Archives

  • 2018-07
  • 2018-10
  • 2018-11
  • 2019-04
  • 2019-05
  • 2019-06
  • 2019-07
  • 2019-08
  • 2019-09
  • 2019-10
  • 2019-11
  • 2019-12
  • 2020-01
  • 2020-02
  • 2020-03
  • 2020-04
  • 2020-05
  • 2020-06
  • 2020-07
  • 2020-08
  • 2020-09
  • 2020-10
  • 2020-11
  • 2020-12
  • 2021-01
  • 2021-02
  • 2021-03
  • 2021-04
  • 2021-05
  • 2021-06
  • 2021-07
  • 2021-08
  • 2021-09
  • 2021-10
  • 2021-11
  • 2021-12
  • 2022-01
  • 2022-02
  • 2022-03
  • 2022-04
  • 2022-05
  • 2022-06
  • 2022-07
  • 2022-08
  • 2022-09
  • 2022-10
  • 2022-11
  • 2022-12
  • 2023-01
  • 2023-02
  • 2023-03
  • 2023-04
  • 2023-05
  • 2023-06
  • 2023-07
  • 2023-08
  • 2023-09
  • 2023-10
  • 2023-11
  • 2023-12
  • 2024-01
  • 2024-02
  • 2024-03
  • 2024-04

    • Numerous published reports have examined the potential of

    2018-10-22

    Numerous published reports have examined the potential of differentiated cell types derived from mouse and human ESCs to repair nonhuman target organs in intact animals. Recent studies, however, have yielded both encouragement and caution, with restoration of function evident to some degree in many cases, but coexisting in others with the troubling finding that the grafts contained evidence of cancerous growth (Fujikawa et al., 2005; Ishii et al., 2007; Kroon et al., 2008; Leor et al., 2007; Li et al., 2009; Roy et al., 2006; Hentze et al., 2009). Although ESCs offer great promise in regenerative medicine in terms of both the variety of tissues obtainable and the expansion potential of precursors, their slowly emergent clinical status reflects, in part, an inherent risk that arises due to the lack of understanding of the hazard of formation of teratomas arising from differentiated ESC-derivative populations. In view of the magnitude of this risk, selection schemes have been devised using genetically modified cell lines to either remove undifferentiated ES autotaxin inhibitor or purify ESC-derived populations that have been directed into specific lineages (Ishii et al., 2007; Kattman et al., 2006; Huber et al., 2007; Anderson et al., 2007; Fukuda et al., 2006; Soria et al., 2000; Saldeen et al., 2006). However, few, if any, of these experiments have exhaustively tested such cell populations for their tumor potential in vivo. In addition, despite genetic selection, the resulting populations still contained some undifferentiated ESCs (Ying et al., 2003) or produced obvious tumor growths in animal transplant tests (Ishii et al., 2007; Li et al., 2009; Chung et al., 2006). An explanation for these observations may lie in the less than ideal stringency of a single selection step. We desired to address the concern of residual tumorigenicity in one instance of high priority in the field of regenerative medicine: the derivation of differentiated pancreatic β cells from ESCs. Aiming to achieve efficient elimination of tumorigenicity of heterogeneous differentiated ESC-derived populations, we devised a three-step selective process that appears to completely remove all tumorigenic cells from concurrently enriched definitive endoderm cells, which include pancreatic precursors and progeny, while simultaneously eliminating another troublesome contamination: extraembryonic visceral endoderm (VYS). Commonly generated during typical ESC differentiation cultures during which postgastrulation germ layer derivatives are formed, VYS has overlapping genetic expression profiles with definitive endoderm including, for example, alpha fetoprotein, Foxa2, Sox17, Hnf4α, and Hnf1β (Sherwood et al., 2007; Dufort et al., 1998), that can confound careful gene expression analyses and potentially lead to erroneous conclusions. Effective methods for enriching definitive endoderm-committed cells would be of great value and have been pursued. To this end, several studies have taken advantage of the possible differential expression of CXCR4 in definitive versus visceral endoderm, and studied sorted CXCR4+ cells (D\'Amour et al., 2005; Gouon-Evans et al., 2006; Yasunaga et al., 2005). However, CXCR4 may not be an ideal marker to use for definitive endoderm enrichment for the following reasons. First, some studies have shown that CXCR4 is also highly expressed in visceral endoderm (Sherwood et al., 2007), and in many neuronal and mesodermal cells at early stages (McGrath et al., 1999). CXCR4 is expressed in many nonendodermal cell populations including neural, vascular, cardiac and skeletal muscle satellite cells, and lymphopoietic, myelopoietic, and hematopoietic stem cells (reviewed in (Miller et al., 2008)). Furthermore, CXCR4 expression appears to be downregulated in definitive endoderm after e8.5 of mouse embryonic development (McGrath et al., 1999), thereby potentially allowing some highly desired endodermal cell types in ESC-derived cultures to escape selection. Lastly, selective techniques would ideally be able to simultaneously remove all residual cell populations that could give rise to teratomas; however, as CXCR4 is also expressed in undifferentiated ESCs (our unpublished observations and (Baharvand et al., 2006)) this is not likely to be the case in CXCR4+ selected cell populations.