Mycophenolate mofetil inhibits T-cell proliferation in kidney transplant recipients without lowering intracellular dGTP and GTP

To study if mycophenolic acid (MPA), the active metabolite of mycophenolate mofetil (MMF), indeed inhibits T-cell proliferation in kidney transplant recipients by lowering intracellular deoxyguanosine triphosphate (dGTP) and guanosine triphosphate (GTP) levels. Blood was drawn from 11 kidney transplant recipients. Ex vivo T-cell proliferation was measured by stimulation with phytohemagglutin (PHA) and anti-CD3 monoclonal antibody (mAb). Plasma MPA levels and intracellular dGTP and GTP in peripheral blood mononuclear cells were measured. MMF induces a significant decrease in T-lymphocyte proliferation at all time points (i.e. 24 h, 10 days and 8 weeks) after stimulation with both PHA (P = 0.001, 0.002 and 0.013 respectively) and anti-CD3 mAb (P = 0.004, 0.004 and 0.005 respectively). There was no significant change in intracellular dGTP (P = 0.31, 0.16 and 0.35) or GTP levels (P = 0.99, 0.32 and 0.49) between baseline and day 1, day 10 or week 8. All MPA levels were above the minimal required concentration for the inhibition of lymphocyte proliferation. MMF inhibits T-lymphocyte proliferation in kidney transplant recipients without lowering intracellular dGTP or GTP levels. This suggests another mechanism underlying its immunosuppressive capacity.