Infection enhancement of influenza A NWS virus in primary murine macrophages by anti-hemagglutinin monoclonal antibody

A deterministic model for homologous antibody dependant enhancement on influenza infection

Antibody dependant enhancement refers that viral infectivity was unexpectedly enhanced at low antibody concentration compared to when antibodies were absent, such as Dengue, Zika and influenza virus. To mathematically describe switch from enhancement to neutralisation with increase of antibody concentration, one hyperbolic tangent variant is used as switching function in existed models. However, switching function with hyperbolic tangent contains four parameters, and does not always increase with antibody concentration. To address this problem, we proposed a monotonically increasing Logistical function variant as switching function, which only contains position parameter and magnitude parameter. Analysing influenza viral titre estimated from 21 focus reduction assay (FRA) datasets from neutralisation group (viral titre lower than negative control on all serial dilutions) and 20 FRA dataset from enhancement group (viral titre higher than negative control on high serial dilution), switching function with Logistic function performs better than existed model independent of both groups and exhibited different behaviour/character; specifically, magnitude parameter estimated from enhancement group is lower, but position parameter estimated from enhancement group is higher. A lower magnitude parameter refers that enhancement group more rapidly switches from enhancement to neutralisation with increase of antibody concentration, and a higher position parameter indicates that enhancement group provides a larger antibody concentration interval corresponding to enhancement. Integrating estimated neutralisation kinetics with viral replication, we demonstrated that antibody-induced bistable influenza kinetics exist independent of both groups. However, comparing with neutralisation group, enhancement group provides higher threshold value of antibody concentration corresponding to influenza infectivity. This explains the observed phenomenon that antibody dependent enhancement enhances susceptibility, severity, and mortality to influenza infection. On population level, antibody dependant enhancement can promote H1N1 and H3N2 influenza virus cooperate to sustain long-term circulation on human populations according to antigenic seniority theory.

Enterovirus Antibodies: Friends and Foes

Enteroviruses (EV) initiate replication by binding to their cellular receptors, leading to the uncoating and release of the viral genome into the cytosol of the host cell. Neutralising antibodies (NAbs) binding to epitopes on enteroviral capsid proteins can inhibit this infectious process through several mechanisms of neutralisation in vitro. Fc-mediated antibody effector functions such as antibody-dependent cell-mediated cytotoxicity and antibody-dependent cellular phagocytosis have also been described for some EV. However, antibody binding to virions does not always result in viral neutralisation. Non-neutralising antibodies, or sub-neutralising concentrations of antibodies, can enhance infection of viruses, leading to more severe pathologies. This phenomenon, known as antibody-dependent enhancement (ADE) of infection, has been described in vitro and/or in vivo for EV including poliovirus, coxsackievirus B and EV-A71. It has been shown that ADE of EV infection is mediated by FcγRs expressed by monocytes, macrophages, B lymphocytes and granulocytes. Antibodies play a crucial role in the diagnosis and monitoring of infections. They are valuable markers that have been used to establish a link between enteroviral infection and chronic diseases such as type 1 diabetes. Monoclonal and polyclonal antibodies targeting enteroviral proteins have been developed and shown to be effective to prevent or combat EV infections in vitro and in vivo. In addition, vaccines are under development, and clinical trials of vaccines are underway or have been completed, providing hope for the prevention of diseases due to EV. However, the ADE of the infection should be considered in the development of anti-EV antibodies or safe vaccines.

Fc-FcγR interactions during infections: From neutralizing antibodies to antibody-dependent enhancement

Advances in antibody technologies have resulted in the development of potent antibody-based therapeutics with proven clinical efficacy against infectious diseases. Several monoclonal antibodies (mAbs), mainly against viruses such as SARS-CoV-2, HIV-1, Ebola virus, influenza virus, and hepatitis B virus, are currently undergoing clinical testing or are already in use. Although these mAbs exhibit potent neutralizing activity that effectively blocks host cell infection, their antiviral activity results not only from Fab-mediated virus neutralization, but also from the protective effector functions mediated through the interaction of their Fc domains with Fcγ receptors (FcγRs) on effector leukocytes. Fc-FcγR interactions confer pleiotropic protective activities, including the clearance of opsonized virions and infected cells, as well as the induction of antiviral T-cell responses. However, excessive or inappropriate activation of specific FcγR pathways can lead to disease enhancement and exacerbated pathology, as seen in the context of dengue virus infections. A comprehensive understanding of the diversity of Fc effector functions during infection has guided the development of engineered antiviral antibodies optimized for maximal effector activity, as well as the design of targeted therapeutic approaches to prevent antibody-dependent enhancement of disease.

Antibody-dependent enhancement (ADE) of SARS-CoV-2 in patients exposed to MERS-CoV and SARS-CoV-2 antigens

This study evaluated the potential for antibody-dependent enhancement (ADE) in serum samples from patients exposed to Middle East respiratory syndrome coronavirus (MERS-CoV). Furthermore, we evaluated the effect of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination on ADE in individuals with a MERS infection history. We performed ADE assay in sera from MERS recovered and SARS-CoV-2-vaccinated individuals using BHK cells expressing FcgRIIa, SARS-CoV-2, and MERS-CoV pseudoviruses (PVs). Further, we analyzed the association of ADE to serum IgG levels and neutralization. Out of 16 MERS patients, nine demonstrated ADE against SARS-CoV-2 PV, however, none of the samples demonstrated ADE against MERS-CoV PV. Furthermore, out of the seven patients exposed to SARS-CoV-2 vaccination after MERS-CoV infection, only one patient (acutely infected with MERS-CoV) showed ADE for SARS-CoV-2 PV. Further analysis indicated that IgG1, IgG2, and IgG3 against SARS-CoV-2 S1 and RBD subunits, IgG1 and IgG2 against the MERS-CoV S1 subunit, and serum neutralizing activity were low in ADE-positive samples. In summary, samples from MERS-CoV-infected patients exhibited ADE against SARS-CoV-2 and was significantly associated with low levels of neutralizing antibodies. Subsequent exposure to SARS-CoV-2 vaccination resulted in diminished ADE activity while the PV neutralization assay demonstrated a broadly reactive antibody response in some patient samples.

Evaluation of Antibody-Dependent Fc-Mediated Viral Entry, as Compared With Neutralization, in SARS-CoV-2 Infection

Fc-mediated virus entry has been observed for many viruses, but the characterization of this activity in convalescent plasma against SARS-CoV-2 Variants of Concern (VOC) is undefined. In this study, we evaluated Fc-mediated viral entry (FVE) on FcγRIIa-expressing HEK293 cells in the presence of SARS-CoV-2 convalescent plasma and compared it with SARS-CoV-2 pseudovirus neutralization using ACE2-expressing HEK293 cells. The plasma were collected early in the pandemic from 39 individuals. We observed both neutralization and FVE against the infecting Washington SARS-CoV-2 strain for 31% of plasmas, neutralization, but not FVE for 61% of plasmas, and no neutralization or FVE for 8% of plasmas. Neutralization titer correlated significantly with the plasma dilution at which maximum FVE was observed, indicating Fc-mediated uptake peaked as neutralization potency waned. While total Spike-specific plasma IgG levels were similar between plasma that mediated FVE and those that did not, Spike-specific plasma IgM levels were significantly higher in plasma that did not mediate FVE. Plasma neutralization titers against the Alpha (B.1.1.7), Beta (B.1.351), Gamma (P.1) and Delta (B.1.617.2) VOC were significantly lower than titers against the Washington strain, while plasma FVE activity against the VOC was either higher or similar. This is the first report to demonstrate a functional shift in convalescent plasma antibodies from neutralizing and FVE-mediating against the earlier Washington strain, to an activity mediating only FVE and no neutralization activity against the emerging VOC, specifically the Beta (B.1.351) and Gamma (P.1) VOC. It will be important to determine the in vivo relevance of these findings.

