US Patent 6995009 Packaging cell

A virus-producing cell sustaining the ability to produce viruses at high titer is successfully constructed by expressing the virus structural gene under the regulation of EF1α promoter. In this virus-producing cell, the virus structural gene is ligated to a selection marker gene via IRES and domains other than the protein coding domain are eliminated from the DNA encoding virus structural proteins. Thus, reduction of the titer due to cell passages can be prevented and emergence of wild type viruses caused by unfavorable recombination of the virus genome can be inhibited.