When the Food and Drug Administration approved abatacept in December 2021 as prophylaxis for acute graft-versus-host disease (aGVHD) in adults and children 2 years and older who are undergoing hematopoietic stem cell transplantation (HSCT), the announcement was notable for couple of key reasons.
Abatacept was approved based on results from the ABA2 trial, which evaluated 142 adults and children with hematologic malignancies who received a four-dose regimen of abatacept in addition to standard of care – a calcineurin inhibitor (CNI) plus methotrexate (MTX) – prior to undergoing an 8/8 HLA-matched, unrelated donor (URD) HSCT, or standard of care alone.
Another arm of the trial examined 43 recipients of a 7/8 HLA-mismatched URD HSCT who received abatacept plus standard of care, compared with a prespecified registry cohort group provided by the Center for International Blood and Marrow Transplant Research, who received CNI and MTX.
Results published in the Journal of Clinical Oncology showed the proportion of patients in the 8/8 group with severe aGVHD in the abatacept group 100 days after HSCT was not significantly lower, compared with the standard of care group (6.8% vs. 14.8%; P = .13), but there was a significant improvement in severe aGVHD–free survival (SGFS) 180 days after HSCT in the abatacept group, compared with the group that received standard of care (93.2% vs. 80%; P = .05).
Among patients in the 7/8 group, there was a significant difference in the proportion of patients with severe aGVHD favoring the abatacept group (2.3% vs. 30.2%; P < .001), and significantly improved SGFS, compared with the CIBMTR registry cohort (97.7% vs. 58.7%; P < .001)
A post hoc analysis of ABA2 published as a research letter in Blood Advances assessed abatacept using real-world data from CIBMTR. Researchers compared the 8/8 group that received standard of care with the 7/8 group that received abatacept plus standard of care and found no significant differences between relapse-free survival and overall survival for patients in the 8/8 group (adjusted hazard ratio, 0.60; 95% confidence interval, 0.28-1.28; P = .19) and 7/8 group (aHR, 0.77; 95% CI, 0.34-1.71; P = .51).
Stephen Spellman
The results suggest “abatacept may eliminate that risk of a mismatched transplant in the setting of that analysis and that small cohort that was assessed there, which is good news for patients that may not have a fully matched donor on the registry,” said Stephen Spellman, vice president at Be The Match Research (operated by the National Marrow Donor Program), and senior scientific director of CIBMTR. The findings from ABA2 “were even more impressive than necessarily expected, especially in the 7/8 arm. This is a truly substantial reduction in acute GVHD risk in that patient population,” he said in an interview.