Background. We have previously shown that oxidative stress alone can promote transformation of human B cells infected with Epstein-Barr virus (EBV) in vitro, an accepted model mimicking posttransplant lymphoproliferative disorders (PTLDs). Our laboratory has investigated the direct effects of cyclosporine A (CyA) as an oxidant promoting B-cell transformation and we have proposed that CyA directly promotes B-cell transformation and that this effect can be blocked by antioxidants. Methods. Human splenocytes were prepared by centrifugation and plating technique to provide a greater than 80% pure preparation of B cells that was used for the direct oxidative stress experiments. These cells were cocultured with CyA (500 ng/ml) and hydrogen peroxide (H2O2, 0.15 mM) with or without antioxidant vitamin E (40 μM). Oxidative stress was evaluated by using a commercial lipid hydroperoxide (LPO) assay kit. In another set of three separate experiments, human B lymphocytes infected with EBV were cultured with CyA (500 ng/ml), H2O2 (0.15 mM), and vitamin E (40 μM). B-Cell transformation by EBV was evaluated by counting colony number and [3H]-thymidine incorporation. Results. At therapeutic concentrations, CyA (500 ng/mL) had an oxidative effect on human splenocytes in vitro, similar to the effect of H2O2 (90 and 97% increases, respectively in LPO production over control P < 0.005), which was abrogated by the addition of vitamin E. Similarly, both CyA and H2O2 promoted transformation of B cells infected with EBV(75 and 108% increases respectively in colony counts over control, P < 0.005). This effect was also blocked by vitamin E. Conclusions. Both CyA and H2O2 have a direct oxidative effect on human B cells and cause promotion of EBV-induced transformation of B cells. These effects are blocked by the antioxidant vitamin E. These findings may have future therapeutic implications for PTLDs.
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