Complete correction of murine phenylketonuria by selection-enhanced hepatocyte transplantation

Hepatocyte transplantation for genetic liver diseases has several potential advantages over gene therapy. However, low efficiency of cell engraftment has limited its clinical implementation. This problem could be overcome by selectively expanding transplanted donor cells until they replace enough of the liver mass to achieve therapeutic benefit. We previously described a gene therapy method to selectively expand hepatocytes deficient in cytochrome p450 reductase (Cypor) using acetaminophen (APAP). Because Cypor is required for the transformation of APAP to a hepatotoxic metabolite, Cypor deficient cells are protected from toxicity and are able to expand following APAP-induced liver injury. Here, we apply this selection system to correct a mouse model of phenylketonuria (PKU) by cell transplantation. Hepatocytes from a wildtype donor animal were edited in vitro to create Cypor deficiency and then transplanted into PKU animals. Following selection with APAP, blood phenylalanine concentrations were fully normalized and remained stable following APAP withdrawal. Cypor-deficient hepatocytes expanded from <1% to ~14% in corrected animals, and they showed no abnormalities in blood chemistries, liver histology, or drug metabolism. We conclude that APAP-mediated selection of transplanted hepatocytes is a potential therapeutic for PKU with long-term efficacy and a favorable safety profile.