Dengue is a rapidly emerging, mosquito-borne viral infection, with an estimated 400 million infections occurring annually. To gain insight into dengue immunity, we characterized 145 human monoclonal antibodies (mAbs) and identified a previously unknown epitope, the envelope dimer epitope (EDE), that bridges two envelope protein subunits that make up the 90 repeating dimers on the mature virion. The mAbs to EDE were broadly reactive across the dengue serocomplex and fully neutralized virus produced in either insect cells or primary human cells, with 50% neutralization in the low picomolar range. Our results provide a path to a subunit vaccine against dengue virus and have implications for the design and monitoring of future vaccine trials in which the induction of antibody to the EDE should be prioritized.

Humans who experience a primary dengue virus (DENV) infection develop antibodies that preferentially neutralize the homologous serotype responsible for infection. Affected individuals also generate cross-reactive antibodies against heterologous DENV serotypes, which are non-neutralizing. Dengue cross-reactive, non-neutralizing antibodies can enhance infection of Fc receptor bearing cells and, potentially, exacerbate disease. The actual binding sites of human antibody on the DENV particle are not well defined. We characterized the specificity and neutralization potency of polyclonal serum antibodies and memory B-cell derived monoclonal antibodies (hMAbs) from 2 individuals exposed to primary DENV infections. Most DENV-specific hMAbs were serotype cross-reactive and weakly neutralizing. Moreover, many hMAbs bound to the viral pre-membrane protein and other sites on the virus that were not preserved when the viral envelope protein was produced as a soluble, recombinant antigen (rE protein). Nonetheless, by modifying the screening procedure to detect rare antibodies that bound to rE, we were able to isolate and map human antibodies that strongly neutralized the homologous serotype of DENV. Our MAbs results indicate that, in these two individuals exposed to primary DENV infections, a small fraction of the total antibody response was responsible for virus neutralization.

The four serotypes of dengue virus (DENV) cause the most important and rapidly emerging arboviral diseases in humans. The recent phase 2b and 3 studies of a tetravalent dengue vaccine reported a moderate efficacy despite the presence of neutralizing antibodies, highlighting the need for a better understanding of neutralizing antibodies in polyclonal human sera. Certain type-specific (TS) antibodies were recently discovered to account for the monotypic neutralizing activity and protection after primary DENV infection. The nature of neutralizing antibodies after secondary DENV infection remains largely unknown. In this study, we examined sera from 10 vaccinees with well-documented exposure to first and second DENV serotypes through heterotypic immunization with live-attenuated vaccines. Higher serum IgG avidities to both exposed and nonexposed serotypes were found after secondary immunization than after primary immunization. Using a two-step depletion protocol to remove different anti-envelope antibodies, including group-reactive (GR) and complex-reactive (CR) antibodies separately, we found GR and CR antibodies together contributed to more than 50% of neutralizing activities against multiple serotypes after secondary immunization. Similar findings were demonstrated in patients after secondary infection. Anti-envelope antibodies recognizing previously exposed serotypes consisted of a large proportion of GR antibodies, CR antibodies, and a small proportion of TS antibodies, whereas those recognizing nonexposed serotypes consisted of GR and CR antibodies. These findings have implications for sequential heterotypic immunization or primary immunization of DENV-primed individuals as alternative strategies for DENV vaccination. The complexity of neutralizing antibodies after secondary infection provides new insights into the difficulty of their application as surrogates of protection. IMPORTANCEThe four serotypes of dengue virus (DENV) are the leading cause of arboviral diseases in humans. Despite the presence of neutralizing antibodies, a moderate efficacy was recently reported in phase 2b and 3 trials of a dengue vaccine; a better understanding of neutralizing antibodies in polyclonal human sera is urgently needed. We studied vaccinees who received heterotypic immunization of live-attenuated vaccines, as they were known to have received the first and second DENV serotype exposures. We found anti-envelope antibodies consist of group-reactive (GR), complex-reactive (CR), and type-specific (TS) antibodies, and that both GR and CR antibodies contribute significantly to multitypic neutralizing activities after secondary DENV immunization. These findings have implications for alternative strategies for DENV vaccination. Certain TS antibodies were recently discovered to contribute to the monotypic neutralizing activity and protection after primary DENV infection; our findings of the complexity of neutralizing activities after secondary immunization/infection provide new insights for neutralizing antibodies as surroga...

The role of the α-helical domain (MH) of dengue virus (DENV) precursor membrane protein in replication was investigated by site-directed mutagenesis. Proline substitutions of three residues (120, 123 and 127) at the C-terminus, but not those at the N-terminus of MH domain, reduced the virus-like particles of DENV1, DENV2 and DENV4 detected in supernatants. In a DENV2 replicon trans-packaging system, these three mutations suppressed particles detected; two of them (I123P and V127P) also affected viral entry. In the context of DENV2 genome-length RNA, all three mutations reduced virion assembly and virus spreading in cell culture. Analysis of revertants showed that mutation A120P could partially support viral infection cycle; in contrast, mutations I123P and V127P were lethal, and adaptations of I123P→I123L and V127P→ V127L were required to restore the viral infection cycle. These findings demonstrate that the C-terminus of the MH domain is involved in both assembly and entry of DENV.