The bone marrow is conventionally thought of as the location in the body where blood is made. Production of blood is regulated by the body’s needs and originates from a specialized type of stem cell called the “hematopoietic” stem cell.

There have been numerous studies demonstrating that the bone marrow also contains stem cells that are capable of regenerating injured heart tissue. Controversy exists as to which specific type of bone marrow stem cell is better at regenerating heart tissue, however the concept is not new. Back in 1999 researchers from the University of Toronto in Canada demonstrated that subsequent to induction of cardiac injury in laboratory rats, the injection of bone marrow stem cells that have been treated with a chemical agent (5-azacytidine) would cause significant recovery of the injury [1]. Treatment with the chemical agent resulted in cells that resembled heart cells in the test-tube, which were subsequently transplanted into the animal.

Later studies showed that for certain types of heart injury it was not necessary to treat the bone marrow stem cells with chemical agents, but that simple administration of these cells, either directly into the heart [2], or intravenously [3], was able to cause a therapeutic response.

Today at the American Heart Association’s Annual Meeting in Orlando Florida researchers from the University of Rostock presented data using stem cells from the bone marrow together with coronary artery bypass surgery in treating patients with heart failure due to poor circulation.

The researchers presented data on 10 patients that were administered a purified population of bone marrow stem cells. These stem cells were selected using a magnetic-based approach for expression of the protein CD133, which is associated with enhanced stem cell activity. The purpose was to increase circulation by causing formation of new blood vessels, as well as possibly increasing ability of the heart muscle to regenerate.

The study demonstrated efficacy in the treated patients based on increase cardiac muscle contraction ability as compared to patients that had bypass surgery but did not receive stem cells. However the number of subjects was too small to draw definitive conclusions. No treatment associated adverse effects were noted.

1. Tomita, S., et al., Autologous transplantation of bone marrow cells improves damaged heart function. Circulation, 1999. 100(19 Suppl): p. II247-56.

2. Barile, L., et al., Bone marrow-derived cells can acquire cardiac stem cells properties in damaged heart. J Cell Mol Med, 2009.

3. Krause, U., et al., Intravenous delivery of autologous mesenchymal stem cells limits infarct size and improves left ventricular function in the infarcted porcine heart. Stem Cells Dev, 2007. 16(1): p. 31-7.

Stem cells that make blood are heavily concentrated in the bone marrow. These cells are called "hematopoietic stem cells". When patients with leukemia are given a bone marrow transplant, they first receive high doses of radiation and chemotherapy in order to kill both the leukemic cells, as well as the healthy blood cells in the bone marrow. Subsequently the patients are given healthy bone marrow from a patient that has been matched immunologically. The new bone marrow contains high numbers of stem cells that take over the task of making new blood cells for the body. In some situations the leukemia comes back, however a bigger cause of mortality is when the blood cells made by the new bone marrow start attacking the recipient. This is a condition called graft versus host.

One of the advancements in bone marrow transplantation was the use of stem cells collected from the blood instead of the bone marrow. While under normal circumstances there are very little hematopoietic stem cells circulating in the blood, it was observed many years ago that after administration of certain compounds, the number of stem cells in the blood increases. This led scientists to try to find agents that can be used in patients that make stem cells leave bone marrow and enter circulation. There are three reasons why this would be important. Firstly, the process of extracting bone marrow from donors is very difficult. It involves sometimes more than 30 punctures into the hip bone. Secondly, there is some evidence that when the stem cells are collected from the blood, they have less potential to stimulate graft versus host disease. Thirdly, outside of the context of transplantation, it is known that bone marrow stem cells have ability to accelerate healing of tissues. Thus if there was a drug that could induce stem cells to leave the bone marrow and enter circulation, this drug would have many benefits.

The first stem cell mobilizer to be approved was granulocyte colony stimulating factor (G-CSF). This is a protein that is made by many cells in the body, especially by cells of the immune system. G-CSF specifically tells the bone marrow cell to make more granulocytes, these are cells that fight infections. In the process of infection, cells of the immune system called macrophages, start to produce G-CSF in response to bacteria and cause production of granulocytes which can then go and fight the bacteria. Interestingly, it was found that G-CSF also would instruct the bone marrow stem cells to exit the bone marrow and enter circulation.

This led to a variety of studies demonstrating that G-CSF "mobilized" stem cells can be collected from the blood of donors and used as an alternative to harvesting of donor bone marrow. In the majority of hospitals that perform transplants, donor collection is now performed by mobilization of stem cells.

Studies have reported that stem cells mobilized by G-CSF appear to have some beneficial effects in patients who have had heart attacks. Other studies have shown that stem cells mobilized by G-CSF may help patients with heart failure due to poor blood supply to the heart. For example, Maier et al. published a paper (Myocardial salvage through coronary collateral growth by granulocyte colony-stimulating factor in chronic coronary artery disease: a controlled randomized trial. Circulation. 2009 Oct 6;120(14):1355-63) in which 52 patients suffering from coronary artery disease were given either placebo or G-CSF for 2 weeks. Increases in the blood supply to the heart, and heart function were observed in the treated patients.

