The β-NGF/TrkA Signalling Pathway Is Associated With the Production of Anti-Nucleoprotein IgG in Convalescent COVID-19

BackgroundThe presentation of SARS-CoV-2 infection varies from asymptomatic to severe COVID-19. Similarly, high variability in the presence, titre and duration of specific antibodies has been reported. While some host factors determining these differences, such as age and ethnicity have been identified, the underlying molecular mechanisms underpinning these differences remain poorly defined.MethodsWe analysed serum and PBMC from 17 subjects with a previous PCR-confirmed SARS-CoV-2 infection and 10 unexposed volunteers following the first wave of the pandemic, in the UK. Anti-NP IgG and neutralising antibodies were measured, as well as a panel of infection and inflammation related cytokines. The virus-specific T cell response was determined by IFN-γ ELISPOT and flow cytometry after overnight incubation of PBMCs with pools of selected SARS-CoV-2 specific peptides.ResultsSeven of 17 convalescent subjects had undetectable levels of anti-NP IgG, and a positive correlation was shown between anti-NP IgG levels and the titre of neutralising antibodies (IC50). In contrast, a discrepancy was noted between antibody levels and T cell IFN-γ production by ELISpot following stimulation with specific peptides. Among the analysed cytokines, β-NGF and IL-1α levels were significantly different between anti-NP positive and negative subjects, and only β-NGF significantly correlated with anti-NP positivity. Interestingly, CD4+ T cells of anti-NP negative subjects expressed lower amounts of the β-NGF-specific receptor TrkA.ConclusionsOur results suggest that the β-NGF/TrkA signalling pathway is associated with the production of anti-NP specific antibody in mild SARS-CoV-2 infection and the mechanistic regulation of this pathway in COVID-19 requires further investigation.

Rapid isolation and resolution immune evasion and viral fitness across contemporary SARS-CoV-2 variants

From late 2020 the world observed the rapid emergence of many distinct SARS-CoV-2 variants. At the same time, pandemic responses coalesced into significant global vaccine roll-out that have now significantly lowered Covid-19 hospital and mortality rates in the developed world. Over this period, we developed a rapid platform (R-20) for viral isolation and characterisation using primary remnant diagnostic swabs. This combined with quarantine testing and genomics surveillance, enabled the rapid isolation and characterisation of all major SARS-CoV-2 variants (all variants of concern and 6 variants of interest) globally with a 4-month period. This platform facilitated viral variant isolation and enabled rapid resolution of variant phenotype by allowing determining end point viral titers from primary nasopharyngeal swabs and through ranking of evasion of neutralising antibodies. In late 2021, when the Delta variant was dominating, Omicron rapidly emerged. Using this platform, we isolated and tested the first cases of this variant within Australia. In this setting we observed Omicron to diverge from other variants at two levels: Firstly, it ranks at the mots evasive to neutralisation antibodies compared to all VOCs and major VUIs. Secondly, it no longer engages TMPRSS2 during the late stages of fusion.

Modelling upper respiratory viral load dynamics of SARS-CoV-2

Relationships between viral load, severity of illness, and transmissibility of virus are fundamental to understanding pathogenesis and devising better therapeutic and prevention strategies for COVID-19. Here we present within-host modelling of viral load dynamics observed in the upper respiratory tract (URT), drawing upon 2172 serial measurements from 605 subjects, collected from 17 different studies. We developed a mechanistic model to describe viral load dynamics and host response and contrast this with simpler mixed-effects regression analysis of peak viral load and its subsequent decline. We observed wide variation in URT viral load between individuals, over 5 orders of magnitude, at any given point in time since symptom onset. This variation was not explained by age, sex, or severity of illness, and these variables were not associated with the modelled early or late phases of immune-mediated control of viral load. We explored the application of the mechanistic model to identify measured immune responses associated with the control of the viral load. Neutralising antibodies correlated strongly with modelled immune-mediated control of viral load amongst subjects who produced neutralising antibodies. Our models can be used to identify host and viral factors which control URT viral load dynamics, informing future treatment and transmission blocking interventions.

