Antibody-dependent-cellular-cytotoxicity-inducing antibodies significantly affect the post-exposure treatment of Ebola virus infection

Treatment of Ebola Virus Disease: From Serotherapy to the Use of Monoclonal Antibodies

Ebola virus disease (EVD) is an acute illness with a high-case fatality rate (CFR) caused by an RNA virus belonging to the Filoviridae family. Over the past 50 years, regular EVD outbreaks have been reported. The West African EVD outbreak of 2013-2016 proved to be significantly more widespread and complex than previous ones, resulting in approximately 11,000 deaths. A coordinated international effort was required to bring the outbreak under control. One of the main challenges faced by clinicians and researchers combating EVD was the absence of vaccines and preventive treatments. Only recently have efforts led to the development of effective therapeutic options. Among these, monoclonal antibody-based drugs have emerged as the most promising agents for the urgent treatment of EVD. This article aims to review the key milestones in the development of antibody-based therapies for EVD, tracing the journey from the use of convalescent serum to the creation of effective monoclonal antibody-based drugs and their combinations.

A Hidden Guardian: The Stability and Spectrum of Antibody-Dependent Cell-Mediated Cytotoxicity in COVID-19 Response in Chinese Adults

OBJECTIVES

Identifying immune-protective biomarkers is crucial for the effective management and mitigation of current and future COVID-19 outbreaks, particularly in preventing or counteracting the immune evasion exhibited by the Omicron variants. The emergence of SARS-CoV-2 variants, especially those within the Omicron lineage, has highlighted their capacity to evade neutralizing antibodies, emphasizing the need to understand the role of antibody-dependent cell-mediated cytotoxicity (ADCC) in combating these infections.

METHODS

This study, conducted in Qichun City, Hubei province, from December 2021 to March 2023, involved 50 healthy Chinese adults who had received two doses of inactivated vaccines and had subsequently experienced mild infections with the Omicron BA.5 variant. Blood samples from these 50 healthy Chinese adults were collected at six distinct time points: at baseline and at the 1st, 3rd, 6th, and 9th months following the third dose of the inactivated vaccine, as well as 3 months post-breakthrough infection. Their sera were analyzed to assess ADCC and neutralization effects.

RESULTS

The results indicated that the antibodies elicited by the inactivated SARS-CoV-2 vaccine targeted the spike protein, exhibiting both pre-existing neutralizing and ADCC activities against Omicron variants BA.5 and XBB.1.5. Notably, the ADCC activity demonstrated greater stability compared to that of the neutralizing effects, persisting for at least 15 months post-vaccination, and could be augmented by additional vaccine doses and breakthrough infections. The ADCC effect associated with hybrid immunity effectively targets a spectrum of prospective Omicron variants, including BA.2.86, CH.1.1, EG.5.1, and JN.1.

CONCLUSIONS

In light of its stability and broad-spectrum efficacy, we recommend the use of the ADCC effect as a biomarker for assessing protective immunity and guiding the development of vaccines and monoclonal antibodies.

Interaction of the endogenous antibody response with activating FcγRs enhance control of Mayaro virus through monocytes

Mayaro virus (MAYV) is an emerging arbovirus. Previous studies have shown antibody Fc effector functions are critical for optimal monoclonal antibody-mediated protection against alphaviruses; however, the requirement of Fc gamma receptors (FcγRs) for protection during natural infection has not been evaluated. Here, we showed mice lacking activating FcγRs (FcRγ-/-) developed prolonged clinical disease with increased MAYV in joint-associated tissues. Viral reduction was associated with anti-MAYV cell surface binding antibodies rather than neutralizing antibodies. Lack of Fc-FcγR engagement increased the number of monocytes present in the joint-associated tissue through chronic timepoints. Single-cell RNA sequencing showed elevated levels of pro-inflammatory monocytes in joint-associated tissue with increased MAYV RNA present in FcRγ-/- monocytes and macrophages. Transfer of FcRγ-/- monocytes into wild type animals was sufficient to increase virus in joint-associated tissue. Overall, this study suggests that engagement of antibody Fc with activating FcγRs promotes protective responses during MAYV infection and prevents a pro-viral role for monocytes.

A pan-orthoebolavirus neutralizing antibody encoded by mRNA effectively prevents virus infection

Orthoebolavirus is a genus of hazardous pathogens that has caused over 30 outbreaks. However, currently approved therapies are limited in scope, as they are only effective against the Ebola virus and lack cross-protection against other orthoebolaviruses. Here, we demonstrate that a previously isolated human-derived antibody, 2G1, can recognize the glycoprotein (GP) of every orthoebolavirus species. The cryo-electron microscopy structure of 2G1 Fab in complex with the GPΔMucin trimer reveals that 2G1 binds a quaternary pocket formed by three subunits from two GP protomers. 2G1 recognizes highly conserved epitopes among filoviruses and achieves neutralization by blocking GP proteolysis. We designed an efficient mRNA module capable of producing test antibodies at expression levels exceeding 1500 ng/mL in vitro. The lipid nanoparticle (LNP)-encapsulated mRNA-2G1 exhibited potent neutralizing activities against the HIV-pseudotyped Ebola and Sudan viruses that were 19.8 and 12.5 times that of IgG format, respectively. In mice, the antibodies encoded by the mRNA-2G1-LNP peaked within 24 h, effectively blocking the invasion of pseudoviruses with no apparent liver toxicity. This study suggests that the 2G1 antibody and its mRNA formulation represent promising candidate interventions for orthoebolavirus disease, and it provides an efficient mRNA framework applicable to antibody-based therapies.

Safety and Immunogenicity of Accelerated Heterologous 2-Dose Ebola Vaccine Regimens in Adults With and Without HIV in Africa

BACKGROUND

Shorter prophylactic vaccine schedules may offer more rapid protection against Ebola in resource-limited settings.

METHODS

This randomized, observer-blind, placebo-controlled, phase 2 trial conducted in 5 sub-Saharan African countries included people without human immunodeficiency virus (HIV) (PWOH, n = 249) and people with HIV (PWH, n = 250). Adult participants received 1 of 2 accelerated Ebola vaccine regimens (MVA-BN-Filo, Ad26.ZEBOV administered 14 days apart [n = 79] or Ad26.ZEBOV, MVA-BN-Filo administered 28 days apart [n = 322]) or saline/placebo (n = 98). The primary endpoints were safety (adverse events [AEs]) and immunogenicity (Ebola virus [EBOV] glycoprotein-specific binding antibody responses). Binding antibody responders were defined as participants with a >2.5-fold increase from baseline or the lower limit of quantification if negative at baseline.

RESULTS

The mean age was 33.4 years, 52% of participants were female, and among PWH, the median CD4+ cell count was 560.0 (interquartile range, 418.0-752.0) cells/μL. AEs were generally mild/moderate with no vaccine-related serious AEs or remarkable safety profile differences by HIV status. At 21 days post-dose 2, EBOV glycoprotein-specific binding antibody response rates in vaccine recipients were 99% for the 14-day regimen (geometric mean concentrations [GMCs]: 5168 enzyme-linked immunosorbent assay units [EU]/mL in PWOH; 2509 EU/mL in PWH) and 98% for the 28-day regimen (GMCs: 6037 EU/mL in PWOH; 2939 EU/mL in PWH). At 12 months post-dose 2, GMCs in PWOH and PWH were 635 and 514 EU/mL, respectively, for the 14-day regimen and 331 and 360 EU/mL, respectively, for the 28-day regimen.

CONCLUSIONS

Accelerated 14- and 28-day Ebola vaccine regimens were safe and immunogenic in PWOH and PWH in Africa. Clinical Trials Registration. NCT02598388.

Afucosylated anti-EBOV antibody MIL77-3 engages sGP to elicit NK cytotoxicity

MIL77-3 is one component of antibody cocktail that is produced in our lab and represents an effective regimen for animals suffering from Zaire Ebolavirus (EBOV) infection. MIL77-3 is engineered to increase its affinity for the FcγRIIIa (CD16a) by deleting the fucose in the framework region. The potential effects of this modification on host immune responses, however, remain largely unknown. Herein, we demonstrated that MIL77-3 recognized secreted glycoproptein (sGP), produced by EBOV, and formed the immunocomplex to potently augment antibody-dependent cytotoxicity of human peripheral blood-derived natural killer cells (pNKs), including CD56dim and CD56bright subpopulations, in contrast to the counterparts (Mab114, rEBOV548, fucosylated MIL77-3). Intriguingly, this effect was not observed when NK92-CD16a cell line was utilized and restored by the addition of beads-coupled or membrane-anchored sGP in combination with MIL77-3. Furthermore, sGP bound to unrecognized receptors on T cells contaminated in pNKs rather than NK92-CD16a cells. Administration of beads-coupled sGP/MIL77-3 complex in mice elicited NK activation. Overall, this work reveals an immune-stimulating function of sGP/MIL77-3 complex by triggering cytotoxic activity of NK cells, highlighting the necessity to evaluate the potential impact of MIL77-3 on host immune reaction in clinical trials.

