Genetic Switch to Making More Blood-Making Stem Cells Found


A coalition of stem cell scientists, co-led in Canada by Dr. John Dick, Senior Scientist, Princess Margaret Cancer Centre, University Health Network (UHN) and Professor, Department of Molecular Genetics, University of Toronto, and in the Netherlands by Dr. Gerald de Haan, Scientific Co-Director, European Institute for the Biology of Ageing, University Medical Centre Groningen, the Netherlands, have uncovered a genetic switch that can potentially increase the supply of stem cells for cancer patients who need transplantation therapy to fight their disease.

Their findings were published in the journal Cell Stem Cell and constitute proof-of-concept experiments that may provide a viable new approach to making more stem cells from umbilical cord blood.

“Stem cells are rare in cord blood and often there are not enough present in a typical collection to be useful for human transplantation. The goal is to find ways to make more of them and enable more patients to make use of blood stem cell therapy,” says Dr. Dick. “Our discovery shows a method that could be harnessed over the long-term into a clinical therapy and we could take advantage of cord blood being collected in various public banks that are now growing across the country.”

Currently, all patients who require stem cell transplants must be matched to an adult donor. The donor and the recipient must share a common set of cell surface proteins called “human leukocyte antigens” HLAs. HLAs are found on the surfaces of all nucleated cells in our bodies and these proteins are encoded by a cluster of genes called the “Major Histocompatibility Complex,” (MHC) which is found on chromosome six.

Map of MHC

There are two main types of MHC genes: Class I and Class II.

MHC Functions

Class I MHC contains three genes (HLA-A, B, and C). The three proteins encoded by these genes, HLA-A, -B, & -C, are found on the surfaces of almost all cells in our bodies. The exceptions are red blood cells and platelets, which do not have nuclei. Class II MHC genes consist of HLA-DR, DQ, and DP, and the proteins encoded by these genes are exclusive found on the surfaces of immune cells called “antigen-presenting cells” (includes macrophages, dendritic cells and B cells). Antigen-presenting cells recognize foreign substances in our bodies, grab them and, if you will, hold them up for everyone to see. The cells that usually respond to antigen presentation are immune cells called “T-cells.” T-cells are equipped with an antigen receptor that only binds antigens when those antigens are complexed with HLA proteins.

If you are given cells from another person who is genetically distinct from you, the HLA proteins on the surfaces of those cells are recognized by antigen-presenting cells as foreign substances. The antigen-presenting cells will them present pieces of the foreign HLA proteins on their surfaces, and T-cells will be sensitized to those proteins. These T-cells will them attack and destroy any cells in your body that have those foreign HLA proteins. This is the basis of transplant rejection and is the main reason transplant patients must continue to take drugs that prevent their T-cells from recognizing foreign HLA proteins as foreign.

When it comes to bone marrow transplantations, patients can almost never find a donor whose HLA surface proteins match perfectly. However, if the HLA proteins of the donor are too different from those of the recipient, then the cells from the bone marrow transplant attack the recipient’s cells and destroy them. This is called “Graft versus Host Disease” (GVHD). The inability of leukemia and lymphoma and other patients to receive bone marrow transplants is the unavailability of matching bone marrow. Globally, many thousands of patients are unable to get stem cell transplants needed to combat blood cancers such as leukemia because there is no donor match.

“About 40,000 people receive stem cell transplants each year, but that represents only about one-third of the patients who require this therapy,” says Dr. Dick. “That’s why there is a big push in research to explore cord blood as a source because it is readily available and increases the opportunity to find tissue matches. The key is to expand stem cells from cord blood to make many more samples available to meet this need. And we’re making progress.”

Umbilical cord blood, however, is different from adult bone marrow. The cells in umbilical cord blood are more immature and not nearly as likely to generate GVHD. Therefore, less perfect HLA matches can be used to treat patients in need of a bone marrow transplant. Unfortunately, umbilical cord blood has the drawback of have far fewer stem cells than adult bone marrow. If the number of blood-making (hematopoietic) stem cells in umbilical cord blood can be increased, then umbilical cord blood would become even more useful from a clinical perspective.

There has been a good deal of research into expanding the number of stem cells present in cord blood, the Dick/de Haan teams took a different approach. When a stem cell divides it produces a large number of “progenitor cells” that retain key properties of being able to develop into every one of the 10 mature blood cell types. These progenitor cells, however, have lost the critical ability to self-renew.

