Letters to Nature: “Therapeutic haemoglobin syntheseis in B-thalassaemic mice expressing lentivirus-encoded human B-globin”

β-globin could treat β-thalassaemia SCD. The stable introduction of a functional β-globin gene in haematopoietic stem cells could be a powerful approach to treat β-thalassaemia and sickle-cell disease. Genetic approaches aiming to increase normal β-globin expression in the progeny of autologous hematopoietic stem cells might circumvent the limitations and risks of allogeneic cell transplants. However, low-level expression, position effects and transcriptional silencing hampered the effectiveness of viral transduction of the human β-globin gene when it was linked to minimal regulatory sequences. Here we show that the use of recombinant lentiviruses enables efficient transfer and faithful integration of the human β-globin gene together with large segments of its locus control region. In long-term recipients of unselected transduced bone marrow cells, tetramers of two murine α-globin and two human βA-globin molecules account for up to 13% of total hemoglobin in mature red cells of normal mice. In β-thalassaemic heterozygous mice higher percentages are obtained (17% to 24%), which are sufficient to ameliorate anemia and red cell morphology. Such levels should be of therapeutic benefit in patients with severe defects in hemoglobin production.
Onco-retroviral-mediated transfer in mouse hematopoietic stem cells (HSCs) permits erythroid-specific expression of the human 13-globin gene, but the expression is low and limited by chromosomal position effects The same outcome prevails in transgenic mice unless genomic elements encompassing DNase I hypersensitive sites (HS) located 60 kilobases (kb) upstream of the human 13-globin gene, referred to as the locus control region (LCR), are linked to the globin gene Incorporation of small elements spanning DNase HS2, HS3 and HS4 into viral vectors increases 13-globin expression in mouse erythroleukaemia (MEL) cells However, low-level expression, strong position effects and transcriptional inactivation are still observed in bone marrow chimaeras Studies in transgenic mice12 and deletional analyses13 support the view that coordinated interaction of several genetic elements including the LCR is required for physiologic 13-globin gene expression.

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