To create the IPS cells, the scientists started with cells from the skin of the diseased mice, explains lead author Jacob Hanna, a postdoctoral researcher in the Jaenisch lab. These cells were modified by a standard lab technique employing retroviruses customized to insert genes into the cell’s DNA. The inserted genes were Oct4, Sox2, Lif4 and c-Myc, known to act together as master regulators to keep cells in an embryonic-stem-cell-like state. IPS cells were selected based on their morphology and then verified to express gene markers specific to embryonic stem cells. To decrease or eliminate possible cancer in the treated mice, the c-Myc gene was removed by genetic manipulation from the IPS cells.
Next, the researchers followed a well-established protocol for differentiating embryonic stem cells into precursors of bone marrow adult stem cells, which can be transplanted into mice to generate normal blood cells. The scientists created such precursor cells from the IPS cells, replaced the defective blood-production gene in the precursor cells with a normal gene, and injected the resulting cells back into the diseased mice.
The blood of treated mice was tested with standard analyses employed for human patients. The analyses showed that the disease was corrected, with measurements of blood and kidney functions similar to those of normal mice.
“This demonstrates that IPS cells have the same potential for therapy as embryonic stem cells, without the ethical and practical issues raised in creating embryonic stem cells,” says Jaenisch.
While IPS cells offer tremendous promise for regenerative medicine, scientists caution that major challenges must be overcome before medical applications can be considered. First among these is to find a better delivery system, since retroviruses bring other changes to the genome that are far too random to let loose in humans. “We need a delivery system that doesn’t integrate itself into the genome,” says Hanna. “Retroviruses can disrupt genes that should not be disrupted or activate genes that should not be activated.”
Potential alternatives include other forms of viruses, synthesized versions of the proteins created by the four master regulator genes that are modified to enter the cell nucleus, and small molecules, Hanna says.
Despite the rapid progress being made with IPS cells, Jaenisch emphasizes that this field is very young, and that it’s critical to continue full research on embryonic stem cells as well. “We wouldn’t have known anything about IPS cells if we hadn’t worked with embryonic stem cells,” says Jaenisch. “For the foreseeable future, there will remain a continued need for embryonic stem cells as the crucial assessment tool for measuring the therapeutic potential of IPS cells.”
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Written by Eric Bender
Rudolf Jaenisch’s primary affiliation is with Whitehead Institute of Biomedical Research, where his laboratory is located and all his research is conducted. He also is a professor of biology at Massachusetts Institute of Technology.
Whitehead Institute for Biomedical Research is a nonprofit, independent research and educational institution. Wholly independent in its governance, finances and research programs, Whitehead shares a close affiliation with Massachusetts Institute of Technology through its faculty, who hold joint MIT appointments.
Science Express online, December 6, 2007
“Treatment of Sickle-Cell Anemia Mouse Model with iPS Cells Generated from Autologous Skin”
Jacob Hanna(1), Marius Wernig(1), Styliani Markoulaki(1), Chiao-Wang Sun(2), Alexander Meissner(1), John P. Cassady(1,3), Caroline Beard(1), Tobias Brambrink(1), Li-Chen Wu(2), Tim M. Townes(2), Rudolf Jaenisch(1,3)
(1) The Whitehead Institute for Biomedical Research, Cambridge, Massachusetts 02142
(2) University of Alabama, Department of Biochemistry and Molecular Genetics, Schools of Medicine and Dentistry, Birmingham, Alabama 35294
(3) MIT Department of Biology, Cambridge, Massachusetts 02142 |
