Patent Publication Number: US-11046956-B2

Title: Method of treatment

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of application Ser. No. 13/996,984, filed Oct. 7, 2013, now issued as U.S. Pat. No. 10,301,620, which is the National Stage of International Application No. PCT/AU2011/001653, filed Dec. 20, 2011, and claims priority from Australian Provisional Patent Application No. 2010905599, filed on Dec. 22, 2010, entitled “A method of treatment”, each of which applications are incorporated herein by reference in their entireties. 
    
    
     STATEMENT REGARDING SEQUENCE LISTING 
     The Sequence Listing associated with this application is provided in text format in lieu of a paper copy, and is hereby incorporated by reference into the specification. The name of the text file containing the Sequence Listing is HRGA-002/01US_ST25.txt. The text file is about 278 KB, was created on Jun. 17, 2019, and is being submitted electronically via EFS-Web. 
     FIELD 
     The present disclosure teaches the treatment of a blood pathology, such as a blood pathology associated with impaired hemoglobin synthesis including the treatment of (3-thalassemia or a related hemoglobinopathy. 
     BACKGROUND 
     Bibliographic details of the publications referred to by author in this specification are collected alphabetically at the end of the description. 
     Reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in any country. 
     Thalassemia is an inherited autosomal recessive blood disorder caused by the faulty synthesis of hemoglobin. This arises by one or more genetic defects affecting synthesis of the α- or β-globin chains which make up hemoglobin. 
     The World Health Organization (WHO) has conservatively estimated that approximately 7 percent of the world&#39;s population are carriers of various types of hemoglobinopathies, with an estimated 300,000 severely affected patients born worldwide each year. Although thalassemia is most common in Mediterranean, Middle Eastern, African and Asian populations (Olivieri (1999)  N Engl J Med  341:99-109; Thein (2005)  Hematology: 31-37), the ever rising rates of population migration mean this condition is encountered with increasing frequency in many parts of the world, including Northern Europe, North America and Australia. Thalassemia is fatal if left untreated and patients are dependent on a regular blood transfusion every 3-4 weeks for the rest of their lives. 
     There are over 200 β-globin gene mutations (Olivieri (1999) supra) which impair β-globin synthesis, resulting in imbalanced globin chain synthesis and β-thalassemia. In these situations, the excess, unbound α-globin chains precipitate in erythroid progenitor cells resulting in premature cell death, ineffective erythropoiesis and severe anemia. The key role of globin imbalance in contributing to thalassemia severity is most clearly illustrated in individuals who inherit an abnormal number of functional α-globin genes along with β-globin mutations. Individuals who co-inherit α-thalassemia with homozygous β-thalassemia have an improved phenotype and suffer less severe anemia than if either set of mutations was inherited alone (Camaschella et al. (1995)  Am J Hematol  48:82-87; Cao et al (1991)  Am J Pediatr Hematol Oncol.  13:179-188; Kanavakis et al. (2004)  Blood Cells Mol Dis  32:319-324; Schrier (2002)  Curr Opin Hematol  9:123-126; Thein (2005)  Haematologica  90:649-660). The degree of correction is closely related to the degree to which globin chain balance has been restored (Thein et al (1984)  Br J Haematol.  56:333-337). One mutated copy of α-globin generally has minimal impact but two or three mutated α-globin genes can improve β-thalassemic phenotypes significantly (Camaschella et al. (1995) supra; Cao et al. (1991) supra; Kanavakis et al. (2004) supra; Schrier (2002) supra; Thein (2005) supra). Therefore, alterations in α-globin chain synthesis can have considerable effects on β-thalassemic phenotypes and can even confer transfusion independence. Given that excess production of α-globin leads to widespread detrimental effects in β-thalassemia, reduction of α-globin synthesis would likely improve the β-thalassemic phenotype, raising the possibility of reducing α-globin expression as a therapy for β-thalassemia. The difficulty, however, is to specifically target α-globin gene expression. 
     Expression and synthesis of the α-globin and β-globin chains of hemoglobin is balanced during normal erythropoiesis and any disruptions in the α:β-globin synthesis ratios results in thalassemia (Olivieri (1999) supra; Thein (2005) supra). β-Thalassemia arises when α-globin is synthesized at levels exceeding the binding capacity of available β-globin chains, usually due to mutations affecting the β-globin locus which reduce β-globin expression (Schrier (1994)  Annu Rev Med  45:211-218). Conversely, α-thalassemia occurs due to mutations which result in decreased α-globin expression, leading to an excess of β-globin chains (Schrier (1994) supra). Reduced expression of either of the globin chains leads to decreased formation of functional hemoglobin tetramers, yet this plays a relatively minor role in contributing to the severely anemic phenotype characteristic of the thalassemias. Instead, it is the damage caused at the cellular level by excess, improperly paired globin chains, which leads to premature cell death and accounts for the majority of the pathology (Schrier (1994) supra). Excess α-globin results in the formulation of large, insoluble aggregates which can be visualized by light microscopy in an estimated one third of β-thalassemic red blood cells (RBCs) [Fessas (1963)  Blood  21:21-32], and occurs even in the earliest erythroid precursor cells (Schrier (1994) supra). These α-globin aggregates cause mechanical damage to membrane structures and trigger premature apoptosis in erythroid progenitor cells, leading to ineffective erythropoiesis (Thein (2005) supra; Kanavakis et al. (2004) supra). Furthermore, the excess α-globin is heavily oxidized (Advani et al. (1992)  Blood  79:1064-1067) and each globin chain also carries a heme bound iron which can induce generation of reactive oxygen species (ROS) [Schrier et al. (2003)  Redox Rep.  8:241-245]. It is believed that the increased ROS oxidizes adjacent membrane proteins, leading to severe membrane abnormalities and unstable cell membranes and this results ultimately in hemolysis and ungreatly exacerbating the anemic phenotype in β-thalassemia (Advani et al. (1992) supra). 
     RNAi is a highly conserved, naturally occurring mechanism of gene suppression found in plant, yeast and mammalian cells, which can be mediated by naturally occurring or synthetic short interfering RNAs (siRNA) [Hannon (2002)  Nature  418:244-251]. In mammalian cells, RNAi can be induced using dsRNA of 19-21 bp with characteristic two nucleotide 3′ overhangs and 5′ phosphate groups. These are incorporated into an RNA induced silencing complex (RISC) and used as a template for cleavage of endogenous mRNA. Since targeting is dependent mainly on Watson-Crick base-pairing, it is theoretically possible to utilize this pathway to reduce expression of any gene in a sequence-specific manner. 
     Sarakul et al. (2008)  Biochemical and Biosphysical Research Communication  369:935-938 disclosed the use of siRNA at a specific region of Exon2 of the α-globin gene locus. However, other target sites within the gene were ineffective in reducing expression. Chinese Patent Application No. 100567490 (CN 100567490) also used siRNA to target specific sites with variable effectiveness. These sites were defined as α2 and α3 (referred to herein as “CNα2” and “CNα3”, respectively). CNα3 targets codons 127 to 133 which is SEQ ID NO:3 in Sarakul et al. (2008) supra. The latter authors stated that only one sequence (SEQ ID NO:1, targeting codons 41 to 47 in Exon2) had any effect. Hence, there is clearly inconsistency between the data by Sarakul et al. (2008) supra and CN100567490. This highlights the difficulty in designing effective siRNA molecules. The present disclosure included siRNA encoding SEQ ID NO: 1, (targeting codons 41 to 47 in Exon2) as a control (referred to as Hs-siα5) and found that this siRNA was the least effective in reducing alpha-globin expression compared to all other siRNA tested. Also demonstrating that siRNA targeting other regions not anticipated by Sarakul et al. (2008) supra and CN100567490 are potentially more effective in reducing α-globin. 
     In order to assess the feasibility of RNAi-mediated therapy, a mouse model has been developed. The most well characterized is the heterozygous β-globin knockout (β-KO) model (Yang et al. (1995)  Proc Natl Acad Sci USA  92:11608-11612), which displays distinct hematological abnormalities consistent with β-thalassemia (wide variations of red cell distribution width (RDWs), significant reductions in hemoglobin (Hb) and hematocrit (HCT) levels) [Yang et al. (1995) supra; Beauchemin et al. (2004)  J Biol chem.  279:19471-19480; Vadolas et al. (2005)  Biochim Biophys Acta  1728:150-162). In order to assess the effects of reduced α-globin expression in β-thalassemic mice, heterozygous α-globin knockout mice (α-KO) were crossed with thalassemic β-KO mice (Beauchemin et al. (2004) supra; Al-Hasani et al. (2004)  Transgenic Res  13:235-243; Paszty et al. (1995)  Nat Genet  11:33-39). The resultant double heterozygous (DH) α-KO/β-KO progeny expressed reduced, but balanced, levels of both α-globin and β-globin and displayed a normal range of RDWs with Hb and HCT almost completely restored to wild type (WT) levels. Furthermore, the reduced drive for extramedullary erythropoiesis combined with reduced clearance of damaged RBC, resulted in a marked reduction in spleen size indistinguishable from those found in WT mice. 
     Whilst intuitively there are benefits of reducing α-globin expression in the context of β-thalassemia, there have been no reported substantial reductions of α-globin using methods which are conducive to therapy in humans. An siRNA approach was investigated to mediate reductions in α-globin expression in mice. One highly effective siRNA sequence (siα4), located in the 3′ untranslated region, was demonstrated to reduce α-globin expression in hemoglobinized murine erythroleukemic (MEL) cells by approximately 65% at both the RNA and the protein levels (Voon et al. (2008)  Haematologica  93:1238-1242). The efficacy of siα4 was further confirmed by testing this sequence in primary cultures of erythropoietic progenitor cells 
     There is a need to use gene silencing technology to greater effect to treat β-thalassemia and related conditions arising from an excess amount of α-globin in humans. 
     SUMMARY 
     The present disclosure teaches a method for treating β-thalassemia or a related hemoglobinopathy associated with an excess of α-globin in humans. Related conditions include HbE disease and sickle cell disease (SCD). The method enabled herein targets the α-globin genetic locus to reduce its expression thereby reducing levels of the α-globin chain. Reference to the human α-globin genetic locus includes HBA1 (SEQ ID NO:41) and HBA2 (SEQ ID NO:573). This in turn corrects or at least improves or reduces the α:β-globin ratio imbalance which leads to an amelioration of the symptoms or underlying cause of β-thalassemia. In an embodiment, the agent is an RNA such as a single or double (duplex) short, interfering RNA (siRNA) oligonucleotide or a hairpin form thereof or a chemically modified or synthetic or mimetic form thereof which targets a mRNA species transcribed from the α-globin genetic locus at a site selected from the 5′ untranslated region (5′-UTR), Exon1, Exon3 and the 3′-UTR or a boundary region between. The oligonucleotide may be synthetically derived or produced by expression of a DNA sequence in an expression vector such as a Lentiviral vector. Generally, down-regulation of the α-globin genetic locus is mediated via RNAi. In an embodiment, the ratios of α-globin and β-globin are improved to near normal levels. In an embodiment, the RNAi approach is used in conjunction with gene therapy to restore normal or near normal β-globin levels. 
     The present specification is instructional on a gene silencing approach to reduce expression of the α-globin genetic locus to non-zero expression levels which means expression of the α-globin genetic locus or levels of α-globin protein is from about 30% to 95% of the levels in a cell from a non-β-thalassemic subject (“normal control”). Examples of RNA molecules are those which target or comprise a nucleotide sequence of α-globin mRNA selected from SEQ ID NOs:25 and 26 (sense and anti-sense Hs-siα1), 27 and 28 (sense and antisense Hs-siα2), 29 and 30 (sense and antisense Hs-siα3), 31 and 32 (sense and antisense Hs-siα4). However, any site within the 5′-UTR, Exon1, Exon3 or the 3′-UTR or boundary regions inbetween and which results in a reduction in α-globin levels may be targeted. 
     Examples of mimetics include peptide-oligonucleotide chimeras referred to as a peptide oligonucleotide. Examples of other modified forms include branched oligonucleotides hairpin oligonucleotides and synthetic oligonucleotide comprising chemically modified bases or bonds between bases. Hairpin RNA species are particularly useful in the practice of the present method. 
     In an embodiment, the agent is an siRNA oligonucleotide comprising a molecule of from about 15 to about 50 bp in length of HBA1 and/or HBA2 mRNA. Exemplary oligonucleotides target a region on α-globin mRNA selected from SEQ ID NO:42 to SEQ ID NO:572 and SEQ ID NO:574 to SEQ ID NO:1179. Whilst the 15mer oligonucleotides are exemplary target sequences, the present disclosure teaches oligonucleotides from 15 to 50 nucleotides in length which target or comprise a sequence comprising a sequence set forth in one of the 15mers. Particular examples of targets include SEQ ID NO:25, 26, 27, 28, 29, 30, 31 and 32. The RNAi-mediated silencing may also employ RNA species comprising a nucleotide sequence selected from SEQ ID NO:25, 26, 27, 27, 28, 29, 30, 31 and 32. 
     The method contemplated herein does not extend to the specific target site Hs-siα5 disclosed by Sarakul et al (2008) supra and CN 100567490 and sites α2 and α3 also disclosed by the Chinese patent application. The Hs-siα5 is used herein as a control. 
     Enabled herein is a method for treating a human subject with β-thalassemia or a related hemoglobinopathy, the method comprising administering to the subject an amount of an agent effective to reduce expression of the α-globin genetic locus thereby reducing levels of α-globin and ameliorating the effects of an α- and β-globin chain imbalance. Reducing expression of the α-globin genetic sequence includes targeting α-globin mRNA. The method may be practices alone or in combination within gene therapy to introduce a functional β-globin-encoding nucleic acid molecule. 
     Further taught herein is the use of an agent which reduces expression of the α-globin genetic locus in the manufacture of a medicament in the treatment of β-thalassemia or a related hemoglobinopathy in a subject. 
     The present disclosure provides a method for treating a human subject with β-thalassemia or a related hemoglobinopathy, the method comprising administering to the subject an effective amount of a RNA which targets an mRNA species encoding α-globin at a site selected from the 5′-UTR, Exon1, Exon3 and 3′-UTR or a boundary region inbetween to thereby reduce the amount of α-globin produced to non-zero levels and ameliorate the effects of an α- and β-globin chain imbalance. 
     The agents may be oligonucleotides such as an RNA species or may be a cellular or viral vector capable of producing a DNA-derived or RNA-derived RNA species. 
     In an embodiment, an agent is provided comprising a RNA which targets an mRNA species encoding α-globin at a site selected from the 5′-UTR, Exon1, Exon3 and the 3′-UTR and a boundary region inbetween to reduce the amount of α-globin produced for use in ameliorating the symptoms of β-thalassemia or a related hemoglobinopathy in a subject. 
     In an embodiment, the RNA is an siRNA or a chemically modified or mimetic thereof. This includes a hairpin RNA species. Examples of RNA molecules comprise or target a sequence selected from SEQ ID NO:25, 26, 27, 28, 29, 30, 31 and 32. Other examples, are agents which target SEQ ID NO:42 to 572 or SEQ ID NO: 574 to 1179 with the exception of CNα2, CNα3 and Hs-siα5. 
     Systems for the treatment of β-thalassemia or a related hemoglobinopathy arising from an imbalance of α-globin and β-globin chains are also contemplated herein. One such system taught herein the use of a combination of β-globin gene therapy and RNAi-mediated reduction in α-globin. In an example of this system, a Lentiviral (LV) vector is used to deliver a β-globin-encoding nucleic acid molecule and RNAi sequences to specifically target α-globin mRNA at a site selected from its 5′-UTR, Exon1, Exon3 and 3′-UTR or a boundary region inbetween. The system aims to normalize α:β-globin ratios. Conveniently, the RNAi-encoding sequences are inserted in a 5′-UTR or 3′-UTR or intron in the β-globin-encoding sequence. 
     In an embodiment, the instant disclosure teaches a RNA which targets a mRNA species encoding α-globin at a site selected from the 5′-UTR, Exon1, Exon3 and the 3′-UTR and a boundary inbetween to reduce the amount of α-globin produced in the manufacture of a medicament in the treatment of β-thalassemia or a related hemoglobinopathy in a subject. 
     Another aspect enabled herein is directed to a vector comprising a nucleic acid molecule encoding human β-globin operably linked to a promoter and one or more second nucleic acid molecules inserted in the 5′-UTR and/or 3′-UTR region and/or an intron of the β-globin-encoding nucleic acid molecule which second nucleic acid molecule encodes an RNA which targets an mRNA species encoding α-globin at a site selected from the 5′ untranslated region (5′-UTR), Exon1, Exon3 and the 3′-UTR or a boundary region inbetween. In an embodiment, the vector provides therapeutic levels of β-globin while reducing α-globin levels. 
     A summary of sequence identifiers used throughout the subject specification is provided in Table 1. Abbreviations referred to herein are defined in Table 2. 
                     TABLE 1                  Summary of sequence identifiers                     SEQUENCE           ID NO:   DESCRIPTION                             1   si-α1 sense       2   si-α1 antisense       3   si-α2 sense       4   si-α2 antisense       5   si-α3 sense       6   si-α3 antisense       7   si-α4 sense       8   si-α4 antisense       9   pshα1 oligo       10   pshα1 oligo FWD       11   pshα1 oligo       12   pshα1 oligo REV       13   pshα2 oligo       14   pshα2 oligo FWD       15   pshα2 oligo       16   pshα2 oligo REV       17   pshα3 oligo       18   pshα3 oligo FWD       19   pshα3 oligo       20   pshα3 oligo REV       21   pshα4 oligo       22   pshα4 oligo FWD       23   pshα4 oligo       24   pshα4 oligo REV       25   Hs_si-α1 sense       26   Hs_si-α1 antisense       27   Hs_si-α2 sense       28   Hs_siα2 antisense       29   Hs_si-α3 sense       30   Hs_si-α3 antisense       31   Hs_si-α4 sense       32   Hs_si-α4-antisense       33   Hs_si-α5 sense       34   Hs_si-α5 antisense       35   Stealth si-α1 sense       36   Stealth si-α1 antisense       37   Stealth si-α2 sense       38   Stealth si-α2 antisense       39   Stealth si-α3 sense       40   Stealth si-α3 antisense       41   Nucleotide sequence of hemoglobin α1 (HBA1) mRNA       42 to 572   15mer sense oligonucleotides which represent targets           on HBA1 mRNA 1         573   Nucleotide seuqence of hemoglobin α1 (HBA2) mRNA       574-1179   15mer sense oligonucleotides which represent targets           on HBA2 mRNA 2         1180   Complement in sam edirection after T to U           conversion-HBA1       1181   Amino acid sequence of human αglobin-2                 1 Target sequences based on HBA1 (NM_000558.3).         2 Target sequences based on HBA2 (NM_000517.4).            
Insofar as the target is mRNA, T nucleotides are U nucleotides. Both RNA and DNA sequences are encompassed herein.
 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Abbreviations 
               
