Are there stem cell treatments available for blood disorders?
Yes. Hematopoietic stem cell transplants from bone marrow, umbilical cord and peripheral blood are approved by Health Canada and the FDA to help treat a variety of different blood-based cancers including multiple myeloma, leukemia and lymphoma, and other blood disorders, including anemia, thalassemia and severe combined immune deficiency or SCID.
For more about stem cell clinical trials for blood disorders click here. (For printed version: http://goo.gl/jfVZe)
How close are we? What do we know about blood disorders?
- The blood is composed of many different cells and disease can strike any of them.
- Hematopoietic stem cells live in the bone marrow and churn out upwards of 7 billion cells every day to replenish the supply of red and white blood cells exhausted through wear and tear.
- Hematopoietic stem cells make either myeloid cells (for example, red blood cells that carry oxygen to the tissues) or lymphoid cells (B and T cells that fight specific infections in the body).
- Blood diseases are typically caused by congenital or inborn deficiencies (for example, sickle cell anemia), immune deficiencies (SCID), autoimmune mechanisms (immune thrombocytopenia purpura), and cancer (leukemia, myeloma, lymphoma).
- Standard treatments include blood transfusions, drugs to stimulate blood cell production, and hematopoietic stem cell transplantation to supply new, healthy red and white blood cells after cytotoxic (chemotherapy and radiation) treatment.
- Hematopoietic stem cell transplantation is an aggressive form of therapy and although it can be used to successfully treat many blood disorders, including thalassemia, SCID, multiple myeloma, leukemia and lymphoma, more than 50%of patients are still not cured of their disease.
- Researchers are actively investigating the role played by cancer stem cells in disease relapse.
How can stem cells play a part?
Hematopoietic stem cells are uniquely positioned as a cell therapy for blood disorders because their normal job in the body is to make all the red and white blood cells that populate the bone marrow and blood. Of all stem cells currently studied, hematopoietic stem cells from the bone marrow have the longest history of clinical use, dating back to the 1950s when a transplant was performed in an attempt to cure a lethal form of leukemia. In the 1970s, scientists discovered that hematopoietic stem cells were also present in umbilical cord blood as well as peripheral blood. Years of research have paid off and hematopoietic stem cell transplantation is now routinely used to treat many blood disorders. Scientists continue to improve transplantation methods and to compare the benefits hematopoietic stem cells from bone marrow, umbilical cord blood and peripheral blood. As the field moves forward, scientists are also learning more about cancer stem cells and developing more precise ways to study blood disorders.
Are there lots of groups working on developing a stem cell therapy?
There are countless research teams around the globe working to develop stem cell therapies for blood disorders and to learn more about cancer stem cells. Their common goals are to identify which stem cells would be the best therapies for blood disorders and what role cancer stem cells play in initiating disease and contributing to relapse.
Canadian scientists have played an illustrious role in stem cell research in blood diseases. Drs. James Till and Ernest McCulloch were the first to prove the existence of stem cells in the 1960s. They also defined the fundamental character of stem cells as having the ability to self-renew, forming new stem cells, and to differentiate, making specialized cells. Their experiments set the stage for bone marrow transplantation for treating bone marrow failure in patients with blood cancers and aplastic anemia. By the late 1970s, Till and McCulloch’s studies on leukemia paved the way for the idea that a small number of cancer stem cells in a tumour contribute to its formation, which led to the discovery of cancer stem cells in leukemia by Canadian scientist Dr. John Dick. These cells are thought to be partially responsible for the recurrence of cancer following chemo and radiation therapies, so killing them might lead to longer remissions, if not cures.
Stem cell research for blood diseases is unfolding along a number of different avenues. In the case of hematopoietic stem cell transplantation, pre-clinical research efforts have been translated successfully into clinical therapies for rescuing some patients with blood disorders, and new methods for controlling the side-effects are constantly being developed. Clinical trials comparing alternative sources of hematopoietic stem cells and testing other types of stem cells are also underway, as is basic research on targeting cancer stem cells.
What research is underway?
The road to finding new stem cell therapies for blood disorders is paved with many challenges that will take time to overcome. But the wealth of information generated from labs around the globe is converging to help with the transition from basic research to the clinic. The results are very promising and in time may point to new stem cell therapies that not only cure blood diseases but also target disease relapse.
Current research using bone marrow stem cells
In the past 40 years, transplants of hematopoietic stem cells from bone marrow have been the most widely used of all stem cell therapies. Transplants can be autologous (from the patient) or allogeneic (from a donor). Autologous transplants circumvent the problem of graft rejection but, for reasons that may include age, poor health or bone marrow disorders, not all patients are candidates. The biggest stumbling blocks to the more widespread use of allogeneic transplants are the availability of suitable donors and the need to match a donor graft as precisely as possible to the recipient.
