What could explain failure to luspatercept in patients with transfusion-dependent beta thalassemia?

Luspatercept works by trapping TGF beta ligands (GDF 11 and 15) and optimizing maturation and differentiation of erythroid precursors, thus facilitating increased output of red cells.

In individuals who have beta zero-beta zero thalassemia, this must mean that the cells coming out would contain hemog...