Role of pre-existing immunity in driving the dengue virus serotype 2 genotype shift in the Philippines: A retrospective analysis of serological data

OBJECTIVE

The invasion of dengue virus (DENV)-2 Cosmopolitan genotype into the Philippines, where the Asian II genotype previously circulated challenges the principle of dengue serotype-specific immunity. Assessment of antibodies in this population may provide a mechanistic basis for how new genotypes emerge in dengue-endemic areas.

METHODS

We evaluated the neutralizing antibody (nAb) and antibody-dependent enhancement (ADE) responses against the two genotypes using archived serum samples collected from 333 patients with confirmed dengue in Metro Manila, Philippines, before, during, and after the introduction of the Cosmopolitan genotype. We quantified nAb titers in baby hamster kidney (BHK-21) cells with or without the Fcγ receptor IIA (FcγRIIA) to detect the capacity of virus-antibody complexes to neutralize or enhance DENV.

RESULTS

The nAb potency of the archived serum samples against the two genotypes was greatly affected by the presence of FcγRIIA. We found significant differences in nAb titers between the two genotypes in BHK-21 cells with FcγRIIA (P <0.0001). The archived serum samples were incapable of fully neutralizing the Cosmopolitan genotype, but instead strongly promoted its ADE compared to the Asian II genotype (P <0.0001).

CONCLUSION

These results reinforce the role of pre-existing immunity in driving genotype shifts. Our finding that specific genotypes exhibit differing susceptibilities to ADE by cross-reactive antibodies may have implications for dengue vaccine development.

A second local dengue fever outbreak: A field experience from Muscat Governorate in Oman, 2022

Background

Dengue fever is an infectious disease of global health concern. This study aimed to describe the epidemiology and field experience of a locally transmitted outbreak of dengue fever in Muscat Governorate, Oman from mid-March to mid-April 2022, and the multi-sectoral approach to control the outbreak.

Methods

Data were collected from an electronic e-notification system, active surveillance and contact investigations.

Results

Of 250 suspected and probable cases, 169 were confirmed as dengue fever with DENV-2 serotype. Of these, 108 (63.9%) were male and 94 (55.6%) were Omani. The mean age was 39 years (standard deviation 13 years). Fever was the most common symptom and occurred in 100% of cases. Haemorrhagic manifestations occurred in 10% (n=17) of cases. Hospitalization was required for 93 cases (55.1%). The field investigation included 3444 houses and other suspected sites. Breeding sites for Aedes aegypti were identified in 565 (18.5%) sites visited. Interventions to control the outbreak included environmental and entomological assessment of the affected houses and surrounding areas (400 m radius of each house).

Conclusion

Outbreaks are expected to continue, with the possibility of severe cases due to antibody-dependent enhancement. More data are required to understand the genetics, geographical spread and behaviour of A. aegypti in Oman.

Neurological Manifestations of Perinatal Dengue

Dengue viruses (DENVs) are single-stranded RNA viruses belonging to the family Flaviviridae. There are four distinct antigenically related serotypes, DENVs types 1, 2, 3, and 4. These are all mosquito-borne human pathogens. Congenital dengue disease occurs when there is mother-to-fetus transmission of the virus and should be suspected in endemic regions in neonates presenting with fever, maculopapular rash, and thrombocytopenia. Although most of the infected infants remain asymptomatic, some can develop clinical manifestations such as sepsis-like illness, gastric bleeding, circulatory failure, and death. Neurological manifestations include intracerebral hemorrhages, neurological malformations, and acute focal/disseminated encephalitis/encephalomyelitis. Dengue NS1Ag, a highly conserved glycoprotein, can help the detection of cases in the viremic stage. We do not have proven specific therapies yet; management is largely supportive and is focused on close monitoring and maintaining adequate intravascular volume.

Impact of tetravalent dengue vaccination with screening, ADE, and altered infectivity on single-serotype dengue and Zika transmission

Acquired immunity to a dengue virus serotype (whether by infection or the only licensed dengue vaccine) can produce antibody-dependent enhancement (ADE) in later infections with another dengue serotype, resulting in higher viral loads and more severe symptoms such as dengue hemorrhagic fever, unless the person already has immunity to multiple dengue serotypes. Screening to confirm dengue seropositivity is therefore recommended before vaccination. Recent studies suggest that the closely-related Zika virus may also interact with dengue through ADE. This study uses a mathematical model to evaluate the likely impact of imperfect screening and dengue vaccination on the spread of both viruses in a population where only one dengue serotype circulates, although the vaccine may take against any or all of the four recognized serotypes. Analysis focuses on the reproductive numbers of the viruses. Results indicate that vaccination increases the spread of Zika through induced ADE, while its impact on the spread of dengue depends on screening specificity and serotype-specific vaccine efficacies, as well as the intensity of ADE. Numerical analysis identifies the roles played by age-in and catch-up vaccination as well as screening characteristics and prior dengue exposure.

Development of a rapid assay system for detecting antibody-dependent enhancement of dengue virus infection

Antibody-dependent enhancement (ADE) is one of the pathogenic mechanisms related to disease severity in dengue virus infection. Conventional assays for detecting ADE activity usually require several days. In this study, we established a rapid assay system to evaluate ADE activity in dengue-seropositive samples using single round infectious particles (SRIPs). Human Fc-gamma receptor-bearing cells (K562 and Mylc cells) were infected with SRIP antigen in the presence of human serum samples to measure ADE activity. Two assay protocols were introduced: (i) rapid assay with 5 h of incubation, and (ii) semi-rapid assay with 24 h of incubation. The rapid assay requires a large quantity of SRIP antigen and gives results in half a day. Although the semi-rapid assay requires slightly more than a day, it can be performed using only a small amount of SRIP. Interestingly, the range of the number of Mylc cells required for the semi-rapid assay was wider than that of K562 cells. Significant correlations were observed between the rapid and semi-rapid assays for both cell types. Although it is difficult to judge which protocol best reflects the current immune status in vivo, both assays could rapidly provide valuable information regarding the risk assessment for severe diseases.

The resurgence risk of COVID-19 in China in the presence of immunity waning and ADE: A mathematical modelling study

The mass vaccination program has been actively promoted since the end of 2020. However, waning immunity, antibody-dependent enhancement (ADE), and increased transmissibility of variants make the herd immunity untenable and the implementation of dynamic zero-COVID policy challenging in China. To explore how long the vaccination program can prevent China at low resurgence risk, and how these factors affect the long-term trajectory of the COVID-19 epidemics, we developed a dynamic transmission model of COVID-19 incorporating vaccination and waning immunity, calibrated using the data of accumulative vaccine doses administered and the COVID-19 epidemic in 2020 in mainland China. The prediction suggests that the vaccination coverage with at least one dose reach 95.87%, and two doses reach 77.92% on 31 August 2021. However, despite the mass vaccination, randomly introducing infected cases in the post-vaccination period causes large outbreaks quickly with waning immunity, particularly for SARS-CoV-2 variants with higher transmissibility. The results showed that with the current vaccination program and 50% of the population wearing masks, mainland China can be protected at low resurgence risk until 8 January 2023. However, ADE and higher transmissibility for variants would significantly shorten the low-risk period by over 1 year. Furthermore, intermittent outbreaks can occur while the peak values of the subsequent outbreaks decrease, indicating that subsequent outbreaks boosted immunity in the population level, further indicating that follow-up vaccination programs can help mitigate or avoid the possible outbreaks. The findings revealed that the integrated effects of multiple factors: waning immunity, ADE, relaxed interventions, and higher variant transmissibility, make controlling COVID-19 challenging. We should prepare for a long struggle with COVID-19, and not entirely rely on the COVID-19 vaccine.

