Highlights
- Pre-existing antibodies to DENV1 correlate with high ZIKV neutralizing responses
- Antibodies to the EDIII lateral ridge correlate with serum neutralization of ZIKV
- Recurrent VH3-23/VK1-5 antibodies to the EDIII potently neutralize ZIKV and DENV1
- The structures of VH3-23/VK1-5 antibodies with the EDIIIs of DENV1 and ZIKV were solved
Summary
Antibodies to Zika virus (ZIKV) can be protective. To examine the antibody response in individuals who develop high titers of anti-ZIKV antibodies, we screened cohorts in Brazil and Mexico for ZIKV envelope domain III (ZEDIII) binding and neutralization. We find that serologic reactivity to dengue 1 virus (DENV1) EDIII before ZIKV exposure is associated with increased ZIKV neutralizing titers after exposure. Antibody cloning shows that donors with high ZIKV neutralizing antibody titers have expanded clones of memory B cells that express the same immunoglobulin VH3-23/VK1-5 genes. These recurring antibodies cross-react with DENV1, but not other flaviviruses, neutralize both DENV1 and ZIKV, and protect mice against ZIKV challenge. Structural analyses reveal the mechanism of recognition of the ZEDIII lateral ridge by VH3-23/VK1-5 antibodies. Serologic testing shows that antibodies to this region correlate with serum neutralizing activity to ZIKV. Thus, high neutralizing responses to ZIKV are associated with pre-existing reactivity to DENV1 in humans.
Introduction
Zika virus (ZIKV) infection typically produces mild symptoms consisting of fever, rash, and arthralgia that resolve rapidly, and the infection is also occasionally associated with Guillain-Barré syndrome (Lessler et al., 2016, Miner and Diamond, 2017, Weaver et al., 2016). However, when infection occurs during pregnancy, vertical transmission can lead to a spectrum of devastating neurodevelopmental aberrations, collectively referred to as congenital Zika syndrome. Although the data are still incomplete, infants born to mothers infected with ZIKV during pregnancy carry an up to 42% risk of developing overt clinical or neuroimaging abnormalities (Brasil et al., 2016, Costa et al., 2016, França et al., 2016).
ZIKV belongs to the Flavivirus genus, which includes yellow fever (YFV), West Nile (WNV), and the four serotypes of dengue virus (DENV1–DENV4). These positive-stranded RNA viruses are responsible for considerable morbidity and mortality in the equatorial and subequatorial regions populated by their mosquito vectors (Kramer et al., 2007, Murray et al., 2013, Weaver and Reisen, 2010). Unlike most other flaviviruses, ZIKV can also be transmitted sexually, and on occasion persists for months (Barzon et al., 2016, Foy et al., 2011, Murray et al., 2017, Suy et al., 2016).
All flaviviruses display a single envelope protein, E, that is highly conserved between different members of this virus family. The E protein ectodomain consists of three structural domains. Domain I (EDI) contains the N terminus, domain II (EDII) is an extended finger-like structure that includes the dimerization domain and also a pH-sensitive fusion loop that mediates viral fusion in the lysosomes. Finally, domain III (EDIII) is an immunoglobulin-like domain that mediates attachment to target cells (Barba-Spaeth et al., 2016, Dai et al., 2016, Kostyuchenko et al., 2016, Modis et al., 2003, Mukhopadhyay et al., 2005, Rey et al., 1995, Sirohi et al., 2016, Zhang et al., 2004). Several human neutralizing antibodies targeting different E protein epitopes have been described. Antibodies against the EDIII of flaviviruses are among the most potent neutralizers in this group (Beasley and Barrett, 2002, Crill and Roehrig, 2001, Screaton et al., 2015).
Due to the conserved structural features of the E protein, antibodies that develop in response to infection by one flavivirus may also recognize others (Heinz and Stiasny, 2017). Cross-reactivity can lead to cross-protection, as first documented by Sabin, who showed experimentally in humans that exposure to DENV1 could provide short-term protection from subsequent challenge with DENV2. In contrast, immunity to the autologous strain was long lasting (Sabin, 1950). More recently, human monoclonal antibodies to DENV have been shown to cross-neutralize ZIKV, and vice versa (Barba-Spaeth et al., 2016, Stettler et al., 2016, Swanstrom et al., 2016). However, there is concern that cross-reacting antibodies that fail to neutralize the virus may enhance rather than curb subsequent flavivirus infections (Harrison, 2016, Wahala and Silva, 2011). In vitro and in vivo experiments in mice suggest that this phenomenon, commonly referred to as antibody-dependent enhancement (ADE), extends to ZIKV (Bardina et al., 2017, Dejnirattisai et al., 2016, Harrison, 2016, Priyamvada et al., 2016). For this reason, a desirable goal for ZIKV vaccines is to elicit robust and protective antibodies, while avoiding antibodies that bind to the virus but are non-neutralizing and potentially enhancing. Doing so requires a detailed understanding of the neutralizing antibody response to ZIKV.
Several human antibodies to ZIKV have been cloned from convalescent individuals by methods utilizing B cell transformation with Epstein-Barr virus (Sapparapu et al., 2016, Stettler et al., 2016). However, individual donors were not selected for high neutralization titers; whether their antibodies are representative of optimal immune responses and how these antibodies might relate to previous flavivirus exposure remains unknown.
Here, we report on the characteristics of the neutralizing antibody responses that developed in individuals with high levels of serum ZIKV neutralizing activity from two independent cohorts after recent ZIKV outbreaks in Brazil and Mexico and on their relationship to previous flavivirus exposure.
