Current Opinion in Molecular Therapeutics 2009 11(4): 360-363 Thomson Reuters (Scientific) Ltd ISSN 2040-3445
EDITORIAL
Stem cell therapies: On track but suffer setback Walter H Gunzburg1,2* & Brian Salmons3
Addresses 1 University of Veterinary Medicine, Institute of Virology, Department of Pathobiology, Veterinaerplatz 1, A-1210 Vienna, Austria Email:
[email protected] National University of Singapore, Department of Microbiology, Block MD4, 5 Science Drive 2, Singapore 117597 2
SG Austria (Austrianova Singapore), 20 Biopolis Way, Centros, Biopolis, Singapore 138669 3
*To whom correspondence should be addressed
Stem cells have been proposed to hold promise for the treatment of a wide variety of diseases. Two types of mammalian stem cells can be used for such treatments: (i) embryonic stem cells that are isolated from the inner cell mass of blastocysts and can differentiate into all specialized embryonic tissues; and (ii) adult stem cells that are present within in adult tissues, where the stem cells act as a repair system for the body, replenishing specialized cells, but also maintaining the normal turnover of regenerative organs, such as the blood, skin or intestinal tissues. Highly plastic adult stem cells from a variety of sources, such as umbilical cord blood and bone marrow, are routinely used in the treatment of leukemias and certain immunodeficiencies. Several clinical trials are ongoing, albeit in early phases, that use stem cells to treat ailments as diverse as cardiovascular diseases, neurodegenerative diseases and diabetes. Progress in the use of stem cells to treat brain injury, liver diseases and leukemia are reviewed in this issue of Current Opinion in Molecular Therapeutics [1-3]. During the past few months, major developments for stem cell therapies, some of which are discussed in this editorial (along with the first reports of a stem cell therapy-derived tumor in a patient), have occurred.
Recently approved clinical trials Three biotechnology companies (ReNeuron Group plc, Geron Corp and StemCells Inc) have received approval by the regulatory authorities to proceed with clinical trials that involve the transplantation of fetal stem cells into the brain or embryonic stem cells into the spinal cord. These companies are working with well characterized stem cells that have been extensively tested in animal models, and for which preclinical data on safety and efficacy are available.
Mesenchymal stem cells There has been much interest in mesenchymal stem cells (MSCs) because, unlike other stem cells, these cells appear
to evade the host immune system, and have an innate ability to home and engraft. Several randomized phase I and II clinical trials to evaluate the possible therapeutic effects of the administration of allogeneic MSCs in patients with multiple sclerosis, GvHD, severe chronic myocardial ischemia, kidney disease and Crohn's disease are ongoing, with trials also being considered for the treatment of inflammatory lung diseases. The reason for MSCs not eliciting an immune response might be because these cells lack MHC protein expression [4]. However, to function therapeutically, the MSCs may have to differentiate after implantation in the patient, and this differentiation may be accompanied by an upregulation of MHC protein expression, which would make the MSCs more visible to the host immune system. This potential adverse effect has not yet been investigated in clinical trials.
