A Novel Recombinant Eklf-GATA1 Fusion Protein Reduces Sickling of Erythrocytes Cultured from CD34⁺ Cells with Sickle Cell Disease

Current gene therapy approaches for treatment of hemoglobinopathies involve viral transduction of hematopoietic stem cells with antisickling globin genes. Hemoglobin A2 (HA2, α2δ2), expressed at a low level due to the lack of Eklf binding motif in its promoter region, is fully functional and could be a valid anti-sickling agent in sickle cell disease, as well as a substitute of hemoglobin A in β-thalassemia. We had previously demonstrated that two Eklf-GATA1 fusion proteins could significantly activate δ-globin expression in CD34⁺ cells from healthy and sickle trait donor's blood. Here we report the effects of Eklf-GATA1 on hemoglobin expression and phenotypic correction using erythrocytes cultured from CD34⁺ cells with sickle cell disease. We found that enforced expression of Eklf-GATA1 fusion protein enhanced globin gene expression in the erythrocytesas compared with vector control. The long-form Eklf-GATA1 up-regulated β-globin gene expression 2.0-fold, δ-globin gene expression 4.3-fold, and γ-globin gene expression 2.6-fold. The medium-form EKLF-GATA1 up-regulated δ-globin gene expression 2.3-fold and γ-globin 1.3-fold, but had no significant effect on β-globin gene expression. HPLC revealed a percentage of HA₂+HbF was increased from 8.1 % in vector-transduced cells to 19.7% in medium-form Eklf-GATA-transduced-cells (p<0.01) and 14.4% in long-form Eklf-GATA-transduced-cells (p<0.01). Upon deoxygenation, the percentage of sickling erythrocyte was lower to 79.8% in medium-form Eklf-GATA-transduced cells as compared with 89.8% in vector-transduced-cells (p<0.05). Flow cytometry analyses of CD71/GPA and thiazole orange staining indicated that erythroid cell differentiation and enucleation were not affected by Eklf-GATA1. Our results shown that long form Eklf-GATA1 fusion protein has major effects on d- and g-globin induction than β-globin; the medium form Eklf-GATA1 elevated δ- and γ-globin expression without an effect on β-globin expression. Our results indicate that these fusion constructs could be a valuable genetic therapeutic tool for hemoglobinopathies, and warrant further preclinical study and evaluation.