Peripheral Arterial Disease

PAD is a greater health care burden than coronary artery disease in the U.S. Approximately 8 million Americans are afflicted with PAD.

Critical limb threatening ischemia, (CLTI(, is the most severe form of PAD and is characterized by foot pain and gangrene. CLTI is a significant risk for amputation of the leg and has a quality of life equivalent to terminal cancer.

Surgical interventions have provided excellent results in treating CLTI however up to 30%of patients with CLTI will not be candidates for angioplasty of bypass and the only treatment option for relief of pain or removal of an infected ulcer is amputation. Over 53,000 amputations are performed each year ranking as the 6th costliest operation at 10.6 billion dollar expense to our health care system.

Diabetic patients are especially at risk for limb amputation due to infection and more extensive hardening of the arteries. The incidence of diabetes and its vascular complications continues to rise each year.

With the support of the CMMRF the ICVBM is addressing the critical need for effective therapies to prevent amputations .

With research funds we have created a diabetic mouse model of CLTI and we are testing new cell types and preparations

Miller has discovered that mesenchymal[1] stem cells grown in clusters, called spheroids, are able to regenerate skeletal muscle in the diabetic mice with limb ischemia. More excitingly, we have found that those mice treated with MSC spheroids have complete return of muscle function and limb function. Thus a discovery that we plan to quickly translate into a clinical trial.

We are collaborating with Dr. David Mooney from Harvard University who has developed a gel material that can envelope the stem cell and then be injected into the muscle of a leg with PAD. In addition, with the Mason’s research funds, we have purchased the Buchi Encapsulator. This device encapsulates cells [2]which protects them from getting cleared by the recipient’s immune system yet still allows the cells to secrete growth factors that stimulate new blood vessels to grow.

A recent paper in Nature Medicine showed that encapsulated human islet cells when injected into a diabetic mouse survived for 175 days and controlled the mouse’s blood sugar.

We plan to use this encapsulating shield for our MSC spheroids. If the cells can survive longer they may be more effective in restoring blood flow to the leg and promote wound healing.

What is even more exciting is that the Buchi encapsulator is a sterile system and thus whatever we create can be used in humans in clinical trials.

Furthermore the Buchi device allows us to package other cargo in capsules such as growth factors or genes, that can target diseased tissue.

The ICVBM is leading the field in stem cell biology to treat PAD by developing an induced pluripotent[3] stem cell that can directly grow into a functioning blood vessel when injected into muscle. This iPSC mesodermal[4] cell is a discovery of Dr. Mervin Yoder at IU and a close collaborator of the ICVBM. We are currently assessing these iPSCs in our mouse models of limb ischemic and plan to move this novel cell population into a clinical trial.

We are now using induced pluripotent stem cells that have been genetically modified to lack expression of what are called major histocompatibility antigens. Because these cells lack these antigens they can be transplanted into an unrelated patient without the patient’s immune system recognizing them and thus they will be more effective as they will last longer.

[1] Mesenchymal refers to the cell type. We could call these bone marrow derived stem cells.

[2] Mesenchymal stem cells but also other cell types, such as beta cells that secrete insulin and can control diabetes.

[3] Pluripotent refers to the ability of these cells to grow into all tissue of the human body. We are able to take a well differentiated adult cell from the skin and revert it back to an embryonic like state that is pluripotent, that is the potential to differentiate into plural/multiple tissue types. Once in this pluripotent state we then have to get the cell to grow or differentiate into a heart cell or brain cell. In this process the pluripotent stem cell has to be directed to turn into a brain cell by culturing with growth factors. So in effect we go from an adult cell back to a fetal cell then forward again to an adult cell that we need. Induced pluripotent stem cells have the same properties of forming new adult cells for treating disease as embryonic cells without the ethical concerns of collecting cells from a viable embryo

[4] “Mesodermal” is a term used to describe this specific induced pluripotent derived cell. It is similar to the term “mesemenchymal” in that it refers generally to cells that make up connective tissue.


Article originally published at IU School of Medicine Website
on March 17, 2021

Michael P. Murphy, MD

Michael P. Murphy, MD

Critical Limb Threatening Ischemia (CLTI) is the most severe form of peripheral arterial disease caused by atherosclerotic occlusion of blood vessels to the lower extremities. It is often associated with excruciating pain and leads to the development of skin ulcers or gangrene.