            
           
           
               
               
            
               
                 Abbreviation 
                 Definition 
               
               
                   
               
               
                 α-KO 
                 α-Globin knock-out genotype 
               
               
                 β-KO 
                 β-globin knock-out genotype 
               
               
                 CNα2 
                 Target site disclosed in Chinese Patent Application 
               
               
                   
                 No. 100567490 
               
               
                 CNα3 
                 Target site disclosed in Chinese Patent Application 
               
               
                   
                 No. 100567490 
               
               
                 DCFH 
                 2,7-Dichlorfluorescein 
               
               
                 DH 
                 Double heterozygous 
               
               
                 FBE 
                 Full blood examination 
               
               
                 FCS 
                 Fetal calf serum 
               
               
                 Hb 
                 Hemoglobin 
               
               
                 HBA 
                 Hemoglobin α-globin. Includes HBA1 and HBA2. 
               
               
                 HCT 
                 Hematocrit 
               
               
                 LTR 
                 Long term repeat 
               
               
                 LV 
                 Lentiviral vector 
               
               
                 LVβ 
                 Leniviral vector comprising nucleic acid encoding β-globin 
               
               
                 MEL cells 
                 Murine erythroleukemic cells 
               
               
                 Retic 
                 Reticulocyte 
               
               
                 RBC 
                 Red blood cell 
               
               
                 RDW 
                 Red cell distribution width 
               
               
                 RISC 
                 RNA induced silencing complex 
               
               
                 ROS 
                 Reactive oxygen species 
               
               
                 RRE 
                 Rev-responsive element 
               
               
                 SA 
                 Splicing acceptor 
               
               
                 SD 
                 Splicing donor 
               
               
                 SIN 
                 Self inactivating 
               
               
                 shRNA 
                 Short hairpin RNA 
               
               
                 siRNA 
                 Short, interfering RNA 
               
               
                 siα1, siα2 
                 siRNA&#39;s targeting the 5′ end region of the 
               
               
                   
                 human α-globin gene 
               
               
                 siα3, siα4 
                 siRNA&#39;s targeting the 3′ end region of the 
               
               
                   
                 human α-globin gene 
               
               
                 siα5 
                 siRNA targeting Exon2 of the human α-globin gene 
               
               
                 WT 
                 Wild-type 
               
               
                   
               
            
           
         
       
     
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a graphical representation showing the restoration of globin balance in primary erythropoietic cells from heterozygous β-KO mice. (A) Relative α:β-globin RNA ratios in cultured primary erythroid progenitor cells from (i) WT (wild type) and heterozygous β-KO (knock out) and (ii) heterozygous β-KO cells treated with 10 μg, 5 μg or 1 μg of siα4 or an siLuc (luciferase) irrelevant control. (B) Relative levels of ROS (reactive oxygen species) in cultured primary erythroid progenitor cells from (i) WT and heterozygous β-KO and (ii) heterozygous β-KO cells treated with 10 μg, 5 μg or 1 μg of siα4 or an siLuc irrelevant control. All values shown represent the mean average of at least three independent experiments±standard deviation. 
         FIG. 2A  is a schematic representation of dominant human α2-globin mRNA and siRNA binding sites. The human α2 and αl globin genes are identical through the coding regions and differ only slightly in the UTRs (untranslated regions) so all siRNA sequences except Hs-siα4 target both α-globin genes. Standard siRNAs designed using Qiagen algorithms are represented in blue and a published sequence, Hs-siα5, is represented in green. The modified, 25-mer Stealth sequences are represented in red. The equivalent human homologs of previously tested murine siRNA sequences have been indicated in grey.  FIG. 2B  and  FIG. 2C  provides a schematic representation of the nucleotide sequence of mRNA (coding and non-coding) of HBA1 (SEQ ID NO: 41) showing location of various human and murine target siRNAs. Patentα2 and Patentα3 refer to the sequences disclosed in CN 100567490. 
         FIG. 3  is a graphical representation showing relative α-globin mRNA expression in K562 cells 24 and 48 hours post electroporation with various siRNAs targeting human α-globin. Relative α-globin RNA expression levels were detected by real-time PCR 24 and 48 hours post electroporation with 1 μg of various siRNA sequences targeted to α-globin. Relative expression of α-globin was calculated by normalizing to expression levels in mock electroporated K562 cells using β-actin expression as an RNA loading control. An siRNA sequence targeting luciferase (siLuc) was included in all experiments as an irrelevant control. Values represent the mean average of at least three independent experiments±SD. 
         FIG. 4  is a graphical representation showing relative α-globin mRNA expression in K562 cells 24 and 48 hours post electroporation with various siRNAs targeting human α-globin. Relative α-globin RNA expression levels were detected by real-time PCR 24 and 48 hours post electroporation with 500 ng of various siRNA sequences targeted to α-globin. Relative expression of α-globin was calculated by normalizing to expression levels in mock electroporated K562 cells using β-actin expression as an RNA loading control. Values represent the mean average of at least three independent experiments±SD. 
         FIG. 5  is a diagrammatic representation of a lentiviral vector (LV) containing the human β0-globin gene under the control of the pol II β-globin promoter. Schematic representation of LV in its proviral form. LTR deleted of 400 bp in the HIV U3 region (LTR), rev-responsive element (RRE), splicing donor (SD) and splicing acceptor (SA) sites, human β-globin gene, β-globin promoter (p), and Dnase I-hypersensitive sites HS2 and HS3 and β-globin LCR are shown. shRNA1 and shRNA2 represent α-globin-specific shRNA insertion sites. 
         FIG. 6  is a diagrammatic representation of the LVβ vector. (A) LVβ vector encodes an adult β-globin (β A(T87Q) ) that forms functional Hb distinguishable from normal Hb by HPLC. The β-globin is placed under control of the human β-globin LCR, β-globin promoter (βp), and 3′ β-globin enhancer. Intron-II is artificial, containing a 375 bp deletion to remove an A/T rich region that has been shown to reduce viral titre. Safety modifications include 2 stop codons in the Ψ packaging signal, a 400 bp deletion in the U3 of the right HIV LTR and 2×250 bp cHS4 chromatin insulators. Additional features include: central polypurine tract/DNA flap (cPPT/flap); RRE, Rev-responsive element; polypurine tract (ppt). 
     
