Reprogrammed Adult Cells Treat Sickle-Cell Anemia in Mice

Mice with a human sickle-cell anemia disease trait have been effectively treated in a process that begins by directly reprogramming their own cells to an embryonic-stem-cell-like state, without the use of eggs. This is the first proof-of-principle of therapeutic application in mice of directly reprogrammed induced pluripotent stem (IPS) cells, which recently have been derived in mice as well as humans.

The research, reported in the journal Science Express online on December 6, 2007, was performed out in the laboratory of the Whitehead Institute for Biomedical research (Cambridge, MA, USA) member Dr. Rudolf Jaenisch. The IPS cells were derived using modifications of the approach originally discovered in 2006 by the Shinya Yamanaka laboratory at Kyoto University (Japan). "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,” stated Dr. Jaenisch.

The scientists evaluated a therapeutic application of IPS cells with the sickle-cell anemia model mouse developed by the laboratory of Dr. Tim Townes, from the University of Alabama at Birmingham (USA). Sickle-cell anemia is a disease of the blood marrow caused by a defect in a single gene. The mouse model had been designed to include relevant human genes involved in blood production, including the defective version of that gene.

To create the IPS cells, the scientists began with cells from the skin of the diseased mice, explained lead investigator Dr. Jacob Hanna, a postdoctoral researcher in the Jaenisch lab. These cells were modified by a standard lab technique employing retroviruses engineered 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 chosen based on their morphology and then confirmed 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 evaluated with traditional analyses employed for human patients. The analyses demonstrated 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,” noted Dr. Jaenisch.

While IPS cells offer enormous promise for regenerative medicine, scientists cautioned that key challenges must be overcome before medical applications can be considered. First among these is to devise 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,” said Dr. Hanna. "Retroviruses can disrupt genes that should not be disrupted or activate genes that should not be activated.”

Potential options 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, according to Dr. Hanna.

In spite of the rapid progress being made with IPS cells, Dr. Jaenisch stressed that this field is very young, and that it is critical to continue thorough studies on embryonic stem cells as well. "We wouldn't have known anything about IPS cells if we hadn't worked with embryonic stem cells,” commented Dr. 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.”


Related Links:
Whitehead Institute for Biomedical Research
Kyoto University