CRISPR/Cas9 gene therapy increases the risk of tumorigenesis in the mouse model of hereditary tyrosinemia type I.

BACKGROUND & AIMS: The therapeutic potential of CRISPR gene editing has been demonstrated in various animal models; however, little is known about its long-term consequences. This study seeks to bridge this gap by investigating the lasting consequences of CRISPR gene therapy in an animal model of hereditary tyrosinemia type I (HT-I). We compared the standard of care-nitisinone, a small molecule inhibitor of hydroxyphenylpyruvate dioxygenase (HPD)-with the deletion of the Hpd gene by CRISPR gene therapy. Both treatments block flux through tyrosine catabolism and thereby prevent the accumulation of toxic catabolites in HT-I. METHODS: We assessed the efficacy and safety of CRISPR gene editing in fumarylacetoacetate hydrolase-deficient (Fah-/-) mice, the mouse model of HT-I, 12 months post treatment with either nitisinone or CRISPR deletion of Hpd. We deleted the Hpd gene using an adenovirus containing Cas9 and an adeno-associated virus containing two sgRNA against the Hpd gene. Primary endpoints were survival, urine biochemistry, liver (immuno)histochemistry, and genetic analyses. RESULTS: CRISPR deletion and pharmacological inhibition of HPD both demonstrate efficient metabolic correction and rescue of lethality. Surprisingly, we detected a markedly increased incidence of hepatocellular cancer in the CRISPR gene therapy group (71%, 12/17 mice) compared with four control groups (nitisinone [19%, four of 21 mice], sgRNA only [6%, one of 16 mice], Cas9 only [11%, two of 19 mice], and hydrodynamic tail vein injection of both CRISPR constructs [24%, four of 17 mice]). All analyzed tumors in the CRISPR gene therapy group were deleted for Hpd but showed on-and-off target vector integrations. CONCLUSIONS: CRISPR gene therapy increases the risk of hepatocellular cancer in the mouse model of HT-I. Because HT-I is characterized by inherent cancer susceptibility, this severe adverse event exposes the potential limitations of CRISPR gene therapy in cancer-prone disorders. IMPACT AND IMPLICATIONS: Not much is known about the long-term consequences of somatic gene editing. Our study investigates CRISPR gene therapy in tyrosinemia type I using viral vectors. Although the CRISPR-based therapy effectively treated the metabolic condition, it was associated with a higher incidence of liver cancer than the current standard of care. These findings highlight the potential risks of using CRISPR gene therapy in conditions predisposed to cancer development.