This application provides a method to establish and construct cell lines expressing pathogens without destruction of the host cells. The invention allows for the formation of cell lines for the purpose of continuous expression, release, and harvesting of the pathogen and maintain the consistency of the final biological pro duct. Although the invention is intended for pathogen antigen expression, the invention allows for the production of any antigen by the described methods. The establishment of a chronically infected celline can be used for reagent, diagnostic, quantification, or vaccine purposes. We have used the procedure to select for a host cell line that naturally adapts to HIV-1 replication without affecting the host cell's ability to survive. This allowed for the establishment of a chronic HIV-1 expressing cell line that continuously expresses HIV-1 particles.