Protective non-neutralizing SARS-CoV-2 monoclonal antibodies

CoronaVac-induced antibodies that facilitate Fc-mediated neutrophil phagocytosis track with COVID-19 disease resolution

Although severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants raise concerns about decreased vaccine efficacy, vaccines continue to confer robust protection in humans, implying that immunity beyond neutralization contributes to vaccine efficacy. In addition to neutralization, antibodies can mediate various Fc-dependent effector functions, including antibody-dependent cellular phagocytosis (ADCP), antibody-dependent neutrophil phagocytosis (ADNP) and antibody-dependent cellular cytotoxicity (ADCC). However, the specific role of each Fc-mediated effector function in contributing to COVID-19 disease attenuation in human remains unclear. To fully define the potential immune correlates of Fc-mediated effector functions, we comprehensively analysed the above Fc-mediated effector functions in two study cohorts. In the CoronaVac vaccinee cohort, individuals without breakthrough infection exhibited higher levels of ADCP and ADNP activities with a greater degree of cross-reactivity compared to those who had breakthrough infection. A predictive model was established incorporating ADNP activity and IgG titre, achieving an area under the curve (AUC) of 0.837. In the COVID-19 patient cohort, BA.5-specific ADCP and ADNP responses were significantly reduced in COVID-19 patients with fatal outcomes compared to milder outcomes. The prognostic model incorporating WT, BA.5, and XBB.1.5 spike-specific ADNP demonstrated effective predictive ability, achieving an AUC of 0.890. Meanwhile, transcriptomic analysis of peripheral blood mononuclear cells (PBMCs) from COVID-19 patients in the acute phases of infection highlighted remarkably upregulation of neutrophil activity and phagocytic function, further reinforcing the essential role of ADNP. Collectively, our findings underscored Fc-mediated effector activities, especially neutrophil phagocytosis, as significant antibody biomarkers for the risk of SARS-CoV-2 breakthrough infection and COVID-19 prognosis.

In vivo determination of protective antibody thresholds for SARS-CoV-2 variants using mouse models

Neutralizing antibody titres have been shown to correlate with immune protection against COVID-19 and can be used to estimate vaccine effectiveness. Numerous studies have explored the relationship between neutralizing antibodies and protection. However, there remains a lack of quantitative data directly assessing the minimum effective protective neutralizing antibody titre in in vivo. In this study, we utilized eight cohorts of participants with diverse immune backgrounds for evaluation of protective antibody response. To precisely assess the lower threshold of neutralizing antibody titres required for effective protection against SARS-CoV-2 infections, we employed plasma adoptive transfer from different cohorts into mice. This study demonstrated that neutralizing titres in the plasma of recipient mice correlated well with those in human donors, and a positive linear correlation was observed between the human and mouse recipients of transferred plasma neutralizing titre. A pseudotyped virus neutralizing titres greater than 7 was identified as the minimum threshold necessary to reduce viral titres in infected mice, establishing a crucial baseline for effective protection. Furthermore, despite the variability in immune backgrounds, these diverse cohorts' plasma exhibited a similar neutralizing antibody threshold necessary for protection. This finding has significant implications for vaccine design and the assessment of immune competence.

Severe Acute Respiratory Syndrome Coronavirus 2 Immunology and Coronavirus Disease 2019 Clinical Outcomes

The humoral and cellular immune response are the key players in preventing viral infection and limiting disease severity, particular in the context of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and coronavirus disease 2019. In this review, we discuss how immune responses generated by prior infection and vaccination influence the outcomes of SARS-CoV-2 infection. We aim to provide an overview of the role of humoral and cellular immunity, with a particular focus on CD8+ T cell responses, to delineate how different immune compartments contribute to the control of infection and modulation of disease outcomes.