Currently G-CSF sells more than a billion dollars a year for use in a variety of diseases. Since the original patents on G-CSF have expired, there has been a great interest in the development of other stem cell mobilizers. However, to develop newer drugs that cause mobilization, it may be worthwhile to discuss the mechanisms by which G-CSF induces this process. It is known that in transplantation of stem cells, that the recipient can receive stem cells intravenously, but somehow they home to the bone marrow. This homing mechanism is mediated by the protein stromal derived factor (SDF)-1, which is made at a stable rate by the other cells in the bone marrow that are not stem cells. The hematopoietic stem cells recognize concentrations of SDF-1 based on receptors called CXCR-4. When G-CSF is administered, numerous biochemical pathways are activated that seem to converge, at least in part, to disrupting the interaction between the SDF-1 made by the bone marrow and the CXCR-4 that is on the stem cells.

The company Anormed recognized the importance of this interaction and started making chemical drugs that would block it. As we stated, G-CSF causes a variety of biological effects, however, by selectively targeting the essential interaction, the ability to increase mobilization should theoretically be more potent. Indeed, Anormed developed the drug Mozobil, which appears to be 10-100 times more potent than G-CSF at mobilizing stem cells, and was sold to Genzyme in a deal worth half a billion dollars. Mozobil received FDA approval and is currently used alone or sometimes in combination with G-CSF.
Recognition of the importance of the SDF-1-CXCR4 interaction led the company NOXXON to develop drugs to target this. However, unlike Anormed, which used conventional small molecules, NOXXON used a new technology called Aptamers, which are nucleic acids that can be engineered to specifically block interactions between proteins. The process of generating aptamers to target proteins involves selection in vitro, which can be accomplished at a more rapid rate as compared to what can be done for small molecules.

Today NOXXON announced that is has successfully administered its NOX-A12 aptamer-based mobilizer to healthy volunteers as part of a Phase I clinical trial. Usually the purpose of a Phase I trial is to determine the distribution of a drug in the human body, and to test for possible adverse effects. The dose chosen from a Phase I is then used to conduct Phase II studies in which biological effect is tested. The NOX-A12 trial was conducted in Germany with the approval of the Clinical Trial Application by the Federal Institute for Drugs and Medical Devices (Bundesinstitut für Arzneimittel und Medizinprodukte, BfArM). The study is evaluating effects in 42 volunteers with the aim of assessing efficacy in patients with multiple myeloma or non-Hodgkin’s lymphoma in a Phase II trial that is planned for mid 2010. The company states that it plans to obtain marketing approval by 2014. Marketing approval for a drug is granted after 2 double blind, placebo controlled, Phase III studies are performed in which the primary endpoints show a statistically significant improvement over placebo.

The choice of multiple myeloma or non-Hodgkin’s lymphoma as conditions for evaluating NOXA-A12 may be due to the high incidence of patients with these conditions who are poor mobilizers. In these conditions, part of the protocols used clinically, involve mobilizing the bone marrow, administration of chemotherapy, and subsequent reintroduction of the bone marrow into the body.

There are several types of stem cell therapy that are in development. They can be broadly broken down into cells that come from the same patient, called autologous, and cells that derived from another source, called allogeneic. Autologous stem cells have the advantage not causing worries regarding immune rejection. Unfortunately, in many conditions that require stem cell therapy, such as peripheral artery disease, or coronary heart disease, the original stem cell pool in the patient is depleted. This is because on the one hand the body is constantly using the stem cells to try to heal itself, and on the other hand, there is an underlying inflammation in the conditions mentioned that suppress stem cell activity. Therefore, in some situations it is better to use "fresh" stem cells from another donor.

Mesenchymal stem cells can be extracted from bone marrow, fat, and several other sources. In contrast to the current dogma (which appears to be scientifically incorrect) that stem cells that make blood can not be transplanted without immune suppression, the current thinking for mesenchymal stem cells is that immune suppression is not needed when they are transplanted. Part of the reason for this is that mesenchymal stem cells have been published in many papers to actually "immune modulate". In other words, mesenchymal stem cells appear to have the ability to reprogram the immune system so as to not destroy them, but at the same time they allow the immune system to continue performing its usual function of destroying pathogens.

In a recent paper (Chin et al. Cryopreserved mesenchymal stromal cell treatment is safe and feasible for severe dilated ischemic cardiomyopathy. Cytotherapy. 2009 Nov 2) the use of mesenchymal stem cells was evaluated after the cells have been stored frozen. The importance of this is that an ideal stem cell treatment would be a "universal donor" stem cell "drug" in that cells could be shipped to the point of care frozen and used in the convenience of a doctor’s office, without the need for expensive equipment that is currently a requirement in the medical practice of stem cell therapy.

