Ganciclovir Suppresses Human T Lymphocyte Proliferation In Vitro.

Clinically significant cytomegalovirus (CMV) infection in allogeneic blood or marrow transplant recipients has dramatically declined in recent years by the strategy of early detection of reactivation and pre-emptive therapy with Ganciclovir (GCV). We have previously shown that even in the absence of overt CMV disease, persisting post-transplant antigenemia predicts for increased late relapse and treatment failure. (Nakamura, et al BBMT 2004) In other words, frequent CMV reactivation serves as a surrogate for impaired post-transplant immune reconstitution. To explain the observed association between CMV reactivation and relapse we also raised the possibility that several weeks of GCV therapy could exert a deleterious effect on a fragile immune system. Clinical association between GCV administration and impaired lymphocyte function has not received attention previously; perhaps because of confounding effects from the underlying conditions (HIV or post-transplant) that induce CMV reactivation. We examined the effect of GCV in vitro on normal human PBMCs. Human PBMCs were extracted from normal volunteers and subjected to mitogenic stimulation (PHA) in the absence or presence of varying concentrations of GCV. PHA-induced proliferation, measured by uptake of 3[H]-thymidine after 5 days incubation in RPMI-10% AB serum, was reduced by 35% at peak therapeutic concentrations (10mg/ml) of GCV as opposed to 73% by Tacrolimus (10ng/ml). GCV did not induce lymphocyte apoptosis in the presence or absence of stimulation. Flow cytometry-based BrdU incorporation assays show that GCV exerts a time-dependent impairment of DNA synthesis in lymphocytes. Collectively, these results show that GCV suppresses T-lymphocyte proliferation in vitro at therapeutic concentrations and the likely mechanism of action is inhibition of DNA synthesis. Further work is ongoing to evaluate the effect of GCV on proliferative responses to specific antigens and to confirm these effects in comparison to other drugs used in the transplant setting.

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