After establishing a procedure to restore vision in people whose cornea has been damaged by physical or chemical injury by harvesting limbal stem cells from the healthy eye and transplanting them to the eye that has been damaged, the Hyderabad-based LV Prasad Eye Institute has moved to the next stage. The Institute has successfully converted skin cells of mice into induced pluripotent stem cells (iPS cells) that behave like embryonic stem cells.
The work on standardising the procedure of reprogramming skin cells into iPS cells started 6-7 months ago. It took 3-4 months to establish the protocol for converting skin cells into iPS cells.
“We were able to produce iPS cells 2-3 months ago,” said. Dr. D. Balasubramanian, Research Director of the Institute. They are now in the process of characterising the iPS cells in order to do the same with human skin cells.
“The protocol [of converting human skin cells to iPS cells] is the same, but human cells [when compared to mouse cells] behave differently,” he said. “The real test is when we try doing it using human cells.”
The central idea behind the work on iPS cells is to find a way to treat people with hereditary (genetic) diseases such as retinitis pigmentosa.
When the technique of producing human iPS cells is perfected, the skin cells of patients with retinal problems such as retinitis pigmentosa will be reprogrammed into iPS cells. The iPS cells will then be directed to become one of the types of retinal cells. Since the iPS cells will still have the defective gene, a normal gene will be synthesised and delivered into the iPS cells using a viral vector. The delivered normal gene is expected to cure the patient.
“The presence of defective genes [in addition to the normal gene] will not be a problem. We want to see if the normal gene overrides the effect of the defective gene,” he said.
There is hope that this procedure should work as research in 2007 at MIT, Cambridge, showed that a mouse suffering from sickle cell anaemia could be cured. In this case, the researchers first converted the skin cells of the mouse into iPS cells and then directed the iPS cells to become red blood cells. A normal gene was introduced into the iPS cells and these cells were then transplanted into the mouse. The mouse no longer suffered from anaemia.
The LV Prasad Eye Institute is working on introducing the normal gene through two routes. The first will use a viral vector, mostly a weak attenuated adeno virus that cannot cause any disease. The second alternative is the non-viral introduction.
“The efficiency of gene delivery into the host cell is much higher when a viral vector is used,” he said. “But we would prefer a non-viral vehicle.”
Having produced iPS cells using mice, work is on to deliver a normal gene into the iPS cells. “We should be able to convert human skin cells into iPS cells and introduce the cells with the normal gene in a year’s time,” he said. A patient with retinitis pigmentosa has already been chosen for the human study to treat the disease through cell therapy.
The biggest advantage of using iPS cells is that skin cells from the patient suffering from a disease are used for the cell therapy. Therefore, the question of rejection due to tissue mismatch does not arise.
The iPS cells have another advantage. As adult cells from the skin are used, the technique sidesteps the ethical problems that embryonic stem cell research faces. The technique of producing induced pluripotent stem cells by reprogramming adult skin cells was first done in 2006 by Dr. Shinya Yamanaka at Kyoto University.
Two Chinese teams in Beijing recently succeeded in producing mouse pups using iPS cells. Pups created by one of the teams were able to sire over 200 second-generation pups. More than 100 third-generation pups were also produced.
