Evaluation of optimal expression cassette in retrovirus vector for beta-thalassemia gene therapy

Combining gene therapy and fetal hemoglobin induction for treatment of β-thalassemia

β-thalassemias are caused by nearly 300 mutations of the β-globin gene, leading to a low or absent production of adult hemoglobin (HbA). Two major therapeutic approaches have recently been proposed: gene therapy and induction of fetal hemoglobin (HbF) with the objective of achieving clinically relevant levels of Hbs. The objective of this article is to describe the development of therapeutic strategies based on a combination of gene therapy and induction of HbFs. An increase of β-globin gene expression in β-thalassemia cells can be achieved by gene therapy, although de novo production of clinically relevant levels of adult Hb may be difficult to obtain. On the other hand, an increased production of HbF is beneficial in β-thalassemia. The combination of gene therapy and HbF induction appears to be a pertinent strategy to achieve clinically relevant results.

Alternative options for DNA-based experimental therapy of β-thalassemia

INTRODUCTION

Beta-thalassemias are caused by more than 200 mutations of the β-globin gene, leading to low or absent production of adult hemoglobin. Achievements have been made with innovative therapeutic strategies for β-thalassemias, based on research conducted at the levels of gene structure, transcription, mRNA processing and protein synthesis.

AREAS COVERED

The objective of this review is to describe the development of therapeutic strategies employing viral and non-viral DNA-based approaches for treatment of β-thalassemia.

EXPERT OPINION

Modification of β-globin gene expression in β-thalassemia cells has been achieved by gene therapy, correction of the mutated β-globin gene and RNA repair. In addition, cellular therapy has been proposed for β-thalassemia, including reprogramming of somatic cells to generate induced pluripotent stem cells to be genetically corrected. Based on the concept that increased production of fetal hemoglobin (HbF) is beneficial in β-thalassemia, DNA-based approaches to increase HbF production have been optimized, including treatment of target cells with lentiviral vectors carrying γ-globin genes. Finally, DNA-based targeting of α-globin gene expression has been applied to reduce the excess of α-globin production by β-thalassemia cells, one of the major causes of the clinical phenotype.

In vitro and in vivo expression of human erythrocyte pyruvate kinase in erythroid cells: a gene therapy approach

Human pyruvate kinase deficiency (PKD), an autosomal recessive disorder produced by mutations in the PKLR gene, is the most common cause of chronic nonspherocytic hemolytic anemia. Transduction of wild-type erythroid (R-type) pyruvate kinase (RPK) cDNA into deficient hematopoietic stem cells could be of potential use as rescue therapy in severe clinical cases. In this study, gammaretroviral vectors expressing human RPK were designed as possible gene therapy candidates for this disease. Through real-time quantitative reverse transcriptase-polymerase chain reaction, Western blotting, and flow cytometric analysis, we demonstrate stable RPK expression in both undifferentiated and differentiated murine erythroleukemia cells. In this in vitro assay, the proportion of transduced cells and the intensity of expression of the transgene remained unaltered after 6 months of culture. Moreover, transplanting human RPK-transduced Lin(-)Sca-1(+) mouse cells in myeloablated primary and secondary recipients rendered high proportions of erythroid precursors and mature erythrocytes expressing RPK, without inducing hematopoietic effects. These findings suggest that retroviral vectors could be useful for the delivery and expression of RPK in erythroid cells, and provide evidence of the potential use of gene therapy strategies to phenotypically correct erythroid PKD.

Knockdown of mouse adult beta-globin gene expression in MEL cells by retrovirus vector-mediated RNA interference

RNA interference (RNAi) efficiently induces sequence-specific gene silencing in mammalian cells through short interfering RNA (siRNA) of 21-23 nucleotides synthesized in vitro or expressed by DNA-based vector. However, introduction of siRNA into mammalian cells by transfection limits the application of RNAi, especially when it is necessary to generate long-term gene silencing in vivo. Virus vector-mediated RNAi provides an alternative to transfection. In the present study, we investigated such transduction system and showed that retrovirus vector-mediated RNAi can substantially down-regulate expression of mouse adult beta-globin gene in MEL cells. The results suggest that retrovirus vector-delivered RNAi may find its use in functional genomics and in gene therapy.