Experimental Hematology 2013;41:663–664

INSIDE THIS ISSUE

Engraftable CD34D cells from human embryonic stem cells

See Kim et al.,

pages 749–758.

0301-472X/$ - see front

http://dx.doi.org/10.10

Until recently, protocols for generating CD34þ cells fromhuman embryonic stem cells (hESCs) have mostly reliedon either embryoid body formation or coculture on mousefeeder cell lines, both of which pose significant challengesfor their clinical utility. Moreover, the level of engraftmentachieved after transplantation of hESC-derived CD34þ

cells has remained low, raising concerns regarding theirinvivo potential. Based on a previous study from this group,Kimet al. hypothesized that a combination ofmesenchymalstromal cells and macrophages could recapitulate a bonemarrow microenvironment in vitro, inductive to the gener-

þ

ation of CD34 cells from hESCs. In this study, these two types of human cells were used as feeder cells to direct the differentiation of hESCs into CD34þ cells.The hESC-derived CD34þ cells generated in this manner express cell surface markers and genes associatedwith hematopoietic stem cells. Most importantly, they demonstrate high levels of engraftment and develop-ment of multilineage blood cells following transplantation into the pre-immune fetal sheep model. Tohumanize the differentiation protocol further, the authors cultured undifferentiated hESCs in a humanserum–based matrix to replace Matrigel, a mouse sarcoma tumor-derivative matrix. This study providesa clinically applicable methodology to generate engraftable CD34þ HSCs from hESCs and offers a frame-work for the design of more effective in vitro platforms for efficient differentiation of hESCs.

G6PD deficiency in a Zebrafish model

See Patrinostro et al.,

pages 697–710.

Glucose-6-phosphate dehydrogenase (G6PD) defi-ciency is the most common enzymopathy andgenetic mutation worldwide. The zebrafish hasbeen used in the modeling and discovery of newmechanisms involved with the development of thehematopoietic system, of which erythropoiesis isa foremost process. The zebrafish allows for unparal-leled insight and visualization into the early develop-mental events governing the blood system because ofits relatively rapid development that is external toanymaternal environment. In this article by Patrinos- tro et al., the authors use morpholino-based downre- gulation of g6pd expression to reduce G6pd protein and activity levels significantly in the developingzebrafish. G6pd-deficient animals developed erythrocytic hemolysis when exposed to several prooxidantcompounds, including naphthol, menthol, and primaquine, which typically lead to hemolytic crises inpersons with G6PD deficiency. Animals showed high levels of reactive oxygen species (ROS) and subse-quently developed significant red cell apoptosis, resulting in anemia and substantial cardiac edema, similarto the severe clinical presentation of G6PD-deficient individuals during a hemolytic crisis. This modelsystem will be useful in trying to elucidate the nature of ROS and its effects on the developing organism,as well as the biological response to increased ROS. It can also be used to study the effects of ROS-inducedhemolysis on the hematopoietic system. Finally, researchers can use this system to search for new and novelcompounds or drugs to reduce ROS and its deleterious effects.

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Myelodysplastic syndrome and the genomic instability hypothesis

See Zhou et al.,

pages 665–674.

Myelodysplastic syndrome (MDS) has received increased atten-tion from both the scientific community and the public, in partbecause the number of people who are most susceptible todeveloping this hematologic malignancy, in particular theelderly and cancer survivors, is expanding dramatically. There-fore, there is a pressing need to understand more about themolecular pathogenesis and underlying biology of this disease, so that unique or improved therapeutic strategies can be devel- oped. In this review, Zhou et al. highlight recent advances in our understanding of MDS, including theidentification and functional characterization of many novel gene perturbations that might be acquiredby patients with the disease. As a result, the authors discuss the emerging notion that MDS is a genomicinstability syndrome, possibly reflecting an underlying problem in DNA repair. They also summarizeseveral seminal studies on the maintenance of genomic integrity within hematopoietic stem cells,believed to be the cell of origin in MDS, and their differentiating progeny. In addition to raisingintriguing new questions, these studies provide rare insights into the response of hematopoietic stemcells to DNA damage. The review provides a balance between clinical findings and the appropriatemouse phenotypes, as well as from hematopoietic stem cell research with and without links to aging.The article is authored by specialists in all crucial areas under discussion and should be interestingreading for researchers in the field.

Efficient platelet production from human pluripotent stem cell–derived megakaryocytes usinga two-directional flow bioreactor

See Nakagawa et al.,

pages 742–748.

The underlying mechanisms of platelet biogen-esis from megakaryocytes remain elusive. Underconditions recapitulating platelet release basedon in vivo behavior of thrombopoiesis withinmouse bone marrow, shear stress induced byblood flow in capillary vessels of bone marrowappears to stimulate the adjacent megakaryo-cytes to promote platelet yield. Recently, a seriesof articles have reported the application of shearstress to in vitro thrombopoiesis using one direc- tional flow. In this study, Nakagawa et al. propose a novel bioreactor system to recapitulate the in vivo situation of platelet production. Theyderived megakaryocytes successfully from human pluripotent stem cells by applying in a three-dimensional bioreactor a one-directional flow and a second flow-mediated fixation of megakaryocytesin appropriate positions. The pressure flow held the megakaryocytes in the chambers of the bioreactor,and the main flow produced shear stress on the megakaryocytes’ surface. The authors concluded that theangle between the main flow direction and the megakaryocyte surface was one of the critical factors forefficient platelet production. In a 90-degree situation, platelet production seemed to be slightly betterthan in static culture; however, in a 60-degree situation, platelet production efficiency increased 3.6-fold compared with static cultures. This novel finding will definitively influence the future planningof ex vivo platelet production systems from human pluripotent stem cell–derived megakaryocytes fortransfusion medicine.