Engineered flavivirus vaccines control induction of crossreactive infection-enhancing and -neutralizing antibodies

Flaviviruses are important human pathogens because of their global distribution and disease severity. The high structural similarity among flaviviruses induces cross-immunity, with individual flaviviruses exhibiting crossreactive infection-enhancing and/or -neutralizing activities against other flaviviruses. Unlike neutralizing antibodies, enhancing antibodies may increase the risk of disease severity. Vaccine-induced enhancement remains a concern in the development of flavivirus vaccines. Here, we immunized mice with DNA vaccine candidates (pcJEME, pcWNME or pcZIKME) against Japanese encephalitis virus (JEV), West Nile virus (WNV) or Zika virus (ZIKV), respectively, and investigated crossreactive neutralizing and enhancing antibody activities against seven flaviviruses. pcZIKME induced higher cross-neutralization against dengue viruses than against JEV and WNV. Moreover, pcZIKME with a single amino acid substitution (D87N) showed an increase in crossreactive neutralizing activity and a decrease in enhancing activities against other flaviviruses. A similar trend was observed in pcWNME. Engineered antigen might contribute to the development of safe and effective flavivirus vaccines.

A human monoclonal antibody to neutralize all four serotypes of dengue virus derived from patients at the convalescent phase of infection

Dengue virus (DENV) is a prevalent mosquito-transmitted human pathogen, causing about 100 million cases of acute dengue fever and 21,000 deaths annually worldwide. Therapeutic neutralizing antibodies against dengue virus might be effective to treat severe dengue fever. Here, we showed that human monoclonal antibody (HMAb) 9C7 bound to all four intact serotypes of DENV but not to the recombinant envelope protein, suggesting HMAb 9C7 recognized a conformational epitope of the envelope protein. Taken together our results suggested that HMAb 9C7 neutralized all four serotypes of DENV in vitro and, for DENV-1, indicated activity at the pre- and post-attachment steps in the viral life cycle. HMAb 9C7 potently protected suckling mice from lethal challenge with all four serotypes of DENV. FcγRII-mediated uptake of immune complexes and antibody-dependent enhancement at low doses of the antibody were abolished by two Leu-to-Ala (9C7-LALA) mutations or deletion of nine amino acids (9C7-9del) in HMAb 9C7 Fc. Therefore, HMAb 9C7 represented a promising prophylactic and therapeutic agent against all four serotypes of DENV.

Non-neutralizing antibodies: Deleterious or propitious during SARS-CoV-2 infection?

Antibody-dependent enhancement (ADE) is a complex phenomenon mediated by antibodies, frequently pre-existing non-neutralizing or sub-neutralizing antibodies. In the course of infectious diseases, ADE may be responsible for worsening the clinical course of the disease by increasing the virulence of pathogens (ADE of infection) or enhancing disease severity (ADE of disease). Here we reviewed the mechanisms thought to be behind the ADE phenomenon and its potential relationship with COVID-19 severity. Since the early COVID-19 epidemics, ADE has been mentioned as a possible mechanism involved in severe COVID-19 disease and, later, as a potential risk in the case of infection after vaccination. However, current data do not support its role in disease severity, both after infection and reinfection.

A fulminant case of Epstein-Barr Virus encephalitis with multiorgan dysfunction

Epstein-Barr Virus also known as Human herpesvirus 4 usually causes infectious mononucleosis which is a benign disease with mild or no symptoms. Death due to Epstein-Barr Virus infections is extremely rare. We present a case of fulminant Epstein-Barr Virus encephalitis who developed multiorgan dysfunction on second day and succumbed within 52 h of symptom onset.

Anti-SARS-CoV2 antibody-mediated cytokine release syndrome in a patient with acute promyelocytic leukemia

BACKGROUND

Passive immunization against SARS-CoV-2 limits viral burden and death from COVID-19; however, it poses a theoretical risk of disease exacerbation through antibody-dependent enhancement (ADE). ADE after anti-SARS-CoV2 antibody treatment has not been reported, and therefore the potential risk and promoting factors remain unknown.

CASE PRESENTATION

A 75-year-old female was admitted to the emergency room with recurrent, unexplained bruises and leukocytopenia, anemia, and thrombocytopenia. Evaluation of a bone marrow biopsy established the diagnosis of an acute promyelocytic leukemia (APL). SARS-CoV-2 RT-PCR testing of nasal and throat swabs on admission was negative. During the routine SARS-CoV-2 testing of inpatients, our patient tested positive for SARS-CoV-2 on day 14 after admission without typical COVID-19 symptoms. Due to disease- and therapy-related immunosuppression and advanced age conferring a high risk of progressing to severe COVID-19, casirivimab and imdevimab were administered as a preemptive approach. The patient developed immune activation and cytokine release syndrome (CRS) occurring within four hours of preemptive anti-SARS-CoV2 antibody (casirivimab/imdevimab) infusion. Immune activation and CRS were evidenced by a rapid increase in serum cytokines (IL-6, TNFα, IL-8, IL-10), acute respiratory insufficiency, and progressive acute respiratory distress syndrome.

DISCUSSION AND CONCLUSION

The temporal relationship between therapeutic antibody administration and the rapid laboratory, radiological, and clinical deterioration suggests that CRS was an antibody-related adverse event, potentially exacerbated by APL treatment-mediated differentiation of leukemic blasts and promyelocytes. This case highlights the need for careful assessment of life-threatening adverse events after passive SARS-CoV-2 immunization, especially in the clinical context of patients with complex immune and hematological landscapes.

A mathematical model to evaluate the role of memory B and T cells in heterologous secondary dengue infection

We propose a mathematical model to investigate the antibody-dependent enhancement (ADE) phenomenon during secondary dengue infection. The model consists of an ODE system that describes the interaction of the dengue virus with macrophages and memory B and T cell role during the infection. The qualitative model analysis is done in terms of memory B and T cell cloning parameters and the basic reproduction number R₀. In the absence of memory B and T cell cloning, if R₀<1 the dengue virus population extinguishes, while for R₀>1, it tends asymptotically to a positive equilibrium. However, when we consider the memory B cell cloning, it is possible to occur dengue infection even when R₀<1. Memory T cells have an essential role in eliminating the possibility of ADE occurrence when R₀<1.

Efficacy of a live attenuated highly pathogenic PRRSV vaccine against a NADC30-like strain challenge: implications for ADE of PRRSV

BACKGROUND

Porcine reproductive and respiratory syndrome virus (PRRSV) infection can cause severe reproductive failure in sows and respiratory distress in pigs of all ages, leading to major economic losses. To date, there are still no effective strategies to prevent and control PRRSV. Antibody-dependent enhancement (ADE), a phenomenon in which preexisting non-neutralizing antibodies or sub-neutralizing antibodies facilitate virus entry and replication, may be a significant obstacle in the development of effective vaccines for many viruses, including PRRSV. However, the contribution of ADE to PRRSV infection remains controversial, especially in vivo. Whether attenuated PRRSV vaccines prevent or worsen subsequent disease in pigs infected by novel PRRSV strains requires more research. In the present study, in vivo experiments were conducted to evaluate ADE under different immune statuses, which were produced by waiting different lengths of time after vaccination with a commercially available attenuated highly pathogenic PRRSV (HP-PRRSV) vaccine (JXA1-R) before challenging the pigs with a novel heterologous NADC30-like strain.

