Core reagents for infectious disease research

Monkeypox virus (MPXV)is an enveloped double-stranded DNA virus, belonging to the genus Orthopoxvirus in the poxviridae family. Monkeypox virus has two different infectious virions: the intracellular mature virus (MV) and the extracellular enveloped viruses (EV). When the virus invades the host cell to complete the replication process, the MV cell surface binding protein E8L binds to the cell surface chondroitin sulfate, to provide viral particles attached to the target cell. A30L is also considered an important target in monkeypox virus research as an envelope protein for virus entry into a host and cell-cell fusion (syncytial formation). In addition, the envelope glycoprotein A35R on the surface of EV was predicted to affect the intercellular diffusion of virions. The combination of A29L with heparin on the cell surface promoted the fusion of viral membrane and host plasma membrane. Further, B21R, an important target protein with several key immuno-dominant epitopes, is the focus of monkeypox virus research.

Jynneos, a vaccine for smallpox and monkeypox developed by Danish vaccine company Bavarian Nordic, is the only vaccine approved to protect against monkeypox so far. However, people had stopped smallpox vaccination since it disappear, which means that the current population is generally not immune to smallpox and monkeypox. In addition, A virology expert Chang Rongshan said that the new crown global pandemic may have affected human immunity levels, causing monkeypox to gain more adaptability than ever before in human populations after smallpox disappeared. Therefore, it is necessary to reserve specific vaccines and antiviral drugs while closely monitoring the international monkeypox epidemic.

Coronavirus (CoV) is a large class of viruses that are widely present in nature and  cause illnesses ranging from the common cold to more severe diseases. There are currently eight kinds of coronaviruses found, of which HCoV-229E, HCoV-OC43, HCoV-NL63 and HCoV-HKU1 are more common in the population and less pathogenic; Sars-CoV, MERS-CoV and 2019-nCoV are common susceptible, highly epidemic, and highly contagious diseases. Recently, scientists discovered a canine coronavirus (CCoV-HUpN-2018) in Malaysia and Haiti, which is the eighth coronavirus after SARS-COV-2.

The Spike protein of coronavirus is the main antigen of the virus, which can bind to the receptor and play an important role in the process of  infection. Therefore, S protein and its subunits are generally considered during neutralizing antibodies and vaccine design.

The influenza virus belongs to the family Orthomyxoviridae. Human influenza virus infections have a worldwide distribution. Seasonal influenza epidemics occur regularly both in the Northern and the Southern hemispheres during  winter and are estimated to cause approximately 500,000 deaths per year worldwide.

The influenza virus constitutes by envelope, matrix, and core protein. Hemagglutinin (HA) and neuraminidase (NA) are glycoproteins embedded in the envelope, playing an important role in the virus invasion and release process. Therefore, NA and HA are now important targets in the research and development of influenza vaccines and therapeutic drugs.

Rabies virus (RABV) ）is a neurotropic virus that causes rabies in humans and animals.  The mortality rate is nearly 100% after the manifestation of clinical symptoms . According to the World Health Organization, Rabies occurs in more than 150 countries and territories, leading to the death of about 59,000 people  each year.

Rabies virus is mainly composed of Glycoprotein, Nucleoprotein, Polymerase or  Largeprotein, Phosphoprotein, and Matrixpotein. Among them, the G protein is the only protein that is across the membrane structure and fixed on the viral envelope. It can bind with the acetylcholine receptor and determine the rabies virus neuronophagia. In addition, it is the key to inducing neutralizing antibodies and is widely applied in the assessment of rabies vaccine development and vaccination  tests.

Ebola virus (EBOV) is a class A bioterrorism agent, known to cause a severe and often deadly illness known as Ebola virus disease (EVD). It is the deadliest viral hemorrhagic fever in the world today, with mortality ranging from 50% to 90%.

The Ebola virus contains 7 structural proteins, which are nucleoprotein (NP), VP35, VP40, glycoprotein (GP), VP30, VP24, and L (RNA polymerase).  GP is a key protein that is responsible for the virus’s ability to bind to and infect targeted cells and has been used as an important target for vaccine and antibody therapy.

