Specific egg yolk immunoglobulin as a promising non-antibiotic biotherapeutic product against Acinetobacter baumannii pneumonia infection.

Acinetobacter baumannii is a serious health threat with a high mortality rate. We have already reported prophylactic effects of IgYs raised against OmpA and Omp34 as well as against inactivated whole-cell (IWC) of A. baumannii in a murine pneumonia model. However, the infection was exacerbated in the mice group that received IgYs raised against the combination of OmpA and Omp34. The current study was conducted to propose reasons for the observed antibody-dependent enhancement (ADE) in addition to the therapeutic effect of specific IgYs in the murine pneumonia model. This phenomenon was hypothetically attributed to topologically inaccessible similar epitopes of OmpA and Omp34 sharing similarity with peptides of mice proteins. In silico analyses revealed that some inaccessible peptides of OmpA shared similarity with peptides of Omp34 and Mus musculus. Specific anti-OmpA and anti-Omp34 IgYs cross-reacted with Omp34 and OmpA respectively. Specific IgYs showed different protectivity against A. baumannii AbI101 in the murine pneumonia model. IgYs triggered against OmpA or IWC of A. baumannii were the most protective antibodies. IgY triggered against Omp34 is ranked next after those against OmpA. The lowest protection was observed in mice received IgYs raised against the combination of rOmpA and rOmp34. In conclusion, specific IgYs against OmpA, Omp34, and IWC of A. baumannii could serve as novel biotherapeutics against A. baumannii pneumonia.

Antibody-independent and dependent infection of human myeloid cells with dengue virus is inhibited by carrageenan.

This study demonstrated that the λ-carrageenan is a potent and selective inhibitor of the primary infection of human myeloid U937 and K562 cells with the four DENV serotypes, achieving a higher than 99 % reduction in virus production at the highest tested concentration of 20 µg/mL, without affecting cell viability at concentrations up to 1000 µg/mL. Since antibody-dependent enhancement (ADE) is thought to play a main role in the aggravation of severe DENV disease, we also evaluated the activity of carrageenan against ADE of DENV infection. The λ-carrageenan was also effective to block the antibody dependent infection mediated by Fcγ-RII in both cell lines, causing 96-99 % inhibition in virus production from cells infected with immune complexes of DENV-2 and DENV-3. Moreover, the inhibitory effectiveness of carrageenan was similar against prM-mediated ADE or E-mediated ADE. Mechanistic studies indicated that DENV-2 entry is the main antiviral target for carrageenan in DENV or DENV-Ab infected human myeloid cells since a strong inhibitory effect was observed when the carrageenan was present only during adsorption at 4 °C or internalization at 37 °C, whereas the infection was not altered when the compound was added after virus internalization. Thus, our findings have shown that carrageenan may be considered an interesting antiviral agent able to block DENV entry during both primary and antibody-dependent infection of human myeloid cells.

Role of antibody-dependent enhancement (ADE) in the virulence of SARS-CoV-2 and its mitigation strategies for the development of vaccines and immunotherapies to counter COVID-19.

Coronavirus disease-2019 (COVID-19) pandemic has become a global threat and death tolls are increasing worldwide. The SARS-CoV-2 though shares similarities with SARS-CoV and MERS-CoV, immunopathology of the novel virus is not understood properly. Previous reports from SARS and MERS-CoV documents that preexisting, non-neutralizing or poorly neutralizing antibodies developed as a result of vaccine or infection enhance subsequent infection, a phenomenon called as antibody-dependent enhancement (ADE). Since immunotherapy has been implicated for COVID-19 treatment and vaccine is under development, due consideration has to be provided on ADE to prevent untoward reactions. ADE mitigation strategies like the development of vaccine or immunotherapeutics targeting receptor binding motif can be designed to minimize ADE of SARS-CoV-2 since full-length protein-based approach can lead to ADE as reported in MERS-CoV. The present mini-review aims to address the phenomenon of ADE of SARS-CoV-2 through the lessons learned from SARS-CoV and MERS-CoV and ways to mitigate them so as to develop better vaccines and immunotherapeutics against SARS-CoV-2.

Prospect of SARS-CoV-2 spike protein: Potential role in vaccine and therapeutic development.