Hematopoietic stem cell transplantation is an aggressive therapy and despite its success for treating many blood disorders, upwards of 50% of patients are still not cured of their disease. In addition to infectious complications and the problem of graft versus host disease, where the T cells in the allogeneic graft attack the recipient’s tissues, some researchers theorize that a small population of cancer stem cells may be the reason that initial treatment successes so often end in relapse.
In addition to studying cancer stem cells, scientists are also exploring ways to use gene therapy to help people who have hematopoietic stem cell disorders. Gene therapy has been used with some success to treat immune deficiencies such as SCID but there is still a long way to go before it becomes the standard of care for treating the vast array of blood disorders. Scientists are striving to perfect the process first animal models of blood diseases. They are working out the conditions for growing hematopoietic stem cells that make the corrected genes of interest more efficiently, and developing gene therapy methods that don’t cause downstream cancers, such as leukemia.
Current research using umbilical cord blood stem cells
As home to a variety of different types of stem cells, umbilical cord blood has tremendous potential as a cell therapy and is now routinely used as an alternative to bone marrow transplantation. The first cord blood transplant occurred between a brother and sister in 1988 to treat Fanconi’s anemia, a genetic condition that tends to lead to myeloid leukemia and bone marrow failure. This transplant was matched but subsequent efforts showed that it was also possible to transplant mismatched cord blood, with less graft versus host disease and the same survival benefit as mismatched bone marrow transplants.
Cord blood has many advantages compared with other stem cell sources. It is easy to obtain without risk to the donors, there are less stringent matching requirements, less chance of transmitting infectious viruses, and no ethical issues associated with its use. Cord blood is also very easy to “tissue type” and once frozen it can be quickly thawed and made available when it is needed. Today, the practice of using cord blood transplants as a source of hematopoietic stem cells has saved countless lives for which no matched bone marrow is available.
The collection of cord blood in public banks worldwide has reached over 550,000 cord blood units and facilitated over 20,000 cord blood transplants for treating various blood diseases. The major limitation with cord blood transplants is that the numbers of stem cells per cord is only enough to treat a child or small adult. Scientists are looking for ways around this by trying to expand the numbers of stem cells from cord blood, by doing double cord blood transplants, and by testing alternative routes of injection.
Current research using peripheral blood stem cells
Low levels of hematopoietic stem cells can be found in the blood of healthy individuals. These are called peripheral blood stem cells. In the 1970s, scientists discovered that peripheral blood stem cells are also present in the blood of patients with myeloid leukemia. Through the 1980s, they learned that they could harvest peripheral blood stem cells in patients with leukemia, lymphoma, myeloma and solid tumours, and use the stem cells as autologous transplants to boost blood production. That led them to ask whether peripheral blood stem cells could also be used as allogeneic transplants.
Today, peripheral blood stem cells are routinely used for this purpose, and a growing number of clinical trials are comparing matched peripheral blood and matched bone marrow allogeneic transplants. While engraftment is faster using peripheral blood stem cell transplants, the higher levels of graft versus host disease is still a concern. However, the practicality of easily harvesting peripheral blood is definitely worth continued research.
Current research using induced pluripotent stem cells
In 2006, Dr. Shinya Yamanaka showed he could turn back the clock on adult skin cells and reprogram them to a younger, embryonic-like state. The cells are called pluripotent because they are no longer locked into making only one cell type but instead can produce a variety of different cells. (In Latin, ‘pluripotent’ means ‘very many’ and ‘having power’.)
Since the technology was first developed, scientists now have methods in place for turning induced pluripotent stem cells or iPS cells from skin into a variety of variety of specialized cells, including blood. Scientists can also use iPS cells in the lab to create diseased cells and these are excellent tools for understanding blood diseases and screening candidate drugs. The combination of gene therapy and iPS technology is also very promising, and it was with great excitement that scientists found that genetically corrected skin cells from patients with Fanconi’s anemia could be reprogrammed into patient-specific iPS cells that could go on to make healthy red and white blood cells in the laboratory. They were also able to successfully correct a genetic blood deficiency in mice using the iPS/gene therapy combination.
Despite these early successes, scientists are proceeding with extreme caution as there are a number of barriers to overcome prior to safely using iPS technology in patients with blood diseases.
Further reading on blood disorders
Readers may wish to peruse the recommended sites and articles below for more information about blood disorders and the possible applications of stem cells to treat these diseases.