Assessing the Safety of Stem Cell Therapeutics
2011; Elsevier BV; Volume: 8; Issue: 6 Linguagem: Inglês
10.1016/j.stem.2011.05.012
ISSN1934-5909
AutoresChristopher E. Goldring, Paul Duffy, Nissim Benvenisty, Peter W. Andrews, Uri Ben‐David, Rowena Eakins, Neil S. French, Neil A. Hanley, Lorna Kelly, Neil R. Kitteringham, Jens Kurth, Deborah Ladenheim, Hugh Laverty, James W. McBlane, Gopalan Narayanan, Sara Patel, Jens Reinhardt, Annamaria Rossi, Michaela Sharpe, B. Kevin Park,
Tópico(s)3D Printing in Biomedical Research
ResumoUnprecedented developments in stem cell research herald a new era of hope and expectation for novel therapies. However, they also present a major challenge for regulators since safety assessment criteria, designed for conventional agents, are largely inappropriate for cell-based therapies. This article aims to set out the safety issues pertaining to novel stem cell-derived treatments, to identify knowledge gaps that require further research, and to suggest a roadmap for developing safety assessment criteria. It is essential that regulators, pharmaceutical providers, and safety scientists work together to frame new safety guidelines, based on “acceptable risk,” so that patients are adequately protected but the safety “bar” is not set so high that exciting new treatments are lost. Unprecedented developments in stem cell research herald a new era of hope and expectation for novel therapies. However, they also present a major challenge for regulators since safety assessment criteria, designed for conventional agents, are largely inappropriate for cell-based therapies. This article aims to set out the safety issues pertaining to novel stem cell-derived treatments, to identify knowledge gaps that require further research, and to suggest a roadmap for developing safety assessment criteria. It is essential that regulators, pharmaceutical providers, and safety scientists work together to frame new safety guidelines, based on “acceptable risk,” so that patients are adequately protected but the safety “bar” is not set so high that exciting new treatments are lost. Immense expectation surrounds the area of stem cell therapeutics. Pressures are building to accelerate their development, from patients requiring effective therapy as well as companies requiring new products for dwindling pipelines and needing to diversify portfolios. This anticipation is independent of the source of stem cells (adult versus embryonic, or patient-derived autologous cells versus healthy donor adult or embryonic allogeneic cells). However, as with all new treatments, our knowledge about the safety of these medicinal products is still limited and needs to be expanded to assess their therapeutic safety more effectively. The purpose of this article (which arose from discussions at a workshop hosted by the MRC Center for Drug Safety Science in Liverpool) is to outline the major safety issues associated with stem cell therapeutics, to identify the gaps in our knowledge with respect to these issues, and to propose a set of recommendations designed to facilitate the development and clinical application of stem cell therapies from an industrial, clinical, and regulatory perspective. In 2008, the ISSCR published a detailed set of guidelines for the translation of stem cell research into clinical practice (Hyun et al., 2008Hyun I. Lindvall O. Ahrlund-Richter L. Cattaneo E. Cavazzana-Calvo M. Cossu G. De Luca M. Fox I.J. Gerstle C. Goldstein R.A. et al.New ISSCR guidelines underscore major principles for responsible translational stem cell research.Cell Stem Cell. 2008; 3: 607-609Abstract Full Text Full Text PDF PubMed Scopus (174) Google Scholar). While there is some overlap in the issues addressed by both publications, the current article focuses specifically on the broader principles associated with the safe use of stem cell therapies and is intended to complement the ISSCR guidelines. Since they were first isolated by James Thomson (Thomson et al., 1998Thomson J.A. Itskovitz-Eldor J. Shapiro S.S. Waknitz M.A. Swiergiel J.J. Marshall V.S. Jones J.M. 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Zorn A.M. et al.Directed differentiation of human pluripotent stem cells into intestinal tissue in vitro.Nature. 