Escape Mutations, Ganciclovir Resistance, and Teratoma Formation in Human iPSCs Expressing an HSVtk Suicide Gene

Area of Science:

• Stem cell biology
• Gene therapy
• Cancer research

Background:

• Human pluripotent stem cells (hPSCs) offer therapeutic potential but risk tumor formation from residual undifferentiated cells.
• Suicide gene therapy is a proposed strategy to eliminate contaminating undifferentiated cells in hPSC-derived products.

Purpose of the Study:

• To engineer a suicide gene system for selective elimination of undifferentiated hPSCs.
• To evaluate the in vivo efficacy of a let7 miRNA-regulated herpes simplex virus thymidine kinase (HSVtk) suicide gene in preventing teratoma formation.

Main Methods:

• Engineered a lentiviral vector encoding HSVtk regulated by let7 miRNAs for targeted expression in undifferentiated hPSCs.
• Administered ganciclovir (GCV) in vivo to assess selective cell killing and teratoma prevention in mice xenografted with engineered induced pluripotent stem cells (iPSCs).
• Performed clonal analysis to investigate the mechanisms of GCV resistance.

Main Results:

• Engineered iPSCs expressing let7-regulated HSVtk were selectively killed by GCV in vitro.
• In vivo GCV administration did not prevent teratoma formation, despite longer latency.
• GCV treatment selected for resistant iPSCs, with some cases showing pre-existing inactivating mutations in the HSVtk gene.

Conclusions:

• A let7 miRNA-regulated HSVtk suicide gene system can selectively eliminate undifferentiated hPSCs in vitro.
• In vivo efficacy is limited by the emergence of GCV resistance, potentially due to pre-existing mutations.
• The findings necessitate re-evaluation of suicide gene strategies for hPSC-based cell therapies.