The present invention involves a recombinant virus which comprises at least one foreign nucleic acid inserted within a non-essential region of the viral genome of a virus, wherein each such foreign nucleic acid encodes a protein. The protein which is encoded is selected from the groups consisting of a feline CD28 protein or an immunogenic portion thereof, a feline cD80 protein or an immunogenic portion thereof, a feline CD86 protein or an immunogenic portion thereof, or a feline CTLA-4 protein or an immunogenic portion thereof. The protein is capable of being expressed when the recombinant virus is introduced into an appropiate host. The present invention also involves a recombinant virus further comprising a foreign nucleic acid encoding an immunogen derived from a pathogen. The present invention also comprises recombinant viruses which are capable of enhancing an immune response in a feline. The present invention also comprises recombinant viruses which are capable of suppressing an immune respons in a feline.