The present invention relates in general to the field of TNF ligand family members. In more detail the present invention relates to polypeptides comprising at least three components A, each of which comprises the sequence of a TNF homology domain (THD) of a TNF ligand family member, or a functional derivative thereof, and comprising at least one component B consisting of a VL region and a VH region linked directly to each other with a linker sequence L which has a length of <;12 amino acids. Furthermore, the present invention also relates to nucleic acids encoding such polypeptides and pharmaceutical compositions thereof.