For many liver diseases, including those of inborn genetic origin, transplantation of donor organs is currently the only curative option. The derivation of cellular liver transplants from embryonic stem (ES) cells as an alternative source of tissue would need to be both autologous and free of the genetic disease, requirements that are not easily surmountable and also ethically controversial with ES cells derived from potentially viable fertilized or patient-specific somatic cell nuclear transfer embryos. One approach to produce autologous, disease-free ES cells from patients that may resolve these problems is the derivation of uniparental embryonic stem cells from the patient's gametes. Uniparental embryos such as parthenogenetic embryos have limited developmental capacity due to genomic imprinting but can produce ES cell lines. We have established that hematopoietic stem cells derived from murine uniparental ES cells can reconstitute adult hematopoiesis with no apparent pathology. To investigate the potential of uniparental cells for liver replacement, we now propose to use maternally (oocyte)-derived (parthenogenetic /gynogenetic) and paternally derived (androgenetic;two sperm genomes) fetal ES cell derivatives to functionally repopulate the liver in fumarylacetoacetate hydrolase (Fah) deficient adults. As a therapeutic approach, we will also transplant hepatic progenitors derived in vitro from uniparental ES cells. As each gamete contains a subset of the genome, diploid uniparental embryos are homozygous at a proportion of loci that are heterozygous in the gamete donor. This can be exploited to produce patient-derived ES cells without an errant allele (including large genetic lesions) in diseases associated with heterozygosity. Using the heterozygous phenotypic PiZ mouse model for alpha-1-antitrypsin deficiency, we will perform a proof of principle experiment involving elimination of the PiZ locus in uniparental ES cells. For patients of recessive genetic disorders, mutant allele-free, uniparental ES cell lines derived from parents or siblings could provide immune-compatible transplantable tissue, since MHC homozygous, mutant allele-free, uniparental lines with a matched subset of the recipient's MHC could be identified. Using mouse strains with different MHC loci, we will investigate the engraftment of MHC homozygous cellular liver transplants in MHC heterozygous recipients, i.e. determine the relevance of hybrid resistance.This proposal will investigate the capacity of embryonic stem cells derived from oocytes or sperm only to be used for liver transplantation and correction of genetic liver diseases. These embryonic stem cells would be derived from the respective patient's sperm or oocytes, and thus limit rejection problems associated with the use of existing embryonic stem cell lines.
