Gaofu team's new Zika vaccine "kills two birds with one stone"!

■ Reporter Feng Lifei

In a study published online on July 15 in "Nature-Immunology", a new protective Zika vaccine based on structural biology was designed by Gao Fu, academician of the Institute of Microbiology of the Chinese Academy of Sciences, Dai Lianpan, Yan Jinghua, etc.
The anti-epidemic "arsenal" has added another weapon
.

Zika virus is notorious because it causes microcephaly and other irreversible serious birth defects in newborns
.

The new vaccine designed this time will kill two birds with one stone.
It can not only prevent Zika virus from invading the fetus, but also cut off the severe antibody-dependent enhancement (ADE) effect of Zika pre-existing antibodies against dengue virus infection
.

The vaccine dilemma

Zika virus is mainly transmitted by Aedes aegypti and was first isolated in monkeys in the Zika Forest in Uganda in 1947
.

Under normal circumstances, Zika virus infects humans and only causes low-grade fever, maculopapular rash, joint pain, conjunctivitis, etc.
However, it may cause microcephaly and other irreversible birth defects in babies after it infects pregnant women
.

WHO believes that to deal with future epidemics, the development of vaccines is the focus
.

"Zika virus and dengue virus are both Flaviviruses, their antigenicity is similar, and both belong to the superserum family
.

The ADE between Zika and Dengue serotypes is a key safety issue that urgently needs to be resolved in vaccine development.
In particular, the two types of viruses can be transmitted by the same vector-Aedes aegypti, and their epidemic areas overlap, making vaccine development more difficult
.

In this regard, Gao Fu and others stated in the article that an ideal Zika vaccine should have three characteristics: prevention of mother-to-child transmission of Zika virus; prevention of dengue ADE caused by Zika virus infection; prevention of Zika vaccine immunization Dengue ADE
.

"Cut" can be cut and "reason" is not chaotic

To solve the safety problem of Zika vaccine development, it is necessary to find the "link" that connects the "cross-species" ADE effect between Zika and Dengue virus and cut it
.

Previous studies have shown that the cross-antibodies that cause the ADE effect of Zika or Dengue virus mainly target the conserved region of the fusion peptide (FL) of the virus surface structural protein prM and E protein
.

"But 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
.

How can we "kill" the "conservative" FL epitope and at the same time block the mother-to-child transmission of Zika virus?

In order to solve this problem, the Gaofu team has carried out research on Zika virus since 2016, and analyzed the crystal structure of the protective immunogen E protein of Zika virus (the E protein on the surface of the flavivirus is like a key to help the virus open The gate of the host cell), a series of neutralizing/protecting antibodies targeting different domains of E protein have been isolated, and the structural basis of representative ADE antibodies targeting FL epitopes has been analyzed
.

In the new study, the researchers adopted a reverse vaccinology strategy of "antibody-guided vaccine design"
.
Based on the structural basis of ADE antibody binding to FL, the Zika immunogen E protein was rationally modified, the purpose of which is to eliminate FL epitopes and maintain the integrity of other neutralizing antibody epitopes
.

They replaced the FL of the Zika E protein with the homologous sequence of the insect-specific flavivirus in the flavivirus genus with the furthest evolutionary relationship through the method of homologous substitution, thereby changing the three FL epitopes that bind ADE antibodies.
Key amino acids
.

Subsequently, the researchers used a series of neutralizing protective antibodies and ADE antibodies to screen the modified E protein antigens positively and negatively to obtain a construction that satisfies both FL epitope elimination and neutralization epitope maintenance
.
Among them, two designs, MutB and MutC, were prepared into chimpanzee adenovirus vector (AdC7) vaccines for evaluation
.

The result is "two birds with one stone"
.
On the one hand, a single immunization with the MutB/C vaccine can produce a clear immune response, which completely protects mice against Zika virus.
The viral load cannot be detected in all target tissues infected by the virus, which can completely block the Zika virus.
Mother-to-child transmission
.
On the other hand, the two vaccine immune sera completely eliminated the ADE of the four serotypes of dengue virus; the adoptive test of the serum confirmed that the MutB/C vaccine immune sera would not cause the ADE of dengue virus infection, while the wild-type construction (WT) It will speed up the death of animals and aggravate the disease
.

"This is a very good study.
The structure-based antigen design is used to solve the problem of ADE
in Zika vaccines .
" A reviewer said in the review that the Zika virus WTFL epitope was sequenced by arthropod-specific sequences.
The substitution not only maintains the conformation and immunogenicity of the antigen, but also avoids the binding of WTFL-specific antibodies
.

Enriching the "Arsenal" of Anti-epidemic

The researchers did not stop there
.
Knowing this, but also knowing why, they further explored the immunological basis of the modified vaccine MutB/C to eliminate ADE
.

Using the single-cell sequencing method of B cell receptor (BCR), they analyzed the characteristics of antigen-specific BCR in the lymph nodes of mice after immunization
.
The results showed that the humoral immunity stimulated by the wild-type vaccine has obvious immunodominance, and more than 60% of BCR use 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
.

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 new research will help enrich our country’s "arms arsenal" in fighting the epidemic
.
As another reviewer said, “This study proposes a beautiful solution to a long-standing problem in this field, and rationally designs an improved Zika virus immunogen
.
Eliminating ADE is the development of an effective Zika vaccine.
An important step
in the

Gao Fu and others also pointed out in the article that this study provides immunological trends for future clinical trials of vaccines through mouse models, and also provides new insights for vaccine-oriented protein design
.
The rational design of a new Zika vaccine that eliminates ADE will guide the future clinical use of Zika vaccine
.

Related paper information: https://doi.
org/10.
1038/s41590-021-00966-6