Human Immunodeficiency Virus (HIV) is a retrovirus that attacks the body’s immune system and causes Immunodeficiency. According to the World Health Organization, there were an estimated 30.2-45.1 million people worldwide living with HIV, and approximately 680,000 people died from HIV-related causes in 2020.  Based on genetic characteristics and differences in the viral antigens, HIV is classified into types 1 and 2 (HIV-1, HIV-2). HIV-2 is mainly distributed in West Africa, while HIV-1 is widely distributed around the world and is the main cause of the AIDS epidemic worldwide.

HIV-1 virus particle consists of a core and an envelope protein. The trimers of gp120 surface protein are anchored to the membrane by the trimers of the transmembrane protein gp41, participating in the fusion and invasion of virus and host cell membrane. During this process, the gp120 will bind to the CD4 and to the co-receptor on the host cell, resulting in loss of immune function and promoting viral persistence by influencing the immune response of T cells to the virus. Therefore, Gp120 is known as a popular target for HIV prevention and treatment.

Varicella-zoster virus (VZV)highly contagious enveloped DNA virus that is common in children. The initial infection causes chickenpox in children, and the virus remains latent in the body after recovery. In a few patients, the virus recurs in adults and causes herpes zoster.

VZV virus contains six glycoproteins, gE, gB, gH, gI, gC and gL.  In infected cells, gE is the most abundant protein expressed by VZV and plays an important role in viral replication and cell-to-cell transmission. As a recognizable antigen, gE becomes a target for vaccine research.

Zika virus (ZIKV)is a mosquito-borne flavivirus. In recent years, the outbreak of the Zika virus in South America, Southeast Asia, and other regions has caused millions of infections. Clinical analysis has shown that Zika virus infection is significantly associated with neurological disorders such as microcephaly in newborns and Guillain-Barre syndrome in adults.

Zika virus RNA encodes 3 structural proteins (C, prM/M and E) and 7 non-structural proteins (NS1, NS2A, NS2B, NS3, NS4A, NS4B, and NS5). NS1 is a secreted protein that interacts with the host cells with high immunogenicity. So, NS1 is used as a diagnostic marker for ZIKV infection and as a component of several experimental vaccines.

Respiratory syncytial virus (RSV) is a common respiratory virus that is widely distributed all over the world, mainly infecting infants and elderly people. It is reported that there are more than 33 million children under the age of five in the world infected by RSV per year, which is a major cause of infant mortality in the developing world.

The viral genome of RSV encodes 11 proteins, of which Fusion protein (F) and Attachment glycoprotein (G) are the two main protective antigens of the virus. The G protein is mainly related to the severity of the infection and is responsible for fusing with host cells. The F protein causes the fusion of the viral capsid with the host cell membrane and plays an important role in immunopathology triggered by RSV infection. Therefore, both proteins are currently considered hot antigens for the development of antibodies, vaccines, and other therapeutic agents.

Nipah Virus (NiV) is a new zoonotic virus that causes widespread vasculitis, fever, severe headache,  meningitis, and other symptoms in infected people, causing serious harm to humans and animals. It is another zoonotic disease that has caused widespread concern and panic in the world after mad cow disease in the UK, foot-and-mouth disease in pigs on Taiwan Island, and avian influenza in Hong Kong.

The NiV genome encodes six structural proteins, including nucleocapsid protein (N), phosphoprotein (P), matrix protein (M), fusion protein (F), attachment glycoprotein (G), and large protein or RNA polymerase protein (L).  G protein and F protein play key roles in the process of virus entry into host cells and induction of neutralizing antibodies. G proteins attach to cell receptors and trigger F glycoproteins for membrane fusion and generally be considered a target for vaccine development and prevention of NiV. F protein expressed in vitro can be used as a diagnostic antigen for monitoring and detection of NiV,

Severe fever with thrombocytopenia syndrome bunyavirus (SFTSV) is an acute infectious disease that causes severe fever with thrombocytopenia syndrome, mainly transmitted by tick bites with a peak epidemic from April to September. The clinical manifestations are characterized by fever with thrombocytopenia, and a few patients with seriously and rapidly progressive disease may die from multiple organ failure.

