Optimizing autologous cell grafts to improve stem cell gene therapy
2016; Elsevier BV; Volume: 44; Issue: 7 Linguagem: Inglês
10.1016/j.exphem.2016.04.007
ISSN1873-2399
AutoresNikoletta Psatha, Garyfalia Karponi, Evangelia Yannaki,
Tópico(s)Mesenchymal stem cell research
Resumo•Challenges and interventions in optimizing cell grafts for gene therapy are discussed.•Large numbers of transduced hematopoietic stem cells (HSCs) with enhanced engraftment capacity are required for successful gene therapy.•Enrichment of HSC grafts may reduce target cell numbers and vector load.•Expansion of transduced HSCs without differentiation will potentially increase the effective dose of infused cells.•Priming of transduced HSCs with effector molecules will potentially enhance their repopulating capacity. Over the past decade, stem cell gene therapy has achieved unprecedented curative outcomes for several genetic disorders. Despite the unequivocal success, clinical gene therapy still faces challenges. Genetically engineered hematopoietic stem cells are particularly vulnerable to attenuation of their repopulating capacity once exposed to culture conditions, ultimately leading to low engraftment levels posttransplant. This becomes of particular importance when transduction rates are low or/and competitive transplant conditions are generated by reduced-intensity conditioning in the absence of a selective advantage of the transduced over the unmodified cells. These limitations could partially be overcome by introducing megadoses of genetically modified CD34+ cells into conditioned patients or by transplanting hematopoietic stem cells hematopoietic stem cells with high engrafting and repopulating potential. On the basis of the lessons gained from cord blood transplantation, we summarize the most promising approaches to date of increasing either the numbers of hematopoietic stem cells for transplantation or/and their engraftability, as a platform toward the optimization of engineered stem cell grafts. Over the past decade, stem cell gene therapy has achieved unprecedented curative outcomes for several genetic disorders. Despite the unequivocal success, clinical gene therapy still faces challenges. Genetically engineered hematopoietic stem cells are particularly vulnerable to attenuation of their repopulating capacity once exposed to culture conditions, ultimately leading to low engraftment levels posttransplant. This becomes of particular importance when transduction rates are low or/and competitive transplant conditions are generated by reduced-intensity conditioning in the absence of a selective advantage of the transduced over the unmodified cells. These limitations could partially be overcome by introducing megadoses of genetically modified CD34+ cells into conditioned patients or by transplanting hematopoietic stem cells hematopoietic stem cells with high engrafting and repopulating potential. On the basis of the lessons gained from cord blood transplantation, we summarize the most promising approaches to date of increasing either the numbers of hematopoietic stem cells for transplantation or/and their engraftability, as a platform toward the optimization of engineered stem cell grafts. Hematopoietic stem cell gene therapy (HSC-GT) represents an autologous therapeutic intervention by which a normal copy of a deficient gene is introduced into a patient's own HSCs to re-establish effective gene function. As such, HSC-GT bypasses the immunologic risks of allogeneic HSC transplantation and the immune suppression needed to prevent or control these risks. Today, HSC-GT offers a curative potential for diseases in which hematopoietic cell transplantation is suboptimal (i.e., metachromatic leukodystrophy) [1Peters C. Steward C.G. 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Although a single HSC is, theoretically, capable and sufficient to eventually repopulate the hematopoietic system in mice, the delayed reconstitution from a single cell or limited numbers of HSCs in humans is not compatible with life, and large numbers of infused cells are required for rapid engraftment and hematologic reconstitution after HSC transplantation [9Wagner J.E. Barker J.N. DeFor T.E. et al.Transplantation of unrelated donor umbilical cord blood in 102 patients with malignant and nonmalignant diseases: Influence of CD34 cell dose and HLA disparity on treatment-related mortality and survival.Blood. 2002; 100: 1611-1618Crossref PubMed Scopus (33) Google Scholar, 10Gluckman E. Rocha V. Boyer-Chammard A. et al.Eurocord Transplant Group and the European Blood and Marrow Transplantation Group. Outcome of cord-blood transplantation from related and unrelated donors.N Engl J Med. 1997; 337: 373-381Crossref PubMed Scopus (0) Google Scholar]. 