Application of molecular genetics to the design of live herpes simplex virus vaccines

In principle, several avenues for attenuation of herpes simplex viruses (HSV) are now available. These include intermixing of HSV-1 and HSV-2 genes by recombination, altering the regulation of gene expression and the deletion of viral genes not required for replication of the virus in permissive cells in culture. Results of analyses of HSV-1 x HSV-2 recombinants and of mutants containing a deletion in a gene expressed early in infection showed a loss of virulence when infected by intracerebral route into adult Balb/c mice. In addition, immunization of the mice by intracerebral route with relatively low doses of virus protected the mice from challenge with high doses (3000 LD50) of virulent virus. The application of genetic engineering to the construction of live vaccines is discussed.