Infection secondary to pharmacologic immunosuppression is an important cause of morbidity and death in feline renal transplant recipients. The prevalence of infection in 169 feline renal allograft recipients was 25%.1 Viral infections were thought to comprise 13% of the infections, and 11 of 13 cats with suspected viral infections had severe upper respiratory tract disease, commonly within a month of transplantation.
Feline renal transplant recipients are particularly susceptible to reactivation of latent FHV-1 infection as a result of the stress of illness, surgery, and pharmacologic immunosuppression.2 Exclusion of cats with a history of upper respiratory tract disease as candidates for transplantation is not possible because of the high prevalence of FHV-1 infection in the general population. Also, some cats with latent infection may lack a history of upper respiratory tract disease. Presently, there is no uniformly effective systemic treatment for disease caused by FHV-1.2
The immunosuppressive agent leflunomide [N-(4-trifluoromethylphenyl)-methylisoxazol-4-carboxamide; HWA 486] is a synthetic organic isoxazole that is metabolized by the intestinal mucosa to its active form, A77. This metabolite inhibits fibroblast, smooth muscle, and T and B lymphocyte proliferation by inhibiting dihydroorotate dehydrogenase, an enzyme involved in pyrimidine biosynthesis.3,4 Leflunomide can also inhibit several protein tyrosine kinases, including those of the src family, the Janus kinase family, and epidermal growth factor receptor kinase.3,5,6
Leflunomide, an immunosuppressive drug with a relatively low adverse effect profile, is presently approved for treatment of rheumatoid arthritis in humans.7,8 Leflunomide controls allograft rejection in small and large animal models and has been used successfully to manage refractory immune-mediated disease in dogs.5,9-12 A recent clinical study13 revealed that leflunomide possesses substantial immune suppressive potency in human renal and liver transplant recipients and may be safely administered for > 300 days.
In addition to its immunosuppressive effects, leflunomide appears to have antiherpesviral properties, both in vitro and in vivo.14–17 The replication of HSV-1, an alphaherpesvirus, and CMV, a betaherpesvirus, is inhibited following treatment of cell monolayers with A77,15,16 and leflunomide reduces viral load by 4 to 6 orders of magnitude in animals infected with rat-origin CMV.14 Results of electron microscopic studies15,16,18 suggest a unique mechanism of action that relates to interference of herpesviral nucleocapsid tegmentation. Leflunomide has been used successfully to treat primary CMV infection and ganciclovir-resistant CMV infection in human transplant patients.17,19,20 Given that HSV-1 is more closely related to FHV-1 than to CMV, we hypothesized that A77 would similarly inhibit the replication of FHV-1. The purpose of the study reported here was to examine the effect of A77 on FHV-1 replication in vitro.
Herpes simplex virus-1
Crandell Rees feline kidney
Fetal bovine serum
Lab-Tek chamber slides, Nalge Nunc International, Naperville, Ill.
Philips CM120 electron microscope, FEI Co, Hillsboro, Ore.
NucPrep, Applied Biosystems, Foster City, Calif.
6700 automated nucleic acid workstation, Applied Biosystems, Foster City, Calif.
7700 ABI PRISM SDS instrument, Applied Biosystems, Foster City, Calif.
Applied Biosystems, Foster City, Calif.
Amplitaq Gold, Applied Biosystems, Foster City, Calif.
Annexin V-FITC apoptosis detection kit I, BD PharMingen, San Diego, Calif.
CellTiter 96 AQueous One Solution cell proliferation assay, Promega Corp, Madison, Wis.
StatXact 7, Cytel Software Corp, Cambridge, Mass.
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