IMPORTANCE

Zaire Ebolavirus (EBOV) is highly lethal and causes sporadic outbreaks. The passive administration of monoclonal antibodies (mAbs) represents a promising treatment regimen against EBOV. Mounting evidence has shown that the efficacy of a subset of therapeutic mAbs in vivo is intimately associated with its capacity to trigger NK activity, supporting glycomodification of Fc region of anti-EBOV mAbs as a putative strategy to enhance Fc-mediated immune effector function as well as protection in vivo. Our work here uncovers the potential harmful influence of this modification on host immune responses, especially for mAbs with cross-reactivity to secreted glycoproptein (sGP) (e.g., MIL77-3), and highlights it is necessary to evaluate the NK-stimulating activity of a fucosylated mAb engaged with sGP when a new candidate is developed.

Activating FcγRs on monocytes are necessary for optimal Mayaro virus clearance

Mayaro virus (MAYV) is an emerging arbovirus. Previous studies have shown antibody Fc effector functions are critical for optimal monoclonal antibody-mediated protection against alphaviruses; however, the requirement of Fc gamma receptors (FcγRs) for protection during natural infection has not been evaluated. Here, we showed mice lacking activating FcγRs (FcRγ-/-) developed prolonged clinical disease with more virus in joint-associated tissues. Viral clearance was associated with anti-MAYV cell surface binding rather than neutralizing antibodies. Lack of Fc-FcγR engagement increased the number of monocytes through chronic timepoints. Single cell RNA sequencing showed elevated levels of pro-inflammatory monocytes in joint-associated tissue with increased MAYV RNA present in FcRγ-/- monocytes and macrophages. Transfer of FcRγ-/- monocytes into wild type animals was sufficient to increase virus in joint-associated tissue. Overall, this study suggests that engagement of antibody Fc with activating FcγRs promotes protective responses during MAYV infection and prevents monocytes from being potential targets of infection.

Replicon particle vaccination induces non-neutralizing anti-nucleoprotein antibody-mediated control of Crimean-Congo hemorrhagic fever virus

Crimean-Congo hemorrhagic fever virus (CCHFV) can cause severe human disease and is considered a WHO priority pathogen due to the lack of efficacious vaccines and antivirals. A CCHF virus replicon particle (VRP) has previously shown protective efficacy in a lethal Ifnar-/- mouse model when administered as a single dose at least 3 days prior to challenge. Here, we determine that non-specific immune responses are not sufficient to confer short-term protection, since Lassa virus VRP vaccination 3 days prior to CCHFV challenge was not protective. We also investigate how CCHF VRP vaccination confers protective efficacy by examining viral kinetics, histopathology, clinical analytes and immunity early after challenge (3 and 6 days post infection) and compare to unvaccinated controls. We characterize how these effects differ based on vaccination period and correspond to previously reported CCHF VRP-mediated protection. Vaccinating Ifnar-/- mice with CCHF VRP 28, 14, 7, or 3 days prior to challenge, all known to confer complete protection, significantly reduced CCHFV viral load, mucosal shedding, and markers of clinical disease, with greater reductions associated with longer vaccination periods. Interestingly, there were no significant differences in innate immune responses, T cell activation, or antibody titers after challenge between groups of mice vaccinated a week or more before challenge, but higher anti-NP antibody avidity and effector function (ADCD) were positively associated with longer vaccination periods. These findings support the importance of antibody-mediated responses in VRP vaccine-mediated protection against CCHFV infection.

Safety and Immunogenicity of an Accelerated Ebola Vaccination Schedule in People with and without Human Immunodeficiency Virus: A Randomized Clinical Trial

The safety and immunogenicity of the two-dose Ebola vaccine regimen MVA-BN-Filo, Ad26.ZEBOV, 14 days apart, was evaluated in people without HIV (PWOH) and living with HIV (PLWH). In this observer-blind, placebo-controlled, phase 2 trial, healthy adults were randomized (4:1) to receive MVA-BN-Filo (dose 1) and Ad26.ZEBOV (dose 2), or two doses of saline/placebo, administered intramuscularly 14 days apart. The primary endpoints were safety (adverse events (AEs)) and immunogenicity (Ebola virus (EBOV) glycoprotein-specific binding antibody responses). Among 75 participants (n = 50 PWOH; n = 25 PLWH), 37% were female, the mean age was 44 years, and 56% were Black/African American. AEs were generally mild/moderate, with no vaccine-related serious AEs. At 21 days post-dose 2, EBOV glycoprotein-specific binding antibody responder rates were 100% among PWOH and 95% among PLWH; geometric mean antibody concentrations were 6286 EU/mL (n = 36) and 2005 EU/mL (n = 19), respectively. A total of 45 neutralizing and other functional antibody responses were frequently observed. Ebola-specific CD4+ and CD8+ T-cell responses were polyfunctional and durable to at least 12 months post-dose 2. The regimen was well tolerated and generated robust, durable immune responses in PWOH and PLWH. Findings support continued evaluation of accelerated vaccine schedules for rapid deployment in populations at immediate risk. Trial registration: NCT02598388 (submitted 14 November 2015).

Natural products as a source of Coronavirus entry inhibitors

The COVID-19 pandemic has had a significant and lasting impact on the world. Four years on, despite the existence of effective vaccines, the continuous emergence of new SARS-CoV-2 variants remains a challenge for long-term immunity. Additionally, there remain few purpose-built antivirals to protect individuals at risk of severe disease in the event of future coronavirus outbreaks. A promising mechanism of action for novel coronavirus antivirals is the inhibition of viral entry. To facilitate entry, the coronavirus spike glycoprotein interacts with angiotensin converting enzyme 2 (ACE2) on respiratory epithelial cells. Blocking this interaction and consequently viral replication may be an effective strategy for treating infection, however further research is needed to better characterize candidate molecules with antiviral activity before progressing to animal studies and clinical trials. In general, antiviral drugs are developed from purely synthetic compounds or synthetic derivatives of natural products such as plant secondary metabolites. While the former is often favored due to the higher specificity afforded by rational drug design, natural products offer several unique advantages that make them worthy of further study including diverse bioactivity and the ability to work synergistically with other drugs. Accordingly, there has recently been a renewed interest in natural product-derived antivirals in the wake of the COVID-19 pandemic. This review provides a summary of recent research into coronavirus entry inhibitors, with a focus on natural compounds derived from plants, honey, and marine sponges.

Inactivated Recombinant Rabies Virus Displaying the Nipah Virus Envelope Glycoproteins Induces Systemic Immune Responses in Mice

Nipah virus (NiV) causes severe, lethal encephalitis in humans and pigs. However, there is no licensed vaccine available to prevent NiV infection. In this study, we used the reverse genetic system based on the attenuated rabies virus strain SRV9 to construct two recombinant viruses, rSRV9-NiV-F and rSRV9-NiV-G, which displayed the NiV envelope glycoproteins F and G, respectively. Following three immunizations in BALB/c mice, the inactivated rSRV9-NiV-F and rSRV9-NiV-G alone or in combination, mixed with the adjuvants ISA 201 VG and poly (I:C), were able to induce the antigen-specific cellular and Th1-biased humoral immune responses. The specific antibodies against rSRV9-NiV-F and rSRV9-NiV-G had reactivity with two constructed bacterial-like particles displaying the F and G antigens of NiV. These data demonstrate that rSRV9-NiV-F or rSRV9-NiV-G has the potential to be developed into a promising vaccine candidate against NiV infection.

Oral Immunization with rVSV Bivalent Vaccine Elicits Protective Immune Responses, Including ADCC, against Both SARS-CoV-2 and Influenza A Viruses

COVID-19 and influenza both cause enormous disease burdens, and vaccines are the primary measures for their control. Since these viral diseases are transmitted through the mucosal surface of the respiratory tract, developing an effective and convenient mucosal vaccine should be a high priority. We previously reported a recombinant vesicular stomatitis virus (rVSV)-based bivalent vaccine (v-EM2/SPΔC1Delta) that protects animals from both SARS-CoV-2 and influenza viruses via intramuscular and intranasal immunization. Here, we further investigated the immune response induced by oral immunization with this vaccine and its protective efficacy in mice. The results demonstrated that the oral delivery, like the intranasal route, elicited strong and protective systemic immune responses against SARS-CoV-2 and influenza A virus. This included high levels of neutralizing antibodies (NAbs) against SARS-CoV-2, as well as strong anti-SARS-CoV-2 spike protein (SP) antibody-dependent cellular cytotoxicity (ADCC) and anti-influenza M2 ADCC responses in mice sera. Furthermore, it provided efficient protection against challenge with influenza H1N1 virus in a mouse model, with a 100% survival rate and a significantly low lung viral load of influenza virus. All these findings provide substantial evidence for the effectiveness of oral immunization with the rVSV bivalent vaccine.

