Contributions
Abstract: EP1302
Type: E-Poster Presentation
Session title: Thalassemias
Background
β-thalassemia is a genetic disorder characterized by anemia, ineffective erythropoiesis and iron overload. Patients affected by the most severe form of the disease, transfusion-dependent thalassemia (TDT), require lifelong blood transfusion and an iron chelation therapy, symptomatic treatments that affect the quality of life. The only well-established curative therapy is allogenic bone marrow (BM) transplantation, but it is applicable only to a minority of patients because of the scarcity of suitable donors. Other recently approved treatments (i.e. gene therapy and luspatercept), despite promising, are only partially effective and/or suitable for selected patients. For these reasons, the identification of novel therapeutic approaches is a clinical need. We have already proved that the selective BM deletion of transferrin receptor 2 (TFR2), a partner of Erythropoietin receptor, improves erythropoiesis and ameliorates anemia in a non-transfusion-dependent thalassemia murine model, despite the persistence of the genetic defect (Artuso et al., Blood 2018; Casu, Pettinato et al., Blood 2020).
Aims
Here, we investigate whether Tfr2 targeting might represent a therapeutic option for TDT.
Methods
TDT mice (Hbbth1/th2) with BM Tfr2 heterozygous deletion (Tfr2BMhetero/Hbbth1/th2) were generated by transplantation of fetal liver cells (FLT) harvested from day 14.5 Tfr2+/-/Hbbth1/th2 (or Hbbth1/th2 as a control) embryos. Two x 106 fetal liver cells were retro-orbitally injected into lethally irradiated 8-week-old C57BL/6-Ly-5.1 wild-type male mice. Complete blood count was evaluated 8 and 12 weeks after FLT, when mice were sacrificed, before the onset of blood transfusion requirement. A full phenotypic analysis was performed to analyze the hematological parameters, erythropoiesis and the iron phenotype.
Results
Twelve weeks after FLT, chimerism was superior to 90% in all mice and the mortality rate was consistently higher among Hbbth1/th2 than Tfr2BMhetero/Hbbth1/th2 mice (50% and 20%, respectively). BM Tfr2 haploinsufficiency was sufficient to increase RBC count, Hb levels and hematocrit, despite the attenuation of the beneficial effect over time due to the worsening of anemia. Tfr2 heterozygous deletion decreased the total amount of Ter119+ cells and of polychromatic erythroblasts in the BM, showing a partial improvement of ineffective erythropoiesis. As expected, splenomegaly was not alleviated, while hepatic iron overload was reduced. Moreover, BM Tfr2 haploinsufficiency partially corrected cardiomegaly, a secondary TDT complication caused by chronic anemia and iron overload, and attenuated the endoplasmic reticulum stress in the BM, preventing the activation of the unfolded protein response. However, whether this effect is directly due to the deletion of Tfr2 or it is an indirect consequence of the improved cell fitness is still unknown and worth to be assessed.
Conclusion
Overall our data show that Tfr2 targeting might represent a valuable therapeutic option for the most severe form of β-thalassemia, ameliorating several features of the disease. However, the effect of full BM Tfr2 inactivation, that we expect more efficient in correcting anemia and ineffective erythropoiesis, and the potential role of Tfr2 deletion in the reduction of blood transfusion requirement, the standard treatment for TDT but correlated to several complications, remain to be evaluated.
Keyword(s): Anemia, Beta thalassemia, Erythropoieisis, Iron
Abstract: EP1302
Type: E-Poster Presentation
Session title: Thalassemias
Background
β-thalassemia is a genetic disorder characterized by anemia, ineffective erythropoiesis and iron overload. Patients affected by the most severe form of the disease, transfusion-dependent thalassemia (TDT), require lifelong blood transfusion and an iron chelation therapy, symptomatic treatments that affect the quality of life. The only well-established curative therapy is allogenic bone marrow (BM) transplantation, but it is applicable only to a minority of patients because of the scarcity of suitable donors. Other recently approved treatments (i.e. gene therapy and luspatercept), despite promising, are only partially effective and/or suitable for selected patients. For these reasons, the identification of novel therapeutic approaches is a clinical need. We have already proved that the selective BM deletion of transferrin receptor 2 (TFR2), a partner of Erythropoietin receptor, improves erythropoiesis and ameliorates anemia in a non-transfusion-dependent thalassemia murine model, despite the persistence of the genetic defect (Artuso et al., Blood 2018; Casu, Pettinato et al., Blood 2020).
Aims
Here, we investigate whether Tfr2 targeting might represent a therapeutic option for TDT.
Methods
TDT mice (Hbbth1/th2) with BM Tfr2 heterozygous deletion (Tfr2BMhetero/Hbbth1/th2) were generated by transplantation of fetal liver cells (FLT) harvested from day 14.5 Tfr2+/-/Hbbth1/th2 (or Hbbth1/th2 as a control) embryos. Two x 106 fetal liver cells were retro-orbitally injected into lethally irradiated 8-week-old C57BL/6-Ly-5.1 wild-type male mice. Complete blood count was evaluated 8 and 12 weeks after FLT, when mice were sacrificed, before the onset of blood transfusion requirement. A full phenotypic analysis was performed to analyze the hematological parameters, erythropoiesis and the iron phenotype.
Results
Twelve weeks after FLT, chimerism was superior to 90% in all mice and the mortality rate was consistently higher among Hbbth1/th2 than Tfr2BMhetero/Hbbth1/th2 mice (50% and 20%, respectively). BM Tfr2 haploinsufficiency was sufficient to increase RBC count, Hb levels and hematocrit, despite the attenuation of the beneficial effect over time due to the worsening of anemia. Tfr2 heterozygous deletion decreased the total amount of Ter119+ cells and of polychromatic erythroblasts in the BM, showing a partial improvement of ineffective erythropoiesis. As expected, splenomegaly was not alleviated, while hepatic iron overload was reduced. Moreover, BM Tfr2 haploinsufficiency partially corrected cardiomegaly, a secondary TDT complication caused by chronic anemia and iron overload, and attenuated the endoplasmic reticulum stress in the BM, preventing the activation of the unfolded protein response. However, whether this effect is directly due to the deletion of Tfr2 or it is an indirect consequence of the improved cell fitness is still unknown and worth to be assessed.
Conclusion
Overall our data show that Tfr2 targeting might represent a valuable therapeutic option for the most severe form of β-thalassemia, ameliorating several features of the disease. However, the effect of full BM Tfr2 inactivation, that we expect more efficient in correcting anemia and ineffective erythropoiesis, and the potential role of Tfr2 deletion in the reduction of blood transfusion requirement, the standard treatment for TDT but correlated to several complications, remain to be evaluated.
Keyword(s): Anemia, Beta thalassemia, Erythropoieisis, Iron