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iPSC-Derived Modified Endothelial Progenitor Cells Repress Tumorigenesis

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Review of “Antitumor Effects of CD40 Ligand-Expressing Endothelial Progenitor Cells Derived From Human Induced Pluripotent Stem Cells in a Metastatic Breast Cancer Model” from Stem Cells TM by Stuart P. Atkinson.

Endothelial progenitor cells (EPCs) differentiate into the cells that make up the lining of blood vessels, and so play roles in vasculogenesis and angiogenesis. EPCs from the bone marrow are recruited to tumours to aid neovascularization and so have become an attractive cell type as vehicles for anti-tumorigenic therapeutics [1, 2]. Embryonic stem cells (ESCs) represent a source for the large numbers of modified EPCs required to therapeutically inhibit tumorigenesis [3], although patient-specific induced pluripotent stem cells (iPSCs) represent a more attractive option. Now, in Stem Cells Translation Medicine, the group of Shu Wang at the National University of Singapore describe the derivation of EPCs from human iPSCs, their therapeutic modification, and their ability to inhibit tumor growth in a mouse breast cancer model [4].

The authors generated EPCs from iPSCs using a protocol designed for ESCs [5], which involved the plating of iPSC embryoid bodies onto Matrigel-coated plates in the presence of BMP4 (days 0–7), Activin A (days 1–4), FGF2 (day 2 onward), VEGF (day 4 onward), and SB431542 (a TGF- inhibitor, from day 7 onward) for 2 weeks. This gave a mixed population of cells with 20% expressing CD34, a hematopoietic stem cell marker, with some co-expression of endothelial cell markers (CD31, Flk1, and VE-cadherin). Enrichment of CD34+ cells and expansion in an endothelial growth medium led to the enrichment of cells with endothelial cell marker expression which readily formed tubule-like structures on seeding onto Matrigel, suggesting them to be iPSC-derived EPCs. The authors then tested the tumor targeting capability of iPSC-EPCs labelled with the near-infrared fluorescent dye DiR in two established mouse breast cancer models. In the orthotopic breast cancer model around 12% of tail injected iPSC-EPCs homed to the mammary pad region, while in the breast cancer lung metastasis model iPSC-EPCs were distributed predominantly to the lung region. Injections of iPSC-EPCs did not however have significant effect on tumor growth or on overall survival, but transducing cells with a baculovirus expressing CD40L, a member of the TNF gene family which can induce apoptosis [6, 7], and injection into the breast cancer lung metastasis, increased levels of pro-apoptotic cytokines in lung tissues, indicating the induction of apoptosis by CD40L carried by the EPCs (See figure). Excitingly, assessment of tumor size demonstrated an inhibitory effect of CD40L-expressing iPS-EPCs, while survival was also significantly prolonged.

In conclusion, the authors demonstrate that it is feasible to generate cells carrying an anti-tumorigenic therapeutic agent (CD40L) which target tumors and inhibit their growth from patient-specific iPSCs. This study also demonstrates the utility of baculovirus-mediated genetic modification; baculoviruses have a large cloning capacity, are easy to produce and also have low cytotoxicity to transduced cells. They do however only mediate transient gene expression, and so the authors are at this moment studying methods to achieve stable expression of transgenes in the differentiated progeny of iPSCs.

References

  1. Arap W and Pasqualini R Engineered embryonic endothelial progenitor cells as therapeutic Trojan horses. Cancer Cell 2004;5:406-408.
  2. Wei J, Blum S, Unger M, et al. Embryonic endothelial progenitor cells armed with a suicide gene target hypoxic lung metastases after intravenous delivery. Cancer Cell 2004;5:477-488.
  3. Su W, Wang L, Zhou M, et al. Human embryonic stem cell-derived endothelial cells as cellular delivery vehicles for treatment of metastatic breast cancer. Cell Transplant 2013;22:2079-2090.
  4. Purwanti YI, Chen C, Lam DH, et al. Antitumor Effects of CD40 Ligand-Expressing Endothelial Progenitor Cells Derived From Human Induced Pluripotent Stem Cells in a Metastatic Breast Cancer Model. Stem Cells Transl Med 2014.
  5. James D, Nam HS, Seandel M, et al. Expansion and maintenance of human embryonic stem cell-derived endothelial cells by TGFbeta inhibition is Id1 dependent. Nat Biotechnol 2010;28:161-166.
  6. Ullenhag G and Loskog AS AdCD40L--crossing the valley of death? Int Rev Immunol 2012;31:289-298.
  7. Loskog AS, Fransson ME, and Totterman TT AdCD40L gene therapy counteracts T regulatory cells and cures aggressive tumors in an orthotopic bladder cancer model. Clin Cancer Res 2005;11:8816-8821.