A Pseudovirus-Based Entry Assay to Evaluate Neutralizing Activity against Respiratory Syncytial Virus

Respiratory syncytial virus (RSV) infection can cause life-threatening pneumonia and bronchiolitis, posing a significant threat to human health worldwide, especially to children and the elderly. Currently, there is no specific treatment for RSV infection. The most effective measures for preventing RSV infection are vaccines and prophylactic medications. However, not all population groups are eligible for the approved vaccines or antibody-based preventive medications. Therefore, there is an urgent need to develop novel vaccines and prophylactic drugs available for people of all ages. High-throughput assays that evaluate the efficacy of viral entry inhibitors or vaccine-induced neutralizing antibodies in blocking RSV entry are crucial for evaluating vaccine and prophylactic drug candidates. We developed an efficient entry assay using a lentiviral pseudovirus carrying the fusion (F) protein of type A or B RSV. In addition, the essential parameters were systematically optimized, including the number of transfected plasmids, storage conditions of the pseudovirus, cell types, cell numbers, virus inoculum, and time point of detection. Furthermore, the convalescent sera exhibited comparable inhibitory activity in this assay as in the authentic RSV virus neutralization assay. We established a robust pseudovirus-based entry assay for RSV, which holds excellent promise for studying entry mechanisms, evaluating viral entry inhibitors, and assessing vaccine-elicited neutralizing antibodies against RSV.

Polyfunctional antibodies: a path towards precision vaccines for vulnerable populations

Vaccine efficacy determined within the controlled environment of a clinical trial is usually substantially greater than real-world vaccine effectiveness. Typically, this results from reduced protection of immunologically vulnerable populations, such as children, elderly individuals and people with chronic comorbidities. Consequently, these high-risk groups are frequently recommended tailored immunisation schedules to boost responses. In addition, diverse groups of healthy adults may also be variably protected by the same vaccine regimen. Current population-based vaccination strategies that consider basic clinical parameters offer a glimpse into what may be achievable if more nuanced aspects of the immune response are considered in vaccine design. To date, vaccine development has been largely empirical. However, next-generation approaches require more rational strategies. We foresee a generation of precision vaccines that consider the mechanistic basis of vaccine response variations associated with both immunogenetic and baseline health differences. Recent efforts have highlighted the importance of balanced and diverse extra-neutralising antibody functions for vaccine-induced protection. However, in immunologically vulnerable populations, significant modulation of polyfunctional antibody responses that mediate both neutralisation and effector functions has been observed. Here, we review the current understanding of key genetic and inflammatory modulators of antibody polyfunctionality that affect vaccination outcomes and consider how this knowledge may be harnessed to tailor vaccine design for improved public health.

Development of a reporter gene assay for antibody dependent cellular cytotoxicity activity determination of anti-rabies virus glycoprotein antibodies

Rabies is a viral disease that is nearly 100% fatal once clinical signs and symptoms develop. Post-exposure prophylaxis can efficiently prevent rabies, and antibody (Ab) induction by vaccination or passive immunization of human rabies immunoglobulin (HRIG) or monoclonal antibodies (mAbs) play an integral role in prevention against rabies. In addition to their capacity to neutralize viruses, antibodies exert their antiviral effects by antibody-dependent cellular cytotoxicity (ADCC), which plays an important role in antiviral immunity and clearance of viral infections. For antibodies against rabies virus (RABV), evaluation of ADCC activity was neglected. Here, we developed a robust cell-based reporter gene assay (RGA) for the determination of the ADCC activity of anti-RABV antibodies using CVS-N2c-293 cells, which stably express the glycoprotein (G) of RABV strain CVS-N2c as target cells, and Jurkat cells, which stably express FcγRⅢa and nuclear factor of activated T cells (NFAT) reporter gene as effector cells (Jurkat/NFAT-luc/FcγRⅢa cells). The experimental parameters were carefully optimized, and the established ADCC assay was systematically validated according to the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH) Q2 guideline. We also evaluated the ADCC activity of anti-RABV antibodies, including mAbs, HRIG, and vaccine induced antisera, and found that all test antibodies exhibited ADCC activity with varied strengths. The established RGA provides a novel method for evaluating the ADCC of anti-RABV antibodies.

Pseudotyped Viruses for Marburgvirus and Ebolavirus

Marburg virus (MARV) and Ebola virus (EBOV) of the Filoviridae family are the most lethal viruses in terms of mortality rate. However, the development of antiviral treatment is hampered by the requirement for biosafety level-4 (BSL-4) containment. The establishment of BSL-2 pseudotyped viruses can provide important tools for the study of filoviruses. This chapter summarizes general information on the filoviruses and then focuses on the construction of replication-deficient pseudotyped MARV and EBOV (e.g., lentivirus system and vesicular stomatitis virus system). It also details the potential applications of the pseudotyped viruses, including neutralization antibody detection, the study of infection mechanisms, the evaluation of antibody-dependent enhancement, virus entry inhibitor screening, and glycoprotein mutation analysis.

Assays Based on Pseudotyped Viruses

Pseudotyped viruses are more and more widely used in virus research and the evaluation of antiviral products because of their high safety, simple operation, high accessibility, ease in achieving standardization, and high throughput. The development of measures based on pseudotyped virus is closely related to the characteristics of viruses, and it is also necessary to follow the principles of assay development. Only in the process of method development, where the key parameters that affect the results are systematically optimized and the preliminary established method is fully validated, can the accuracy, reliability, and repeatability of the test results be ensured. Only the method established on this basis can be transferred to different laboratories and make the results of different laboratories comparable. This paper summarizes the specific aspects and general principles in the development of assays based on pseudotyped virus, which is of reference value for the development of similar methods.

Application of Pseudotyped Viruses

Highly pathogenic emerging and reemerging viruses have serious public health and socioeconomic implications. Although conventional live virus research methods can more reliably investigate disease pathogenicity and evaluate antiviral products, they usually depend on high-level biosafety laboratories and skilled researchers; these requirements hinder in vitro assessments of efficacy, as well as efforts to test vaccines and antibody drugs. In contrast, pseudotyped viruses (i.e., single-round infectious viruses that mimic the membrane structures of various live viruses) are widely used in studies of highly pathogenic viruses because they can be handled in biosafety level 2 facilities. This chapter provides a concise overview of various aspects of pseudotyped virus technologies, including (1) exploration of the mechanisms of viral infection; (2) evaluation of the efficacies of vaccines and monoclonal antibodies based on pseudovirion-based neutralization assay; (3) assessment of antiviral agents (i.e., antibody-based drugs and inhibitors); (4) establishment of animal models of pseudotyped virus infection in vivo; (5) investigation of the evolution, infectivity, and antigenicity of viral variants and viral glycosylation; and (6) prediction of antibody-dependent cell-mediated cytotoxic activity.

Pseudotyped Viruses

Pseudotyped viruses have been constructed for many viruses. They can mimic the authentic virus and have many advantages compared to authentic viruses. Thus, they have been widely used as a surrogate of authentic virus for viral function analysis, detection of neutralizing antibodies, screening viral entry inhibitors, and others. This chapter reviewed the progress in the field of pseudotyped viruses in general, including the definition and the advantages of pseudotyped viruses, their potential usage, different strategies or vectors used for the construction of pseudotyped viruses, and factors that affect the construction of pseudotyped viruses.

The efficiency of convalescent plasma in COVID-19 patients: A systematic review and meta-analysis of randomized controlled clinical trials

The objective of this study was to assess whether convalescent plasma therapy could offer survival advantages for patients with novel coronavirus disease 2019 (COVID-19). An electronic search of Pubmed, Web of Science, Embase, Cochrane library and MedRxiv was performed from January 1st, 2020 to April 1st, 2022. We included studies containing patients with COVID-19 and treated with CCP. Data were independently extracted by two reviewers and synthesized with a random-effect analysis model. The primary outcome was 28-d mortality. Secondary outcomes included length of hospital stay, ventilation-free days, 14-d mortality, improvements of symptoms, progression of diseases and requirements of mechanical ventilation. Safety outcomes included the incidence of all adverse events (AEs) and serious adverse events (SAEs). The Cochrane risk-of-bias assessment tool 2.0 was used to assess the potential risk of bias in eligible studies. The heterogeneity of results was assessed by I^2 test and Q statistic test. The possibility of publication bias was assessed by conducting Begg and Egger test. GRADE (Grading of Recommendations Assessment, Development and Evaluation) method were used for quality of evidence. This study had been registered on PROSPERO, CRD42021273608. 32 RCTs comprising 21478 patients with Covid-19 were included. Compared to the control group, COVID-19 patients receiving CCP were not associated with significantly reduced 28-d mortality (CCP 20.0% vs control 20.8%; risk ratio 0.94; 95% CI 0.87-1.02; p = 0.16; I² = 8%). For all secondary outcomes, there were no significant differences between CCP group and control group. The incidence of AEs (26.9% vs 19.4%,; risk ratio 1.14; 95% CI 0.99-01.31; p = 0.06; I² = 38%) and SAEs (16.3% vs 13.5%; risk ratio 1.03; 95% CI 0.87-1.20; p = 0.76; I² = 42%) tended to be higher in the CCP group compared to the control group, while the differences did not reach statistical significance. In all, CCP therapy was not related to significantly improved 28-d mortality or symptoms recovery, and should not be viewed as a routine treatment for COVID-19 patients.

