Functional requirements for phenotypic correction of murine beta-thalassemia: implications for human gene therapy.

Abstract

As initial human gene therapy trials for beta-thalassemia are contemplated, 2 critical questions important to trial design and planning have emerged. First, what proportion of genetically corrected hematopoietic stem cells (HSCs) will be needed to achieve a therapeutic benefit? Second, what level of expression of a transferred globin gene will be required to improve beta-thalassemic erythropoiesis? These questions were directly addressed by means of a murine model of severe beta-thalassemia. Generation of beta-thalassemic mice chimeric for a minority proportion of genetically normal HSCs demonstrated that normal HSC chimerism levels as low as 10% to 20% resulted in significant increases in hemoglobin (Hb) level and diminished extramedullary erythropoiesis. A large majority of the peripheral red cells in these mice were derived from the small minority of normal HSCs. In a separate set of independent experiments, beta-thalassemic mice were bred with transgenic mice that expressed different levels of human globins. Human gamma-globin messenger RNA (mRNA) expression at 7% of the level of total endogenous alpha-globin mRNA in thalassemic erythroid cells resulted in improved red cell morphology, a greater than 2-g/dL increase in Hb, and diminished reticulocytosis and extramedullary erythropoiesis. Furthermore, gamma-globin mRNA expression at 13% resulted in a 3-g/dL increase in Hb and nearly complete correction of red cell morphology and other indices of inefficient erythropoiesis. These data indicate that a significant therapeutic benefit could be achieved with expression of a transferred globin gene at about 15% of the level of total alpha-globin mRNA in patients with severe beta-thalassemia in whom 20% of erythroid precursors express the vector genome.

• Authors: D A Persons, E R Allay, D E Sabatino, P Kelly, D M Bodine, A W Nienhuis
• Journal: Blood (Blood) Vol. 97 Issue 10 Pg. 3275-82 (May 15 2001) ISSN: 0006-4971 [Print] United States
• PMID: 11342459 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• Hemoglobins
• RNA, Messenger
• Globins

Topics

• Animals
• Disease Models, Animal
• Erythrocytes (metabolism, pathology)
• Erythropoiesis
• Gene Expression
• Genetic Therapy
• Globins (genetics)
• Hematopoiesis, Extramedullary
• Hematopoietic Stem Cells (metabolism)
• Hemoglobins (analysis)
• Humans
• Mice
• Mice, Inbred C57BL
• Mice, Transgenic
• Phenotype
• RNA, Messenger (analysis)
• Reticulocyte Count
• beta-Thalassemia (blood, genetics, therapy)