Identification of the critical attribute(s) of EBV gp350 antigen required for elicitation of a neutralizing antibody response in vivo

Vaccine prophylaxis with EBV glycoprotein 350 (gp350) subunit plus adjuvant has been demonstrated clinically to protect individuals against infectious mononucleosis (IM), but the specifications of the antigen required to elicit this protection has remained largely theoretical. Previous studies have shown that antibodies to gp350 comprise the principle component of EBV-neutralizing sera. Further, a murine monoclonal antibody against gp350 (clone 72A1) is able to prevent infection by the virus both in vitro and in vivo. In the present study, we identify the 72A1 epitope on recombinant gp350 antigen as the site required for binding to CD21 on human B cells. We also identify the need for conformational-dependence of the antigen to generate EBV-neutralizing antibodies in vivo. Further, we have characterized the glycosylation status and antigenicity profiles of both native and denatured CHO-produced soluble gp350 as well as non-glycosylated protein produced in Escherichia coli. Collectively our in vitro and in vivo data demonstrate the requirement for a conformationally accessible 72A1 epitope on gp350 to elicit EBV-neutralizing responses, and establish this as a critical attribute of this vaccine antigen. These data provide direction for commercial vaccine development, as the absence of this epitope on either E. coli-expressed or denatured gp350, may limit production and purification options for the antigen.