Viral vectors

1. A herpes virus which lacks a functional ICP34.5 encoding gene and which comprises: (i) a heterologous gene encoding a prodrug converting enzyme; and (ii) a heterologous gene encoding a protein capable of causing cell to cell fusion.

2. A virus according to claim 1 wherein said prodrug converting enzyme is a cytosine deaminase.

3. A virus according to claim 1 wherein said protein capable of causing cell to cell fusion is a gibbon ape leukaemia fusogenic glycoprotein.

4. A virus according to claim 1 , which further comprises a heterologous gene encoding an immunomodulatory protein.

5. A virus according to claim 4 wherein the immunomodulatory protein is GM-CSF, TNF-α or CD40L.

6. A virus according to claim 1 which comprises one or more further heterologous genes capable of enhancing the anti-tumour therapeutic effect of the virus.

7. A virus according to claim 1 which further lacks a functional gene encoding ICP47.

8. A virus according to claim 1 which further lacks a functional gene encoding ICP6, glycoprotein H and/or thymidine kinase.

9. A virus according to claim 1 which further lacks a gene encoding a functional protein capable of inhibiting dendritic cell function.

10. A virus according to claim 9 in which said gene encoding a functional protein capable of inhibiting dendritic cell function is UL43 or vhs.

11. A virus according to claim 1 which is a strain of herpes simplex virus 1 or 2.

12. A virus according to claim 1 which is a non-laboratory virus strain.

13. A pharmaceutical composition comprising as active ingredient a virus according to claim 1 and a pharmaceutically acceptable carrier or diluent.

14. A method of treating a tumour in an individual in need thereof by administering to said individual an effective amount of the virus according to claim 1 .

15. A method according to claim 14 wherein said virus is administered by direct intra-tumoral inoculation.