Vaccine-Associated Enhanced Respiratory Disease following Influenza Virus Infection in Ferrets Recapitulates the Model in Pigs

Influenza A virus (IAV) causes respiratory disease in swine and humans. Vaccines are used to prevent influenza illness in both populations but must be frequently updated due to rapidly evolving strains. Mismatch between the circulating strains and the strains contained in vaccines may cause loss of efficacy. Whole inactivated virus (WIV) vaccines with adjuvant, utilized by the swine industry, are effective against antigenically similar viruses; however, vaccine-associated enhanced respiratory disease (VAERD) may happen when the WIV is antigenically mismatched with the infecting virus. VAERD is a repeatable model in pigs, but had yet to be experimentally demonstrated in other mammalian species. We recapitulated VAERD in ferrets, a standard benchmark animal model for studying human influenza infection, in a direct comparison to VAERD in pigs. Both species were vaccinated with WIV with oil-in-water adjuvant containing a δ-1 H1N2 (1B.2.2) derived from the pre-2009 human seasonal lineage, then challenged with a 2009 pandemic H1N1 (H1N1pdm09, 1A.3.3.2) 5 weeks after vaccination. Nonvaccinated and challenged groups showed typical signs of influenza disease, but the mismatched vaccinated and challenged pigs and ferrets showed elevated clinical signs, despite similar viral loads. VAERD-affected pigs exhibited a 2-fold increase in lung lesions, while VAERD-affected ferrets showed a 4-fold increase. Similar to pigs, antibodies from VAERD-affected ferrets preferentially bound to the HA2 domain of the H1N1pdm09 challenge strain. These results indicate that VAERD is not limited to pigs, as demonstrated here in ferrets, and the need to consider VAERD when evaluating new vaccine platforms and strategies. IMPORTANCE We demonstrated the susceptibility of ferrets, a laboratory model species for human influenza A virus research, to vaccine-associated enhanced respiratory disease (VAERD) using an experimental model previously demonstrated in pigs. Ferrets developed clinical characteristics of VAERD very similar to that in pigs. The hemagglutinin (HA) stalk is a potential vaccine target to develop more efficacious, broadly reactive influenza vaccine platforms and strategies. However, non-neutralizing antibodies directed toward a conserved epitope on the HA stalk induced by an oil-in-water, adjuvanted, whole influenza virus vaccine were previously shown in VAERD-affected pigs and were also identified here in VAERD-affected ferrets. The induction of VAERD in ferrets highlights the potential risk of mismatched influenza vaccines for humans and the need to consider VAERD when designing and evaluating vaccine strategies.

Neutralizing Antibodies and Antibody-Dependent Enhancement in COVID-19: A Perspective

Antibody-dependent enhancement (ADE) is an alternative route of viral entry in the susceptible host cell. In this process, antiviral antibodies enhance the entry access of virus in the cells via interaction with the complement or Fc receptors leading to the worsening of infection. SARS-CoV-2 variants pose a general concern for the efficacy of neutralizing antibodies that may fail to neutralize infection, raising the possibility of a more severe form of COVID-19. Data from various studies on respiratory viruses raise the speculation that antibodies elicited against SARS-CoV-2 and during COVID-19 recovery could potentially exacerbate the infection through ADE at sub-neutralizing concentrations; this may contribute to disease pathogenesis. It is, therefore, of utmost importance to study the effectiveness of the anti-SARS-CoV-2 antibodies in COVID-19-infected subjects. Theoretically, ADE remains a general concern for the efficacy of antibodies elicited during infection, most notably in convalescent plasma therapy and in response to vaccines where it could be counterproductive.

COVID-19: inflammatory responses, structure-based drug design and potential therapeutics

The COVID-19 pandemic caused by SARS-CoV-2 is responsible for the global health emergency. Here, we explore the diverse mechanisms of SARS-CoV-induced inflammation. We presume that SARS-CoV-2 likely contributes analogous inflammatory responses. Possible therapeutic mechanisms for reducing SARS-CoV-2-mediated inflammatory responses comprise FcR inactivation. Currently, there is no specific remedy available against the SARS-CoV-2. Consequently, recognizing efficacious antiviral leads to combat the virus is crucially desired. The coronavirus (CoV) main protease (Mpro also called 3CLpro), which plays an indispensable role in viral replication and transcription, is an interesting target for drug design. This review compiles the latest advances in biological and structural research, along with development of inhibitors targeting CoV Mpros. It is anticipated that inhibitors targeting CoV Mpros could be advanced into wide-spectrum antiviral drugs in case of COVID-19 and other CoV-related diseases. The crystal structural and docking results have shown that Ebselen, N3, TDZD-8 and α-ketoamide (13b) inhibitors can bind to the substrate-binding pocket of COVID-19 Mpro. α-ketoamide-based inhibitor 13b inhibits the replication of SARS-CoV-2 in human Calu3 lung cells. Quantitative real-time RT-PCR (qRT-PCR) showed that the treatment with Ebselen, TDZD-8 and N3 reduced the amounts of SARS-CoV-2, respectively, 20.3-, 10.19- and 8.4-fold compared to the treatment in the absence of inhibitor. Moreover, repurposing of already present drugs to treat COVID-19 serves as one of the competent and economic therapeutic strategies. Several anti-malarial, anti-HIV and anti-inflammatory drugs as mentioned in Table 2 were found effective for the COVID-19 treatment. Further, hydroxychloroquine (HCQ) was found more potent than chloroquine (CQ) in inhibiting SARS-CoV-2 in vitro. Furthermore, convalescent plasma from patients who have recuperated from viral infections can be employed as a therapy without the appearance of severe adverse events. Hence, it might be valuable to examine the safety and efficacy of convalescent plasma transfusion in SARS-CoV-2-infected patients.

ACE2 can act as the secondary receptor in the FcγR-dependent ADE of SARS-CoV-2 infection

It is unknown whether antibody-mediated enhancement (ADE) contributes to the pathogenesis of COVID-19, and the conditions for ADE needs to be elucidated. We demonstrated that without inducing an ACE2-independent ADE on Raji cells, the neutralizing antibody CB6, a mouse anti-S1 serum and convalescent plasma, induced ADE on cells expressing FcγRIIA/CD32A and low levels of endogenous ACE2. ADE occurred at sub-neutralizing antibody concentrations, indicating that unneutralized S protein was required for ADE. The enhanced infectivity of 614G variant was higher than that of 614D wildtype in the presence of antibodies, further suggesting that ADE may be influenced by virus strains with different ACE2-binding affinity. Finally, knockdown of ACE2 or treatment with a fusion-inhibition peptide EK1C4 significantly reduced ADE. In conclusion, we identified an ADE mechanism mediated by neutralizing antibodies against SARS-CoV-2. ACE2 may act as a secondary receptor required for the antibody- and FcγR-mediated enhanced entry of SARS-CoV-2.

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NAbs induced ADE of SARS-CoV-2 on cells expressing FcγRIIA and ACE2

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Unneutralized S protein was required for ADE

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ADE may be influenced by virus strains with different ACE2-binding affinity

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ACE2 acts as a secondary receptor required for the Ab- and FcγR-mediated ADE

Human Coronaviruses: Counteracting the Damage by Storm

Over the past 18 years, three highly pathogenic human (h) coronaviruses (CoVs) have caused severe outbreaks, the most recent causative agent, SARS-CoV-2, being the first to cause a pandemic. Although much progress has been made since the COVID-19 pandemic started, much about SARS-CoV-2 and its disease, COVID-19, is still poorly understood. The highly pathogenic hCoVs differ in some respects, but also share some similarities in clinical presentation, the risk factors associated with severe disease, and the characteristic immunopathology associated with the progression to severe disease. This review aims to highlight these overlapping aspects of the highly pathogenic hCoVs-SARS-CoV, MERS-CoV, and SARS-CoV-2-briefly discussing the importance of an appropriately regulated immune response; how the immune response to these highly pathogenic hCoVs might be dysregulated through interferon (IFN) inhibition, antibody-dependent enhancement (ADE), and long non-coding RNA (lncRNA); and how these could link to the ensuing cytokine storm. The treatment approaches to highly pathogenic hCoV infections are discussed and it is suggested that a greater focus be placed on T-cell vaccines that elicit a cell-mediated immune response, using rapamycin as a potential agent to improve vaccine responses in the elderly and obese, and the potential of stapled peptides as antiviral agents.