    
    
     DETAILED DESCRIPTION 
     Throughout this specification, unless the context requires otherwise, the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element or integer or method step or group of elements or integers or method steps but not the exclusion of any other element or integer or group of elements or integers or method steps. 
     As used in the subject specification, the singular forms “a”, “an” and “the” include plural aspects unless the context clearly dictates otherwise. Thus, for example, reference to “medicament” includes a single medicament, as well as two or more medicaments; reference to “an agent” includes a single agent, as well as two or more agents; reference to “the disclosure” includes a single or multiple aspects taught herein. Aspects taught and enabled herein in the context of the treatment of a blood pathology such as β-thalassemia are encompassed by the term “invention”. All such aspects are enabled within the width of the present invention. 
     β-Thalassemia is an inherited hemoglobinopathy caused by defective synthesis of the β-globin chain of hemoglobin. This leads to an imbalance of α- and β-globin chains. Excess α-globin precipitates in erythroid progenitor cells resulting in cell death, ineffective erythropoiesis and severe anemia. In accordance with the teachings of the present disclosure, a system is developed to specifically target expression of the α-globin genetic locus to reduce levels of α-globin. A reduction in the levels of α-globin in β-thalassemia patients helps reduce the imbalance of α- and β-globin chains thereby ameliorating the symptoms of β-thalassemia in subjects. By targeting expression of the α-globin genetic locus includes specifically targeting mRNA species encoding α-globin. Generally, the α-globin mRNA is targeted at a site selected from the 5′-UTR, Exon1, Exon3, the 3′-UTR and a boundary region inbetween. The α-globin expression may be targeted alone or in combination with gene therapy to elevate β-globin levels. Reference to α-globin includes hemoglobin α-globin 1 (HBA1; SEQ ID NO:41) and hemoglobin α-globin 2 (HBA2; SEQ ID NO:604573). 
     Accordingly, an aspect enabled herein is a method comprising the step of administering an agent to a human subject having or suspected of having β-thalassemia or a related hemoglobinopathy wherein the agent is provided in an amount which reduces to non-zero levels the expression of the α-globin genetic locus thereby reducing levels of α-globin and ameliorating the effects of an α- and β-globin chain imbalance. 
     Taught herein is a method for treating a human subject with β-thalassemia or a related hemoglobinopathy, the method comprising administering to the subject an amount of an agent effective to reduce expression of the α-globin genetic locus thereby reducing levels of α-globin and ameliorating the effects of an α- and β-globin chain imbalance. 
     The present disclosure is instructional on a therapeutic system for treating β-thalassemia or a related hemoglobinopathy in a human subject, the system comprising reducing expression of genetic material encoding the α-globin chain of hemoglobin to thereby reduce levels of α-globin. Such a system facilitates correction, improvement or reduction in the ratio of α- and β-globin chains. Reduced levels of free α-globin chains leads to a reduction in its precipitation in erythroid progenitor cells. Reference to “β-thalassemia” includes blood pathology conditions such as a blood pathology associated with impaired haemoglobin synthesis. Such conditions include those resulting in an α:β-globin imbalance, and which result in an excess of α-globin. Related hemoglobinopathies include HbE and sickle cell disease. 
     Further taught herein is a method of treating a blood pathology associated with an excess of α-globin in a subject, the method comprising administering to the subject an effective amount of an agent which reduces the level of expression of the α-globin genetic locus, the level being from between less than the level of expression determined prior to intervention to a level above zero, thereby reducing α-globin production and normalizing α- and β-globin levels. 
     Taught herein is a method for treating a human subject with β-thalassemia or a related hemoglobinopathy, the method comprising administering to the subject an effective amount of a RNA which targets an mRNA species encoding α-globin at a site selected from the 5′-UTR, Exon1, Exon3, the 3′-UTR and a boundary region inbetween to thereby reduce the amount of α-globin produced to non-zero levels and ameliorate the effects of an α- and 3-globin chain imbalance. 
     The agent may target any part of the α-globin genetic locus, including exons, introns, 5′-UTR, 3′-UTR and boundary regions of mRNA transcribed from the locus. In an embodiment, the agent targets a region selected from the 5′-UTR, Exon1, Exon3, 3′-UTR and any intronic region on an mRNA species encoding α-globin. The agent does not target the exact Hs-siα5 site as disclosed by Sarakul et al, (2008) supra and in CN 100567490 or the sites referred to in CN 100567490 as α2 and α3 (CNα2 and CNα3, respectively). The agent may target any site either side of Hs-siα5, CNα2 and CNα3 which results in reduced expression of the α-globin locus. This extends to from one nucleotide to up to 50 nucleotides 5′ or 3′ of Hs-siα5, CNα2 and/or CNα3. Hence, Exon2 of the α-globin mRNA may also be targeted but not at Hs-siα5. 
     The agent taught herein induces a level of gene silencing of the α-globin genetic locus. An example of such a type of agent is an agent which induces RNAi-mediated gene silencing. The agent may, for example, be a nucleic acid molecule or a component of RNA induced silencing complex (RISC). In an embodiment, the agent is an oligonucleotide in single or double stranded form such as a single or double stranded (duplex) short, interfering RNA (siRNA) molecule or hairpin RNA which comprises a strand having some nucleotide identity to a nucleotide sequence within an mRNA encoded by the α-globin genetic locus such as SEQ ID NO:25, 26, 27, 28, 29, 30, 31 or 32. 
     In an embodiment, the agent is an siRNA of from about 15 to 50 bp in length such as 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49 or 50 bp in length or a hairpin form thereof. The agent may extend to larger or smaller nucleic acid molecules. 
     The RNA may correspond to any region within the α-globin genetic locus or mRNA encoded thereby such as the 5′-UTR portion and exon therein and/or the 3′-UTR portion. Furthermore, the siRNA may correspond to any region within the α-globin genetic locus or more particularly mRNA encoded thereby such as the 5′-UTR portion and/or the 3′-UTR portion. Generally, the RNA targets or comprises a nucleotide sequence selected from the 5′-UTR, Exon1, Exon3, 3′-UTR or a boundary region inbetween such as SEQ ID NO:25 through 32. 
     In an embodiment, the agent is an siRNA comprising at least 15 bp which targets or comprises a sequence on the α-globin mRNA nucleotide sequence selected from the list consisting of SEQ ID NO:42 to SEQ ID NO: 572 and SEQ ID NO:574 to SEQ ID NO: 1179, inclusive. It is a proviso herein that the agent does not target the exact sequence corresponding to Hs-siα5 (Sarakul et al. (2008) supra; CN 100567490) (for the α2 and α3 sequences of CN 100567490 (CNα2 and CNα3, respectively). In an embodiment, the siRNA comprises or targets a nucleotide sequence selected from SEQ ID NO:25, 26, 27, 28, 29, 30, 31 and 32. 
     Taught herein is an agent comprising a short interfering RNA (siRNA) agent or a chemically modified or mimetic form thereof which targets an mRNA species encoding α-globin at a site selected from the 5′-UTR, Exon1, Exon3, the 3′-UTR and a boundary inbetween to reduce the amount of α-globin produced for use in ameliorating the symptoms of β-thalassemia or a related hemoglobinopathy in a subject. 
     Enabled herein is a method for treating a human subject with β-thalassemia or a related hemoglobinopathy, the method comprising administering to the subject an amount of an siRNA targeting or comprising a nucleotide sequence selected from SEQ ID NO:42 to SEQ ID NO: 572 (HBA1) and SEQ ID NO:574 to SEQ ID NO:1179 (HBA2) effective to down-regulate expression of the α-globin genetic locus for a time and under conditions sufficient to reduce levels of α-globin. Excluded from this embodiment is Hs-siα5, CNα2 and CNα3. 
     As taught herein, the expression “reducing expression of the α-globin genetic locus” means that levels of mRNA encoding α-globin or levels of α-globin translated from the mRNA is reduced to a level of about 30% to about 95% of the level in a cell from a subject who does not have β-thalassemia. It also includes reducing the level of α-globin produced to 30%-95% of the level in a cell from a subject without β-thalassemia. This is regarded as a “normal cell” or a “normal control” or “statistically determined normal levels”. By “30% to 95%” means 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94 or 95%. 
     Hence, it is not the aim of the instant method to totally eliminate expression of α-globin. Rather, the intention is to reduce expression to non-zero levels. This means to a level of from 30% to 95% relative to a normal control. In an embodiment, the level of expression of the α-globin genetic locus is reduced from less than the level prior to intervention to above zero levels, thereby reducing α-globin production and normalizing α- and β-globin levels. In another embodiment, the expression of the α-globin genetic locus is reduced to a level at which equi-amounts of α-globin and β-globin are produced. In yet another embodiment, the RNAi agents are expressed in a 5′-UTR, 3′-UTR or intronic region of a β-globin nucleic acid molecule used in gene therapy to elevate β-globin levels. 
     The present disclosure teaches agents, such as oligonucleotides and similar species for use in reducing expression of a genetic locus or mRNA encoding human α-globin. This is accomplished by providing oligonucleotides which target or comprise at least a portion of a nucleotide sequence corresponding to α-globin mRNA. By “target” includes a sequence which is complementary to the mRNA sequence to facilitate complementary nucleotide pair binding. Hence, the oligonucleotide encompasses RNA encoding all or a portion of α-globin including pre-mRNA. In an embodiment, the agent herein induces gene silencing mechanisms such as RNAi-medicated gene silencing. The term “gene silencing” does not necessarily mean inducing zero expression but a level of expression from greater than zero expression to a level less than the level prior to intervention. 
     Agents taught herein include sense oligomeric compounds, sense oligonucleotides, alternate splicers, primers, probes, and other oligomeric compounds which comprise a nucleotide sequence having identity to at least a portion of mRNA encoding α-globin or complementary thereto. As such, these compounds may be introduced in the form of single-stranded, double-stranded, circular or hairpin oligomeric compounds and may contain structural elements such as internal or terminal bulges or loops as well as branches. Once introduced to a cell, the agents of the present invention may elicit the action of one or more enzymes or structural proteins or complexes to effect modification of the α-globin mRNA or α-globin genetic locus. An example of such a complex is RISC. 
     When in oligomeric form, the agent may be single-stranded sense oligonucleotide or double-stranded (duplex) structures, such as double-stranded RNA (dsRNA) molecules or may be chemical or synthetic or mimetic forms thereof. A chemically modified form includes branched and hairpin oligonucleotides. The oligomer may be synthetically produced or derived by expression of DNA or an RNA vector system to generate short hairpin loops. In one embodiment, the DNA or RNA system can generate short hairpin RNA that specifically targets the reduction in expression of α-globin. 
     In the context of the method taught herein, the term “oligonucleotide” refers to an oligomer or polymer of ribonucleic acid (RNA) or mimetics, chimeras, analogs and homologs thereof. This term includes oligonucleotides composed of naturally occurring nucleobases, sugars and covalent intemucleoside (backbone) linkages as well as oligonucleotides having non-naturally occurring portions which function similarly. Such modified or substituted oligonucleotides are often preferred over native forms because of desirable properties such as, for example, enhanced cellular uptake, enhanced affinity for a target nucleic acid and increases stability in the presence of nucleases. 
     Whilst oligonucleotides are one form of the agents enabled by the present disclosure, other families of compounds are contemplated, including but not limited to oligonucleotide analogs and mimetics including chimeras with peptides referred to as “peptide oligonucleotides”. The term “chimeras” also refers to oligonucleotides comprising modified internucleoside linkages between naturally occurring nucleotides. 
     As described above, an agent in the form of an oligonucleotide generally comprises from about 15 to about 50 nucleobases (i.e. from about 15 to about 50-linked nucleosides). 
     “Targeting” an oligonucleotide agent to a particular site with α-globin mRNA in the context of the present disclosure is a multi-step process and involves in one aspect base pairing of complementary strands. 
     The targeting process usually includes determination of at least one target region, segment, or site within the α-globin mRNA which leads to reduced but not zero expression. Within the context of the present disclosure, the term “region” is defined as a portion of the target nucleic acid having at least one identifiable structure, function, or characteristic. Within regions of target nucleic acids are segments. “Segments” are defined as smaller or sub-portions of regions within a target nucleic acid. “Sites”, as used in the present invention, are defined as positions within a target nucleic acid. 