Trial registration number

CRD42021273608. Registration on February 28, 2022.

Systematic review registration

https://www.crd.york.ac.uk/prospero/, Identifier CRD42022313265.

Role of Fc Core Fucosylation in the Effector Function of IgG1 Antibodies

The presence of fucose on IgG1 Asn-297 N-linked glycan is the modification of the human IgG1 Fc structure with the most significant impact on FcɣRIII affinity. It also significantly enhances the efficacy of antibody dependent cellular cytotoxicity (ADCC) by natural killer (NK) cells in vitro, induced by IgG1 therapeutic monoclonal antibodies (mAbs). The effect of afucosylation on ADCC or antibody dependent phagocytosis (ADCP) mediated by macrophages or polymorphonuclear neutrophils (PMN) is less clear. Evidence for enhanced efficacy of afucosylated therapeutic mAbs in vivo has also been reported. This has led to the development of several therapeutic antibodies with low Fc core fucose to treat cancer and inflammatory diseases, seven of which have already been approved for clinical use. More recently, the regulation of IgG Fc core fucosylation has been shown to take place naturally during the B-cell immune response: A decrease in α-1,6 fucose has been observed in polyclonal, antigen-specific IgG1 antibodies which are generated during alloimmunization of pregnant women by fetal erythrocyte or platelet antigens and following infection by some enveloped viruses and parasites. Low IgG1 Fc core fucose on antigen-specific polyclonal IgG1 has been linked to disease severity in several cases, such as SARS-CoV 2 and Dengue virus infection and during alloimmunization, highlighting the in vivo significance of this phenomenon. This review aims to summarize the current knowledge about human IgG1 Fc core fucosylation and its regulation and function in vivo, in the context of both therapeutic antibodies and the natural immune response. The parallels in these two areas are informative about the mechanisms and in vivo effects of Fc core fucosylation, and may allow to further exploit the desired properties of this modification in different clinical contexts.

TIM-1 Augments Cellular Entry of Ebola Virus Species and Mutants, Which Is Blocked by Recombinant TIM-1 Protein

Ebola virus, a member of the Filoviridae family, utilizes the attachment factors on host cells to support its entry and cause severe tissue damage. TIM-1 has been identified as a predominant attachment factor via interaction with phosphatidylserine (PS) localized on the viral envelope and glycoprotein (GP). In this study, we give the first demonstration that TIM-1 enhances the cellular entry of three species of Ebola virus, as well as those harboring GP mutations (A82V, T544I, and A82V T544I). Furthermore, two TIM-1 variants (i.e., TIM-1-359aa and TIM-1-364aa) had comparable effects on promoting Zaire Ebola virus (EBOV) attachment, internalization, and infection. Importantly, recombinant TIM-1 ectodomain (ECD) protein could decrease the infectivity of Ebola virus and display synergistic inhibitory effects with ADI-15946, a monoclonal antibody with broad neutralizing activity to Ebola virus. Of note, EBOV strains harboring GP mutations (K510E and D552N), which were refractory to antibody treatment, were still sensitive to TIM-1 protein-mediated impairment of infectivity, indicating that TIM-1 protein may represent an alternative therapeutic regimen when antibody evasion occurs. IMPORTANCE The viral genome has acquired numerous mutations with the potential to increase transmission during the 2013-to-2016 outbreak of Ebola virus. EBOV strains harboring GP mutations (A82V, T544I, and A82V T544I), which have been identified to increase viral infectivity in humans, have attracted our attention. Herein, we give the first report that polymorphic TIM-1 enhances the infectivity of three species of Ebola virus, as well as those harboring GP mutations (A82V, T544I, and A82V T544I). We show that recombinant TIM-1 ECD protein could decrease the infectivity of Ebola virus with or without a point mutation and displays synergistic inhibitory effects with ADI-15946. Furthermore, TIM-1 protein potently blocked cell entry of antibody-evading Ebola virus species. These findings highlight the role of TIM-1 in Ebola virus infection and indicate that TIM-1 protein represents a potential therapeutic avenue for Ebola virus and its mutated species.

NK Cell Subset Redistribution and Antibody Dependent Activation after Ebola Vaccination in Africans

Natural killer cells play an important role in the control of viral infections both by regulating acquired immune responses and as potent innate or antibody-mediated cytotoxic effector cells. NK cells have been implicated in control of Ebola virus infections and our previous studies in European trial participants have demonstrated durable activation, proliferation and antibody-dependent NK cell activation after heterologous two-dose Ebola vaccination with adenovirus type 26.ZEBOV followed by modified vaccinia Ankara-BN-Filo. Regional variation in immunity and environmental exposure to pathogens, in particular human cytomegalovirus, have profound impacts on NK cell functional capacity. We therefore assessed the NK cell phenotype and function in African trial participants with universal exposure to HCMV. We demonstrate a significant redistribution of NK cell subsets after vaccine dose two, involving the enrichment of less differentiated CD56^dimCD57⁻ and CD56^dimFcεR1γ⁺ (canonical) cells and the increased proliferation of these subsets. Sera taken after vaccine dose two support robust antibody-dependent NK cell activation in a standard NK cell readout; these responses correlate strongly with the concentration of anti-Ebola glycoprotein specific antibodies. These sera also promote comparable IFN-γ production in autologous NK cells taken at baseline and post-vaccine dose two. However, degranulation responses of post-vaccination NK cells were reduced compared to baseline NK cells and these effects could not be directly attributed to alterations in NK cell phenotype after vaccination. These studies demonstrate consistent changes in NK cell phenotypic composition and robust antibody-dependent NK cell function and reveal novel characteristics of these responses after heterologous two dose Ebola vaccination in African individuals.

Complement-Mediated Neutralisation Identified in Ebola Virus Disease Survivor Plasma: Implications for Protection and Pathogenesis

The 2013-2016 Ebola virus (EBOV) epidemic in West Africa was unprecedented in case numbers and fatalities, and sporadic outbreaks continue to arise. Antibodies to the EBOV glycoprotein (GP) are strongly associated with survival and their use in immunotherapy is often initially based on their performance in neutralisation assays. Other immune effector functions also contribute to EBOV protection but are more complex to measure. Their interactions with the complement system in particular are comparatively under-researched and commonly excluded from cellular immunoassays. Using EBOV convalescent plasma samples from the 2013-2016 epidemic, we investigated antibody and complement-mediated neutralisation and how these interactions can influence immunity in response to EBOV-GP and its secreted form (EBOV-sGP). We defined two cohorts: one with low-neutralising titres in relation to EBOV-GP IgG titres (LN cohort) and the other with a direct linear relationship between neutralisation and EBOV-GP IgG titres (N cohort). Using flow cytometry antibody-dependent complement deposition (ADCD) assays, we found that the LN cohort was equally efficient at mediating ADCD in response to the EBOV-GP but was significantly lower in response to the EBOV-sGP, compared to the N cohort. Using wild-type EBOV neutralisation assays with a cohort of the LN plasma, we observed a significant increase in neutralisation associated with the addition of pooled human plasma as a source of complement. Flow cytometry ADCD was also applied using the GP of the highly virulent Sudan virus (SUDV) of the Sudan ebolavirus species. There are no licensed vaccines or therapeutics against SUDV and it overlaps in endemicity with EBOV. We found that the LN plasma was significantly less efficient at cross-reacting and mediating ADCD. Overall, we found a differential response in ADCD between LN and N plasma in response to various Ebolavirus glycoproteins, and that these interactions could significantly improve EBOV neutralisation for selected LN plasma samples. Preservation of the complement system in immunoassays could augment our understanding of neutralisation and thus protection against infection.

