Frequently Asked Questions

Regenerative medicine involves repairing underlying disease states rather than just treating symptoms. It also includes the “making” of new tissues and organs to repair or replace those tissues or organs not functioning 100% due to age, disease, damage, or a congenital condition. This field holds the promise of regenerating damaged tissues using “cell therapies.”

The hope in regenerative medicine is that physicians and scientists will be able to grow tissues and whole organs in the laboratory and safely implant them when the body cannot heal itself. This addresses the huge clinical need that cannot be met by transplantation, because the availability of donor organs meets only a minute fraction of the need.

The Regenerative Medicine Research facilities, are located at the Texas Heart Institute—the Denton A. Cooley Building. The areas of regenerative medicine research at THI include: cell and gene therapy for treatment of cardiovascular diseases; cell profiling; tissue engineering of bio-artificial organs and vasculature; cell programming and reprogramming; cell-based prevention of disease; stem cell and cancer cell research; aging as a failure of stem cells; sex differences in cardiovascular and vascular cell-based therapies; and autologous cell therapy to treat and slow the progression of disease.

Regenerative medicine is a multidisciplinary field that employs biologists (cell, molecular, biochemical), engineers (biomedical, mechanical, electrical), and medical personnel (surgeons, cardiologists, research nurses) to work together. Regenerative medicine teams employ workers with B.S., B.S.N., M.S., Ph.D., M.D., D.V.M., and other advanced degrees.

The regenerative medicine field is diverse, spanning many research and clinical disciplines. There is no single society or organization that fully represents regenerative medicine, however below are a few resources with more detailed information.

• NIH RePORT
• NIH NHLBI Cardiovascular Cell Therapy Research Network
• Alliance for Regenerative Medicine
• FDA For Consumers- Adult Stem Cell Research Shows Promise
• FDA What are stem cells and how are they regulated?
• NIH Stem Cell Information FAQ
• NIH Clinical Trials.gov 

Stem cells are immature cells that exist in everyone throughout life and have the capability of becoming more specialized cells. Stem cells exist in virtually every organ and tissue, in bone marrow, and in blood. They hold the unique potential to become any of the specialized cell types in our body. Stem cells have two main characteristics: (1) the ability to multiply or self-renew and (2) the ability to “differentiate” — to become different specialized cells.

Stem cells are isolated from three major sources: our bone marrow, our blood, and our tissues such as fat, muscle, heart, skin, etc.

One way adult stem cells can repair the heart is by being injected into the heart where they “regenerate” into new heart muscle tissue and new blood vessel cells.

Yes. Stem cells are currently used in clinical trials. In fact, several research groups are studying the use of blood stem cells, also known as hematopoietic stem cells. In addition to the well known use in cancer treatment regimens (ie bone marrow transplants) stem cells are currently used in clinical trials for a variety of heart and vascular conditions including: heart failure, heart attacks, peripheral vascular disease, cardiomyopathy and stroke. To learn about current clinical trials, see www.clinicaltrials.gov. and “Search for Studies.”

Identifying stem cells in the blood may determine which patients are most likely to respond to stem cell therapy and indicate those who may not. The types of stem cells in blood can also potentially give you insight into your relative health compared to others in your age category.

We are studying the different cell populations in blood to help determine which patients may be most likely to respond to stem cell therapy. Right now we have identified stem cells that may be important and are testing them in ongoing studies.

Researchers are developing methods to use a patient’s own stem cells for treatment of heart disease. However, this may not be the best source of therapeutic cells, depending on the patient ‘s health. For example, cells from blood, fat tissue, and bone marrow are being investigated. In some cases, doctors may need to utilize cells from a donor.

There are experiments that have shown female stem cells are more potent and have more longevity than stem cells from males.

Biorepositories (or biobanks) are essentially “libraries” where biospecimens (material taken from the human body, such as tissue, blood, plasma, cells and urine) are preserved and made available for scientists and clinicians to study or evaluate at a later date.

Biorepositories allow researchers to study the biospecimens from each patient at a deeper level (cellular or molecular), which may reveal the underlying mechanisms involved with the disease’s progression or repair after a treatment and ultimately improve future therapies.

“Profiling” of specimens involves the use of various techniques to identify any unique variable or characteristic in the patient’s biospecimen that is associated with their age, sex/gender, disease, medical condition, or response to treatment.

Because all of the blood and cells within the heart have been removed and the remaining scaffold appears translucent white.

The heart is decellularized so that the non-cellular framework of the organ (known as the extracellular matrix) can serve as a scaffold. The decellularized heart retains the extracellular “frame” of the organ, including chambers, valves, and blood vessels, although all the living cells have been removed. The scaffold can then be reseeded with healthy adult stem cells that can “regenerate” the heart into a healthy functioning organ. Eventually, the hope is that these regenerated hearts can be transplanted into patients.