SARS-CoV-2 virus lacking the envelope and membrane open-reading frames as a vaccine platform

To address the need for broadly protective SARS-CoV-2 vaccines, we developed an attenuated a SARS-CoV-2 vaccine virus that lacks the open reading frames of two viral structural proteins: the envelope (E) and membrane (M) proteins. This vaccine virus (ΔEM) replicates in a cell line stably expressing E and M but not in wild-type cells. Vaccination with ΔEM elicits a CD8 T-cell response against the viral spike and nucleocapsid proteins. Two vaccinations with ΔEM provide better protection of the lower respiratory tissues than a single dose against the Delta and Omicron XBB variants in hamsters. Moreover, ΔEM is effective as a booster in hamsters previously vaccinated with an mRNA-based vaccine, providing higher levels of protection in both respiratory tissues compared to the mRNA vaccine booster. Collectively, our data demonstrate the feasibility of a SARS-CoV-2 ΔEM vaccine candidate virus as a vaccine platform.

Identification of three novel B cell epitopes targeting the bovine viral diarrhea virus NS3 protein for use in diagnostics and vaccine development

Bovine viral diarrhea virus (BVDV) is a major pathogen in cattle herds, widely distributed across the globe and causing significant economic losses to the cattle industry. The nonstructural protein NS3 is highly conserved across BVDV subtypes. Identifying and screening epitopes on BVDV NS3 is crucial for developing sensitive, specific diagnostic tools. In this study, we obtained three monoclonal antibodies (mAbs) against the NS3 protein: 2F7, 3E8, and 4D6. Three novel linear B-cell epitope 100EYG102, 384FLDIA388, and 100EYGVK104 were identified through reactions of these mAbs with a series of continuous-truncated peptides and one of which a rare three-amino-acid B-cell epitope 100EYG102. Critical amino acid residues were further characterized through alanine (A)-scanning mutagenesis. Sequence alignment revealed that 100EYG102 and 100EYGVK104 were highly conserved allowing mAbs 2F7 and 4D6 to recognize all BVDV subtypes. In contrast, 384FLDIA388 was specifically conserved in BVDV-1 and BVDV-3 enabling 3E8 mAb to differential diagnosis BVDV-2 from other BVDV subtypes. Additionally, preliminary diagnostic assays for BVDV were established by western blotting and peptide-based blocking ELISA. Moreover, we observed that these mAbs could inhibit the replication of BVDV. These findings provide a theoretical foundation for developing of therapeutic strategies for nonstructural protein and accurate diagnostic procedures.

Immunogenic Properties of a Novel Hepatitis A Vaccine Candidate Based on a Fast-Growing Viral Strain

BACKGROUND/OBJECTIVES

Hepatitis A virus (HAV) yearly causes over 150 million new infections and around 40,000 deaths. Current vaccines are based on strains that grow poorly in cell culture, leading to high production costs and limited availability. This study aimed to compare the immunogenic properties of a novel HAV vaccine candidate based on the fast-growing HM175-HP strain with those of the parental slow-growing HM175-L0 strain, which derives from the cytopathic HM175 strain, like the prototype strain used in certain existing vaccines.

METHODS

The humoral and cellular immune response elicited by either HM175-HP or HM175-L0 vaccines was assessed in female BALB/c mice.

RESULTS

Both HM175-HP and HM175-L0 vaccines induced comparable levels of anti-HAV IgG, as well as similar numbers of antibody-secreting cells and cellular proliferation rates in immunized mice. Importantly, anti-HAV antibodies developed by HM175-HP-immunized mice were able to neutralize the HM175-L0 strain. In addition, both vaccines induced anti-HAV IgG1 antibodies, which are associated with Th2 immune response, but the HM175-HP vaccine showed a tendency to produce a greater IgG2a response, suggesting that it might elicit a higher Th1 response, which is of utmost importance for host defense against viruses.