The establishment of common regulatory guidelines Another important development has been the establishment of guidelines for the therapeutic use of stem cells by an international group that comprises many of the leading stem cell researchers and clinicians, as well as policy makers, ethicists, representatives from the biotechnology and pharmaceutical industry, and members of the public. These guidelines for stem cell therapy are designed to ensure that rigorous best practices are applied to the clinical translation of stem cell research from the laboratory. The guidelines were originally proposed at the 6th Annual Meeting of the International Society for Stem Cell Research (ISSCR) in 2008 [5]. The goal is that these guidelines will enable patients with incurable diseases and disabling conditions to objectively assess the value of curative experimental stem cell therapies and to protect these patients from traveling thousands of miles in search of a new stem cell therapy when the treatment is not based on reliable preclinical data. Furthermore, as recently highlighted by James Wilson
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(University of Pennsylvania), the guidelines should help to protect the nascent field from the detrimental effects of negative results or adverse events that may arise from treatments that fall outside established and pre-approved clinical trials, and thus hopefully prevent a repeat of the hype and disappointment that helped lead to the decline of gene therapy at the beginning of this century [6]. The ISSCR guidelines address all types of human stem cells, as well as direct derivatives of these cells, and focus on the three major areas of the clinical translational process: (i) cell processing and manufacturing; (ii) preclinical studies; and (iii) clinical research [5]. The guidelines also make specific recommendations for ethical oversight, the peer review of clinical trials, the informed consent and protection of participants, the avoidance of conflict of interest, trial design and reporting, and the long-term follow up of patients. Existing trial regulations related to informed consent, clinical follow up, independent expert review, and institutional support and accountability are confirmed. Additional points include issues of social justice, such as public engagement in policy making and fair access to treatment, including offering affordable treatments to patients in resource-poor countries. The guidelines allow for the treatment of a specific patient, or small numbers of patients, outside of a clinical trial in "exceptional circumstances of justified medical need" for which reasonable scientific evidence exists that the patient(s) might benefit and not be harmed [7]. The Chinese Ministry of Health has recently implemented regulations on the clinical application of advanced therapies, such as treatments that involve stem cells. While the new regulations may help to reduce the number of patients seeking unproven stem cell treatments [8], China was also the first country to approve a gene therapy, Gendicine, for market authorization. Gendicine is an infectious, replication-incompetent, recombinant human adenovirus vector engineered to deliver and express the human wild-type p53 tumor suppressor gene into tumor cells. Gendicine, in combination with chemo- and radiotherapy, has improved treatment efficacy by greater than 3-fold [9]. The decision by the State Food and Drug Administration of China to grant a market license for Gendicine in 2003 was controversial, although similar gene therapies are currently close to approval in both the US and EU. In this light, China can be seen as an advocate for the gene therapy field. To have such advocates for the field of stem cell therapy as well may be important.
The development of a solid tumor in a patient who had received stem cell therapy Until recently, the only type of tumor associated with stem cell transplantation has been donor-type leukemia that may develop following hematopoietic stem cell transplantation. This type of leukemia is most often associated with the transplantation of stem cells derived from umbilical cord blood, rather than cells derived from adult bone marrow or peripheral blood, as the cells derived from umbilical cord blood are more immature and thus potentially more
prone to transformation [10,11]. Although human embryonic stem cells can form teratomas in animal models [12-14], a fact that has raised safety concerns about the use of such cells in humans, there was no evidence that such tumors could arise in humans until February 2009, when Amariglio et al reported that neural stem cell transplantations lead to a donor-cell-derived brain tumor in a boy with ataxia telangiectasia [15]. This report has resulted in several commentaries, editorials and press releases by biotechnology companies involved in the development of stem cell therapies that try to place this study in context. As a result of this report, several issues have been raised: • Patients with ataxia telangiectasia are prone to developing cancer because this disease results in a progressive neurodegenerative disorder that is characterized by a weakened immune system. • There is no published evidence in animal models that stem cell therapy would reverse or halt the disease process. This brings into question the basis for which the therapy was administered to the patient. In addition, there is no clear rationale for how stem cell transplantation might have worked had the therapy been successful. • The patient was treated with at least three independent intracerebellar and intrathecal injections of human fetal neural stem cells from different donors between 2001 and 2004. The cells came from undefined brain regions of 8-week-old fetal brain tissue, and were expanded in culture for 12 to 16 days. Between 50 and 100 million cells were administered per injection into the white matter of the patient's cerebellum by direct injection and into the spinal cord using a lumbar puncture technique. This number of cells is much greater than previously used in other trials in which cells derived from fetal tissues have been transplanted into animals or patients. • Although this treatment occurred 7 years before the development of guidelines, the use of a mixture of cells that are both poorly characterized and obtained from multiple donors, does not meet the recent guidelines of the ISSCR [5]. As many biotechnology companies have highlighted, stem cell therapies being developed as therapeutic agents use only well-defined cells. • The medical history of this patient and possible follow-on or additional treatments are not documented. • Approximately 5 years after the initiation of stem cell therapy, the patient was diagnosed with a multifocal brain tumor. Surgery was performed on the spinal growths 5 years after the first stem cell treatment, and the removed tissue was consistent with a low-grade glianeuronal neoplasm. • Amariglio et al reported that the child remained stable after the surgery to remove the tumor in 2006 and further intervention has not yet been indicated [15]. • Evidence was presented that the tumor was of non-host origin, suggesting the tumor was derived from the transplanted neural stem cells. Microsatellite and HLA analysis demonstrated that the tumor was derived from cells from at least two of the donors.