RESULTS

Piglets that were vaccinated before being challenged with PRRSV exhibited lower mortality rates, lower body temperatures, higher bodyweight gain, and lower viremia. These results demonstrate that vaccination with JXA1-R alleviated the clinical signs of PRRSV infection in all vaccinated groups.

CONCLUSIONS

The obtained data indicate that the attenuated vaccine test here provided partial protection against the NADC30-like strain HNhx. No signs of enhanced PRRSV infection were observed under the applied experimental conditions. Our results provide some insight into the molecular mechanisms underlying vaccine-induced protection or enhancement in PRRSV.

Dynamics of host immune responses to SARS-CoV-2

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the most recent global health threat, is spreading throughout the world with worrisome speed, and the current wave of coronavirus disease 2019 (COVID-19) seems to have no mercy. While this mysterious virus challenges our ability to control viral infections, our opportunities to control the COVID-19 pandemic are gradually fading. Currently, pandemic management relies on preventive interventions. Although prevention is a good strategy to mitigate SARS-CoV-2 transmission, it still cannot be considered an absolute solution to eliminate this pandemic. Currently, developing a potent immunity against this viral infection seems to be the most promising strategy to drive down this ongoing global tragedy. However, with the emergence of new challenges in the context of immune responses to COVID-19, the road to control this devastating pandemic seems bumpier; thus, it is pivotal to characterize the dynamics of host immune responses to COVID-19, in order to develop efficient prophylactic and therapeutic tools. This begs the question of whether the effector mechanisms of the immune system are indeed potent or a possible contributing factor to developing more severe and lethal forms of COVID-19. In this review, the possible role of the immunopathologic phenomena including antibody-dependent enhancement, cytokine storm, and original antigenic sin in severity and mortality of COVID-19 will be discussed.

The COVID-19 Vaccine Landscape

The history of vaccine development spans centuries. At first, whole pathogens were used as vaccine agents, either inactivated or attenuated, to reduce virulence in humans. Safety and tolerability were increased by including only specific proteins as antigens and using cell culture methods, while novel vaccine strategies, like nucleic acid- or vector-based vaccines, hold high promise for the future. Vaccines have generally not been employed as the primary tools in outbreak response, but this might change since advances in medical technology in the last decades have made the concept of developing vaccines against novel pathogens a realistic strategy. Wandering the uncharted territory of a novel pathogen, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), we can learn from other human Betacoronaviridae that emerged in the last decades, SARS-CoV-1 and MERS-CoV. We can identify the most likely target structures of immunity, establish animal models that emulate human disease and immunity as closely as possible, and learn about complex mechanisms of immune interaction such as cross-reactivity or antibody-dependent enhancement (ADE). However, significant knowledge gaps remain. What are the correlates of protection? How do we best induce immunity in vulnerable populations like the elderly? Will the immunity induced by vaccination (or by natural infection) wane over time? To date, at least 149 vaccine candidates against SARS-CoV-2 are under development. At the time of writing, at least 17 candidates have already progressed past preclinical studies (in vitro models and in vivo animal experiments) into clinical development. This chapter will provide an overview of this rapidly developing field.

Use of convalescent plasma for COVID-19 in India: A review & practical guidelines

Convalescent plasma (CP) therapy is one of the promising therapies being tried for COVID-19 patients. This passive immunity mode involves separating preformed antibodies against SARS-CoV-2 from a recently recovered COVID-19 patient and infusing it into a patient with active disease or an exposed individual for prophylaxis. Its advantages include ease of production, rapid deployment, specificity against the target infectious agent, and scalability. In the current pandemic, it has been used on a large scale across the globe and also in India. However, unequivocal proof of efficacy and effectiveness in COVID-19 is still not available. Various CP therapy parameters such as donor selection, antibody quantification, timing of use, and dosing need to be considered before its use. The current review attempts to summarize the available evidence and provide recommendations for setting up CP protocols in clinical and research settings.

mRNA vaccine: a potential therapeutic strategy

mRNA vaccines have tremendous potential to fight against cancer and viral diseases due to superiorities in safety, efficacy and industrial production. In recent decades, we have witnessed the development of different kinds of mRNAs by sequence optimization to overcome the disadvantage of excessive mRNA immunogenicity, instability and inefficiency. Based on the immunological study, mRNA vaccines are coupled with immunologic adjuvant and various delivery strategies. Except for sequence optimization, the assistance of mRNA-delivering strategies is another method to stabilize mRNAs and improve their efficacy. The understanding of increasing the antigen reactiveness gains insight into mRNA-induced innate immunity and adaptive immunity without antibody-dependent enhancement activity. Therefore, to address the problem, scientists further exploited carrier-based mRNA vaccines (lipid-based delivery, polymer-based delivery, peptide-based delivery, virus-like replicon particle and cationic nanoemulsion), naked mRNA vaccines and dendritic cells-based mRNA vaccines. The article will discuss the molecular biology of mRNA vaccines and underlying anti-virus and anti-tumor mechanisms, with an introduction of their immunological phenomena, delivery strategies, their importance on Corona Virus Disease 2019 (COVID-19) and related clinical trials against cancer and viral diseases. Finally, we will discuss the challenge of mRNA vaccines against bacterial and parasitic diseases.

Current Status of COVID-19 Vaccine Development: Focusing on Antigen Design and Clinical Trials on Later Stages

The global outbreak of coronavirus disease 2019 (COVID-19) is still threatening human health, economy, and social life worldwide. As a counteraction for this devastating disease, a number of vaccines are being developed with unprecedented speed combined with new technologies. As COVID-19 vaccines are being developed in the absence of a licensed human coronavirus vaccine, there remain further questions regarding the long-term efficacy and safety of the vaccines, as well as immunological mechanisms in depth. This review article discusses the current status of COVID-19 vaccine development, mainly focusing on antigen design, clinical trials in later stages, and immunological considerations for further study.

Neutralization of Zika virus by E protein domain III-Specific human monoclonal antibody

Zika virus (ZIKV) infection in both infants and adults is associated with neurological complications including, but not limited to, microcephaly and Guillain-Barre syndrome. Antibody therapy can be effective against virus infection. We isolated ZIKV envelope domain III-specific neutralizing antibodies (nAbs) from two convalescent patients with ZIKV infection. One antibody, 2F-8, exhibited potent in vitro neutralizing activity against Asian and American strains of ZIKV. To prevent FcγR-mediated antibody-dependent enhancement, we prepared IgG₁ with LALA variation. A single dose of 2F-8 in the context of IgG₁ or IgG₁-LALA prior to or post lethal ZIKV challenge conferred complete protection in mice.

Zika virus envelope nanoparticle antibodies protect mice without risk of disease enhancement

Background

Zika virus (ZIKV), an arbovirus capable of causing neurological abnormalities, is a recognised human pathogen, for which a vaccine is required. As ZIKV antibodies can mediate antibody-dependent enhancement (ADE) of dengue virus (DENV) infection, a ZIKV vaccine must not only protect against ZIKV but must also not sensitise vaccinees to severe dengue.

