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Will iPS Cells Enhance Therapeutic Applicability of Cord Blood Cells and Banking?

2010; Elsevier BV; Volume: 6; Issue: 1 Linguagem: Inglês

10.1016/j.stem.2009.12.008

1934-5909

Hal E. Broxmeyer,

Renal and related cancers

The exciting development of induced pluripotent stem cells (iPSCs), and the discovery that iPSCs can be derived from cord blood (CB), combined with the presence of nonhematopoietic stem and progenitor cells in CB may lead to enhanced therapeutic applicability of this cell source and induce increased CB banking. The exciting development of induced pluripotent stem cells (iPSCs), and the discovery that iPSCs can be derived from cord blood (CB), combined with the presence of nonhematopoietic stem and progenitor cells in CB may lead to enhanced therapeutic applicability of this cell source and induce increased CB banking. Hematopoietic stem cells (HSCs) and progenitors (HPCs) in bone marrow (BM) have been used clinically for over 40 years. In addition, cord blood (CB) and public CB banking have worked in synergy to help patients in need of HSC and HPC transplants to treat a wide variety of malignant and nonmalignant diseases (Broxmeyer and Smith, 2009Broxmeyer H.E. Smith F.O. Cord Blood Hematopoietic Cell Transplantation.in: Appelbaum F.R. Forman S.J. Negrin R.S. Blume K.G. Wiley-Blackwell, West Sussex, United Kingdom2009: 559-576Google Scholar). What we know about HSCs and HPCs and how best to use them for clinical efficacy developed over decades of extensive controlled laboratory and clinical studies. This learning process is ongoing. Despite considerable progress to date, the field has still not figured out how to expand human HSCs ex vivo for effective clinical transplantation, even though this step was accomplished decades ago for mouse HSCs and human and mouse HPCs, highlighting the need for patience and careful laboratory and clinical studies before rushing into new treatment modalities. The diverse arena of stem cell biology includes embryonic stem cells (ESCs), as well as other nonhematopoietic stem and progenitor cells, such as mesenchymal stem or stromal cells (MSCs), endothelial progenitor cells (EPCs), and recently induced pluripotent stem cells (iPSCs) (Yamanaka, 2009Yamanaka S. Cell. 2009; 137: 13-17Abstract Full Text Full Text PDF PubMed Scopus (567) Google Scholar). In each case, many important questions remain to be answered, including whether many adult populations are truly stem cells, what their true range of differentiation capacities are, to what degree the fate of ESCs, MSCs, EPCs, other tissue-specific stem and progenitor cells, and iPSCs can be finely regulated, and if they will be clinically useful. Stem cells and the growing field of regenerative medicine elicit excitement and anticipation across the globe. However, with hope comes occasional hype that, in turn, can yield unanticipated false hope, based on premature clinical efforts that may provide no recognizable benefit, which in the end dampens public enthusiasm for future applications, or worse, negatively impacts patients. Although success can never be guaranteed with new treatments, we should remain vigilant and not sacrifice rigorous controls during experimental design in order to ensure that any results attained will be informative, especially at the clinical level. Safety is a primary concern. In our efforts to establish the field of CB HSC and HPC transplantation during the 1980s, we spent many years on experimentation and had numerous intense discussions on the feasibility and ethical considerations of using CB for transplantation, well before identifying a first disease to be treated (Fanconi anemia) and candidate locale for the first transplant (Dr. Eliane Gluckman's group at the Hopital St. Louis in Paris) (reviewed in Broxmeyer and Smith, 2009Broxmeyer H.E. Smith F.O. Cord Blood Hematopoietic Cell Transplantation.in: Appelbaum F.R. Forman S.J. Negrin R.S. Blume K.G. Wiley-Blackwell, West Sussex, United Kingdom2009: 559-576Google Scholar). After deciding on the disease and transplant unit to target, we exchanged experimental expertise and unpublished data with Dr. Gluckman