Depending on the size of the heart, decellularization can take from 30 to 120 hours.

Yes, at THI we are testing various types of adult stem cells that can be used to recellularize hearts that we have previously decellularized. This is the way we are “growing” hearts in the lab.

No, embryonic cells are not being used to regrow human hearts. At THI we are testing various adult stem cells to grow hearts.

The idea is to use a patient’s own stem cells to avoid the need for anti-rejection medications like those required for organ transplant patients. However, depending on the results of our study of blood stem cells that determine response to therapy, we may use donor stem cells.

Because rebuilding organs to full functional capacity is extremely difficult, we estimate 10 to 15 years before these organs might be ready for human use. However, along the way we are developing cardiac patches, valves and other therapies that will take a shorter time than building a whole organ.

The multidisciplinary nature of the work we do attracts researchers from a variety of backgrounds in the biological sciences, engineering and medicine. I have a BS degree in biology and physical science, a PhD in Pharmacology, and post-doctoral training in molecular biology and cardiology. But in my lab, we have engineers (biomedical and electrical), surgeons, cardiologists, physiologists, and cell biologists. They have PhDs, MDs, master’s degrees, BS degrees and high school degrees. The specific education and training requirements vary based on the area you are interested in and the role you want to play. However, I would say a universal requirement is the ability to think and be passionate about the work you’re doing each and every day.

I see both situations benefiting from this science and technology. Because these organs can be recellularized with an individual’s own cells, the new organs will most likely be used for planned transplantations. If a heart valve or a cardiac patch turns out to work without cells, or if any tissue only requires bathing in cells for a few days, then we could use the method for some emergency transplants, too.

In regenerative medicine, the plan is to grow organs for all types of patients. If the patient is able to receive an organ from a suitable donor in a timely fashion, then that will most likely be the route taken. However, there are many patients who are waiting for a suitable match or have many other factors that do not allow them to be on a transplant list. We will be able to work with those patients.

It is important to remember that when you get an organ transplant today, you unfortunately are trading one problem for another – because you now have to avoid rejection of the new organ. This is usually managed by taking drugs that help to prevent rejection for the rest of your life. These drugs can have side effects like high blood pressure, diabetes, and often damage your kidneys and vasculature.

This is why we want to build organs or tissues using your own cells. That way you can not only have a new organ but avoid the need to take rejection-preventing drugs that can cause other problems. If we can succeed in this area, I suspect anyone who needs a transplant but can wait for the time it takes to build one will benefit. That being said, if organ donors exist, I don’t think anyone will say no to that route, which has proven to help so many in life-threatening, organ-failure situations. Having both options available helps to better treat patients needing this critical support.

We see this methodology being used for every organ. However, the anatomy and physiology of some organs are much more complex than others. A heart is more challenging and more complex than a liver, for example. Knowing this, we suspect the liver will be the first bioengineered organ to be transplanted, likely for patients with acute liver failure. Still, all organ types are needed and we hope this methodology will help to address those needs.

We can decellularize any tissue that gets a blood supply including intestines, the pancreas and skin.

In our decellularization technique, the extracellular matrix composition and architecture of the tissue we are stripping remains intact. Since both of these components are unharmed during decellularization, we are able to harness the perfect scaffold that nature has already grown for us. This matrix and scaffolding actually helps to instruct the cells that grow on it and makes sure they organize to grow and become a functional organ.

Tissues, such as intestine and skin, are being developed by some of my colleagues in the field. As I understand, these other tissues work well in low pressure settings such as the right side of the heart, but in high blood pressure settings the thin tissues like intestine and skin tend to fail. That doesn’t mean they can’t be helpful, though; they are being used for wounds and for breast reconstruction and seem to be working for these applications. So while simple sheets of tissue like intestine and skin can work really well to address things like burns, they won’t work to build a heart, which is where my lab’s focus is currently.

This is a goal I raised a few years ago. I think it may be possible, but not yet. We have a lot of work to do with organs first. It’s a great question, though.

Pig hearts are similar in size and anatomy to human hearts, so they make a suitable donor tissue for building a new human heart for patients in need. However, other pig organs may not be as suitable. For example, we don’t think pig liver would be quite as good. Other organs beyond a heart could still be viable options, like pancreas, kidney, lung and gall bladder, which are being studied in other labs.

As we work towards building a new organ, there are many applications of the extracellular matrix. One example is it allows us to develop novel structures that can be used to build “mini” organs. These “mini” organs could be used to screen new drugs and chemicals before moving toward pre-clinical and clinical tests. Other potential uses could be for development of vaccines, living energy sources, biological bioreactors for biomolecules or other factors where cells can generate a product more efficiently, as opposed to being synthetically made.

As for growing meat, it is possible, but as a vegetarian I have to admit this is not something I think about.