Methods

The N-terminal 80% of ZIKV envelope protein (80E) was expressed in Pichia pastoris and its capacity to self-assemble into particulate structures evaluated using dynamic light scattering and electron microscopy. Antigenic integrity of the 80E protein was evaluated using ZIKV-specific monoclonal antibodies. Its immunogenicity and protective efficacy were assessed in BALB/c and C57BL/6 Stat2^−/− mice, respectively. Its capacity to enhance DENV and ZIKV infection was assessed in AG129 and C57BL/6 Stat2^−/− mice, respectively.

Findings

ZIKV-80E protein self-assembled into discrete nanoparticles (NPs), which preserved the antigenic integrity of neutralising epitopes on E domain III (EDIII) and elicited potent ZIKV-neutralising antibodies predominantly against this domain in BALB/c mice. These antibodies conferred statistically significant protection in vivo (p = 0.01, Mantel–Cox test), and did not exacerbate sub-lethal DENV-2 or ZIKV challenges in vivo.

Interpretation

Yeast-expressed ZIKV-80E, which forms highly immunogenic EDIII-displaying NPs, elicits ZIKV EDIII-specific antibodies capable of offering significant protection in vivo, without the potential risk of ADE upon subsequent DENV-2 or ZIKV infection. This offers a promising vaccine candidate for further development.

Funding

This study was supported partly by ICGEB, India, and by NIAID, USA.

A human bispecific neutralization antibody against four serotypes of dengue virus

In tropical and subtropical countries, dengue virus (DENV) infections have been increasing; however, we still lack effective therapy. In the present study, we aimed to engineer a bispecific antibody (subsequently named LUZ-8F2-6B1), based on monoclonal antibody 6B1, which has anti DENV-1, 2, and 3 activity, and 8F2, which has anti DENV-4 activity. LUZ-8F2-6B1 displayed potent neutralization activity against four serotypes of DENV by binding to the envelop protein. In vivo, we demonstrated that LUZ-8F2-6B1 could provide protection against infection by four serotypes of DENV in a mouse model. In addition, the deletion of nine amino acids in the Fc region (LUZ-8F2-6B1-9del) completely abolished the antibody-dependent enhancement observed at lower doses of the antibody. Thus, LUZ-8F2-6B1 is a promising, safe, and effective agent for the prophylaxis and treatment of DENV infection.

Two immunogenic recombinant protein vaccine candidates showed disparate protective efficacy against Zika virus infection in rhesus macaques

Zika virus (ZIKV) infection has caused major public health problems recently. To develop subunit vaccines for ZIKV, we have previously constructed recombinant ZIKV envelope protein domain III (EDIII), and the entire ectodomain (E80, which comprises EDI, EDII and EDIII), as vaccine candidates and showed both of them being immunogenic and protective in murine models. In this follow-up study, we compared these vaccine candidates in non-human primates. Both of them elicited neutralizing antibody responses, but only E80 immunization inhibited ZIKV infection in both peripheral blood and monkey tissues, whereas EDIII increased blood ZIKV RNA through possibly antibody-dependent enhancement. Further investigations revealed that the virion-binding antibody response in E80 immunized monkeys persisted longer and stronger than in EDIII immunized monkeys. These results demonstrate that E80 is superior to EDIII as a vaccine candidate, and that the magnitude, quality and durability of virion-binding neutralizing antibodies are correlates of protection.

Immunity after COVID-19: Protection or sensitization?

Motivated by historical and present clinical observations, we discuss the possible unfavorable evolution of the immunity (similar to documented antibody-dependent enhancement scenarios) after a first infection with COVID-19. More precisely we ask the question of how the epidemic outcomes are affected if the initial infection does not provide immunity but rather sensitization to future challenges. We first provide background comparison with the 2003 SARS epidemic. Then we use a compartmental epidemic model structured by immunity level that we fit to available data; using several scenarios of the fragilization dynamics, we derive quantitative insights into the additional expected numbers of severe cases and deaths.

Antibody-Dependent Enhancement and the Critical Pattern of COVID-19: Possibilities and Considerations

Coronavirus disease 2019 (COVID-19), a pandemic infection with profound effects on human society, has challenged our ability to control viral infections. Although at the beginning of the COVID-19 outbreak, the epidemic seemed controllable in Southern Iran, the disease presented a critical pattern as of May 2020. After a few months of the emergence of COVID-19, its severity and mortality increased dramatically. It has been proposed that antibodies produced during previous exposure to local circulating human coronaviruses or possibly severe acute respiratory syndrome coronavirus 2 might contribute to the development of more severe and lethal presentations of COVID-19 possibly by triggering antibody-dependent enhancement. The binding of virions complexed with antibodies to Fcγ receptors on the target cells initiates receptor-mediated signaling events, leading to enhanced expression of inflammatory cytokines and suppression of intracellular antiviral responses at the transcriptome level, followed by endocytosis of the virus and subsequent activation of immune cells. The activated immune cells might accumulate in the lung and promote cytokine storm and lymphopenia. Furthermore, the formation of immune complexes can promote complement activation and subsequent tissue damage. Although there are currently no clinical data to support this hypothesis, a better understanding of these immunopathologic phenomena and their relation to the disease course and severity might give insights into the development of the most efficient prophylactic and therapeutic approaches. This review demonstrates the critical pattern of COVID-19 in Southern Iran and highlights the possible interplay of factors leading to this condition.

The Role of Autophagy-Mediated Dengue Virus Antibody-Dependent Enhancement Infection of THP-1 Cells

BACKGROUND

Antibody-dependent enhancement (ADE) of dengue virus (DENV) infection is identified as the main risk factor of severe dengue diseases. The underlying mechanisms leading to severe dengue fever remain unclear.

METHODS

THP-1 cells were treated with an autophagy inducer (rapamycin) or inhibitor (3-methyladenine [3-MA]) and infected with DENV and DENV-ADE. In order to investigate the expression profile of autophagy-related genes in DENV-ADE and DENV direct infection of THP-1 cells, the PCR array including 84 autophagy-related genes was selected to detect the expression of related genes, and then heat map and clustergram were established by analysis software to compare the expression differences of these genes between the DENV-ADE and DENV direct infection.

RESULTS

Autophagy-inducing complex related genes ATG5 and ATG12 were upregulated, and autophagosomes were also observed by transmission electron microscopy among DENV-ADE- and DENV-infected THP-1 cells, which indicated that autophagy was involved in dengue infection. The results show that 3-MA has a significant inhibitory effect on ATG12 in THP-1 cells; on the contrary, the expression of ATG12 was upreg-ulated in THP-1 cells that were treated with rapamycin. The autophagy-related genes ESR1, INS, BNIP3, FAS, TGM2, ATG9B, and DAPK1 exhibited significant differences between DENV-ADE and DENV direct infection groups.

CONCLUSION

In the present study, an additional mechanism of autophagy was inhibited by the autophagy inhibitor (3-MA) in DENV- and DENV-ADE-infected THP-1 cells. Our finding provided a clear link between autophagy and antibody-enhanced infection of DENV.