and her team, prior to releasing the frozen HLA-matched sibling CB unit from my proof-of-principle CB bank. As a precaution in case of engraftment failure, we had the sibling CB donor ready as a backup in the event that her BM was needed to rescue the CB recipient. We hoped not to need her BM, given that the donor was less than 1 year old at that time. After the first transplant successfully demonstrated CB donor cell engraftment, and an additional three of four successes were attained (one for leukemia and two for Fanconi anemia), I was asked what the future of CB transplantation might have been, had the first attempt not succeeded. In response, I predicted that, at worst, CB engraftment failure might have resulted in cessation of subsequent attempts, especially if the patient was harmed or died, but more likely a negative outcome would have substantially slowed efforts toward future attempts. The important message to be gleaned from our experience is to encourage emerging fields that aim to apply other stem cell populations and regenerative medicine techniques not to rush into clinical trial until pros and cons and ethical concerns are carefully considered and to ensure that a reasonable back-up plan is in place before human intervention is undertaken. This caution, born of experience, is especially timely in the context of published reports purporting, without adequate data and appropriate controls, the usefulness of CB for regenerative medicine. With this caveat in mind, recent publications demonstrating generation of iPSCs from human CB (Haase et al., 2009Haase A. Olmer R. Schwanke K. Wunderlich S. Merkert S. Hess C. Zweigerdt R. Gruh I. Meyer J. Wagner S. et al.Cell Stem Cell. 2009; 5: 434-441Abstract Full Text Full Text PDF PubMed Scopus (391) Google Scholar, Giorgetti et al., 2009Giorgetti A. Montserrat N. Aasen T. Gonzalez F. Rodriguez-Piza I. Vassena R. Raya A. Boue S. Barrero M.J. Corbella B.A. et al.Cell Stem Cell. 2009; 5: 353-357Abstract Full Text Full Text PDF PubMed Scopus (331) Google Scholar, Ye et al., 2009Ye Z. Zhang H. Mali P. Dowey S. Williams D.M. Jang Y.-Y. Dang C.V. Spivak J.L. Moliterno A.R. Cheng L. Blood. 2009; (in press. Published online Oct 1, 2009)https://doi.org/10.1182/blood-2009-04-217406Crossref Scopus (311) Google Scholar), and the identification of MSCs, EPCs, and other stem and progenitor cell types in CB (Broxmeyer and Smith, 2009Broxmeyer H.E. Smith F.O. Cord Blood Hematopoietic Cell Transplantation.in: Appelbaum F.R. Forman S.J. Negrin R.S. Blume K.G. Wiley-Blackwell, West Sussex, United Kingdom2009: 559-576Google Scholar), indicate that it is appropriate to consider the potential future of CB biology, transplantation, and banking. Since our initial laboratory (Broxmeyer et al., 1989Broxmeyer H.E. Douglas G.W. Hangoc G. Cooper S. Bard J. English D. Arny M. Thomas L. Boyse E.A. Proc. Natl. Acad. Sci. USA. 1989; 86: 3828-3832Crossref PubMed Scopus (1010) Google Scholar) and clinical (Gluckman et al., 1989Gluckman E. Broxmeyer H.E. Auerbach A.D. Friedman H. Douglas G.W. Devergie A. Esperou H. Thierry D. Socie G. Lehn P. et al.N. Engl. J. Med. 1989; 321: 1174-1178Crossref PubMed Scopus (1752) Google Scholar) studies that suggested and proved the presence of transplantable HSCs and HPCs in human umbilical CB, banked allogeneic CB has been used to treat over 20,000 patients suffering from the wide range of diseases treated by BM transplantation. Unrelated allogeneic CB transplantation is possible because of the existence of public CB banks that store HLA-defined CB units for purchase. There are also private family CB banks that store autologous or related allogeneic CB and charge both upfront and maintenance fees. Currently, the odds of an individual using privately stored CB are extremely low (Kaimal et al., 2009Kaimal A.J. Smith C.C. Laros R.K. Caughey A.B. Cheng Y.W. Obstet. Gynecol. 2009; 114: 848-855Crossref PubMed Scopus (32) Google Scholar), and yet there are three times as many CB samples stored in private family versus public banks. Recent cost and use evaluations for these different banks have been reported by Kaimal et al., 2009Kaimal A.J. Smith C.C. Laros R.K. Caughey A.B. Cheng Y.W. Obstet. Gynecol. 