Study of Antibody-Dependent Reactions of Mast Cells In Vitro and in a Model of Severe Influenza Infection in Mice

We investigated the reaction of mouse peritoneal mast cells (MCs) in vitro after IgG-containing immune complex introduction using A/H5N1 and A/H1N1pdm09 influenza viruses as antigens. The sera of immune mice served as a source of IgG antibodies. The concentration of histamine in the supernatants was determined at 4 hours after incubation with antisera and virus. We compared the contribution of MCs to the pathogenesis of post-immunization influenza infection with A/H5N1 and A/H1N1 influenza viruses in mice. The mice were immunized parenterally with inactivated viruses and challenged with lethal doses of drift A/H5N1 and A/H1N1 influenza viruses on the 14th day after immunization. Simultaneously, half of the mice were injected intraperitoneally with a mixture of histamine receptor blockers (chloropyramine and quamatel). In in vitro experiments, the immune complex formed by A/H5N1 virus and antiserum caused a significant increase in the histamine release compared to immune serum or the virus alone. With regard to the A/H1N1 virus, such an increase was not significant. A/H1N1 immunization caused detectable HI response in mice at 12th day after immunization, in contrast to the A/H5N1 virus. After challenge of A/H5N1-immunized mice, administration of antihistamines increased the survival rate by up to 90%. When infecting the A/H1N1-immunized mice, 90% of the animals were already protected from lethal infection by day 14; the administration of histamine receptor blockers did not increase survival. Histological examination of the lungs has shown that toluidine blue staining allows to estimate the degree of MC degranulation. The possibility of in vitro activation of murine MCs by IgG-containing immune complexes has been shown. In a model of influenza infection, it was shown that the administration of histamine receptor blockers increased survival. When the protection was formed faster due to the earlier production of HI antibodies, the administration of histamine receptor blockers did not significantly affect the course of the infection. These data allow to propose that even if there are antibody-dependent MC reactions, they can be easily stopped by the administration of histamine receptor blockers.

Allergy: Type I, II, III, and IV

Hypersensitivity reactions are overreactions of the immune system clinically seen as allergic and autoimmune diseases. Gell and Coombs originally described four different types of hypersensitivity reactions almost 60 years ago, and their description still applies in large parts. However, some modifications and extensions have been included in original definition. Especially in allergic diseases, it became clear that often, multiple types of hypersensitivity reaction can occur simultaneously. This improved insight is not only important for a better understanding of hypersensitivity disorders, but is especially of importance for improved diagnostics and directing therapeutic interventions.

An Overview About the Role of Adaptive Immunity in Keeping SARS-CoV-2 Reinfections at Bay

Coronavirus disease 2019 (COVID-19) is a worldwide emergency that has affected millions of populations in developed and underdeveloped countries. To our surprise, many people have been tested positive twice. Few cases of true reinfections involved genetic alterations in the virus. Appearance of multiple positive tests may be due to human errors or remnant genetic material, but genetic modification in virus represents very serious issue of controlling this pandemic. It is the need of the day that all the gaps and deficiencies, represented by variable response of adaptive immune system toward this infection, be filled and rectified. We have discussed reinfections with variable outcomes along with the possible reasons for variable response. Phenomena such as T cell memory, absence of cross-reactive immunity, T cell exhaustion, drawbacks pertaining to neutralizing antibodies, and immune enhancement are crucial areas by which adaptive immune response can weaken considerably. Earlier and stronger herd immunity is also at the mercy of strong adaptive immune system to avoid future pandemics by the same microorganism. Likewise, consequences of this phenomenon should also be considered during vaccine development as resources worth billions are being used and staked. Many countries have entered the second/third waves of COVID-19. Therefore, we need to come up with ways toward uniform strengthening of adaptive immune response to fight off this pandemic. Also, to develop and maintain constant resistance to severe acute respiratory syndrome coronavirus (SARS-CoV-2), the mentioned weakened links in the chain of adaptive immunity may be explored to keep viral invasion and physiological damage to minimum.

Cellular and Humoral Immune Responses in Covid-19 and Immunotherapeutic Approaches

Coronavirus disease 2019 (Covid-19), caused by the novel coronavirus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), can range in severity from asymptomatic to severe/critical disease. SARS-CoV-2 uses angiotensin-converting enzyme 2 to infect cells leading to a strong inflammatory response, which is most profound in patients who progress to severe Covid-19. Recent studies have begun to unravel some of the differences in the innate and adaptive immune response to SARS-CoV-2 in patients with different degrees of disease severity. These studies have attributed the severe form of Covid-19 to a dysfunctional innate immune response, such as a delayed and/or deficient type I interferon response, coupled with an exaggerated and/or a dysfunctional adaptive immunity. Differences in T-cell (including CD4+ T-cells, CD8+ T-cells, T follicular helper cells, γδ-T-cells, and regulatory T-cells) and B-cell (transitional cells, double-negative 2 cells, antibody-secreting cells) responses have been identified in patients with severe disease compared to mild cases. Moreover, differences in the kinetic/titer of neutralizing antibody responses have been described in severe disease, which may be confounded by antibody-dependent enhancement. Importantly, the presence of preexisting autoantibodies against type I interferon has been described as a major cause of severe/critical disease. Additionally, priorVaccine and multiple vaccine exposure, trained innate immunity, cross-reactive immunity, and serological immune imprinting may all contribute towards disease severity and outcome. Several therapeutic and preventative approaches have been under intense investigations; these include vaccines (three of which have passed Phase 3 clinical trials), therapeutic antibodies, and immunosuppressants.

Learning from the past: development of safe and effective COVID-19 vaccines

The rapid spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has elicited an equally rapid response aiming to develop a COVID-19 vaccine. These efforts are encouraging; however, comprehensive efficacy and safety evaluations are essential in the development of a vaccine, and we can learn from previous vaccine development campaigns. In this Perspective, we summarize examples of vaccine-associated disease enhancement in the history of developing vaccines against respiratory syncytial virus, dengue virus, SARS-CoV and Middle East respiratory syndrome coronavirus, which highlight the importance of a robust safety and efficacy profile, and present recommendations for preclinical and clinical evaluation of COVID-19 vaccine candidates as well as for vaccine design and optimization.

SARS-CoV-2 mediated lung inflammatory responses in host: targeting the cytokine storm for therapeutic interventions

The recent exposure of novel coronavirus strain, severe acute respiratory syndrome (SARS-CoV-2) has spread to different countries at an alarming rate. Faster transmission rate and genetic modifications have provoked scientists to search for an immediate solution. With an increasing death rate, it becomes important to throw some light on the life cycle of the virus and its associated pathogenesis in the form of lung inflammation through cytokine storm (CS) production. This paper highlights the different stages of viral-mediated inflammatory responses in the host respiratory system. Previously, known anti-inflammatory drugs and therapeutic strategies that might show potential in controlling the CS of Coronavirus disease-2019 (COVID-19) is also mentioned in this study. Our critical analysis provides insights into the inflammation cycle induced in the lungs by early virus replication, downregulation and shedding of angiotensin-converting enzyme 2 (ACE2), and in the CS production. Identification of suitable targets within the inflammatory pathways for devising the therapeutic strategies useful in controlling the prognosis of COVID-19 finds a special mention in this article. However, antibody-dependent enhancement is the key aspect to consider before testing any drug/compound for therapeutic purposes. Our in-depth analysis would provide similarities and differences between the inflammatory responses induced by SARS-CoV and SARS-CoV-2, providing an excellent avenue to further look at how earlier outbreaks of coronaviruses were controlled and where new steps are required?

Prevention and treatment of COVID-19: Focus on interferons, chloroquine/hydroxychloroquine, azithromycin, and vaccine

The ongoing pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has drawn the attention of researchers and clinicians from several disciplines and sectors who are trying to find durable solutions both at preventive and treatment levels. To date, there is no approved effective treatment or vaccine available to control the coronavirus disease-2019 (COVID-19). The preliminary in vitro studies on viral infection models showed potential antiviral activities of type I and III interferons (IFNs), chloroquine (CQ)/hydroxychloroquine (HCQ), and azithromycin (AZM); however, the clinical studies on COVID-19 patients treated with CQ/HCQ and AZM led to controversies in different regions due to their adverse side effects, as well as their combined treatment could prolong the QT interval. Interestingly, the treatment with type I IFNs showed encouraging results. Moreover, the different preliminary reports of COVID-19 candidate vaccines showcase promising results by inducing the production of a high level of neutralizing antibodies (NAbs) and specific T cell-mediated immune response in almost all participants. The present review aims to summarize and analyze the recent progress evidence concerning the use of IFNs, CQ/HCQ, and AZM for the treatment of COVID-19. The available data on immunization options to prevent the COVID-19 are also analyzed with the aim to present the promising options which could be investigated in future for sustainable control of the pandemic.

Antibody-dependent enhancement and SARS-CoV-2 vaccines and therapies

Antibody-based drugs and vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are being expedited through preclinical and clinical development. Data from the study of SARS-CoV and other respiratory viruses suggest that anti-SARS-CoV-2 antibodies could exacerbate COVID-19 through antibody-dependent enhancement (ADE). Previous respiratory syncytial virus and dengue virus vaccine studies revealed human clinical safety risks related to ADE, resulting in failed vaccine trials. Here, we describe key ADE mechanisms and discuss mitigation strategies for SARS-CoV-2 vaccines and therapies in development. We also outline recently published data to evaluate the risks and opportunities for antibody-based protection against SARS-CoV-2.

