Protective Capacity of the Human Anamnestic Antibody Response during Acute Dengue Virus Infection

Abstract

Half of the world's population is exposed to the risk of dengue virus infection. Although a vaccine for dengue virus is now available in a few countries, its reported overall efficacy of about 60% is not ideal. Protective immune correlates following natural dengue virus infection remain undefined, which makes it difficult to predict the efficacy of new vaccines. In this study, we address the protective capacity of dengue virus-specific antibodies that are produced by plasmablasts a few days after natural secondary infection. Among a panel of 18 dengue virus-reactive human monoclonal antibodies, four groups of antibodies were identified based on their binding properties. While antibodies targeting the fusion loop of the glycoprotein of dengue virus dominated the antibody response, two smaller groups of antibodies bound to previously undescribed epitopes in domain II of the E protein. The latter, largely serotype-cross-reactive antibodies, demonstrated increased stability of binding at pH 5. These antibodies possessed weak to moderate neutralization capacity in vitro but were the most efficacious in promoting the survival of infected mice. Our data suggest that the cross-reactive anamnestic antibody response has a protective capacity despite moderate neutralization in vitro and a moderate decrease of viremia in vivo.IMPORTANCE Antibodies can protect from symptomatic dengue virus infection. However, it is not easy to assess which classes of antibodies provide protection because in vitro assays are not always predictive of in vivo protection. During a repeat infection, dengue virus-specific immune memory cells are reactivated and large amounts of antibodies are produced. By studying antibodies cloned from patients with heterologous secondary infection, we tested the protective value of the serotype-cross-reactive “recall” or “anamnestic” response. We found that results from in vitro neutralization assays did not always correlate with the ability of the antibodies to reduce viremia in a mouse model. In addition, a decrease of viremia in mice did not necessarily improve survival. The most protective antibodies were stable at pH 5, suggesting that antibody binding in the endosomes, after the antibody-virus complex is internalized, might be important to block virus spread in the organism.

Altered monocyte response to the dengue virus in those with varying severity of past dengue infection

“…ELISA plates were coated with anti-V5 tag antibodies, followed by incubation of V5-tagged wildtype or mutated E proteins produced in S2 cells. This indirect ELISA method facilitates immobilization of E protein as dimers and the method and its validation have been described in detail before (Xu et al, 2016). Each serum sample was incubated on 12 E protein mutants and the WT E protein.…”

“…Therefore, we tested whether the serum from individuals with past SD and NSD had different repertoires, particularly with regards to fusion-loop specificity. We used 12 alanine-replacement E protein mutants from DENV-2 to test loss of binding to the mutated E protein dimers in the sera of all individuals (Xu et al, 2016). Three mutations were in the fusion loop whereas the other nine were reported previously to be dominant epitopes of patient-derived monoclonal antibodies (Dejnirattisai et al, 2015).…”

Adaptive Immunity to Dengue Virus: Slippery Slope or Solid Ground for Rational Vaccine Design?

“…At high concentrations, cross-reactive antibodies induce the formation of large viral aggregates able to cross-link inhibitory FcγRIIB, thereby blocking infection and avoiding ADE [ 116 ]; however, as their levels are declining over time, there is an increased risk of ADE due to sub-neutralising antibody concentrations [ 30 ]. Upon secondary infection with a heterologous DENV serotype, cross-reactive MBCs generated during primary infection preferentially expand and dominate over serotype-specific responses [ 70 , 111 , 112 , 115 , 117 , 118 , 119 , 120 , 121 , 122 , 123 ]. The resulting cross-reactive antibodies were shown to have higher binding avidities and neutralising potencies than those found in primary DENV infection, being able to neutralise not only the current and previous infecting serotype but also serotypes to which individuals have not yet been exposed (‘non-exposed’ serotypes) [ 112 , 113 , 117 , 118 , 124 , 125 , 126 ].…”

“…Several screening studies observed immunodominance of the EDI/II region in DENV-immune donors and found that it was mainly targeted by cross-reactive antibodies displaying weak neutralising activity [ 104 , 105 , 106 , 110 , 121 , 142 , 143 , 144 , 145 ]. The majority of these antibodies have been mapped to a region comprising the FL in EDII (amino acids 98 to 110), termed the fusion loop epitope (FLE) [ 71 , 104 , 105 , 110 , 123 , 142 , 144 , 146 ]. Trp101 has been identified as a key residue for the binding of various mAbs to the FLE, with many also being sensitive to substitution of the neighbouring residues Gly106, Leu107, and Phe108 [ 104 , 105 , 109 , 123 , 125 , 147 , 148 , 149 , 150 ].…”

“…The majority of these antibodies have been mapped to a region comprising the FL in EDII (amino acids 98 to 110), termed the fusion loop epitope (FLE) [ 71 , 104 , 105 , 110 , 123 , 142 , 144 , 146 ]. Trp101 has been identified as a key residue for the binding of various mAbs to the FLE, with many also being sensitive to substitution of the neighbouring residues Gly106, Leu107, and Phe108 [ 104 , 105 , 109 , 123 , 125 , 147 , 148 , 149 , 150 ]. High conservation at these amino acid positions enables FLE-specific mAbs to cross-react with all DENV serotypes as well as other flaviviruses [ 68 , 104 , 105 , 142 , 146 , 148 , 150 , 151 , 152 ].…”