2009; 114: 848-855Crossref PubMed Scopus (32) Google Scholar. The emerging fields of stem cell biology and regenerative medicine have the potential to influence the growth of both types of CB banks and ultimately may alter the existing cost per use calculations. Examples of developing areas that may impact the field of CB banking are the presence of nonhematopoietic stem and progenitor cells in or produced from CB. These findings and the potential advantages and limitations of these cells are discussed below. iPSCs have been generated from numerous somatic cell types (reviewed in Maherali and Hochedlinger, 2008Maherali N. Hochedlinger K. Cell Stem Cell. 2008; 3: 595-605Abstract Full Text Full Text PDF PubMed Scopus (404) Google Scholar) and recently also from various subpopulations of CB, as described below. There is some suggestion, not yet rigorously proven, that the more immature the adult starting cell population, the easier and more efficient it may be to generate iPSCs. If this hypothesis is true, CB may represent an advantageous cell source for iPSC generation, given that it contains more immature and cytokine-responsive subsets of HSC and HPC than adult BM (Broxmeyer and Smith, 2009Broxmeyer H.E. Smith F.O. Cord Blood Hematopoietic Cell Transplantation.in: Appelbaum F.R. Forman S.J. Negrin R.S. Blume K.G. Wiley-Blackwell, West Sussex, United Kingdom2009: 559-576Google Scholar). Furthermore, CB HPCs respond to ex vivo stimulation of proliferation and expansion more rapidly and, to a greater extent, and contain longer teleomeres than BM HPCs. Human HSC engraftment of nonobese diabetic (NOD) severe combined immunodeficient (SCID) mice is greater with CB than BM. EPCs from CB have greater proliferative capacity than those from BM (Yoder and Ingram, 2009Yoder M.C. Ingram D.A. Curr. Opin. Hematol. 2009; 16: 269-273Crossref PubMed Scopus (77) Google Scholar). These traits, in part, may have contributed to the selection of immature CB subpopulations for use in iPSC generation. Specifically, Haase et al., 2009Haase A. Olmer R. Schwanke K. Wunderlich S. Merkert S. Hess C. Zweigerdt R. Gruh I. Meyer J. Wagner S. et al.Cell Stem Cell. 2009; 5: 434-441Abstract Full Text Full Text PDF PubMed Scopus (391) Google Scholar used lentiviral vector-mediated gene transduction of OCT4, SOX2, NANOG, and LIN28 into endothelial cells derived from human CB. The resulting iPSCs expressed ESC markers OCT4, SOX2, NANOG, Lin28, SSEA-3, SSEA-4, and TRA-1-60, with no obvious chromosomal abnormalities noted by passage 32. Notably, the efficiency of reprogramming correlated with the proliferative activity of the targeted endothelial cells. Functionally, iPSCs differentiated into endoderm, ectoderm, and mesoderm germ layers in SCID-beige murine hosts, and cardiomyocytes with ventricular and pacemaker-like activity and β-adrenergic signaling capacity were produced in vitro. Taking a different approach, Giorgetti et al., 2009Giorgetti A. Montserrat N. Aasen T. Gonzalez F. Rodriguez-Piza I. Vassena R. Raya A. Boue S. Barrero M.J. Corbella B.A. et al.Cell Stem Cell. 2009; 5: 353-357Abstract Full Text Full Text PDF PubMed Scopus (331) Google Scholar used retroviral transduction of CD133+ CB cells (enriched in HSC and HPC) with OCT4, SOX2, KLF4, and c-MYC genes or with only OCT4 and SOX2. iPSCs maintained a normal karyotype for more than ten passages, formed embryoid bodies with high efficiency, and gave rise to intratesticular teratomas containing three embryonic germ layers in SCID-beige mice. With this method, iPSCs were generated from frozen CB stored for more than 5 years. Finally, Ye et al., 2009Ye Z. Zhang H. Mali P. Dowey S. Williams D.M. Jang Y.-Y. Dang C.V. Spivak J.L. Moliterno A.R. Cheng L. Blood. 