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.