In an article published in the Journal of Neuroinflammation (2015 12(1):241), Dr. Reint Jellema, in collaboration with scientists from Maastricht University, Maastricht University Medical Center and Máxima Medical Center Veldhoven in the Netherlands, and Athersys scientists described the results of experiments designed to evaluate the potential for Multipotent Adult Progenitor Cells (MAPCs) to stroke patients.
In the series of experiments described in this publication, Jellema and others examined pre-term sheep that suffered strokes while still in the womb. Such injuries in human babies are one of the main causes of cerebral palsy. In the case of these pre-term sheep, the intravenous administration of MAPCs reduced both the number and duration of seizures compared to placebo-treated animals.
Seizures commonly follow strokes in new born babies and these strokes usually cause several detrimental neurodevelopmental outcomes. MAPC treatment significantly reduced inflammation in the injured brain. The implanted cells reduced activation and proliferation of immune cells in the brain. In general the immune response after the onset of the stroke was tamped down.
This paper provides further evidence that multipotent adult progenitor cells (MAPCs) have can provide benefit following strokes. Such injuries are caused by oxygen deprivation to the brain before or during birth and are a leading cause of cerebral palsy.
“This study in a large animal model of pre-term hypoxic-ischemic injury further demonstrates the potential for MultiStem therapy to provide benefit to patients suffering from an acute neurological injury,” said Dr. Robert Mays, Vice President and Head of Neuroscience Research at Athersys. “These results are consistent with those from previous studies testing our cells in rodent models of hypoxic ischemia and ischemic stroke, and confirm our previous findings supporting the biological mechanisms through which MAPC treatment provides benefit following acute neurological injury. The results strengthen the biologic rationale for our ongoing clinical and preclinical research in ischemic stroke and hypoxic-ischemic injury, as well as traumatic brain and spinal cord injury.”
A study at the Texas Health Science Center has shown that stem cell treatments that quash inflammation soon after traumatic brain injury (TBI) might also offer lasting cognitive gains.
TBI sometimes causes severe brain damage, and it can also lead to recurrent inflammation of the brain. This ongoing inflammation can extend the damage to the brain. Only a few drugs help (anti-inflammatory drugs for example). Up to half of patients with serious TBI need surgery, but some stem cells like a sub group of mesenchymal stem cells called multipotent adult progenitor cells (MAPCs) can reduce short-term inflammation, and induce functional improvement in mice with TBI. Unfortunately, few groups have gauged the long-term effects of MAPCs on TBI.
In an article that appeared in the journal Stem Cells Translational Medicine, a research team led by the Director of the Children’s Program in Regenerative Medicine, Charles Cox, reported the use of human MAPCs in mice that had suffered TBI.
In this study, Cox and his colleagues infused MAPCs into the bloodstream of two groups of mice 2, and 24 hours after suffering a TBI. The first group of mice received two million cells per kilogram, and mice in the other group received an MAPC dose five times stronger.
Four months after MAPC administration, those mice that had received the stronger dose continued to experience less brain inflammation and better cognition. Spatial learning was increased and motor deficits had decreased.
According to Cox, the intravenously administered MAPCs did not cross the blood/brain barrier. Since immune cells can cross the blood/brain barrier for a short period of time after a TBI and cause autoimmunity, this result shows that the MAPCs are quelling inflammation through “paracrine” mechanisms (paracrine means that molecules are secreted by the cells and these secreted molecules elicit various responses from nearby cells). Cox made this clear: “We spent 18 months looking for them in the brain. There was little to no engraftment there.”
Rather than entering the brain, the MAPCs “set up shop in the spleen, a giant reservoir of T and B cells. The MAPCs change the spleen’s output to anti-inflammatory cells and cytokines, which communicate with immune cells in the brain—microglia—and change their response to injury from hyper-to-anti- inflammatory. The cells alter the innate immune response to injury. We have shown this in a sequence of papers.”
University of Cambridge neurologist, Stefano Pluchino, has worked with immune regulatory stem cells. Pluchino said that Cox’s study shows a “good dose response” on disability and behavior “after hyperacute, or acute, intravenous injection of MAPCs.” However, Pluchino noted that the description of the effects of MAPCs on microglia (white blood cells in the brain that gobble up foreign matter and cell debris) is “speculative.” Pluchino continued: “It is not clear whether these counts have been done on the injured brain hemisphere, and whether MAPC effects were observable on the unaffected hemisphere. The distribution and half-life of these MAPCs is not clear” and has never been demonstrated convincingly in Athersys papers (side note: Athersys is the company that isolates and grows the human MAPCs). “It is also not clear if effects in the Cox study were a ‘false positive,’ secondary to a paradoxical immune suppression the xenograft modulates.” That is, a false positive could occur because human cells in animal bodies rouse immune reactions. “It is not clear where in the body these MAPCs would work, either out or into the injured brain.” Additionally the mechanism by which these cells act does not seem to be clear, according to Pluchino.
