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Expression of erythropoietin in cats treated with a recombinant adeno-associated viral vector

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  • 1 Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610.
  • | 2 Applied Genetic Technologies Corp, Sid Martin Biotechnology Institute, 12085 Research Dr, Alachua, FL 32615.
  • | 3 Present address is North Florida Veterinary Specialists, 275 Corporate Way, Orange Park, FL 32073.
  • | 4 Applied Genetic Technologies Corp, Sid Martin Biotechnology Institute, 12085 Research Dr, Alachua, FL 32615.
  • | 5 Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610.
  • | 6 Powell Gene Therapy Center, University of Florida, Gainesville, FL 32610.
  • | 7 Powell Gene Therapy Center, University of Florida, Gainesville, FL 32610.
  • | 8 Cytovet Diagnostics, 5234 Sail Wind Cir, Orlando, FL 32810.
  • | 9 Present address is IDEXX Veterinary Services Inc, 501 W Lake St, Elmhurst, IL 60126.
  • | 10 James A. Baker Institute for Animal Health, Cornell University, Ithaca, NY 14853.
  • | 11 Present address is Department of Veterinary Sciences, Gluck Equine Research Center, University of Kentucky, Lexington, KY 40546.
  • | 12 Powell Gene Therapy Center, University of Florida, Gainesville, FL 32610.
  • | 13 Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610.

Abstract

Objective—To characterize the biological effects of IM administration of a recombinant adeno-associated virus serotype 2 (rAAV2) vector containing feline erythropoietin (fEPO) cDNA and determine whether readministration of the vector or removal of muscle tissue at the injection sites alters those effects.

Animals—10 healthy 7-week-old specific pathogenfree cats.

Procedure—Cats received 1 × 107 infective units (iU; n = 3), 1 × 108 iU (3), or 1 × 109 iU (2) of rAAV2-fEPO vector IM (day 0). Two control cats received an rAAV2 vector containing the LacZ gene (1 × 109 iU, IM). In all cats, hematologic variables and serum fEPO concentration were measured at intervals; anti-rAAV2 antibody titer was measured on day 227. In cats that did not respond to treatment, the rAAV2- fEPO vector was readministered. Injection sites were subsequently surgically removed.

Results—Compared with control cats, cats treated with 1 × 109 iU of rAAV2-fEPO vector had increased Hct and serum fEPO concentrations. One of these cats developed pure RBC aplasia; its Hct normalized following injection site excision. Cats receiving lower doses of vector had no response; on retreatment, 1 of those cats developed sustained erythrocytosis that persisted despite injection site removal and the others did not respond or responded transiently. Antibodies against rAAV2 were detected in all vector-treated cats.

Conclusions and Clinical Relevance—Gene therapy may be an effective treatment for cats with hypoproliferative anemia. However, rAAV2-fEPO vector administration may result in pure RBC aplasia or pathologic erythrocytosis, and injection site removal does not consistently abolish the biological response. (Am J Vet Res 2005;66:450–456)

Abstract

Objective—To characterize the biological effects of IM administration of a recombinant adeno-associated virus serotype 2 (rAAV2) vector containing feline erythropoietin (fEPO) cDNA and determine whether readministration of the vector or removal of muscle tissue at the injection sites alters those effects.

Animals—10 healthy 7-week-old specific pathogenfree cats.

Procedure—Cats received 1 × 107 infective units (iU; n = 3), 1 × 108 iU (3), or 1 × 109 iU (2) of rAAV2-fEPO vector IM (day 0). Two control cats received an rAAV2 vector containing the LacZ gene (1 × 109 iU, IM). In all cats, hematologic variables and serum fEPO concentration were measured at intervals; anti-rAAV2 antibody titer was measured on day 227. In cats that did not respond to treatment, the rAAV2- fEPO vector was readministered. Injection sites were subsequently surgically removed.

Results—Compared with control cats, cats treated with 1 × 109 iU of rAAV2-fEPO vector had increased Hct and serum fEPO concentrations. One of these cats developed pure RBC aplasia; its Hct normalized following injection site excision. Cats receiving lower doses of vector had no response; on retreatment, 1 of those cats developed sustained erythrocytosis that persisted despite injection site removal and the others did not respond or responded transiently. Antibodies against rAAV2 were detected in all vector-treated cats.

Conclusions and Clinical Relevance—Gene therapy may be an effective treatment for cats with hypoproliferative anemia. However, rAAV2-fEPO vector administration may result in pure RBC aplasia or pathologic erythrocytosis, and injection site removal does not consistently abolish the biological response. (Am J Vet Res 2005;66:450–456)