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Abstract: Abatacept plus calcineurin inhibitors/methotrexate (CNI/MTX) is the first US Food and Drug Administration (FDA)-approved regimen for acute graft-versus-host disease (aGVHD) prophylaxis during unrelated-donor hematopoietic cell transplantation (URD-HCT). Using Center for International Blood and Marrow Transplant Research data, we investigated its impact in patients receiving 7/8 HLA-mismatched unrelated donor (MMUD) or 8/8 HLA-matched unrelated donor (MUD) URD-HCT between 2011 and 2018. Primary outcomes included day-180, 1-year, and 2-year overall survival (OS) and relapse-free survival (RFS) for abatacept + CNI/MTX vs CNI/MTX, CNI/MTX + antithymocyte globulin (ATG), and posttransplant cyclophosphamide-based prophylaxis (PT-Cy). For 7/8 MMUDs, day-180 OS (primary end point supporting FDA approval) was significantly higher for abatacept + CNI/MTX vs CNI/MTX (98% vs 75%; P = .0028). Two-year RFS was significantly higher for abatacept + CNI/MTX vs CNI/MTX (74% vs 49%; P = .0098) and CNI/MTX + ATG (77% vs 35%; P = .0002), and similar vs PT-Cy (72% vs 56%; P = .1058). For 8/8 MUDs, 2-year RFS for abatacept + CNI/MTX was numerically higher vs CNI/MTX (63% vs 52%; P = .1497), with an improved hazard ratio (HR) of 0.46 (0.25-0.86), and vs CNI/MTX + ATG (66% vs 55%; P = .1193; HR, 0.39 [0.21-0.73]), and was similar vs PT-Cy (68% vs 57%; P = .2356; HR, 0.54 [0.26-1.11]). For 7/8 MMUD and 8/8 MUD recipients, abatacept + CNI/MTX prophylaxis improved survival outcomes vs CNI/MTX and CNI/MTX + ATG; outcomes were similar to PT-Cy-based regimens. Abatacept + CNI/MTX may facilitate unrelated donor pool expansion for HCT., (© 2024 American Society of Hematology. Published by Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.)

In the ABA2 study, the T-cell costimulation blockade agent, abatacept, was safe and effective in preventing acute graft-versus-host disease (aGVHD) after unrelated-donor hematopoietic cell transplant (HCT), leading to US Food and Drug Administration approval. Here, we performed a determination of abatacept pharmacokinetics (PK), which enabled an examination of how abatacept exposure-response relationships affected clinical outcomes. We performed a population PK analysis of IV abatacept using nonlinear mixed-effect modeling and assessed the association between abatacept exposure and key transplant outcomes. We tested the association between the trough after dose 1 (Ctrough&#95;1) and grade (GR) 2 or 4 aGVHD (GR2-4 aGVHD) through day +100. An optimal Ctrough&#95;1 threshold was identified via recursive partitioning and classification tree analysis. This demonstrated that abatacept PK was characterized by a 2-compartment model with first-order elimination. The ABA2 dosing regimen was based on previous work targeting a steady-state abatacept trough of 10 μg/mL. However, a higher Ctrough&#95;1 (≥39 μg/mL, attained in ∼60% of patients on ABA2) was associated with a favorable GR2-4 aGVHD risk (hazard ratio, 0.35; 95% confidence interval, 0.19-0.65; P < .001), with a Ctrough&#95;1 <39 μg/mL associated with GR2-4 aGVHD risk indistinguishable from placebo (P = .37). Importantly, no significant association was found between Ctrough&#95;1 and key safety indicators, including relapse, and cytomegalovirus or Epstein-Barr virus viremia. These data demonstrate that a higher abatacept Ctrough&#95;1 (≥39 μg/mL) was associated with a favorable GR2-4 aGVHD risk, without any observed exposure-toxicity relationships. This trial was registered at www.clinicaltrials.gov as #NCT01743131., (© 2023 by The American Society of Hematology.)