A phase II study of sirolimus, tacrolimus and rabbit anti-thymocyte globulin as GVHD prophylaxis after unrelated-donor PBSC transplant.

We report on a prospective phase II trial of 32 patients who underwent unrelated-donor hematopoietic cell transplantation, with a tacrolimus, sirolimus and rabbit anti-thymoctye globulin GVHD prophylactic regimen. The primary study endpoint was incidence of grades II-IV acute (aGVHD), with 80% power to detect a 30% decrease compared with institutional historical controls. Median age at transplant was 60 (19-71). In total, 23 patients (72%) received reduced-intensity conditioning, whereas the remainder received full-intensity regimens. Median follow-up for surviving patients was 35 months (range: 21-49). The cumulative incidence of aGVHD was 37.3%, and the 2-year cumulative incidence of chronic GVHD was 63%. We observed thrombotic microangiopathy in seven patients (21.8%), one of whom also developed sinusoidal obstructive syndrome (SOS). Four of the 32 patients (12.5%) failed to engraft, and 3 of these 4 died. As a result, enrollment to this trial was closed before the targeted accrual of 60 patients. Two-year OS was 65.5% and EFS was 61.3%. Two-year cumulative incidence of relapse was 12.5% and non-relapse mortality (NRM) was 15.6%. NRM and aGVHD rates were lower than historical rates. However, the unexpectedly high incidence of graft failure requires caution in the design of future studies with this regimen.