Postgrafting Immunosuppression with Prolonged Mycophenolate Mofetil (MMF) and Truncated Cyclosporine (CSP) Failed To Reduce the Incidence of Graft-Versus-Host Disease (GVHD) after Unrelated Donor Hematopoietic Cell Transplantation (HCT) with Nonmyeloablative Conditioning.

Background. We previously reported data from 103 pts receiving PBSC from HLA-matched unrelated donors after conditioning with 2 Gy total body irradiation (TBI) plus 90 mg/m2 fludarabine. Postgrafting immunosuppression included MMF (administered from day 0 until day +40 with taper through day +96), and CSP (given from day -3 to day +100, with taper through day 180) (historical group). The incidences of grade III–IV acute and chronic extensive GVHD were 14% and 48%, respectively. Several studies have suggested that CSP could prevent activation-induced cell death of T-cells, and thus potentially delay the eradication of donor-versus-host alloreactive T-cells, preventing tolerance induction. Conversely, antimetabolite inhibitors, such as MMF, could delete alloreactive T-cells by induction of activation-induced cell death and apoptosis, and thus might favor tolerance induction

Pts and Methods. Here, we investigated whether postgrafting immunosuppression with prolonged MMF (given at 15 mg/kg orally thrice a day from day 0 to day +30, then at 15 mg/kg orally twice a day until day 150, and then tapered at day 150 and discontinued at day 180) and truncated CSP (abruptly discontinued on day 80), would promote tolerance induction and reduce the incidence of GVHD (current protocol, n=71) after unrelated HCT with nonmyeloablative conditioning.

Results. Sustained donor engraftment was achieved in 68 pts (96%) in the current protocol, versus in 98 pts (95%) in the historical group. Grades II, III and IV acute GVHD were seen in 36 (50.7%), 11 (15.5%) and 7 (9.9%) pts, respectively, in the current protocol, versus 39 (37.9%), 11 (10.7%) and 4 (3.9%) pts, respectively, in the historical group. The incidences of grade II–IV and grade III–IV acute GVHD were 75% and 23% in the current protocol, versus 52% (P=.05) and 14% (P=.14) in the historical group. The 1-yr incidence of chronic GVHD was 46% in the current protocol, versus 48% in the historical group. Finally, the 1-yr probabilities of relapse, nonrelapse mortality and progression-free survival were 24%, 36% and 40%, respectively, in the current protocol, versus 26% (P=.9), 18% (P=.005) and 56% (P=.04) in the historical group. The increased incidence of nonrelapse mortality in the current protocol was not due only to the increased incidence of grade II–IV acute GVHD, since nonrelapse mortality remained significantly higher in the current protocol than in the historical group after adjusting for occurrence of grade II and grade III–IV acute GVHD (P=.04). Evaluation of pretransplant comorbidities is ongoing.

Conclusions. Postgrafting immunosuppression with prolonged MMF and truncated CSP failed to decrease the incidence of GVHD after nonmyeloablative conditioning with URD. Ongoing efforts are directed at reducing the risk of acute GVHD after nonmyeloablative conditioning for unrelated donors by replacing tacrolimus for CSP, and by adding sirolimus to MMF and CSP.