New Stem Cell Technology to Form Blood Vessels and Treat Peripheral Artery Disease

How to make new blood vessels for patients who need them? Researchers at the University of Indiana University School of Medicine have developed a new therapy for illnesses such as peripheral artery disease. Diseases such a peripheral artery disease can lead to skin problems, gangrene and sometimes amputation.

Our bodies have the ability to repair blood vessels and creating new ones, because of a cell type called “endothelial colony-forming cells.” Unfortunately, these cells tend to lose their ability to proliferate and form new blood vessels as patients age or develop diseases like peripheral arterial disease, according to Mervin C. Yoder Jr., M.D., who is the Richard and Pauline Klingler Professor of Pediatrics at IU and leader of the research team.

Physicians can prescribe drugs that improve blood flow to patients with peripheral artery disease, but if the blood vessels are reduced in number or function, the benefits from such drugs are minimal. A better treatment might be to introduce “younger,” more effective endothelial colony forming into the affected tissues. In this case, such a treatment would jump-start the creation of new blood vessels. Gathering such cells, however is rather difficult, since endothelial colony-forming cells are somewhat difficult to find in adults, especially in those with peripheral arterial disease. Fortunately, endothelial colony-forming cells are rather numerous in umbilical cord blood.

Yoder and his colleagues published their work in the journal Nature Biotechnology, and they have reported that they have developed a potential therapy by using patient-specific induced pluripotent stem cells (iPSCs). Induced pluripotent stem cells are pluripotent stem cells that are derived from normal adult cells by means of genetic engineering and cell culture techniques. Once an iPSC line has been derived from a patient, they can potentially be differentiated into any adult cells type, including endothelial colony-forming cells.

In this paper, Yoder and his research team developed a novel methodology to differentiate iPSCs into cells with the characteristics of the endothelial colony-forming cells that are found in umbilical cord blood. These laboratory-generated endothelial colony-forming cells were injected into mice, and they proliferated and generated human blood vessels that nicely restored blood flow to damaged tissues in mouse retinas and limbs

Another problem addressed in this paper was growing endothelial colony-forming cells from umbilical cord in culture so that they can achieve sufficient numbers for therapies. In this paper, Yoder and his team designed a cell culture system that was able to dramatically expand these iPSC-derived endothelial colony-forming cells in culture from one founding cell to 100 million new cells in a little less than three months.

“This is one of the first studies using induced pluripotent stem cells that has [sic] been able to produce new cells in clinically relevant numbers — enough to enable a clinical trial,” Dr. Yoder said. According to Yoder, the next steps will be to reach solidify an agreement with a facility approved to produce cells for use in human testing. Additionally, Yoder would like to treat more than just peripheral artery disease, since he and his colleagues are evaluating the potential uses of these cells to treat diseases of the eye and lungs that involve blood flow problems.

Getting Stem Cells to Engraft More Effectively – With A Little Help From My “Friends”

The old Beatles song, “With A Little Help from My Friends” begins:

What would you think if I sang out of tune
Would you stand up and walk out on me?
Lend me your ears and I’ll sing you a song
And I’ll try not to sing out of key
Oh I get by with a little help from my friends
Mm I get high with a little help from my friends
Mm going to try with a little help from my friends

For mesenchymal stem cells, a little help from circulating stem cells, that is, their “friends” can make all the difference.

Ruei-Zeng Lin, in the laboratory of Juan M. Melero-Martin at the Boston Children’s Hospital and Department of Surgery at Harvard Medical School, in Boston, Massachusetts, have made a profound discovery that was published in the Proceedings of the National Academy of Sciences USA. They have shown that cells called “endothelial colony-forming cells” or ECFCs that not only circulate throughout the bloodstream but also contribute to the formation of new blood vessels, can function as “nurse cells” that positively regulate the regenerative potential of human mesenchymal stem cells.

Mesenchymal stem cells (MSCs) secrete a whole cocktail of healing molecules, but these cells also respond to several different molecules made by other cells, and ECFCs make some of these pro-MSC molecules.

In their experiment, Lin and others injected human MSCs isolated from white fat and bone marrow aspirates underneath the skin of immunodeficient mice in the presence or absence of ECFCs derived from human umbilical cord blood. The results were quite telling.

The engraftment of the MSCs (engraftment means the ability of the implanted stem cells to survive, differentiate and integrate into existing tissues) was regulated by a protein secreted by ECFCs called “platelet-derived growth factor BB” or PDGF-BB. When MSCs and ECFCs were transplanted together, the ECFCs significantly enhanced MSC engraftment. The MSCs not only survived better, showed much less cell death, but they also preserved the stem cell-character of the MSCs. THis is was established by the fact that when the implanted MSCs were removed and reimplanted into another mouse, these cells could repopulate secondary grafts. However, if MSCs were implanted without ECFCs, MSC engraftment was negligible. Also, if a drug called Tyrphostin AG1296 was used, MSCs engraftment was also negligible. Tyrphostin AG1296 inhibits the receptor for PDGF-BB and completely abrogates any EFCF-related enhancement of MSC function.  This shows that the enhancement of MSC engraftment by ECFCs is largely dependent on PDGF-BB-mediated signaling.

Strangely, transplanted MSCs that had been co-transplanted with ECFCs displayed fate-restricted differentiation in animals.  This simply means that the fat-based stem cells differentiated into fat and the bone marrow-derived MSCs differentiated into bone.  It seems that with the increased growth and stem cell function comes a more restricted differentiation program as well.  This could potentially prevent the phenomenon of “out-of-place” differentiation also known as heterotypic differentiation, which can cause the formation things like bone during fat transplantation or other such things.

These experiments show that blood-derived ECFCs can amplify the regenerative potential of MSCs via PDGF-BB – based signaling.  These data also suggest that the systematic use of ECFCs can improve MSC transplantation, and provides new insights into the therapeutic capabilities of ECFCs.  The authors add: “We foresee the use of ECFCs as a means to improve the outcome of MSC transplantation.”

This is a remarkable preclinical trial, but before it can work in humans, it must prove its efficacy and safety in human clinical trials and in other preclinical trials as well.