2026 Eastern States Conference

Title: Impact of Adding Abatacept to Antithymocyte Globulin for Acute Graft-Versus-Host Disease Prophylaxis in Matched Unrelated Donor Hematopoietic Stem Cell Transplantation 

Authors: Daniel Wroblewski, PharmD; Carissa Ganihong, PharmD, BCOP; Maribel Pereiras, PharmD, BCPS, BCOP; Simon Gelman, PhD ; Siddhartha Reddy, MD; Michele Lyne Donato, MD

Objective: Compare abatacept and rabbit antithymocyte globulin combination therapy versus rabbit antithymocyte globulin (rATG) acute graft-versus-host disease (GVHD) prophylaxis outcomes in matched unrelated donor hematopoietic stem cell transplantation (HSCT).

Self Assessment Question: (T/F): Abatacept inhibits alloreactive T-cell proliferation and cytokine production while preserving other aspects of immune function.

Background: This study evaluates survival, GVHD, chimerism, and safety outcomes in patients receiving abatacept and rATG combination therapy versus rATG alone for acute GVHD prophylaxis in matched unrelated donor HSCT.

Methods: This single-center, retrospective, observational study included patients undergoing their first allogeneic HSCT from a 10/10 matched unrelated donor for acute myeloid leukemia or myelodysplastic syndrome at Hackensack University Medical Center between January 1, 2019 and December 31, 2024. The primary outcome was GVHD-free, relapse-free survival (GRFS) at 1 year. Secondary outcomes included cumulative incidence of grade 2-4 and grade 3-4 acute GVHD (aGVHD) by day 180 after transplantation, incidence of chronic GVHD (cGVHD) at 1 year, time to neutrophil and platelet engraftment, full donor chimerism at day 30 and day 90 after transplantation, relapse-free survival (RFS) at 1 year, and overall survival (OS) at 1 year. Safety outcomes, including incidence of cytomegalovirus (CMV) and Epstein-Barr virus (EBV) reactivation within the first 100 days post-transplantation, documented adverse reactions to abatacept, and non-relapse mortality (NRM) at day 180 and 1 year, were also evaluated.

Results: 
Among 155 patients, 76 received abatacept and rATG and 79 received rATG alone for GVHD prophylaxis. Bone marrow stem cell source and favorable performance status were more common in the rATG arm, while post-transplant maintenance was more frequent in patients receiving abatacept and rATG. Otherwise, baseline characteristics were similar among groups. At 1 year, GRFS was lower with abatacept and rATG prophylaxis (10% vs 30%, p=0.018), as was NRM at day 180 (1.3% vs 8.9%) and 1 year (6.6% vs 19%, p=0.02). cGVHD by 1 year was higher with abatacept and rATG prophylaxis (mild-severe: 73.2% vs 50.7%, p=0.009; moderate-severe: 38% vs 14.5%, p=0.002). EBV reactivation by day 100 was more common with rATG alone (63.3% vs 30.3%, p=0.0001). 

Conclusion: 
The addition of abatacept to rATG-based GVHD prophylaxis was associated with inferior GRFS at 1 year, driven by a higher incidence of cGVHD.  It was also associated with improved NRM , with similar rates of aGVHD in patients undergoing MUD allogeneic HSCT. Similar results were reported in prior studies where abatacept-based prophylaxis showed benefit in aGVHD, NRM, and relapse, but not cGVHD. Further studies are warranted to clarify the role of abatacept and rATG prophylaxis in this setting.