Background
Phase III double-blind placebo-controlled RCT. 336 adult patients (≥18 years) with transfusion-dependent beta-thalassemia (≥6 RBC units per 24 weeks despite optimized supportive care). Any beta-thalassemia genotype including HbE/β-thal. Randomized 2:1. Luspatercept (ACE-536) is a TGF-β ligand trap that enhances late-stage erythropoiesis by inhibiting aberrant Smad2/3 signaling in ineffective erythropoiesis. First non-transfusion, non-transplant therapy to demonstrate efficacy in transfusion-dependent beta-thalassemia.
Interventions and follow up
Arm A: Luspatercept 1.0 mg/kg SC q3w (escalating up to 1.25 mg/kg based on response) for ≥48 week
Arm B: Placebo SC q3w for ≥48 week
Primary endpoint: ≥33% reduction in transfusion burden vs placebo during weeks 13–24, with ≥2 RBC units reductio
mFollow up: 48 weeks (primary analysis)
Arm B: Placebo SC q3w for ≥48 week
Primary endpoint: ≥33% reduction in transfusion burden vs placebo during weeks 13–24, with ≥2 RBC units reductio
mFollow up: 48 weeks (primary analysis)
Results
Transfusion reduction ≥33%: 21.4% (luspatercept) vs 4.5% (placebo), P<.001
Transfusion reduction ≥50% (weeks 37–48): 19.6% vs 3.6%
Transfusion independence ≥12 weeks: 11% (luspatercept) vs 1% (placebo)
Mean RBC units reduced: −0.95 units/12 weeks (luspatercept) vs +0.09 (placebo)
Transfusion reduction ≥50% (weeks 37–48): 19.6% vs 3.6%
Transfusion independence ≥12 weeks: 11% (luspatercept) vs 1% (placebo)
Mean RBC units reduced: −0.95 units/12 weeks (luspatercept) vs +0.09 (placebo)
Adverse events
Main adverse events: Grade ≥3 AEs: 49% (luspatercept) vs 47% (placebo). Bone pain 20% vs 8%, arthralgia 19% vs 8%, dizziness 11% vs 6%, hypertension 10% vs 6%, headache 26% vs 24%. Thromboembolic events: 3% vs 3% (not increased). Discontinuation due to AEs: 5% vs 5%.
Conclusions
Luspatercept significantly reduced transfusion burden in adults with transfusion-dependent beta-thalassemia, with 21% achieving ≥33% reduction vs 4.5% on placebo, establishing a new disease-modifying option in this population.
Key Limitations
Key Limitations: Only 21% achieved the primary endpoint, meaning 79% of luspatercept patients did not meet the ≥33% transfusion reduction threshold. No transfusion independence was achieved as a standard outcome. Primary endpoint interval (weeks 13–24) may not reflect long-term benefit. Effect size larger in non-β0/β0 genotypes; β0/β0 patients had lower response rates. No quality of life or iron burden improvement data from primary analysis. Not curative; does not address underlying thalassemia.
Clinical Context
FDA approved August 2020 (Reblozyl) for transfusion-dependent beta-thalassemia in adults ≥18. Also approved for MDS-RS and lower-risk MDS. ESMO-MCBS score: 3. Luspatercept is guideline-listed (NCCN, EHA) as an option for transfusion-dependent beta-thal patients not suitable for or awaiting transplant/gene therapy. Beti-cel (Zynteglo) gene therapy (approved 2022) offers potential cure for eligible patients, but its commercial discontinuation by bluebird bio in April 2024 has affected availability.
References