The present invention generally relates to the field of herpesviruses and herpesvirus proteins that can be used for the production of antibodies or therapeutic agents, such as vaccines. More specifically, the present invention relates to a modified herpesvirus glycoprotein B that comprises one or more mutations at defined positions in the primary structure of the protein which retain a stable prefusion conformation which is highly advantageous for the production of antibodies or therapeutic agents, such as vaccines. The invention further relates to nucleic acid molecules which encode such a modified herpesvirus glycoprotein B. The invention further provides methods for producing antibodies or therapeutic agents, such as vaccines, which make use of the modified herpesvirus glycoprotein B or a nucleic acid molecule encoding it. Kits comprising the modified herpesvirus glycoprotein B are provided as well. Finally, the invention also relates to the use of the modified herpesvirus glycoprotein B or a nucleic acid molecule encoding same for drug screening.