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Gene Defect Corrected in Human Stem Cells

New research outlines a path toward new therapies with induced pluripotent stem cells.

For the first time, researchers have fixed the gene defect in cells from patients with an inherited disease, and then transformed the tissue into stem cells with the potential to reverse their condition. While scientists haven’t yet tested the treatment in humans, the research could mark the beginning of a new age of curative treatments for many genetic disorders.

Correcting cells: Scientists corrected the genetic deficits in cells from patients with Fanconi anemia and then reprogrammed them into induced pluripotent stem cells. The cells can then be coaxed to differentiate into red blood cells. (Colonies of blood cells are shown at the bottom of the image.)

The proof of concept study, led by Juan Carlos Izpisua Belmonte at the Salk Institute for Biological Studies, in La Jolla, CA, focused on patients with a rare condition, Fanconi anemia, which causes skeletal problems and bone-marrow failure, and raises sufferers’ risk of cancer.

Researchers took skin cells from six patients and used a virus to deliver a functional copy of one of the faulty genes responsible for the condition. The method had previously been shown to correct the gene defect in mice.

Next, researchers used cell programming techniques that have emerged in the past two years to transform the cells into stem cells capable of growing into any tissue type–including the healthy blood cells needed to correct the patients’ inherited anemia. Known as induced pluripotent stem cell (iPS) reprogramming, this involves introducing four genes known to be active in the developing embryo, which in turn change the cells’ pattern of gene expression to one that resembles an embryonic cell rather than an adult one.

“Our work demonstrates that it is possible to combine gene and cell therapy using iPS technology to generate disease-free cells,” says Belmonte. The research was published online in the journal Natureon Sunday.

IPS cells are a particularly attractive medical tool for two key reasons. Unlike embryonic stem cells, iPS cells avoid the ethical controversy associated with harvesting human embryos. And because they come from the patient’s own body, they will not be rejected by the immune system.

To test the therapy, scientists would need to grow blood progenitor cells from the genetically corrected iPS cells, and then transplant them back into patients, generating a supply of healthy blood cells. Belmonte notes, however, that the iPS cells that his team generated in the course of the study were not suitable for clinical use.

“Serious concerns need addressing before attempting any clinical trial with iPS-derived cells; perhaps the most important is that of tumor formation,” says Belmonte. This is because the virally delivered genes used to reprogram the skin cells can remain embedded in the cell’s DNA even after reprogramming. These genes are thought to become active during the cell-differentiation process, considerably raising the long-term risk of cancer.

In recent weeks, however, scientists have published two new methods of making iPS cells that do not involve viruses and thus may overcome this problem.

Experts say that the research is an important proof of concept. “This is an exciting bit of science,” says Chris Mason, a professor of regenerative medicine at University College London, who was not directly involved in the research. “It’s likely to be the first of a slew of similar papers that may offer hope for conditions where today there is no real therapy, let alone a cure.”

So far, Belmonte’s approach is applicable only to diseases in which the genetic defect that underlies the disease has been identified. “But there are quite a few of these–and the number will increase,” says Mason. Blood disorders are likely to be the first targets for therapy because corrected cells can easily be transferred back to the patient via bone-marrow transplants.

Belmonte adds that in the future, the correction of more-complex genetic disorders might become possible, thereby significantly increasing the number of diseases that might be treated with altered iPS cells.

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