Mycophenolate mofetil does not suppress the graft-versus-leukemia effect or the activity of lymphokine-activated killer (LAK) cells in a murine model

Abstract

Background: Graft-versus-leukemia (GVL) effect is an essential component in the course of allogeneic stem cell transplantation (SCT). However, both prevention and treatment of established graft-versus-host disease (GVHD), including with drugs such as cyclosporine, can suppress GVL effects. Mycophenolate mofetil (MMF) is becoming a standard of care in SCT recipients for better prevention of GVHD as well as for promoting stem cell engraftment.

Aims: To evaluate the effect of MMF, an immunosuppressive drug increasingly used for prevention of GVHD, on disease recurrence following SCT in a preclinical animal model. Since GVL effects may be also induced by alloreactive natural killer (NK) cells, the goal was to investigate the effects of MMF on the activity of lymphokine-activated killer (LAK) cells.

Methods: MMF was administered by daily intraperitoneal injection starting at day 1 post-SCT. Cytotoxic LAK activity was measured by 5-h 35S-release assay, and GVL was tested by the appearance of BCL1 leukemia in a semi-mismatched (C57BL/6 donors to [BALB/c x C57BL/6] F1 recipients) murine model.

Results: A dosage regimen of 28-200 mg/kg per day MMF had no negative effect on either cytotoxic LAK activity or GVL (as measured by finding of leukemic cells in recipient spleen by PCR or the appearance of clinical leukemia with adoptive transfer).

Conclusions: These results suggest that MMF does not impair GVL effects or reduce LAK cell activity in mice.

Fig. 1

PCR of spleens from BCL1-inoculated mice harvested from 120 mg/kg per day MMF (group c, lanes 1 and 2), 200 mg/kg per day MMF (group d, lane 3), SCT control mice (group e, lane 4), leukemia control mice (group f, lanes 5 and 6), and BCL1 cells (lane 7) as a positive control. The arrow identifies the positive PCR bands for BCL1. It can be seen that the PCR is negative for leukemia in both MMF-treated and untreated groups, while positive in the controls.

Fig. 2

Appearance of BCL1 leukemia in untreated adoptive recipient BALB/c mice receiving 10⁵ spleen cells obtained from each experimental group (i.e., leukemia control, SCT control, SCT+MMF 120 mg/kg, and SCT+MMF 200 mg/kg; n=16 for each group).

Fig. 3

IFN-α (mean ± SD) in plasma of F₁ mice transplanted with C57BL/6 spleen cells and treated daily with MMF (either 120 mg/kg per day [n=4] or 200 mg/kg per day [n=2]) for 7 days. SCT control (n=5) and leukemia control (n=5) are F₁ mice transplanted with C57BL/6 spleen cells plus BCL1 cells or BCL1 cells alone, respectively, and which received no further treatment. MMF120 and SCT group were significantly higher than the leukemia control (p<0.001 and p=0.003, respectively).

Fig. 4

Survival in percentage following induction of GVHD in animals with or without treatment with mycophenolate mofetil (MMF). Death was a result of GVHD. MST of mice with GVHD treated with MMF was significantly shorter than in SCT control. GVHD control control mice receiving no posttransplant treatment (n=20); MMF 28 treated with 28 mg/kg per day MMF (n=16); MMF 90 treated with 90 mg/kg per day MMF (n=16); High dose MMF treated with a combination of 120 and 200 mg/kg per day MMF (n=11).

Fig. 5

Mean body weight following induction of GVHD in animals with or without treatment with mycophenolate mofetil (MMF). Weight loss is similar for all groups. SCT control control mice receiving no posttransplant treatment (n=8); MMF 28 treated with 28 mg/kg per day MMF (n=8); MMF 90 treated with 90 mg/kg per day MMF (n=8); HD MMF high-dose MMF representing treated with combination of 120 and 200 mg/kg per day MMF (n=11).