The purpose of this study is to estimate overall survival (OS) for participants treated with abatacept versus those not treated with abatacept prior to hematopoietic stem cell transplantation (HSCT). Participants were included if their donors were unrelated and had 1-allele mismatched human leukocyte antigen (HLA) status.

Inclusion Criteria:

• Participants who underwent first allogenic transplant in the US
• Participants with an unrelated donor who are HLA-matched at 7/8 loci (A, B, C, DRB1)
• Participants at least 6 years old with weight at least 20 kilograms
• Participants with a Karnofsky/Lansky Performance Score ≥80%
• Participants whose first allogeneic transplant occurred from January 1, 2011 to December 31, 2018
• Participants with any of the following diseases: AML, ALL, CML, MDS, HL, NHL
• Participants with any of the following graft versus host disease (GVHD) prophylaxis treatments:
• CNI plus MTX (with or without ATG and with or without abatacept); or
• Post-transplant cyclophosphamide (PT-Cy) without antithymocyte globulin (ATG)
• Participants treated with any of the following conditioning regiments: total body irradiation (TBI)/cyclophosphamide (Cy), busulfan (Bu)/Cy, Bu/fludarabine (flu), Flu/Melphalan (MEL)

Exclusion Criteria:

• Participants with missing information on ATG (yes/no)
• Participants receiving alemtuzumab (Campath)
• Participants with cord blood grafts
• Participants with non-MDS myeloproliferative disorders (NOTE: Participants with chronic myelomonocytic leukemia [CMMoL] will be included)
• Participants who did not consent to participate in research
• Participants treated at embargoed centers for research
• Participants treated with abatacept and ATG
• Among non-abatacept treated participants, participants transplanted at centers with abatacept trial participants
• Participants with any of the following missing propensity score variables:
• Disease status at transplantation (early, intermediate, advanced HL and NHL-chemosensitive)
• Age
• Gender (male, female)
• HSCT graft source (bone marrow [BM], peripheral blood [PB])
• Conditioning intensity (myeloablative, non-myeloablative / reduced intensity)
• Karnofsky/Lansky Performance Score (80%, 90-100%)
• CNI type (tacrolimus, CsA)

This study uses data routinely collected into the Center for International Blood and Marrow Transplant Research (CIBMTR) database. From the patterns of use analysis of the CIBMTR database, the majority of participants who received calcineurin inhibitor (CNI) plus methotrexate (MTX) plus abatacept were treated between 2011 and 2018. The study population has been selected to approximate the inclusion and exclusion criteria of the ABA2 clinical trial as closely as possible.