Abstract: Disclosed is a chimaeric polypeptide comprising: a binding portion having specific binding affinity for a eukaryotic target cell surface component and an effector portion comprising an amino acid sequence capable of exerting a biological effect; whereby binding of the polypeptide to the cell surface component induces internalization of at least the effector portion so as to allow the amino acid sequence to exert its biological effect, together with a vaccine comprising the chimaeric polypeptide of the invention, and a method of modulating the immune response of a human or animal subject.