But, Pluchino added: “Athersys is already in clinic with MAPCs in graft vs. host disease, myocardial infarction, stroke, progressing towards a phase I/II clinical trial in multiple sclerosis, and completing the pre-clinical work in traumatic brain and spinal cord injuries. Everything looks great. The company is solid. The data is convincing in terms of behavioral and pathological analyses. But the points I have raised are far from clarified.”
Cox admitted that Pluchino’s points are valid. He pointed out that human cells were used in rodents, since the FDA wants pre-clinical studies in laboratory animals in order to first evaluate the safety and efficacy of the exact cells to be used in a proposed therapy before they head to the clinic. “As we are not seeking engraftment of these cells, and would not plan to immunosuppress a trauma patient, we have not pursued animal models that use immunosuppression. Our study was designed with translationally relevant end-points, recognizing the limitations of not having a final mechanism of action determined. The growing consensus is there are many mechanism(s) of action in cell therapies.”
Cox also agreed that the suggested effects of MAPCs on microglia, “is not truly a proof of mechanism.” However, Cox and his co-workers have developed a protocol that can potentially more accurately quantify microglia in mice. “We ultimately plan more mechanistic studies to define endogenous microglia versus infiltrating microglia and the effects of various cell therapies. “
Additionally, Cox also said that: “We have published work showing the majority of acutely infused MSCs and MAPCs are lodged in the lung after intravenous delivery. This was an acute study in non-injured animals, but others have shown similar data.” In another study, Cox’s research group showed that the cells cluster in the spleen, which corroborates work by other research groups that have used umbilical cord cells to treat stroke.
Finally, Cox disagrees that the suppression of immune cell function in animals by human cells is appropriately characterized as “a false positive.” Cox explained that the infused cells induce a “modulation of the innate immune response, and typically, the immune rejection of a transplant is associated with immune activation, not suppression. So it well may be a ‘true positive.’”
In order for MAPCs to make to the clinical trial stage, Cox will need to investigate the mechanisms by which MAPCs suppress inflammation and if their purported effects on microglia in the central nervous system are real. He will also need to show that these cells work in other types of laboratory animals beside mice. Rats will probably be next, and after that, my guess is that the FDA would allow Athersys to apply for a New Drug Application.
Research led by Charles Cox at the University of Texas Health Science Center has shown that stem cell therapy given during the critical time window after traumatic brain injury promotes lasting cognitive improvement. These experiments, which were published in the latest issue of the journal Stem Cells Translational Medicine, provide a pre-clinical model for experiments with larger animals.
After the brain has suffered a traumatic injury, there are few treatment options. Damage to the brain can be severe, and can also cause ongoing neurological impairment. Approximately half of all patients with severe head injuries need surgery to remove or repair ruptured blood vessels or bruised brain tissue.
In this work from Cox’s lab, stem cells from bone marrow known as multipotent adult progenitor cells (MAPCs) were used. MAPCs seem to be a subpopulation of mesenchymal stem cells, and they have a documented ability to reduce inflammation in mice immediately after traumatic brain injury. Unfortunately, no one has measured the ability of MAPCs to improve the condition of the brain over time.
Cox, Distinguished Professor of Pediatric Surgery at the UTHealth Medical School and in collaboration with the Children’s Fund, Inc., injected two groups of brain-injured mice with MAPCs two hours after injury and then once again 24 hours later. One group received a dose of 2 million cells per kilogram and the other a dose five times greater.
After four months, those mice that had received the stronger dose not only continued to have less inflammation, but they also showed significant gains in cognitive function. Laboratory examination of the brains of these rodents confirmed that those that had received the higher dose of MAPCs had better brain function than those that had received the lower dose.
According to Cox, “Based on our data, we saw improved spatial learning, improved motor deficits and fewer active antibodies in the mice that were given the stronger concentration of MAPCs.” Cox also indicated that this study indicates that intravenous injection of MAPCs might very well become a viable treatment for people with traumatic brain injury in the future.
Cox, who directs the Pediatric Surgical Translational Laboratories and Pediatric Program in Regenerative Medicine at UTHealth, is a leader in the field of autologous and blood cord stem cells for traumatic brain injury in children and adults. Results from a phase 1 study were published in a March 2011 issue of Neurosurgery, the journal of the Congress of Neurological Surgeons. Cox also directs the Pediatric Trauma Program at Children’s Memorial Hermann Hospital.
Solid organ transplantation is a procedure that has saved untold millions of lives. Unfortunately, the tendency for an organ to be rejected by the immune system of the organ recipient is a formidable problem that is addressed in two ways. One of these is through tissue matching of the organ to the recipient. The other is through the use of immunosuppressive drugs that suppress the immune system. Neither one of these strategies is without caveats.
Tissue typing begins with a blood test to determine the organ recipient’s blood type. If the organ contains a blood type that is incompatible with the immune system of the organ recipient, the result will be catastrophic. Hyperacute rejection is the name given to organ rejection that occurs minutes to hours after the organ was transplanted. Hyperacute rejection occurs because the recipient has pre-existing antibodies in their body that recognizes and begins to destroy the graft. These antibodies can result from prior blood transfusions, multiple pregnancies, prior transplantation, or xenografts against which humans already have antibodies. Massive blood clotting within the capillaries of the organ clog the blood vessels and prevent perfusion of the graft with blood. The organ must come out or the patient will die.
