2016 Stem Cell Conferences
By Ben Best
Clinical Trial of iPSCs
Shinya Yamanaka, MD, PhD (Director, Center for iPS Cell Research and Application, Kyoto University, Kyoto, Japan) was involved in the world's first clinical trial of iPSCs, which cost about a million dollars, was very time-consuming and only resulted in treatment for one patient. Dr. Yamanaka has concluded that for the foreseeable future, well HLA-matched iPSCs from donors must be used rather than iPSCs derived from the intended patient.1
Because HLAs differ so much between individuals, transplantation of an organ or tissue results in a strong immune system rejection in proportion to the HLA mis-match. But a reasonably good match of HLAs between an organ donor and an organ recipient can minimize the amount of immune suppressant drugs required. Close matching of three HLAs (HLA-A, HLA-B, and HLA-DR) have the strongest influence on whether a kidney transplant will be successful.2
Dr. Yamanaka wants to create banks of 140 different iPS Cell lines, which could provide a good match for 90% of the population of Japan (which is genetically very uniform). Each of the HLAs should be homozygous, meaning the same HLA type is inherited from both parents. To find the 140 ideal iPSC donors will require screening about 160,000 Japanese.3
Masayo Takahashi, MD, PhD (Project Leader, Retinal Regeneration, RIKEN Center for Developmental Biology, Kobe, Japan) conducted the world's first clinical trial using iPSCs for regenerative medicine. More than 7% of those over age 75 lose the ability to read or recognize faces due to degeneration of the macula of the retina in the eye.4 Dr. Takahashi used skin cells from two people with macular degeneration to create iPSCs, which she differentiated into retinal cells.5
There are no standards for differentiating in such a way as to ensure that the cells do not become cancerous in the process. So she did extensive testing of the cells on laboratory mice to ensure that there was no chance of cancer.6 She generated sheets of cells, rather than use an artificial scaffold,7 and transplanted the cells into the first patient from whom the cells had been derived. The transplant halted the macular degeneration and improved the patient's vision.5 One year after surgery there was no sign that any of the transplanted cells had become cancerous.8
But Dr. Yamanaka's team detected mutations in the second patient's iPSCs as Dr. Takahashi was preparing to transplant them. Although there was no definitive evidence that the mutations would become cancerous, in the interest of safety, there was no second transplant.5 Together, the two cases had cost about a million dollars, and had taken ten months ― mostly due to cautious measures taken to avoid the possibility of cancer. This convinced Dr. Yamanaka that patient-derived iPSC therapy is not currently practical.
Koji Eto, MD, PhD (Professor, Department of Clinical Application, Kyoto University, Kyoto, Japan) has worked on the derivation of platelets from iPSCs. Platelets are blood components found only in mammals, and which stop bleeding by adhering to blood vessel walls. Patients with deficient platelets rely on transfusions from donors, but these transfusions generally result in harmful immune system reactions.9 Platelets derived from iPSCs would avoid this immune system incompatibility. Dr. Eto has been perfecting methods to derive platelets from iPSCs, but his major problem has been that the number of platelets he is able to derive is too low to be clinically useful.10,11
Experiments with iPSCs
Hideyuki Okano, MD, PhD (Professor and Dean, School of Medicine, Keio University, Tokyo, Japan) has been working to derive neural stem cells from iPSCs that can be used to treat spinal cord injuries. In deriving neural stem cells from iPSCs, Dr. Okano has taken great care to prevent them from becoming cancerous.12
Despite iPSCs coming from the patient for whom the neural stem cells are intended, there is still danger that imperfections in the differentiation process can lead to immune system rejection.12 Dr. Okano has restored motor function in spinal cord injury in mice by transplanting neural cells derived from human iPSCs into the mice.13 He has also treated spinal cord injury in monkeys using neural stem cells derived from human iPSCs.14 In neither experiment did cancer occur.