     Alternative RNA transcripts can be produced from the same genomic region of DNA. These alternative transcripts are generally known as “variants”. “Pre-mRNA variants” are transcripts produced from the same genomic DNA that differ from other transcripts produced from the same genomic DNA in either their start or stop position and contain both intronic and exonic sequence. Pre-mRNA variants of the α-globin genetic locus are contemplated herein as a target for sense-mediated gene silencing. 
     Target segments can include RNA sequences that comprise at least the 15 consecutive nucleobases from the 5′-terminus of the α-globin mRNA transcript. Similarly, target segments include RNA sequences that comprise at least the 15 consecutive nucleobases from the 3′-terminus of one of the α-globin mRNA transcript. The skilled artisan would, without undue experimentation, be able to identify further useful target segments. SEQ ID NO:42 through SEQ ID NO:572 and SEQ ID NO:574 to SEQ ID NO: 1179 represent targets of 15 bases (15 mer&#39;s) within the α-globin mRNA. In terms of siRNA, the nucleotide sequence of a nucleotide strand of the siRNA may comprise a sequence selected from SEQ ID NO:42 to SEQ ID NO:572 and SEQ ID NO:574 to SEQ ID NO: 1179. This includes hairpin RNAs. In an embodiment, the sequence or targeted sequence is selected from SEQ ID NO:25, 26, 27, 28, 29, 30, 31 and 32. 
     Once one or more target regions, segments or sites have been identified, sense oligonucleotides are chosen which give the desired effect of reducing translation to α-globin protein. It is not the intention of the method to eliminate all expression of the α-globin genetic locus. It is proposed that α-globin production or gene expression be between 30% and 95% the level in a normal cell (i.e. a cell from a subject who does not have β-thalassemia). 
     As is known in the art, a nucleoside is a base-sugar combination. The base portion of the nucleoside is normally a heterocyclic base. The two most common classes of such heterocyclic bases are the purines and the pyrimidines. Nucleotides are nucleosides that further include a phosphate group covalently linked to the sugar portion of the nucleoside. For those nucleosides that include a pentofuranosyl sugar, the phosphate group can be linked to either the 2′, 3′ or 5′ hydroxyl moiety of the sugar. In forming oligonucleotides, the phosphate groups covalently link adjacent nucleosides to one another to form a linear polymeric compound. In turn, the respective ends of this linear polymeric compound can be further joined to form a circular compound, however, linear compounds are generally preferred. In addition, linear compounds may have internal nucleobase complementarity and may, therefore, fold in a manner as to produce a fully or partially double-stranded compound. Within oligonucleotides, the phosphate groups are commonly referred to as forming the internucleoside backbone of the oligonucleotide. The normal linkage or backbone of RNA and DNA is a 3′ to 5′ phosphodiester linkage. 
     Examples of modified oligonucleotides useful in the present method include oligonucleotides containing modified backbones or non-natural intemucleoside linkages. Oligonucleotides having modified backbones include those that retain a phosphorus atom in the backbone and those that do not have a phosphorus atom in the backbone. Modified oligonucleotides that do not have a phosphorus atom in their intemucleoside backbone can also be considered to be oligonucleosides. 
     Useful modified oligonucleotide backbones containing a phosphorus atom therein include, for example, phosphorothioates, chiral phosphorothioates, phosphorodithioates, phosphotriesters, aminoalkylphosphotriesters, methyl and other alkyl phosphonates including 3′-alkylene phosphonates, 5′-alkylene phosphonates and chiral phosphonates, phosphinates, phosphoramidates including 3′-amino phosphoramidate and aminoalkylphosphoramidates, thionophosphoramidates, thionoalkylphosphonates, thionoalkylphosphotriesters, selenophosphates and boranophosphates having normal 3′-5′ linkages, 2′-5′ linked analogs of these, and those having inverted polarity wherein one or more intemucleotide linkages is a 3′ to 3′, 5′ to 5′ or 2′ to 2′ linkage. Useful oligonucleotides having inverted polarity comprise a single 3′ to 3′ linkage at the 3′-most intemucleotide linkage, i.e. a single inverted nucleoside residue which may be abasic (the nucleobase is missing or has a hydroxyl group in place thereof). Various salts, mixed salts and free acid forms are also included. 
     Useful modified oligonucleotide backbones that do not include a phosphorus atom therein have backbones that are formed by short chain alkyl or cycloalkyl intemucleoside linkages, mixed heteroatom and alkyl or cycloalkyl intemucleoside linkages, or one or more short chain heteroatomic or heterocyclic intemucleoside linkages. These include those having morpholino linkages (formed in part from the sugar portion of a nucleoside); siloxane backbones; sulfide, sulfoxide and sulfone backbones; formacetyl and thioformacetyl backbones; methylene formacetyl and thioformacetyl backbones; riboacetyl backbones; alkene containing backbones; sulfamate backbones; methyleneimino and methylenehydrazino backbones; sulfonate and sulphonamide backbones; amide backbones; and others having mixed N, O, S and CH 2  component parts. 
     In other useful oligonucleotide mimetics, both the sugar and the intemucleoside linkage (i.e. the backbone), of the nucleotide units are replaced with novel groups. The nucleobase units are maintained for sequence identity with the region of α-globin transcript. One such compound is referred to as a peptide oligonucleotide. In peptide oligonucleotides, the sugar-backbone of an oligonucleotide is replaced with an amide containing backbone, in particular an aminoethylglycine backbone. The nucleobases are retained and are bound directly or indirectly to aza nitrogen atoms of the amide portion of the backbone. Teaching of peptide oligonucleotide compounds can be found in Nielsen et al. (1992)  Science  254:1497-1500. 
     In an embodiment, oligonucleotides are provided with phosphorothioate backbones and oligonucleosides with heteroatom backbones, and in particular —CH 2 —NH—O—CH 2 —, —CH 2 —N(CH 3 )—O—CH 2 — [known as a methylene (methlimino) or MMI backbone], —CH 2 —O—N(CH 3 )—CH 2 —, —CH 2 —N(CH 3 )—N(CH 3 )—CH 2 — and —O—N(CH 3 )—CH 2 —CH 2 —. 
     Modified oligonucleotides may also contain one or more substituted sugar moieties. Useful oligonucleotides comprise one of the following at the 2′ position: OH; F; O—, S- or N-alkyl; O—, S- or N-alkenyl; O—, S- or N-alkynyl; or O-alkyl-O-alkyl, wherein the alkyl, alkenyl and alkynyl may be substituted or unsubstituted C 1  to C 10  alkyl or C 2  to C 10  alkenyl and alkynyl. Particularly preferred are O[(CH 2 ) n O] m CH 3 , O(CH 2 ) n OCH 3 , O(CH 2 ) n NH 2 , O(CH 2 ) n CH 3 , O(CH 2 ) n ONH 2 , and O(CH 2 ) n ON[(CH 2 ) n CH 3 ] 2 , where n and m are from 1 to about 10. Other preferred oligonucleotides comprise one of the following at the 2′ position: C 1  to C 10  lower alkyl, substituted lower alkyl, alkenyl, alkynyl, alkaryl, aralkyl, O-alkaryl or O-aralkyl, SH, SCH 3 , OCN, Cl, Br, CN, CF 3 , OCF 3 , SOCH 3 , SO 2 CH 3 , ONO 2 , NO 2 , N 3 , NH 2 , heterocycloalkyl, heterocycloalkaryl, aminoalkylamino, polyalkylamino, substituted silyl, an RNA cleaving group, a reporter group, an intercalators, a group for improving the pharmacokinetic properties of an oligonucleotide, or a group for improving the pharmacodynamic properties of an oligonucleotide, and other substituents having similar properties. One type of modification includes 2′-methoxyethoxy (2′-O—CH 2 —CH 2 —OCH 3 , also known as 2′-O-(2-methoxyethyl) or 2′-MOE) [Martin et al. (1995)  Helv. Chim. Acta,  78:486-504] i.e. an alkoxyalkoxy group. A further preferred modification includes 2′-dimethylaminooxyethoxy, i.e. a O(CH 2 ) 2 ON(CH 3 ) 2  group, also known as 2′-DMAOE, as described in examples herein below, and 2′-dimethylaminoethoxyethoxy (also known in the art as 2′-O-dimethyl-amino-ethoxy-ethyl or 2′-DMAEOE), i.e. 2′-O—CH 2 —O—CH 2 —N(CH 3 ) 2 . 
     Other modifications include 2′-methoxy (2′-O—CH 3 ), 2′-aminopropoxy (2′-OCH 2 CH 2 CH 2 NH 2 ), 2′-allyl (2′-CH 2 —CH═CH 2 ), 2′-O-allyl (2′O—CH 2 —CH═CH 2 ) and 2′-fluoro (2′-F). The 2′-modification may be in the arabino (up) position or ribo (down) position. Similar modifications may also be made at other positions on the oligonucleotide, particularly the 3′ position of the sugar on the 3′ terminal nucleotide or in 2′-5′ linked oligonucleotides and the 5′ position of 5′ terminal nucleotide. Oligonucleotides may also have sugar mimetics such as cyclobutyl moieties in place of the pentofuranosyl sugar. 
     A further useful modification of the sugar includes Locked Nucleic Acids (LNAs) in which the 2′-hydroxyl group is linked to the 3′ or 4′ carbon atom of the sugar ring, thereby forming a bicyclic sugar moiety. The linkage is generally a methylene (—CH 2 -) n  group bridging the 2′ oxygen atom and the 4′ carbon atom wherein n is 1 or 2. 
     Oligonucleotides may also include nucleobase (often referred to in the art simply as “base”) modifications or substitutions. As used herein, “unmodified” or “natural” nucleobases include the purine bases adenine (A) and guanine (G), and the pyrimidine bases thymine (T), cytosine (C) and uracil (U). Modified nucleobases include other synthetic and natural nucleobases such as 5-methylcytosine (5-me-C), 5-hydroxymethyl cytosine, xanthine, hypoxanthine, 2-aminoadenine, 6-methyl and other alkyl derivatives of adenine and guanine, 2-propyl and other alkyl derivatives of adenine and guanine, 2-thiouracil, 2-thiotheymine and 2-thiocytosine, 5-halouracil and cytosine, 5-propynyl (—C≡C—CH 3 ) uracil and cytosine and other alkynyl derivatives of pyrimidine bases, 6-azo uracil, cytosine and thymine, 5-uracil (pseudouracil), 4-thiouracil, 8-halo, 8-amino, 8-thiol, 8-thioalkyl, 8-hydroxyl and other 8-substituted adenines and guanines, 5-halo particularly 5-bromo, 5-trifluoromethyl and other 5-substituted uracils and cytosines, 7-methylguanine and 7-methyladenine, 2-F-adenine, 2-amino-adenine, 8-azaguanine and 8-azaadenine, 7-deazaguanine and 7-deazaadenine and 3-deazaguanine and 3-deazaadenine. Further modified nucleobases include tricyclic pryimidines such as phenoxazine cytidine (1H-pyrimido[5,4-b][1,4]benzoxazin-2(3H)-one), phenothiazine cytidine (1H-pyrimido[5,4-b][1,4]benzothiazin-2(3H)-one), G-clamps such as a substituted phenoxazine cytidine (e.g. 9-(2-aminoethoxy)-H-pyrimido[5,4-b][1,4]benzoxazin-2(3H)-one), carbazole cytidine (2H-pyrimido[4,5-b]indol-2-one), pyridoindole cytidine (H-pyrido[3′,2′:4,5]pyrrole[2,3-d]pyrimidin-2-one). Modified nucleobases may also include those in which the purine or pyrimidine base is replaced with other heterocycles, for example 7-deaza-adenine, 7-deazaguanosine, 2-aminopyridine and 2-pyridone. Certain of these nucleobases are particularly useful for increasing the binding affinity of the agents of the present invention. These include 5-substituted pyrimidines, 6-azapyrimidines and N-2, N-6 and 0-6 substituted purines, including 2-aminoprophyladenine, 5-prophynyluracil and 5-propynylcytosine. 5-methylcytosine substitutions have been shown to increase nucleic acid duplex stability. 
     Another modification of the oligonucleotides enabled herein involves chemically linking to the oligonucleotide one or more moieties or conjugates which enhance the activity, cellular distribution or cellular uptake of the oligonucleotide. These moieties or conjugates can include conjugate groups covalently bound to functional groups such as primary or secondary hydroxyl groups. Conjugate groups of the invention include intercalators, reporter molecules, polyamines, polyamides, polyethylene glycols, polyethers, groups that enhance the pharmacodynamic properties of oligomers, and groups that enhance the pharmacokinetic properties of oligomers. Typical conjugate groups include cholesterols, lipids, phospholipids, biotin, phenazine, folate, phenanthridine, anthraquinone, acridine, fluoresceins, rhodamines, coumarins and dyes. Groups that enhance the pharmacodynamic properties, in the context of this invention, include groups that improve uptake, enhance resistance to degradation, and/or strengthen sequence-specific hybridization with the target nucleic acid. Groups that enhance the pharmacokinetic properties, in the context of the present invention, include groups that improve uptake, distribution, metabolism or excretion of the compounds of the present invention. Conjugate moieties include but are not limited to lipid moieties such as a cholesterol moiety, cholic acid, a thioether, e.g. hexyl-S-tritylthiol, a thiocholesterol, an aliphatic chain, e.g. dodecandiol or undecyl residues, a phospholipid, e.g. di-hexadecyl-rac-glycerol or triethyl-ammonium 1,2-di-O-hexadecyl-rac-glycero-3-H-phosphonate, a polyamine or a polyethylene glycol chain, or adamantine acetic acid, a palmitoyl moiety, or an octadecylamine or hexylamino-carbonyl-oxycholeterol moiety. Oligonucleosides of the invention may also be conjugated to active drug substances, for example, aspirin, warfarin, phenylbutazone, ibuprofen, suprofen, fenbufen, ketoprofen, (S)-(+)-pranoprofen, carprofen, dansylsarcosine, 2,3,5-triiodobenzoic acid, flufenamic acid, folinic acid, a benzothiadiazide, chlorothiazide, a diazepine, indomethicin, a barbiturate, a cephalosporin, a sulfa drug, an antidiabetic, an antibacterial or an antibiotic. 
     It is not necessary for all positions in a given compound to be uniformly modified, and in fact more than one of the aforementioned modifications may be incorporated in a single compound or even at a single nucleoside within an oligonucleotide. 