2011; 470: 105-109Crossref PubMed Scopus (1045) Google Scholar). Several pluripotent and multipotent stem cell-based therapeutics have entered clinical trials. Table 1 shows a summary of selected stem cell-based therapeutics approved for clinical trials by the United States Food and Drug Administration (FDA) or the UK Medicines and Healthcare Products Regulatory Agency (MHRA) to treat injuries to the central nervous system, myocardial infarction, and diabetes. Clearly, the explosive growth in interest in the use of induced pluripotent stem cells (iPSCs) opens up novel avenues of therapeutic development based on adult stem cells, thereby avoiding some of the ethical issues surrounding the use of human embryos to derive hESCs; however, translation of iPSC research into therapeutics is still at an early stage (for reviews on this subject see Nelson et al., 2010Nelson T.J. Martinez-Fernandez A. Yamada S. Ikeda Y. Perez-Terzic C. Terzic A. Induced pluripotent stem cells: advances to applications.Stem Cells Cloning. 2010; 3: 29-37PubMed Google Scholar, Nishikawa et al., 2008Nishikawa S. Goldstein R.A. Nierras C.R. The promise of human induced pluripotent stem cells for research and therapy.Nat. Rev. Mol. Cell Biol. 2008; 9: 725-729Crossref PubMed Scopus (339) Google Scholar, Vitale et al., 2011Vitale A.M. Wolvetang E. Mackay-Sim A. Induced pluripotent stem cells: A new technology to study human diseases.Int. J. Biochem. Cell Biol. 2011; 43: 843-846Crossref PubMed Scopus (34) Google Scholar).Table 1Selected Pluripotent and Multipotent Stem Cell-Based Therapeutics Currently Undergoing Clinical Trials in the US and UKConditionInterventionSponsorStudy DesignSample sizeInclusion CriteriaTime FrameReferenceSpinal cord injury (SCI)GRNOPC1: oligodendrocyte progenitor cellsGeron Corp.Non-randomized, single arm, uncontrolled1018–65 years, M+F. Neurologically complete, traumatic SCI. Single lesion12 monthshttp://clinicaltrials.gov/ct2/show/NCT01217008?term=GRNOPC1&rank=1Stable ischemic stroke (IS)CTX0E03: neural stem cellsReNeuron Ltd.Non-randomized, single administration, ascending dose12M, > 60. Unilateral IS, > 1cm infarction. NIHSS minimum 62 year monitoring. 8 year follow-up trialhttp://clinicaltrials.gov/ct2/show/NCT01151124?term=ctx0e03&rank=1Acute myocardial infarction (AMI)AMI MultiStemAthersys Inc.Non-randomized control and treatment groups. 3 dose escalation cohorts2818–80 years, M+F. 1st time diagnosis of ST-elevated AMIAdverse events during 24 hr. Postacute events 30 days. 12 month follow-uphttp://clinicaltrials.gov/ct2/show/NCT00677222?term=multistem&rank=3Neuronal ceroid lipofuscinosis (Batten's disease, NCL)Procedure HuCNS-SC: human neural stem cellsStem Cells Inc.Phase 1b. Single group assessment66 months–6 yr M+F. CLN1 or CLN2 mutation. Clinical diagnosis of NCL12 monthshttp://clinicaltrials.gov/ct2/show/study/NCT01238315?term=HuCNS-SC&rank=2Stargardt's diseaseRetinal pigment epithelial (RPE) derived from human embryonic stem cellsAdvanced Cell Technology Inc. (ATC)Nonrandomized, single administration12Not yet publishedNot yet publishedhttp://www.advancedcell.com/news-and-media/press-releases/advanced-cell-technology-receives-fda-clearance-for-the-first-clinical-trial-using-embryonic-stem-cel/Dry age-related macular degeneration (AMD)Retinal pigment epithelial (RPE) derived from human embryonic stem cellsAdvanced Cell Technology Inc. (ATC)Nonrandomized, single administration12Not yet publishedNot yet publishedhttp://www.actcblog.com/2011/01/act-receives-fda-clearance-for-clinical-trials-using-escs-to-treat-amd-afflicts-10-15-million-americans.htmlType 1 diabetes mellitus (DM)PROCHYMAL: ex vivo adult mesenchymal stem cellsOsiris TherapeuticsRandomized placebo controlled, double blind. Phase 26012-35 M+F. Type 1 DM, at least 1 DM-related autoantibody. Some beta-cell functionNot yet publishedhttp://clinicaltrials.gov/ct2/show/NCT00690066 Open table in a new tab As well as iPSCs, other types of adult stem cells, such as mesenchymal stem cells (MSCs), have been shown to differentiate in vitro into cell lines displaying osteogenic, chondrogenic, or adipogenic characteristics (Prockop, 1997Prockop D.J. Marrow stromal cells as stem cells for nonhematopoietic tissues.Science. 