Viral vector

1. A lentiviral vector genome for producing a lentiviral vector particle, the lentiviral vector genome comprising: (i) an open reading frame (ORF) upstream of a promoter, wherein the promoter controls the expression of at least one downstream nucleotide sequence of interest (NOI), and (ii) a packaging signal;

wherein the ORF is a heterologous sequence;

wherein the ORF is a second NOI, or wherein the ORF encodes a reporter, a selectable marker, or a modulator;

wherein the ORE is operably linked to an upstream lentiviral long terminal repeat (LTR);

wherein the lentiviral vector genome is self-inactivating (SIN); and

wherein nucleic acid sequences encoding functional Rev and functional Rev Response Element (RRE) are absent from the lentiviral vector genome; and

wherein the lentiviral vector genome lacks a non-lentiviral 5′ LTR.

2. The lentiviral vector genome of claim 1 , wherein the ORF encodes the reporter or the selectable marker.

3. The lentiviral vector genome of claim 1 , wherein the ORF encodes the modulator.

4. The lentiviral vector genome according to claim 3 , wherein the modulator is selected from the group consisting of a tetracycline repressor and a tetracycline-controlled transactivator.

5. The lentiviral vector genome according to claim 4 , wherein the tetracycline repressor is codon optimised for expression in a mammalian cell.

6. The lentiviral vector genome according to claim 4 , wherein the coding sequence for the tetracycline repressor is linked to a nuclear localization signal.

7. The lentiviral vector genome according to claim 1 , wherein the at least one downstream NOI is operably linked to a tetracycline operator.

8. The lentiviral vector genome according to claim 1 , further comprising a tetracycline repressor coding sequence downstream of the promoter.

9. The lentiviral vector genome according to claim 1 , wherein the vector genome is a non-primate lentivirus vector genome.

10. The lentiviral vector genome according to claim 1 , wherein the vector genome is selected from the group consisting of HIV-1, HIV-2, SIV, FIV, BIV, EIAV, CEV, CAEV, MVV, and visna lentivirus vector genomes.

11. The lentiviral vector genome according to claim 1 , wherein the vector genome comprises a central polypurine tract (cPPT) sequence.

12. The lentiviral vector genome according to claim 1 , wherein the vector genome comprises a post-transcriptional regulatory element or a translational element.

13. The lentiviral vector genome according to claim 1 , wherein the vector genome comprises a gag packaging signal having ATG motifs, and wherein the ATG motifs are ATTG motifs.

14. The lentiviral vector genome according to claim 1 , wherein the vector genome comprises R regions having substantially the same distance between the R regions as that in a wild type lentiviral vector genome.

15. The lentiviral vector genome according to claim 1 , wherein the vector genome comprises a 3′ U3 region from a viral promoter or a eukaryotic promoter.

16. The lentiviral vector genome according to claim 15 , wherein the viral promoter or the eukaryotic promoter is a wild type promoter.

17. The lentiviral vector genome according to claim 15 , wherein the viral promoter is an EIAV or an MLV U3 region.

18. The lentiviral vector genome according to claim 1 , wherein the vector genome is bi- or tricistronic.

19. A lentiviral vector particle comprising the lentiviral vector genome of claim 1 .

20. An isolated cell transduced with the lentiviral vector particle according to claim 19 .

21. A pharmaceutical composition comprising the lentiviral vector particle of claim 19 , together with a pharmaceutically acceptable carrier or a pharmaceutical diluent.

22. A pharmaceutical composition comprising the lentiviral vector genome of claim 1 , together with a pharmaceutically acceptable carrier or a pharmaceutical diluent.

23. The lentiviral vector genome of claim 1 , wherein a nucleic acid sequence encoding at least one of auxiliary genes vpr, vif, tat and nef is removed from the genome or disrupted, such that the at least one auxiliary gene is incapable of encoding a functional auxiliary protein.

24. A set of DNA constructs comprising the vector genome according to claim 1 , and a DNA construct comprising a nucleic acid sequence encoding Gag and Pol, operably linked to a promoter.

25. The set of DNA constructs according to claim 24 , further comprising a DNA construct comprising a nucleic acid sequence encoding Env, operably linked to a promoter.

26. An isolated cell transduced with the set of DNA constructs according to claim 25 .

27. A lentiviral vector production system for producing a lentiviral vector particle, which system comprises the lentiviral vector genome of claim 1 , a nucleic acid sequence encoding Gag and Pol, and a nucleic acid sequence encoding Env, wherein the nucleic acid sequence encoding Gag and Pol, and the nucleic acid sequence encoding Env are operably linked to one or more internal regulatory elements, wherein a nucleic acid sequence encoding functional Rev is absent from the lentiviral vector production system, and wherein the lentiviral vector production system lacks a non-lentiviral 5′ LTR.

28. The lentiviral vector production system according to claim 27 , wherein the system comprises three DNA constructs, (i) the vector genome, (ii) the nucleic acid sequence encoding Gag and Pol, and (iii) the nucleic acid sequence encoding Env.

29. The lentiviral vector production system of claim 27 , wherein the nucleic acid sequence encoding Gag and Pol is codon optimised.

30. The lentiviral vector production system of claim 27 , wherein a nucleic acid sequence encoding at least one of auxiliary genes vpr, vif, tat and nef is removed from the system or disrupted, such that the at least one auxiliary gene is incapable of encoding a functional auxiliary protein.

31. A process for preparing a lentiviral vector particle comprising introducing the lentiviral vector production system according to claim 27 into a host cell and obtaining the lentiviral vector particle.