The stem cells, derived from human umbilical cord-blood and coaxed into an embryonic-like state, were grown without the conventional use of viruses, which can mutate genes and initiate cancers, researchers said.

This safer method of growing the cells paves the way for a stem cell bank of cord-blood derived iPSCs to advance regenerative medicine research, researchers added.
In a study published in the journal Circulation, stem cell biologist Elias Zambidis and his colleagues described laboratory experiments with these non-viral, human retinal iPSCs, created using the virus-free method Zambidis first reported in 2011.
"We began with stem cells taken from cord-blood, which have fewer acquired mutations and little, if any, epigenetic memory, which cells accumulate as time goes on," said Zambidis, associate professor of oncology and pediatrics at the Johns Hopkins Institute for Cell Engineering and the Kimmel Cancer Center.
The scientists converted these cells to a status last experienced when they were part of six-day-old embryos.

Instead of using viruses to deliver a gene package to the cells to turn on processes that convert the cells back to stem cell states, researchers used plasmids, rings of DNA that replicate briefly inside cells and then degrade.

Next, the scientists identified high-quality, multipotent, vascular stem cells generated from these iPSC that can make a type of blood vessel-rich tissue necessary for repairing retinal and other human material.

They identified these cells by looking for cell surface proteins called CD31 and CD146. Zambidis said that they were able to create twice as many well-functioning vascular stem cells as compared with iPSCs made with other methods, and, "more importantly these cells engrafted and integrated into functioning blood vessels in damaged mouse retina."
The team injected the newly derived iPSCs into mice with damaged retinas, the light-sensitive part of the eyeball. Injections were given in the eye, the sinus cavity near the eye or into a tail vein.

When the scientists took images of the mice retinas, they found that the iPSCs, regardless of injection location, engrafted and repaired blood vessel structures in the retina.
"The blood vessels enlarged like a balloon in each of the locations where the iPSCs engrafted," said Zambidis.

The scientists said their cord blood-derived iPSCs compared very well with the ability of human embryonic-derived iPSCs to repair retinal damage.
Zambidis said there are plans to conduct additional experiments of their cells in diabetic rats, whose conditions more closely resemble human vascular damage to the retina than the mouse model used for the current study.


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