Study of cross-reactive human antibodies against dengue virus envelope protein : implication for dengue vaccine

Abstract

With an estimated 390 million infections and approximately 90 million apparent infections annually, the four serotypes of dengue virus (DENV) continue to be a global threat with no licensed vaccine available. A better understanding of correlates between protection and humoral immune responses is needed. First, we characterized cross-reactive human anti-E mAbs derived from patients after primary and secondary DENV infections. Group-reactive (GR) anti-E mAbs that recognized four DENV serotypes and another flavivirus, West Nile virus (WNV), were found as the predominant cross-reactive anti-E mAbs. The epitopes of 32 GR mAbs were found at residues in the fusion loop (FL) of E protein domain II and residues involving both FL and bc loop as a new epitope. The neutralizing potency and binding avidity of GR mAbs derived from secondary infection were stronger than those derived from primary infection. Second, we investigated cross-reactive anti-E Abs in human polyclonal sera after secondary DENV infection. Stronger Ab responses to E protein, higher binding avidity and multitypic neutralizing pattern to both exposed and non-exposed serotypes were found in sera after secondary DENV infection, compared with those after primary infection. Depletion with WNV antigen resulted in a significant reduction of neutralizing activities against four DENV serotypes, suggesting that GR Abs contribute greatly to neutralizing activities after secondary infection. Third, we investigated whether E protein ectodomain alone can preserve the conformation of E protein. We found that C-terminal α-helices domains of E protein were involved in prM-E interaction and maintenance of the stability of prM protein. E protein affected the recognition of prM protein by anti-prM mAbs; moreover, E protein ectodomain alone can be recognized well by all anti-E mAbs tested. Taken together, our study of GR anti-E Abs at both monoclonal and polyclonal levels suggest the weakly neutralizing GR anti-E Abs generated from primary DENV infection become potent neutralizing against four serotypes after secondary infection. The observations that the dengue immune status of host affects the quality of cross-reactive Abs generated have implications for new strategies of DENV vaccines. Moreover, E protein ectodomain alone could be a promising subunit immunogen without inducing potentially harmful anti-prM response.