It is intended to provide a recombinant herpesvirus； a process for producing the same； and a pharmacological composition comprising a recombinant herpes virus. Further, it is intended to provide a vector comprising a herpesvirus genome gene and a BAC vector sequence； a cell comprising such a vector； a fragment capable of homologous recombination with herpesvirus genome； and a nucleic acid cassette comprising a BAC vector sequence. The objects have been attained by the development of a process for producing a recombinant herpesvirus in which use is made of a BAC vector sequence.
