The development of an advanced lentiviral gene therapy for beta-thalassemia.

Lentiviral vector (LV)-mediated hematopoietic stem cell (HSC) gene therapy is under clinical development and offers a curative potential for β-thalassemia. LV is an important gene therapy agent that directly influences the therapeutic effects and treatment costs. In this study, we constructed and evaluated several erythroid-specific LVs (PR, PRIN, P6PR, I8, and HS40) carrying a modified human β-globin gene. All LVs displayed high vector titer and expressed β-globin in vitro in both murine and human erythroid cells. Notably, the novel recombinant HS40 LV, which contains a tandem HS40/HS2 enhancer and a chimeric β-globin/B19 p6 promoter, exhibited optimal viral titer and β-globin expression. HS40 LV-β-globin modified thalassemia Hbbth3/+ (th3) mouse HSCs were transplanted into th3 mice treated with a 7.5 Gy conditioning regimen. The transplanted mice displayed persistent LV human β-globin expression in blood, liver, spleen, and bone marrow. Furthermore, the treated mice showed marked amelioration of hematological indices, including increased hemoglobin levels and reduced anisocytosis, poikilocytosis, and reticulocyte count. This was accompanied by histopathological remission, evidenced by reduced extramedullary hematopoiesis and iron deposition in the liver and spleen. Importantly, th3 mice receiving an increased dose of 9.5 Gy conditioning achieved higher engraftment of the LV-modified cells, accompanied by a more profound phenotypic improvement. In conclusion, these results demonstrated a significant therapeutic effect of the HS40 LV in β-thalassemia mice, even at 30 % LV gene transfer levels. The novel HS40 LV represents a promising candidate for clinical translation in the treatment of β-thalassemia.