Persistence of immunity and impact of a third (booster) dose of an inactivated SARS-CoV-2 vaccine, BBV152; a phase 2, double-blind, randomised controlled trial

Background: Neutralising antibody responses to SARS-CoV-2 vaccines have been reported to decline within 6 months of vaccination, particularly against Variants of Concern (VOC). We assessed the immunogenicity and safety of a booster dose of BBV152 administered 6 months after the second of a two-dose primary vaccination series. Methods: In an ongoing phase 2 trial (ClinicalTrials.gov: NCT04471519) the protocol was amended after six months to re-consent and randomise 184 previously vaccinated participants to receive a third dose of vaccine or placebo on Day 215. The primary outcome was to measure neutralising antibody titres by plaque-reduction neutralisation test (PRNT50) four weeks after the booster; safety as serious adverse events (SAE) was the key secondary outcome. Findings: Four weeks after a second BBV152 vaccination geometric mean titres (GMTs) of neutralising antibodies were 197.0 PRNT50 (95% CI: 155.6,249.4); this level declined to 23.9 PRNT50 (14.0,40.6) six months later, with a seroconversion rate of 75.4% (95% CI: 68.4,81.6). Four weeks after booster vaccination the GMT increased on Day 243 to 746.6 PRNT50 (514.9,1081) compared with 100.7 PRNT50 (43.6,232.6) in the placebo group. Corresponding seroconversion rates were 98.7% (92.8,99.9) and 79.8% (69.6,87.8). Increased titres in the placebo group were attributed to natural infection as the study was conducted during the second wave of COVID-19 in India. PRNT50 titres against the SARS-CoV-2 variants increased Alpha (32.6 fold), Beta (161.0 fold), Delta (264.7 fold), and Delta plus (174.2 fold) after the booster vaccination. We found that vaccine induces both memory B and T cells with a distinct AIM+ specific CD4+T central and effector memory phenotype, including CD8+ TEMRA phenotype. Reactogenicity after vaccine and placebo was minimal and comparable, and no SAEs were reported. Interpretation: Six months after a two dose BBV152 vaccination series cell mediated immunity and neutralising antibodies to both homologous (D614G) and heterologous strains (Alpha, Beta, Delta and Delta plus) persisted above baseline, although the magnitude of the responses had declined. Neutralising antibodies against homologous and heterologous SARS-CoV-2 variants increased 19 to 97 fold after a third vaccination. Booster BBV152 vaccination is safe and may be necessary to ensure persistent immunity to prevent breakthrough infections.

Three doses of the BNT162b2 vaccine confer neutralising antibody capacity against the SARS-CoV-2 B.1.1.529 (Omicron) variant of concern

We report the levels of neutralising antibodies against Wuhan, Delta and Omicron variants in healthy individuals pre-infected or not with SARS-CoV-2 and immunized with three doses of the BNT162b2 vaccine. Our observations support the rapid administration of a booster vaccine dose to prevent infection and disease caused by Omicron.

Neutralising antibody activity against SARS-CoV-2 variants, including Omicron, in an elderly cohort vaccinated with BNT162b2

SARS-CoV-2 variants threaten the effectiveness of tools we have developed to mitigate against serious COVID-19. This is especially true in clinically vulnerable sections of society including the elderly. Using sera from BNT162b2 (Pfizer-BioNTech) vaccinated individuals aged between 70 and 89 (vaccinated with two doses 3-weeks apart) we examined the neutralising antibody (nAb) response to wildtype SARS-CoV-2. Between 3 and 20-weeks post 2nd dose, nAb titres dropped 4.9-fold to a median titre of 21.3 (ND80) with 21.6% of individuals having no detectable nAbs at the later time point. Experiments examining the neutralisation of twenty-one different SARS-CoV-2 variant spike proteins confirmed a significant potential for antigenic escape, especially for the Omicron (BA.1), Beta (B.1.351), Delta (B.1.617.2), Theta (P.3), C.1.2 and B.1.638 variants. Interestingly, however, the recently-emerged sub-lineage AY.4.2 was more efficiently neutralised than parental Delta pseudotypes. Combining pseudotype neutralisation with specific receptor binding domain (RBD) ELISAs we confirmed that changes to position 484 in the spike RBD were predominantly responsible for SARS-CoV-2 nAb escape, although the effect of spike mutations is both combinatorial and additive. Lastly, using sera from the same individuals boosted with a 3rd dose of BNT162b2 we showed that high overall levels of neutralising antibody titre can provide significant levels of cross-protection against Omicron. These data provide evidence that SARS-CoV-2 neutralising antibodies wane over time and that antigenically variable SARS-CoV-2 variants are circulating, highlighting the importance of ongoing surveillance and booster programmes. Furthermore, they provide important data to inform risk assessment of new SARS-CoV-2 variants, such as Omicron, as they emerge.