1997; 276: 71-74Crossref PubMed Scopus (4015) Google Scholar). Moreover, they have an immunomodulatory effect on their direct environment (Aggarwal and Pittenger, 2005Aggarwal S. Pittenger M.F. Human mesenchymal stem cells modulate allogeneic immune cell responses.Blood. 2005; 105: 1815-1822Crossref PubMed Scopus (3395) Google Scholar), and they are able to secrete cytokines that are able to initiate intrinsic tissue regenerative processes (Caplan and Dennis, 2006Caplan A.I. Dennis J.E. Mesenchymal stem cells as trophic mediators.J. Cell. Biochem. 2006; 98: 1076-1084Crossref PubMed Scopus (2139) Google Scholar). However, in contrast to iPSCs, MSCs are limited in their differentiation capacity. Nevertheless, due to their availability and potentially beneficial properties— through either autologous or allogenic donation—MSCs have been in the spotlight for regenerative medicine for various indications. As of May 5th, 2011, 168 studies have been registered at the U.S. NIH Clinical Trials registry (http://clinicaltrials.gov/ct2/results?term=mesenchymal+stem+cells) and 12 studies have been registered and uploaded onto the EU Clinical Trials Register (https://www.clinicaltrialsregister.eu/ctr-search/). Clearly, stem cell-based therapies bring with them new safety challenges that cannot be addressed using standard analytical procedures developed for low-molecular-weight drugs or other biopharmaceuticals. A particular difficulty is the ability to monitor cell biodistribution, since once administered, the cells may be essentially indistinguishable from host cells. The ability to track the therapeutic cells is key to an objective assessment of risk with respect to inappropriate ectopic tissue formation or of tumorigencity. This is especially important where the cells are administered intravenously, rather than locally, since broad dissemination is likely to occur. The ability to determine the biodistribution of administered cells raises technical issues, as monitoring the fate of exogenous cells will require the development of novel technologies. Furthermore, the detection of misplaced cells may necessitate a mechanism for their removal, which again may not be technically feasible at present. Thus, there is a major need for technological advances in biomonitoring alongside the development of novel means for eliminating administered cells that become inappropriately located. Eliminating errant cells is likely to be a more challenging task and may involve incorporation of a “self-destruct” mechanism programmed into the cells to elicit apoptosis in response to a given stimulus. A major concern with stem cell therapy is that of tumorigenic potential. The delivery of a cell with unlimited potential for renewal and the capacity to differentiate into any human cell type carries a burden of safety concern not associated with any other class of treatment. Whether these concerns are justified by solid research support is probably the most significant safety question that needs to be addressed at the current time. The finding that undifferentiated stem cells, introduced into immunocompromised animals, are capable of forming teratomas (tumors that are composed of a haphazard array of somatic cell types, sometimes arranged into tissues, and normally corresponding to all three germ layers) emphasizes the importance of addressing this issue. Furthermore, if the cells contain genetic abnormalities, these could potentially develop into teratocarcinomas (Ben-David and Benvenisty, 2011Ben-David U. Benvenisty N. The tumorigenicity of human embryonic and induced pluripotent stem cells.Nat. Rev. Cancer. 2011; 11: 268-277Crossref PubMed Scopus (593) Google Scholar, Blum and Benvenisty, 2008Blum B. Benvenisty N. The tumorigenicity of human embryonic stem cells.Adv. Cancer Res. 2008; 100: 133-158Crossref PubMed Scopus (321) Google Scholar), which are tumors composed of a teratoma element together with persisting undifferentiated stem cells. These would be expected to be highly malignant, like the corresponding testicular germ cell tumors that occur in young men. Another evident safety issue that needs to be tackled by stem cell therapy providers is that of immunogenicity. Although there are reports of immune privilege of human embryonic stem cells (Drukker and Benvenisty, 2004Drukker M. Benvenisty N. The immunogenicity of human embryonic stem-derived cells.Trends Biotechnol. 