Application of pseudovirus system in the development of vaccine, antiviral-drugs, and neutralizing antibodies

Pseudoviruses are viral particles coated with a heterologous envelope protein, which mediates the entry of pseudoviruses as efficiently as that of the live viruses possessing high pathogenicity and infectivity. Due to the deletion of the envelope protein gene and the absence of pathogenic genes, pseudoviruses have no autonomous replication ability and can infect host cells for only a single cycle. In addition, pseudoviruses have the desired characteristics of high safety, strong operability, and can be easily used to perform rapid throughput detection. Therefore, pseudoviruses are widely employed in the mechanistic investigation of viral infection, the screening and evaluation of monoclonal antibodies and antiviral drugs, and the detection of neutralizing antibody titers in serum after vaccination. In this review, we will discuss the construction of pseudoviruses based on different packaging systems, their current applications especially in the research of SARS-CoV-2, limitations, and further directions.

FcγR Genetic Variation and HIV-1 Vaccine Efficacy: Context And Considerations

Receptors for the crystallisable fragment (Fc) of immunoglobulin (Ig) G, Fcγ receptors (FcγRs), link the humoral and cellular arms of the immune response, providing a diverse armamentarium of antimicrobial effector functions. Findings from HIV-1 vaccine efficacy trials highlight the need for further study of Fc-FcR interactions in understanding what may constitute vaccine-induced protective immunity. These include host genetic correlates identified within the low affinity Fcγ-receptor locus in three HIV-1 efficacy trials – VAX004, RV144, and HVTN 505. This perspective summarizes our present knowledge of FcγR genetics in the context of findings from HIV-1 efficacy trials, and draws on genetic variation described in other contexts, such as mother-to-child HIV-1 transmission and HIV-1 disease progression, to explore the potential contribution of FcγR variability in modulating different HIV-1 vaccine efficacy outcomes. Appreciating the complexity and the importance of the collective contribution of variation within the FCGR gene locus is important for understanding the role of FcγRs in protection against HIV-1 acquisition.

Discovery and evolution of 12N-substituted aloperine derivatives as anti-SARS-CoV-2 agents through targeting late entry stage

So far, there is still no specific drug against COVID-19. Taking compound 1 with anti-EBOV activity as the lead, fifty-four 12N-substituted aloperine derivatives were synthesized and evaluated for the anti-SARS-CoV-2 activities using pseudotyped virus model. Among them, 8a exhibited the most potential effects against both pseudotyped and authentic SARS-CoV-2, as well as SARS-CoV and MERS-CoV, indicating a broad-spectrum anti-coronavirus profile. The mechanism study disclosed that 8a might block a late stage of viral entry, mainly via inhibiting host cathepsin B activity rather than directly targeting cathepsin B protein. Also, 8a could significantly reduce the release of multiple inflammatory cytokines in a time- and dose-dependent manner, such as IL-6, IL-1β, IL-8 and MCP-1, the major contributors to cytokine storm. Therefore, 8a is a promising agent with the advantages of broad-spectrum anti-coronavirus and anti-cytokine effects, thus worthy of further investigation.

Antibody-dependent cellular cytotoxicity response to SARS-CoV-2 in COVID-19 patients

Antibody-dependent cellular cytotoxicity (ADCC) responses to viral infection are a form of antibody regulated immune responses mediated through the Fc fragment. Whether severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) triggered ADCC responses contributes to COVID-19 disease development is currently not well understood. To understand the potential correlation between ADCC responses and COVID-19 disease development, we analyzed the ADCC activity and neutralizing antibody response in 255 individuals ranging from asymptomatic to fatal infections over 1 year post disease. ADCC was elicited by 10 days post-infection, peaked by 11-20 days, and remained detectable until 400 days post-infection. In general, patients with severe disease had higher ADCC activities. Notably, patients who had severe disease and recovered had higher ADCC activities than patients who had severe disease and deceased. Importantly, ADCC activities were mediated by a diversity of epitopes in SARS-COV-2-infected mice and induced to comparable levels against SARS-CoV-2 variants of concern (VOCs) (B.1.1.7, B.1.351, and P.1) as that against the D614G mutant in human patients and vaccinated mice. Our study indicates anti-SARS-CoV-2 ADCC as a major trait of COVID-19 patients with various conditions, which can be applied to estimate the extra-neutralization level against COVID-19, especially lethal COVID-19.

Review: Insights on Current FDA-Approved Monoclonal Antibodies Against Ebola Virus Infection

The unprecedented 2013-2016 West Africa Ebola outbreak accelerated several medical countermeasures (MCMs) against Ebola virus disease (EVD). Several investigational products (IPs) were used throughout the outbreak but were not conclusive for efficacy results. Only the Randomized Controlled Trial (RCT) on ZMapp was promising but inconclusive. More recently, during the second-largest Ebola outbreak in North Kivu and Ituri provinces, Democratic Republic of the Congo (DRC), four IPs, including one small molecule (Remdesivir), two monoclonal antibody (mAb) cocktails (ZMapp and REGN-EB3) and a single mAb (mAb114), were evaluated in an RCT, the Pamoja Tulinde Maisha (PALM) study. Two products (REGN-EB3 and mAb114) demonstrated efficacy as compared to the control arm, ZMapp. There were remarkably few side effects recorded in the trial. The FDA approved both medications in this scientifically sound study, marking a watershed moment in the field of EVD therapy. These products can be produced relatively inexpensively and can be stockpiled. The administration of mAbs in EVD patients appears to be safe and effective, while several critical knowledge gaps remain; the impact of early administration of Ebola-specific mAbs on developing a robust immune response for future Ebola virus exposure is unknown. The viral mutation escape, leading to resistance, presents a potential limitation for single mAb therapy; further improvements need to be explored. Understanding the contribution of Fc-mediated antibody functions such as antibody-dependent cellular cytotoxicity (ADCC) of those approved mAbs is still critical. The potential merit of combination therapy and post-exposure prophylaxis (PEP) need to be demonstrated. Furthermore, the PALM trial has accounted for 30% of mortality despite the administration of specific treatments. The putative role of EBOV soluble Glycoprotein (sGP) as a decoy to the immune system, the virus persistence, and relapses might be investigated for treatment failure. The development of pan-filovirus or pan-species mAbs remains essential for protection. The interaction between FDA-approved mAbs and vaccines remains unclear and needs to be investigated. In this review, we summarize the efficacy and safety results of the PALM study and review current research questions for the further development of mAbs in pre-exposure or emergency post-exposure use.

SARS-CoV-2 Spike Pseudoviruses: A Useful Tool to Study Virus Entry and Address Emerging Neutralization Escape Phenotypes

SARS-CoV-2 genetic variants are emerging around the globe. Unfortunately, several SARS-CoV-2 variants, especially variants of concern (VOCs), are less susceptible to neutralization by the convalescent and post-vaccination sera, raising concerns of increased disease transmissibility and severity. Recent data suggests that SARS-CoV-2 neutralizing antibody levels are a reliable correlate of vaccine-mediated protection. However, currently used BSL3-based virus micro-neutralization (MN) assays are more laborious, time-consuming, and expensive, underscoring the need for BSL2-based, cost-effective neutralization assays against SARS-CoV-2 variants. In light of this unmet need, we have developed a BSL-2 pseudovirus-based neutralization assay (PBNA) in cells expressing the human angiotensin-converting enzyme-2 (hACE2) receptor for SARS-CoV-2. The assay is reproducible (R2 = 0.96), demonstrates a good dynamic range and high sensitivity. Our data suggest that the biological Anti-SARS-CoV-2 research reagents such as NIBSC 20/130 show lower neutralization against B.1.351 SA (South Africa) and B.1.1.7 UK (United Kingdom) VOC, whereas a commercially available monoclonal antibody MM43 retains activity against both these variants. SARS-CoV-2 spike PBNAs for VOCs would be useful tools to measure the neutralization ability of candidate vaccines in both preclinical models and clinical trials and would further help develop effective prophylactic countermeasures against emerging neutralization escape phenotypes.

Efficacy of convalescent plasma for treatment of COVID-19 in Uganda

RATIONALE

Convalescent plasma (CCP) has been studied as a potential therapy for COVID-19, but data on its efficacy in Africa are limited.

OBJECTIVE

In this trial we set out to determine the efficacy of CCP for treatment of COVID-19 in Uganda.

MEASUREMENTS

Patients with a positive SARS-CoV-2 reverse transcriptase (RT)-PCR test irrespective of disease severity were hospitalised and randomised to receive either COVID-19 CCP plus standard of care (SOC) or SOC alone. The primary outcome was time to viral clearance, defined as having two consecutive RT-PCR-negative tests by day 28. Secondary outcomes included time to symptom resolution, clinical status on the modified WHO Ordinal Clinical Scale (≥1-point increase), progression to severe/critical condition (defined as oxygen saturation <93% or needing oxygen), mortality and safety.

