Phenotypic correction of feline lipoprotein lipase deficiency by adenoviral gene transfer

Previous studies have revealed that adenovirus-mediated ectopic liver expre ssion of human LPL (huLPL) can efficiently mediate plasma triacylglycerol ( TG) catabolism in mice despite its native expression in adipose and muscle tissue. We aimed to explore the feasibility of liver-directed gene transfer and enzyme replacement for human LPL deficiency in a larger, naturally occ urring feline animal model of complete LPL deficiency that is remarkably si milar in phenotype to the human disorder. A cohort of LPL-deficient (LPL-/- ) cats was given an intravenous injection of 8 X 10(9) PFU/kg of a CMV prom oter/enhancer-driven, E1/E3-deleted adenoviral (Ad) vector containing a 1.3 6-kb huLPL cDNA (Ad-LPL) or reporter alkaline phosphatase gene (Ad-AP). Aft er Ad-LPL administration, active, heparin-releasable huLPL was readily dete cted along with a 10-fold reduction in plasma TGs, disappearance of plasma TG-rich lipoproteins up to day 14, and enhanced clearance of an excess intr avenous fat toad on day 9. However, antibody against the huLPL protein was detected on day 14 in cats receiving Ad-LPL and adenovirus-specific neutral izing antibody was present 7 days after gene transfer in both cat cohorts. Tissue-specific expression of the huLPL transgene relative to controls was confirmed by RT-PCR. While huLPL expression was evident in the liver, other tissues including spleen and lung expressed huLPL message, in direct corre lation with histological evidence of increased Oil red O (ORO)-positive neu tral lipid influx. In contrast, intravenous LPL enzyme replacement therapy (ERT) led to rapid disappearance of 9000 mU/kg of active bovine LPL enzyme from the circulation, with tilt occurring at <10 min in two LPL-/- cats. He parin injection 1 hr later released <10% of the original bovine LPL, furthe r indicating its rapid systemic clearance, inactivation, or degradation as well as its ineffectiveness as a viable therapeutic alternative for complet e LPL deficiency. Although LPL gene transfer and expression via this first- generation Ad vector was limited by the immune response against both the hu man LPL protein and adenovirus our results dearly provide a key advance sup porting further development of LPL gene therapy as a viable therapeutic opt ion for clinical LPL deficiency.