Principles Learned from the International Race to Develop a Safe and Effective COVID-19 Vaccine

Vaccines against COVID-19 have the potential to protect people before they are exposed to the infective form of the virus. However, because of the involvement of pathogenic immune processes in many severe presentations of COVID-19, eliciting an immune response with a vaccine must strike a delicate balance to achieve viral clearance without also inducing immune-mediated harm. This Outlook synthesizes current laboratory findings to define which parts of the immune system help with recovery from and protection against the virus and which can lead to adverse outcomes. To inform our understanding, we analyze research about the immune mechanisms implicated in SARS-CoV, from the 2003 outbreak, and SARS-CoV-2, the virus causing COVID-19. The impact of how innate immunity, humoral immunity, and cell-mediated immunity play a role in a harmful versus helpful response is discussed, establishing principles to guide the development and evaluation of a safe but effective COVID-19 vaccine. The principles derived include (i) targeting the appropriate specificity and effector function of the humoral response, (ii) eliciting a T cell response, especially a cytotoxic T cell response, to achieve safe, yet effective, immune protection from COVID-19, and (iii) monitoring for the possibility of acute lung injury during SARS-CoV-2 infection post-vaccination in preclinical and clinical studies. These principles can not only guide efforts toward a safe and effective COVID-19 vaccine, but also the development of effective vaccines for viral pandemics to come.

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.

Antibody-dependent enhancement (ADE) has been described as a mechanism that contributes to the pathogenesis of dengue virus infection. Limited evidence also suggests that it can also occur in other viral infections. Here, the authors explore the history of the ADE phenomenon, discuss the diversity of Fc effector functions and consider its potential relevance in the context of SARS-CoV-2 infection.

Understanding SARS-CoV-2-Mediated Inflammatory Responses: From Mechanisms to Potential Therapeutic Tools

Currently there is no effective antiviral therapy for SARS-CoV-2 infection, which frequently leads to fatal inflammatory responses and acute lung injury. Here, we discuss the various mechanisms of SARS-CoV-mediated inflammation. We also assume that SARS-CoV-2 likely shares similar inflammatory responses. Potential therapeutic tools to reduce SARS-CoV-2-induced inflammatory responses include various methods to block FcR activation. In the absence of a proven clinical FcR blocker, the use of intravenous immunoglobulin to block FcR activation may be a viable option for the urgent treatment of pulmonary inflammation to prevent severe lung injury. Such treatment may also be combined with systemic anti-inflammatory drugs or corticosteroids. However, these strategies, as proposed here, remain to be clinically tested for effectiveness.

Impact of immune enhancement on Covid-19 polyclonal hyperimmune globulin therapy and vaccine development

The pandemic spread of a novel coronavirus - SARS coronavirus-2 (SARS-CoV-2) as a cause of acute respiratory illness, named Covid-19, is placing the healthcare systems of many countries under unprecedented stress. Global economies are also spiraling towards a recession in fear of this new life-threatening disease. Vaccines that prevent SARS-CoV-2 infection and therapeutics that reduces the risk of severe Covid-19 are thus urgently needed. A rapid method to derive antiviral treatment for Covid-19 is the use of convalescent plasma derived hyperimmune globulin. However, both hyperimmune globulin and vaccine development face a common hurdle - the risk of antibody-mediated disease enhancement. The goal of this review is to examine the body of evidence supporting the hypothesis of immune enhancement that could be pertinent to Covid-19. We also discuss how this risk could be mitigated so that both hyperimmune globulin and vaccines could be rapidly translated to overcome the current global health crisis.

Antibody-based therapeutic interventions: possible strategy to counter chikungunya viral infection

Chikungunya virus (CHIKV), a mosquito-transmitted disease that belongs to the genus Alphaviruses, has been emerged as an epidemic threat over the last two decades, and the recent co-emergence of this virus along with other circulating arboviruses and comorbidities has influenced atypical mortality rate up to 10%. Genetic variation in the virus has resulted in its adaptability towards the new vector Aedes albopictus other than Aedes aegypti, which has widen the horizon of distribution towards non-tropical and non-endemic areas. As of now, no licensed vaccines or therapies are available against CHIKV; the treatment regimens for CHIKV are mostly symptomatic, based on the clinical manifestations. Development of small molecule drugs and neutralizing antibodies are potential alternatives of worth investigating until an efficient or safe vaccine is approved. Neutralizing antibodies play an important role in antiviral immunity, and their presence is a hallmark of viral infection. In this review, we describe prospects for effective vaccines and highlight importance of neutralizing antibody-based therapeutic and prophylactic applications to combat CHIKV infections. We further discuss about the progress made towards CHIKV therapeutic interventions as well as challenges and limitation associated with the vaccine development. Furthermore this review describes the lesson learned from chikungunya natural infection, which could help in better understanding for future development of antibody-based therapeutic measures.

Evolution of Therapeutic Antibodies, Influenza Virus Biology, Influenza, and Influenza Immunotherapy

This narrative review article summarizes past and current technologies for generating antibodies for passive immunization/immunotherapy. Contemporary DNA and protein technologies have facilitated the development of engineered therapeutic monoclonal antibodies in a variety of formats according to the required effector functions. Chimeric, humanized, and human monoclonal antibodies to antigenic/epitopic myriads with less immunogenicity than animal-derived antibodies in human recipients can be produced in vitro. Immunotherapy with ready-to-use antibodies has gained wide acceptance as a powerful treatment against both infectious and noninfectious diseases. Influenza, a highly contagious disease, precipitates annual epidemics and occasional pandemics, resulting in high health and economic burden worldwide. Currently available drugs are becoming less and less effective against this rapidly mutating virus. Alternative treatment strategies are needed, particularly for individuals at high risk for severe morbidity. In a setting where vaccines are not yet protective or available, human antibodies that are broadly effective against various influenza subtypes could be highly efficacious in lowering morbidity and mortality and controlling unprecedented epidemic/pandemic. Prototypes of human single-chain antibodies to several conserved proteins of influenza virus with no Fc portion (hence, no ADE effect in recipients) are available. These antibodies have high potential as a novel, safe, and effective anti-influenza agent.

Antibody-mediated enhancement aggravates chikungunya virus infection and disease severity

The arthropod-transmitted chikungunya virus (CHIKV) causes a flu-like disease that is characterized by incapacitating arthralgia. The re-emergence of CHIKV and the continual risk of new epidemics have reignited research in CHIKV pathogenesis. Virus-specific antibodies have been shown to control virus clearance, but antibodies present at sub-neutralizing concentrations can also augment virus infection that exacerbates disease severity. To explore this occurrence, CHIKV infection was investigated in the presence of CHIKV-specific antibodies in both primary human cells and a murine macrophage cell line, RAW264.7. Enhanced attachment of CHIKV to the primary human monocytes and B cells was observed while increased viral replication was detected in RAW264.7 cells. Blocking of specific Fc receptors (FcγRs) led to the abrogation of these observations. Furthermore, experimental infection in adult mice showed that animals had higher viral RNA loads and endured more severe joint inflammation in the presence of sub-neutralizing concentrations of CHIKV-specific antibodies. In addition, CHIKV infection in 11 days old mice under enhancing condition resulted in higher muscles viral RNA load detected and death. These observations provide the first evidence of antibody-mediated enhancement in CHIKV infection and pathogenesis and could also be relevant for other important arboviruses such as Zika virus.

A Structural and Mathematical Modeling Analysis of the Likelihood of Antibody-Dependent Enhancement in Influenza

Broadly neutralizing monoclonal antibodies (bNAbs) for viral infections, such as HIV, respiratory syncytial virus (RSV), and influenza, are increasingly entering clinical development. For influenza, most neutralizing antibodies target influenza virus hemagglutinin. These bNAbs represent an emerging, promising modality for treatment and prophylaxis of influenza due to their multiple mechanisms of antiviral action and generally safe profile. Preclinical work in other viral diseases, such as dengue, has demonstrated the potential for antibody-based therapies to enhance viral uptake, leading to enhanced viremia and worsening of disease. This phenomenon is referred to as antibody-dependent enhancement (ADE). In the context of influenza, ADE has been used to explain several preclinical and clinical phenomena. Using structural and viral kinetics modeling, we assess the role of ADE in the treatment of influenza with a bNAb.