MAIN RESULTS

A total of 136 patients were randomised, 69 to CCP+SOC and 67 to SOC only. The median age was 50 years (IQR: 38.5-62.0), 71.3% were male and the median duration of symptom was 7 days (IQR=4-8). Time to viral clearance was not different between the CCP+SOC and SOC arms (median of 6 days (IQR=4-11) vs 4 (IQR=4-6), p=0.196). There were no statistically significant differences in secondary outcomes in CCP+SOC versus SOC: time to symptom resolution (median=7 (IQR=5-7) vs 7 (IQR=5-10) days, p=0.450), disease progression (9 (22.0%) vs 7 (24.0%) patients, p=0.830) and mortality (10 (14.5%) vs 8 (11.9%) deaths, p=0.476).

CONCLUSION

In this African trial, CCP therapy did not result in beneficial virological or clinical improvements. Further trials are needed to determine subgroups of patients who may benefit from CCP in Africa.Trial registration number NCT04542941.

Human Cathelicidin Inhibits SARS-CoV-2 Infection: Killing Two Birds with One Stone

SARS-CoV-2 infection begins with the association of its spike 1 (S1) protein with host angiotensin-converting enzyme-2 (ACE2). Targeting the interaction between S1 and ACE2 is a practical strategy against SARS-CoV-2 infection. Herein, we show encouraging results indicating that human cathelicidin LL37 can simultaneously block viral S1 and cloak ACE2. LL37 binds to the receptor-binding domain (RBD) of S1 with high affinity (11.2 nM) and decreases subsequent recruitment of ACE2. Owing to the RBD blockade, LL37 inhibits SARS-CoV-2 S pseudovirion infection, with a half-maximal inhibitory concentration of 4.74 μg/mL. Interestingly, LL37 also binds to ACE2 with an affinity of 25.5 nM and cloaks the ligand-binding domain (LBD), thereby decreasing S1 adherence and protecting cells against pseudovirion infection in vitro. Intranasal administration of LL37 to C57 mice infected with adenovirus expressing human ACE2 either before or after pseudovirion invasion decreased lung infection. The study identified a versatile antimicrobial peptide in humans as an inhibitor of SARS-CoV-2 attachment using dual mechanisms, thus providing a potential candidate for coronavirus disease 2019 (COVID-19) prevention and treatment.

Associations Between Antibody Fc-Mediated Effector Functions and Long-Term Sequelae in Ebola Virus Survivors

Antibodies that mediate non-neutralizing functions play an important role in the immune response to Ebola virus (EBOV) and are thought to impact disease outcome. EBOV has also been associated with long term sequelae in survivors, however, the extent to which antibodies that mediate non-neutralizing functions are associated with the development of these sequelae is unknown. Here, the presence of antibodies mediating different effector functions and how they relate to long-term sequelae two years after the 2007 Bundibugyo Ebola virus (BDBV) outbreak was investigated. The majority of survivors demonstrated robust antibody effector functional activity and demonstrated persistent polyfunctional antibody profiles to the EBOV glycoprotein (GP) two years after infection. These functions were strongly associated with the levels of GP-specific IgG1. The odds of developing hearing loss, one of the more common sequelae to BDBV was reduced when antibodies mediating antibody dependent cellular phagocytosis (ADCP), antibody dependent complement deposition (ADCD), or activating NK cells (ADNKA) were observed. In addition, hearing loss was associated with increased levels of several pro-inflammatory cytokines and levels of these pro-inflammatory cytokines were associated with lower ADCP. These results are indicating that a skewed antibody profile and persistent inflammation may contribute to long term outcome in survivors of BDBV infection.

On the road to ending the COVID-19 pandemic: Are we there yet?

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged into the human population in late 2019 and caused the global COVID-19 pandemic. SARS-CoV-2 has spread to more than 215 countries and infected many millions of people. Despite the introduction of numerous governmental and public health measures to control disease spread, infections continue at an unabated pace, suggesting that effective vaccines and antiviral drugs will be required to curtail disease, end the pandemic, and restore societal norms. Here, we review the current developments in antibody and vaccine countermeasures to limit or prevent disease.

Membrane Nanoparticles Derived from ACE2-Rich Cells Block SARS-CoV-2 Infection

The ongoing COVID-19 pandemic worldwide necessitates the development of therapeutics against SARS-CoV-2. ACE2 is the main receptor of SARS-CoV-2 S1 and mediates viral entry into host cells. Herein, membrane nanoparticles (NPs) prepared from ACE2-rich cells were discovered to have potent capacity to block SARS-CoV-2 infection. The membranes of human embryonic kidney-239T cells highly expressing ACE2 were applied to prepare NPs using an extrusion method. The nanomaterials, termed ACE2-NPs, contained 265.1 ng mg-1 ACE2 on the surface and acted as baits to trap S1 in a dose-dependent manner, resulting in reduced recruitment of the viral ligand to HK-2 human renal tubular epithelial cells. Aside from affecting receptor recongnition, S1 translocated to the cytoplasm and induced apoptosis by reducing optic atrophy 1 expression and increasing cytochrome c release, which was also inhibited by ACE2-NPs. Further investigations revealed that ACE2-NPs efficiently suppressed SARS-CoV-2 S pseudovirions entry into host cells and blocked viral infection in vitro and in vivo. This study characterizes easy-to-produce memrbane nanoantagonists of SARS-CoV-2 that enrich the existing antiviral arsenal and provide possibilities for COVID-19 treatment.

Membrane Nanoparticles Derived from ACE2-Rich Cells Block SARS-CoV-2 Infection

The ongoing COVID-19 pandemic worldwide necessitates the development of therapeutics against SARS-CoV-2. ACE2 is the main receptor of SARS-CoV-2 S1 and mediates viral entry into host cells. Herein, membrane nanoparticles (NPs) prepared from ACE2-rich cells were discovered to have potent capacity to block SARS-CoV-2 infection. The membranes of human embryonic kidney-239T cells highly expressing ACE2 were applied to prepare NPs using an extrusion method. The nanomaterials, termed ACE2-NPs, contained 265.1 ng mg^-1 ACE2 on the surface and acted as baits to trap S1 in a dose-dependent manner, resulting in reduced recruitment of the viral ligand to HK-2 human renal tubular epithelial cells. Aside from affecting receptor recongnition, S1 translocated to the cytoplasm and induced apoptosis by reducing optic atrophy 1 expression and increasing cytochrome c release, which was also inhibited by ACE2-NPs. Further investigations revealed that ACE2-NPs efficiently suppressed SARS-CoV-2 S pseudovirions entry into host cells and blocked viral infection in vitro and in vivo. This study characterizes easy-to-produce memrbane nanoantagonists of SARS-CoV-2 that enrich the existing antiviral arsenal and provide possibilities for COVID-19 treatment.

Antibody affinity as a driver of signal generation in a paper-based immunoassay for Ebola virus surveillance

During epidemics, such as the frequent and devastating Ebola virus outbreaks that have historically plagued regions of Africa, serological surveillance efforts are critical for viral containment and the development of effective antiviral therapeutics. Antibody serology can also be used retrospectively for population-level surveillance to provide a more complete estimate of total infections. Ebola surveillance efforts rely on enzyme-linked immunosorbent assays (ELISAs), which restrict testing to laboratories and are not adaptable for use in resource-limited settings. In this manuscript, we describe a paper-based immunoassay capable of detecting anti-Ebola IgG using Ebola virus envelope glycoprotein ectodomain (GP) as the affinity reagent. We evaluated seven monoclonal antibodies (mAbs) against GP—KZ52, 13C6, 4G7, 2G4, c6D8, 13F6, and 4F3—to elucidate the impact of binding affinity and binding epitope on assay performance and, ultimately, result interpretation. We used biolayer interferometry to characterize the binding of each antibody to GP before assessing their performance in our paper-based device. Binding affinity (K_D) and on rate (k_on) were major factors influencing the sensitivity of the paper-based immunoassay. mAbs with the best K_D (3–25 nM) exhibited the lowest limits of detection (ca. μg mL⁻¹), while mAbs with K_D > 25 nM were undetectable in our device. Additionally, and most surprisingly, we determined that observed signals in paper devices were directly proportional to k_on. These results highlight the importance of ensuring that the quality of recognition reagents is sufficient to support desired assay performance and suggest that the strength of an individual’s immune response can impact the interpretation of assay results.

Human neutralizing antibodies against SARS-CoV-2 require intact Fc effector functions for optimal therapeutic protection

SARS-CoV-2 has caused the global COVID-19 pandemic. Although passively delivered neutralizing antibodies against SARS-CoV-2 show promise in clinical trials, their mechanism of action in vivo is incompletely understood. Here, we define correlates of protection of neutralizing human monoclonal antibodies (mAbs) in SARS-CoV-2-infected animals. Whereas Fc effector functions are dispensable when representative neutralizing mAbs are administered as prophylaxis, they are required for optimal protection as therapy. When given after infection, intact mAbs reduce SARS-CoV-2 burden and lung disease in mice and hamsters better than loss-of-function Fc variant mAbs. Fc engagement of neutralizing antibodies mitigates inflammation and improves respiratory mechanics, and transcriptional profiling suggests these phenotypes are associated with diminished innate immune signaling and preserved tissue repair. Immune cell depletions establish that neutralizing mAbs require monocytes and CD8+ T cells for optimal clinical and virological benefit. Thus, potently neutralizing mAbs utilize Fc effector functions during therapy to mitigate lung infection and disease.