     Taught herein is sense oligonucleotides which are chimeric compounds. “Chimeric” sense oligonucleotides or “chimeras”, in the context of the present method, are oligonucleotides which contain two or more chemically distinct regions, each made up of at lest one monomer unit, i.e. a nucleotide in the case of an oligonucleotide compound. These oligonucleotides typically contain at least one region wherein the oligonucleotide is modified so as to confer upon the oligonucleotide increased resistance to nuclease degradation, increased cellular uptake, increased stability and/or increased binding affinity of the target nucleic acid. 
     Chimeric oligonucleotides may be formed as composite structures of two or more oligonucleotides, modified oligonucleotides, oligonucleosides and/or oligonucleotide mimetics as described above. 
     A gene therapy approach may also be used to obtain DNA-derived or RNA-derived siRNA or other RNA species including hairpin RNAs. 
     A nucleic acid sequence encoding an RNA species such as siRNA may be introduced into a cell in a vector such that the nucleic acid sequence remains extrachromosomal. In such a situation, the nucleic acid sequence will be expressed by the cell from the extrachromosomal location. Alternatively, cells may be engineered by inserting the nucleic acid sequence into the chromosome. Vectors for introduction of nucleic acid sequence both for recombination and for extrachromosomal maintenance are known in the art and any suitable vector may be used. Methods for introducing nucleic acids into cells such as electroporation, calcium phosphate co-precipitation and viral transduction are known in the art. 
     In particular, a number of viruses have been used as nucleic acid transfer vectors or as the basis for preparing nucleic acid transfer vectors, including papovaviruses (e.g. SV40, Madzak et al. (1992)  J Gen Virol  73:1533-1536), adenovirus (Berkner (1992)  Curr Top Microbiol Immunol  158:39-66; Berkner et al. (1988)  BioTechniques  6:616-629; Gorziglia and Kapikian (1992)  J Virol  66:4407-4412; Quantin et al. (1992)  Proc Natl Acad Sci USA  89:2581-2584; Rosenfeld et al. (1992)  Cell  68:143-155; Wilkinson et al. (1992)  Nucleic Acids Res  20:233-2239; Stratford-Perricaudet et al. (1990)  Hum Gene Ther  1:241-256; Schneider et al. (1998)  Nat Genetics  18:180-183), vaccinia virus (Moss (1992)  Curr Top Microbiol Immunol  158:5-38; Moss (1996)  Proc Natl Acad Sci USA  93:11341-11348), adeno-associated virus (Muzyczka (1992)  Curr Top Microbiol Immunol  158:97-129; Ohi et al. (1990)  Gene  89:279-282; Russell and Hirata (1998)  Nat Genetics  18:323-328), herpesviruses including HSV and EBV (Margolskee (1992)  Curr Top Microbiol Immunol  158:67-95; Johnson et al. (1992)  J Virol  66:2952-2965; Fink et al. (1992)  Hum Gene Ther  3:1-19; Breakefield and Geller (1987)  Mol Neurobiol  1:339-371; Freese et al. (1990)  Biochem Pharmaco.  40:2189-2199; Fink et al. (1996) Ann Rev Neurosci  19:265-287), lentiviruses (Naldini et al (1996)  Science  272:263-267), Sindbis and Semliki Forest virus (Berglund et al. (1993)  Biotechnology  11:916-920) and retroviruses of avian (Bandyopadhyay and Temin (1984)  Mol Cell Biol  4:749-754; Petropoulos et al. (1992)  J Virol  66:3391-3397), murine (Miller (1992)  Curr Top Microbiol Immunol  158:1-24; Miller et al. (1985)  Mol Cell Biol  5:431-437; Sorge et al. (1984)  Mol Cell Biol  4:1730-1737; Mann and Baltimore (1985)  J Virol  54:401-407; Miller et al. (1988)  J Virol  62:4337-4345) and human (Shimada et al. (1991)  J Clin Invest  88:1043-1047; Helseth et al. (1990)  J Virol  64:2416-2420; Page et al. (1990)  J Virol  64:5270-5276; Buchschacher and Panganiban (1982)  J Virol  66:2731-2739) origin. Lentiviral vectors represent a particularly useful vector for gene therapy. In one embodiment, the lentivirus vector comprises a mono-cistronic vector for tissue-specific expression of an siRNA or other RNA species using a erythroid-derived polymerase (pol) II promoter. 
     In an embodiment, the vector contains the human β-globin gene under the control of the pol II β-globin promoter. Hairpin RNAs targeting sites on the α-globin gene or transcript can be inserted in introns or in the 3′- or 5′-UTR of the β-globin gene. 
     Taught herein is a vector comprising a nucleic acid molecule encoding human β-globin operably linked to a promoter and one or more nucleic acid molecules inserted in the 5′- and/or 3′-UTR region and/or intronic regions of the β-globin nucleic acid molecule encoding an RNA which targets an mRNA species encoding α-globin at a site selected from the 5′ untranslated region (5′-UTR), Exon1, Exon3 and the 3′-UTR or a boundary region inbetween. 
     In an embodiment, the promoter is the pol II or pol III promoter. 
     In an embodiment, the second nucleic acid molecule encodes an RNA which targets or comprises α-globin mRNA selected from SEQ ID NO:25, 26, 27, 28, 29, 30, 31 and 32. 
     In an embodiment, the RNA molecules targeting the α-globin mRNA species are encoded by sequences inserted into β-globin nucleic acid molecule so as to facilitate combination therapy of providing β-globin and reducing α-globin. 
     Non-viral nucleic acid transfer methods are known in the art such as chemical techniques including calcium phosphate co-precipitation, mechanical techniques, for example, microinjection, membrane fusion-mediated transfer via liposomes and direct DNA uptake and receptor-mediated DNA transfer. Viral-mediated nucleic acid transfer can be combined with direct in vivo nucleic acid transfer using liposome delivery, allowing one to direct the viral vectors to particular cells. Alternatively, the retroviral vector producer cell line can be injected into particular tissue. Injection of producer cells would then provide a continuous source of vector particles. 
     The agent herein may also be admixed, encapsulated, conjugated or otherwise associated with other molecules, molecule structures or mixtures of compounds, as for example, liposomes, receptor-targeted molecules, oral, rectal, topical or other formulations, for assisting in uptake, distribution and/or absorption. 
     The agents contemplated for use herein encompass any pharmaceutically acceptable salts, esters, or salts or such esters, or any other compound which, upon administration to a human, is capable of providing (directly or indirectly) the biologically active metabolite or residue thereof. Accordingly, for example, the disclosure if also drawn to prodrugs and pharmaceutically acceptable salts of the compounds of the invention, pharmaceutically acceptable salts of such prodrugs and other bioequivalents. 
     The term “prodrug” indicates a therapeutic agent that is prepared in an inactive form that is converted to an active form (i.e. drug) within the body or cells thereof by the action of endogenous enzymes or other chemicals and/or conditions. In an example, prodrug versions of the oligonucleotides described herein are prepared as SATE [(S-acetyl-2-thioethyl) phosphate] derivatives. 
     The term “pharmaceutically acceptable salts” refers to physiologically and pharmaceutically acceptable salts of the compounds, i.e. salts that retain the desired biological activity of the parent compound and do not impart undesired toxicological effects thereof. 
     Also taught herein are pharmaceutical compositions and formulations which include the agents herein described. The pharmaceutical compositions may be administered in any number of ways depending upon whether local or systemic treatment is desired and upon the area to be treated. Administration may be topical (including ophthalmic and to mucous membranes including vaginal and rectal delivery), pulmonary, e.g. by inhalation or insufflation of powders or aerosols, including by nebulizer; intratracheal, intranasal, epidermal and transdermal, oral or parenteral. Parenteral administration includes intravenous, intraarterial, subcutaneous, intraperitoneal or intramuscular injection or infusion; or intracranial, e.g. intrathecal or intraventricular, administration. Oligonucleotides with at least one 2-O-methoxyethyl modification are believed to be particularly useful for oral administration. Pharmaceutical compositions and formulations for topical administration may include transdermal patches, ointments, lotions, creams, gels, drops, suppositories, sprays, liquids and powders. Conventional pharmaceutical carriers, aqueous, powder or oily bases, thickeners and the like may be necessary or desirable. Coated condoms, gloves and the like may also be useful. 
     The pharmaceutical formulations herein, which may conveniently be presented in unit dosage form, may be prepared according to conventional techniques well known in the pharmaceutical industry. Such techniques include the step of brining into association the active ingredients with the pharmaceutical carrier(s) or excipient(s). In general, the formulations are prepared by uniformly and intimately bringing into association the active ingredients with liquid carriers or finely divided solid carriers or both, and then, if necessary, shaping the product. 
     The compositions herein may be formulated into any of many possible dosage forms such as, but not limited to, tablets, capsules, gel capsules, liquid syrups, soft gels, suppositories and enemas. The compositions herein may also be formulated a suspensions in aqueous, non-aqueous or mixed media. Aqueous suspensions may further contain substances which increase the viscosity of the suspension including, for example, sodium carboxymethylcellulose, sorbitol and/or dextran. The suspension may also contain stabilizers. 
     Pharmaceutical compositions include, but are not limited to, solutions, emulsions, foams and liposome-containing formulations. The pharmaceutical compositions and formulations may comprise one or more penetration enhancers, carriers, excipients or other active or inactive ingredients. 
     Formulations enabled herein include liposomal formulations. The term “liposome” means a vesicle composed of amphililic lipids arranged in a spherical bilayer or bilayers. Liposomes are unilamellar or multilamellar vesicles which have a membrane formed from a lipophilic material and an aqueous interior that contains the composition to be delivered. Cationic liposomes are positively charged liposomes which are believed to interact with negatively charged RNA molecules to form a stable complex. Liposomes that are pH-sensitive or negatively-charged are believed to entrap DNA rather than complex with it. Both cationic and noncationic liposomes have been used to deliver RNA to cells. 
     Liposomes also include “sterically stabilized” liposomes, a term which, as used herein, refers to liposomes comprising one or more specialized lipids that, when incorporated into liposomes, result in enhanced circulation lifetimes relative to liposomes lacking such specialized lipids. Examples of sterically stabilized liposomes are those in which part of the vesicle-forming lipid portion of the liposome comprises one or more glycolipids or is derivatized withy one or more hydrophilic polymers, such as a polyethylene glycol (PEG) moiety. 
     In one embodiment, various penetration enhancers are employed to effect the efficient delivery of nucleic acids, such as oligonucleotides. In addition to aiding the diffusion of non-lipophilic drugs across cell membranes, penetration enhancers also enhance the permeability of lipophilic drugs. Penetration enhancers may be classified as belonging to one of five broad categories, i.e. surfactants, fatty acids, bile salts, chelating agents and non-chelating non-surfactants. 
     The skilled artisan will recognize that formulations are routinely designed according to their intended uses, i.e. route of administration. 
     Useful formulations for topical administration include those in which the oligonucleotides are in admixture with a topical delivery agent such as lipids, liposomes, fatty acids, fatty acid esters, steroids, chelating agents and surfactants. Lipids and liposomes include neutral (e.g. dioleoylphosphatidyl DOPE ethanolamine, dimyristoylphophatidyl choline DMPC, distearolyphosphatidyl choline) negative (e.g. dimyristoylphosphatidyl glycerol DMPG) and cationic (e.g. dioleoyltetramethylaminopropyl DOTAP and dioleoylphosphatidyl ethanolamine DOTMA). 
     For topical or other administration, the oligonucleotides may be encapsulated within liposomes or may form complexes thereto, in particular to cationic liposomes. Alternatively, oligonucleotides may be complexed to lipids, in particular to cationic lipids. 
     Compositions and formulations for oral administration include powders or granules, microparticulates, nanoparticulates, suspensions or solutions in water or non-aqueous media, capsules, gel capsules, sachets, tablets or minitablets. Thickeners, flavoring agents, diluents, emulsifiers, dispersing aids or binders may be desirable. Oral formulations include those in which oligonucleotides are administered in conjunction with one or more penetration enhancers surfactants and chelators. Useful surfactants include fatty acids and/or esters or salts thereof, bile acids and/or salts thereof. 
     The term “subject” as used herein includes a human subject. The human subject may be male or female and any age from infant to elderly. For animal model studies, the subject may be a non-human animal including a laboratory test animal, farm animal or primate. 
     Compositions and formulations for parenteral, intrathecal or intraventricular administration may include sterile aqueous solutions which may also contain buffers, diluents and other suitable additives such as, but not limited to, penetration enhancers, carrier compounds and other pharmaceutically acceptable carriers or excipients. The compositions may also be cell based or viral compositions. 