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As the patient developed the brain tumor more than 4 years after the initial injections, researchers may need to monitor patients long-term to evaluate safety. Amariglio et al suggest that neuronal stem/progenitor cells may have a role in gliomagenesis and conclude that the safety of these therapies must be assessed [15], a point that is re-iterated by Clive Svendsen (University of Wisconsin) in his commentary in Nature Reports Stem Cells [16]. In this commentary, Dr Svendsen argues that the outcome of this series of unregulated stem cell transplants could have been predicted and avoided based on the current understanding of the process by which fetal tissue stem cells grow and differentiate in animal models. Dr Svendsen argues that the tumor that arose in this patient is benign and states, "the cells began to form lumps of growing tissue, or tumors, that had both neural and glial cells. This is exactly what these cells are designed to do by nature. Taken at a very early stage of development perhaps from a region that is destined to make billions of cells (the human cortex), the fetal cells tried to make a mini-brain in the spinal cord. Although it was difficult to establish from the limited data in this report, there were no overt signs of excessive cell growth, perivascular cuffing or chromosomal abnormalities within the growing cells, all of which would suggest a cancerous tumor. There was simply a lump of apparently benign cells that contained healthy neurons and astrocytes near the area of the injection [16]."
allowing the production and release of therapeutic factors, and possibly either physiological or engineered control of this process. Microbeads made of polymers of cellulose sulfate are of particular interest, as no evidence of adverse events have been reported in patients up to 2 years after these microbeads were administered [20,21]. The GMP production of cellulose sulphate encapsulated cells is possible, as these cells can be frozen for long-term storage and many cell types have been successfully encapsulated [22]. The encapsulation of cells would allow suicide genes to be used as a failsafe because, regardless of the material used, encapsulated cells are protected from the host immune system. However, the encapsulation of cells may not be an option if the stem cells need to physically integrate into the patient's tissue to provide a therapeutic effect.
Suggested reading 1.
iljan EA, Sinden J: Stem cell treatment of ischemic brain injury. M Curr Opin Mol Ther (2009) 11(4):394-403.
2.
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3.
rentjens RJ: Cellular therapies in acute lymphoid leukemia. B Curr Opin Mol Ther (2009) 11(4):375-382.
4.
eirelles Lda S, Nardi NB: Methodology, biology and clinical M applications of mesenchymal stem cells. Front Biosci (2009) 14:4281-4298.
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yun I, Lindvall O, Ahrlund-Richter L, Cattaneo E, Cavazzana-Calvo H M, Cossu G, De Luca M, Fox IJ, Gerstle C, Goldstein RA, Hermerén G et al: New ISSCR guidelines underscore major principles for responsible translational stem cell research. Cell Stem Cell (2008) 3(6):607-609.
6.
ilson JM: Medicine. A history lesson for stem cells. Science W (2009) 324(5928):727-728.
7.
International Society for Stem Cell Research: Deerfield, IL, USA (2009). www.isscr.org
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yranoski D: Stem-cell therapy faces more scrutiny in China. C Nature (2009) 459(7244):146-147.
9.
eng Z, Yu Q, Bao L: The application of gene therapy in China. P IDrugs (2008) 11(5):346-350.