Immunotherapeutics for Ebola Virus Disease: Hope on the Horizon

Ebola virus disease (EVD) remains among the biggest public health threats in Africa, even though recently a vaccine was approved for human use. However, in outbreak situations treatment strategies are needed in combination with vaccination campaigns to impact and stop the spread of the disease. Here, we discuss the development of the immunotherapeutics against EDV both targeting the virus itself and bolstering the immunological environment of the host at both the pre-clinical and clinical level. The early development of antibody therapy in preclinical settings and the early pitfalls in the implementation of this therapeutic strategy are discussed. We also consider the advancement of the production, modulation, and specificity of the antibody treatment that garnered increased success in preclinical studies to the point that it was warranted to test them in a clinical setting. Initial clinical trials in an outbreak scenario proved difficult to definitively confirm the efficacy of the implemented treatment. Upon further modification and with the experiences from the challenging outbreak conditions in mind, the PALM clinical trial demonstrated efficacy of an antibody cocktail which recently received approval for human use.

Ebola virus glycoprotein stimulates IL-18-dependent natural killer cell responses

BACKGROUND

NK cells are activated by innate cytokines and viral ligands to kill virus-infected cells. These functions are enhanced during secondary immune responses and after vaccination by synergy with effector T cells and virus-specific antibodies. In human Ebola virus infection, clinical outcome is strongly associated with the initial innate cytokine response, but the role of NK cells has not been thoroughly examined.

METHODS

The novel 2-dose heterologous Adenovirus type 26.ZEBOV (Ad26.ZEBOV) and modified vaccinia Ankara-BN-Filo (MVA-BN-Filo) vaccine regimen is safe and provides specific immunity against Ebola glycoprotein, and is currently in phase 2 and 3 studies. Here, we analyzed NK cell phenotype and function in response to Ad26.ZEBOV, MVA-BN-Filo vaccination regimen and in response to in vitro Ebola glycoprotein stimulation of PBMCs isolated before and after vaccination.

RESULTS

We show enhanced NK cell proliferation and activation after vaccination compared with baseline. Ebola glycoprotein–induced activation of NK cells was dependent on accessory cells and TLR-4–dependent innate cytokine secretion (predominantly from CD14⁺ monocytes) and enriched within less differentiated NK cell subsets. Optimal NK cell responses were dependent on IL-18 and IL-12, whereas IFN-γ secretion was restricted by high concentrations of IL-10.

CONCLUSION

This study demonstrates the induction of NK cell effector functions early after Ad26.ZEBOV, MVA-BN-Filo vaccination and provides a mechanism for the activation and regulation of NK cells by Ebola glycoprotein.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02313077.

FUNDING

United Kingdom Medical Research Council Studentship in Vaccine Research, Innovative Medicines Initiative 2 Joint Undertaking, EBOVAC (grant 115861) and Crucell Holland (now Janssen Vaccines and Prevention B.V.), European Union’s Horizon 2020 research and innovation programme and European Federation of Pharmaceutical Industries and Associations (EFPIA).

Durable natural killer cell responses after heterologous two-dose Ebola vaccination

Natural killer (NK) cells are implicated among immune effectors after vaccination against viral pathogens, including Ebola virus. The two-dose heterologous Ebola virus vaccine regimen, adenovirus type 26.ZEBOV followed by modified vaccinia Ankara-BN-Filo (EBOVAC2 consortium, EU Innovative Medicines Initiative), induces NK cell activation and anti-Ebola glycoprotein (GP) antibody-dependent NK cell activation post-dose 1, which is further elevated post-dose 2. Here, in a multicentre, phase 2 clinical trial (EBL2001), we demonstrate durable ex vivo NK cell activation 180 days after dose 2, with responses enriched in CD56^bright NK cells. In vitro antibody-dependent responses to immobilised Ebola GP increased after dose 1, and remained elevated compared to pre-vaccination levels in serum collected 180 days later. Peak NK cell responses were observed post-dose 2 and NK cell IFN-γ responses remained significantly elevated at 180 days post-dose 2. Individual variation in NK cell responses were influenced by both anti-Ebola GP antibody concentrations and intrinsic interindividual differences in NK cell functional capacity. In summary, this study demonstrates durable NK cell responses after Ad26.ZEBOV, MVA-BN-Filo Ebola virus vaccination and could inform the immunological evaluation of future iterations of the vaccine regimen and vaccination schedules.

Recent advances in immunotherapies against infectious diseases

Immunotherapies are disease management strategies that target or manipulate components of the immune system. Infectious diseases pose a significant threat to human health as evidenced by countries continuing to grapple with several emerging and re-emerging diseases, the most recent global health threat being the SARS-CoV2 pandemic. As such, various immunotherapeutic approaches are increasingly being investigated as alternative therapies for infectious diseases, resulting in significant advances towards the uncovering of pathogen-host immunity interactions. Novel and innovative therapeutic strategies are necessary to overcome the challenges typically faced by existing infectious disease prevention and control methods such as lack of adequate efficacy, drug toxicity, and the emergence of drug resistance. As evidenced by recent developments and success of pharmaceuticals such as monoclonal antibodies (mAbs), immunotherapies already show abundant promise to overcome such limitations while also advancing the frontiers of medicine. In this review, we summarize some of the most notable inroads made to combat infectious disease, over mainly the last 5 years, through the use of immunotherapies such as vaccines, mAb-based therapies, T-cell-based therapies, manipulation of cytokine levels, and checkpoint inhibition. While its most general applications are founded in cancer treatment, advances made towards the curative treatment of human immunodeficiency virus, tuberculosis, malaria, zika virus and, most recently COVID-19, reinforce the role of immunotherapeutic strategies in the broader field of disease control. Ultimately, the comprehensive specificity, safety, and cost of immunotherapeutics will impact its widespread implementation.

Human neutralizing antibodies against SARS-CoV-2 require intact Fc effector functions and monocytes for optimal therapeutic protection

SARS-CoV-2 has caused the global COVID-19 pandemic. Although passively delivered neutralizing antibodies against SARS-CoV-2 show promise in clinical trials, their mechanism of action in vivo is incompletely understood. Here, we define correlates of protection of neutralizing human monoclonal antibodies (mAbs) in SARS-CoV-2-infected animals. Whereas Fc effector functions are dispensable when representative neutralizing mAbs are administered as prophylaxis, they are required for optimal protection as therapy. When given after infection, intact mAbs reduce SARS-CoV-2 burden and lung disease in mice and hamsters better than loss-of-function Fc variant mAbs. Fc engagement of neutralizing antibodies mitigates inflammation and improves respiratory mechanics, and transcriptional profiling suggests these phenotypes are associated with diminished innate immune signaling and preserved tissue repair. Immune cell depletions establish that neutralizing mAbs require monocytes for therapeutic efficacy. Thus, potently neutralizing mAbs require Fc effector functions for maximal therapeutic benefit during therapy to modulate protective immune responses and mitigate lung disease.

Development of an antibody-dependent cellular cytotoxicity reporter assay for measuring anti-Middle East Respiratory Syndrome antibody bioactivity

Middle East Respiratory Syndrome coronavirus (MERS-CoV) is a highly virulent pathogen that causes Middle East Respiratory Syndrome (MERS). Anti-MERS-CoV antibodies play an integral role in the prevention and treatment against MERS-CoV infections. Bioactivity is a key quality attribute of therapeutic antibodies, and high accuracy and precision are required. The major methods for evaluating the antiviral effect of antiviral antibodies include neutralization assays using live viruses or pseudoviruses are highly variable. Recent studies have demonstrated that the antibody-dependent cellular cytotoxicity (ADCC) activity of antiviral antibodies is more consistent with the virus clearance effect in vivo than neutralization activity. However, no reports evaluating the ADCC activity of anti-MERS antibodies have been published to date. Here, we describe the development of a robust and reliable cell-based reporter gene assay for the determination of ADCC activity of anti-MERS antibodies using 293T/MERS cells stably expressing the spike protein of MERS-CoV (MERS-S) as target cells and the engineered Jurkat/NFAT-luc/FcγRIIIa stably expressing FcγRIIIA and NFAT reporter gene as effector cells. According to the ICH-Q2 analytical method guidelines, we carefully optimized the experimental conditions and assessed the performance of our assay. In addition, we found that the ADCC activity of afucosylated anti-MERS antibodies is higher than their fucosylated counterparts. The establishment of this ADCC determination system provides a novel method for evaluating the bioactivity of anti-MERS antibodies and improving ADCC activity through modification of N-glycosylation of the Fc segment.