Dengue virus susceptibility in novel immortalized myeloid cells

Human dendritic cells (DCs) are the main target cells of dengue virus (DENV). Because humans injected with even a small volume of DENV from mosquito saliva display a high level of viremia, DCs are expected to be highly susceptible to DENV. In the present study, we assessed the efficiency of DENV infection using the novel immortalized human myeloid cell lines iPS-ML and iPS-DC. To prepare the DC-like myeloid cell line (iPS-DC), iPS-ML cells were cultured in the presence of IL-4 for 72 h. iPS-DC cells were the most susceptible to DENV, followed by iPS-ML, Vero and K562 cells. In contrast, the highest infective yield titer was observed in Vero cells. To investigate further uses of iPS-ML and iPS-DC, these cells were applied to an assay measuring antibody-dependent enhancement (ADE) activity in DENV infection. Serum samples collected from healthy Thai participants and mouse monoclonal antibodies displayed similar ADE activity patterns when examined with iPS-ML, iPS-DC, or K562 cells, the last of which are usually used in conventional ADE assays. Interestingly, iPS-ML cells showed greater susceptibility to ADE activity than iPS-DC and K562 cells. Here, we demonstrated the potential utility of the novel immortalized human myeloid cell lines iPS-ML and iPS-DC in future research on DENV.

SARS-CoV-2 neutralizing antibody levels are correlated with severity of COVID-19 pneumonia

The emerging coronavirus disease 2019 (COVID-19) has become a serious global public health threat. With more and more recovered patients, it is urgently needed for evaluation of the neutralizing antibody (NAb) in these patients. In this study, we collected blood samples from 49 patients recently recovered from COVID-19. Serum NAbs were measured using a novel surrogate virus neutralization test (sVNT). Factors associated with NAb titers were analyzed using Ordinary Least Squares regression model. The median age of the study participants was 37 years (IQR, 30.0-54.5) and 55.1 % (27/49) of which were male. The median time to blood collection (for NAb analysis) from illness onset, viral clearance and discharge were 43.0 days (IQR, 36.0-50.0), 27.0 days (IQR, 20.5-37) and 17.0 days (IQR, 15.0-33.0), respectively. Patients had a median NAb titer of 1: 40 (IQR, 1:15-1:120). NAbs were not detected in two asymptomatic children who quickly cleared the virus. NAb titers were higher in patients with older age (p = 0.020), symptomatic infection (p = 0.044), more profound lung involvement (p＜0.001), abnormal C-reactive protein level (p＜0.01) and elevated lactate dehydrogenase (p = 0.019). Multivariable analysis revealed that severity of pneumonia and having comorbidity positively correlated with NAb titers in recovered patients (p = 0.02), while use of corticosteroids negatively impacted NAb titers (p = 0.01). Our study suggests that some COVID-19 patients may not have detectable NAb after recovery. SARS-CoV-2 NAb titers are positively correlated with severity of COVID-19 pneumonia.

Avian anti-NS1 IgY antibodies neutralize dengue virus infection and protect against lethal dengue virus challenge

Dengue is the most prevalent arboviral disease in humans and a continually increasing global public health burden. To date, there are no approved antiviral therapies against dengue virus (DENV) and the only licensed vaccine, Dengvaxia, is exclusively indicated for individuals with prior DENV infection. Endothelial hyperpermeability and vascular leak, pathogenic hallmarks of severe dengue disease, can be directly triggered by DENV non-structural protein 1 (NS1). As such, anti-NS1 antibodies can prevent NS1-triggered endothelial dysfunction in vitro and pathogenesis in vivo. Recently, goose-derived anti-DENV immunoglobulin Y (IgY) antibodies were shown to neutralize DENV and Zika virus (ZIKV) infection without adverse effects, such as antibody-dependent enhancement (ADE). In this study, we used egg yolks from DENV-immunized geese to purify IgY antibodies specific to DENV NS1 epitopes. We determined that 2 anti-NS1 IgY antibodies, NS1-1 and NS1-8, were capable of neutralizing DENV infection in vitro. In addition, these antibodies did not cross-react with the DENV Envelope (E) protein nor enhance DENV or ZIKV infection in vitro. Intriguingly, NS1-8, but not NS1-1, partially blocked NS1-induced endothelial dysfunction in vitro while neither antibody blocked binding of soluble NS1 to cells. Finally, prophylactic treatment of mice with NS1-8 conferred significant protection against lethal DENV challenge. Although further research is needed to define the mechanism of action of these antibodies, our findings highlight the potential of anti-NS1 IgY as a promising prophylactic approach against DENV infection.

Dengue and Zika virus infections are enhanced by live attenuated dengue vaccine but not by recombinant DSV4 vaccine candidate in mouse models

Background

A tetravalent live attenuated dengue vaccine, Dengvaxia, sensitised naïve recipients to severe dengue illness upon a subsequent natural dengue infection and is suspected to be due to antibody-dependent enhancement (ADE). ADE has also been implicated in the severe neurological outcomes of Zika virus (ZIKV) infection. It has become evident that cross-reactive antibodies targeting the viral pre-membrane protein and fusion-loop epitope are ADE-competent. A pre-clinical tetravalent dengue sub-unit vaccine candidate, DSV4, eliminates these ADE-competent epitopes.

Methods

We compared protective efficacy and ADE-competence of murine polyclonal antibodies induced by DSV4, Dengvaxia and an ‘in house’ tetravalent mixture of all four laboratory DENV strains, TV DENV, using established mouse models.

Findings

DSV4-induced antibodies, known to be predominantly type-specific, provided significant protection against lethal DENV challenge, but did not promote ADE of either DENV or ZIKV infection in vivo. Antibodies elicited by Dengvaxia and TV DENV, which are predominantly cross-reactive, not only failed to offer protection against lethal DENV challenge, but also promoted ADE of both DENV and ZIKV infection in vivo.

Interpretation

Protective efficacy against DENV infection may be linked to the induction of neutralising antibodies which are type-specific rather than cross-reactive. Whole virus-based dengue vaccines may be associated with ADE risk, despite their potent virus-neutralising capacity. Vaccines designed to eliminate ADE-competent epitopes may help eliminate/minimise ADE risk.

Funding

This study was supported partly by ICGEB, India, the National Biopharma Mission, DBT, Government of India, Sun Pharmaceutical Industries Limited, India, and NIAID, NIH, USA.

COVID-19: Understanding the science of antibody testing and lessons from the HIV epidemic

Potential pitfalls in the development, deployment and interpretation of antibody tests for COVID-19 are discussed. Lessons learned from the experience with the introduction of antibody tests for HIV are highlighted.Each test will need to be separately vetted for performance and clinical implementation based upon rigorous clinical trial data. The issues we highlight will also be similarly important for vaccine and therapeutic drug efficacy trials.

What are the roles of antibodies versus a durable, high quality T-cell response in protective immunity against SARS-CoV-2?

The first SARS-CoV-2 vaccine(s) will likely be licensed based on neutralizing antibodies in Phase 2 trials, but there are significant concerns about using antibody response in coronavirus infections as a sole metric of protective immunity. Antibody response is often a poor marker of prior coronavirus infection, particularly in mild infections, and is shorter-lived than virus-reactive T-cells; strong antibody response correlates with more severe clinical disease while T-cell response is correlated with less severe disease; and antibody-dependent enhancement of pathology and clinical severity has been described. Indeed, it is unclear whether antibody production is protective or pathogenic in coronavirus infections. Early data with SARS-CoV-2 support these findings. Data from coronavirus infections in animals and humans emphasize the generation of a high-quality T cell response in protective immunity. Yellow Fever and smallpox vaccines are excellent benchmarks for primary immune response to viral vaccination and induce long-lived virus-reactive CD8 T-cells, which are present and measurable within 1–4 months of vaccination. Progress in laboratory markers for SARS-CoV2 has been made with identification of epitopes on CD4 and CD8 T-cells in convalescent blood. These are much less dominated by spike protein than in previous coronavirus infections. Although most vaccine candidates are focusing on spike protein as antigen, natural infection by SARS-CoV-2 induces broad epitope coverage, cross-reactive with other betacoronviruses. It will be important to understand the relation between breadth, functionality and durability of T-cell responses and resulting protective immunity. It would be a public health and general trust-in-medicine nightmare - including a boost to anti-vaccine forces - if immune protection wears off or new disease patterns develop among the immunized. Data correlating clinical outcomes with laboratory markers of cell-mediated immunity, not only with antibody response, after SARS-CoV-2 natural infection and vaccines may prove critically valuable if protective immunity fades or if new patterns of disease emerge.

