The present invention provides a recombinant influenza virus vector comprising an NS gene encoding a truncated NS1 protein of at least 73 and up to 122 amino acids of the N-terminus of the respective wild type NS 1 protein, wherein said vector replicates in IFN-sensitive tumor cells and does not replicate in normal, non-tumor cells, and expresses a heterologous immunostimulatory polypetide. The invention further provides a pharmaceutical composition containing said influenza virus vector, its use for the treatment of cancer patients and methods for producing said influenza virus vaccine.
