Background
Phase II, randomized, double-blind study (ABA2). 142 patients undergoing allo-HCT from 7/8 HLA-mismatched unrelated donors (MMUD, 1-antigen mismatch), the highest-risk standard unrelated donor setting. Abatacept (CTLA4-Ig) blocks T-cell co-stimulation via the CD28/B7 pathway, potentially augmenting standard calcineurin-based prophylaxis where acute GVHD rates are high (~50%) with Tac/MTX.
Interventions and follow up
Arm A: abatacept 10mg/kg IV days −1, +5, +14, +28 (4 doses) + tacrolimus + methotrexate
Arm B: placebo IV ×4 doses + tacrolimus + methotrexate
Primary endpoint: Severe acute GVHD (grade III–IV) at day 100 in 7/8 MMUD recipients
Median follow up: 24 months
Arm B: placebo IV ×4 doses + tacrolimus + methotrexate
Primary endpoint: Severe acute GVHD (grade III–IV) at day 100 in 7/8 MMUD recipients
Median follow up: 24 months
Results
Grade III–IV aGVHD (7/8 MMUD): 6.8% (abatacept) vs 14.8% (placebo) — P=.05
Grade II–IV aGVHD: 38.5% vs 45.3% — NS
1-year GVHD-free OS (7/8 MMUD): 73.1% vs 60.0% — P=.14 (NS)
1-year OS (7/8 MMUD): 82.1% vs 73.9% — NS
8/8 MUD exploratory cohort (abatacept added): grade III–IV aGVHD 2.3% — lower than historical
Grade II–IV aGVHD: 38.5% vs 45.3% — NS
1-year GVHD-free OS (7/8 MMUD): 73.1% vs 60.0% — P=.14 (NS)
1-year OS (7/8 MMUD): 82.1% vs 73.9% — NS
8/8 MUD exploratory cohort (abatacept added): grade III–IV aGVHD 2.3% — lower than historical
Adverse events
Infections: 43.6% (abatacept) vs 47.8% (placebo) — NS, no excess infection
Non-relapse mortality: 1-year NRM 7.7% vs 11.5% — NS
Other: no excess cytopenias or infusion reactions; no safety signal with the 4-dose schedule
Non-relapse mortality: 1-year NRM 7.7% vs 11.5% — NS
Other: no excess cytopenias or infusion reactions; no safety signal with the 4-dose schedule
Conclusions
Abatacept added to Tac/MTX significantly reduced severe (grade III–IV) acute GVHD in 7/8 MMUD allo-HCT (14.8% to 6.8%) with an acceptable safety profile, supporting FDA approval for this specific indication.
Key Limitations
Phase II study, underpowered for OS endpoints. The primary endpoint (grade III–IV aGVHD) was met but grade II–IV was not significantly different, suggesting abatacept specifically prevents the most severe GVHD. Long-term impact on chronic GVHD, relapse, and OS requires larger trials. PTCy-based prophylaxis expansion to MMUD may supersede abatacept; approval was specifically for 7/8 MMUD, not broader mismatched or haploidentical settings.
Clinical Context
FDA approved abatacept (Orencia) in December 2021 for prevention of acute GVHD in combination with calcineurin inhibitor-based prophylaxis in adults and pediatric patients ≥2 years undergoing allo-HCT from 7/8 MMUD — the first new GVHD prophylaxis approval in decades for the MMUD setting. Abatacept may serve as a bridge until PTCy-based strategies are validated across the full spectrum of donor mismatches (ACCESS, BMT CTN 1702).
References