Immunologic aspects of characteristics, diagnosis, and treatment of coronavirus disease 2019 (COVID-19)

On March 11, 2020, the World Health Organization declared the worldwide spread of the infectious disease COVID-19, caused by a new strain of coronavirus, SARS-CoV-2, as a pandemic. Like in all other infectious diseases, the host immune system plays a key role in our defense against SARS-CoV-2 infection. However, viruses are able to evade the immune attack and proliferate and, in susceptible individuals, cause severe inflammatory response known as cytokine storm, particularly in the lungs. The advancement in our understanding of the mechanisms underlying the host immune responses promises to facilitate the development of approaches for prevention or treatment of diseases. Components of immune system, such as antibodies, can also be used to develop sensitive and specific diagnostic methods as well as novel therapeutic agents. In this review, we summarize our knowledge about how the host mounts immune responses to infection by SARS-CoV-2. We also describe the diagnostic methods being used for COVID-19 identification and summarize the current status of various therapeutic strategies, including vaccination, being considered for treatment of the disease.

Semi-quantification of antibody-dependent enhancement (ADE) in the uptake of Adenovirus serotype 5 into THP-1 cells

Replication defective recombinant Ad5 vectors (rAdV5) are extensively explored for its applications in gene therapy and vaccine delivery. Ad5 enter into monocytes and macrophages through CAR independent route as an immune complex termed as antibody-dependent enhancement (ADE). We developed an effective method for estimating the ADE of rAdV5 encoding GFP (rAdV5-GFP) into THP-1 cells, using fluorimetric semi-quantification of GFP. Initially, twenty numbers of human sera samples were screened in HeLa cells for anti-Ad5 antibody titer using neutralization assay. Uptake of rAdV5-GFP in THP-1 cells was observed only after pre-incubation with the serially diluted human sera which are attributed to ADE. The optimal dilution which showed the maximum GFP expression as per the fluorescence microscopic analysis in THP-1 cells was used for further analysis. Fluorimetric analysis of the THP-1 cell lysate showed a maximum GFP intensity of 17058 RFU, which was equivalent to the 0.397 pmoles of Alexa Fluor 488 under the same experimental condition. Similarly, immunoblot analysis of GFP in THP-1 cell lysate and HeLa cell lysate confirmed the entry of rAdV5-GFP into the cells. The assay can serve as a platform for understanding the molecular events involved in ADE for the uptake of viruses into immune cells.

An epidemiological survey of the current status of Zika and the immune interaction between dengue and Zika infection in Southern Taiwan

OBJECTIVES

This study was performed to examine the current status of Zika and the effects of pre-existing dengue immunity on Zika virus (ZIKV) infection in Southern Taiwan.

METHODS

A phylogenetic tree was used to analyze the phylogeny of detected ZIKVs. Paired sera from dengue patients were collected for the determination of dengue and Zika infection. Plaque reduction neutralization tests (PRNT) and quantitative reverse transcription PCR (qRT-PCR) were used to determine the titers of neutralizing antibodies and viruses, respectively. An antibody-dependent enhancement (ADE) assay was used to evaluate the effect of anti-dengue antibodies on ZIKV infection.

RESULTS

Epidemiological data indicated the continuous importation of ZIKV infection from neighboring Zika epidemic countries into Taiwan. A total of 78 dengue patients were enrolled and 21 paired serum samples were obtained. PRNT₉₀ results for the 21 samples identified eight cases of primary dengue infection and 13 cases of secondary dengue infection; two samples were positive for ZIKV (MR766). Results from the ADE assay indicated that convalescent sera from primary and secondary dengue infection patients displayed significant ADE of the ZIKV infection when compared to healthy controls (p < 0.05).

CONCLUSIONS

This study suggests that pre-existing dengue immunity facilitates ZIKV infection and that the continuous importation of ZIKV infection may pose a threat to indigenous Zika emergence in Southern Taiwan.

Dengue vaccine development: status and future

Dengue, the most common arbovirus, represents an increasingly significant cause of morbidity worldwide, including in travelers. After decades of research, the first dengue vaccine was licensed in 2015: CYD-TDV, a tetravalent live attenuated vaccine with a yellow fever vaccine backbone. Recent analyses have shown that vaccine performance is dependent on serostatus. In those who have had a previous dengue infection, i.e., who are seropositive, the efficacy is high and the vaccine is safe. However, in seronegative vaccinees, approximately 3 years after vaccination the vaccine increases the risk of developing severe dengue when the individual experiences a natural dengue infection.

The World Health Organization recommends that this vaccine be administered only to seropositive individuals. Current efforts are underway to develop rapid diagnostic tests to facilitate prevaccination screening. Two second-generation dengue vaccine candidates, both also live attenuated recombinant vaccines in late-stage development, may not present the same limitations because of differences in the backbone used, but results of phase 3 trials need to be available before firm conclusions can be drawn.

Dengue is increasingly frequent in travelers, but the only licensed dengue vaccine to date can be used only in seropositive individuals. However, the vast majority of travelers are seronegative. Furthermore, the primary series of three doses given 6 months apart renders this vaccine difficult in the travel medicine context.

Severe dengue in travellers: pathogenesis, risk and clinical management

RATIONALE FOR REVIEW

Dengue is a frequent cause of febrile illness among travellers and has overtaken malaria as the leading cause of febrile illness for those traveling to Southeast Asia. The purpose is to review the risk of dengue and severe dengue in travellers with a particular focus on the pathogenesis and clinical management of severe dengue.

RISK, PATHOGENESIS AND CLINICAL MANAGEMENT

The risk of travel-acquired dengue depends on destination, season and duration of travel and activities during travel. Seroconversion rates reported in travellers, therefore, vary between <1% and >20%. The most common life-threatening clinical response to dengue infection is the dengue vascular permeability syndrome, epidemiologically linked to secondary infection, but can also occur in primary infection. Tertiary and quaternary infections are usually associated with mild or no disease. Antibody-dependent enhancement, viral factors, age, host factors and clinical experience of the managing physician modulate the risk of progressing to severe dengue. The relative risk of severe dengue in secondary versus primary infection ranges from 2 to 7. The absolute risk of severe dengue in children in highly endemic areas is ~0.1% per year for primary infections and 0.4% for secondary infections. About 2-4% of secondary infections lead to severe dengue. Severe dengue and death are both relatively rare in general travellers but more frequently in those visiting friends and relatives. Clinical management of severe dengue depends on judicious use of fluid rehydration.

CONCLUSIONS

Although dengue is a frequent cause of travel illness, severe dengue and deaths are rare. Nevertheless, dengue infections can interrupt travel and lead to evacuation and major out-of-pocket costs. Dengue is more frequent than many other travel-related vaccine preventable diseases, such as hepatitis A, hepatitis B, rabies, Japanese encephalitis and yellow fever, indicating a need for a dengue vaccine for travellers.

