There currently exists a need for novel, immunogenic carrier proteins for new anti-bacterial polysaccharide (PS) conjugate vaccines, as well as a vaccine that is protective against Epstein-Barr virus (EBV) infection. The latter vaccine would have a potential global impact on the incidence of infectious mononucleosis, Hodgkin's and non- Hodgkin's lymphoma, nasopharyngeal carcinoma, and lymphoproliferative syndrome. The EBV protein, gp350, is the major target for EBV neutralizing antibody, as well as a ligand for CD21, a potent co-activator of the B cell antigen receptor. CD21 is also expressed by follicular dendritic cells where it mediates antigen trapping, important for induction of the germinal center reaction. Thus, gp350 in the form of a multimeric gp350-PS conjugate, has the potential to serve as both a potent carrier protein for PS-specific conjugate vaccines as well as an antibody-mediated vaccine for EBV. In preliminary studies we have: 1) expressed and purified a recombinant glycosylated N-terminal 72kDa fragment of the gp350 molecule, 2) conjugated multiple copies of gp350 to pneumococcal capsular polysaccharide, serotype 14 (PPS14) [PPS14-gp350], 3) demonstrated the ability of PPS14-gp350 to specifically bind to CD21 expressed on rhesus and human, but not murine, B cells, and 4) induced boosted plasma IgG anti-PPS14 and IgG anti-gp350 antibodies in young adult rhesus monkeys following i.m. immunization with as little as 0.05 mg of PPS14- gp350 adsorbed on alum. The goal of this proposal is to establish a proof-of-principle in non-human primates, for using gp350 clinically, as a combined novel carrier protein for PS conjugate vaccines and as a protective, antibody-based vaccine for EBV. In this proposal we will utilize young adult rhesus monkeys to: 1) directly compare the ability of alum-adsorbed unconjugated or PPS14-conjugated monomeric or unconjugated dimeric gp350 to elicit high titer and high affinity, EBV-neutralizing anti-gp350 antibody and gp350-specific T cell priming, and 2) directly compare the ability of diphtheria toxoid (DT) [an established carrier protein for conjugate vaccines], conjugated to PPS14, with PPS14- conjugated monomeric gp350 to elicit high titer and high affinity, protective anti-PPS14 antibody, and to determine the role of CD21 binding in the adjuvanticity of gp350 as a carrier protein for PPS14. These pre-clinical studies will form the basis for progressing directly to human clinical trials. Currently, there is no prophylactic vaccine for the Epstein-Barr virus (EBV), which is implicated in the pathogenesis of infectious mononucleosis, nasopharyngeal carcinoma, Burkitt lymphoma, non-Hodgkin's lymphoma, and lymphoproliferative syndrome in immunosuppressed patients. Further, there is also a need for novel protein carriers for polysaccharide conjugate vaccines, which elicit antibody-mediated protection against extracellular bacteria, due to the phenomenon of cross-inhibition. The proposed studies, using the rhesus macaque as an in vivo model, will determine the feasibility of using the EBV envelope protein, gp350, an intrinsically immunostimulatory molecule, as a combined novel carrier for polysaccharide-based conjugate vaccines and as a target antigen for a potent antibody-mediated prophylactic vaccine against EBV infection.
| Cui, Xinle; Cao, Zhouhong; Sen, Goutam et al. (2013) A novel tetrameric gp350 1-470 as a potential Epstein-Barr virus vaccine. Vaccine 31:3039-45 |