Each organ has its own complexity in anatomy and physiology. Organs, such as the liver, have some regenerative capacity already and will most likely be easier to regenerate and then transplant. The heart has little natural regenerative capacity and requires more work to build a truly functional heart for transplantation.

As we work to build a whole heart, we are learning how the pieces can be built, such as the aorta, valves and myocardial patches. These individual pieces can also be grown for transplantation and help to restore part(s) of a damaged heart or an aging heart that has lost its ability to pump correctly.

One of the major hurdles we have to building a whole heart is to identify the number of cells and type of cells needed. In building the heart, we believe we will need hundreds of billions of cells, including blood vessel cells, nerves, underlying fibroblasts and cardiac muscle cells. These cells have to assemble into the correct organization and then relearn to communicate with each other appropriately and work in concert to function as one whole organ.

Learning to create whole organs that are more complex, like the heart, will take more time than an organ that isn’t as challenging to produce, like a liver. However, we are making positive progress.

Cells are a huge hurdle. We estimate it requires hundreds of billions of cells to build a whole heart. Another challenge is keeping the organs alive and sterile in the lab while they develop. The organs don’t have an immune system, so keeping them clean, “free of microbes” or “free of microorganisms” is a big deal.

There is a lot of research on how to remove the cells without damaging the extracellular matrix. Methods include both mechanical and chemical solutions, and the chosen method depends on the organ of interest.

For the heart, we use an anion detergent solution. We tried several detergents (soaps) for stripping cells, and ultimately we settled on one called sodium dodecyl sulfate (this is the main ingredient in shampoo). We developed a protocol for decellularizing which reduces the amount of DNA present while preserving the glycoaminoglycans (GAGs) and mechanical and structural properties. A review article was recently published by my group that describes a lot of the decellularization processes being investigated worldwide.

Also see this Nature News Feature | Tissue engineering: How to build a heart

We are still in the research phases of our work, so we don’t yet know what potential side effects could occur. We have to build organs that can survive long term, function properly (i.e. do the normal work assigned to that organ), and have the ability to effectively respond to injury. If any of these three things are lacking in some way, this could result in a side effect.

Our moonshot goal is to develop a heart that is made up of the patient’s own cells. In theory, this will prevent the chance of the patient’s body rejecting the heart. However, as more is learned about stem cells, it may very well be that cells from young healthy donors are the better source. If this is the case, we will still need to address the same rejection issues we face today when we transplant organs (i.e. the patient must take medicines to suppress the immune system so that their body does not reject the organ).

Until we know more and are further along in the research, it’s too soon to tell what, if any, side effects we’ll have with this method of transplantation.

Before we can move to clinical trials, organs will be investigated in pre-clinical trials with large animals to test safety and efficacy.

Do you believe that the issues involved with organ transplantation can be solved through stem cells and tissue engineering?
Many issues associated with organ transplantation absolutely can be solved through stem cell and tissue engineering. For example, cell therapy is a regenerative medicine strategy that can be used to intervene early after an injury occurs to treat the underline injury rather than the symptoms associated with the injury and potentially prevent the need for organ transplantation. In addition, tissue engineering provides an opportunity to repair or replace injured organs and tissue. Regenerative medicine is a new field that for the first time has the opportunity to address the major underlying issues that cause disease rather that simple treat the symptoms

Stem cells are a major component of tissue engineering. Basically, stem are cells that can do two things: first make more of themselves or self-renew or second differentiate into multiple kinds of cells. In tissue engineering we typically combine some sort of material a scaffold if you will, or some other material with cells to build a new structure that allows those cells to function at a sight of injury or disease. Or we use some sort of engineered material to deliver cells in a new way to region of damage.

Breakthroughs in my research have really come:

1) with an understanding of how to manufacture or scale up stem cells

2) with the whole idea of decellularization of complex organs and tissues and 3) with the findings about abilities to transplant stem cells or the chemicals or microRNAs or other compounds of stem cell secrete without even needing the cells themselves.

Building new bioreactors, finding ways to grow enough cells (billions of), finding how to derive stem cells from an adult individual, and the advent new materials that can be used for scaffolds are all significant contributions to our research. As for how close we are to being able to engineer and transplant human organs, well it depends on the organ, Dr. Tony Atala will tell you that he’s already transplanted most of a bladder, a simple balloon; but transplanting a more complex organ such as heart, liver, lung or kidney is still several years away.

The Stem Cell Center at the Texas Heart Institute is actively enrolling patients in studies using adult stem cells for various diseases of the heart and the circulatory system. Patients and doctors hoping to learn more about stem cell therapy are encouraged to contact us directly. Visit the Stem Cell Center Clinical Trials page for more information about our current trials, including the NIH-sponsored Cardiovascular Cell Therapy Research Network (CCTRN), and learn how to contact our team.

Early tests have shown that stem cell-based therapies can reverse (at least in part) the heart damage that results in heart failure.

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