In the publication the scientists treated three patients with dilated cardiomyopathy with mesenchymal stem cells that were previously frozen. Stem cells were injected directly into the heart muscle as the patients were undergoing coronary artery bypass surgery. All three patients responded better than what would have been expected had they undergone surgery alone in terms of cardiac function, ejection volume, and reduction of scarring. Although the study was uncontrolled and therefore efficacy data is not solid, the fact that the procedure was performed safely, without adverse effects at 1-year follow-up suggests that more studies need to be performed to evaluate efficacy of this approach.

Cord blood is known to contain large numbers of stem cells. Currently, it is used as an alternative to bone marrow transplantation for certain conditions. Advantages of cord blood over bone marrow include the fact that it does not need to be as closely matched between donor and recipient as bone marrow does, and additionally, because the cord blood stem cells are younger, theoretically they should be more potent at re-establishing production of blood cells after a transplant.

In conventional cord blood transplants, which are usually performed for conditions such as leukemias, the immune system of the recipient is destroyed in order to allow the donor cord blood cells to engraft. Additionally, by providing large doses of chemotherapy, not only is the recipient immune system destroyed but many of the leukemic cells are also killed. The widespread use of cord blood in treatment of leukemias has led to a dogma being generated that cord blood transplants are useless when used for other treatments. Essentially, most hematologists believe that if a cord blood transplant is performed without prior treatment of the recipient with chemotherapy/immune suppressants, then one of two things will happen. The cord blood cells will either attack the recipient, a process called graft versus host disease, or conversely, the recipient immune system cells will destroy the cord blood cells, a process called host versus graft.

The current dogma, however, appears to be wrong. Firstly, cord blood administration has been performed in thousands of patients without adverse effects in absence of immune suppression. Why would someone administer cord blood for reasons besides stem cell transplants? Originally, cord blood was used as an alternative source of blood when adult blood shortages existed. The unique property of cord blood is that it contains fetal hemoglobin, which is much more effective at transporting oxygen than adult hemoglobin. Secondly, human cord blood has been used without suppression of the immune system in animal studies for conditions such as type I diabetes, ALS, and Parkinson’s Disease. The apparent ability of cord blood to induce therapeutic effects suggests that the cells were not rejected. Scientists at the Institute for Cellular Medicine have used cord blood derived cells in treatment of heart failure, which was described in a publication (Ichim et al. Placental mesenchymal and cord blood stem cell therapy for dilated cardiomyopathy. Reprod Biomed Online. 2008 Jun;16(6):898-905). The scientific rational for how cord blood stem cells may be administered without graft versus host or host versus graft reactions is provided in a paper written by the Institute for Cellular Medicine and Medistem, which is freely available at http://www.translational-medicine.com/content/5/1/8 .

A paper published today (Finney et al. Umbilical cord blood-selected CD133(+) cells exhibit vasculogenic functionality in vitro and in vivo. Cytotherapy. 2009 Nov 2.) from the Mary Laughlin’s group describes the use of cord blood cells in creation of new blood vessels. Several conditions would benefit from the creation of new blood vessels, for example, in diseases such as ischemic heart disease or peripheral artery disease, the body tries to make new blood vessels in order to compensate for occlusion in the existing blood vessels. Unfortunately, the body cannot make enough new blood vessels to keep up with demand. If cord blood stem cells could be used to make new blood vessels, this treatment would have numerous applications.

In the publication, the researchers describe that cord blood contains a higher number of cells expressing the CD133 marker. These are cells that on the one hand can make new blood cells (called hematopoietic stem cells), but have also been postulated by others to have the ability to generate the cells that line the blood vessels (endothelial cells).

By culturing purified cord blood CD133 cells with existing blood vessel cells outside of the body, the scientists found that the CD133 cells would increase the rate at which the blood vessel cells multiplied. Using this knowledge, the next question was whether the CD133 cells could stimulate formation of new blood vessels in animal models.

One of the major arteries that feeds the leg, called the femoral artery, was blocked in order to mimic conditions of decreased blood flow. Usually this results decreased function of the leg and death of muscle tissue. Administration of CD133 cells was shown to stimulate new blood vessel formation, preserve leg function, and decrease the amount of cell death in the digits of the mouse limbs. Activity of CD133 cells derived from cord blood seemed to be higher than that of bone marrow derived cells.

These studies suggest that cord blood derived stem cells may be therapeutically useful in conditions requiring formation of new blood vessels. In fact, a company called Medistem actually has filed patents on the use of drugs already approved for other indications in order to modify umbilical cord blood to increase potency in the stimulation of new blood vessels in patients with critical limb ischemia, an advanced form of peripheral artery disease.