Fc receptors in antibody-dependent enhancement of viral infections

Sensitization of the humoral immune response to invading viruses and production of antiviral antibodies forms part of the host antiviral repertoire. Paradoxically, for a number of viral pathogens, under certain conditions, antibodies provide an attractive means of enhanced virus entry and replication in a number of cell types. Known as antibody‐dependent enhancement (ADE) of infection, the phenomenon occurs when virus‐antibody immunocomplexes interact with cells bearing complement or Fc receptors, promoting internalization of the virus and increasing infection. Frequently associated with exacerbation of viral disease, ADE of infection presents a major obstacle to the prevention of viral disease by vaccination and is thought to be partly responsible for the adverse effects of novel antiviral therapeutics such as intravenous immunoglobulins. There is a growing body of work examining the intracellular signaling pathways and epitopes responsible for mediating ADE, with a view to aiding rational design of antiviral strategies. With in vitro studies also confirming ADE as a feature of infection for a growing number of viruses, challenges remain in understanding the multilayered molecular mechanisms of ADE and its effect on viral pathogenesis.

Strain Interactions as a Mechanism for Dominant Strain Alternation and Incidence Oscillation in Infectious Diseases: Seasonal Influenza as a Case Study

Background

Many human infectious diseases are caused by pathogens that have multiple strains and show oscillation in infection incidence and alternation of dominant strains which together are referred to as epidemic cycling. Understanding the underlying mechanisms of epidemic cycling is essential for forecasting outbreaks of epidemics and therefore important for public health planning. Current theoretical effort is mainly focused on the factors that are extrinsic to the pathogens themselves (“extrinsic factors”) such as environmental variation and seasonal change in human behaviours and susceptibility. Nevertheless, co-circulation of different strains of a pathogen was usually observed and thus strains interact with one another within concurrent infection and during sequential infection. The existence of these intrinsic factors is common and may be involved in the generation of epidemic cycling of multi-strain pathogens.

Methods and Findings

To explore the mechanisms that are intrinsic to the pathogens themselves (“intrinsic factors”) for epidemic cycling, we consider a multi-strain SIRS model including cross-immunity and infectivity enhancement and use seasonal influenza as an example to parameterize the model. The Kullback-Leibler information distance was calculated to measure the match between the model outputs and the typical features of seasonal flu (an outbreak duration of 11 weeks and an annual attack rate of 15%). Results show that interactions among strains can generate seasonal influenza with these characteristic features, provided that: the infectivity of a single strain within concurrent infection is enhanced 2−7 times that within a single infection; cross-immunity as a result of past infection is 0.5–0.8 and lasts 2–9 years; while other parameters are within their widely accepted ranges (such as a 2–3 day infectious period and the basic reproductive number of 1.8–3.0). Moreover, the observed alternation of the dominant strain among epidemics emerges naturally from the best fit model. Alternative modelling that also includes seasonal forcing in transmissibility shows that both external mechanisms (i.e. seasonal forcing) and the intrinsic mechanisms (i.e., strain interactions) are equally able to generate the observed time-series in seasonal flu.

Conclusions

The intrinsic mechanism of strain interactions alone can generate the observed patterns of seasonal flu epidemics, but according to Kullback-Leibler information distance the importance of extrinsic mechanisms cannot be excluded. The intrinsic mechanism illustrated here to explain seasonal flu may also apply to other infectious diseases caused by polymorphic pathogens.

Randomized controlled ferret study to assess the direct impact of 2008-09 trivalent inactivated influenza vaccine on A(H1N1)pdm09 disease risk

During spring-summer 2009, several observational studies from Canada showed increased risk of medically-attended, laboratory-confirmed A(H1N1)pdm09 illness among prior recipients of 2008-09 trivalent inactivated influenza vaccine (TIV). Explanatory hypotheses included direct and indirect vaccine effects. In a randomized placebo-controlled ferret study, we tested whether prior receipt of 2008-09 TIV may have directly influenced A(H1N1)pdm09 illness. Thirty-two ferrets (16/group) received 0.5 mL intra-muscular injections of the Canadian-manufactured, commercially-available, non-adjuvanted, split 2008-09 Fluviral or PBS placebo on days 0 and 28. On day 49 all animals were challenged (Ch0) with A(H1N1)pdm09. Four ferrets per group were randomly selected for sacrifice at day 5 post-challenge (Ch+5) and the rest followed until Ch+14. Sera were tested for antibody to vaccine antigens and A(H1N1)pdm09 by hemagglutination inhibition (HI), microneutralization (MN), nucleoprotein-based ELISA and HA1-based microarray assays. Clinical characteristics and nasal virus titers were recorded pre-challenge then post-challenge until sacrifice when lung virus titers, cytokines and inflammatory scores were determined. Baseline characteristics were similar between the two groups of influenza-naïve animals. Antibody rise to vaccine antigens was evident by ELISA and HA1-based microarray but not by HI or MN assays; virus challenge raised antibody to A(H1N1)pdm09 by all assays in both groups. Beginning at Ch+2, vaccinated animals experienced greater loss of appetite and weight than placebo animals, reaching the greatest between-group difference in weight loss relative to baseline at Ch+5 (7.4% vs. 5.2%; p = 0.01). At Ch+5 vaccinated animals had higher lung virus titers (log-mean 4.96 vs. 4.23pfu/mL, respectively; p = 0.01), lung inflammatory scores (5.8 vs. 2.1, respectively; p = 0.051) and cytokine levels (p>0.05). At Ch+14, both groups had recovered. Findings in influenza-naïve, systematically-infected ferrets may not replicate the human experience. While they cannot be considered conclusive to explain human observations, these ferret findings are consistent with direct, adverse effect of prior 2008-09 TIV receipt on A(H1N1)pdm09 illness. As such, they warrant further in-depth investigation and search for possible mechanistic explanations.

Induction of Inducible Nitric Oxide (NO) Synthase mRNA and NO Production in Macrophages Infected with Influenza A/PR/8 Virus and Stimulated with Its Ether-Split Product

We investigated the inductive activity of infective influenza A/PR/8/34 (PR8) virus and its ether-split product (ESP) on the expression of inducible nitric oxide (NO) synthase (iNOS) and NO production in RAW264.7 (RAW) cells, a murine macrophage (M psi) cell line, and thioglycolate-elicited peritoneal M psi (TPM). In both cells, PR8 virus infection induced iNOS mRNA between 4 hr and 24 hr, attaining a peak value at 12 hr. In correlation with induction of iNOS mRNA, NO amounts increased significantly from 12 to 24 hr. Moreover, this study demonstrated that ESP with the same hemagglutination titer as PR8 virus could induce iNOS mRNA and NO production, although the inductive activity of ESP was weaker than that of PR8 virus. Considering the dual role (beneficial and detrimental roles) of NO on certain inflammatory disorders and virus infections, the inductive activity of influenza virus on the iNOS-mediated NO production independent of its infectivity might contribute to a modification of influenza virus infection.

Proinflammatory cytokine response and viral replication in mouse bone marrow derived macrophages infected with influenza H1N1 and H5N1 viruses

The pathogenesis of human influenza H5N1 virus infection remains poorly understood and controversial. Cytokine dysregulation in human infection has been hypothesized to contribute to disease severity. We developed in vitro cultures of mouse bone marrow derived macrophages (BMDMΦ) from C57BL/6N mouse to compare influenza A (H5N1 and H1N1) virus replication and pro-inflammatory cytokine and chemokine responses. While both H1N1 and H5N1 viruses infected the mouse bone marrow derived macrophages, only the H1N1 virus had showed evidence of productive viral replication from the infected cells. In comparison with human seasonal influenza H1N1 (A/HK/54/98) and mouse adapted influenza H1N1 (A/WSN/33) viruses, the highly pathogenic influenza H5N1 virus (A/HK/483/97) was a more potent inducer of the chemokine, CXCL 10 (IP-10), while there was not a clear differential TNF-α protein expression pattern. Although human influenza viruses rarely cause infection in mice without prior adaption, the use of in vitro cell cultures of primary mouse cells is of interest, especially given the availability of gene-defective (knock-out) mice for specific genes.