The standard of care for CTLI is to improve blood flow to the leg with either a surgical bypass or angioplasty with stents to open the atherosclerotic blockages. Unfortunately, about 30 percent of patients with CLTI will not be candidates for a surgical bypass or angioplasty and amputation is the only treatment available to remove a painful or infected leg. In the United States. Amputations are the sixth costliest operation to the national health care system, with over 53,000 performed each year. This cost has driven interest in cell-based therapies for wound healing and restoring blood perfusion in critical limb ischemia patients.

The Indiana Center for Regenerative Medicine and Engineering (ICRME) has been at the national forefront in developing cutting-edge approaches to treat “no option” for revascularization CLTI patients. Michael P. Murphy, MD, the Cryptic Masons Medical Research Foundation Professor of Vascular Biology Research, has been actively focusing of cell-based approaches for cardiovascular disease for over the past 20 years beginning as a research fellow at Harvard University Medical School.

Murphy conducted the first trial in the U.S. using a patient’s own bone marrow cells to prevent amputations. His pioneering work culminated in the MOBILE (MarrOwStim Treatment of LimB IschemIa in Subjects with Severe Peripheral ArteriaL DiseasE) trial—a randomized, placebo-controlled trial that assessed the ability of intra-muscular injection of a patient’s bone marrow cells to prevent amputation.

The MOBILE study demonstrated that cell therapy was safe, however there was not a significant difference in amputation rates at one-year between the cell treated and placebo groups. The MOBILE trial was uniquely designed to distribute patients with diabetes and a foot ulcer evenly between study groups so that additional analyses could assess these factors on outcomes.

Murphy’s group found that diabetes and presence of a foot ulcer had a negative effect on cell therapy and they surmised that any future trials would require a potentially more potent cell population as bone marrow progenitor cells from patients with advanced disease and age are impaired in their regenerative potential.

“My moonshot is to develop an effective strategy that incorporates a multi-modal approach to limb preservation in the diabetic patient with vascular disease,” said Murphy.

To get to the moon, Murphy has teamed up with Sashwati Roy, PhD, professor of surgery and Director of Clinical Research at the IU Health Comprehensive Wound Center. Roy has been focusing on diabetic wounds and has developed a unique wound dressing, an electroceutical pad, that transmits an electrical current into the soft tissue of the wound that disrupts the biofilm produced by invading bacteria. Once the biofilm is disrupted, antibiotics and other treatments will have a more profound effect in eradicating the bacteria and stimulating the wound to heal.

Murphy also has joined forces with Emily Hopewell, PhD, Director of Cell and Gene Therapy Manufacturing at IU School of Medicine, and Erik Woods, PhD of Ossium Health, Inc. Ossium Health has isolated a unique cell, a mesenchymal stromal cell (MSC) from the vertebral bodies of young, healthy organ donors. These vertebral body MSCs (VB-MSCs) have shown a significant effect in promoting muscle and blood vessel regeneration in a diabetic mouse model of CLTI, and Murphy and Hopewell are working on getting FDA approval to use VB-MSCs in the next generation of clinical trials.

Murphy and Roy are planning a program grant through the National Institutes of Health that will explore the potential synergy of intra-muscular injection (two doses) and application of Roy’s electroceutical dressing for foot wounds in reducing amputation rates in CLTI in a multi-center clinical trial.

Murphy explained that creation of the Indiana Center for Regenerative Medicine and Engineering at IU School of Medicine has helped to advance his research. The Indiana Center for Regenerative Medicine and Engineering under Chandan K. Sen, PhD, the J. Stanley Battersby Chair and Professor of Surgery, Director of the Indiana Center for Regenerative Medicine and Engineering who is a renowned leader in regenerative medicine, has added many benefits to researchers by aiding his expertise in clinical trial design, preclinical animal models, funding mechanisms, and as a collaborator.

As an educational institute, Murphy’s lab is also creating future scientists and surgeons. Murphy hosts both medical students and residents in the laboratory under the division of vascular surgery within a two-year research fellowship.

“My laboratory, as well as some of my colleagues' laboratories, offers a two-year fellowship. During that time, residents and fellows could earn a master's degree, which I highly recommend, in biostatistics, immunology or clinical research,” said Murphy.

Murphy’s work, along with the Indiana Center for Regenerative Medicine and Engineering and IU School of Medicine, have gained prestige as leaders in their prospective fields. Murphy hopes to help Hoosiers who have been told that the only option for their condition is amputation and change their outlook and options.