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DURHAM, N.C.—Stem cells attract a significant amount of interest in the industry for their potential in a variety of fields, especially regenerative medicine. The current leading method for reprogramming induced pluripotent stem cells (iPSCs) consists of combining iPSCs with mouse or human stromal cells during differentiation, but this approach runs the risk of foreign DNA being introduced to the reprogrammed cells.
Researchers from the Department of Medicine and Institute for Human Genetics at University of California, San Francisco, however, have developed a new method that stands to offer purer, safer stem cells that are patient- specific and lack the risk of rejection and damage by alien DNA. The work was led by Dr. Yuet Wai Kan and Dr. Lin Ye.
The new study focused on CD34+ cells, a type of blood stem cell that has been linked to proliferation. The issue with this class of cells is that in order to collect enough of them from a patient to produce blood requires a large amount of blood to be collected.
This new method makes use of Sendai viral vectors to generate iPSCs "from adult mobilized CD34+ and peripheral blood mononuclear cells (MNC)," said Kan. "Sendai virus is an RNA virus that carries no risk of altering the host genome, so is considered an efficient solution for generating safe iPSC."
"Just 2 milliliters of blood yielded iPS cells from which hematopoietic stem and progenitor cells could be generated. These cells could contain up to 40 percent CD34+ cells, of which approximately 25 percent were the type of precursors that could be differentiated into mature blood cells. These interesting findings reveal a protocol for the generation iPSCs using a readily available cell type," said Ye. "We also found that MNCs can be efficiently reprogrammed into iPSCs as readily as CD34+ cells. Furthermore, these MNCs derived iPSCs can be terminally differentiated into mature blood cells."
An MNC is any blood cell that features a round nucleus, and can include lymphocytes, monocytes or macrophages.
"Currently, there are only two no-integrating methods that have been used to generate iPSCs: the EBNA1/OriP plasmid and Sendai viral vector. The EBNA1/OriP plasmid method requires a large amount of blood to prepare enough MNCs (1–2X106) for reprogramming. Sendai viral vectors need many fewer blood cells (2–3X104)," Ye explains. "In this study, MNCs prepared from 2 ml of blood are more than enough to generate functional iPSCs. In addition, with the EBNA1/OriP plasmid DNA vectors, as they are introduced into the nucleus, occasional integration into the host genome cannot be ruled out. In contrast, Sendai viral vectors-mediated reprogramming is efficient, and as an RNA virus that only replicates in cytoplasm, it does not enter the nucleus and therefore will not integrate into the host genome."
Sendai viral vectors generate iPSCs through the over-expression of four transcription factors (OCT4, SOX2, KLF4 and cMYC) in somatic cells and inducing somatic cell reprogramming, says Ye. When Sendai viral vectors are manipulated to carry the four transcription factors, they can infect somatic cells to induce reprogramming. And since the Sendai viral genome "has been altered to carry temperature sensitive mutations, the virus could be removed when cells divide," he adds.
"The development of iPSC technology opens up a new avenue for the field of personalized regenerative medicine since it is possible to generate patient-specific pluripotent stem cells for modeling disease and for developing cell therapies," says Ye.
He notes that their laboratory has begun examining the possibility of using this technology to treat sickle cell anemia and thalassemia, two blood disorders in which the body produces abnormal red blood cells or hemoglobin. In sickle cell anemia, a mutation in the hemoglobin gene causes the body to produce red blood cells shaped like a sickle, rather than a disc, which can hamper blood flow. In thalassemia, an abnormal form of hemoglobin is produced that leads to damage and destruction of red blood cells, resulting in anemia.
"Our laboratory has been interested in studying sickle cell anemia and thalassemia for some years and is now exploring the feasibility of using the iPSC technology to treat these diseases," says Ye. "The proposed approach is to generate iPSCs from these patients, correct the b-globin-gene mutations and differentiate the iPSCs to hematopoietic cells for autotransplantation. We will conduct gene correction in iPSCs as well as in-vivo study to find out whether the hematopoietic progenitor cells differentiated from iPSCs could be engrafted or not."
The results of this study were published in STEM CELLS Translational Medicine. The paper, "Blood cell-derived induced pluripotent stem cells free of reprogramming factors generated by Sendai viral vectors," first appeared online July 11.