2004; 22: 136-141Abstract Full Text Full Text PDF PubMed Scopus (178) Google Scholar), any foreign cell introduced into a patient will be subject to immune surveillance (Swijnenburg et al., 2008Swijnenburg R.J. Schrepfer S. Govaert J.A. Cao F. Ransohoff K. Sheikh A.Y. Haddad M. Connolly A.J. Davis M.M. Robbins R.C. Wu J.C. Immunosuppressive therapy mitigates immunological rejection of human embryonic stem cell xenografts.Proc. Natl. Acad. Sci. USA. 2008; 105: 12991-12996Crossref PubMed Scopus (238) Google Scholar). While site of administration and multiple dosing may impact host-induced immunogenicity, a further significant difference between animal and human studies is that immunosuppression can be used in animal studies but may not be medically acceptable or necessary in trials in patients. In addition to establishing the efficacy of stem cell therapies, the successful implementation of novel cell-based treatments will rely heavily on our ability to resolve these important safety issues, at both the preclinical and the clinical stages. Every step in the process of developing stem cell therapies requires rigorous scrutiny, from the origin of the cells used through expansion, manipulation, and preclinical evaluation to eventual engraftment in the host (Halme and Kessler, 2006Halme D.G. Kessler D.A. FDA regulation of stem-cell-based therapies.N. Engl. J. Med. 2006; 355: 1730-1735Crossref PubMed Scopus (286) Google Scholar, National Institutes of Health, 2006National Institutes of Health. (2006). Regenerative Medicine. http://stemcellsnihgov/info/scireport/2006reporthtm.Google Scholar) (see Figure 1). Importantly, the stem cell therapy field needs to interact at the level of therapy provider, safety scientist, and drug regulator in order to define the “acceptable risk” associated with a particular treatment and to set in place a framework for accurate assessment of that “risk.” In our increasingly risk-averse society it is easy to err on the side of caution, but it should be acknowledged that if the safety “bar” is set unreasonably high then the enormous potential and promise of revolutionary medical treatments may never be realized. In order to minimize patient risk, each stage of the cell therapy production should be assessed for potential safety concerns, before introduction to a human subject. This evaluation includes the manufacturing process itself, as well as the characterization and formal safety assessment of the finished product. A key area that must be addressed is the manufacturing process, i.e., the need for consistency of manufacture to ensure the reproducible quality of the product. When preparing cells in vitro for transplant, it is essential to ensure that the culture is fully defined and characterized, as the consequences of poor definition may be far reaching. The importance of this issue from a regulatory perspective was underlined by the temporary hold placed by the FDA on Geron's first-in-human trial of an ESC-derived treatment for spinal cord injury (GRNOPC1) (Geron, 2009aGeron (2009a). Geron Comments on FDA Hold on Spinal Cord Injury Trial (http://www.geron.com/media/pressview.aspx?id=1188).Google Scholar). One of the concerns raised by the FDA—but subsequently allayed by the company—was surety that the manufactured cell product was fully characterized and that the mixtures of cells were predictable and free from contamination (Geron, 2009bGeron (2009b). Geron receives FDA clearance to begin world's first human clinical trial of embryonic stem cell-based therapy (http://www.geron.com/media/pressview.aspx?id=1148).Google Scholar). Clearly, for new treatments targeting clinical conditions of a less serious nature, the level of stringency of product quality may be set even higher to avoid the administration of undifferentiated cell contaminants. Most, if not all, cell types acquire chromosomal aberrations during expansion in culture. As chromosomal aberrations are a hallmark of human cancer (Hanahan and Weinberg, 2011Hanahan D. Weinberg R.A. Hallmarks of cancer: the next generation.Cell. 2011; 144: 646-674Abstract Full Text Full Text PDF PubMed Scopus (35544) Google Scholar), it is very important to perform a detailed analysis of the genome prior to any cell-based treatment. The inherent genetic instability of hESCs and iPSCs in culture has been demonstrated (Baker et al., 2007Baker D.E. Harrison N.J. Maltby E. Smith K. Moore H.D. Shaw P.J. Heath P.R. Holden H. Andrews P.W. Adaptation to culture of human embryonic stem cells and oncogenesis in vivo.Nat. Biotechnol. 