2009; (in press. Published online Oct 1, 2009)https://doi.org/10.1182/blood-2009-04-217406Crossref Scopus (311) Google Scholar derived iPSCs from CD34+ CB cells that were stored frozen for up to 8 years and then transduced with retroviral vectors expressing OCT4, SOX2, KLF4, and cMYC. iPSCs expressed TRA-1-60, as well as endogenous OCT4 and NANOG, and maintained a normal karyotype through at least nine cell passages. Pluripotency was demonstrated on the basis of embryoid body formation and the development of teratomas after injection into immune-deficient mice. The CB iPSC studies, though important, do not directly address whether CB will be a more appropriate starting population for iPSC production relative to other cell types, and it remains unclear whether any iPSCs will be therapeutically useful. The authors note that the younger age of CB cells may mean that CB-derived iPSCs may harbor fewer genetic abnormalities and insults, which may allow for more efficient iPSC generation compared to other adult somatic cell types, and thus offer advantages for use in iPSC production. The availability of banked CB was noted as another potential advantage of CB as a starting population. Successful therapeutic use of nonhematopoietic stem and progenitor cells found in, or generated from, CB will increase the clinical applicability of CB, thereby enhancing the need for additional public banks, as well as for an expanded inventory of HLA-characterized CB units present in each bank. Should CB be proven to offer additional therapeutic uses, the likelihood that parents or grandparents will pay to store their child's or grandchild's CB for personal or related family use will also increase. The important caveat, of course, is that such nonhematopoietic stem and progenitor cells found in, or generated from, CB or another other cell type have not yet demonstrated therapeutic efficacy. Unfortunately, families are not necessarily informed that use of these non-HSC and HPCs remains an unproven therapeutic concept. It is important that CB banks, whether private family or public, do not overstate or oversell the efficacy of their product without proof that the benefits are real, rather than merely potential advantages. With numerous births a year, the vast majority of which have not been collected for CB banking, I don't consider it likely that public banks will experience a decline in donations because of private family banking. In fact, I predict that with proper and honest advertising and with more infrastructure and government support, the number of parents willing to donate to public banks will increase. In the end, the choice of donating to a public or private family bank is a private parental decision, but one that needs to be made with appropriate information, not misinformation. On the experimental side, iPSC technology has advanced rapidly as a result of the efforts of many labs worldwide. For example, viable mice have been generated from mouse iPSCs through tetraploid complementation, a mouse model of sickle cell anemia was treated with autologous iPSCs after gene correction of the human sickle hemoglobin, and iPSCs have been generated from different patients, thereby allowing disease modeling (Saha and Jaenisch, 2009Saha K. Jaenisch R. Cell Stem Cell. 2009; 5: 584-595Abstract Full Text Full Text PDF PubMed Scopus (316) Google Scholar). Furthermore, additives are being evaluated for the capacity to enhance genetic factor-mediated reprogramming or to replace genetic intervention completely (reviewed in Feng et al., 2009Feng B. Ng J.H. Heng J.C. Ng H.H. Cell Stem Cell. 2009; 4: 301-312Abstract Full Text Full Text PDF PubMed Scopus (311) Google Scholar). Successful iPSC generation remains variable and inefficient, and several methods to overcome this hurdle, such as disabling the p53 tumor-suppressor gene, also promote the possibility that resulting lines will themselves give rise to cancer. Furthermore, little is known regarding the efficiency and specificity of the processes used to generate differentiated progeny from iPSCs derived from various somatic sources and how complex it may be to finely regulate these protocols. Fully reprogrammed iPSCs attain an essentially ESC-like state, but ESCs themselves can manifest a degree of genetic instability, especially under stress (Mantel et al., 2007Mantel C. Guo Y. Lee M.-R. Kim M.-K. Han M.-K. Shibayama H. Fukuda S. Yoder M.C. Pelus L.M. Kim K.-S. et al.Blood. 