Using induced pluripotent stem cells to have heart muscle cells is one of the goals of regenerative medicine. Successful cultivation of heart muscle cells from a patient’s own cells would provide material to replace dead heart muscle, and could potentially extend the life of a heart-sick patient.
Unfortunately, induced pluripotent stem cells, which are made by applying genetic engineering techniques to a patient’s own adult cells, like embryonic stem cells, will cause tumors when implanted into a living organism. To beat the problem of tumor formation, scientists must be able to efficiently isolate the cells that have properly differentiated from those cells that have not differentiated.
A new paper from a laboratory the Emory University School of Medicine in Atlanta, Georgia, have used “molecular beacons” to purify heart muscle cells from induced pluripotent stem cells, thus bringing us one step closer to a protocol that isolates pure heart muscle cells from induced pluripotent stem cells made from a patient’s own cells.
Molecular beacons are nanoscale probes that fluoresce when they bind to a cell-specific messenger RNA molecule. Because heart muscle cells express several genes that are only found in heart muscle cells, Kiwon Ban in the laboratory of Young-Sup Yoon designed heart muscle-specific molecular beacons and used them to purify heart muscle cells from cultured induced pluripotent stem cells from both mice and humans.
The molecular beacons made by this team successfully isolated heart muscle cells from an established heart muscle cell line called HL-1. Then Ban and co-workers applied these heart-specific molecular beacons to successfully isolate heart muscle cells that were made from human embryonic stem cells and human induced pluripotent stem cells. The purity of their isolated heart muscle cells topped 99% purity.
Finally, Ban and others implanted these heart muscle cells into the hearts of laboratory mice that had suffered heart attacks. When heart muscle cells that had not been purified were used, tumors resulted. However, when heart muscle cells that had been purified with their molecular beacons were transplanted, no tumors were observed and the heart function of the mice that received them steadily increased.
Because the molecular beacons are not toxic to the cells, they are an ideal way to isolate cells that have fully differentiated to the desired cell fate away from potentially tumor-causing undifferentiated cells. in the words of Ban and his colleagues, “This purification technique in combination with cardiomyocytes (heart muscle cells) generated from patient-specific hiPSCs will be of great value for drug screening and disease modeling, as well as cell therapy.”
Two patients afflicted with amyotrophic lateral sclerosis have received stem cell injections into their spinal cords at the University of Michigan Health System. These are the first two subjects in a national clinical trial.
Both of these volunteers have returned home and will continue to receive medical follow-up and monitoring in order to assess the safety of this procedure and to detect any potential improvements in the condition of these patients.
Additional patients with this condition, which is also known as Lou Gehring’s disease, are being evaluated for possible participation in the trial at U-M and Emory University. This phase 2 trial is approved by the US Food and Drug Administration (US FDA) and is being funded by a Maryland-based company called Neuralstem, Inc., the proprietor of this stem cell product.
Neuralstem, Inc., has developed a neural stem cell line called NSI-566. When injected into the central nervous system of a living animal, these cells will divide up to 60 times and differentiate into a variety of neural cells (neurons, glial cells, etc.). Several publications have shown that injected NSI-566 cells survive when injected into the spinal cord, differentiate into several different neural cell types, and successfully integrate into the presently existing neural network.
In ALS patients, motor neurons progressively die off in the spinal cord, which limits voluntary movement. ALS is a progressive neurodegenerative disease that affects nerve cells in the brain and spinal cord, leading to complete paralysis, and eventually, death. According to the ALS Association, as many as 30,000 Americans have the disease, and about 5,600 people in the U.S. are diagnosed with ALS each year. The goal of this treatment strategy is to stabilize ALS patients and to replace dead or dying neurons and to slow the progressive decline and loss of movements, walking, and eventually breathing.
Eva Feldman, professor of neurology at the U-M Medical School, is the principal investigator for this clinical trial, and serves as an unpaid consultant to Neuralstem, Inc. Dr. Feldman led the analysis of the results from the Phase 1 trial, which ended in 2012. In this Phase 1 trial, 100,000 cells were delivered to each patient, and the patients tolerated them well and experienced to severe side effects. One subgroup of patients seemed to experience interruption of the progression of ALS symptoms.
Feldman commented, “We’re going to be permitted to give more injections and more stem cells, in Phase 2. We’re very excited that we have been able to bring this important work to the University of Michigan.”
Parag Patil, a neurosurgeon and biomedical engineer, performed both operations on the trial participants. In each case, the patient’s spinal column was unroofed and the spinal cord exposed to receive the cells. The stem cells are then introduced by means of a custom-designed delivery device that is affixed to the subject’s spinal bones so that it moves with the patient’s breathing throughout the process.
Patil, as assistant professor, also serves as a paid engineering consultant to Neuralstem, Inc., in order to further prefect the injection device. A third participant in this clinical trial received a stem cell injection in September at Emory University in Atlanta, Georgia. This Phase 2 dose escalation trial is designed to treat up to 15 ambulatory patients in five different dosing cohorts, and will do so under an accelerated dosing and treatment schedule. The first 12 patients will be divided into four cohorts and each will receive injections only in the cervical region of the spinal cord, where breathing function is controlled.