2007; 25: 207-215Crossref PubMed Scopus (481) Google Scholar, Mayshar et al., 2010Mayshar Y. Ben-David U. Lavon N. Biancotti J.C. Yakir B. Clark A.T. Plath K. Lowry W.E. Benvenisty N. Identification and classification of chromosomal aberrations in human induced pluripotent stem cells.Cell Stem Cell. 2010; 7: 521-531Abstract Full Text Full Text PDF PubMed Scopus (557) Google Scholar), and evidence for the instability of adult stem cells in culture is also beginning to emerge (Sareen et al., 2009Sareen D. McMillan E. Ebert A.D. Shelley B.C. Johnson J.A. Meisner L.F. Svendsen C.N. Chromosome 7 and 19 trisomy in cultured human neural progenitor cells.PLoS ONE. 2009; 4: e7630Crossref PubMed Scopus (53) Google Scholar, Ueyama et al., 2011Ueyama H. Horibe T. Hinotsu S. Tanaka T. Inoue T. Urushihara H. Kitagawa A. Kawakami K. Chromosomal variability of human mesenchymal stem cells cultured under hypoxic conditions.J Cell Mol. Med. 2011; (in press. Published online March 21, 2011)https://doi.org/10.1111/j.1582-4934.2011.01303.xCrossref Scopus (55) Google Scholar). Consequently, not only gross karyotype but also detailed genetic profiling must be undertaken before engraftment into the host (Stephenson et al., 2010Stephenson E. Ogilvie C.M. Patel H. Cornwell G. Jacquet L. Kadeva N. Braude P. Ilic D. Safety paradigm: genetic evaluation of therapeutic grade human embryonic stem cells.J. R. Soc. Interface. 2010; 7: S677-S688Crossref PubMed Scopus (29) Google Scholar). As somatic cells within the body are often seen with copy-number variations (CNVs), any minor aberration that occurs in culture will not necessarily prevent its clinical use. The functional significance of specific aberrations that tend to occur in stem cell cultures will need to be assessed in safety preclinical trials. Acceptable degrees of genetic change must be established by a thorough examination of subcellular architecture, including chromosomes, small CNVs, and even point mutations (Gore et al., 2011Gore A. Li Z. Fung H.L. Young J.E. Agarwal S. Antosiewicz-Bourget J. Canto I. Giorgetti A. Israel M.A. Kiskinis E. et al.Somatic coding mutations in human induced pluripotent stem cells.Nature. 2011; 471: 63-67Crossref PubMed Scopus (944) Google Scholar, Laurent et al., 2011Laurent L.C. Ulitsky I. Slavin I. Tran H. Schork A. Morey R. Lynch C. Harness J.V. Lee S. Barrero M.J. et al.Dynamic changes in the copy number of pluripotency and cell proliferation genes in human ESCs and iPSCs during reprogramming and time in culture.Cell Stem Cell. 2011; 8: 106-118Abstract Full Text Full Text PDF PubMed Scopus (642) Google Scholar). Cell-surface markers and expression of transcription factors, as well as proliferation capacity and differentiation propensity, should also be evaluated, as these parameters have been suggested to change during the acquisition of genetic alterations (Blum and Benvenisty, 2009Blum B. Benvenisty N. The tumorigenicity of diploid and aneuploid human pluripotent stem cells.Cell Cycle. 2009; 8: 3822-3830Crossref PubMed Scopus (105) Google Scholar). Additionally, it is imperative to assess the heterogeneity of a culture, as the engraftment of undifferentiated or incorrectly differentiated cells may present a substantial tumorigenic or immunogenic risk to the recipient (Baker et al., 2007Baker D.E. Harrison N.J. Maltby E. Smith K. Moore H.D. Shaw P.J. Heath P.R. Holden H. Andrews P.W. Adaptation to culture of human embryonic stem cells and oncogenesis in vivo.Nat. Biotechnol. 2007; 25: 207-215Crossref PubMed Scopus (481) Google Scholar, Ben-David and Benvenisty, 2011Ben-David U. Benvenisty N. The tumorigenicity of human embryonic and induced pluripotent stem cells.Nat. Rev. Cancer. 2011; 11: 268-277Crossref PubMed Scopus (593) Google Scholar, Fairchild, 2010Fairchild P.J. The challenge of immunogenicity in the quest for induced pluripotency.Nat. Rev. Immunol. 