Currently, neither antiviral drugs nor vaccines are available for severe fever with thrombocytopenia syndrome virus (SFTSV). The envelope protein glycoprotein N (gN) on the surface of viruses is the main antigenic component that can attach to cell receptors and trigger fusion glycoprotein (F) for membrane fusion. Therefore, gN is widely recognized by neutralizing antibodies and is an ideal vaccine target.

Millions of people worldwide are exposed to herpes simplex virus(HSV) annually. Post-exposure, the virus may remain asymptomatic or cause mild to life threatening complications. HSV can be broadly divided into two serotypes: HSV-1 and HSV-2. HSV-1 and HSV-2 belong to the alpha-herpesvirus subfamily, which generally has a short replicative cycle and is capable of infecting broad range of hosts.

Mature HSV is covered by an envelope that expresses at least 12 different glycoproteins: gB, gC, gD, gE, gG, gH, gI, gJ, gK, gL, gM, and gN on their surface, in distinct shapes and sizes. Some exist as heterodimers (gH/gL and gE/gI), while most exist as monomers.

Viruses attach to cell surface receptors heparan sulfate proteoglycan (HSPGs) of the host via viral glycoproteins gB and/or gC. Glycoproteins gD, gH/gL, and gB bind to cell membrane receptors that subsequently trigger membrane fusion. Cell membrane receptors using gD, gH/gL, and gB glycoproteins triggers direct membrane fusion. As such, Glycoprotein gD is a common target of host cellular humoral and cellular immunity, as such, remains an important target for vaccine design.

Epstein-Barr virus (EBV) is a ubiquitous member of the γ-herpesvirus subfamily, which establishes lifelong latency in 95% of the human population. EBV infections during childhood and adolescence are usually asymptomatic but may cause infectious mononucleosis (IM). As an oncogenic virus, EBV is associated with approximately 200,000 new cases of malignancies and causes 140,000 deaths each year worldwide. However, effective vaccines and therapeutics against EBV infection remain unavailable.

EBV enters epithelial cells at the plasma membrane, but endocytosis is needed for B cell infection. B cell entry is initiated by gp350/gp220 binding to the complement receptor-2 (CR2) or to CR1, and then gHgL/gp42 binds to HLA-II to trigger pre-fusion gB. During entry into epithelial cells, BMRF2 binds to integrins and then gHgL binds to EphA2 to activate pre-fusion gB. Glycoprotein B (gB) is the primary fusogen essential for EBV entry into host cells. gH/gL and gB proteins coordinate to mediate EBV fusion and entry into B cells and epithelial cells, suggesting that inoculation with these proteins may trigger antibodies that prevent EBV infection.

Hendra virus (HeV) is a member of the paramyxovirus family, genus Henipar virus. Infection with HeV in humans may present as a mild flu-like illness in mild cases or cause encephalitis, fatal respiratory or neurological disease in more severe cases. Currently, there are no approved HeV antiviral therapeutics or vaccines for human use. The viral envelope carries surface projections composed of the viral transmembrane anchored fusion (F) and attachment (G) glycoproteins which have been the major target of antiviral strategies. G glycoprotein is a type II membrane glycoprotein consisting of a stalk and globular head domain which binds ephrin receptors. The fusion (F) glycoprotein mediates the membrane fusion process between the virion and host cell.  Following virus attachment to an ephrin receptor-bearing host cell, the fusion-promoting activity of G is initiated through its binding to receptor which facilitates the triggering of conformational changes in F, transitioning the molecule from its pre-fusion to post-fusion form. This drives the membrane fusion process between the virion and host cell delivering the viral nucleocapsid into the cytoplasm.