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In this review, based mostly on lessons gained in the UCBT setting, we summarize current approaches and considerations toward this goal and deliberate on how these may be optimized for effective GT applications. Although the last decade granted clinical GT with sound achievements, successful implementation of GT still faces major constraints including, in certain cases, limited efficacy resulting from suboptimal transduction efficiency or engraftment incompetence of the gene-modified cells [6Cavazzana-Calvo M. Payen E. Negre O. et al.Transfusion independence and HMGA2 activation after gene therapy of human β-thalassaemia.Nature. 2010; 467: 318-322Crossref PubMed Scopus (540) Google Scholar, 12Grez M. Reichenbach J. Schwäble J. Seger R. Dinauer M.C. Thrasher A.J. Gene therapy of chronic granulomatous disease: The engraftment dilemma.Mol Ther. 2011; 19: 28-35Abstract Full Text Full Text PDF PubMed Scopus (68) Google Scholar, 13Kang H.J. Bartholomae C.C. 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The incorporation of elements of the human locus control region (LCR) into globin vectors improved gene transfer into HSCs, but at the expense of a severe compromise of vector titers because of the substantial length of the micro-LCR cassettes [14Hargrove P.W. Kepes S. Hanawa H. et al.Globin lentiviral vector insertions can perturb the expression of endogenous genes in beta-thalassemic hematopoietic cells.Mol Ther. 2008; 16: 525-533Abstract Full Text Full Text PDF PubMed Scopus (70) Google Scholar, 15Urbinati F. Arumugam P. Higashimoto T. et al.Mechanism of reduction in titers from lentivirus vectors carrying large inserts in the 3′LTR.Mol Ther. 2009; 17: 1527-1536Abstract Full Text Full Text PDF PubMed Scopus (39) Google Scholar]. The problem is further intensified when chromatin insulators are inserted into already large vector constructs, to protect the transgene expression from chromosomal position effects and/or shield the target genome from genotoxic events [15Urbinati F. 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Short-term (colony-forming units [CFUs]) as well as long-term culture-initiating cell (LTC-IC) culture-based assays, together with xenogeneic transplantation models, are frequently used to assess the potency of human HSCs to sustain functional hematopoiesis and characterize “true” HSCs [38Doulatov S. Notta F. Laurenti E. Dick J.E. Hematopoiesis: A human perspective.Cell Stem Cell. 2012; 10: 120-136Abstract Full Text Full Text PDF PubMed Scopus (212) Google Scholar]. On the basis of such studies, populations of CD34+/CD90+/CD133+ cells [38Doulatov S. Notta F. Laurenti E. Dick J.E. Hematopoiesis: A human perspective.Cell Stem Cell. 2012; 10: 120-136Abstract Full Text Full Text PDF PubMed Scopus (212) Google Scholar], CD34+/CD38−/CD133+ and CD34+/CD38−/CD45RA−/CD90+ cells [37Majeti R. Park C.Y. Weissman I.L. 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By this approach, they demonstrated that only 7% to 35% of cells identified as HSCs with the previous solely immunophenotype-based approaches were LT-HSCs [40Chen J.Y. Miyanishi M. Wang S.K. et al.Hoxb5 marks long-term haematopoietic stem cells and reveals a homogenous perivascular niche.Nature. 2016; 530: 223-227Crossref PubMed Scopus (0) Google Scholar]. A number of groups used various CD34+-enriched cell populations to exploit the higher repopulating capacity of specific, competitive, CD34+ cell subpopulations or to indirectly improve the suboptimal transduction efficiencies or even reduce the high vector production costs by targeting lower cell numbers. Baldwin et al. [41Baldwin K. Urbinati F. 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These data imply that in a clinical setting, transduction of CD34+/CD38− cells would allow the use of limited amounts of viral vector to achieve high rates of transduced HSCs with good engraftment capacity, thus generating treatment opportunities for more patients. In another approach to target HSCs with a more primitive phenotype, Brendel et al. [42Brendel C. Goebel B. Daniela A. et al.CD133-targeted gene transfer into long-term repopulating hematopoietic stem cells.Mol Ther. 2015; 23: 63-70Abstract Full Text Full Text PDF PubMed Scopus (10) Google Scholar] has recently reported that direct gene transfer into unstimulated CD34+ cells by a receptor-targeting CD133-LV lentiviral vector, which uses the CD133 surface marker of primitive HSCs as entry receptor. This allows for sustained long-term engraftment of gene-corrected cells in immunodeficient mice, even after secondary transplantation [42Brendel C. Goebel B. 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