Recombinant human acid alpha-glucosidase generated in bacteria: antigenic, but enzymatically inactive

Production of a functional human acid maltase in tobacco seeds: biochemical analysis, uptake by human GSDII cells, and in vivo studies in GAA knockout mice

Genetic deficiency of acid alpha glucosidase (GAA) results in glycogen storage disease type II (GSDII) or Pompe's disease. To investigate whether we could generate a functional recombinant human GAA enzyme (tobrhGAA) in tobacco seeds for future enzyme replacement therapy, we subcloned the human GAA cDNA into the plant expression plasmid-pBI101 under the control of the soybean β-conglycinin seed-specific promoter and biochemically analyzed the tobrhGAA. Tobacco seeds contain the metabolic machinery that is more compatible with mammalian glycosylation-phosphorylation and processing. We found the tobrhGAA to be enzymatically active was readily taken up by GSDII fibroblasts and in white blood cells from whole blood to reverse the defect. The tobrhGAA corrected the enzyme defect in tissues at 7 days after a single dose following intraperitoneal (IP) administration in GAA knockout (GAA(-/-)) mice. Additionally, we could purify the tobrhGAA since it bound tightly to the matrix of Sephadex G100 and can be eluted by competition with maltose. These data demonstrate indirectly that the tobrhGAA is fully functional, predominantly proteolytically cleaved and contains the minimal phosphorylation and mannose-6-phosphate residues essential for biological activity.

Correction of glycogen storage disease type II by enzyme replacement with a recombinant human acid maltase produced by over-expression in a CHO-DHFR(neg) cell line

Inherited genetic deficiency of lysosomal acid alpha glucosidase or acid maltase (GAA) results in the autosomal recessive glycogen storage disease type II (GSD II). To investigate whether we could generate a functional recombinant human GAA (rhGAA) for enzyme replacement therapy, we subcloned the cDNAs for human GAA and mouse dihydrofolate reductase (DHFR) into DHFR(neg) Chinese hamster ovary cells and established a stable cotransformant that expressed rhGAA. We cultured the recombinant cells in media with progressively increasing concentrations of methotrexate and found that human GAA enzyme activity increased to over 2,000 IU per gram protein. Importantly, the human GAA enzyme activity correlated to equivalent amounts of human GAA protein by rocketimmunoelectrophoresis. We confirmed that the human GAA enzyme activity corresponded to an amplification in human GAA mRNA by Northern analysis and human GAA cDNA copy number by Southern analysis. Exposing the rhGAA to human GSDII fibroblast cells or patient's lymphocytes or monocytes resulted in uptake of the rhGAA and reversal of the enzymatic defect. Mannose-6-phosphate in the media blocked uptake. GAA -/- mice were treated with the rhGAA at 1 mg/kg, which resulted in heterozygous levels of GAA in tissues, most notably skeletal muscle, heart and diaphragm after two infusions. More importantly, after multiple infusions, hind, and fore-limb muscle weakness was reversed. This rhGAA would be ideal for enzyme replacement therapy in GSD II.

High-level production of recombinant human lysosomal acid alpha-glucosidase in Chinese hamster ovary cells which targets to heart muscle and corrects glycogen accumulation in fibroblasts from patients with Pompe disease

Infantile Pompe disease is a fatal genetic muscle disorder caused by a deficiency of acid alpha-glucosidase, a glycogen-degrading lysosomal enzyme. We constructed a plasmid containing a 5'-shortened human acid alpha-glucosidase cDNA driven by the cytomegalovirus promoter, as well as the aminoglycoside phosphotransferase and dihydrofolate reductase genes. Following transfection in dihydrofolate reductase-deficient Chinese hamster ovary cells, selection with Geneticin, and amplification with methotrexate, a cell line producing high levels of the alpha-glucosidase was established. In 48 hr, the cells cultured in Iscove's medium with 5 mM butyrate secreted 110-kDa precursor enzyme that accumulated to 91 micrograms.ml-1 in the medium (activity, > 22.6 mumol.hr-1.ml-1). This enzyme has a pH optimum similar to that of the mature form, but a lower Vmax and Km for 4-methylumbelliferyl-alpha-D-glucoside. It is efficiently taken up by fibroblasts from Pompe patients, restoring normal levels of acid alpha-glucosidase and glycogen. The uptake is blocked by mannose 6-phosphate. Following intravenous injection, high enzyme levels are seen in heart and liver. An efficient production system now exists for recombinant human acid alpha-glucosidase targeted to heart and capable of correcting fibroblasts from patients with Pompe disease.