Management of the virulent influenza virus infection by oral formulation of nonhydrolized carnosine and isopeptide of carnosine attenuating proinflammatory cytokine-induced nitric oxide production

Inducible nitric oxide synthase (iNOS) plays an important role in mediating inflammation. In our studies, we found that iNOS-derived NO was significantly increased in the serum samples of 150 patients infected with influenza A virus in comparison with samples of 140 healthy individuals. In human lung epithelial cells, infection with influenza A virus or stimulation with poly(I:C) + interferon-gamma resulted in increased mRNA and protein levels of both interleukin-32 and iNOS, with subsequent release of NO. Activated macrophages are also a source of nitric oxide (NO), which is largely produced by iNOS in response to proinflammatory cytokines. In this review article, the presented findings have many important implications for understanding the Influenza A (H1N1) viral pathogenesis, prevention, and treatment. The direct viral cytotoxicity (referred cytopathic effect) is only a fraction of several types of events induced by virus infection. Nitric oxide and oxygen free radicals such as superoxide anion (O₂⁻˙) are generated markedly in influenza A (including H1N1) virus-infected host boosts, and these molecular species are identified as the potent pathogenic agents. The mutual interaction of NO with O₂⁻˙ resulting in formation of peroxynitrite is operative in the pathogenic mechanism of influenza virus pneumonia. The toxicity and reactivity of oxygen radicals, generated in excessive amounts mediate the overreaction of the host's immune response against the organs or tissues in which viruses are replicating, and this may explain the mechanism of tissue injuries observed in influenza virus infection of various types. The authors revealed the protection that carnosine and its bioavailable nonhydrolized forms provide against peroxynitrite damage and other types of viral injuries in which immunologic interactions are usually involved. Carnosine (beta-alanyl-L-histidine) shows the pharmacologic intracellular correction of NO release which might be one of the important factors of natural immunity in controlling the initial stages of influenza A virus infection (inhibition of virus replication) and virus-induced regulation of cytokine gene expression. The protective effects of orally applied nonhydrolized formulated species of carnosine include at least direct interaction with nitric oxide, inhibition of cytotoxic NO-induced proinflammatory condition, and attenuation of the effects of cytokines and chemokines that can exert profound effects on inflammatory cells. These data are consistent with the hypothesis that natural products, such as chicken soup and chicken breast extracts rich in carnosine and its derivative anserine (beta-alanyl-1-methyl-L-histidine) could contribute to the pathogenesis and prevention of influenza virus infections and cold but have a limitation due to susceptibility to enzymatic hydrolysis of dipeptides with serum carnosinase and urine excretion after oral ingestion of a commercial chicken extract. The developed and patented by the authors formulations of nonhydrolized in digestive tract and blood natural carnosine peptide and isopeptide (gamma-glutamyl-carnosine) products have a promise in the Influenza A (H1N1) virus infection disease control and prevention.

Monoclonal antibodies directed against protective antigen of Bacillus anthracis enhance lethal toxin activity in vivo

Protective antigen (PA) from Bacillus anthracis binds to cellular receptors, combines with lethal factor (LF) forming lethal toxin (LeTx), and facilitates the translocation of LF into the cytosol. LeTx is cytotoxic for J774A.1 cells, a murine macrophage cell line, and causes death of Fisher 344 rats when injected intravenously. PA is also the major protective component in anthrax vaccines. Antibody-dependent enhancement has been reported for several viral diseases, a bacterial infection, and for B. anthracis LeTx in vitro cytotoxicity. Further screening of our 73 PA monoclonal antibodies (mAbs) identified a total of 17 PA mAbs that enhanced in vitro cytotoxicity at suboptimal concentrations of LeTx. A competitive binding enzyme-linked immunosorbent assay showed that these 17 PA mAbs identified eight different antigenic regions on PA. Eight of the 17 PA mAbs that enhanced LeTx in vitro cytoxicity were examined for their activity in vivo. Of the eight mAbs that were injected intravenously with a sublethal concentration of LeTx into male Fisher 344 rats, four mAbs enhanced the lethality of LeTx and resulted in the death of animals, whereas control animals did not succumb to intoxication. This is the first demonstration that PA mAbs can enhance LeTx intoxication in vivo.

Characterization of antibodies specific for hemagglutinin and neuraminidase proteins of the 1918 and 2009 pandemic H1N1 viruses

Serologic studies have detected protective immunity against 2009 pandemic H1N1 influenza virus (H1N1-2009) in some people. However, further study of preexisting immunity has been complicated by the complexity of the human immunological background. Here, we immunized mice with HA- and NA-encoding plasmids. The cross-neutralizing activity of the anti-HA antisera and the effect of the anti-NA antisera on viral infectivity were evaluated using H1N1-1918- and 2009-pseudotyped particles (pps) and an H1N1-2009 isolate. Antibodies to H1N1-2009 HA (09HA) neutralized pps harboring 09HA or H1N1-1918 HA (18HA); similarly, antibodies to 18HA neutralized pps harboring 18HA or 09HA. Antibodies to 09HA and 18HA also neutralized the H1N1-2009 virus with high efficiency. Antibodies to H1N1-1918 NA (18NA) or H1N1-2009 NA (09NA) both enhanced the infectivity of pps harboring 09NA and 18NA. Although anti-09NA and -18NA antibodies significantly reduced cytopathic effects in multiple-cycle infection assays, conversely, these antibodies enhanced the infectivity of H1N1-2009 in single-cycle infection assays. Our study demonstrates the existence of cross-protection between antibodies against these two antigenically related virus strains and shows that anti-NA antibodies have a dual effect that requires reexamination of their role in human immunity.

Assessment of the efficacy of commercially available and candidate vaccines against a pandemic H1N1 2009 virus

Background. The emergence and global spread of the pandemic H1N1 2009 influenza virus have raised questions regarding the protective effect of available seasonal vaccines and the efficacy of a newly produced matched vaccine.

Methods. Ferrets were immunized with the 2008–2009 formulations of commercially available live attenuated (FluMist; MedImmune) or split-inactivated (Fluviral; GlaxoSmithKline) vaccines, a commercial swine vaccine (FluSure; Pfizer), or a laboratory-produced matched inactivated whole-virus vaccine (A/Mexico/InDRE4487/2009). Adaptive immune responses were monitored, and the animals were challenged with A/Mexico/InDRE4487/2009 after 5 weeks.

Results. Only animals that received the swine or matched vaccines developed detectable hemagglutination- inhibiting antibodies against the challenge virus, whereas a T cell response was exclusively detected in animals vaccinated with FluMist. After challenge, all animals had high levels of virus replication in the upper respiratory tract. However, preexisting anti—pandemic H1N1 2009 antibodies resulted in reduced clinical signs and improved survival. Surprisingly, FluMist was associated with a slight increase in mortality and greater lung damage, which correlated with early up-regulation of interleukin-10.

Conclusions. The present study demonstrates that a single dose of matched inactivated vaccine confers partial protection against a pandemic H1N1 2009 virus, and it suggests that a higher dose or prime-boost regimen may be required. The consequences of mismatched immunity to influenza merit further investigation.

Association between the 2008-09 seasonal influenza vaccine and pandemic H1N1 illness during Spring-Summer 2009: four observational studies from Canada

BACKGROUND

In late spring 2009, concern was raised in Canada that prior vaccination with the 2008-09 trivalent inactivated influenza vaccine (TIV) was associated with increased risk of pandemic influenza A (H1N1) (pH1N1) illness. Several epidemiologic investigations were conducted through the summer to assess this putative association.

METHODS AND FINDINGS

STUDIES INCLUDED

(1) test-negative case-control design based on Canada's sentinel vaccine effectiveness monitoring system in British Columbia, Alberta, Ontario, and Quebec; (2) conventional case-control design using population controls in Quebec; (3) test-negative case-control design in Ontario; and (4) prospective household transmission (cohort) study in Quebec. Logistic regression was used to estimate odds ratios for TIV effect on community- or hospital-based laboratory-confirmed seasonal or pH1N1 influenza cases compared to controls with restriction, stratification, and adjustment for covariates including combinations of age, sex, comorbidity, timeliness of medical visit, prior physician visits, and/or health care worker (HCW) status. For the prospective study risk ratios were computed. Based on the sentinel study of 672 cases and 857 controls, 2008-09 TIV was associated with statistically significant protection against seasonal influenza (odds ratio 0.44, 95% CI 0.33-0.59). In contrast, estimates from the sentinel and three other observational studies, involving a total of 1,226 laboratory-confirmed pH1N1 cases and 1,505 controls, indicated that prior receipt of 2008-09 TIV was associated with increased risk of medically attended pH1N1 illness during the spring-summer 2009, with estimated risk or odds ratios ranging from 1.4 to 2.5. Risk of pH1N1 hospitalization was not further increased among vaccinated people when comparing hospitalized to community cases.

