Abstract: The invention provides a recombinant viral particle for delivering a nucleic acid to mammalian cells, the particle comprising an MLV-env protein that binds to an MLV-env receptor expressed on the surface of a target cell so as to cause infection thereof, and a surface-exposed EGF that binds to an EGF receptor generally not expressed on the surface of the target cell, but expressed on non-target cells that also express the MLV-env receptor, such that binding of the viral particle to the EGF receptor via EGF inhibits infection of the non-target cell by the viral particle.

Abstract: A viral vector for the integration and expression of at least one heterologous gene in fowl pest cells consists wholly or in part of the proviral genome of fowl pest erythroblastosis or of a related virus in which said heterologous gene(s) replace(s) the v-erbA gene and/or the v-erB gene. Said gene(s) is(are) controlled either by an LTR promoter of the same virus, in which case the heterologous gene(s); mimics(s) the gene(s) it(they) replace, or by a heterologous promoter, in which case the additional att sequence is situated upstream of said heterologous promoter.