The recent outbreak of the betacoronavirus SARS-CoV-2 has become a significant concern to public health care worldwide. As of August 19, 2020, more than 22,140,472 people are infected, and over 781,135 people have died due to this deadly virus. In the USA alone, over 5,482,602 people are currently infected, and more than 171,823 people have died. SARS-CoV-2 has shown a higher infectivity rate and a more extended incubation period as compared to previous coronaviruses. SARS-CoV-2 binds much more strongly than SARS-CoV to the same host receptor, angiotensin-converting enzyme 2 (ACE2). Previously, several methods to develop a vaccine against SARS-CoV or MERS-CoV have been tried with limited success. Since SARS-CoV-2 uses the spike (S) protein for entry to the host cell, it is one of the most preferred targets for making vaccines or therapeutics against SARS-CoV-2. In this review, we have summarised the characteristics of the S protein, as well as the different approaches being used for the development of vaccines and/or therapeutics based on the S protein.

The role of IgG Fc receptors in antibody-dependent enhancement.

Antibody-dependent enhancement (ADE) is a mechanism by which the pathogenesis of certain viral infections is enhanced in the presence of sub-neutralizing or cross-reactive non-neutralizing antiviral antibodies. In vitro modelling of ADE has attributed enhanced pathogenesis to Fcγ receptor (FcγR)-mediated viral entry, rather than canonical viral receptor-mediated entry. However, the putative FcγR-dependent mechanisms of ADE overlap with the role of these receptors in mediating antiviral protection in various viral infections, necessitating a detailed understanding of how this diverse family of receptors functions in protection and pathogenesis. Here, we discuss the diversity of immune responses mediated upon FcγR engagement and review the available experimental evidence supporting the role of FcγRs in antiviral protection and pathogenesis through ADE. We explore FcγR engagement in the context of a range of different viral infections, including dengue virus and SARS-CoV, and consider ADE in the context of the ongoing SARS-CoV-2 pandemic.

Immunoglobulins in the treatment of COVID-19 infection: Proceed with caution!

The COVID-19 pandemic is one of the greatest infectious challenges in recent history. Presently, few treatment options exist and the availability of effective vaccines is at least one year away. There is an urgent need to find currently available, effective therapies in the treatment of patients with COVID-19 infection. In this review, we compare and contrast the use of intravenous immunoglobulin and hyperimmune globulin in the treatment of COVID-19 infection.

A conceptual model for optimizing vaccine coverage to reduce vector-borne infections in the presence of antibody-dependent enhancement.

BACKGROUND: Many vector-borne diseases co-circulate, as the viruses from the same family are also transmitted by the same vector species. For example, Zika and dengue viruses belong to the same Flavivirus family and are primarily transmitted by a common mosquito species Aedes aegypti. Zika outbreaks have also commonly occurred in dengue-endemic areas, and co-circulation and co-infection of both viruses have been reported. As recent immunological cross-reactivity studies have confirmed that convalescent plasma following dengue infection can enhance Zika infection, and as global efforts of developing dengue and Zika vaccines are intensified, it is important to examine whether and how vaccination against one disease in a large population may affect infection dynamics of another disease due to antibody-dependent enhancement. METHODS: Through a conceptual co-infection dynamics model parametrized by reported dengue and Zika epidemic and immunological cross-reactivity characteristics, we evaluate impact of a hypothetical dengue vaccination program on Zika infection dynamics in a single season when only one particular dengue serotype is involved. RESULTS: We show that an appropriately designed and optimized dengue vaccination program can not only help control the dengue spread but also, counter-intuitively, reduce Zika infections. We identify optimal dengue vaccination coverages for controlling dengue and simultaneously reducing Zika infections, as well as the critical coverages exceeding which dengue vaccination will increase Zika infections. CONCLUSION: This study based on a conceptual model shows the promise of an integrative vector-borne disease control strategy involving optimal vaccination programs, in regions where different viruses or different serotypes of the same virus co-circulate, and convalescent plasma following infection from one virus (serotype) can enhance infection against another virus (serotype). The conceptual model provides a first step towards well-designed regional and global vector-borne disease immunization programs.

Anti-Idiotypic Antibodies Specific to prM Monoantibody Prevent Antibody Dependent Enhancement of Dengue Virus Infection.