Human cells have on their surfaces particular proteins that are encoded by genes located on the short arm of chromosome 6 called the major histocompatibility complex or MHC. the MHC genes encode human leukocyte antigens or HLAs. HLA proteins are extremely variable from person to person, and this seems to be the case because the more variation we have in our HLA proteins, the better job the immune system does recognizing foreign invaders.
Each individual expresses MHC genes from each chromosome. Therefore, your cells contain a mosaic of surface proteins, some of which are encoded by the HLAs encoded by the chromosome you inherited from your father and others of which are encoded by the chromosome your inherited from your mother.
The MHC molecules are divided into 2 classes. Class I molecules are normally expressed on all nucleated cells, but class II molecules are expressed only on the so-called “professional antigen-presenting cells” or APCs. APCs include cells that have names like dendritic cells, activated macrophages, and B cells. T lymphocytes only recognize foreign substances when they are bound to an MHC protein. Class I molecules present antigens from within the cell, which includes bits from viruses, tumors and things like that. Class II molecules present extracellular antigens such as extracellular bacteria and so on to a subclass of T cells called T helper cells, which express a molecule called “CD4” on their cell surface.
All this might seem very confusing, but it is vital to ensuring that the organ is properly received by the organ recipient. Some types of MHC are very different and will elicit robust immune responses against them, but others are not as different and can be rather well tolerated. How does the doctor which are which? Through three tests: 1) Blood type is the first one. If this does not match, you are out of luck; 2) lymphocytotoxicity assay in which blood from a patient is tested to determine if it reacts with lymphocytes from the blood of the donor. A positive crossmatch is a contraindication to transplantation because of the risk of hyperacute rejection. This is used mainly in kidney transplantation; 3) Panel-reactive antibody (PRA) screens in which the the serum of a patient is screened for antibodies against the lymphocytes from the donor. The presence of such antibodies is contraindicated for transplantation. Finally, there is a test that is not used a great called the mixed lymphocyte reaction test that uses lymphocytes from the blood of the organ donor and the organ recipient to see if they activate one another. This test takes a long time and can be difficult to interpret.
Once the patient receives the transplant, they are usually put on immunosuppressive drugs. These drugs include cyclosporine, tacrolimus, sirolimus, mycophenolate, and azathioprine. Each of these drugs has a boatload of side effects that range from hair loss, diabetes mellitus, nerve problems, increased risk of illness and tumors, and so on. None of these side effects are desirable, especially since the drug must be taken for the rest of your life after you receive the transplant.
Enter a new paper from University Hospital in Regensburg, Germany from the laboratory of Marc Dahkle that used particular stem cells from bone marrow to induce toleration of grafted heart tissue in laboratory animals without any drugs. This paper was published in Stem Cells Translational Medicine and is potentially landmark in what it shows.
In this paper, Dahkle and his colleagues used stem cells from the bone marrow known as multipotential adult progenitor cells or MAPCs. MAPCs have been thought to be a subtype of mesenchymal stem cell in the bone marrow because they have several cell surface markers in common. However, there are some subtle differences between these two types of cells. First of all, the MAPCs are larger than their mesenchymal stem cell counterparts. Secondly, MAPCs can be cultured more long-term, which increases the attractiveness of these cells for therapeutic purposes.
In this paper, the Dahkle group transplanted heart tissue from two unrelated strains of rats. Four days before the transplantation, the donor rats received an infusion of MAPCs into their tail veins. There were a whole slew of control rats that were used as well, but the upshot of all this is that the rats that received the MAPCs before the transplantation plus a very low dose of the immunosuppressive drug mycophenolate did not show any signs of rejection of the transplanted heart tissue. If that wasn’t enough, when the transplanted heart tissue was then extirpated and re-transplanted into another rat, those grafts that came from MAPC-treated rats survived without any drugs, but those that came from non-MAPC-treated rats did not.
Because control experiments showed that the rats treated with cyclosporine did not reject their grafts, Dahkle and others used this system to determine the mechanism by which MAPCs prevent immune rejection of the grafted tissue. They discovered that the MAPCs seem to work though a white blood cell called a macrophage. Somehow, the MAPCs signal to the macrophages to suppress rejection of the graft. If a drug (clodronate) that obliterates the macrophages was given to the rats with the MAPCs, the stem cells were unable to suppress the immunological rejection of the graft.
In this paper, the authors conclude that “When these data are taken together, our current approach advances the concept of cell-based immunomodulation in solid organ transplantation by demonstrating that third-party, adherent, adult stem cells from the bone marrow are capable of acting as a universal cell product that mediates long-term survival of fully allogeneic organ grafts.” Revolutionary is a good word for this findings of this paper. Hopefully, further pre-clinical trials will eventually give way to clinical trials in human patients that will allow human patients to have their lives saved by an organ transplant without the curse of taking immunosuppressive drugs for the rest of their lives.