Dengue virus (DENV)belongs to the family Flaviviridae, genus Flavivirus, which is a single-stranded ribonucleic acid virus. It infects approximately 5-20 billion people each year, putting more than 300 million people at risk and causing 60,000 deaths each year. The efficacy of the only licensed dengue vaccine, Dengvaxia, against all four dengue serotypes has been less than ideal in real-world settings. In addition, there is a lack of clinically approved antiviral drugs against dengue virus.

The DENV genome encodes a single polyprotein that is processed into three structural proteins: capsid (C), precursor membrane (prM) and envelope (E), and seven non-structural proteins required for viral replication. The E protein is the major envelope glycoprotein, located in the lipid bilayer of the viral particle, constitutes the protrusion on the surface of the viral particle, contains a variety of B-cell and T-cell antigenic epitopes, and is the main protective antigen of dengue virus. NS1 protein is an important non-structural protein encoded by dengue virus. It has been shown that the non-structural protein NS1 cannot induce ADE(Antibody-Dependent Enhancement) action, so the preparation of non-structural protein NS1 subunit vaccine or genetically engineered vaccine by DNA recombinant technology may obtain satisfactory immune effect.

Group A Rotaviruses (RVs) are small bowel pathogens that infect the young of many avian and mammalian species and remain the most common cause of acute, severe gastroenteritis among infants and young children worldwide. RVs cause between 128,000 and 215,000 deaths each year. However, there are few types of rotavirus vaccines, which can be said to be in short supply. In addition, the high requirements for the number of doses and the age of vaccination of rotavirus vaccines pose challenges to the operation capacity of prevention systems in different countries, and the inevitable problem arises: the rotavirus vaccine coverage in different regions is not equal，and it is necessary to develop rotavirus

RVs belong to the Reoviridae family and are comprised of a variety of icosahedral, nonenveloped multisegmented double-stranded RNA viruses. RVs have three concentric layers of proteins that surround the 11 dsRNA segments encoding six structural (VP) and six nonstructural proteins (NSP). The outermost capsid layer is formed by trimers of VP7 that constitute the smooth surface of the virion and by trimers of the spike protein VP4, which serves as the RV cell attachment protein. VP7 and VP4 cause neutralizing antibody production in the host and are thought to be important for protective immunity.

Coxsackievirus A16 (CVA16) is the major etiological agent responsible for Hand, foot, and mouth disease (HFMD). HFMD has been prevalent in the Asia-Pacific region, causing significant morbidity and mortality, particularly in infants and young children. Accumulating reports suggest that CA16 infections can be associated with serious complications like myocarditis, irreversible shock, aseptic meningitis, and even death. However, there are no effective vaccines or therapeutic drugs available for CVA16 infection. Development of a safe and effective vaccine has been of high priority in vaccine research.

CVA16 is a nonenveloped virus of 30 nm in diameter with a single-stranded, positive-sense RNA genome of 7.4 kb in length packaged in a protein shell termed capsid14. The viral genome encodes a large polyprotein precursor, which is subsequently processed into structural protein P1 and nonstructural proteins P2 and P314. P1 can be further cleaved by a viral protease to yield capsid subunit proteins VP0, VP1, and VP3, among which VP0 undergoes autocleavage to produce VP2 and VP4 which stabilizes the capsid structure and results in infectious viral particles. It has been reported that immunization with VLPs containing VP0, VP1, VP3 potently elicited CVA16-specific serum antibody responses in mice, making it a potential target to combat CVA16.

Human cytomegalovirus (HCMV) infection, the most common cause of congenital disease globally, affecting an estimated 1 million newborns annually, can result in lifelong sequelae in infants, such as sensorineural hearing loss and brain damage. Hence, an effective HCMV vaccine is urgently needed to prevent infection and HCMV-associated diseases.

