Graft Versus Host Disease Prophylaxis with Everolimus and Tacrolimus in Patients with Myelodysplastic Syndromes (MDS) and Acute Myeloid Leukaemia (AML) Receiving Allogeneic Peripheral Blood Stem Cell Transplantation (PBSCT).

Introduction: The use of a calcineurin-inhibitor in combination with methotrexate is the current standard in the prophylaxis of graft versus host disease (GVHD). Everolimus is a newly developed m-TOR inhibitor, which, besides a potent immunosuppressive action including the stimulation of regulatory CD4+foxp3+ T-cells (Tregs), seems to mediate anti-neoplastic effects in MDS and AML.

Methods: We report results of a prospective study investigating for the first time a combination of everolimus (days 0–56) with tacrolimus (starting day 0) in 16 patients with MDS (RCMD n=3, RAEB-1 n=3, RAEB-2 n=3, CMMOL-1 n=1, CMMOL-2 n=1, MDS/AML n=1) or de novo AML (n=4) undergoing allogeneic myeloablative conditioning (busulfan 16 mg/kg over 4 days, fludarabine 120 mg/m² over 4 days) followed by a median of 7.0 x 10⁶/kg CD34+ peripheral blood stem cells (PBSC) from related (n=2) or unrelated donors (n=14). It is of note that 5 unrelated donor/recipient pairs displayed one allel-mismatch whereas all others were matched in 10 out 10 HLA characters. The median age of the patients was 61 years (range 47–69) and the majority (n=7) of MDS patients were classified INT-2 or HIGH according to IPSS.

Results: All patients engrafted a median of 14 days (platelets) and 17 days (neutrophils) after transplant. On day 21 and 56 after PBSCT the median number of CD4+foxp3+ cells in the blood was not significantly different from normal donors (patients, n=5: 3.2 and 2.3 x 10⁴/ul, controls n=4: 3.7 x 10⁴/ul) Nevertheless, the rate of acute GVHD was moderate with five patients (31 %) developing acute GVHD grade II and only one patient experiencing grade IV GVHD after cessation of immunosuppression due to thrombotic-thrombocytopenic purpura (TTP). Decrease of thrombocytes together clinical signs of TTP were seen in two additional patients while four patients developed VOD of the liver, which was fatal in one case. Extensive chronic GVHD was seen in 50 % of evaluable patients. Mucositis CTC grade III was observed in 5 patients only. The total day 100 mortality rate was 19 % and currently eleven out of sixteen patients (69%) are alive and in remission.

Conclusion: Everolimus and tacrolimus are highly efficient in preventing GVHD after unrelated PBSCT in older patients with MDS and AML, which seems not to be mediated by an increase in Tregs. Nevertheless, side effects associated with thrombotic microangiopathy might be more prevalent compared to other regimens.