Recombinant herpesvirus of turkeys and uses thereof

#The ability to isolate DNA and clone such isolated DNA into bacterial plasmids has greatly expanded the approaches available to make viral vaccines. The methods used to make the present invention involve modifying cloned DNA sequences from various viral pathogens of animals, by insertions, deletions, single or multiple base changes, and subsequent insertions of these modified sequences into the genome of the virus. One utility of the addition of a foreign sequence is achieved when the foreign sequence encodes a foreign protein that is expressed during viral infection of the animal. The resulting live virus may then be used in a vaccine to elicit an immune response in a host animal and provide protection to the animal against disease. A virus with these characteristics is referred to as a viral vector, because it becomes a living vector that will carry and express the foreign protein in the host animal. In effect it becomes an elaborate delivery system for the foreign protein(s).

#More specifically, the present invention relates to the use of herpesvirus of turkeys (HVT) as a viral vector for vaccination of birds against disease. The group of herpesviruses comprise various pathogenic agents that infect and cause disease in a number of target species: swine, cattle, chickens, horses, dogs, cats, etc. Each herpesvirus is specific for its host species, but they are all related in the structure of their genomes, their mode of replication, and to some extent in the pathology they cause in the host animal and in the mechanism of the host immune response to the virus infection.

#The application of recombinant DNA techniques to animal viruses has a relatively recent history. The first viruses to be engineered have been those with the smallest genomes. In the case of the papovaviruses, because these viruses are so small and cannot accommodate much extra DNA, their use in genetic engineering has been as defective replicons. Foreign gene expression from these viruses requires a wild-type helper virus and is limited to cell culture systems. For adenoviruses, there is a small amount of nonessential DNA that can be replaced by foreign sequences. The only foreign DNA that seems to have been expressed in adenoviruses are the T-antigen genes from papovaviruses (Mansour, et al., Proc. Natl. Acad. Sci. US, 1985; Thummel, et al., Cell, 1983; Scolnick, et al., Cell, 1981; Thummel, et al., Cell, 1981), and the herpes simplex virus (HSV) thymidine kinase gene (Haj-Ahmed and Graham, J. of Virology, 1986). These publications do not identify the nonessential regions in HVT wherein foreign DNA may be inserted, nor do they teach how to achieve the expression of foreign genes in HVT, e.g., which promoter sequence and termination sequence to use.

#FIGS. 1A, 1B, and 1C show details of HVT Construction and Map Data.

#FIG. 1A shows BamHI restriction fragment map of the HVT genome. Fragments are numbered in order of decreasing size; letters refer to small fragments whose comparative size has not been determined.

#FIG. 1B shows BamHI #16 fragment of the HVT genome showing location of .beta.-galactosidase gene insertion in S-HVT-001.

#The present invention provides a recombinant herpesvirus of turkeys (HVT) comprising a foreign DNA sequence inserted into a non-essential site in the HVT genome. The foreign DNA sequence is capable of being expressed in a host cell infected with the recombinant HVT and its expression is under control of a promoter located upstream of the foreign DNA sequence.

#For purposes of this invention "a non-essential site in the HVT genome" means a region in the HVT genome which is not necessary for the viral infection or replication.

#For purposes of this invention, "a foreign DNA sequence" means DNA which codes for a gene or part thereof that does not naturally in the HVT genome.