A clinical and epidemiological survey of the largest dengue outbreak in Southern Taiwan in 2015

OBJECTIVES

This study examined the epidemiological, clinical, and immunological characteristics of the 2015 dengue outbreak in Taiwan.

METHODS

Clinical data were collected from dengue fever (DF) and dengue hemorrhagic fever (DHF) patients. A phylogenetic tree was used to analyze the source of the outbreak strain. Paired plasma samples from DF/DHF patients were used for antibody-dependent enhancement (ADE) assay and cytokine multiplex biometric immunoassay to validate the immunological mechanism.

RESULTS

This outbreak mainly occurred in two of the southern cities of Taiwan: Tainan (n=22 777; 52%) and Kaohsiung (n=19 784; 45%). A high DHF death rate was noted (34.6%). The case (DHF) and control (DF) study indicated that older age (>60 years), type II diabetes, and hypertension were risk factors correlated with the development of DHF (p< 0.0001). The phylogenetic tree results suggested that the outbreak-associated strain was dengue virus serotype 2 and cosmopolitan genotype, forming a stable cluster with the isolates from Thailand and Indonesia (bootstrap value of 99%). Cytokine analyses demonstrated that levels of interleukin (IL)-6, IL-4, IL-13, IL-1β, interferon gamma (IFN-γ), and granulocyte-macrophage colony-stimulating factor (GM-CSF) were significantly higher in DHF patients compared to DF patients (p< 0.001). The ADE assay showed that diluted plasma containing preexisting dengue antibodies from DHF patients significantly enhanced dengue infection (p< 0.05).

CONCLUSION

The results suggest that older age, type II diabetes, hypertension, immunological cytokine dysregulation, and preexisting dengue antibodies inducing ADE infection are correlated with dengue severity. This study also indicates that the largest dengue outbreak in Taiwan might have been a result of imported DF from dengue epidemic regions.

Extensive genomic recoding by codon-pair deoptimization selective for mammals is a flexible tool to generate attenuated vaccine candidates for dengue virus 2

The four serotypes of dengue virus (DENV) are the leading etiologic agent of disease caused by arthropod-borne viruses (arboviruses) in the world, with billions at risk of DENV infection spread by infected mosquitoes. DENV causes illness ranging from dengue fever (DF) to life-threatening dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). DENV proliferates well in two different host systems, an invertebrate mosquito vector and vertebrate primate host, which have a distinct difference in their preference of codon pairs (CP) for translation (different "codon pair bias"). Consequently, arboviruses must delicately balance the use of codon pairs between mammals and arthropods, which presents an Achilles' heel that we have exploited by specifically shifting the codon pair preference in the E and NS3 ORFs away from mammals while keeping the CPB favorable for mosquito ORFs. Here we report that recoding of the ORFs has led to variants that were over-attenuated in rhesus macaques although induction of protective antibodies in animals vaccinated with the smallest recoded ORF (E) was observed. The flexibility of our synthetic vaccine design (by decreasing the number of unfavorable CPs in the E ORF), allowed us to construct two new vaccine candidates (E^hminA and E^hminB) with intermediate attenuation in cell culture and neonatal mice, a result demonstrating proof of concept. New DENV vaccine candidates are being developed based on selective attenuation by dramatic recoding, with flexibility in balancing the attenuation and immunogenicity by marrying rational design and empirical modification.

Evaluation of the protective ability of plasma from Japanese individuals against mosquito-borne viral infections

Background

Most of the Japanese population is seropositive for anti-Japanese encephalitis virus (JEV) antibodies because of previous JEV vaccination or natural infection. Because the virological characteristics of JEV are similar to those of West Nile virus (WNV) and dengue virus (DENV), we hypothesized that anti-JEV antibodies can cross-react with WNV and DENV antigens, leading to protection against infection by these viruses.

Methods

Using isolated intravenous immunoglobulin (IVIG) from plasma collected in Japan, neutralizing activities against WNV and DENV and antibody-dependent enhancement (ADE) of these viral infections were evaluated using an in vitro assay to determine the potency of immunity against these viruses.

Results

The prepared IVIG showed considerable neutralizing activity of 2.57 log10 reduction factor against WNV infection but showed little effect against DENV infection. A strong correlation was observed between the neutralizing activity of individual plasma samples against JEV and WNV (ρ=0.768). Moreover, IVIG showed no significant ADE of WNV infection.

Conclusions

Based on these results, we presume that the Japanese population is generally protected from WNV infection. Furthermore, IVIG prepared from plasma donations from Japanese individuals is expected to be an effective therapeutic agent based on its neutralizing activity against JEV and WNV.

Cross-reactive dengue virus-derived monoclonal antibodies to Zika virus envelope protein: Panacea or Pandora's box?

Background

Dengue Virus (DENV) and Zika Virus (ZIKV) are closely related flaviviruses, circulating in overlapping geographical regions. The recent ZIKV epidemic has been linked to an explosion in reports of microcephaly and neurological defects. It is conceivable that our knowledge of DENV might potentiate the development of a ZIKV vaccine due to the close phylogenetic relationship between these flaviviruses and cross-reactive antibodies, principally to the envelope protein (E protein). Alternatively, cross-reactive antibodies that are generated following vaccination or infection, might become damaging during subsequent infections.

Main body

The aims of this review are to collate and analyse data from a recent series of DENV-derived monoclonal antibody (mAb) panels from different research groups. These panels measured DENV-mAb activity against ZIKV in terms of antibody-dependent enhancement (ADE) and neutralisation. Methodology used across groups was compared and critiqued. Furthermore, the specific antibody targets on E protein were considered and their therapeutic potential evaluated. Shortcomings of hmAb panels suggest ADE may be over-estimated and neutralisation underestimated, as compared to clinical situations. It remains unknown whether preference of enhancement or neutralisation by antibodies to ZIKV E protein is dictated by quantitative aspects of antibody titre or epitope specific variation. Additionally, little is known about how duration between flavivirus reinfections affect secondary antibody response.

Conclusion

This review concludes that our current knowledge of cross-reactive antibodies to E protein is inadequate to anticipate the outcome of deploying an E protein based vaccine to regions co-infected by DENV and ZIKV.

Recent advances in understanding the adaptive immune response to Zika virus and the effect of previous flavivirus exposure

Zika virus (ZIKV) caused explosive epidemics across the Americas, starting in Brazil in 2015, and has been associated with severe manifestations such as microcephaly in babies born to infected mothers and Guillain-Barré syndrome in adults. As the underlying mechanisms of pathogenesis remain largely unknown, diverse investigations have focused on a potential role for flavivirus cross-reactive antibodies in enhancing ZIKV infection. Antibody-dependent enhancement is especially concerning due to structural similarities between ZIKV and other flaviviruses, especially dengue virus (DENV), that co-circulate in areas affected by ZIKV. Conversely, investigating cross-neutralizing antibodies is important for understanding protection among flaviviruses, including ZIKV. In this review, we discuss the latest findings regarding ZIKV-induced adaptive immunity, such as monoclonal and polyclonal antibody responses, structural immunology, and T cell-mediated responses. Much progress has been made in a short amount of time, but many questions remain. Fully understanding the specificity, magnitude, and kinetics of B cell/antibody and T cell responses in ZIKV-infected individuals with or without prior exposure to flaviviruses is of great relevance for diagnostics and vaccine development.