2010; 10: 868-875Crossref PubMed Scopus (66) Google Scholar). As the passage number of a stem cell lines increases, so too does the potential for chromosomal aberrations to arise (Hovatta et al., 2010Hovatta O. Jaconi M. Töhönen V. Béna F. Gimelli S. Bosman A. Holm F. Wyder S. Zdobnov E.M. Irion O. et al.A teratocarcinoma-like human embryonic stem cell (hESC) line and four hESC lines reveal potentially oncogenic genomic changes.PLoS ONE. 2010; 5: e10263Crossref PubMed Scopus (39) Google Scholar, Maitra et al., 2005Maitra A. Arking D.E. Shivapurkar N. Ikeda M. Stastny V. Kassauei K. Sui G. Cutler D.J. Liu Y. Brimble S.N. et al.Genomic alterations in cultured human embryonic stem cells.Nat. Genet. 2005; 37: 1099-1103Crossref PubMed Scopus (523) Google Scholar). Therefore, minimizing the culture time might be required in order to decrease the chance for in vitro genetic alterations. It is clear that conventional preclinical absorption, distribution, metabolism, excretion, and toxicity (ADMET) studies cannot be directly applied to cell-based products where there is a requirement to track differentiation and migration in vivo. How therefore can a dosing regimen be meaningfully calculated and pharmacokinetics/pharmacodynamics (PK/PD) be assessed? Such strategies are normally heavily reliant on risk-benefit analyses, but it presents a major challenge to make this analysis when the risks are poorly understood and the benefits are at present unknown. Dosing regimens are conventionally based on in vivo dose response curves, but this method is difficult to translate to cell-based therapeutics. In determining an appropriate posology, it will be important to consider both evidence from dose-determining studies (i.e., it is necessary to consider how to derive a human equivalent dose; in many cases, animal models of disease are rodents— therefore, how will we determine how to scale up doses?) and rationale (comprising scientific and clinical logic). Dose selection considerations need to include both what is maximally feasible in the species chosen and the relevance to the intended human therapeutic dose. Data derived from tests with syngeneic cells can be useful to establish the dosing principles but are unlikely to contribute much to quantitative considerations, which are an essential part of determining initial human doses. It is also important to consider the route of administration of a product, i.e., whether it is administered systemically or locally. For example, MSCs are seen to home to sites of injury but a large proportion will accumulate in the lungs if administered systemically (Gao et al., 2001Gao J. Dennis J.E. Muzic R.F. Lundberg M. Caplan A.I. The dynamic in vivo distribution of bone marrow-derived mesenchymal stem cells after infusion.Cells Tissues Organs (Print). 2001; 169: 12-20Crossref PubMed Scopus (741) Google Scholar, Noort et al., 2002Noort W.A. Kruisselbrink A.B. in't Anker P.S. Kruger M. van Bezooijen R.L. de Paus R.A. Heemskerk M.H. Lowik C.W. Falkenburg J.H. Willemze R. et al.Mesenchymal stem cells promote engraftment of human umbilical cord blood-derived CD34(+) cells in NOD/SCID mice.Exp. Hematol. 2002; 30: 870-878Abstract Full Text Full Text PDF PubMed Scopus (413) Google Scholar). When selecting a relevant disease/injury model, it is important to understand both its attributes and limitations. When a well-developed animal model is available, evidence for robust proof-of-concept preclinical test results is valuable and informative, particularly if the targeted clinical indication requires administration of the stem cell-based product into a highly vulnerable anatomical site (Fink, 2009Fink Jr., D.W. FDA regulation of stem cell-based products.Science. 2009; 324: 1662-1663Crossref PubMed Scopus (110) Google Scholar). A major issue for preclinical testing is the immunological relevance of testing human cells in an animal model. In certain circumstances, it may be possible to generate an analogous species-specific product, but this is not trivial and differences between the cells are likely to exist, which may limit the utility of this approach. Immunosuppression or immune-deficient animal models are likely to be employed, but this approach may mask immune-modulatory or immunotoxicological aspects of
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