Dengue virus (DENV) co-circulates as four serotypes (DENV1-4). Primary infection only leads to self-limited dengue fever. But secondary infection with another serotype carries a higher risk of increased disease severity, causing life-threatening dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS). Serotype cross-reactive antibodies facilitate DENV infection in Fc-receptor-bearing cells by promoting virus entry via Fcγ receptors (FcγR), a process known as antibody dependent enhancement (ADE). Most studies suggested that enhancing antibodies were mainly specific to the structural premembrane protein (prM) of DENV. However, there is still no effective drugs or vaccines to prevent ADE. In this study, we firstly confirmed that both DENV-2 infected human sera (anti-DENV-2) and DENV-2 prM monoclonal antibody (prM mAb) could significantly enhance DENV-1 infection in K562 cells. Then we developed anti-idiotypic antibodies (prM-AIDs) specific to prM mAb by immunizing of Balb/c mice. Results showed that these polyclonal antibodies can dramatically reduce ADE phenomenon of DENV-1 infection in K562 cells. To further confirm the anti-ADE effect of prM-AIDs in vivo, interferon-α and γ receptor-deficient mice (AG6) were used as the mouse model for DENV infection. We found that administration of DENV-2 prM mAb indeed caused a higher DENV-1 titer as well as interleukin-10 (IL-10) and alaninea minotransferase (ALT) in mice infected with DENV-1, similar to clinical ADE symptoms. But when we supplemented prM-AIDs to DENV-1 challenged AG6 mice, the viral titer, IL-10 and ALT were obviously decreased to the negative control level. Of note, the number of platelets in peripheral blood of prM-AIDs group were significantly increased at day 3 post infection with DENV-1 compared that of prM-mAb group. These results confirmed that our prM-AIDs could prevent ADE not only in vitro but also in vivo, suggested that anti-idiotypic antibodies might be a new choice to be considered to treat DENV infection.

Inhibition of endoplasmic reticulum glucosidases is required for in vitro and in vivo dengue antiviral activity by the iminosugar UV-4.

The antiviral activity of UV-4 was previously demonstrated against dengue virus serotype 2 (DENV2) in multiple mouse models. Herein, step-wise minimal effective dose and therapeutic window of efficacy studies of UV-4B (UV-4 hydrochloride salt) were conducted in an antibody-dependent enhancement (ADE) mouse model of severe DENV2 infection in AG129 mice lacking types I and II interferon receptors. Significant survival benefit was demonstrated with 10-20 mg/kg of UV-4B administered thrice daily (TID) for seven days with initiation of treatment up to 48 h after infection. UV-4B also reduced infectious virus production in in vitro antiviral activity assays against all four DENV serotypes, including clinical isolates. A set of purified enzyme, in vitro, and in vivo studies demonstrated that inhibition of endoplasmic reticulum (ER) α-glucosidases and not the glycosphingolipid pathway appears to be responsible for the antiviral activity of UV-4B against DENV. Along with a comprehensive safety package, these and previously published data provided support for an Investigational New Drug (IND) filing and Phases 1 and 2 clinical trials for UV-4B with an indication of acute dengue disease.

Antibody with an engineered Fc region as a therapeutic agent against dengue virus infection.

Antibody-dependent enhancement (ADE) of dengue virus (DENV) infectivity is thought to play a crucial role in severe dengue disease. It occurs when pre-existing sub-neutralizing anti-DENV antibody (Ab) produced from a primary infection encounters a DENV serotype different from that of the initial infection and forms immune complexes, which enable the efficient infection of Fcγ receptor-bearing cells. However, the exact role played by Abs during a secondary infection of patients remains unknown. We previously obtained a broadly cross-reactive neutralizing IgG1 human monoclonal anti-DENV envelope (E) Ab (HuMAb) D23-1G7C2-IgG1 from a DENV-infected patient; however, D23-1G7C2-IgG1 had ADE activity. With the aim of being able to reduce the ADE activity, we exchanged the Fc region of D23-1G7C2 to generate Abs bearing each of the three other IgG subclasses (IgG2-4). In addition, N297A, a mutation known to reduce the affinity of the IgG1 Fc region for Fcγ receptors, was introduced into D23-1G7C2-IgG1. Swapping D23-1G7C2-IgG1 to IgG2 or IgG4 subclasses reduced ADE activity in FcγRI and FcγRII-bearing THP-1 cells. By contrast, in FcγRII-bearing K562 cells, the change to IgG2 increased ADE activity. Introducing the N297A mutation into D23-1G7C2-IgG1 resulted in a marked reduction in ADE activity in both cell types. Compared to D23-1G7C2-IgG1, D23-1G7C2-IgG1-N297A was less protective in IFN-α/ß/γ receptor knockout mice infected with a lethal dose of recombinant chimeric DENV, carrying prME of DENV-2 in Japanese encephalitis virus (80% vs. 40% survival, respectively). These observations provide valuable information regarding the use of recombinant Abs as therapeutics.

