Prevention of orthotopic liver allograft rejection in rats with a short-term brequinar sodium therapy. Analysis of intragraft cytokine gene expression.

Brequinar sodium (BQR) is a new immunosuppressive drug that is highly effective in preventing graft rejection in several different experimental settings, including primary allografts and xenografts. A short course of BQR treatment during the onset of allograft rejection can induce the permanent survival of liver and kidney allografts in rats. To study the molecular basis of BQR-induced prolongation of allograft survival, we analyzed the intragraft pattern of IL-1 alpha, IL-2, IL-2R, IL-4, IL-6, IL-10, and TNF gene expression in the ACI-to-LEW liver allograft model. A semiquantitative polymerase chain reaction was developed to measure cytokine gene expression in control and BQR-treated liver graft recipients at various days after transplantation. Untreated control liver allografts expressed all of the cytokines analyzed. There was a marked increase in the steady state level of transcripts for each cytokine as graft rejection proceeded. The treatment of liver graft recipients with 12 mg/kg/day of BQR on days 6, 7, and 8 after transplantation suppressed the expression of all these cytokines within 24 hr of administration. The early suppression of cytokine expression was associated with a modest but distinct reduction in the infiltration of inflammatory cells into the liver grafts. The reduction in the level of transcripts for IL-4, IL-6, and IL-10 persisted in long-term survivors (30 days after transplantation). In contrast, there was a significant increase in the level of transcripts for IL-1 alpha, IL-2, and IL-2R in these long-term survivors. Our results demonstrated clearly that the pattern of cytokine gene expression during allograft rejection is significantly altered by a 3-day course of therapy with BQR. The temporary down-regulation of cytokine gene expression may be responsible for an altered immunological state that results in the prolonged survival of liver allografts.