Wound Healing Therapy That Combines Gene and Stem Cell Therapy


Researchers from Johns Hopkins University have examined wound healing in older mice and discovered that increasing blood flow to the wound can increase the rate of wound healing. Increasing blood flow to the wound requires a combination of gene therapy and the same stem cells the body already uses to heal itself.

John W. Harmon is professor of surgery at Johns Hopkins School of Medicine, and in a presentation to the American College of Surgeons’ Surgical Club, made the case that harnessing the power of bone marrow stem cells can increase the rate at which older people heal.

As we age, our wounds do not heal as fast. However, Harmon thinks that harnessing the power of bone marrow stem cells can remedy this disparity in healing rates.

To heal burns or other wounds, stem cells from the one marrow rush into action and home to the wound where they can differentiate into blood vessels, skin, and other reparative tissues. Stem cell homing is mediated by a protein called Hypoxia-Inducible-Factor-1 (HIF-1). According to Harmon, in older patients, few of these stem cells are released from the bone marrow and there is a deficiency of HIF-1. HIF-1 was actually discovered about 15 years ago by one of Harmon’s collaborators, a Johns Hopkins scientist named Gregg J. Semenza.

HIF-1
HIF-1

Harmon’s first strategy was to boost HIF-1 levels by means of gene therapy. This simply consisted of injecting the rodents with a copy of the HIF-1 gene that yielded higher levels of HIF-1 expression.

Even though higher levels of HIF-1 improved wound healing rates, burns were another story. To accelerate burn healing, Harmon and his co-workers used bone marrow stem cells from younger mice combined with the increased levels of HIF-1. This combination of HIF-1 and bone marrow stem cells from younger mice led to accelerated healing of burns so that after 17 days, almost all the mice had completely healed burns. These animals that healed so fast showed better blood flow to the wound and more blood vessels supplying the wound.

Harmon said that while this strategy is promising, he think that a procedure that uses a patient’s own bone marrow cells would work better since such cells would have a much lower chance of being rejected by the patient’s immune system. In the meantime, HIF-1 gene therapy has been successfully used in humans with a sudden lack of blood flow to a limb (see Rajagopalan S., et al., Circulation. 2007 Mar 13;115(10):1234-43). Harmon postulated that “it’s not a stretch of the imagination to think this could someday be used in elderly people with burns or other difficult wounds.”

Bioprinted Amniotic Fluid-Derived Stem Cells Accelerate The Healing of Large Skin Wounds


Bioprinting is a contrived term that describes the deposition of cells on surfaces by means of inkjet printer technology. Because the inkjet squirts small quantities of ink in a precisely specified shape and pattern, inkjets can be adapted to the application of cells on living surfaces or on scaffolds fashioned in the form of living organs or tissues.

Shay Soker at the Wake Forest Institute for Regenerative Medicine in Winston-Salem, North Carolina, has published a remarkable study that uses inkjet technology to deposit stem cells over large skin wounds. His study shows that bioprinting is a potentially very efficient way to deliver stem cells to wounds.

There are on estimate a half a million burns treated in the US each year. Extensive burns and so-called full thickness skin wounds are usually very traumatic for patients. The mortality rates of burns are about 5% and cost ~2 billion per year. Present strategies for treating burns tend to produce extensive scarring and relatively poor cosmetic outcomes.

Tissue engineering approached have the potential to provide more effective treatments for such injuries. Graft products such as Dermagraft and TransCyte from Advanced BioHealing and Apligraft from Organogenesis are cellularized graft products composed or a polymer scaffold that is seeded with cells. Unfortunately, these are expensive to make. Cell spraying and bioprinting, which deposits cells encased in hydrogel spheres all around the wound are a cheaper and potentially more attractive approach to wound therapy.

Soker’s team used stem cells from amniotic fluid and mesenchymal stem cells for this experiments. These stem cells were grown in culture, mixed in fibrin-collagen hydrogels, and bioprinted to surgically-produced wounds on the backs of hairless (nude) mice. The wounds all closed at approximately the same rate over a two-week period for those wounds treated with amniotic-fluid stem cells or mesenchymal stem cells. Wound closing was slow for those treated with only hydrogels.

