Gene Therapy for Severe Haemoglobin Disorders


Sickle cell disease (SCD) and β‐thalassaemia result from inherited mutations that cause structural abnormality or deficient synthesis of adult haemoglobin. Palliative therapies improve the quality/duration of life for many, but side effects result from long‐term use. Bone marrow transplantation can be curative, but is limited to individuals with a matched donor. Thus, gene delivery into the patient's haematopoietic stem cells is a desirable therapy. Lentiviral vectors encoding for erythroid‐specific expression of either γ‐ or β‐globin genes have been developed for this purpose. These vectors have been used to cure SCD and β‐thalassaemia in mouse models with positive results emerging from clinical trials. Concurrently, innovative strategies intending to reactivate endogenous γ‐globin expression or correct β‐globin mutations at the genome level are showing promise for the future. Ultimately, clinical utility of all these approaches depend on safety and efficacy so that a cure can be consistently achieved.

Key Concepts:

  • Sickle cell disease (SCD) and β‐thalassaemia are the most common single gene disorders, and a worldwide health concern.

  • The switch from foetal to adult haemoglobin production after birth marks the onset of disease.

  • Haematopoietic stem cell transplant is curative, but available to only a limited number of patients making gene therapy a highly desirable alternative.

  • Lentiviral vectors made possible the delivery of complex, erythroid‐specific globin expression cassettes into haematopoietic stem cells.

  • Mouse models of SCD and β‐thalassaemia have been cured with lentiviral vectors encoding for high‐level, erythroid specific expression of γ‐ and β‐globin genes.

  • The first adult β‐thalassaemia major patient treated with a β‐globin lentiviral vector remains transfusion‐independent and in good health 6 years after therapy.

Keywords: sickle cell disease; β‐thalassaemia; bone marrow transplant; haematopoietic stem cells; β‐globin; γ‐globin; retrovirus; lentivirus; gene therapy

Figure 1.

Genomic structural organisation of the human α‐globin and β‐globin loci and developmental expression patterns of the various types of haemoglobin. Diagram of the α‐globin locus on chromosome 16 and the β‐globin locus on chromosome 11 and the types of haemoglobin tetramers produced during the indicated stages of human development with respect to the timeline. HbA, adult haemoglobin; HbE, embryonic haemoglobin; HbF, foetal haemoglobin; LCR, locus control region. Reproduced with permission from Wilber et al. (). © American Society of Hematology.

Figure 2.

General structure of a retroviral genome and recombinant vector systems. (a) Graphical representation of a typical MLV pro‐viral genome. Indicated are the 5′ and 3′ LTR sequences, regions for U3, R and U5 and coding regions for gag, pol and envelope (env) proteins. (b) Diagram of vectors encoding for expression of the essential viral proteins (packaging vectors, top two) or recombinant vector genome (transfer vector, bottom) that can be used to make a recombinant retrovirus. The sequences for Gag/Pol and Env are placed on separate vectors to reduce recombination and creation of infectious retrovirus that can replicate in the target cell. This strategy removes most of the coding information from the viral genome to incorporate the therapeutic gene (Transgene). ψ, packaging signal; pA, polyA signal; PBS, primer binding site; PPT, polypurine tract; SA, splice acceptor; SD, splice donor.

Figure 3.

General structure of a HIV genome and recombinant vector systems used to produce lentivirus particles. (a) Graphical representation of a typical HIV pro‐viral genome. Indicated are the 5′ and 3′ LTR sequences, coding regions for gag, pol and envelope (env) proteins and additional accessory proteins Tat, Rev, Nef, Vif, Vpu and Vpr. The tat protein enhances viral gene transcription, the rev protein facilitates nuclear to cytoplasmic transport of viral mRNA and the nef, vif, vpu and vpr proteins are virulence factors. (b) Diagram of a SIN vector genome for an integrated version of the provirus (transfer vector, top). This SIN vector lacks the enhancer sequences in the 3′‐LTR that are duplicated on integration and requires an internal promoter to regulate transcription of the therapeutic gene (Transgene). Also shown are three independent vectors used to express a fusion of gag/pol, rev or env (packaging vectors, bottom three). (c) Recombinant lentivirus particles are produced by transient transfection of human embryonic kidney (HEK‐293 T) cells with a transfer vector and three packaging plasmids. The following day medium is refreshed and cells cultured for an additional 24 h before medium is collected, cleared of debris and filter sterilised. This product can be concentrated to increase particle numbers per mL and applied to cultured cells to determine infectious titre and sterility. ψ, packaging signal; RRE, rev response element; pA, polyA signal; RRE, rev response element.

Figure 4.

Globin lentiviral vectors used to correct murine and human models of β‐thalassaemia and sickle cell disease. Schematics of the integrated provirus genome for lentiviral vectors used by different groups. All vectors are SIN. Highlighted are the constellation of the DNase I HS2, HS3 and HS4 for each LCR and β‐globin promoter (βPr, black box) sequences that are critical for high‐level, erythroid‐specific expression; the genomic globin sequences (orange or green); 3′ UTR sequences (γ: turquoise, β: pink); 3′ enhancer (3′e: purple box) and insulator elements (white boxes). Therapeutic globin sequences are in reverse orientation and include β‐globin (orange arrows) or γ‐globin (green arrows) with amino acid mutations indicated. The length (in base pairs) of each HS, β‐globin promoter and insulator element is indicated.



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Villamizar, Olga, Chambers, Christopher B, and Wilber, Andrew(Oct 2014) Gene Therapy for Severe Haemoglobin Disorders. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0025829]