Guang-Hui Liu, PhD (Professor, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China) has derived iPSCs from patients suffering from a variety of disease conditions, and used those cells to better understand the molecular mechanisms causing those diseases. He has done this with Parkinson's Disease,15 Werner's Syndrome,16 xeroderma pigmentosum,17 and Hutchinson-Gilford progeria syndrome.18 With the latter syndrome, he was able to use gene therapy to correct the disease-causing mutation in the iPSCs (but only in cells, he has not attempted this in patients).19 He has also attempted to use gene therapy to correct mutations in cells from patients having Falconi Anemia.20
Treatment of Patients with MSCs
Katarina Le Blanc, MD, PhD (Professor of Clinical Stem Cell Research, Karolinska Institute, Stockholm, Sweden) has used bone-marrow derived mesenchymal stem cells (MSCs) to treat patients suffering from transplant-induced immune reactions who did not benefit from steroids.21 Whether the MSCs were HLA matched to the patient did not affect the outcome.21 MSCs inhibit the immune system.22 The number of MSCs are normally increased by expansion in tissue culture before being administered to patients. Dr.Le Blanc has found better therapeutic benefit from MSCs that have not been expanded too many times.23 Dr. Le Blanc has found that MSCs are an effective therapy to treat patients who have been newly diagnosed with type 1 diabetes.24
Shigeki Sugii, PhD (Group Leader, Fat Metabolism and Stem Cell Group, Singapore Bioimaging Corsortium, Singapore) has investigated the use of MSCs from fat deposits rather than from bone marrow. MSCs cells can be extracted from fat deposits through liposuction, whereas obtaining MSCs from bone marrow is much more painful and invasive.25 Moreover, MSCs are a thousand times more plentiful in fat than in bone marrow.26 Fat-derived MSCs more readily differentiate into bone or fat cells, whereas bone marrow derived MSCs more readily differentiate into cartilage cells.27 Fat-derived MSCs promote wound-healing.28
Dr. Sugii has found that MSCs from subcutaneous fat proliferate and differentiate better than MSCs from visceral fat26 and are less likely to cause metabolic abnormalities.29 Dr. Sugii has investigated the molecular mechanisms underlying these differences.30
Somatic Stem Cells in Muscle
Pura Munoz-Canoves, PhD (Research Professor, University Pompeu Fabra, Barcelona, Spain) attempts to find means of opposing the loss of muscle function contributing to frailty in the elderly. A young person will typically have twice the number of somatic muscle stem cells as an elderly person.31 Dr. Munoz-Canoves has found that a decline in autophagy in muscle stem cells is a main cause of their loss.32 Autophagy is the process by which defective proteins and organelles are removed from cells, thereby maintaining cell quality. Dr. Munoz-Canoves has shown that she can prevent age-associated decline in muscles of mice by administering to them the autophagy-inducing drug rapamycin.33
Cancer Stem Cells
Jonathan Pachter, PhD (Chief Scientific Officer; Verastem, Inc., Needham, Massachusetts) is attempting to cure cancer by killing cancer stem cells. Chemotherapy or radiation therapy often kills most cancer cells, but often the cancer recurs. Multiple myeloma, for example, recurs more often than not.34 Cancer stem cells are the suspected reason for this problem.35,36
Most cancer cells divide rapidly, so cancer and radiation therapy kill all rapidly dividing cells. Stem cells are characterized by infrequent division, the ability to create at least one copy of itself on division ("self-renewal") and the ability to differentiate into a specific cell type. Infrequent cell division would make cancer stem cells resistant to radiation and chemotherapy. Studies of cancer cells show that only a small percentage can form new tumors on transplantation, so these cells are believed to be cancer stem cells.35
Focal Adhesion Kinase (FAK) is an enzyme believed to promote cancer stem cell growth and migration. So using drugs to inhibit FAK is a strategy to suppress cancer stem cells.37 Dr. Pachter has used FAK inhibitors as well as other drugs to substantially inhibit cancer stem cells in mice as well as in cell cultures.38,39
Oxygen and Stem Cells
Heather O'Leary, PhD (Postdoctoral fellow, Indiana University School of Medicine, Indianapolis, Indiana) is concerned about the effects of oxygen on stem cells. Stem cells normally reside in a low-oxygen environment, but are typically harvested in air, which has a higher oxygen content. Counteracting the oxygen stress associated with stem cell harvesting produces better results.40 Dr. O'Leary has studied the molecular mechanisms reducing the quality of stem cells harvested in air.41
Badrul Yahaya, PhD (Head, Regenerative Medicine Cluster, University Sains Malaysia,Malaysia) wishes to use stem cells to treat Chronic Obstructive Pulmonary Disease (COPD, the fourth leading cause of death in the United States). COPD is caused by chronic exposure to noxious particulate matter (usually cigarette smoke), which obstructs airways and destroys air sacs in the lung.42 COPD could be treated with mesenchymal stem cells, which reduces lung inflammation.43 Dr. Yahaya has shown that fibroblast cells can be delivered to the lungs of rabbits as an aerosol without reduction of cell survival, but cancer cells did not survive.44 Cancer cells are similar to stem cells in that they exist in a low oxygen environment. Dr. O'Leary's work suggests that it will probably be necessary to counteract oxygen stress to deliver stem cells to the lungs as an aerosol to effectively treat COPD.
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