The present invention provides recombinant adenoviral vectors, immunogenic compositions thereof and their uses in medicine. In particular, the present invention provides an adenoviral vector comprising the genome of an adenovirus other than AdHu5 and AdY25, wherein the genome of the adenovirus has been modified such that the vector lacks the native E4 locus of the adenovirus and comprises heterologous E4Orf1, E4Orf2 and E4Orf3 coding regions from AdY25.