Amniotic Fluid Stem Cells
Amniotic Fluid Stem Cells

After the wounds closed, biopsies of the wounds showed that the wounds that had been treated with amniotic fluid stem cells were filled with small blood vessels. Wounds bioprinted with mesenchymal stem cells did not have quite as many blood vessels as those seen in mice treated with amniotic stem cells, and those treated only with hydrogels had hardly any. However, when the biopsies were examined in detail to find the stem cells, they were not to be found. Therefore, the stem cells were not incorporated into the wounds, but induced healing through molecules that they secreted.

Not satisfied with this, Soker and his colleagues examined the gene expression patterns of the amniotic fluid stem cells and compared them to the gene expression patterns of mesenchymal stem cells. As expected, the amniotic fluid stem cells had oodles and oodles of growth factors. Fibroblast growth factors, Insulin-like growth factors, Vascular endothelial growth factor, Hepatic growth factor, and several others were made by amniotic fluid stem cells. Mesenchymal stem cells made their fair share of growth factors, but not nearly as many ans their amniotic fluid counterparts.

From these experiments, Soker concluded that even though bioprinting is a new technology, is can deliver cells effectively to surface wounds. Also, the stem cells do not directly contribute to the healing of the wound, but induce other cells to migrate into the wound and heal it. The delivery of bioprinted cells in hydrogels has the potential to rebuild a tissue from the ground up.

See Aleksander Skardai, et al., “Bioprinted Amniotic-Fluid-Derived Stem Cells Accelerate Healing of Large Skin Wounds,” Stem Cells Translational Medicine 2012;1:792-802.

Sweat Glands Are A Source of Stem Cells for Healing Wounds


When I was a kid, I used to wish that I had no sweat glands. Sweating made me sticky, wet and miserable. Little did I now, that without sweat glands, my body would have quickly overheated to fatal levels. A new study now shows that sweat glands are also the source of healing for wounds.

Human skin contains millions of eccrine sweat glands. These glands are not connected to hair follicles and they function throughout our lives to regulate the temperature of the body. Sweat glands respond to elevated bodily temperatures by secreting a mixture of NaCl and water. The water cools the external bodily temperature and is used to secrete other unwanted molecules. This is the main reason our sweat can smell like the food we ate (garlic, onions, etc.).

A new study by from the University of Michigan Health System shows that sweat glands play a key role in providing cells for recovering skin wounds, such as scrapes, burns and ulcers. These results were recently published in the American Journal of Pathology.

“Skin ulcers – including those caused by diabetes or bed sores – and other non-healing wounds remain a tremendous burden on health services and communities around the world,” says lead author of this work, Laure Rittié, who is a research assistant professor of dermatology at the Univ. of Michigan Medical School. She continued, “Treating chronic wounds costs tens of billions of dollars annually in the U.S. alone, and this price tag just keeps rising. Something isn’t working.”

U of M researchers believe they have discovered one of the body’s most powerful secret healers.

“By identifying a key process of wound closure, we can examine drug therapies with a new target in mind: sweat glands, which are very under-studied,” Rittié says. “We’re hoping this will stimulate research in a promising, new direction.”

Previously, wound healing was thought to originate from cells that came from hair follicles and from intact skin at the edge of the wound. However, the findings from the U of M research group demonstrate that cells arise from beneath the wound, and suggest that human eccrine sweat glands are the source of an important reservoir of adult stem cells that can quickly be recruited to aid wound healing.

Rittié commented: “It may be surprising that it’s taken until now to discover the sweat glands’ vital role in wound repair. But there’s a good reason why these specific glands are under-studied – eccrine sweat glands are unique to humans and absent in the body skin of laboratory animals that are commonly used for wound healing research.” Rittié continued: “We have discovered that humans heal their skin in a very unique way, different from other mammals. The regenerative potential of sweat glands has been one of our body’s best-kept secrets. Our findings certainly advance our understanding of the normal healing process and will hopefully pave the way for designing better, targeted therapies.”