     The formulation of therapeutic compositions and their subsequent administration (dosing) is within the skill of those in the art. Dosing is dependent on severity and responsiveness of the β-thalassemic disease state, with the course of treatment lasting from several days to several months or years, or until a cure is effected or a diminution of the disease state is achieved. Optimal dosing schedules can be calculated from measurements of drug accumulation in the body of the patient. Persons of ordinary skill can easily determine optimum dosages, dosing methodologies and repetition rates. Optimum dosages may vary depending on the relative potency of individual oligonucleotides, and can generally be estimated based on ECsos found to be effective in in vitro and in vivo animal models. In general, dosage is from 0.01 μg to 100 g per kg of body weight, and may be given once or more daily, weekly, monthly or yearly, or even every 2 to 20 years. Persons of ordinary skill in the art can easily estimate repetition rates for dosing based on measured residence times and concentrations of the drug in bodily fluids or tissues. Following successful treatment, it may be desirable to have the patient undergo maintenance therapy to prevent the recurrence of the disease state, wherein the oligonucleotide is administered in maintenance doses, ranging from 0.01 μg to 100 g per kg of body weight, once or more daily, to once every 20 years. 
     The present disclosure is instructional on the use of an agent which reduces expression of the α-globin genetic locus in a subject in the manufacture of a medicament in the treatment of β-thalassemia or a related hemoglobinopathy. 
     A related embodiment teaches an agent which reduces expression of the α-globin genetic locus in a method for treating β-thalassemia or a related hemoglobinopathy. 25 [0107] Further enabled herein is a method for treating β-thalassemia or a related hemoglobinopathy in a human subject, the method comprising administering to the subject an siRNA molecule of from 15 to 50 bp in length which targets a region on α-globin mRNA selected from the list consisting of 5′-UTR, 3′-UTR, Exon1, Exon3 and a boundary or intronic region to thereby reduce the level of expression of the α-globin genetic locus to less than levels prior to intervention to above-zero levels, the amount of siRNA administered being effective to reduce α-globin levels to re-balance the levels of α-globin and β-globin. Targets include SEQ ID NO:42 to SEQ ID NO:572 on HBA1 and SEQ ID NO:574 to SEQ ID NO:1179 on HBA2 with the exception of Hs-siα5, CNα2 and CNα3. 
     Examples of siRNA include SEQ ID NO:25, 26, 27, 28, 29, 30, 31 and 32 as well as hairpin forming thereof. Another aspect enabled herein is directed to a vector comprising a nucleic acid molecule encoding human β-globin operably linked to a promoter and one or more second nucleic acid molecules inserted in the 5′-UTR and/or 3′-UTR region and/or an intron of the β-globin-encoding nucleic acid molecule which second nucleic acid molecule encodes an RNA which targets an mRNA species encoding α-globin at a site selected from the 5′ untranslated region (5′-UTR), Exon1, Exon3 and the 3′-UTR or a boundary region inbetween. In an embodiment, the vector provides therapeutic levels of β-globin while reducing α-globin levels. 
     In an embodiment, the siRNA comprises a nucleotide sequence selected from SEQ ID NO:42 through SEQ ID NO:572 on HBA1 or SEQ ID NO:574 to SEQ ID NO:1179 on HBA2 or targets a nucleotide sequence selected from SEQ ID NO:42 through SEQ ID NO: 572 or SEQ ID NO:574 to SEQ ID NO:1179. 
     EXAMPLES 
     Aspects disclosed herein are now further described by the following non-limiting Examples. 
     Materials and Methods 
     Maintenance of Cell Lines 
     In these studies, human erythroleukaemic K562 cells were maintained in continuous culture in Dulbecco&#39;s Modified Eagle Media (DMEM) (Sigma, Sydney, NSW, Australia) supplemented with 10% v/v fetal calf serum (FCS), 100 U/ml penicillin and 100 g/ml streptomycin. Cells were incubated at 37° C. and passaged every 3-4 days by adding 2 ml of a confluent culture to 20 ml growth medium in an 80 cm 2  flask. Cells were seeded at 1×10 5  cells/ml 12 hours prior to transfection. 
     MEL cells were induced to hemoglobinize by seeding at an initial concentration of 2×10 5  cells per ml in DMEM containing 2% w/v DMSO (Sigma) and incubated at 37° C. After five days of hemoglobinization, cells were resuspended at 5×10 5  cells per ml in fresh DMEM with 2% w/v DMSO (Scher et al. (1982)  Cancer Res.  42:1300-1306) and electroporated approximately 16 hours later. 
     Electroporation of Mammalian Cells 
     Immediately preceding electroporation, cells were washed three times with equal volumes of Opti-Mem reduced serum media (Invitrogen) and resuspended at a final concentration of 1×10 7  K562 cells per ml in Opti-Mem. Electroporations were performed at room temperature in 0.4 cm cuvettes (Bio-Rad, Hercules, Calif.) with 500 μL cell suspension mixed with an appropriate amount of RNA or DNA resuspended at a concentration of 1 μg/μl. Electroporations were performed on the Gene Pulser (Bio-Rad) using the following conditions: 226 Volts, 950 μF and ∞ resistance for K562 cells or 250 Volts. Cells were then cultured in 10 ml DMEM containing 10% v/v FCS. 
     Flow Cytometry 
     At various time points following transfection, cells were analysed with an LSR II flow cytometer (Becton Dickson, Franklin Lakes, Calif., USA). Briefly, 0.1-1×10 6  cells were washed once in PBS supplemented with 1% v/v FBS and resuspended in a final volume of 0.5 ml PBS. For the detection of eGFP reporter gene expression, analysis was performed only on live cells. Data acquisition and analysis were performed using BD FACsDiva software (Becton Dickson). 
     RNA Extractions 
     Cells were collected at appropriate time points after transfections and RNA was extracted using Tri-Reagent (Molecular Research Centre, Cincinnati, Ohio) according to manufacturer&#39;s instructions. Briefly, between 2.5-5×10 6  cells were collected by centrifugation and lysed in 500 μl Tri-Reagent for 5 minutes. 100 μl of chloroform was added and samples were agitated thoroughly for 30 seconds. Phase separation was achieved by centrifugation at 13,000 g for 20 minutes at 4° C. The aqueous phase was collected and RNA was precipitated by incubation with equal volume isopropanol. RNA was collected by centrifugation at 13,000 g for 10 minutes at 4° C., washed with 1 ml 75% v/v ethanol and resuspended in 50 μl nuclease-free H 2 O. Quantity and quality of RNA was determined by spectrophotometry. 
     cDNA Synthesis 
     cDNA was synthesized using SuperScript First-Strand kit (Invitrogen) according to manufacturer&#39;s instructions. In brief, 1 μg of RNA was combined with 1 μl of 0.5 μg/l oligo (dT) primers, 1 μL 10 mM dNTPs and nuclease-free H 2 O to a final volume of 10 μl 1 and incubated at 65° C. for 5 minutes. Reactions were placed on ice prior to the addition of 2 μl reaction buffer (200 mM Tris-HCl (pH 8.4), 500 mM KCl), 4 μl 25 mM MgCl 2 , 2 μl 0.1 mM DTT and 1 μl RNAseOut and incubated at 42° C. for 2 minutes. Reverse transcription then proceeded with the addition of 1 μl Superscript II (50 units/μl) enzyme at 42° C. for 50 minutes followed by termination at 70° C. for 15 minutes. 
     Real-Time PCR 
     All samples were analyzed using primer sets designed using Primer Express software (Applied Biosystems, Epsom, Surrey). Reactions were performed on a 7300 Real-Time PCR System (Applied Biosystems). 25 ng of template cDNA was combined with 2 pmol of the forward primer and 2 pmol of the reverse primer and 12.5 μl SYBR Green Master Mix (Applied Biosystems) to a final volume of 25 μl. Samples were held at 50° C. for 2 minutes then 95° C. for 10 minutes followed by 40 cycles of 15 seconds at 95° C. and 1 minute at 60° C. with data collection occurring at 60° C. A final dissociation stage was performed consisting of 15 seconds at 95° C., 30 seconds at 60° C. and 15 seconds at 95° C. All reactions were performed in triplicates. 
     Data Analysis 
     Triplicate cycle threshold (Ct) values for each sample and primer pair were averaged. The Ct value is the number of cycles required for a label signal to cross the threshold (i.e. exceeds background level). The Ct level is inversely proportional to the amount of target to nucleic acid in a sample. Ct value of the gene of interest (α-globin) was subtracted from the reference gene (β-actin or β-globin) to calculate ΔCt. The formula 2 ΔCt  was applied to give fold-difference between α-globin relative to the reference gene. Reductions of α-globin expression were determined by dividing fold-differences in experimental group against fold-differences in mock electroporated MEL cells. 
     Example 1 
     Phenotypic Improvements in β-Thalassemic Cells 
     One of the mechanisms by which excess α-globin chains are believed to damage erythroid progenitor cells is through the increased generation of ROS (Advani et al. (1992) supra; Schrier and Mohandas (1992)  Blood  79:15896-1592; Schrier et al. (1989)  Blood  74:2194-2202; Scott et al. (1993)  J Clin Invest  91:1706-1712). Each improperly paired α-chain also carries an attached heme group and iron molecule which can be oxidized in the highly oxygenated environment of a RBC (Schrier (2002) supra). The increased ROS arising from imbalanced globin synthesis was detected by incubating cultured mouse β-KO cells with 2,7-dichlorofluorescein diacetate (DCFH) [Amer et al. (2003)  Eur J Haematol  70:84-90; Kong et al. (2004)  J Clin Invest  114:1457-1466, and Wannasuphaphol et al. (2005)  Ann N Y Acad Sci  1054:407-416] ( FIG. 1B (i)). Levels of ROS in cultured erythroid progenitor cells from β-KO and WT mice were similar to levels detected in the peripheral RBCs from these mice, with β-KO cells generating ROS at levels double that of WT mice ( FIG. 1B (i)). However, when β-KO cells were treated with siα4, the reduction in α-globin expression resulted in decreased levels of ROS and partial normalization of thalassemic phenotype as measured by DCFH fluorescence. Cells treated with 10 μg and 5 g of siα4, which showed the greatest decrease in α-globin mRNA, also showed the greatest improvements in ROS levels with reductions of 41%+13% (P&lt;0.05) and 26%+4% (P&lt;0.02), respectively. In contrast, levels of DCFH fluorescence in cells treated with 1 μg and 10 μg siLuc were not significantly different from mock electroporated cells ( FIG. 1B (ii)). 
     Most importantly, the results illustrate that reduced α-globin expression resulted in a detectable phenotypic change in thalassemic erythroid cells, decreasing ROS production to WT levels. This provides clear evidence that the heterozygous β-KO mouse is a suitable in vivo model for testing therapeutic down-regulation of α-globin. In summation, the results provide the basis for an innovative new strategy to treat β-thalassemia. 
     Example 2 
     siRNA-Mediated Reductions of Murine α-Globin 
     In developing a strategy to treat β-thalassemia patients, the susceptibility of human α-globin to siRNA-mediated degradation is tested. 
     Although α-globin is highly conserved between mouse and humans, it is difficult to isolate regions of perfect homology suitable for effective siRNA targeting in the relatively short (˜500 bp) mRNA sequences. Effective siRNA design generally requires a low GC content with a GC bias towards the 5′ end to maintain appropriate thermodynamic stability (Patzel (2007)  Drug Discov Today  12:139-148). However, the α-globin gene is notoriously GC-rich (Higgs et al. (1989)  Blood  73:1081-1104), making siRNA selection somewhat challenging. In addition, many siRNA selection guidelines recommend specific nucleotides in particular positions (Patzel (2007) supra), further limiting the available targets. Hence, siRNAs demonstrated to be effective against murine α-globin may not necessarily remain so against human sequences. Therefore, in order to maximize efficacy, siRNAs specific to human α-globin are designed and screened in an appropriate system. 
     The K562 cells are one of the most well characterized human erythroid cell lines. Originally derived from a patient with chronic myelogenous leukaemia (Lozzio and Lozzio (1975)  Blood  45:321-334), these cells grow continuously in culture and display erythroid characteristics such as the expression of glycophorin A, the major sialoglycoprotein on human red cells (Anderson et al. (1979)  Int J Cancer  23:143-147). In addition, K562 cells express low levels of hemoglobin, consistent with an early erythroid progenitor phenotype (Miller et al. (1984)  Blood  63:195-200). The expressed globin chains are predominantly embryonic in nature, with ε β-like chains and a-like chains, but some fetal hemoglobin (γ 2 α 2 ) is also produced (Rutherford et al. (1981)  Proc Natl Acad Sci USA  78:348-352). α-Globin, therefore, is expressed at low but detectable levels, sufficient for preliminary screening experiments and previous studies using antisense (Ponnazhagan et al. (1994)  J Exp Med  179:733-738) or ribozyme (Shen et al. (1999)  Blood Cells Mol ids  25:361-373) strategies to reduce α-globin have also utilized K562 cells as the model system. 
     In this example, low doses of siRNA were electroporated into K562 cells and reductions were detected by real-time PCR at 24 and 48 hours. The siRNA&#39;s used are shown in Table 3. A total of eight siRNAs targeting human α-globin were tested in this manner and a number of these were found to be effective, generating reductions in α-globin comparable to previously tested strategies. These results identify siRNA sequences which are able to retain a high level of efficacy in primary erythroid progenitor cells. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 siRNA sequences 
               
