent stem cells remains a key goal for the fields of developmental biology and regenerative medicine. Here, we use a novel genetic reporter system to prospectively identify and isolate early hematopoietic cells derived from human embryonic stem cells (hESCs) and human induced pluripotent cells (iPSCs). Cloning the human RUNX1c P1 promoter and +24 enhancer to drive expression of tdTomato (tdTom) in hESCs and iPSCs, we demonstrate that tdTom expression faithfully enriches for RUNX1c-expressing hematopoietic progenitor cells. Time-lapse microscopy demonstrated the tdTom(+) hematopoietic cells to emerge from adherent cells. Furthermore, inhibition of primitive hematopoiesis by blocking Activin/Nodal signaling promoted the expansion and/or survival of the tdTom(+) population. Notably, RUNX1c/tdTom(+) cells represent only a limited subpopulation of the CD34(+) CD45(+) and CD34(+) CD43(+) cells with a unique genetic signature. Using gene array analysis, we find significantly lower expression of Let-7 and mir181a microRNAs in the RUNX1c/tdTom(+) cell population. These phenotypic and genetic analyses comparing the RUNX1c/tdTom(+) population to CD34(+) CD45(+) umbilical cord blood and fetal liver demonstrate several key differences that likely impact the development of HSCs capable of long-term multilineage engraftment from hESCs and iPSCs.

Tu-mor(e) blood cells from human pluripotent stem cells.

Studies by Amabile et al reported in this issue of Blood use a novel strategy of teratoma formation from human induced pluripotent stem cells (iPSCs) to isolate hematopoietic stem/progenitor cells (HSPCs) capable of in vivo engraftment and producing functional lymphocytes.(1)

RUNX1a enhances hematopoietic lineage commitment from human embryonic stem cells and inducible pluripotent stem cells.

Advancements in human pluripotent stem cell (hPSC) research have potential to revolutionize therapeutic transplantation. It has been demonstrated that transcription factors may play key roles in regulating maintenance, expansion, and differentiation of hPSCs. In addition to its regulatory functions in hematopoiesis and blood-related disorders, the transcription factor RUNX1 is also required for the formation of definitive blood stem cells. In this study, we demonstrated that expression of endogenous RUNX1a, an isoform of RUNX1, parallels with lineage commitment and hematopoietic emergence from hPSCs, including both human embryonic stem cells and inducible pluripotent stem cells. In a defined hematopoietic differentiation system, ectopic expression of RUNX1a facilitates emergence of hematopoietic progenitor cells (HPCs) and positively regulates expression of mesoderm and hematopoietic differentiation-related factors, including Brachyury, KDR, SCL, GATA2, and PU.1. HPCs derived from RUNX1a hPSCs show enhanced expansion ability, and the ex vivo-expanded cells are capable of differentiating into multiple lineages. Expression of RUNX1a in embryoid bodies (EBs) promotes definitive hematopoiesis that generates erythrocytes with ß-globin production. Moreover, HPCs generated from RUNX1a EBs possess ≥9-week repopulation ability and show multilineage hematopoietic reconstitution in vivo. Together, our results suggest that RUNX1a facilitates the process of producing therapeutic HPCs from hPSCs.

Expression of chimeric receptor CD4ζ by natural killer cells derived from human pluripotent stem cells improves in vitro activity but does not enhance suppression of HIV infection in vivo.

Cell-based immunotherapy has been gaining interest as an improved means to treat human immunodeficiency virus (HIV)/AIDS. Human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) could become a potential resource. Our previous studies have shown hESC and iPSC-derived natural killer (NK) cells can inhibit HIV-infected targets in vitro. Here, we advance those studies by expressing a HIV chimeric receptor combining the extracellular portion of CD4 to the CD3ζ intracellular signaling chain. We hypothesized that expression of this CD4ζ receptor would more efficiently direct hESC- and iPSC-derived NK cells to target HIV-infected cells. In vitro studies showed the CD4ζ expressing hESC- and iPSC-NK cells inhibited HIV replication in CD4+ T-cells more efficiently than their unmodified counterparts. We then evaluated CD4ζ expressing hESC (CD4ζ-hESC)- and iPSC-NK cells in vivo anti-HIV activity using a humanized mouse model. We demonstrated significant suppression of HIV replication in mice treated with both CD4ζ-modified and -unmodified hESC-/iPSC-NK cells compared with control mice. However, we did not observe significantly increased efficacy of CD4ζ expression in suppression of HIV infection. These studies indicate that hESC/iPSC-based immunotherapy can be used as a unique resource to target HIV/AIDS.