Antibody-dependent enhancement of dengue virus infection is inhibited by SA-17, a doxorubicin derivative.

Antibody-dependent enhancement (ADE) is thought to play a critical role in the exacerbation of dengue virus (DENV)-induced disease during a heterologous re-infection. Despite ADE's clinical impact, only a few antiviral compounds have been assessed for their anti-ADE activity. We reported earlier that SA-17, a doxorubicin derivative, efficiently inhibits the in vitro infection of DENV and yellow fever virus. Here we explored SA-17's mechanism of inhibition and investigated if the compound is active against ADE of DENV infection. Since enhanced infectivity stimulated by antibodies has been observed with standard and immature DENV, both types of virions were included in the study. We observed that SA-17 (i) inhibits DENV infection by preventing binding/entry to the cell and (ii) interferes with antibody-mediated infection of both standard and immature DENV2. SA-17 markedly reduced the infectivity of DENV2 in ADE conditions, with IC50s ranging from 0.26 to 2.89µM. The compound exerted its activity when added before, during, and after antibody-opsonization of standard and immature virus. Thus, molecules with the characteristics of SA-17 may be attractive antiviral agents since they can be used both to block DENV2 entry during primary and secondary infection and to inhibit ADE of standard and immature virus.

Sulfated polysaccharide, curdlan sulfate, efficiently prevents entry/fusion and restricts antibody-dependent enhancement of dengue virus infection in vitro: a possible candidate for clinical application.

Curdlan sulfate (CRDS), a sulfated 1→3-ß-D glucan, previously shown to be a potent HIV entry inhibitor, is characterized in this study as a potent inhibitor of the Dengue virus (DENV). CRDS was identified by in silico blind docking studies to exhibit binding potential to the envelope (E) protein of the DENV. CRDS was shown to inhibit the DENV replication very efficiently in different cells in vitro. Minimal effective concentration of CRDS was as low as 0.1 µg/mL in LLC-MK2 cells, and toxicity was observed only at concentrations over 10 mg/mL. CRDS can also inhibit DENV-1, 3, and 4 efficiently. CRDS did not inhibit the replication of DENV subgenomic replicon. Time of addition experiments demonstrated that the compound not only inhibited viral infection at the host cell binding step, but also at an early post-attachment step of entry (membrane fusion). The direct binding of CRDS to DENV was suggested by an evident reduction in the viral titers after interaction of the virus with CRDS following an ultrafiltration device separation, as well as after virus adsorption to an alkyl CRDS-coated membrane filter. The electron microscopic features also showed that CRDS interacted directly with the viral envelope, and caused changes to the viral surface. CRDS also potently inhibited DENV infection in DC-SIGN expressing cells as well as the antibody-dependent enhancement of DENV-2 infection. Based on these data, a probable binding model of CRDS to DENV E protein was constructed by a flexible receptor and ligand docking study. The binding site of CRDS was predicted to be at the interface between domains II and III of E protein dimer, which is unique to this compound, and is apparently different from the ß-OG binding site. Since CRDS has already been tested in humans without serious side effects, its clinical application can be considered.

Antibody-dependent enhancement of feline infectious peritonitis virus infection in feline alveolar macrophages and human monocyte cell line U937 by serum of cats experimentally or naturally infected with feline coronavirus.

Infection of the type II feline infectious peritonitis virus (FIPV) strain 79-1146 to primary feline alveolar macrophages and human monocyte cell line U937 was enhanced by the sera of cats experimentally infected with the 79-1146 strain, but not those of cats infected with KU-2 or UCD-1 strain of type I FIPV. The experiments using sera of cats with feline infectious peritonitis (FIP) and of cats naturally infected with feline coronavirus (FCoV) revealed that infection of the FIPV 79-1146 strain to the U937 cells was enhanced only by the sera of cats infected with type II FIPV or feline enteric coronavirus. The samples positive for antibody-dependent enhancement (ADE) activity had high neutralizing antibody titers against the FIPV 79-1146 strain and the samples negative for ADE activity had low neutralizing antibody titers. These findings support the previous results where a monoclonal antibody with neutralizing activity had high ADE activity, suggesting that there was a close relationship between the neutralization and enhancement sites. And then it is also suggested that ADE of infection is likely to be induced by re-infection with the same serotype of virus in type II FIPV infection. Furthermore, U937 cells are considered useful and can be substituted for the feline macrophages for determining ADE of FIPV-infection.