Abstract: The invention provides retroviral vectors which can be used for directing gene delivery to a specific sub-population of mammalian cells. The vectors comprise chimeric targeting proteins which specifically alter the host range of the vector. The chimeric targeting proteins contain a ligand moiety which is capable of binding to receptors present on target cells, and an uptake moiety which is capable of promoting entry of the vector into the target cell. The ligand moiety is derived from a cytokine that acts upon the target cells of interest, and the uptake moiety is derived from a retroviral envelope protein.