Target cell specificity of delivery vectors is provided by incorporation of a target cell specific binding domain by the use of any binding domain, which binds specifically to a binding site on the target cell. The binding site may be endogenous to the target cell, provided by engineering the target cell, or a suitable binding site may be associated with the target cell. Target cell may also be associated with a CVR polypeptide to provide specificity for the delivery vector. The association of the CVR polypeptide confers target cell specificity for a second virus host cell range, which specificity differs from the viral host cell range of the endogeneous target cell or animal host cell viral receptors. The CVR polypeptide may thus comprise a chimeric virus binding site which binds a second virus env binding domain specific for a second virus host cell range, selected from at least one of the group consisting of amphotropic, polytropic, xenotropic, ecotropic and tissue specific.