Abstract
<jats:p>PTCy and abatacept have both facilitated the performance of allogeneic stem cell transplant from HLA-mismatched donors. Two recent clinical studies in patients who received bone marrow transplants suggest that intermediate dose (ID) PTCy may be as effective as standard dose for preventing GVHD. As peripheral blood (PB) is the more common stem cell source used today, we tested ID PTCy in combination with standard dose abatacept in consecutively transplanted hematologic malignancy patients. This study was performed in a single institution in which more than 70% of the patients were minorities and received partially mismatched stem cells. There was no 100-day non-relapse mortality and severe acute GVHD was less than 5%. However, due to an excess occurrence of cGVHD approaching 50%, we stopped the use of ID PTCy. We conclude that abatacept plus ID PTCy is inadequate for preventing cGVHD after transplantation with PB stem cells.</jats:p>