2007; 109: 4518-4527Crossref PubMed Scopus (110) Google Scholar). Thus, the field is dealing with safety problems at the level of the iPSC itself, as well as the purity and function of differentiated cells produced from the iPSCs. With these successes and challenges in mind, we can consider how CB might compare to other cell sources for iPSC generation. A concern when planning to transplant iPSC-derived cells is their immune status. The level of GVHD observed in any transplant recipient is enhanced in proportion to HLA disparity, and even perfectly HLA-matched allogeneic cells elicit some level of GVHD, even with prophylaxis. CB may, due in part to its relatively naive immune state, offer an advantage over adult somatic cells for use in generating human iPSCs for allogeneic transplantation. However, extensive in vitro manipulation during the derivation and subsequent differentiation of CB iPSCs may increase their immunogenicity as a result of upregulation of major and/or minor histocompatibility or other loci. In fact, past attempts to expand CB HSCs and HPCs ex vivo for clinical use have elicited enhanced levels of chronic GVHD, and it may be that even newer ex vivo methods used to expand cells will have a similar negative outcome. This possibility will need to be carefully assessed, especially with regard to the generation of nonhematopoietic cells. Although it is clear that iPSCs can be generated from cryopreserved CB (Giorgetti et al., 2009Giorgetti A. Montserrat N. Aasen T. Gonzalez F. Rodriguez-Piza I. Vassena R. Raya A. Boue S. Barrero M.J. Corbella B.A. et al.Cell Stem Cell. 2009; 5: 353-357Abstract Full Text Full Text PDF PubMed Scopus (331) Google Scholar, Ye et al., 2009Ye Z. Zhang H. Mali P. Dowey S. Williams D.M. Jang Y.-Y. Dang C.V. Spivak J.L. Moliterno A.R. Cheng L. Blood. 2009; (in press. Published online Oct 1, 2009)https://doi.org/10.1182/blood-2009-04-217406Crossref Scopus (311) Google Scholar), we don't know how well units of cryopreserved and fresh CB compare in terms of their iPSC derivation efficiency, the genetic stability of resulting lines and their differentiated progeny, or how the length of time spent in frozen storage influences these parameters. Our work with cryopreserved CB demonstrated high-efficiency recovery of functional HSCs and HPCs after 15 years as assessed in vivo and in vitro (Broxmeyer et al., 2003Broxmeyer H.E. Srour E.F. Hangoc G. Cooper S. Anderson J.A. Bodine D. Proc. Natl. Acad. Sci. USA. 2003; 100: 645-650Crossref PubMed Scopus (197) Google Scholar), and our unpublished data demonstrates similar recovery of HSCs and HPCs after 23+ years of cryopreservation. The longest a CB unit has been stored and used successfully for HSC and HPC engraftment in humans is in the 10–12 year range, whereas CB samples are retained for much longer periods, and thus may represent a valuable source of starting material for iPSC generation. It is imperative that the functional capacity of human CB for this application be studied in much greater detail, and after much longer periods of storage than the 5 to 8 + years currently reported. Furthermore, although iPSCs have been generated from subsets of frozen CB, the cryopreservation technique used for HSC and HPCs may not be optimal for generation of iPSCs. If iPSCs generated from CB prove to be of clinical utility, the question of whether iPSCs should be derived prior to freezing or after thawing of the sample will need to be addressed. One might propose to isolate specific subpopulations intended for eventual reprogramming prior to cryopreservation, rather than freezing unseparated cord cells. However, this approach would be unwise, given that it remains to be seen which cells are best suited for reprogramming, and prefractioning would result in the loss of not only the HSC and HPCs but also of other potentially clinically relevant cells. Obviously, already banked units of CB will need to have iPSC generated after defrost, and it may be best to limit iPSC generation to postthaw samples. Of note, the impact of cryopreservation on the function of any established iPSC line is not yet known, regardless of the somatic cell of origin. Although it is not inconceivable that CB iPSCs may offer an alternative source of HSCs and HPCs for transplantation, it is not clear at this stage whether a sufficient number of hematopoietic cells of the