REGULATORY SCIENCE Balancing Tissue and Tumor Formation in … · Balancing Tissue and Tumor...
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www.ScienceTranslationalMedicine.org 15 August 2012 Vol 4 Issue 147 147fs28 1 FOCUS CREDIT: B. STRAUCH/SCIENCE TRANSLATIONAL MEDICINE Innovative cell-based therapies are being developed to repair, replace, or regenerate absent, injured, or diseased tissues and or- gans. Tese investigational therapies ofer promise for the treatment of many serious medical conditions, which is illustrated by the variety of indications currently under investigation in clinical trials (see www. clinicaltrials.gov). In the United States, cell-based regenerative medicine (RM) products are regulated by the U.S. Food and Drug Administration (FDA) through the Center for Biologics Evaluation and Re- search (CBER). Before initiation of a clini- cal trial for a specifc RM product, it is the responsibility of FDA’s CBER review staf to establish whether clinical trial partici- pants would be exposed to substantial and unreasonable risks. From 2007 to 2011, CBER received ~115 original submissions from academic and commercial sponsors requesting per- mission to begin clinical investigations of cell-based RM products for many difer- ent indications, including cardiovascu- lar diseases, diabetes, neurodegenerative disorders, wound healing, and others. For this analysis, the number of submissions excludes products for oncology indications or those manufactured by use of genetic engineering. Te identity and tissue sourc- es of these cell-based RM products span a wide spectrum (Fig. 1), ranging from func- tionally specialized and lineage-restricted cells to products derived from unspecial- ized pluripotent embryonic stem (ES) cells. PROMISE AND RISK Te promise of many cell-based RM prod- ucts is based on their inherent biological properties—high rates of proliferation, mi- gratory (trafcking) ability, plasticity, and capacity for self-renewal. However, these same properties also pose particular chal- lenges during product development. Te potential for tumor formation is a major safety concern for products derived from undiferentiated or incompletely diferenti- ated cells or from cells that have undergone extensive ex vivo manipulation. Indeed, the formation of teratomas afer injection of undiferentiated ES cells into immuno- defcient mice is a distinguishing feature, and the potential for malignant transfor- mation and inappropriate diferentiation of cells undergoing prolonged or rapid ex- pansion is well documented (1–3). Te po- tential for tumor formation should also be considered in the context of the anatomical location of any found tumor or undesired tissue because increased damage to normal host tissue may result if cells proliferate in an anatomically constrained or sensitive area, such as the spinal column or retinal space (4). FDA and other regulatory agencies recognize the inherent risk of tumor for- mation for many cell-based RM products (5–7). Te importance of appropriate pre- clinical testing to identify, characterize, and minimize this risk has also been dis- cussed by the FDA Cellular, Tissue, and Gene Terapies Advisory Committee (8, 9). During FDA/CBER regulatory review, the potential for tumor formation is con- sidered for all cell-based RM products (Fig. 1). Many of the principles described in this article determined the methods of evalua- tion and mitigation strategies that were ap- propriate for each product. Extra caution is warranted for ES cell– derived products to ensure that the propor- tion of residual undiferentiated cells in the fnal product is as low as technically feasible. Other less well understood risk factors, such as chromosomal instability, may be identi- fed and minimized through appropriate preclinical testing (and subsequent changes to product manufacturing processes). An appropriate program could include in vitro testing (such as chromosomal analysis), in vivo evaluation of proliferation and tumor formation afer product administration at the clinically relevant anatomical location, additional product characterization (such as whole-genome microarray analysis), or changes in product manufacturing (such as antibody-mediated cell sorting for the tar- geted depletion of undesired phenotypes). REGULATORY SCIENCE Balancing Tissue and Tumor Formation in Regenerative Medicine Alexander M. Bailey E-mail: [email protected] Ofce of Cellular, Tissue, and Gene Therapies, Center for Biologics Evaluation and Research, FDA, Rockville, MD 20852, USA. A set of general principles can guide preclinical testing strategies for evaluating the tumorigenicity of regenerative medicine products. Fig. 1. FDA/CBER experience. Original submissions (~115) to initiate clinical investigations for cell-based RM products were submitted to FDA/CBER from 2007-2011. The cellular components of these products spanned a wide spectrum of (A) cell types and (B) tissue sources; ~70% of submis- sions were for new products and 30% were for new indications for previously evaluated (cross- referenced) products. Assessment of tumorigenicity risk was performed by direct testing of the product (in vitro or in vivo studies) (43%) or through consideration of product attributes, the scien- tific literature, and/or previous clinical experience (57%). (A) Cell type (B) Tissue source ES cell−derived Other Other Umbilical cord (blood, tissue) Pancreatic islet Neural- lineage Cardiac Keratinocytes/ fibroblasts Mononuclear cells (blood, bone marrow) Mesenchymal stem cells Adipose Blood Dermal tissue Embryonic Fetal tissue Placenta Umbilical cord Bone marrow by guest on October 3, 2020 http://stm.sciencemag.org/ Downloaded from
Transcript of REGULATORY SCIENCE Balancing Tissue and Tumor Formation in … · Balancing Tissue and Tumor...
