Vaccinia virus has been developed into a eukaryotic expression vector. A chimeric gene is formed by ligating vaccinia virus transcriptional regulatory signals to a foreign protein coding sequence. Homologous recombination is used to insert the chimeric gene into a non-essential region of the vaccinia virus genome. During the past year, we have used stronger late promoters to increase the level of expression and develop a new dominant selection system, based on increase the level of expression and develop a new dominant selection system, based on co-expression of the Escherichia coli gpt gene, for isolation of recombinant viruses. The respiratory syncytial virus glycoprotein B gene was employed to construct hybrid genes in order to bring peptide sequences to the cell surface and enhance immunogenicity. The athymic immunodeficient nude mouse was developed as a model for progressive infection with vaccinia virus. We found that the pathogenicity of vaccinia virus for nude mice was abrogated by expression of the lymphokine IL-2. Continued work using a recombinant vaccinia virus that expresses the herpes simplex virus type 1 (HSV-1) glycoprotein D gene for vaccination of mice, established that protective immunity against lethal and latent infections lasted for more than a years, that immunity could be boosted with a second vaccination, but that pre-existing immunity to vaccinia virus was detrimental. Protective immunity to HSV-1 was also induced with a recombinant vaccinia virus that expressed the gB genes. Polyvalent expression vectors were constructed that protected mice against both HSV-1 and influenza virus. In addition, recombinant vaccinia virus was used to determine influenza, HSV-1, and malaria targets of cytotoxic T cells.
