A method of treating a tumor in a subject comprising administering to the subject suffering from the said tumor in a therapeutically effective amount (a) an antibody fusion protein which specifically recognizes (i) the VA, HN or F surface antigen of the New Castle Disease Virus (NDV) and (ii) a surface molecule of a tumor-unspecific T cell or a surface molecule of a dendritic cell, (b) a polynucleotide encoding said antibody fusion protein, (c) a tumor-unspecific T cell bound by the antibody fusion protein, or (d) a dendritic cell bound by the antibody fusion protein.