www.ScienceTranslationalMedicine.org 15 August 2012 Vol 4 Issue 147 147fs28 1
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Innovative cell-based therapies are being developed to repair, replace, or regenerate absent, injured, or diseased tissues and or-gans. T ese investigational therapies of er promise for the treatment of many serious medical conditions, which is illustrated by the variety of indications currently under investigation in clinical trials (see www.clinicaltrials.gov). In the United States, cell-based regenerative medicine (RM) products are regulated by the U.S. Food and Drug Administration (FDA) through the Center for Biologics Evaluation and Re-search (CBER). Before initiation of a clini-cal trial for a specif c RM product, it is the responsibility of FDA’s CBER review staf to establish whether clinical trial partici-pants would be exposed to substantial and unreasonable risks.
From 2007 to 2011, CBER received ~115 original submissions from academic and commercial sponsors requesting per-mission to begin clinical investigations of cell-based RM products for many dif er-ent indications, including cardiovascu-lar diseases, diabetes, neurodegenerative disorders, wound healing, and others. For this analysis, the number of submissions excludes products for oncology indications or those manufactured by use of genetic engineering. T e identity and tissue sourc-es of these cell-based RM products span a wide spectrum (Fig. 1), ranging from func-tionally specialized and lineage-restricted cells to products derived from unspecial-ized pluripotent embryonic stem (ES) cells.
PROMISE AND RISKT e promise of many cell-based RM prod-ucts is based on their inherent biological properties—high rates of proliferation, mi-gratory (traf cking) ability, plasticity, and capacity for self-renewal. However, these
same properties also pose particular chal-lenges during product development. T e potential for tumor formation is a major safety concern for products derived from undif erentiated or incompletely dif erenti-ated cells or from cells that have undergone extensive ex vivo manipulation. Indeed, the formation of teratomas af er injection of undif erentiated ES cells into immuno-def cient mice is a distinguishing feature,and the potential for malignant transfor-mation and inappropriate dif erentiation of cells undergoing prolonged or rapid ex-pansion is well documented (1–3). T e po-tential for tumor formation should also be considered in the context of the anatomical location of any found tumor or undesired tissue because increased damage to normal host tissue may result if cells proliferate in an anatomically constrained or sensitive area, such as the spinal column or retinal space (4).
FDA and other regulatory agencies recognize the inherent risk of tumor for-mation for many cell-based RM products (5–7). T e importance of appropriate pre-clinical testing to identify, characterize, and minimize this risk has also been dis-cussed by the FDA Cellular, Tissue, and Gene T erapies Advisory Committee (8, 9). During FDA/CBER regulatory review, the potential for tumor formation is con-sidered for all cell-based RM products (Fig. 1). Many of the principles described in this article determined the methods of evalua-tion and mitigation strategies that were ap-propriate for each product.
Extra caution is warranted for ES cell–derived products to ensure that the propor-tion of residual undif erentiated cells in the f nal product is as low as technically feasible. Other less well understood risk factors, such as chromosomal instability, may be identi-f ed and minimized through appropriate preclinical testing (and subsequent changes to product manufacturing processes). An appropriate program could include in vitro testing (such as chromosomal analysis), in vivo evaluation of proliferation and tumor formation af er product administration at the clinically relevant anatomical location, additional product characterization (such as whole-genome microarray analysis), or changes in product manufacturing (such as antibody-mediated cell sorting for the tar-geted depletion of undesired phenotypes).