CONCLUSIONS

Prior receipt of 2008-09 TIV was associated with increased risk of medically attended pH1N1 illness during the spring-summer 2009 in Canada. The occurrence of bias (selection, information) or confounding cannot be ruled out. Further experimental and epidemiological assessment is warranted. Possible biological mechanisms and immunoepidemiologic implications are considered.

Antibody dependent enhancement of frog virus 3 infection

Background

Viruses included in the family Iridoviridae are large, icosahedral, dsDNA viruses that are subdivided into 5 genera. Frog virus 3 (FV3) is the type species of the genus Ranavirus and the best studied iridovirus at the molecular level. Typically, antibodies directed against a virus act to neutralize the virus and limit infection. Antibody dependent enhancement occurs when viral antibodies enhance infectivity of the virus rather than neutralize it.

Results

Here we show that anti-FV3 serum present at the time of FV3 infection enhances infectivity of the virus in two non-immune teleost cell lines. We found that antibody dependent enhancement of FV3 was dependent on the Fc portion of anti-FV3 antibodies but not related to complement. Furthermore, the presence of anti-FV3 serum during an FV3 infection in a non-immune mammalian cell line resulted in neutralization of the virus. Our results suggest that a cell surface receptor specific to teleost cell lines is responsible for the enhancement.

Conclusions

This report represents the first evidence of antibody dependent enhancement in iridoviruses. The data suggests that anti-FV3 serum can either neutralize or enhance viral infection and that enhancement is related to a novel antibody dependent enhancement pathway found in teleosts that is Fc dependent.

Pseudovirions as vehicles for the delivery of siRNA

Over the last two decades, small interfering RNA (siRNA)-mediated gene silencing has quickly become one of the most powerful techniques used to study gene function in vitro and a promising area for new therapeutics. Delivery remains a significant impediment to realizing the therapeutic potential of siRNA, a problem that is also tied to immunogenicity and toxicity. Numerous delivery vehicles have been developed, including some that can be categorized as pseudovirions: these are vectors that are directly derived from viruses but whose viral coding sequences have been eliminated, preventing their classification as viral vectors. Characteristics of the pseudovirions discussed in this review, namely phagemids, HSV amplicons, SV40 in vitro-packaged vectors, influenza virosomes, and HVJ-Envelope vectors, make them attractive for the delivery of siRNA-based therapeutics. Pseudovirions were shown to deliver siRNA effector molecules and bring about RNA interference (RNAi) in various cell types in vitro, and in vivo using immune-deficient and immune-competent mouse models. Levels of silencing were not always determined directly, but the duration of siRNA-induced knockdown lasted at least 3 days. We present examples of the use of pseudovirions for the delivery of synthetic siRNA as well as the delivery and expression of DNA-directed siRNA.

Antibody-dependent enhancement of hepatitis C virus infection

Hepatitis C virus (HCV) often causes a persistent infection associated with hypergammaglobulinemia, high levels of antiviral antibody and circulating immune complexes, and immune complex disease. We previously reported that only a limited neutralizing activity to vesicular stomatitis virus or HCV pseudotype is generated in animals immunized with recombinant HCV envelope proteins and chronically infected HCV patient sera. Interestingly, when some of these neutralizing sera were diluted into a range of concentrations below those that reduced virus plaque number, an increase in pseudotype plaque formation was observed. Purified HCV E2-specific human monoclonal antibodies were used to further verify the specificity of this enhancement, and one- to twofold increases were apparent on permissive Huh-7 cells. The enhancement of HCV pseudotype titer could be inhibited by the addition of a Fc-specific anti-human immunoglobulin G Fab fragment to the virus-antibody mixture prior to infection. Treatment of cells with antibody to Fc receptor I (FcRI) or FcRII, but not FcRIII, also led to an inhibition of pseudotype titer enhancement in an additive manner. Human lymphoblastoid cell line (Raji), a poor host for HCV pseudotype infection, exhibited a four- to sixfold enhancement of pseudotype-mediated cell death upon incubation with antibody at nonneutralizing concentrations. A similar enhancement of cell culture-grown HCV infectivity by a human monoclonal antibody was also observed. Taken together, antibodies to viral epitopes enhancing HCV infection need to be taken into consideration for pathogenesis and in the development of an effective vaccine.

Cellular gene transfer mediated by influenza virosomes with encapsulated plasmid DNA

Reconstituted influenza virosomes (virus membrane envelopes) have been used previously to deliver pDNA (plasmid DNA) bound to their external surface to a variety of target cells. Although high transfection efficiencies can be obtained with these complexes in vitro, the virosome-associated DNA is readily accessible to nucleases and could therefore be prone to rapid degradation under in vivo conditions. In the present study, we show a new method for the production of DNA-virosomes resulting in complete protection of the DNA from nucleases. This method relies on the use of the short-chain phospholipid DCPC (dicaproylphosphatidylcholine) for solubilization of the viral membrane. The solubilized viral membrane components are mixed with pDNA and cationic lipid. Reconstitution of the viral envelopes and simultaneous encapsulation of pDNA is achieved by removal of the DCPC from the mixture through dialysis. Analysis by linear sucrose density-gradient centrifugation revealed that protein, phospholipid and pDNA physically associated to particles, which appeared as vesicles with spike proteins inserted in their membranes when analysed by electron microscopy. The DNA-virosomes retained the membrane fusion properties of the native influenza virus. The virosome-associated pDNA was completely protected from degradation by nucleases, providing evidence for the DNA being highly condensed and encapsulated in the lumen of the virosomes. DNA-virosomes, containing reporter gene constructs, transfected a variety of cell lines, with efficiencies approaching 90%. Transfection was completely dependent on the fusogenic properties of the viral spike protein haemagglutinin. Thus, DNA-virosomes prepared by the new procedure are highly efficient vehicles for DNA delivery, offering the advantage of complete DNA protection, which is especially important for future in vivo applications.

Failure of protection and enhanced pneumonia with a US H1N2 swine influenza virus in pigs vaccinated with an inactivated classical swine H1N1 vaccine

Two US swine influenza virus (SIV) isolates, A/Swine/Iowa/15/1930 H1N1 (IA30) and A/Swine/Minnesota/00194/2003 H1N2 (MN03), were evaluated in an in vivo vaccination and challenge model. Inactivated vaccines were prepared from each isolate and used to immunize conventional pigs, followed by challenge with homologous or heterologous virus. Both inactivated vaccines provided complete protection against homologous challenge. However, the IA30 vaccine failed to protect against the heterologous MN03 challenge. Three of the nine pigs in this group had substantially greater percentages of lung lesions, suggesting the vaccine potentiated the pneumonia. In contrast, priming with live IA30 virus provided protection from nasal shedding and virus replication in the lung in MN03 challenged pigs. These data indicate that divergent viruses that did not cross-react serologically did not provide complete cross-protection when used in inactivated vaccines against heterologous challenge and may have enhanced disease. In addition, live virus infection conferred protection against heterologous challenge.

Reconstituted influenza virus envelopes as an efficient carrier system for cellular delivery of small-interfering RNAs

Application of RNA interference for in vivo evaluation of gene function or for therapeutic interventions has been hampered by a lack of suitable delivery methods for small interfering RNA (siRNA). Here, we present reconstituted viral envelopes (virosomes) derived from influenza virus as suitable vehicles for in vitro as well as in vivo delivery of siRNAs. Virosomes are vesicles that bear in their membrane the influenza virus spike protein hemagglutinin (HA). This protein mediates binding of native virus to and fusion with cellular target membranes. Accordingly, virosomes with membrane-incorporated HA bind to cells, are taken up by receptor-mediated endocytosis, and fuse with the endosomal membrane to release their contents into the cytoplasm. When complexed to cationic lipids, siRNA was successfully encapsulated in virosomes. Virosomes with encapsulated siRNA fused with target membranes in a pH-dependent manner and delivered the encapsulated siRNA to several cell lines in vitro. Virosome-delivered siRNA markedly downregulated the synthesis of newly induced and constitutively expressed green fluorescent protein. Moreover, intraperitoneal injection of siRNA-loaded virosomes resulted in delivery of the nucleotides to cells in the peritoneal cavity. Our results indicate that virosomes are a promising delivery device for in vivo application, especially where topical administration of siRNA, for example, to the respiratory tract is envisaged.

