Objective: To compare the in vitro immunosuppressive effects of cyclosporine and 4 novel immunosuppressive drugs on lymphocytes in whole blood collected from healthy cats.
Sample population: Whole blood samples collected from 10 healthy adult domestic shorthair cats.
Procedure: Mitogen-stimulated lymphocyte proliferation in whole blood incubated with and without various concentrations of cyclosporine, tacrolimus, sirolimus, mycophenolic acid (MPA), or A771726 was measured by use of [3H]thymidine incorporation. Drug concentrations that resulted in a 50% inhibition of mitogen-induced proliferation (IC50) were calculated. Lymphocyte viability was determined by use of the trypan blue dye exclusion method.
Results: An obvious dose-response relationship for the antiproliferative effects of each drug was detected. Mean IC50 determined with concanavalin A was 46 nM for cyclosporine, 9 nM for tacrolimus, 12 nM for sirolimus, 16 nM for MPA, and 30 mM for A771726, whereas with pokeweed mitogen, mean IC50 was 33 nM for cyclosporine, 5 nM for tacrolimus, 15 nM for sirolimus, 14 nM for mycophenolic acid, and 25 mM for A771726. Mitogen-stimulated and nonstimulated lymphocytes remained viable, regardless of drug evaluated.
Conclusions and clinical relevance: Tacrolimus, sirolimus, MPA, and A771726 inhibited in vitro mitogen-stimulated proliferation of feline lymphocytes in a dose-dependent manner. These novel immunosuppressive drugs may be useful for management of immune-mediated inflammatory diseases and prevention and treatment of rejection in cats that undergo organ transplantation.