Zika virus is a type of mosquito-borne pathogen.
Infecting pregnant women can cause neonatal microcephaly
The 2015-16 Zika epidemic became an international public health emergency, and no vaccine has been approved yet
The antigenicity of Zika virus is close to that of Dengue virus and belongs to a superserum family
The latest population cohort study found that past Zika virus infection can significantly increase the severity of subsequent dengue virus infections, proving that Zika pre-existing antibodies have a serious antibody dependence enhancement ( ADE ) risk for dengue virus infection ( Science, 369, 1123–1128 (2020) )
Zika / between serotypes of dengue ADE is the focus of vaccine safety issues to be resolved, in particular by the same media these two types of viruses (such as Aedes aegypti) spread and popular areas overlap
Therefore, an ideal Zika vaccine should have the following three characteristics: 1 ) Prevent mother-to-child transmission of Zika virus; 2 ) Prevent dengue ADE caused by Zika virus infection ; 3 ) Prevent dengue caused by Zika vaccine immunization Leather ADE
However, the Zika vaccine currently entering the clinical stage in the world has not been designed to avoid the potential risk of dengue ADE
2021 Nian 7 Yue 15 days, Institute of Microbiology, Chinese Academy of Sciences high-fu, even wearing climbing, Yan Jinghua, etc.
in Nature Immunology , published online entitled Protective Zika vaccines engineered to eliminate enhancement of infection via dengue immunodominance switch research papers, proposed the elimination of dengue ADE 's new strategy for protective Zika vaccines
The Zika / Dengue virus cross-antibody that causes the ADE effect mainly targets the conserved region of the fusion peptide ( FL ) of the viral surface structural protein prM and E protein ( Science 328, 745–748 (2010) ) .
It has been reported internationally that by introducing mutations in FL epitopes or constructing E protein dimers to shield FL epitopes, the ADE of Zika vaccine against dengue virus infection can be significantly reduced .
However, in the mouse model, neither of these two vaccine methods can produce sufficient protective immune responses and completely block the vertical transmission of Zika virus from mother to child ( Cell 168, 1114–1125 e1110 (2017) , Nat.
20, 1291–1298 (2019) ) .
In view of the potential long-term and serious consequences of Zika virus infection on the newborns of pregnant women, Zika vaccines that can induce sterilizing immunity in mothers and infants are particularly important .
The team of Academician Gao Fu has been conducting research on Zika virus since 2016 , and resolved the crystal structure of the protective immunogen E protein of Zika virus , and isolated a series of neutralizing / protecting antibodies targeting different domains of the E protein , Resolved the structural basis of representative ADE antibodies targeting FL epitopes ( Cell Host Microbe 19, 696-704 (2016) ; Sci.
8, 369ra179 (2016)) .
These preliminary foundations provide important guidance for the rational design of Zika vaccines that eliminate ADE .
In this study, the researchers adopted a reverse vaccinology strategy that uses antibodies to guide vaccine design
Based on the structural basis of ADE antibody binding to FL (Figure 1 ), the Zika immunogen E protein was rationally modified to eliminate FL epitopes and maintain the integrity of other neutralizing antibody epitopes
Since the FL region is highly conserved in the Flavivirus genus, the introduction of mutations in the key amino acids of the FL epitope can easily destroy the E protein structure and greatly reduce the immunogenicity of the vaccine
Therefore, the researchers replaced the FL of the Zika E protein with the homologous sequence of the arthropod-specific flavivirus in the flavivirus genus through the method of homology replacement , thereby changing the FL epitope.
The 3 key amino acids that bind to ADE antibody .
Furthermore, a series of neutralizing protective antibodies and ADE antibodies were used to screen the modified E protein antigen in positive and negative directions to obtain a construction that satisfies both FL epitope elimination and neutralization epitope maintenance .
Of which 2
A design MutB and MutC were prepared into chimpanzee adenovirus vector (AdC7) vaccine for evaluation
Antigenic rational design based on the structure of ADE antibody targeting FL epitope
The results showed that, MUTB / C vaccine immunization can generate an immune response of clearing , completely protected mice against challenge Zika virus , in all target tissues are infected with the virus undetectable viral load
In addition, in the pregnant mouse infection model, the vaccine completely blocked the mother-to-child transmission of Zika virus, and the viral load was not detected in the mouse brain and placenta of fetal mice (Figure 2 )
MutB/C vaccine blocks mother-to-child transmission of Zika virus
The researchers further verified the ADE of MutB/C against dengue virus infection through in vitro and in vivo experiments .
Excitingly, the MutB/C vaccine immune serum completely eliminated the ADE against the four serotypes of dengue virus ; the adoptive test of the serum confirmed that the MutB/C vaccine immune serum would not cause the ADE of dengue virus infection , while the wild-type construct ( WT ) will accelerate the death of animals and aggravate the disease (Figure 3 ) .
MutB/C vaccine eliminates the in vitro and in vivo ADEs of dengue virus infection
In order to further explore the immunological basis of the modified vaccine MutB/C to eliminate ADE , the researchers analyzed the characteristics of antigen-specific BCR in the lymph nodes of the immunized mice through the B- cell receptor ( BCR ) single-cell sequencing method .
The results show that the humoral immunity stimulated by the wild-type vaccine has obvious immunodominance, and more than 60% of BCR uses 3 sets of germline genes .
However, MutB/C breaks the original immune advantage and makes the germline genes used by antigen-specific BCR distributed in a distributed manner (Figure 4 ) .
The researchers synthesized the representative dominant antibodies in each immune group in the form of antibody IgG .
The study found that the dominant antibodies induced by the wild-type vaccine all target the FL epitope, and have cross-binding and significant ADE for the four serotypes of dengue virus .
The MutB / C vaccine-induced antibodies hardly advantage in connection with the dengue virus, and no ADE .
Interestingly, through the existing reports of different sources of flavivirus FL
The comparison of epitope murine monoclonal antibodies found that these antibodies all use almost the same germline genes as the antibodies elicited by the wild-type vaccine reported in this article
This suggests that ADE antibodies to FL epitopes of flaviviruses may share a few similar germline genes .
MutB/C vaccine converts the immunodominance occupied by ADE antibodies
The researchers finally analyzed the molecular basis of one of the antigen-modified E protein MutC binding neutralizing antibodies, and found that MutC can still maintain the dimer structure of E protein through new forces , which is very important for activating effective neutralizing antibodies
In addition, the modified FL amino acids produce steric hindrance and charge repulsion to ADE antibodies, thus revealing the structural basis for MutC not to induce the production of ADE antibodies
The study successfully applied structural guidance antigen design to solve the problem of Zika vaccine ADE , and provided a beautiful solution to the long-standing problems in the development of Zika vaccine
The rational design of a new Zika vaccine that eliminates ADE has taken a big step towards the development of a safe and effective Zika vaccine, and will guide the future clinical use of Zika vaccine
Academician Gao Fu, researcher Dai Lianpan, and researcher Yan Jinghua of the Institute of Microbiology, Chinese Academy of Sciences are the co-corresponding authors of the paper
Researcher Dai Lianpan, Dr.
Xu Kun from Hainan Medical University, and Li Jinhe, a doctoral student at the Beijing Institutes for Biological Sciences, Chinese Academy of Sciences, are the first authors of the paper
Professor Xia Ganfeng of Hainan Medical College and others gave important help