| Antibody dependent enhancement (ADE) of dengue viral (DENY) infectivity poses a significant challenge to the development of broadly effective vaccines for the prevention of dengue fever (DF), dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). In this phenomenon, antibodies generated during an initial (primary) infection with one of four circulating DENY serotypes cross-react with, but fail to neutralize, a subsequently infecting serotype. The formation of such immune complexes is thought to enhance DENY infectivity by facilitating entry and subsequent replication of the virus in cells of the immune system that bear antibody Fcy receptors. To address the need to stimulate a balanced neutralizing antibody response against all four DENV serotypes, most current vaccine strategies involve the administration of tetravalent live, attenuated or recombinant viral formulations that typically elicit both serotype-specific neutralizing, and antigenically cross-reactive but non-neutralizing, antibody responses. Thus, in the event that a balanced response is not achieved, all such formulations have the potential to facilitate ADE. In this thesis, I describe a DENY subunit vaccine strategy that involves administration of only one of three domains of the DENY envelope (E) glycoprotein derived from all four DENY serotypes. Domain III (dIII) is attractive for this purpose because it appears to contain epitopes capable of eliciting primarily serotype-specific virus neutralizing antibody responses. Here I examine the potential utility of an E glycoprotein dIII-based strategy to mediate broadly protective (i.e., tetravalent) DENY neutralizing antibody responses with minimal associated ADE activity.;In addition, I investigate the mechanism by which DENY-immune complexes enhance entry and viral infectivity in cells expressing Fcγ receptors utilizing a panel of epitope-matched immunoglobulin switch variants and cell lines engineered to express either FcγRI or FcγRII. Results demonstrate that DENY neutralization is modulated by the antibody Fc region in a manner that is dependent upon IgG subclass, likely through effects on virion and FcγR binding. Thus, the IgG antibody subclass profile generated by DENY infection and/or vaccination appears to be a critically important parameter in the development of safe and effective vaccines for the prevention of DF, DHF and DSS. |