Suicide genes and encapsulation as safety strategies The dose of cells administered to a patient clearly affects the tumorigenic potential of the cells, and Svendsen argues that this fact is one of the reasons that the patient developed a brain tumor [16]. In immunocompromised animal models, even relatively non-tumorigenic cells can result in tumors if high enough doses of cells are administered [17]. There are possible strategies to increase or enhance the safety of both stem cell and other cell therapies. One such strategy is the genetic modification of cells to express suicide genes, as reviewed by Gerald Both in this issue of Current Opinion in Molecular Therapeutics [18]. These genes encode enzymes that activate nontoxic prodrugs, and the active drugs then kill the cells. The suicide gene is thus a failsafe device so that if the stem cells demonstrate any inappropriate activity, the cells can be induced to die by the administration of the prodrug. A potential downside to this approach is that many of these suicide genes encode enzymes of bacterial, viral or yeast origin, which may make the cells susceptible to being recognized as foreign and thus be eliminated by the immune system before any therapeutic effect can occur. The use of encapsulation technologies, or delivery devices, may provide additional safety for stem cell therapies. Such technologies include the encapsulation of living cells in cellulose sulfate, alginate or phycomer beads [19]. Such encapsulated cells survive for long periods inside an immunoprotective scaffold or shell, which is porous, thus
10. A ndo T, Yujiri T, Mitani N, Takeuchi H, Nomiyama J, Suguchi M, Matsubara A, Tanizawa Y: Donor cell-derived acute myeloid leukemia after unrelated umbilical cord blood transplantation. Leukemia (2006) 20(4):744-745. 11. G reaves MG: Cord blood donor cell leukemia in recipients. Leukemia (2006) 20(9):1633–1634. 12. F ujikawa T, Oh SH, Pi L, Hatch HM, Shupe T, Petersen BE: Teratoma formation leads to failure of treatment for type I diabetes using embryonic stem cell-derived insulin-producing cells. Am J Pathol (2005) 166(6):1781-1791. 13. R oy NS, Cleren C, Singh SK, Yang L, Beal MF, Goldman SA: Functional engraftment of human ES cell-derived dopaminergic neurons enriched by coculture with telomerase-immortalized midbrain astrocytes. Nat Med (2006) 12(11):1259-1268. 14. C ao F, Li Z, Lee A, Liu Z, Chen K, Wang H, Cai W, Chen X, Wu JC: Noninvasive de novo imaging of human embryonic stem cell– derived teratoma formation. Cancer Res (2009) 69(7):27092713. 15. A mariglio N, Hirshberg A, Scheithauer BW, Cohen Y, Loewenthal R, Trakhtenbrot L, Paz N, Koren-Michowitz M, Waldman D, Leider-Trejo L, Toren A et al: Donor-derived brain tumor following neural stem cell transplantation in an ataxia telangiectasia patient. PLoS Med (2009) 6(2):e1000029.
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16. S vendsen C: Stem cell clinical trials must be closely monitored. Nature Reports Stem Cells (2009):doi:10.1038/stemcells.2009.34 17. L ewis AM Jr, Alling DW, Banks SM, Soddu S, Cook JL: Evaluating virus-transformed cell tumorigenicity. J Virol Methods (1999) 79(1):41-50.
21. L öhr JM, Kröger J-C, Hoffmeyer A, Freund M, Hain J, Holle A, Knöfel WT, Liebe S, Nizze H, Renner M, Saller R et al: Safety, feasibility and clinical benefit of localized chemotherapy using microencapsulated cells for inoperable pancreatic carcinoma in a phase I/II trial. Cancer Therapy (2003) 1(A):121131.
18. B oth GW: Recent progress in gene-directed enzyme prodrug therapy: An emerging cancer treatment. Curr Opin Mol Ther (2009) 11(4):421-432
22. S almons B, Hauser O, Gunzburg WH, Tabotta W: GMP production of an encapsulated cell therapy product: Issues and considerations. BioProcessing Journal (2007) 4:36-43.
19. H auser O, Prieschl-Grassauer E, Salmons B: Encapsulated, genetically modified, cells producing in vivo therapeutics. Curr Opin Mol Ther (2004) 6(4):412-420. 20. L öhr JM, Hoffmeyer A, Kröger J-C, Freund M, Hain J, Holle A, Karle P, Knöfel WT, Liebe S, Müller P, Nizze H et al: Microencapsulated cell mediated therapy of inoperable pancreatic carcinoma. Lancet (2001) 357(9268):1591-1592.
