Ex vivo lymphocyte proliferative function is severely inhibited in renal transplant patients on mycophenolate mofetil treatment.

Mycophenolate mofetil (MMF) is a recently introduced immunosuppressive drug. Its active form is mycophenolic acid (MPA). MPA specifically inhibits de novo purine synthesis, which is vital for T and B lymphocyte proliferation. We measured lymphocyte subset numbers and mitogen induced proliferation in kidney transplant recipients on different combinations of MMF, cyclosporin A (C), azathioprine (A) and prednisolone (P) (C+A n=70; C+A+P n=15; C+MMF n=45; C+MMF+P n=37) and normals (n=73). Patients on MMF had severely reduced phytohaemagglutinin A (PHA) induced proliferation compared to normals (Nml 2766+/-926 CPM/1000 lymphocytes [mean+/-S.D.]; C+MMF 282+/-406; C+MMF+P 195+/-496); non-MMF patients did not differ from normal. Similar inhibition of Poke Weed Mitogen and Staphylococcal enterotoxin B induced proliferation was observed. Cell cycle studies established that MMF patients had a significantly higher proportion of lymphocytes in the G0/G1 phase following PHA stimulation than the non-MMF patients. All transplant groups had significantly lower B cell numbers than the normal controls but no differences in CD4 and CD8 T cell numbers. All but the C+MMF group had significantly lower CD16+NK cell numbers than normal, while only the non-MMF groups had significantly lower CD56+NK cell numbers. The proliferation assay used was an ex vivo diluted whole blood technique. Removal of residual MPA by washing the plasma out prior to mitogen stimulation led to a significant increase in proliferation in six out of seven cases. In summary we have found that MMF treatment has a strikingly inhibitory effect on patient ex vivo lymphocyte mitogenic function.