quality of those already found in CB could be generated to warrant this type of effort. In fact, it is likely that CB iPSCs will be more valuable as a source of other types of cell or tissue stem and progenitors and their progeny. In particular, the potential to make multiple cell lineages from a single, genetically identical cell source is one of the most desirable qualities of iPSCs derived from any starting population. That said, it remains unclear whether iPSCs derived from CB will be better able to generate nonhematopoietic cell types than iPSCs derived from other tissues. Even if their capacities are only roughly equivalent, the existence of stored, HLA-typed CB units could provide an argument in favor of using CB for this purpose. In addition to HSCs and HPCs, other known stem and progenitor cell types are present in CB that may harbor as yet untested, and thus presently unproven, therapeutic value. This list includes but is not necessarily limited to MSCs and EPCs. MSCs exhibit extensive proliferative capacity in vitro and can differentiate into bone, fat, and cartilage. MSCs may possess immunomodulating activity, but there is a paucity of information regarding characterization and function of MSCs (Prockop, 2009Prockop D.J. Mol. Ther. 2009; 17: 939-946Abstract Full Text Full Text PDF PubMed Scopus (454) Google Scholar). MSCs from CB may be of future use in regenerative medicine, but given that only a subset of CB units contain MSCs, possibly because of decreased frequency of these cells in CB versus BM (Broxmeyer and Smith, 2009Broxmeyer H.E. Smith F.O. Cord Blood Hematopoietic Cell Transplantation.in: Appelbaum F.R. Forman S.J. Negrin R.S. Blume K.G. Wiley-Blackwell, West Sussex, United Kingdom2009: 559-576Google Scholar), CB may not represent an appropriate source of MSCs unless the population isolated from CB samples are found to be more potent than those extracted from BM. EPCs with extensive proliferative capacity are also found in CB, albeit with relatively low frequency. Accurate definition of EPCs is controversial, as is their potential role in angiogenesis (Yoder and Ingram, 2009Yoder M.C. Ingram D.A. Curr. Opin. Hematol. 2009; 16: 269-273Crossref PubMed Scopus (77) Google Scholar). Better understanding of the phenotypic and functional characteristics, frequency and proliferative potential, and immunogenicity of MSCs and EPCs present in CB versus other tissue sources, such as BM, is needed before the clinical use of these populations in general, as well as for CB-derived cells specifically, should be considered for regenerative medicine. Recent excitement with regard to stem and progenitor cell biology as a field, and iPSCs in particular, is warranted in terms of basic biological insights into mechanisms of cell production, differentiation, and action. However, many unknowns remain regarding the realistic potential of iPS and other cell types for regenerative medicine. The clinical potential and safety of these cells and their differentiated offspring have yet to be determined, let alone whether CB may turn out to be a preferable source of nonhematopoietic stem cells and of starting material for iPSC generation. We can be cautiously optimistic and open-minded that clinical utility will eventually result from these evolving fields of study, but we must be realistic and not allow the predicted potential of these cells to get ahead of, or supersede, the rigorous science and controlled clinical efforts necessary to determine whether true applicability for these cells exists, and whether the cells are safe and efficacious. H.E.B. was a founding member of the first private cord blood banking company, Biocyte Corporation, and on their Board of Directors and Medical Scientific Advisory Board (MSAB). In sequence, he was also on the MSABs of the following private cord blood banking companies: ViaCord, ViaCell, and StemCyte. He was an Advisor for the Public Cord Blood Bank at the New York Blood Center and is currently on the MSAB of CordUse, a cord blood banking company. He is a member of the National Marrow Donor Program Cord Blood Committee and was on the HRSA/HHS Advisory Committee for Adult Blood Stem Cell Transplantation.