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

Mark C. Walker Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610.
Applied Genetic Technologies Corp, Sid Martin Biotechnology Institute, 12085 Research Dr, Alachua, FL 32615.
Present address is North Florida Veterinary Specialists, 275 Corporate Way, Orange Park, FL 32073.

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Tamara C. Mandell Applied Genetic Technologies Corp, Sid Martin Biotechnology Institute, 12085 Research Dr, Alachua, FL 32615.

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P. Cynda Crawford Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610.

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Greg G. Simon Powell Gene Therapy Center, University of Florida, Gainesville, FL 32610.

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Kevin S. Cahill Powell Gene Therapy Center, University of Florida, Gainesville, FL 32610.

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Peter J. Fernandes Cytovet Diagnostics, 5234 Sail Wind Cir, Orlando, FL 32810.
Present address is IDEXX Veterinary Services Inc, 501 W Lake St, Elmhurst, IL 60126.

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James N. MacLeod James A. Baker Institute for Animal Health, Cornell University, Ithaca, NY 14853.
Present address is Department of Veterinary Sciences, Gluck Equine Research Center, University of Kentucky, Lexington, KY 40546.

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Barry J. Byrne Powell Gene Therapy Center, University of Florida, Gainesville, FL 32610.

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Julie K. Levy Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610.

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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)

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