Transplant immunosuppression enhances efficiency of adenoviral-mediated gene retransfection: inhibition of interferon-γ and immunoglobin G

Background. Transplant immunosuppression regimen facilitates successful adenovirus-mediated gene transfection and retransfection in the rat lung. Herein, we investigated the effect of this strategy on circulating cytokines and antiadenoviral immunoglobin G antibody. Methods. Male Lewis rats were transfected with 1 × 109 pfu/mL of E1-deleted Ad5CMVLacZ vector transtracheally. Rats were randomly assigned to receive daily intraperitoneal triple immunosuppression regimen consisting of cyclosporine (15 mg/kg per day), azathioprine (6 mg/kg per day), and methylprednisolone (2.5 mg/kg per day), or normal saline solution. Retransfection was performed 35 days later to all nonimmunosuppressed animals, whereas immunosuppressed rats were further randomized to receive retransfection or phosphate-buffered saline. Animals were sacrificed on days 1, 2, 7, 35, 42, and 49 after the initial transfection. β-Galactosidase activity was measured on lung homogenates. Interferon-γ, tumor necrosis factor-α, and antiadenoviral immunoglobin G were measured from the serum. Results. Enhanced and prolonged transgene expression was observed in immunosuppressed animals, especially after retransfection. Concentrations of serum tumor necrosis factor-α in both groups were less than 12 pg/mL throughout the study. A significant increase in serum interferon-γ levels was observed in nonimmunosuppressed animals after retransfection; this was not seen in the immunosuppressed animals. Serum antiadenoviral immunoglobin G titers in both groups were sharply elevated on day 1, and declined to basal levels by day 7, reflecting a preexisting level of humoral immunity to adenovirus. The titer in nonimmunosuppressed rats was significantly increased after retransfection, but remained at very low level in immunosuppressed animals. Conclusions. Inhibition of interferon-γ and antiadenoviral immunoglobin G production by triple immunosuppressants may be part of the mechanisms that lead to enhanced and prolonged transgene expression after retransfection.