R E G U L AT O R Y S C I E N C E
Balancing Tissue and Tumor Formation in Regenerative MedicineAlexander M. Bailey
E-mail: [email protected]
Of ce of Cellular, Tissue, and Gene Therapies, Center for Biologics Evaluation and Research, FDA, Rockville, MD 20852, USA.
A set of general principles can guide preclinical testing strategies for evaluating the tumorigenicity of regenerative medicine products.
Fig. 1. FDA/CBER experience. Original submissions (~115) to initiate clinical investigations for cell-based RM products were submitted to FDA/CBER from 2007-2011. The cellular components of these products spanned a wide spectrum of (A) cell types and (B) tissue sources; ~70% of submis-sions were for new products and 30% were for new indications for previously evaluated (cross-referenced) products. Assessment of tumorigenicity risk was performed by direct testing of the product (in vitro or in vivo studies) (43%) or through consideration of product attributes, the scien-tifi c literature, and/or previous clinical experience (57%).
(A) Cell type (B) Tissue sourceES cell−derived
Other
Other
Umbilical
cord (blood,
tissue)
Pancreatic islet
Neural-
lineage
Cardiac
Keratinocytes/
fibroblasts
Mononuclear
cells (blood,
bone marrow)
Mesenchymal
stem cells
Adipose
Blood
Dermal
tissue
Embryonic
Fetal tissue
Placenta
Umbilical
cord
Bone marrow
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TUMORIGENICITY TESTING CHALLENGESDesigning appropriate preclinical testing programs to evaluate the tumorigenic po-tential of a cell-based RM product is chal-lenging for several reasons: (i) the heteroge-neity and biological complexity of cell-based RM products; (ii) the lack of a complete understanding of cellular product attributes that are reliably predictive for tumorigenic-ity; and (iii) the dif culty of translating pre-clinical test results to the clinical scenario.
T e variability and biological complex-ity of cell-based RM products have made it dif cult to develop and adopt a standard-ized, prescribed set of preclinical studies that are uniformly appropriate. To illustrate this point, consider the following hypo-thetical example of two dif erent cell-based RM products: (i) a three-dimensional, bio-resorbable polymer scaf old seeded with adipose–derived, ex vivo culture–expanded
mesenchymal stem cells (MSCs) that are to be surgically implanted for nerve regenera-tion and (ii) a suspension of ES cell–derived cardiomyocytes that are to be directly inject-ed into the myocardium. T ese hypothetical cell-based RM products are dif erent with respect to their tissue source, cellular phe-notype, manufacturing processes, anatomi-cal site of administration, and (most likely) in vivo tissue distribution. It follows that the preclinical programs to evaluate the safety of these two hypothetical products will dif-fer by necessity.
For the MSC-based product, there is a risk that donor cells may become geneti-cally unstable af er extensive manufactur-ing or interactions with the scaf old pre- or postimplantation. T us, testing that does not include evaluation of the intended clini-cal product—MSCs cultured to the end of product limit and seeded on the polymer scaf old—may not adequately inform clini-
cal risk. T is is equally true for the second hypothetical product, but there is also a greater risk that a suspension of ES cell–derived cardiomyocytes contains residual undif erentiated cells that could form tera-tomas af er administration. To help ensure that the tumorigenicity testing of such a product is interpretable, the study design should include groups of animals that re-ceive undif erentiated ES cells, serial dilu-tions of a population of undif erentiated ES cells combined with ES cell–derived car-diomyocytes, and the f nal intended clini-cal product. T is approach to preclinical tumorigenicity testing, in which the panel of tests is tailored for each specif c prod-uct, is in contrast to the established rodent bioassays used for carcinogenicity testing of small-molecule pharmaceuticals.
As a result of the challenges associated with testing methods for RM products, a panel of tests that consists of both in vitro
Table 1. Assessing tumorigenic potential. Although there currently is no check-the-box standard preclinical animal study design to evaluate a cell-based RM product’s ability to form tumors in vivo, an appreciation of the limitations and challenges associated with animal testing can aid in the design of product-specifi c science-based preclinical testing strategies.
Considerations for cell-based RM products Associated challenges for preclinical animal studies
The cellular component may form tumors after in vivo administration. Comprehensive preclinical testing may be necessary to identify and mini-mize the risk of tumor formation.
