Gene therapy by allele selection in a mouse model of beta-thalassemia

To be of therapeutic use, autologous stem cells derived from patients with inherited genetic disorders require genetic modification via gene repair or insertion. Here, we present proof of principle that, for diseases associated with dominant alleles (gain-of-function or haploinsufficient loss-of-function), disease allele–free ES cells can be derived from afflicted individuals without genome manipulation. This approach capitalizes on the derivation of uniparental cells, such as parthenogenetic (PG) ES cell lines from disease allele–free gametes. Diploid mammalian uniparental embryos with only maternally (oocyte-) or paternally (sperm-)derived genomes fail early in development due to the nonequivalence of parental genomes caused by genomic imprinting. However, these uniparental embryos develop to the blastocyst stage, allowing the derivation of ES cell lines. Using a mouse model for dominant beta-thalassemia, we developed disease allele–free PG ES cell lines from the oocytes of affected animals. Phenotype correction was obtained in donor-genotype recipients after transplantation of in vitro hematopoietic ES cell derivatives. This genetic correction strategy without gene targeting is potentially applicable to any dominant disease. It could also be the sole approach for larger or more complex mutations that cannot be corrected by homologous recombination.