This study is a phase 2 / 3 prospective, double-blind, randomized, multicenter, placebo-controlled study for prevention of acute GVHD (aGVHD) in participants undergoing an unrelated (matched or single allele mismatched) or matched related allogeneic hematopoietic cell transplantation (HCT).

Inclusion Criteria:

• • Male or female participants, >=12 years of age (>= 18 years of age for participants at German sites only), undergoing HCT for hematological malignancies, including leukemia, lymphoma, multiple myeloma, myelodysplastic syndrome, and myeloproliferative neoplasms.
• • Planned myeloablative conditioning regimen.
• • Participants must have a related or unrelated donor as follows:
• - Related donor must be a 6 / 6 match for human leukocyte antigen (HLA)-A, -B, at intermediate (or higher) resolution, and -DR beta 1 (DRB1) at high resolution using deoxyribonucleic acid (DNA)-based typing.
• - Unrelated donor must be 7 / 8 or 8 / 8 match for HLA-A, -B, and -C at intermediate (or higher) resolution, and -DRB1 at high resolution using DNA-based typing.

Exclusion Criteria:

• • Prior autologous or allogeneic HCT.
• • T cell depleted transplant or planned use of anti-T cell antibody therapy either ex vivo or in vivo (ie, anti thymocyte globulin [ATG], alemtuzumab) for GVHD prophylaxis.
• • Planned umbilical cord blood transplant.
• • Planned use of cyclophosphamide after HCT for GVHD prophylaxis.
• • Planned haploidentical donor.

CSL will consider on a case-by-case basis requests to share Individual Patient Data (IPD) with external bona-fide, qualified scientific and medical researchers. For information on the process and requirements for submitting a voluntary data sharing request for IPD, please contact CSL at clinicaltrials@cslbehring.com.

Requests for IPD will generally be considered once review by major regulatory authorities (ie FDA, EMA) is complete and the primary publication is available.

Proposed research should seek to answer a previously unanswered important medical or scientific question.

Applicable country specific privacy and other laws and regulations will be considered and may prevent sharing of IPD.

If the request is approved and the researcher has executed an appropriate data sharing agreement, IPD that has been appropriately anonymized will be available.