Non-primate lentivirus retroviral vectors

A retroviral vector from a non-primate lentivirus, preferably equine infectious anaemia virus (EIAV), has at least one accessory gene deleted, preferably tat , dUTPase, S2 or env. More preferably tat is deleted but the vector includes leader sequences between the 5' LTR and ATG of gag . A minimal vector system for the production of the retroviral vectors further comprises a packaging cell containing a gag/pol gene from a non-primate lentivirus and an env gene. Vectors in three plasmids may be introduced into cells by co-transfection. Also described is a retroviral vector in which one or more nucleotides of the region downstream of nucleotide 350 in the coding sequence of the gag gene is deleted. A hybrid vector comprising a non-primate lentivirus and a pox virus is also described.