Attenuated oncolytic paramyxoviruses encoding avian cytokines

The invention refers to a recombinant oncolytic RNA Newcastle Disease Virus for the treatment of a proliferative disease, comprising at least one transgene coding for an avian cytokine, wherein the recombinant oncolytic RNA Newcastle Disease Virus is obtainable from a velogenic or mesogenic oncolytic RNA Newcastle Disease Virus. Virus-mediated expression of the cytokine in the natural host cells leads to a reduced pathogenicity of the virus for avian species. Furthermore the virus genome can encode binding proteins, prodrug-converting enzymes or/and proteases. The selective expression of these molecules in virus-infected tumor cells increases the anti-tumor effect of the virus.