Pluripotent stem cell applications for regenerative medicine.

PURPOSE OF REVIEW: In this review, we summarize the current status of clinical trials using therapeutic cells produced from human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs). We also discuss combined cell and gene therapy via correction of defined mutations in human pluripotent stem cells and provide commentary on key obstacles facing widescale clinical adoption of pluripotent stem cell-based therapy. RECENT FINDINGS: Initial data suggest that hESC/hiPSC-derived cell products used for retinal repair and spinal cord injury are safe for human use. Early-stage studies for treatment of cardiac injury and diabetes are also in progress. However, there remain key concerns regarding the safety and efficacy of these cells that need to be addressed in additional well designed clinical trials. Advances using the clustered regulatory interspaced short palindromic repeats (CRISPR)/Cas9 gene-editing system offer an improved tool for more rapid and on-target gene correction of genetic diseases. Combined gene and cell therapy using human pluripotent stem cells may provide an additional curative approach for disabling or lethal genetic and degenerative diseases wherein there are currently limited therapeutic opportunities. SUMMARY: Human pluripotent stem cells are emerging as a promising tool to produce cells and tissues suitable for regenerative therapy for a variety of genetic and degenerative diseases.

Functional consequences of human induced pluripotent stem cell therapy: myocardial ATP turnover rate in the in vivo swine heart with postinfarction remodeling.

BACKGROUND: The use of cells derived from human induced pluripotent stem cells as cellular therapy for myocardial injury has yet to be examined in a large-animal model. METHODS AND RESULTS: Immunosuppressed Yorkshire pigs were assigned to 1 of 3 groups: A myocardial infarction group (MI group; distal left anterior descending coronary artery ligation and reperfusion; n=13); a cell-treatment group (MI with 4×10(6) vascular cells derived from human induced pluripotent stem cells administered via a fibrin patch; n=14); and a normal group (n=15). At 4 weeks, left ventricular structural and functional abnormalities were less pronounced in hearts in the cell-treated group than in MI hearts (P<0.05), and these improvements were accompanied by declines in scar size (10.4±1.6% versus 8.3±1.1%, MI versus cell-treatment group, P<0.05). The cell-treated group displayed a significant increase in vascular density and blood flow (0.83±0.11 and 1.05±0.13 mL·min(-1)·g(-1), MI versus cell-treatment group, P<0.05) in the periscar border zone (BZ), which was accompanied by improvements in systolic thickening fractions (infarct zone, -10±7% versus 5±5%; BZ, 7±4% versus 23±6%; P<0.05). Transplantation of vascular cells derived from human induced pluripotent stem cells stimulated c-kit(+) cell recruitment to BZ and the rate of bromodeoxyuridine incorporation in both c-kit(+) cells and cardiomyocytes (P<0.05). Using a magnetic resonance spectroscopic saturation transfer technique, we found that the rate of ATP hydrolysis in BZ of MI hearts was severely reduced, and the severity of this reduction was linearly related to the severity of the elevations of wall stresses (r=0.82, P<0.05). This decline in BZ ATP utilization was markedly attenuated in the cell-treatment group. CONCLUSIONS: Transplantation of vascular cells derived from human induced pluripotent stem cells mobilized endogenous progenitor cells into the BZ, attenuated regional wall stress, stimulated neovascularization, and improved BZ perfusion, which in turn resulted in marked increases in BZ contractile function and ATP turnover rate.

Bioenergetic and functional consequences of cellular therapy: activation of endogenous cardiovascular progenitor cells.