Ross River virus: Molecular and cellular aspects of disease pathogenesis

Ross River virus (RRV) is a mosquito-borne alphavirus indigenous to Australia and the Western Pacific region and is responsible for several thousand cases of human RRV disease (RRVD) per annum. The disease primarily involves polyarthritis/arthralgia, with many patients also presenting with rash, myalgia, fever, and/or lethargy. The symptoms can be debilitating at onset, but they usually resolve within 3-6 months. Recent insights into the RRV-host relationship, associated pathology, and molecular biology of infection have generated a number of potential avenues for improved treatment. Although vaccine development has been proposed, the small market size and potential for antibody-dependent enhancement (ADE) of disease make this approach unattractive. Recent insights into the molecular basis of RRV-ADE and the virus's ability to manipulate host inflammatory and immune responses create potential new opportunities for therapeutic invention. Such interventions should overcome virus-induced dysregulation of protective host responses to promote viral clearance and/or ameliorate inflammatory immunopathology.

Monoclonal antibody analysis of porcine reproductive and respiratory syndrome virus epitopes associated with antibody-dependent enhancement and neutralization of virus infection

Enhanced infection and replication of porcine reproductive and respiratory syndrome (PRRS) virus in the presence of specific antibody has been demonstrated in vitro and in vivo, a phenomenon known as antibody-dependent enhancement (ADE). ADE is considered to be a significant obstacle to developing effective vaccines for many viruses for which ADE has been reported, since virus-specific antibodies of maternal origin or those conferred by vaccination can facilitate the entry of the virus into target cells, sometimes resulting in increased severity of the disease. In this study, the role of specific PRRS viral epitopes in ADE and/or virus neutralization (VN) was assessed in vitro using 14 monoclonal antibodies (mAbs) to 4 PRRS viral proteins: nucleocapsid (N), matrix (M), glycoprotein (GP) 5, and GP3. Each mAb recongnized a distinct epitope on one of these proteins. One-way ADE and VN assays were performed in vitro using homologous PRRS virus isolates in the presence or absence of each mAb. ADE activity was determined by detecting a significant increase of progeny virus yield in porcine alveolar macrophage cultures in the presence of individual mAbs. Neutralizing activity was determined by detecting a significant reduction or complete blocking of virus replication in MARC-145 cells in the presence of individual mAbs. mAbs could be categorized into 3 groups: enhancing, neutralizing and neither. Viral epitopes which are capable of inducing neutralizing antibodies appeared to reside on the M, GP3 and GP5 proteins, while epitopes that may induce ADE-mediating antibody were associated with the N and GP5 proteins. Identification of the viral proteins and antigens and epitopes responsible for ADE- and VN-mediating antibodies may provide the basis for developing efficacious second-generation vaccines for the control of PRRS virus; yet, further epitope mapping remains to be done.

Live, attenuated coronavirus vaccines through the directed deletion of group-specific genes provide protection against feline infectious peritonitis

Feline infectious peritonitis (FIP) is a fatal immunity-mediated disease caused by mutants of a ubiquitous coronavirus. Since previous attempts to protect cats under laboratory and field conditions have been largely unsuccessful, we used our recently developed system of reverse genetics (B. J. Haijema, H. Volders, and P. J. M. Rottier, J. Virol. 77:4528-4538, 2003) for the development of a modified live FIP vaccine. With this objective, we deleted the group-specific gene cluster open reading frame 3abc or 7ab and obtained deletion mutant viruses that not only multiplied well in cell culture but also showed an attenuated phenotype in the cat. At doses at which the wild-type virus would be fatal, the mutants with gene deletions did not cause any clinical symptoms. They still induced an immune response, however, as judged from the high levels of virus-neutralizing antibodies. The FIP virus (FIPV) mutant lacking the 3abc cluster and, to a lesser extent, the mutant missing the 7ab cluster, protected cats against a lethal homologous challenge; no protection was obtained with the mutant devoid of both gene clusters. Our studies show that the deletion of group-specific genes from the coronavirus genome results in live attenuated candidate vaccines against FIPV. More generally, our approach may allow the development of vaccines against infections with other pathogenic coronaviruses, including that causing severe acute respiratory syndrome in humans.

Antibody-dependent enhancement of viral infection: molecular mechanisms and in vivo implications

Besides the common receptor/coreceptor-dependent mechanism of cellular attachment, some viruses rely on antiviral antibodies for their efficient entry into target cells. This mechanism, known as antibody-dependent enhancement (ADE) of viral infection, depends on the cross-linking of complexes of virus-antibody or virus-activated complement components through interaction with cellular molecules such as Fc receptors or complement receptors, leading to enhanced infection of susceptible cells. Recent studies have suggested that additional mechanisms underlie ADE: involvement of complement component C1q and its receptor (Ebola virus), antibody-mediated modulation of the interaction between viral protein and its coreceptor (human immunodeficiency virus) and suppression of cellular antiviral genes by the replication of viruses entering cells via ADE (Ross River virus). Since ADE is exploited by a variety of viruses and has been associated with disease exacerbation, it may have broad relevance to the pathogenesis of viral infection and antiviral strategies.

Antibody-dependent enhancement of Ebola virus infection

Most strains of Ebola virus cause a rapidly fatal hemorrhagic disease in humans, yet there are still no biologic explanations that adequately account for the extreme virulence of these emerging pathogens. Here we show that Ebola Zaire virus infection in humans induces antibodies that enhance viral infectivity. Plasma or serum from convalescing patients enhanced the infection of primate kidney cells by the Zaire virus, and this enhancement was mediated by antibodies to the viral glycoprotein and by complement component C1q. Our results suggest a novel mechanism of antibody-dependent enhancement of Ebola virus infection, one that would account for the dire outcome of Ebola outbreaks in human populations.

Antibody-dependent enhancement of virus infection and disease

In general, virus-specific antibodies are considered antiviral and play an important role in the control of virus infections in a number of ways. However, in some instances, the presence of specific antibodies can be beneficial to the virus. This activity is known as antibody-dependent enhancement (ADE) of virus infection. The ADE of virus infection is a phenomenon in which virus-specific antibodies enhance the entry of virus, and in some cases the replication of virus, into monocytes/macrophages and granulocytic cells through interaction with Fc and/or complement receptors. This phenomenon has been reported in vitro and in vivo for viruses representing numerous families and genera of public health and veterinary importance. These viruses share some common features such as preferential replication in macrophages, ability to establish persistence, and antigenic diversity. For some viruses, ADE of infection has become a great concern to disease control by vaccination. Consequently, numerous approaches have been made to the development of vaccines with minimum or no risk for ADE. Identification of viral epitopes associated with ADE or neutralization is important for this purpose. In addition, clear understanding of the cellular events after virus entry through ADE has become crucial for developing efficient intervention. However, the mechanisms of ADE still remain to be better understood.

Suppression of lipopolysaccharide-induced antiviral transcription factor (STAT-1 and NF-kappa B) complexes by antibody-dependent enhancement of macrophage infection by Ross River virus

Subneutralizing concentrations of antibody may enhance virus infection by bringing the virus-antibody complex into contact with the cell surface Fc receptors; this interaction facilitates entry of virus into the cell and is referred to as antibody-dependent enhancement (ADE) of infection. Northern analysis of macrophage RNA demonstrated that ADE infection by the indigenous Australian alphavirus Ross River (RRV-ADE) ablated or diminished message for tumor necrosis factor alpha (TNF-alpha), nitric-oxide synthase 2 (NOS2), and IFN regulatory factor 1 (IRF-1), as well as for IFN-inducible protein 10 (IP-10) and IFN-beta; the transcription of a control gene was unaffected. Additionally, electrophoretic mobility-shift assay (EMSA) studies showed that transcription factor IFN-alpha-activated factor (AAF), IFN-stimulated gene factor 3 (ISGF3), and nuclear factor-kappaB (NF-kappaB) complex formation in macrophage nuclear extracts were specifically suppressed post-RRV-ADE infection, emphasizing the capacity for ADE infections to compromise antiviral responses at the transcriptional level. The suppression of antiviral transcription factor complexes was shown to depend on replicating virus and was not simply a result of general antibody-Fc-receptor interaction. Although only a minority of cells ( approximately 15%) were shown to be positive for RRV by immunostaining techniques post ADE, molecular (RT-PCR) analysis showed that unstained cells carried RRV-RNA, indicating a higher level of viral infectivity than previously suspected. Electron microscopy studies confirmed this observation. Furthermore, levels of cellular IL-10 protein were dramatically elevated in RRV-ADE cultures. This evidence demonstrates that RRV can potently disrupt the activation of specific antiviral pathways via ADE infection pathways, and may suggest a significant mechanism in the infection and pathogenesis of other ADE viruses.