HCMV infection causes persistent, life-long infection in broad types of host cells mediated by four major envelope glycoprotein complexes (GCs): glycoprotein B (gB) oligomer, gM/gN dimer, gH/gL/gO trimer, and gH/gL/UL128/UL130/UL131A pentamer complex (PC) through distinct entry mechanisms. gB is essential for HCMV viral fusion and is required for entry into all permissive cell types and for cell-to-cell spread, has been identified as one of the major vaccine targets due to its ability to elicit both NAb and non-NAb responses. HCMV gH/gL/gO trimer was demonstrated to promote gB fusion on all cell types. Hence, gH/gL/gO trimer is a potential target for HCMV vaccine and potentially preventing HCMV from escaping current clinically tested vaccine-elicited NAbs.

The mumps virus(MuV) is the virus that causes mumps. MuV contains a single-stranded, negative-sense genome made of ribonucleic acid (RNA). The genome of the mumps virus is encased by N proteins to form a flexible, loosely coiled helical ribonucleoprotein (RNP) complex consisting of the genome surrounded by a nucleocapsid that RdRp is bound to. RNPs are surrounded by an envelope, a lipid membrane, which contains two types of spikes on its surface that correspond to the HN and F glycoproteins.

Together, the HN and F proteins mediate virus-to-cell and cell-to-cell fusion, thereby enabling the virus to spread. MuV first interacts via the HN protein binds to sialic acid receptors on the surface of host cells. Following attachment, the F protein is triggered and begins fusing the viral envelope with the host cell's membrane. The F protein does so by changing from a metastable state to refolding to a more stable hairpin structure, which allows the contents of the virion, including the RNP, to be released into the host cell's cytoplasm. Therefore, HN glycoprotein and the F protein are currently the main targets for MuV vaccine development.

Human metapneumovirus (hMPV), a pneumovirus discovered in 2001, is a leading cause of hospitalizations due to acute lower respiratory tract infections. Primary exposure to hMPV typically occurs before age 5 and is responsible for 6%–40% of respiratory infections among hospitalized and outpatient children , second only to respiratory syncytial virus (RSV). However, there are currently no vaccines or specific anti-viral therapies approved for the prevention or treatment hMPV-associated disease.

Similar to RSV, hMPV encodes three surface glycoproteins: the attachment (G), small hydrophobic (SH), and the fusion(F) glycoproteins. The hMPV F glycoprotein is required for infection and is the only known target of neutralizing antibodies. HMPV F is synthesized as an inactive precursor, F0, that is cleaved by trypsin-like proteases to generate two subunits, F2 and F1, that remain covalently linked by disulfide bonds. Mature hMPV F is a trimer of disulfide-linked heterodimers that adopts a metastable pre-fusion (preF) conformation, and neutralizing antibodies inhibit its transition to an energetically favored post-fusion (postF) conformation, thereby preventing viral fusion with host cells. Recent research identified rare, highly potent broadly neutralizing antibodies that recognize pre-fusion-specific epitopes and structurally characterized an antibody that targets a site of vulnerability at the pre-fusion F trimer apex, this study provides promising monoclonal antibody candidates for passive immunoprophylaxis and informs the rational design of hMPV vaccine immunogens.

Japanese encephalitis virus (JEV) is one of the most important causes of human viral encephalitis, mainly prevalent in eastern and southern Asia. The WHO estimates that there are approximately 68,000 cases of Japanese encephalitis (JE) worldwide each year, resulting in approximately 30% mortality. JEV is an enveloped RNA virus with a single-stranded, positive-sense RNA genome of ~11 kb in length. Its genome encodes a single polyprotein, which is cleaved into three structural proteins (C, prM, and E) and seven nonstructural proteins (NS1, NS2A, NS2B, NS3, NS4A, NS4B, and NS5) by host and virus-encoded proteases. JEV relies on various attachment or entry co-factors to enter host cells. Among these co-factors, hTIM-1 has been identified as an attachment factor to promote JEV infection through interacting with phosphatidylserine (PS) on the viral envelope. Recent research showed that hTIM-1 directly interacts with JEV E protein, in which the PS binding sites of hTIM-1 and K38 in E protein play an important role, the interaction between hTIM-1 and E protein mediates JEV infection. Therefore, JEV E protein is a potential target for new generation vaccine.