Dissecting the Human Antibody Response to Dengue Virus

Dengue fever (DF) and severe dengue (SD) are two forms of an emerging infectious disease that presents a severe public health crisis predominantly in developing countries. Its etiological agent, Dengue virus (DENV), is a mosquito-borne pathogen, which exists as four different serotypes (named DENV1 through 4). Primary natural infections in humans stimulate a highly cross-reactive antibody response, however, protection is observed to be only against the serotype of infection. Extensive work on the mouse antibody response to DENV has mapped strongly neutralizing antibodies to the domain III (EDIII) of the DENV envelope (E) protein. However, recent work showed that after a natural infection in humans, anti-EDIII antibodies contribute very little to protection. Therefore, the human memory antibody response against a natural DENV infection remains poorly understood. Our present studies characterized both circulating polyclonal antibodies from human sera and human monoclonal antibodies from memory B-cells, after late convalescent primary DENV infections. The present body of work shows that after late convalescent natural primary DENV infections, humans produce two uniquely different antibody groups: 1) A cross-reactive, weakly neutralizing group that makes up the dominant proportion of anti-DENV antibodies, and 2) a minor group of strongly neutralizing, type-specific antibodies. Subsequently, we mapped some of these strongly neutralizing type-specific antibodies to a novel complex, quaternary epitope that includes the hinge region between domains I and II (EDI-II) of the E protein. Due to the role of the EDI-DII hinge region in DENV fusion and entry, this epitope offers a functional advantage. As hypothesized, we observed that all neutralizing EDI-DII hinge-binding monoclonal antibodies that were isolated blocked DENV infection at a step post-attachment, while the mechanism of neutralization by human polyclonal sera was more variable. In parallel, we found that the weakly neutralizing, cross-reactive group of antibodies was responsible for antibody-mediated enhancement of infection by heterotypic DENV serotypes. Further investigation mapped these enhancing cross-reactive antibodies to the DENV surface glycoproteins prM and E protein. These studies shed some light on the protective and enhancing DENV epitopes targeted by the human immune response, and set the stage for a safer and efficacious human vaccine against DENV.Doctor of Philosoph