Safety switch for embryonic stem cell-based therapies

by Alexey Bersenev on August 8, 2012 · 0 comments

in embryonic/iPS, methods

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Wouldn’t it be great if we will able to control cell behavior after transplantation? The “safety switch” techniques allow us to do that. We can eliminate transplanted cells in case of cells-associated unwanted adverse effects, such as: excessive proliferation, wayward migration, toxic off-target and graft-versus-host reactions. Currently, the safety switch includes transduction by “suicide genes”, which could be activated by a drug and kill the cells. Safety switch approaches have been explored in clinical trials for the last 10 years.

Safety switch approach was recently proposed for embryonic stem cells (ESC) and their therapeutic derivatives. Suicide gene was linked to ESC-associate pluripotency genetic marker – Nanog:

By introducing a hyperactive variant of herpes simplex virus thymidine kinase (TK) gene into untranslated region of the endogenous NANOG gene of hESCs through homologous recombination, we developed a safe and highly scalable approach to efficiently eliminate the teratomas risk associated with hESCs without apparent negative impact on differentiated cell types.

The authors performed in vivo experiments, comparing neural progenitors, pre-differentiated from conventional ESC and engineered ESC in immunodeficient mice:

While the RA-treated hESC culture formed teratomas in all mock treated SCID mice, GCV treatment abolishes the teratoma formation by these partially differentiated cultures from TK-hESCs.

Some proposed advantages of this approach:

  • Scalability;
  • Use of knock-in homologous recombination, which is not associated with random integration of exogenous DNA;
  • Use FDA approved drugs: ganciclovir (approved on a market) as activator of HSV-thymidine kinase (TK) suicide gene (approved for clinical trials);
  • Use of hyperactive variant of TK gene, instead of wild type, which allows to kill ESC by 1/10 of ganciclovir dose and therefore, make it less toxic;
  • Approach allows (A) to purify residual ESC from their differentiated progeny before transplant and (B) control wayward progeny after transplant (in case of spontaneous reprogramming).

The disadvantage is that cells should be modified genetically.

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