Sustained suppression of peripheral blood immune functions by treatment with mycophenolate mofetil correlates with reduced severity of cardiac allograft rejection.

BACKGROUND: We tested the hypothesis that sustained suppression of immune functions by mycophenolate mofetil (MMF) throughout the dosing interval reduces the severity of rejection. METHODS: Four groups of rat heart allograft recipients were treated orally daily through Day 5 with either: "low-dose" MMF, 10 mg/kg once daily (QD) or 5 mg/kg twice daily (BID); or "high-dose" MMF, 20 mg/kg QD or 10 mg/kg BID. The following were determined for all animals on Day 6: pharmacokinetics (PK, using high-performance liquid chromatography) of mycophenolic acid (MPA); pharmacodynamics (PD, by flow cytometry quantitation of whole blood mitogen-stimulated lymphocyte proliferation and expression of diverse T-cell surface activation molecules); and histologic graft rejection scores (RS). RESULTS: RS correlated with PD for suppression of both lymphocyte proliferation and transferrin receptor expression (r2 = 0.85 and 0.81, respectively) more highly than with MPA plasma levels (r2 = 0.45), which shows the validity of PD as surrogate markers of MMF efficacy. MMF 5 mg/kg BID produced greater (p < 0.001) suppression of lymphocyte proliferation (area under the PD effect-time curve, AUE = 2,010% inhibition. hour) and sustained trough (E0) PD effect (86% suppression) than MMF 10 mg/kg QD (AUE = 1,436% inhibition. hour, E0 = 55%). RS did not differ between the 20 mg/kg QD and 10 mg/kg BID "high-dose" groups, because PD was maximally suppressed. CONCLUSIONS: PD were surrogate markers for MMF immunosuppressive efficacy. MMF 5 mg/kg BID produced more sustained suppression of both PD and rejection than MMF 10 mg/kg QD.

Pharmacodynamics of mycophenolate mofetil after heart transplantation: new mechanisms of action and correlations with histologic severity of graft rejection.

The primary mechanism of action in vivo of mycophenolate mofetil (MMF) is believed to be inhibition of lymphocyte proliferation. We used novel assays of lymphocyte functions (pharmacodynamics, PD) in whole blood collected from rat heart allograft recipients treated with MMF to investigate the mechanisms of action of the active metabolite of MMF, mycophenolate acid (MPA) in vivo. Allograft recipients were treated orally once daily with 3 different doses of MMF. Seven days after transplantation, blood was collected 24h after the penultimate dose and several timepoints after the last dose, after which grafts were removed for microscopic grading of rejection. Lymphocytes in whole blood samples were mitogen stimulated through calcium-dependent and -independent signaling pathways. Inhibition of PD was measured by lymphocyte proliferation and expression of several surface antigens on T cells, and was calculated as area under the time-inhibition of immune function effect curve (AUE0-24h). We found that inhibition of lymphocyte proliferation and antigen expression by MPA correlated highly with MMF-dose, MPA level and with the histologic severities of graft rejection (p <0.05). In summary, MPA suppressed lymphocyte proliferation and expression of T-cell surface antigens in whole blood collected from MMF-treated allograft recipients, thus demonstrating the multiple mechanisms of suppression of rejection on peripheral blood T cells after MMF treatment.