            
           
           
               
               
               
            
               
                 Name 
                 Sequence (5′ to 3′) 
                 SEQ ID NO: 
               
               
                   
               
            
           
           
               
            
               
                 Murine siRNA sequences 
               
            
           
           
               
               
               
            
               
                 si-α1 sense 
                 GGAGCUGAAGCCCUGGAAA 
                  1 
               
               
                 si-α1 antisense 
                 UUUCCAGGGCUUCAGCUCC 
                  2 
               
               
                 si-α2 sense 
                 AGGUCAAGGGUCACGGCAA 
                  3 
               
               
                 si-α2 antisense 
                 UUGCCGUGACCCUUGACCU 
                  4 
               
               
                 si-α3 sense 
                 CCGUGCUGACCUCCAAGUA 
                  5 
               
               
                 si-α3 antisense 
                 UACUUGGAGGUCAGCACGG 
                  6 
               
               
                 si-α4 sense 
                 CCUCUUGGUCUUUGAAUAA 
                  7 
               
               
                 si-α4 antisense 
                 UUAUUCAAAGACCAAGAGG 
                  8 
               
               
                   
               
            
           
           
               
            
               
                 Murine shRNA oligonucleotides 
               
            
           
           
               
               
               
            
               
                 pshα1 oligo 
                 GAT CCC CAT GGA GCT GAA GCC CTG GAA ATT CAA GAG 
                  9 
               
               
                 FWD 
                 ATT TCC AGG GCT TCA GCT CCA TTT TTT A 
                 10 
               
               
                 pshα1 oligo 
                 AGC TTA AAA AAT GGA GCT GAA GCC CTG GAA ATC TCT 
                 11 
               
               
                 REV 
                 TGA ATT TCC AGG GCT TCA GCT CCA TGG G 
                 12 
               
               
                 pshα2 oligo 
                 GAT CCC CCC AGG TCA AGG GTC ACG GCA ATT CAA GAG 
                 13 
               
               
                 FWD 
                 ATT GCC GTG ACC CTT GAC CTG GTT TTT A 
                 14 
               
               
                 pshα2 oligo 
                 AGC TTA AAA ACC AGG TCA AGG GTC ACG GCA ATC TCT 
                 15 
               
               
                 REV 
                 TGA ATT GCC GTG ACC CTT GAC CTG GGG G 
                 16 
               
               
                 pshα3 oligo 
                 GAT CCC CC CCG TGC TGA CCT CCA AGT ATT CAA GAG 
                 17 
               
               
                 FWD 
                 ATA CTT GGA GGT CAG CAC GGT GTT TTT A 
                 18 
               
               
                 pshα3 oligo 
                 AGC TTA AAA ACA CCG TGC TGA CCT CCA AGT ATC TCT 
                 19 
               
               
                 REV 
                 TGA ATA CTT GGA GGT CAG CAC GGT GGG G 
                 20 
               
               
                 pshα4 oligo 
                 GAT CCC CTA CCT CTT GGT CTT TGA ATA ATT CAA GAG 
                 21 
               
               
                 FWD 
                 ATT ATT CAA AGA CCA AGA GGT ATT TTT A 
                 22 
               
               
                 pshα4 oligo 
                 AGC TTA AAA ATA CCT CTT GGT CTT TGA ATA ATC TCT 
                 23 
               
               
                 REV 
                 TGA ATT ATT CAA AGA CCA AGA GGT AGG G 
                 24 
               
               
                   
               
            
           
           
               
            
               
                 Human siRNA sequences 
               
            
           
           
               
               
               
            
               
                 Hs_si-α1 sense 
                 CAGACUCAGAGAGAACCCA 
                 25 
               
               
                 Hs_si-α1 antisense 
                 UGGGUUCUCUCUGAGUCUG 
                 26 
               
               
                 Hs_si-α2 sense 
                 CCGACAAGACCAACGUCAA 
                 27 
               
               
                 Hs_si-α2 antisense 
                 UUGACGUUGGUCUUGUCGG 
                 28 
               
               
                 Hs_si-α3 sense 
                 CCGUGCUGACCUCCAAAUA 
                 29 
               
               
                 Hs_si-α3 antisense 
                 UAUUUGGAGGUCAGCACGG 
                 30 
               
               
                 Hs_si-α4 sense 
                 GGCCCUUCCUGGUCUUUGA 
                 31 
               
               
                 Hs_si-α4 antisense 
                 UCAAAGACCAGGAAGGGCC 
                 32 
               
               
                 Hs_si-α5 sense 
                 GACCUACUUCCCGCACUUC 
                 33 
               
               
                 Hs_si-α5 antisense 
                 GAAGUGCGGGAAGUAGGUC 
                 34 
               
               
                 Stealth si-α1 sense 
                 GCCCUGGAGAGGAUGUUCCUGUCCU 
                 35 
               
               
                 Stealth si-α1 antisense 
                 AGGACAGGAACAUCCUCUCCAGGGC 
                 36 
               
               
                 Stealth si-α2 sense 
                 CCACCAAGACCUACUUCCCGCACUU 
                 37 
               
               
                 Stealth si-α2 antisense 
                 AAGUGCGGGAAGUAGGUCUUGGUGG 
                 38 
               
               
                 Stealth si-α3 sense 
                 CCGUGCUGACCUCCAAAUACCGUUA 
                 39 
               
               
                 Stealth si-α3 antisense 
                 UAACGGUAUUUGGAGGUCAGCACGG 
                 40 
               
               
                   
               
            
           
         
       
     