Dick and his colleagues analyzed mouse and human models of blood development, and they discovered that a microRNA called miR-125a is a genetic switch that is on in stem cells and controls self-renewal, but gets turned off in the progenitor cells.

“Our work shows that if we artificially throw the switch on in those downstream cells, we can endow them with stemness and they basically become stem cells and can be maintained over the long-term,” says Dr. Dick.

In their paper, Dick and de Haan showed that forced expression of miR-125 increases the number of hematopoietic stem cells in a living animal. Also, miR-125 induces stem cell potential in murine and human progenitor cells, and represses, among others, targets of the MAP kinase signaling pathway, which is important in differentiation of cells away from the stem cell fate. Furthermore, since miR-125 function and targets are conserved in human and mouse, what works in mice might very well work in human patients.

graphical abstract CSC_v9

This is proof-of-concept paper – no human trials have been conducted to date, but these data may be the beginnings of making more stem cells from banked cord blood to cure a variety of blood-based conditions.

Here’s to hoping.

Bilateral, Multiple, Intraspinal Stem Cell Injections are Safe for ALS


Jonathan Glass, professor of neurology at Emory University in School of Medicine, is the principal investigator of a phase 2 clinical trial that examined the safety of intraspinal injection of human spinal cord–derived neural stem cells in people with amyotrophic lateral sclerosis (ALS), or Lou Gehrig’s disease.

This clinical trial was not designed to determine whether the treatment was effective, which is odd given that the trial was a phase 2 trial. Glass and his collaborators noted that the transplanted stem cells did not slow down the progression of the disease. However, given that the trial was not designed to detect efficacy, it is difficult to draw any hard-and-fast conclusions.

ALS is a disorder in which the motor neurons of the brain and spinal cord degenerate. Motor neuron degeneration causes progressive loss of muscle control, which includes breathing and swallowing (leading to death). There are no treatments that can stop ALS.

“Though there were two serious complications related to the treatment, the level of acceptable risk for treating patients with ALS, where the prognosis is poor and treatments are limited, is arguably higher than that for more benign disorders,” said Dr. Glass.

In this study, 15 ALS patients who manifested their first signs and symptoms of the disease within two years of the start of the study, were treated at three different university hospitals.

The participants were divided into five treatment groups that received increasing doses of stem cells. This trial was an “open-label” trial, which means that the participants knew they were getting active stem cell treatments.

Participants received bilateral (both sides) injections into the cervical spinal cord between the C3 and C5 regions. The final group received injections into both the lumbar (L2-L4) and cervical cord through two separate surgical procedures.

Vertebral Column regions

The numbers of injections ranged from 10 to 40, and the number of cells injected ranged from two million to 16 million. Because of the large range of injections and stem cells injected, determining the safety of these treatments was probably more important that the efficacy of the treatments.

During the nine months of follow-up, patients were assessed for side effects from the intraspinal injections and progression of the disease, according to the functional rating scale. Most of the side effects were related to temporary pain associated with surgery and to medications that suppress the immune system.

Two people developed serious complications related to the treatment. One patient developed spinal cord swelling that caused pain, sensory loss and partial paralysis, and another patient developed central pain syndrome; a neurological condition caused by damage to or dysfunction of the central nervous system (CNS), which includes the brain, brainstem, and spinal cord. This syndrome can be caused by stroke, multiple sclerosis, tumors, epilepsy, brain or spinal cord trauma, or Parkinson’s disease.

The participants’ functioning was compared to three historical control groups, and there was no difference in how fast the disease progressed between those
who received stem cells and those who did not. This is a significant finding because injecting cells into the spinal cord might actually accelerate the progression of the disease. However, this study seemed to show that 10-40 injections into the spinal do not affect the progression of ALS.

However, Glass cautioned that no conclusions can be draw about effectiveness of the treatment from such a small, non-blinded, non-placebo-controlled study.

“This study was not designed, nor was it large enough, to determine the effectiveness of slowing or stopping the progression of ALS. The importance of this study is that it will allow us to move forward to a larger trial specifically designed to test whether transplantation of human stem cells into the spinal cord will be a positive treatment for patients with ALS,” Dr. Glass said.

These results were published in Jonathan D. Glass et al., “Transplantation of spinal cord–derived neural stem cells for ALS: Analysis of phase 1 and 2 trials,” Neurology, June 2016 DOI:10.1212/WNL.0000000000002889.