The role of heterocellular hereditary persistence of fetal haemoglobin in beta(0)-thalassaemia intermedia

Gene Therapy for Hemoglobinopathies

Gene therapy for β-thalassemia and sickle-cell disease is based on transplantation of genetically corrected, autologous hematopoietic stem cells. Preclinical and clinical studies have shown the safety and efficacy of this therapeutic approach, currently based on lentiviral vectors to transfer a β-globin gene under the transcriptional control of regulatory elements of the β-globin locus. Nevertheless, a number of factors are still limiting its efficacy, such as limited stem-cell dose and quality, suboptimal gene transfer efficiency and gene expression levels, and toxicity of myeloablative regimens. In addition, the cost and complexity of the current vector and cell manufacturing clearly limits its application to patients living in less favored countries, where hemoglobinopathies may reach endemic proportions. Gene-editing technology may provide a therapeutic alternative overcoming some of these limitations, though proving its safety and efficacy will most likely require extensive clinical investigation.

A modified sandwich ELISA for accurate measurement of HbF in α-thalassemia carriers containing Hb Bart's and Hb Portland 1

Hemoglobin F (HbF) in blood lysate can be accurately measured by various methods, including immunoassay. In this study, we have produced polyclonal antibody (pAb) against HbF and established a modified sandwich-type ELISA for HbF quantification in blood lysates. The modified sandwich ELISA utilized anti-γ-globin monoclonal antibody clones Thal N/B as the capture antibody (Ab) coated on solid-phase, fluorescein isothiocyanate (FITC)-labeled pAb as the detecting Ab, and HPR-labeled anti-FITC Ab as the signal-generating Ab. By using an optimized blood lysate dilution, the HbF could be measured with no interference from hemoglobin Bart's (Hb Bart's) and hemoglobin Portland (Hb Portland 1) presented in α-thalassemia carriers. HbF levels measured by the modified sandwich ELISA were comparable to those quantified by the standard cation-exchange high performance liquid chromatography. We suggested that this modified sandwich ELISA was able to accurately measure HbF levels even in α-thalassemia carriers containing Hb Bart's and Hb Portland 1 and be an alternative method for HbF measurement.

Gene Therapy Approaches to Hemoglobinopathies

Gene therapy for hemoglobinopathies is currently based on transplantation of autologous hematopoietic stem cells genetically modified with a lentiviral vector expressing a globin gene under the control of globin transcriptional regulatory elements. Preclinical and early clinical studies showed the safety and potential efficacy of this therapeutic approach as well as the hurdles still limiting its general application. In addition, for both beta-thalassemia and sickle cell disease, an altered bone marrow microenvironment reduces the efficiency of stem cell harvesting as well as engraftment. These hurdles need be addressed for gene therapy for hemoglobinopathies to become a clinical reality.

The expanding spectrum of thalassemia intermedia

The hemoglobin disorders serve as a model for study of the genetic heterogeneity underlying the phenotype of genetic disorders. 'Thalassemia intermedia' is a clinical phenotype which displays marked genotypic variability in different populations or ethnic groups. Two common underlying mechanisms include co-inheritance of alpha globin gene deletions in homozygous thalassemia intermedia and presence of XmnI polymorphism. The newly described mechanisms including unstable hemoglobin disorders and somatic deletions in beta-globin gene are elaborated in the present review.

Variation and heritability of Hb F and F-cells among beta-thalassemia heterozygotes in Hong Kong

Enhanced fetal hemoglobin (Hb F) production can partially compensate for the lack of adult hemoglobin (Hb A) in patients with beta-thalassemia major or intermedia, and ameliorate the clinical severity of these diseases. To further elucidate factors governing Hb F levels, we evaluated demographic, clinical, laboratory, and genetic characteristics in 241 unrelated adult beta-thalassemia carriers in Hong Kong. They had wide variations in Hb F and F-cell numbers skewing toward higher levels. Individuals who coinherited the Xmn IT-allele in the (G)gamma-globin gene promoter had higher Hb F and more F-cells compared with those lacking the Xmn I T-allele. However, both groups exhibited a similarly wide spread of Hb F and F-cells. The correlation of Hb F and F-cells corresponded well to both linear and exponential models, suggesting multiple mechanisms for Hb F augmentation. The heritabilities of Hb F and F-cells were calculated in 66 families (111 parents who were beta-thalassemia carriers and 82 asymptomatic offspring) to be 0.7 to 0.9. The Xmn I polymorphism accounted for 9% of the Hb F and 13% of the F-cell heritabilities. These results suggest that these family members are well suited for genome wide association studies that will identify genetic loci regulating Hb F production, and likely novel pharmacological targets for reactivating Hb F production in adults.

Pathophysiology of beta thalassemia--a guide to molecular therapies

The central mechanism underlying the pathophysiology of the beta thalassemias can be related to the deleterious effects of imbalanced globin chain synthesis on erythroid maturation and survival. An imbalance of the alpha/non-alpha globin chains leads to an excess of unmatched alpha globin which precipitates out, damaging membrane structures leading to accelerated apoptosis and premature destruction of the erythroid precursors in the bone marrow (ineffective erythropoiesis). Close observation of the genotype/phenotype relationships confirms the pathophysiological mechanism and provides clues to molecular therapies, all of which aim to reduce the alpha/non-alpha chain imbalance. They include inheritance of the milder forms of beta thalassemia, co-inheritance of alpha thalassemia, or genetic factors (quantitative trait loci, QTLs) for increasing gamma globin expression. Currently, the most promising molecular therapeutic approaches include increasing beta globin gene expression by stem cell gene therapy and increasing gamma globin expression using pharmacological agents or by transduction of the gamma globin genes.