     Example 3 
     Human siRNA Sequences 
     For identifying effective siRNAs targeting human α-globin (see Table 3), a total of eight siRNA sequences were tested in K562 cells. Qiagen design algorithms were utilized to identify four sequences targeting the major α2-globin gene. Two of four siRNAs selected in this fashion were homologous to murine si-α3 and si-α4, sequences previously demonstrated to be effective in MEL cells (see  FIGS. 2A  and B). However, the si-α4 human homolog binds a region in the 3′ UTR which differs between the human α1 and α2 globin genes. The equivalent region in the α1-globin gene was considered unsuitable for siRNA targeting as it failed to meet many of the recommended guidelines so the Hs-siα4 sequence only targets the α2-globin sequence. In addition to these pre-designed sequences, a fifth siRNA was designed against the 5′ region of Exon 2. A study (Sarakul et al. (2008) supra) has reported that siRNAs targeting this region reduced α-globin expression substantially in cultured normal erythroid precursor cells so the Hs-siα5 sequence was included for comparison. 
     It was also of interest to investigate the effects of varying siRNA composition on silencing ability so, in addition to the five siRNAs synthesized with standard chemistries, three additional Stealth (Trade Mark) siRNAs from Invitrogen were also tested. The Stealth (Trade Mark) siRNAs are blunt-ended 25 bp dsRNA molecules chemically modified to enhance stability and minimize off target effects. As these molecules differ slightly from standard siRNAs, parameters for predicting optimal sequences also varies slightly. Nevertheless, two of the three top Stealth (Trade Mark) sequences recommended by Invitrogen&#39;s algorithms matched target sites selected for standard siRNAs ( FIGS. 2A  and B). The Stealth St-siα3 matched a Qiagen sequence (si-α3) while St-siα2 overlapped with the previously published si-α5 sequence. 
     Example 4 
     siRNA-Mediated Reductions of α-Globin in Human Erythroleukemic Cells 
     α-Globin mRNA in K562s Treated with 1 μg siRNA 
     As the levels of α-globin expression in K562 cells are relatively low, a small quantity of siRNA was initially utilized in order to identify the most effective sequences. 1 g of siRNA was electroporated into 5×10 6  K562 cells and α-globin mRNA expression was determined at 24 and 48 hours by real-time PCR with β-actin as a loading control. 
     Three of the siRNA sequences tested (Hs-siα3, Hs-siα4 and Hs-siα5) had no significant effects on α-globin expression at 24 hours. Interestingly, the St-siα2 and St-siα3 Stealth sequences, which overlap with Hs-siα5 and Hs-siα3, respectively, generated significant reductions in α-globin expression compared to mock electroporated K562s. Both St-siα1 and St-siα3 reduced α-globin expression by ˜50% (P&lt;0.05) while St-siα2 generated a greater reduction of ˜78%±3% (P&lt;0.0005) at the mRNA level. However, the greatest knockdowns were observed in cells treated with 1 μg of Hs-siα1 and Hs-siα2. 1 μg of Hs-siα1 reduced α-globin expression by 90%±4% (P&lt;0.001) while Hs-siα2 generated reductions of 85%±6% (P&lt;0.005) [ FIG. 3 ]. 
     At 48 hours, cells treated with the Stealth sequences appeared to recover α-globin expression while standard siRNAs either retained or increased reductions. Cells treated with St-sial recovered fastest and were no longer significant at 48 hours. St-siα2 was also less active at 48 hours with only 57%+8% (P&lt;0.01) reduction while St-siα3 retained the same degree of efficacy with reductions of 50%+14% (P&lt;0.05). Hs-siα1 and Hs-siα2 both retained efficacies at 48 hours with reductions of 97%+3% (P&lt;0.0005) and 82% (P&lt;0.0001) respectively. Hs-siα4, which only targets α2-globin, was much more effective at 48 hours compared to 24 hours, reducing α-globin by 47%+9% (P&lt;0.05) compared to mock electroporated cells ( FIG. 3 ). 
     Example 5 
     α-Globin mRNA in K562s Treated with 500 ng siRNA 
     In order to better assess the efficacy of each siRNA sequence, smaller amounts of siRNA were delivered into K562s and effects on α-globin expression was again determined by real-time PCR. At 24 hours, this lower dose of siRNA was able to clearly indicate the most effective targets. While all siRNAs except Hs-siα3 and Hs-siα5 generated significant reductions in α-globin, three of these were relatively modest. An amount of 500 ng of Hs-siα4, St-siα1 and St-siα3 reduced α-globin expression by 25%±5%, 19%±7% and 29%±10% respectively, compared to mock electroporated controls (P&lt;0.05) [ FIG. 4 ]. The Hs-siα1, Hs-siα2 and St-siα2 sequences previously demonstrated to be most effective were markedly more so, compared to other targets, at this lower dose. St-siα2 reduced α-globin expression by 70%±9% (P&lt;0.01) while Hs-siα2 generated reductions of 80%±5% (P&lt;0.005). Hs-siα1 remained most effective, reducing α-globin mRNA by 90%±4% (P&lt;0.001) [ FIG. 4 ]. At 48 hours, reductions mediated by St-sial were no longer significant but St-siα3 appeared more effective than at 24 hours, reducing α-globin by 60%±12% (P&lt;0.05) compared to mock electroporated cells. There were no significant changes in all other sequences tested compared to results obtained at 24 hours ( FIG. 4 ). 
     Example 6 
     Development of Vector Delivery System 
     A mono-cistronic vector is developed for the tissue-specific expression of a short hairpin (sh)RNA from an erythroid-derived polymerase (pol) II promoter ( FIG. 5 ). α-Globin-specific shRNAs are generated in erythroid cells. A Lentiviral (LV) β-globin vector ( FIG. 5 ) is modified so that it expresses the shRNA sequence under an erythroid-specific pol II promoter. This means the shRNA sequence will only be produced in erythroid cells. The LV β-globin vector is modified by inserting α-globin-specific shRNA sequences within the 5′UTR or intron 2 of β-globin. This also lowers the concentration shRNA sequences required and, therefore, possible off-target effects. Additional toxicity issues may also be addressed by removing the HS2 and HS3 from β-globin LCR. 
     Example 7 
     Clinical and Animal Trials 
     A Lentiviral (LV) β-globin gene therapy vector (LVβ) is proposed to transfer a therapeutic β-globin transgene with high efficiency and fidelity to hematopoietic stem cells in combination with RNA-mediated silencing to reduce α-globin production. It is proposed that this approach will achieve a normal range of hemoglobin (Hb) A, i.e. 14-17 g/dL. Aspects covering the delivery of therapeutic β-globin are described in Cavazzana-Calvo et al. (2010),  Nature  467:318-322. 
     Hence, this trial is based on a complementary approach of limiting α-globin gene expression by RNAi in combination with a therapeutic β-globin gene expression approach. 
     The LV β-globin gene therapy vector expresses a variant of normal adult β A -globin (β A-T87Q ) which has a therapeutic efficiency in a β-thalassemic mouse model. The RNAi approach includes targeting α-globin mRNA at a site selected from the 5′-UTR, Exon1, Exon3, the 3′-UTR and a boundary region inbetween. In an embodiment, the RNAi approach targets or comprises a nucleotide sequence selected from SEQ ID NO:25, 26, 27, 28, 29, 30, 31 and 32. 
     Conveniently, the RNAi in the form of a short hairpin (sh)RNA is delivered by Lentiviral vectors (LV). In an example Lentilox 3.7 (LL3.7) is a third generation self-inactivating (SIN) LV system (Rubinson et al. (2003),  Nat. Genet  33:401-406). RNAi expression is mediated by type III RNA polymerase (Pol III) or type II (Pol II) transcription in the form of shRNAs. 
     Erythroid progenitor cells extracted from the bone marrow of β-thalassemic patients are cultured for 5 days in the presence of stem cell factor (SCF), dexamethasone (Dex) and erythropoietin (Epo), a combination of factors which promotes the in vitro expansion of erythroblasts. Following expansion, cells are transduced with viral vectors at a multiplicity of infection (MOI) of 1. Replacing the proliferation factors with high concentrations of Epo and insulin induces synchronous erythroid cell differentiation. Three days post viral transduction, GFP expression is used to monitor transduction efficiency and facilitate the isolation of transduced clones by fluorescent cell sorting. The efficacy of shRNA LV vectors is determined by qRT-PCR. T RNAi LV vectors balance globin synthesis to near wild-type (WT) levels. 
     Restriction of RNAi delivery in a time and tissue-specific manner is critical to minimize potentially deleterious off target effects. Pol III- or Pol II-directed intronic RNAi expression systems is used. In this strategy, an RNAi is encoded within an intron of a gene that is specifically expressed in the cell type of interest. Following Pol III or Pol II RNA processing, some of the intron-derived dsRNA fragments can form mature miRNAs thereby silencing the target gene, while the exons are ligated together to form mature mRNA for protein synthesis. 
     For therapy, the synthesis of α- and β-globin proteins must be balanced. The use of RNAi to yield a moderate reduction in α-globin in erythroid cells requires a highly specific and lineage-restricted gene-silencing vector. An erythroid-specific expression system is the LV (β-globin gene therapy vector. 
     An example of a LV system comprises the 5′-LTR, cPPT, RRE, the β-globin gene and one or more nucleic acid molecules encoding chicken globin hypersensitive sites 2, 3 and/or 4 (HS 2, 3, 4, respectively). 
     It is proposed to modify LVβ gene therapy vectors by inserting α-globin-specific RNAi sequences into the intronic region of the β-globin gene. The LVβ vector is based on the design detailed above and proven successful for the correction of SCD and β-thalassemic mice but with the incorporation of a number of modifications to reduce the risk of genotoxicity, including i) utilizing a self-inactivating (SIN) LV vector containing deletions in the LTRs, with complete removal of both viral enhancer and promoter region, ii) use of enhancer/promoter specific for the erythroid lineage, and iii) use of chromatin insulators from the chicken globin hypersensitive site 2, 3 and/or 4 (cHS2-4). Such insulator sites are well characterized in mammalian cells. The cHS4 enhancer blocking activity, for example, is most effective as a doublet and this is the configuration used in the LVβ vector currently under evaluation in phase I/II clinical studies. 
     α-Globin-specific RNAi sequences are inserted within intron II of the β-globin gene, thereby limiting the expression of α-globin in erythroid cells while the β-globin exons are spliced together to form mature mRNA for protein synthesis. 
     A clinically approved LVβ vector is modified to enable intronic delivery of α-globin-specific RNAi molecules. The level of silencing produced by the α-globin-specific shRNA is sequence-dependent, which means that sequences of variable activity can be used to fine tune α-globin levels ( FIG. 6 ). RNAi sequences are inserted into one or more of three locations in the second intron of the β-globin gene encoded by the LVβ vector: 1) positioned near the branch point (BP), 2) inserted into the 375 bp deletion breakpoint, and 3) near the splice donor site. 
     Limited RNAi-mediated reduction of α-globin (by 25-50%) and β-globin transgene expression is proposed to synergise restoration of the α:β globin ratio to equal levels and restore the Hb deficit reported in several β-globin gene therapy studies. The therapeutic potential of LVβ-RNAi vectors is evaluated in two β-thalassemic transplantation models. 
     Model 1: LVβ and LVβ-RNAi vectors are evaluated in intermediate β-thalassemic mice (β-KO +/− ). BM cells are isolated from β-KO +/−  mice, transduced and transplanted into lethally irradiated β-thalassemic mice. Model 2: LVβ and LVβ-RNAi vectors are also evaluated in severe β-thalassemic (β-KO −*− ) mice. Fetal liver (FL) cells are isolated from 13-KO −/−  mice at E13.5, transduced and transplanted into lethally irradiated β-thalassemic mice. 
     BM and FL cells are lineage depleted using the Lineage Cell Depletion Kit (Miltenyi). This procedure generally yields lineage negative (Lin − ) stem cells at purities greater than 80%. Following in vitro stimulation, cells are transferred to retronectin-coated plates and transduced overnight with viral vectors. Cells are then harvested and 1×10 6  cells injected i.v. into β-KO +/−  recipient mice after 1100 cGY of total body irradiation. As transplantation controls, up to 10 mice per control group are transplanted with mock-transduced β-KO +/− , β-KO −/−  and normal cells. Additional controls include cells transduced with LV vectors with and without an irrelevant shRNA targeting sequence. 
     Peripheral blood is collected at several time points following BM/FL transplantation and globin synthesis assessed by qRT-PCR, primer extension and HPLC. Phenotypic correction is determined by FBE and ROS measurements. Recipient mice are euthanized 1-6 months following transplantation. BM, spleen, liver, and heart are harvested and subjected to multiple analyses. Recipient mice of mock-transduced β-KO −/−  FL cells are anticipated to show moribund features by day 30 due to profound anemia. The degree of phenotypic correction is determined by measuring erythroblast (Ter-119 + /CD71 + ) populations in the BM and spleen of treated mice. Prussian blue staining will be used to assess the level of iron deposition, which is an indirect measure of ineffective erythropoiesis. Experiments employ statistically significant numbers of animals and the two-tailed Student&#39;s t test will be used to determine statistical significance. 
     The effects of LVβ-RNAi vectors containing human α-globin-specific RNAi sequences are evaluated. Peripheral blood samples are drawn from healthy donors and from β-thalassemia patients. CD34+ cells are isolated by immunomagnetic cell separation using CD34 MicroBead kit (Miltenyi). Early erythroid progenitors are expanded, followed by synchronous erythroid differentiation. LVβ-RNAi vectors are introduced into cultured human erythroid progenitors and evaluated on days 1-5 following the induction of differentiation. LVβ and LVβ-RNAi gene therapy in two groups of 0-thalassemia patients (HbE and IVS1-110 genotypes). HbE is common in Southeast Asia and causes 40-70% reduction of β-globin synthesis, whereas IVS1-110 is frequently observed in southern Europe resulting in 90% reduction in β-globin synthesis. α/β-Globin synthesis is assessed by qRT-PCR and by [ 3 H] leucine incorporation into globin chains. At least 5 HbE and 5 IVS1-110 patients are examined. As the clinical severity of β-thalassemia is influenced by the presence of α-thalassemia or HbF production, it is necessary to confirm the presence or absence of genetic modifiers of disease. This allows monitoring of balanced α-/non-α-globin synthesis in the β-thalassemia patients. 
     Those skilled in the art will appreciate that aspects described herein are susceptible to variations and modifications other than those specifically taught. It is to be understood that these aspects includes all such variations and modifications. Aspects disclosed herein include all of the steps, features, compositions and compounds, individually or collectively, and any and all combinations of any two or more of the steps or features. 
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