RATIONALE: The mechanism by which endogenous progenitor cells contribute to functional and beneficial effects in stem cell therapy remains unknown. OBJECTIVE: Utilizing a novel (31)P magnetic resonance spectroscopy-2-dimensional chemical shift imaging method, this study examined the heterogeneity and bioenergetic consequences of postinfarction left ventricular (LV) remodeling and the mechanisms of endogenous progenitor cell contribution to the cellular therapy. METHODS AND RESULTS: Human embryonic stem cell-derived vascular cells (hESC-VCs) that stably express green fluorescent protein and firefly luciferase (GFP(+)/Luc(+)) were used for the transplantation. hESC-VCs may release various cytokines to promote angiogenesis, prosurvival, and antiapoptotic effects. Both in vitro and in vivo experiments demonstrated that hESC-VCs effectively inhibit myocyte apoptosis. In the mouse model, a fibrin patch-based cell delivery resulted in a significantly better cell engraftment rate that was accompanied by a better ejection fraction. In the swine model of ischemia-reperfusion, the patch-enhanced delivery of hESC-VCs resulted in alleviation of abnormalities including border zone myocardial perfusion, contractile dysfunction, and LV wall stress. These results were also accompanied by a pronounced recruitment of endogenous c-kit(+) cells to the injury site. These improvements were directly associated with a remarkable improvement in myocardial energetics, as measured by a novel in vivo (31)P magnetic resonance spectroscopy-2-dimensional chemical shift imaging technology. CONCLUSIONS: The findings of this study demonstrate that a severely abnormal heterogeneity of myocardial bioenergetics in hearts with postinfarction LV remodeling can be alleviated by the hESC-VCs therapy. These findings suggest an important therapeutic target of peri-scar border zone and a promising therapeutic potential for using hESC-VCs together with the fibrin patch-based delivery system.

Hemangiosarcoma Cells Promote Conserved Host-derived Hematopoietic Expansion.

Hemangiosarcoma and angiosarcoma are soft-tissue sarcomas of blood vessel-forming cells in dogs and humans, respectively. These vasoformative sarcomas are aggressive and highly metastatic, with disorganized, irregular blood-filled vascular spaces. Our objective was to define molecular programs which support the niche that enables progression of canine hemangiosarcoma and human angiosarcoma. Dog-in-mouse hemangiosarcoma xenografts recapitulated the vasoformative and highly angiogenic morphology and molecular characteristics of primary tumors. Blood vessels in the tumors were complex and disorganized, and they were lined by both donor and host cells. In a series of xenografts, we observed that the transplanted hemangiosarcoma cells created exuberant myeloid hyperplasia and gave rise to lymphoproliferative tumors of mouse origin. Our functional analyses indicate that hemangiosarcoma cells generate a microenvironment that supports expansion and differentiation of hematopoietic progenitor populations. Furthermore, gene expression profiling data revealed hemangiosarcoma cells expressed a repertoire of hematopoietic cytokines capable of regulating the surrounding stromal cells. We conclude that canine hemangiosarcomas, and possibly human angiosarcomas, maintain molecular properties that provide hematopoietic support and facilitate stromal reactions, suggesting their potential involvement in promoting the growth of hematopoietic tumors. SIGNIFICANCE: We demonstrate that hemangiosarcomas regulate molecular programs supporting hematopoietic expansion and differentiation, providing insights into their potential roles in creating a permissive stromal-immune environment for tumor progression.

Concise review: Cord blood banking, transplantation and induced pluripotent stem cell: success and opportunities.

Hematopoietic cell transplantation (HCT) has become a standard practice to treat a number of malignant and nonmalignant hematologic diseases. Bone marrow, mobilized peripheral blood, and umbilical cord blood can all serve as primary sources of cells for HCT. The number of cord blood units currently stored is large, although it represents only a fraction of potential collections. With much of the collection being sequestered in private banks for possible autologous use, there is a reason to expect that public banks may not be able to provide for the demand in coming years as use of cord blood for treatment of patients with diseases such as leukemia and lymphoma continues to increase. We suggest that a possible solution to encourage private banks to share their valuable units is to apply recent methodologies to generate induced pluripotent stem cells from cord cells and to optimize techniques to generate hematopoietic lineages from them. This strategy would allow us to take advantage of the units already collected under appropriate regulatory guidelines, to access a pristine cell that can be converted to a pluripotent cell at a much higher efficiency and in a shorter time period than other cells. The ability to potentially replenish a used cord unit with new cells, as well as extend the potential utility of cord blood for additional therapeutic applications, should allow banks to develop an appropriate business model for both private and public cord blood banks to flourish.