Transient immunosuppression stops rejection of viral transduced EGFP in rabbit retina

Abstract

Abstract: : Purpose:The expression of lentiviral transduced EGFP is detectable in rabbit RPE within 3–5 days after subretinal injection of the vector. Within 2–3 weeks the expressing cells are rejected. In the current experiments we monitor serum antibody titers for EGFP before and after transduction and determine whether systemic immunosuppression prevents rejection. Methods:Lentiviral vector was prepared by the three plasmid method of Naldini et al (1996) with EGFP driven by the CMV promoter. 5 microliters of virus (10^9–11 IU/ml) were injected subretinally. The rabbit retina was examined periodically by fluorescence scanning laser ophthalmoscopy. Ear vein blood samples were taken for ELISA assays of antibody to EGFP. Experiments were performed on 11 eyes of 9 rabbits. Four rabbits were immunosuppressed. by daily administration of cyclosporine (50 mg) orally and azathioprine (8 mg) and methyl prednisone (6.25 mg) intramuscularly for one month, when immunosuppression was stopped. Rabbits were sacrificed after rejection and the transduction site examined histologically. Results:All immunosuppressed rabbits did not reject; all control rabbits did. Immunosuppressed rabbits did not develop antibodies to EGFP; controls did. If the other eye of an immunosuppressed rabbit no longer being immunosuppressed was transduced, both eyes rejected within 2–3 weeks. Conclusions:One month of systemic immunusuppression permanently prevents rejection of RPE expressing EGFP. The lack of rejection is not due to tolerance but to a failure to detect the foreign protein. Detection must depend upon a brief window of time after surgery needed to introduce the vector, perhaps related to a concurrent but transient inflammation. This strategy may be useful in preventing rejection of other foreign proteins and/or cells in the retina.

Keywords: gene transfer/gene therapy • immune tolerance/privilege • gene/expression