Editors' ChoiceStem Cells

Reprogramming Hematopoietic Stem Cells

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Science Translational Medicine  20 Feb 2013:
Vol. 5, Issue 173, pp. 173ec33
DOI: 10.1126/scitranslmed.3005924

Induced pluripotent stem cells (iPSCs) are adult cells that have been genetically reprogrammed to an embryonic stem cell (ESC)–like state by being forced to express genes such as Oct4, Sox2, c-Myc, and Klf4. iPSCs have been made from skin cells, immune cells, and other stem cells, such as mesenchymal stem cells and mobilized CD34+ hematopoietic stem cells (HSCs). However, iPSCs have not been made from nonmobilized CD34+ HSCs in the peripheral blood until now.

Merling et al. derived iPSCs from a small volume of fresh or cryopreserved peripheral blood by reprogramming with an excisable loxP-flanked polycistronic lentiviral or nonintegrating Sendai viral vector. The loxP-flanked lentiviral vector resulted in 1 to 10 iPSC colonies from 20 mL of blood that were almost completely (>95%) reprogrammed. The Sendai viral vector gave variable colony yields (6 to >500) that were variably reprogrammed (10 to 80%). These iPSCs were capable of differentiating into all three germ layers in vitro and in vivo in teratoma assays. After excision of the loxP vectors by use of a transiently expressed Cre recombinase, the iPSCs retained the pluripotency markers, capacity for three germ layer formations, and their sample identity and origin. They also exhibited a normal karyotype and similar DNA methylation profiles to reference human ESC lines. Importantly, Merling and colleagues found that these iPSCs were not derived from lymphocytes or monocytes in the blood because they do not have the characteristic markers of these cells.

The authors described an efficient method of generating transgene-free iPSCs from nonmobilized CD34+ HSCs in peripheral human blood using two different viral vector systems. HSCs are attractive targets for iPSC reprogramming because they may maintain greater genomic stability than that of mature cells and may be predisposed to redifferentiate to HSCs via epigenetic memory, which would be a useful alternative source of stem cells for treating leukemias and lymphomas. Furthermore, the small number of CD34+ HSCs needed to use this method is an advantage over other methods that require mobilization to obtain a larger number of CD34+ HSCs.

R. Merling et al., Transgene-free iPSCs generated from small volume peripheral blood non-mobilized CD34+ cells. Blood, published online 5 February 2013 (10.1182/blood-2012-03-420273). [Abstract]

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