Graft Versus Host Disease (GVHD) Prophylaxis with Everolimus and Tacrolimus Is Associated with a High Incidence of Sinusoidal Obstruction Syndrome and Microangiopathy – Results of the EVTAC Trial

Beyond disease biology, the success of allogeneic hematopoietic stem cell transplantation (HSCT) in patients with hematological malignancies is mainly determined by the occurrence and extent of graft versus host disease (GVHD). Therefore, prevention of GVHD is the major goal and challenge in clinical HSCT. A calcineurin-inhibitor combined with methotrexate is the standard graft versus host disease (GVHD) prophylaxis after allogeneic hematopoietic stem cell transplantation (HSCT). Everolimus is a derivative of sirolimus, which also seems to mediate anti-leukemia effects. Given the potential synergism and favourable toxicity profile of everolimus and tacrolimus (EVTAC) after allogeneic HSCT we sought to investigate the efficacy of this combination in patients with either myelodysplastic syndromes (MDS) or acute myeloid leukemia (AML). We report a combination of everolimus (days 0–56) and Tacrolimus (from day −1 on) in 24 patients (pts, median age 62 years) with either MDS (n=17) or AML (n=7) undergoing intensive busulfan-based conditioning followed by HSCT from related (n=4) or unrelated matched (n=12) or 1-allele mismatched (n=8) donors. All pts engrafted and only one experienced grade IV mucositis. However, although everolimus was scheduled to be administered up to day 56, patients received the drug a median of 44 days (range 10–56) only. The reason for premature discontinuation (50%) were either occurrence of early-onset (day 6) GVHD associated hyperbilirubinemia CTC grade 4 (n=1), transplantation-associated microangiopathy (TMA, n=3), sinusoidal obstructive syndrome (SOS) of the liver (n=6) or a drop of platelets after engraftment by at least 50% (n=2). Nine pts (37%) developed grade II–IV acute GVHD, however, chronic extensive GVHD was observed in 11 of 17 (64%) evaluable pts. TMA occurred in 7 pts (29%) with two cases of acute renal failure. In five out of seven patients with TMA either tacrolimus (n=4) or everolimus (n=1) blood through levels were slightly above the upper target level at the time of TMA appearance. The study was terminated prematurely because additional 6 pts (25%) developed SOS, which was fatal in two cases. With a median follow-up of 26 months, the 2-year overall survival rate is 47%. In conclusion, although this new combination appears to be effective as prophylactic regimen for acute GVHD, the incidence of TMA and SOS seems to be higher compared to other regimens. As a result this combination cannot be recommended as prophylactic regimen after busulfan-based intensive conditioning. However, studies in the context of TBI-based or reduced-intensity conditioning regimens might come to a different conclusion.