The identical clinical product should be tested. Achieving durable cell engraftment in animals may be diffi cult.
If the cells are expected to persist in humans, durable engraftment of the cellular product is necessary for a preclinical study to be informative.
An immune response to human donor cells may prevent durable engraft-ment in an animal model (xenorejection). To address this caveat:
• Use of immuno-compromised (IC) rodents or immuno-suppression (IS) regimens may facilitate engraftment, but IC animals may have shorter life spans, and IS regimens may cause toxicity in the host animal or to the administered cells.
• The use of analogous animal cells may facilitate engraftment, but these cells may also have diff erent bioactivity.
Tumor formation is often a slowly occurring and rare event. Preclinical testing that is not conducted over a suffi cient portion of the expected life span of an animal may yield a false-negative result. A large number of animals may be needed to detect rare tumor formation events.
Some animals spontaneously develop tumors that are unrelated to adminis-tration of the product.
Identifi cation of tumor origin (donor- or host-cell) is necessary. A large num-ber of animals may be needed to distinguish spontaneous tumor formation from those due to the product.
The microenvironment may infl uence a product’s tumorigenic potential. Cell delivery to an anatomical location other than the intended clinical loca-tion may not adequately inform clinical risk.
Scaff olding or other product components may provide environmental cues that infl uence bioactivity.Xenogeneic environments may not provide clini-cally relevant cues, which may infl uence interpretability of results.
Tumor formation may be dose dependent. It may not be possible to administer the absolute clinical dose in an animal model.
The sensitivity of testing methods may need to be confi rmed with appropri-ate positive controls.
A product may induce tumor formation from existing subclinical host malignant cells.
Established animal models relevant to the target patient population may not exist.
Product characteristics may introduce new risk factors for tumor formation. There are no standard preclinical methods of evaluation; new products may require new testing paradigms.
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and in vivo studies is of en the most infor-mative. For example, in vitro testing may identify phenotypic and genomic markers specif c to a population of cells; however, the utility of these markers may be limited by an incomplete understanding of biomarkers that are, in fact, predictive of tumor forma-tion. Moreover, many in vitro assays fail to account for the tumor-promoting or tumor-suppressing ef ects of the local niche within which the cells will reside af er patient ad-ministration, such as inf ammatory status, growth factor concentrations, and extracel-lular matrix presentation. Nevertheless, in vitro tests have utility in many instances. For example, comprehensive evaluation of a cell-based RM product’s growth kinetics, in-cluding determination of proliferation rate or number of population doublings before senescence, may help inform the risk of tu-mor formation. It follows that although in vitro characterization and testing of a cell-based RM product is informative, comple-mentary in vivo testing is of en, though not always, necessary.
IS MY PRODUCT CAPABLE OF TUMOR FORMATION?T e risk of tumor formation for each cell-based RM product is dependent on a con-stellation of product-specif c properties. T ese may include cell type (for example, fetal neural cells versus neonatal f bro-blasts), cell persistence, phenotypic plastic-ity, proliferative capacity, and propensity to migrate from the site of administration. Other critical factors, such as degree of ma-nipulation during manufacturing, the local microenvironment within which the deliv-ered cells will eventually reside, cell dose, and immune status, may also either increase or decrease the likelihood of tumor forma-tion. Accordingly, there is a spectrum of risk among cell-based RM products, and an understanding of these product-specif c risk factors can aid in the development of appropriate preclinical testing strategies. For instance, there is presumably less risk of tumor formation af er administration of low–passage number, dif erentiated f bro-blasts compared with either of the hypo-thetical cell-based RM products discussed above. For the former, animal studies to
evaluate tumorigenicity may not be neces-sary; rather, in vitro characterization of the cellular product and assessment of its bio-logical stability may be suf cient.
