Recombinant retroviruses

A pharmaceutical composition comprising:

• a) a producer cell which produces a replication defective recombinant retrovirus which infects a human host cell, said recombinant retrovirus comprising a recombinant gene operatively linked to a promoter, said gene encoding a protein which is not normally expressed in said human host cells and which converts a purine-based or pyrimidine-based drug to a compound that is toxic to said human host cell;
• and
• b) a pharmaceutically acceptable carrier.

A replication defective recombinant retrovirus which infects a human host cell, said recombinant retrovirus comprising a recombinant gene operably linked to a promoter, said gene encoding a protein which is not normally expressed in said host cell, and which converts a first agent in said host cell to a second agent that is toxic to said host cell.

A producer cell which produces a replication defective recombinant retrovirus which infects a human host cell, said recombinant retrovirus comprising a recombinant gene operably linked to a promoter, said gene encoding a protein not normally expressed in said human cell, and which converts an agent in said human host cell to a second agent that is toxic to said human host cell.

The producer cell of claiim 69, wherein said recombinant retrovirus further comprises a second promoter that is an event-specific promoter operably linked to the gene encoding said protein, and wherein expression of said protein is regulated by said event-specific promoter and said tissue-specific promoter.