Technique for genetically modifying blood stem cells brings cure for blood disea...( The condition of mice with a genetic bl...)

The condition of mice with a genetic blood disease called beta-thalassemia improved significantly following treatment of their blood forming cells with a gene that enabled them to produce the type of hemoglobin normally found only in the fetus. These findings, by investigators at St. Jude Children's Research Hospital, are published in the October issue of Blood.

Beta-thalassemia is a genetic blood disease in which the red blood cells have an abnormal form of the oxygen-carrying molecule called hemoglobin (Hb). Normal Hb is made up of two alpha-globin proteins and two beta-globin proteins. The defective red blood cells in beta-thalassemia arise from hematopoietic stem cells (HSCs) in which both genes for beta-globin are either missing or mutated. In the absence of beta-globin, the other building block of Hb, alpha-globin, accumulates and eventually destroys the red blood cell. HSCs are parent cells in the bone marrow that give rise to blood cells.

The St. Jude team successfully treated beta-thalassemia in mice by using a newly developed vector--or biological ferry composed of DNA housed within a harmless virus--to shuttle a therapeutic gene into the defective HSCs. The gene allowed red cells that were derived from the HSCs to make gamma-globin, a protein that acted as a substitute for beta-globin. The resulting Hb molecule, composed of alpha- and gamma-globin, is called fetal Hb (HbF) because it normally occurs only during the fetal stage of development. The use of HbF prevents the need to introduce normal beta-globin into the body in someone who has never had it before. It is possible that the sudden introduction of beta-globin could trigger an immune response against this protein.

The vector, which used a virus called lentivirus to carry the gamma-globin gene, also carried a special set of additional pieces of DNA called regulatory elements. These elements were part of a section of the normal chromosome containing t
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Contact: Bonnie Cameron
bonnie.cameron@stjude.org
901-495-4815
St. Jude Children's Research Hospital
12-Oct-2004

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