The first cohort of three patients received 10 cervical region injections of 200,000 stem cells per injection. The trial will now progress to a maximum of 20 cervical injections of up to 400,000 stem cells per injection. The last three Phase 2 patients will receive injections into the cervical and lumbar spinal regions, and will receive 20 injections of 400,000 cells in the lumbar region in addition to the cervical injections they have already received. The trial also accelerates the treat schedule, and is designed to progress at the rate of one cohort per month with one month observations periods between cohorts. Researchers expect all of the patients could be treated by the end of the second quarter in 2014.
Globally, thousands of heart patients have been treated with stem cells from bone marrow and other sources. While many of these patients have been helped by these treatments, the results have been inconsistent, and most patients only show a modest improvement in heart function.
The reason for these sometimes underwhelming results seems to result from the fact that implanted stem cells either die soon after they are delivered to the heart or washed out. Since the heart is a pump, it is constantly contracting and having fluid (blood) wash through it. Therefore, it is one of the last places in the body we should expect implanted stem cells to stay put.
To that end, cardiology researchers a Emory University in Atlanta, Georgia have packaged stem cells into small capsules made of alginate (a molecule from seaweed) to keep them in the heart once they are implanted there.
W. Robert Taylor, professor of medicine and director of the cardiology division at Emory University School of Medicine, and his group encapsulated mesenchymal stem cells in alginate and used them to male a “patch” that was applied to the hearts of rats after a heart attack. Taylor’s group compared the recovery of these animals to those rats that had suffered heart attacks, but were treated with non-encapsulated cells, or no cells at all. The rats treated with encapsulated cells not only showed a more robust recovery, but they had larger numbers of stem cells in their hearts and showed better survival.
Of this work, Taylor said, “This approach appears to be an effective way to increase cell retention and survival in the context of cardiac cell therapy. It may be a strategy applicable to many cell types for regenerative therapy in cardiovascular medicine.
Readers of this blog might remember that I have detailed before the inhospitable environment inside the heart after a heart attack. Oxygen levels are low because blood vessels have died, and roving white blood cells are gobbling up cell debris and releasing toxic molecules while they do it. Also the dying cells have released a toxic cocktail of molecules that make the infarcted area very inhospitable. Injecting stem cells into this region is an invitation for more cells to die. Previous experiments have shown that preconditioning stem cells either by genetically engineering them to withstand high stress levels of by growing them in high-stress conditions prior to implantation can increase their survival in the heart.
Taylor also pointed out that the mechanical forces of the contracting heart can squeeze them and displace them from the heart, much like pinching a watermelon seed between your fingers causes it to slip out. “These cells are social creatures and like to be together,” said Taylor. “From some studies of cell therapy after myocardial infarction, one can estimate that more than 90 percent of the cells are lost in the first hour. With numbers like that, it’s easy to make the case that retention is the first place to look to boost effectiveness.”
Encapsulation keeps the mesenchymal stem cells together in the heart and “keeps them happy.” Encapsulation, however, does not completely cut off the cells from their environment. They can still sense the cardiac milieu and release growth factors and cytokines while they are protected from marauding white blood cells and antibodies that might damage, destroy, or displace them.
Alginate already has an impressive medical pedigree as a biomaterial. It is completely non-toxic, and chefs use it to make edible molds to encase other types of tasty morsels. Dentists use alginate to take impressions of a patient’s teeth and it is also used a component of wound dressings. One of Taylor’s co-authors, an Emory University colleague named Collin Weber has used alginate to encapsulate insulin-producing islet-cells that are being tested in clinical trials with diabetics.
Encasing cells in alginate prevents them from replacing dead cells, but mesenchymal stem cells tend to do the majority of their healing by means of “paracrine” mechanisms; that is to say, mesenchymal stem cells tend to secrete growth factors, cytokines and other healing molecules rather than differentiating into heart cells. Mesenchymal stem cells can be isolated from bone marrow or fat.
One month after suffering from a heart attack, those rats that had suffered a heart attack saw their ejection fractions (a measure of how much volume the heart pumps out with every beat) fell from an average of 72% to 34%. However, rats treated with encapsulated mesenchymal stem cells saw an increase in their ejection fractions from 34% to 56%. Those treated with unencapsulated mesenchymal stem cells saw their ejection fractions rise to 39%.
One of the main effects of implanted stem cells is the promotion of the growth of new blood vessels. In capsule-treated rats, the damaged area of the heart had a blood vessel density that was several times that of the hearts of control animals. Also, the area of cell death was much lower in the hearts treated with encapsulated MSCs.
The encapsulated stem cells seem to stay in the heart for just over ten days, which is the time is takes for the alginate hydrogels to break down. Taylor said that he and his lab would like to test several different materials to determine how long these capsules remain bound to the patch.
The goal is to use a patient’ own stem cells as a source for stem cell therapy. Whatever the source of stem cells, a patient’s own stem cells must be grown outside the body for several days in a stem cell laboratory, much like Emory Personalized Immunotherapy Center in order to have enough material for a therapeutic effect.