Quantification of Filovirus Glycoprotein-Specific Antibodies

Serological methods such as the enzyme-linked immunosorbent assay (ELISA) and virus neutralization test are fundamental tools used in diagnosis, seroepidemiological studies of filovirus transmission/prevalence, and the evaluation of vaccine immunogenicity and potential therapeutic antibodies. Filoviruses have a single transmembrane glycoprotein (GP), which is the only known target of neutralizing antibodies. Here we describe serological methods to quantify filovirus GP-specific antibodies.

Substitution of the precursor peptide prevents anti-prM antibody-mediated antibody-dependent enhancement of dengue virus infection

Antibody-dependent enhancement (ADE) is currently considered as the mechanism underlying the pathogenesis of severe dengue disease. Many studies have shown that precursor (pr) peptide-specific antibodies do not efficiently neutralize infection but potently promote ADE of dengue virus (DENV) infection. To explore the effect of pr peptide substitution on neutralization and ADE of DENV infection, the rabbit anti-prM polyclonal antibodies (pAbs) and anti-JEVpr/DENV-M pAbs were prepared, and the neutralization and ADE of these two pAbs were further compared. Here, we report that both anti-JEVpr/DENV-M and anti-prM pAbs exhibited broad cross-reactivity and only partial neutralization with four DENV serotypes and immature DENV. Rabbit anti-prM pAbs showed a significant enhancement in a broad range of serum dilutions. However, there was no statistically significant difference in the enhancing activity of rabbit anti-JEVpr/DENV-M pAbs at various levels of dilution. These results demonstrate that anti-prM antibody-mediated ADE can be prevented by JEV pr peptide replacement. The present study contribute further to research on the pathogenesis of DENV infection.

Zika Virus on a Spreading Spree: what we now know that was unknown in the 1950's

Zika virus (ZIKV) is a mosquito-borne flavivirus that is transmitted through the bite of Aedes spp mosquitoes and less predominantly, through sexual intercourse. Prior to 2007, ZIKV was associated with only sporadic human infections with minimal or no clinical manifestations. Recently the virus has caused disease outbreaks from the Pacific Islands, the Americas, and off the coast of West Africa with approximately 1.62 million people suspected to be infected in more than 60 countries around the globe. The recent ZIKV outbreaks have been associated with guillain-barré syndrome, congenital syndrome (microcephaly, congenital central nervous system anomalies), miscarriages, and even death. This review summarizes the path of ZIKV outbreak within the last decade, highlights three novel modes of ZIKV transmission associated with recent outbreaks, and points to the hallmarks of congenital syndrome. The review concludes with a summary of challenges facing ZIKV research especially the control of ZIKV infection in the wake of most recent data showing that anti-dengue virus antibodies enhance ZIKV infection.

Human antibody response to dengue virus: implications for dengue vaccine design

Dengue, a global health threat, is a leading cause of morbidity and mortality in most tropical and subtropical countries. Dengue can range from asymptomatic, relatively mild dengue fever to severe and life-threatening dengue hemorrhagic fever. Disease severity and outcome is largely associated with the host immune response. Several candidate vaccines in clinical trials appear promising as effective measures for dengue disease control. Vaccine development has been hampered by safety and efficacy issues, driven by a lack of understanding of the host immune response. This review focuses on recent research findings on the dengue host immune response, particularly in humans, and the relevance of these findings to challenges in vaccine development.

Current perspectives on dengue episode in Malaysia

Prevalence of dengue transmission has been alarmed by an estimate of 390 million infections per annum. Urban encroachment, ecological disruption and poor sanitation are all contributory factors of increased epidemiology. Complication however arises from the fact that dengue virus inherently exists as four different serotypes. Secondary infection is often manifested in the more severe form, such that antibody-dependent enhancement (ADE) could aggravate ailment by allowing pre-existing antibodies to form complexes with infecting viruses as means of intrusion. Consequently, increased viraemic titter and suppression of antiviral response are observed. Deep concerns are thus expressed in regards to escalating trend of hospitalisation and mortality rates. In Malaysia, situation is exacerbated by improper clinical management and pending vector control operations. As a preparedness strategy against the potential deadly dengue pandemic, the call for development of a durable and cost-effective dengue vaccine against all infecting serotypes is intensified. Even though several vaccine candidates are currently being evaluated in clinical trials, uncertainties in regards to serotypes interference, incomplete protection and dose adequacy have been raised. Instead of sole reliance on outsourcing, production of local vaccine should be considered in coherent to government's efforts to combat against dengue.

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.

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The iminosugar UV-4B has in vitro activity against all 4 dengue virus serotypes.

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Inhibition of ER α-glucosidases is responsible for UV-4B activity against dengue.

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In vivo efficacy studies inform clinical trial design for UV-4B treatment of dengue.

Dengue virus infection-enhancing antibody activities against Indonesian strains in inhabitants of central Thailand

Dengue virus (DENV) infection-enhancing antibodies are a hypothetic factor to increase the dengue disease severity. In this study, we investigated the enhancing antibodies against Indonesian strains of DENV-1-4 in 50 healthy inhabitants of central Thailand (Bangkok and Uthai Thani). Indonesia and Thailand have seen the highest dengue incidence in Southeast Asia. The infection history of each subject was estimated by comparing his/her neutralizing antibody titers against prototype DENV-1-4 strains. To resolve the difficulty in obtaining foreign live viruses for use as assay antigens, we used a recombinant system to prepare single-round infectious dengue viral particles based on viral sequence information. Irrespective of the previously infecting serotype(s), most serum samples showed significantly higher enhancement titers against Indonesian DENV-2 strains than against Thai DENV-2 strains, whereas the opposite effect was observed for the DENV-3 strains. Equivalent enhancing activities were observed against both DENV-1 and DENV-4. These results suggest that the genotype has an impact on enhancing antibody activities against DENV-2 and DENV-3, because the predominant circulating genotypes of each serotype differ between Indonesia and Thailand.

The Potential Impact of Vaccination on the Dynamics of Dengue Infections

Dengue, classified as a 'neglected topical disease', is currently regarded globally as the most important mosquito-borne viral disease, which inflicts substantial socioeconomic and health burden in many tropical and subtropical regions of the world. While efforts continue towards developing and improving the efficacy of a tetravalent vaccine to protect individuals against all dengue virus serotypes, the long-term epidemiological impact of vaccination remains elusive. We develop a serotype-specific, vector-host compartmental model to evaluate the effect of vaccination in the presence of antibody-dependent enhancement and cross-protection following recovery from primary infection. Reproducing the reported multi-annual patterns of dengue infection, our model projects that vaccination can dramatically reduce the overall incidence of the disease. However, if the duration of vaccine-induced protection is shorter than the average lifetime of the human population, vaccination can potentially increase the incidence of severe infection of dengue haemorrhagic fever due to the effects of antibody-dependent enhancement. The magnitude and timelines for this increase depend strongly on the efficacy and duration of the vaccine-induced protection. Corresponding to the current estimates of vaccine efficacy, we show that dengue eradication is infeasible using an imperfect vaccine. Furthermore, for a vaccine that induces lifetime protection, a nearly full coverage of infant vaccination is required for dengue elimination. Our findings suggest that other vector control measures may still play a significant role in dengue prevention even when a vaccine with high protection efficacy becomes available.

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/β/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.