CONCLUSIONS

Our findings indicated that the fast-growing HM175-HP strain has similar immunogenic properties to the vaccine prototype-like HM175-L0, making it a promising candidate to reduce the elevated costs and time-consuming procedures of producing the current HAV vaccines. The novel HM175-HP-based vaccine would therefore facilitate mass vaccination programs and prevent vaccine shortages.

Longitudinal humoral immunity against SARS-CoV-2 Spike following infection in individuals from Cameroon

In May 2023 the World Health Organization (WHO) declared the end of COVID-19 as a public health emergency. Seroprevalence studies performed in African countries, such as Cameroon, depicted a much higher COVID-19 burden than reported by the WHO. To better understand humoral responses kinetics following infection, we enrolled 333 participants from Yaoundé, Cameroon between March 2020 and January 2022. We measured the levels of antibodies targeting the SARS-CoV-2 receptor-binding-domain (RBD) and the Spike glycoproteins of Delta, Omicron BA.1 and BA.4/5 and the common cold coronavirus HCoV-OC43. We also evaluated plasma capacity to neutralize authentic SARS-CoV-2 virus and to mediate Antibody-Dependent Cellular Cytotoxicity (ADCC). Most individuals mounted a strong antibody response against SARS-CoV-2 Spike. Plasma neutralization waned faster than anti-Spike binding and ADCC. We observed differences in humoral responses by age and circulating variants. Altogether, we show a global overview of antibody dynamics and functionality against SARS-CoV-2 in Cameroon.

The SARS-CoV-2 antibody-dependent enhancement façade

Antibody-dependent enhancement (ADE) is an immunological paradox whereby sensitization following a primary viral infection results in the subsequent enhancement of a similar secondary infection. This idiosyncratic immune response has been established in dengue virus infections, driven by four antigenically related serotypes co-circulating in endemic regions. Several coronaviruses exhibit antibody-mediated mechanisms of viral entry, which has led to speculation of an ADE capacity for SARS-CoV-2, though in vivo and epidemiological evidence do not currently support this phenomenon. Three distinct antibody-dependent mechanisms for SARS-CoV-2 entry have recently been demonstrated: 1. FcR-dependent, 2. ACE2-FcR-interdependent, and 3. FcR-independent. These mechanisms of viral entry may be dependent on SARS-CoV-2 antibody specificity; antibodies targeting the receptor binding domain (RBD) typically result in Fc-dependent and ACE2-FcR-interdependent entry, whereas antibodies targeting the N-terminal domain can induce a conformational change to the RBD that optimizes ACE2-receptor binding domain interactions independent of Fc receptors. Whether these antibody-dependent entry mechanisms of SARS-CoV-2 result in the generation of infectious progenies and enhancement of infection has not been robustly demonstrated. Furthermore, ADE of SARS-CoV-2 mediated by antigenic seniority remains a theoretical concern, as no evidence suggests that SARS-CoV-2 imprinting blunts a subsequent immune response, contributing to severe COVID-19 disease.

Unpredicted Protective Function of Fc-Mediated Inhibitory Antibodies for HIV and SARS-CoV-2 Vaccines

Developing effective vaccines is necessary in combating new virus pandemics. For human immunodeficiency virus (HIV) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the induction of neutralizing antibodies (NAb) is important for vaccine protection; however, the exact mechanisms underlying protection require further study. Recent data emphasize that even Abs that do not exhibit neutralizing activity may contribute to immune defense by Ab Fc-mediated inhibition. Abs exhibiting this function may counter virus mutations, which are acquired to escape from NAbs, and therefore broaden the protective Ab response induced by vaccination. The steps leading to inhibition are complex. How can these functions be measured in vitro? What inhibitory assay is physiologically relevant at mimicking effective in vivo protection? This review provides a comprehensive update on the current knowledge gaps on the Ab Fc-mediated functions involved in HIV and SARS-CoV-2 protection. Understanding the inhibitory effects of these Abs is vital for designing the next generation of protective HIV and SARS-CoV-2 vaccines.