Exploiting Pre-Existing CD4+ T Cell Help from Bacille Calmette-Guérin Vaccination to Improve Antiviral Antibody Responses

The continuing emergence of viral pathogens and their rapid spread into heavily populated areas around the world underscore the urgency for development of highly effective vaccines to generate protective antiviral Ab responses. Many established and newly emerging viral pathogens, including HIV and Ebola viruses, are most prevalent in regions of the world in which Mycobacterium tuberculosis infection remains endemic and vaccination at birth with M. bovis bacille Calmette-Guérin (BCG) is widely used. We have investigated the potential for using CD4⁺ T cells arising in response to BCG as a source of help for driving Ab responses against viral vaccines. To test this approach, we designed vaccines comprised of protein immunogens fused to an immunodominant CD4⁺ T cell epitope of the secreted Ag 85B protein of BCG. Proof-of-concept experiments showed that the presence of BCG-specific Th cells in previously BCG-vaccinated mice had a dose-sparing effect for subsequent vaccination with fusion proteins containing the Ag 85B epitope and consistently induced isotype switching to the IgG2c subclass. Studies using an Ebola virus glycoprotein fused to the Ag 85B epitope showed that prior BCG vaccination promoted high-affinity IgG1 responses that neutralized viral infection. The design of fusion protein vaccines with the ability to recruit BCG-specific CD4⁺ Th cells may be a useful and broadly applicable approach to generating improved vaccines against a range of established and newly emergent viral pathogens.

Challenges in Laboratory Diagnosis of the Novel Coronavirus SARS-CoV-2

The recent outbreak of the Coronavirus disease 2019 (COVID-19) has quickly spread worldwide since its discovery in Wuhan city, China in December 2019. A comprehensive strategy, including surveillance, diagnostics, research, clinical treatment, and development of vaccines, is urgently needed to win the battle against COVID-19. The past three unprecedented outbreaks of emerging human coronavirus infections at the beginning of the 21st century have highlighted the importance of readily available, accurate, and rapid diagnostic technologies to contain emerging and re-emerging pandemics. Real-time reverse transcriptase-polymerase chain reaction (rRT-PCR) based assays performed on respiratory specimens remain the gold standard for COVID-19 diagnostics. However, point-of-care technologies and serologic immunoassays are rapidly emerging with high sensitivity and specificity as well. Even though excellent techniques are available for the diagnosis of symptomatic patients with COVID-19 in well-equipped laboratories; critical gaps still remain in screening asymptomatic people who are in the incubation phase of the virus, as well as in the accurate determination of live viral shedding during convalescence to inform decisions for ending isolation. This review article aims to discuss the currently available laboratory methods and surveillance technologies available for the detection of COVID-19, their performance characteristics and highlight the gaps in current diagnostic capacity, and finally, propose potential solutions. We also summarize the specifications of the majority of the available commercial kits (PCR, EIA, and POC) for laboratory diagnosis of COVID-19.

B Cell Activation and Response Regulation During Viral Infections

Acute viral infections are characterized by rapid increases in viral load, leading to cellular damage and the resulting induction of complex innate and adaptive antiviral immune responses that cause local and systemic inflammation. Successful antiviral immunity requires the activation of many immune cells, including T cells, natural killer cells, and macrophages. B cells play a unique part through their production of antibodies that can both neutralize and clear viral particles before virus entry into a cell. Protective antibodies are produced even before the first exposure of a pathogen, through the regulated secretion of so-called natural antibodies that are generated even in the complete absence of prior microbial exposure. An early wave of rapidly secreted antibodies from extrafollicular (EF) responses draws on the preexisting naive or memory repertoire of B cells to induce a strong protective response that in kinetics tightly follows the clearance of acute infections, such as with influenza virus. Finally, the generation of germinal centers (GCs) provides long-term protection through production of long-lived plasma cells and memory B cells, which shape and broaden the B cell repertoire for more effective responses following repeat exposures. In this study, we review B cell responses to acute viral infections, primarily influenza virus, from the earliest nonspecific B-1 cell to early, antigen-specific EF responses and finally to GC responses. Throughout, we address known factors that lead to distinct B cell response outcomes and discuss how their functions effect viral clearance, highlighting the critical contributions of each response type to the induction of highly protective antiviral humoral immunity.

A Bivalent, Spherical Virus-Like Particle Vaccine Enhances Breadth of Immune Responses against Pathogenic Ebola Viruses in Rhesus Macaques

The 2013-2016 Ebola outbreak in West Africa led to accelerated efforts to develop vaccines against these highly virulent viruses. A live, recombinant vesicular stomatitis virus-based vaccine has been deployed in outbreak settings and appears highly effective. Vaccines based on replication-deficient adenovirus vectors either alone or in combination with a multivalent modified vaccinia Ankara (MVA) Ebola vaccine also appear promising and are progressing in clinical evaluation. However, the ability of current live vector-based approaches to protect against multiple pathogenic species of Ebola is not yet established, and eliciting durable responses may require additional booster vaccinations. Here, we report the development of a bivalent, spherical Ebola virus-like particle (VLP) vaccine that incorporates glycoproteins (GPs) from Zaire Ebola virus (EBOV) and Sudan Ebola virus (SUDV) and is designed to extend the breadth of immunity beyond EBOV. Immunization of rabbits with bivalent Ebola VLPs produced antibodies that neutralized all four pathogenic species of Ebola viruses and elicited antibody-dependent cell-mediated cytotoxicity (ADCC) responses against EBOV and SUDV. Vaccination of rhesus macaques with bivalent VLPs generated strong humoral immune responses, including high titers of binding, as well as neutralizing antibodies and ADCC responses. VLP vaccination led to a significant increase in the frequency of Ebola GP-specific CD4 and CD8 T cell responses. These results demonstrate that a novel bivalent Ebola VLP vaccine elicits strong humoral and cellular immune responses against pathogenic Ebola viruses and support further evaluation of this approach as a potential addition to Ebola vaccine development efforts.IMPORTANCE Ebola outbreaks result in significant morbidity and mortality in affected countries. Although several leading candidate Ebola vaccines have been developed and advanced in clinical testing, additional vaccine candidates may be needed to provide protection against different Ebola species and to extend the durability of protection. A novel approach demonstrated here is to express two genetically diverse glycoproteins on a spherical core, generating a vaccine that can broaden immune responses against known pathogenic Ebola viruses. This approach provides a new method to broaden and potentially extend protective immune responses against Ebola viruses.

Optimal therapeutic activity of monoclonal antibodies against chikungunya virus requires Fc-FcγR interaction on monocytes

Chikungunya virus (CHIKV) is an emerging mosquito-borne virus that has caused explosive outbreaks worldwide. Although neutralizing monoclonal antibodies (mAbs) against CHIKV inhibit infection in animals, the contribution of Fc effector functions to protection remains unknown. Here, we evaluated the activity of therapeutic mAbs that had or lacked the ability to engage complement and Fcγ receptors (FcγR). When administered as post-exposure therapy in mice, the Fc effector functions of mAbs promoted virus clearance from infected cells and reduced joint swelling-results that were corroborated in antibody-treated transgenic animals lacking activating FcγR. The control of CHIKV infection by antibody-FcγR engagement was associated with an accelerated influx of monocytes. A series of immune cell depletions revealed that therapeutic mAbs required monocytes for efficient clearance of CHIKV infection. Overall, our study suggests that in mice, FcγR expression on monocytes is required for optimal therapeutic activity of antibodies against CHIKV and likely other related viruses.

Establishment and validation of a pseudovirus neutralization assay for SARS-CoV-2

Pseudoviruses are useful virological tools because of their safety and versatility, especially for emerging and re-emerging viruses. Due to its high pathogenicity and infectivity and the lack of effective vaccines and therapeutics, live SARS-CoV-2 has to be handled under biosafety level 3 conditions, which has hindered the development of vaccines and therapeutics. Based on a VSV pseudovirus production system, a pseudovirus-based neutralization assay has been developed for evaluating neutralizing antibodies against SARS-CoV-2 in biosafety level 2 facilities. The key parameters for this assay were optimized, including cell types, cell numbers, virus inoculum. When tested against the SARS-CoV-2 pseudovirus, SARS-CoV-2 convalescent patient sera showed high neutralizing potency, which underscore its potential as therapeutics. The limit of detection for this assay was determined as 22.1 and 43.2 for human and mouse serum samples respectively using a panel of 120 negative samples. The cutoff values were set as 30 and 50 for human and mouse serum samples, respectively. This assay showed relatively low coefficient of variations with 15.9% and 16.2% for the intra- and inter-assay analyses respectively. Taken together, we established a robust pseudovirus-based neutralization assay for SARS-CoV-2 and are glad to share pseudoviruses and related protocols with the developers of vaccines or therapeutics to fight against this lethal virus.