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Escape Mutations, Ganciclovir Resistance, and Teratoma Formation in Human iPSCs
Expressing an HSVtk Suicide Gene
#MMPMID26836371
Kotini AG
; de Stanchina E
; Themeli M
; Sadelain M
; Papapetrou EP
Mol Ther Nucleic Acids
2016[Feb]; 5
(2
): e284
PMID26836371
show ga
Human pluripotent stem cells (hPSCs) hold great promise for cell therapy.
However, a major concern is the risk of tumor formation by residual
undifferentiated cells contaminating the hPSC-derived cell product. Suicide genes
could safeguard against such adverse events by enabling elimination of cells gone
astray, but the efficacy of this approach has not yet been thoroughly tested.
Here, we engineered a lentivirally encoded herpes simplex virus thymidine kinase
(HSVtk) with expression restricted to undifferentiated hPSCs through regulation
by the let7 family of miRNAs. We show that induced pluripotent stem cells (iPSCs)
expressing a let7-regulated HSVtk transgene are selectively killed by ganciclovir
(GCV), whereas differentiated cells are fully protected. However, in contrast to
previous studies, we find that in vivo GCV administration results in longer
latency but does not prevent teratoma formation by iPSCs expressing either a
constitutive or a let7-regulated HSVtk, without evidence of silencing of the
HSVtk. Clonal analyses of iPSCs expressing HSVtk revealed frequent emergence of
GCV resistance which, at least in some cases, could be attributed to preexisting
inactivating mutations in the HSVtk coding sequence, selected for upon GCV
treatment. Our findings have important consequences for the future use of suicide
genes in hPSC-based cell therapies.
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