Thymidine kinase deletion mutants of bovine herpesvirus-1, vaccines against infectious bovine rhinotracheitis containing same and methods for the production and use of same

A modified live-virus vaccine for infectious bovine rhinotracheitis comprising:

• (1) a pharmaceutically effective amount of an infectious bovine rhinotracheitis virus which fails to produce any TK as a result of a deletion in the tk gene, produced by a process comprising:
• (a) constructing a hybrid plasmid comprising a cloning vector and a DNA fragment of IBRV containing substantially all of the IBRV tk gene;
• (b) co-transfecting, in tk.sup.+ host cells, the hybrid plasmid of step (a) with infectious DNA from a tk.sup.- IBRV mutagen-induced mutant;
• (c) selecting, in tk.sup.- host cells, for tk.sup.+ IBRV from the virus produced in step (b);
• (d) deleting DNA sequences from the hybrid plasmid of step (a) such that less than substantially all of the IBRV tk gene is present;
• (e) co-transfecting, in tk.sup.+ host cells, IBRV tk.sup.+ DNA derived from the tk.sup.+ IBRV obtained in step (c) with the resulting tk.sup.- hybrid plasmid of step (d);
• and
• (f) selecting, in tk.sup.- host cells, for tk.sup.- IBRV from the virus produced in step (e) so as to produce tk.sup.- IBRV mutants which fail to produce any functional TK as a result of a deletion in the tk gene, and
• (2) a pharmaceutically acceptable carrier or diluent.

A method of immunizing an animal against infectious bovine rhinotracheitis comprising administering, to an animal, a pharmaceutically effective amount of an infectious bovine rhinotracheitis virus which fails to produce any functional TK as a result of a deletion in the tk gene, produced by a process comprising:

• (1) Constructing a hybrid plasmid comprising a cloning vector and a DNA fragment of IBRV containing substantially all of the IBRV tk gene;
• (2) Co-transfecting, in tk.sup.+ host cells, the hybrid plasmid of step (1) with infectious DNA from a tk.sup.- IBRV mutagen-induced mutant;
• (3) Selecting, in tk.sup.- host cells, for tk.sup.+ IBRV from the virus produced in step (2);
• (4) Deleting DNA sequences from the hybrid plasmid of step (1) such that less than substantially all of the IBRV tk gene is present;
• (5) Co-transfecting, in tk.sup.+ host cells, IBRV tk.sup.+ DNA derived from the tk.sup.+ IBRV obtained in step (3) with the resulting tk.sup.- hybrid plasmid of step (4);
• and
• (6) Selecting, in tk.sup.- host cells, for tk.sup.- IBRV from the virus produced in step (5) so as to produce tk.sup.- IBRV mutants which fail to produce any functional TK as a result of a deletion in the tk gene.