A well-designed preclinical testing pro-gram incorporates a tiered approach that is risk based (as determined by comprehensive product characterization) and takes into ac-count the limitations of both in vitro testing and available animal models. If evaluation of tumorigenic potential in an animal model is warranted, an appreciation of some of the associated challenges will aid in the design of an appropriate study (Table 1). For exam-ple, administration of human cells to an im-munocompetent rodent will result in their rapid elimination. If these cells are expected to persist in the clinical setting, it would be dif cult to gauge the level of risk of tumor formation from these results alone. Simi-larly, an animal study that evaluates a route of product administration that is dif erent from what is proposed clinically may not adequately account for the inf uence of the local host microenvironment, which could af ect the product’s ability to form tumors. For instance, results generated from the subcutaneous implantation of a cell-based RM product may not accurately ref ect the bioactivity of a product that is intended for intracranial implantation in humans. Con-sideration of these issues and other chal-lenges, as highlighted above and in Table 1, may aid in the design of an appropriate preclinical program.
FDA/CBER evaluates the safety of in-vestigational cell-based RM products prior to administration in clinical trials. A data-driven, case-by-case approach is employed during the review process to ensure that an appropriate balance is struck between the potential risks and benef ts of a cell-based RM product. While the risk for tumor for-mation may exist, product characterization and preclinical testing paradigms that are appropriately designed and implemented can help to identify, minimize, and man-age this risk. Bearing this in mind, there are considerations that may aid innovators during implementation of preclinical test-ing and product development programs: (i) T ere is a continuum of risk that is depen-dent on a collection of product attributes;
(ii) a preclinical testing program may need to be tailored to the specif c cellular product and level of risk; and (iii) new therapies may require new testing paradigms. Preclini-cal testing strategies that take into account these issues and those highlighted in Table 1 may help to strike a balance between tissue regeneration and tumor formation.
REFERENCES AND NOTES 1. J. A. Thomson, J. Itskovitz-Eldor, S. S. Shapiro, M. A.
Waknitz, J. J. Swiergiel, V. S. Marshall, J. M. Jones, Embry-onic stem cell lines derived from human blastocysts. Sci-ence 282, 1145–1147 (1998).
2. A. H. Brivanlou, F. H. Gage, R. Jaenisch, T. Jessell, D. Melton, J. Rossant, Stem cells. Setting standards for hu-man embryonic stem cells. Science 300, 913–916 (2003).
3. K. E. Hatzistergos, A. Blum, T. Ince, J. M. Grichnik, J. M. Hare, What is the oncologic risk of stem cell treatment for heart disease? Circ. Res. 108, 1300–1303 (2011).
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5. Points to Consider in the Characterization of Cell Lines Used to Produce Biologicals, Center for Biologics Evalu-ation and Research (CBER), FDA (1993). http://www.fda.gov/downloads/biologicsbloodvaccines/safetyavailabil-ity/ucm162863.pdf.
6. Guidance for Industry: Guidance for Human Somatic Cell Therapy and Gene Therapy. CBER, FDA (1998). h t t p : / / w w w. fd a . g ov / b i o l o gi c s b l o o d v a cc i n e s /guidancecomplianceregulatoryinformation/guidances/cellularandgenetherapy/ucm072987.htm.
7. Committee for Advanced Therapies (CAT), Refl ection Paper on Stem Cell-Based Medicinal Products Euro-pean Medicines Agency (2010). http://www.ema.europa.eu/docs/en_GB/document_library/Scientific_guide-line/2011/02/WC500101692.pdf.
8. Cellular Products for Joint Surface Repair - March 2005. Cellular, Tissue, and Gene Therapies Advisory Commit-tee (CTGTAC) Meeting #38 (2005). http://www.fda.gov/ohrms/dockets/ac/05/questions/2005-4093q1.pdf.
9. Cellular Therapies Derived from Human Embryonic Stem Cells - Considerations for Pre-Clinical Safety Testing and Patient Monitoring - April 2008. Cellular, Tissue, and Gene Therapies Advisory Committee (CTGTAC) Meeting #45 (2008). http://www.fda.gov/ohrms/dockets/ac/08/briefi ng/2008-0471B1_1.pdf.
Acknowledgments: The author thanks P. Au, M. Serabian, D. Fink, and T. Chen from FDA/CBER/OCTGT for their assistance in preparing this commentary. Competing interests: The author declares that he has no competing interests.
Citation: A. M. Bailey, Balancing tissue and tumor formation in regenerative medicine. Sci. Transl. Med. 4, 147fs28 (2012).
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Balancing Tissue and Tumor Formation in Regenerative MedicineAlexander M. Bailey
DOI: 10.1126/scitranslmed.3003685, 147fs28147fs28.4Sci Transl Med
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