Successful treatment of murine β-thalassemia intermedia by transfer of the human β-globin gene

Abstract

The ␤-thalassemias are caused by more than 200 mutations that reduce or abolish ␤-globin production. The severity of the resulting anemia can lead to lifelong transfusion dependency. A genetic treatment based on globin gene transfer would require that transgene expression be erythroid specific, elevated, and sustained over time. We report here that long-term synthesis of chimeric hemoglobin (mu␣ 2 :hu␤ 2 A ) could be achieved in mice with ␤-thalassemia intermedia following engraftment with bone marrow cells transduced with a lentiviral vector encoding the human ␤-globin gene. In the absence of any posttransduction selection, the treated chimeras exhibit durably increased hemoglobin levels without diminution over 40 weeks. Ineffective erythropoiesis and extramedullary hematopoiesis (EMH) regress, as reflected by normalization of spleen size, architecture, hematopoietic colony formation, and disappearance of liver EMH. These findings establish that a sustained increase of 3 to 4 g/dL hemoglobin is sufficient to correct ineffective erythropoiesis. Hepatic iron accumulation is markedly decreased in 1-year-old chimeras, indicating persistent protection from secondary organ damage. These results demonstrate for the first time that viral-mediated globin gene transfer in hematopoietic stem cells effectively treats a severe hemoglobin disorder. (Blood. 2002;99:1902-1908 © 2002 by The American Society of Hematology IntroductionThe ␤-thalassemias are inherited anemias caused by mutations that reduce or abolish production of the ␤-globin chain of hemoglobin. [1][2][3] Caused by more than 200 mutations affecting the human ␤-globin gene, they are most prevalent in the Mediterranean region, the Middle East, the Indian subcontinent, and South East Asia, representing a serious health problem in certain areas where gene frequencies reach 3% to 10% of the population. The severity of ␤-thalassemia is directly linked to the degree of imbalance in the production of ␣-and ␤-globin chains. 1-3 The excess ␣-globin chains that are not incorporated into adult hemoglobin (␣ 2 :␤ 2 A ) precipitate in red blood cell (RBC) precursors, impairing erythroid maturation and causing mechanical damage, oxidative membrane destruction, and eventually apoptosis. However, the ␤-thalassemic phenotype is heterogeneous, depending on the genotype as well as the degree of ␥-globin chain expression. 4 In the most severe form found in homozygotes and compound heterozygotes, ␤-thalassemia major, massive medullary cell proliferation and expansion lead to severe skeletal deformities, while extramedullary hematopoiesis (EMH) 1 develops in spleen and liver. Erythropoiesis is nonetheless ineffective and the profound anemia requires regular lifelong blood transfusions; without treatment, the condition is lethal within the first years of life. 5 However, transfusion therapy leads to iron overload, which is itself lethal if untreated. 6 At present, the only means to definitively cure the disease is through hematopoietic stem cell (HSC) replacement. 7,8 But allogeneic b...

A novel murine model of Cooley anemia and its rescue by lentiviral-mediated human β-globin gene transfer

“…This mouse was virtually cured of anemia. The persistent, moderate EMH noted in this mouse, greater than expected for this Hb level, 10 suggests that the chimeric Hbb hu may not be functionally equivalent to Hbb mu .…”

“…Ultimately, like any other medical decision, therapy will be best guided by a rational risk-benefit assessment. Based on our prior reports 9,10 and the present one, we conclude that lentiviral vectors are very promising drugs for the treatment of ␤-thalassemia intermedia and ␤-thalassemia major.…”

“…Using the TNS9 vector, we previously demonstrated efficient gene transfer in bone marrow hematopoietic stem cells, tissue-specific transgene expression, and long-term correction in a mouse model of ␤-thalassemia intermedia. 9,10 In order to fully evaluate the therapeutic potential of TNS9 and its potential clinical applicability to the most severe hemoglobinopathies, it is essential to investigate its efficacy in the context of a fatal anemia. Here we address this requirement by establishing a novel mouse model for the most severe form of ␤-thalassemia, Cooley anemia.…”

“…9 In mice with ␤-thalassemia intermedia, the TNS9 lentiviral vector durably ameliorated anemia. 9,10 A similar vector encoding a variant globin gene reduced sickle cell formation in 2 murine models of sickle cell disease (SCD). 11 Obtained in hitherto available models of severe hemoglobinopathies, these encouraging findings do not address whether stem cell-based gene therapy is potentially curative for a deficiency as profound as that found in Cooley anemia.…”

Lentiviral vectors: optimization of packaging, transduction and gene expression

“…This region, which is 20 kbp long, has been reduced to shorter forms of a few hundred base pairs long that still confer the silencing modulation activity [98,99]. The insertion of the β-LCR sequence within HIV-1 LV vectors has been useful for increasing erythroidspecific synthesis of the β-globin protein in transgenic mice [84,100,101]. In heterotypic expression situations, the insertion into the 3 -LTR of a SIN HIV-1 vector of another erythroid-specific LCR, e.g.…”