SARS-CoV-2 Omicron spike mediated immune escape, infectivity and cell-cell fusion

The Omicron variant emerged in southern Africa in late 2021 and is characterised by multiple spike mutations across all spike domains. Here we show that the Omicron spike confers very significant evasion of vaccine elicited neutralising antibodies that is more pronounced for ChAdOx-1 adenovirus vectored vaccine versus BNT162b2 mRNA vaccine. Indeed neutralisation of Omicron was not detectable for the majority of individuals who had received two doses of ChAdOx-1. Third dose mRNA vaccination rescues neutralisation in the short term. Despite three mutations predicted to favour spike S1/S2 cleavage, observed cleavage efficiency is lower than for wild type Wuhan-1 D614G and Delta. We demonstrate significantly lower infectivity of lung organoids and Calu-3 lung cells expressing endogenous levels of ACE2 and TMPRSS2 but similar infection as compared to Delta when using H1299 lung epithelial cells. Importantly, fusogenicity of the Omicron spike is impaired, leading to marked reduction in syncitia formation. These observations indicate that Omicron has gained immune evasion properties whilst possibly modulating properties associated with replication and pathogenicity.

SARS CoV-2 Variants and Spike Mutations Involved in Second Wave of COVID-19 Pandemic in India

Against the backdrop of the second wave of COVID-19 pandemic in India that started in March 2021, we have monitored the spike (S) protein mutations in all the reported (GISAID portal) whole genome sequences of SARS CoV-2 circulating in India from 1 January 2021 to 31 August 2021. In the 43,102 SARS-CoV-2 genomic sequences analysed, we have identified 24, 260 mutations in the S protein, based on which 265 pango lineages could be categorised. The dominant lineage in most of the 28 states of India and its 8 union territories was B.1.617.2 (the delta variant). However, the states Madhya Pradesh, Jammu & Kashmir, and Punjab had B.1.1.7 (alpha variant) as the major lineage, while the Himachal Pradesh state reported B.1.36 as the dominating lineage. A detailed analysis of various domains of S protein was carried out for detecting mutations having a prevalence of >1%; 70, 18, 7, 3, 9, 4, and 1 (N=112) such mutations were observed in the N -terminal domain, receptor binding domain, C -terminal domain, fusion peptide region, heptapeptide repeat (HR)-1 domains, signal peptide domain, and transmembrane region, respectively. However, no mutations were recorded in the HR-2, and cytoplasmic domains of the S protein. Interestingly, 13.39% (N=15) of these mutations were reported to increase the infectivity and pathogenicity of the virus; 2%(N=3) were known to be vaccine breakthrough mutations; and 0.89%(N=1) were known to escape neutralising antibodies. Biological significance of 82% (N=92) of the reported mutations is yet unknown. As SARS-CoV-2 variants are emerging rapidly, it is critical to continuously monitor local viral mutations to understand national trends of virus circulation. This can tremendously help in designing better preventive regimens in the country, and avoid vaccine breakthrough infections.

Mimicking Native Display of CD0873 on Liposomes Augments Its Potency as an Oral Vaccine against Clostridioides difficile

Mucosal vaccination aims to prevent infection mainly by inducing secretory IgA (sIgA) antibody, which neutralises pathogens and enterotoxins by blocking their attachment to epithelial cells. We previously demonstrated that encapsulated protein antigen CD0873 given orally to hamsters induces neutralising antibodies locally as well as systemically, affording partial protection against Clostridioides difficile infection. The aim of this study was to determine whether displaying CD0873 on liposomes, mimicking native presentation, would drive a stronger antibody response. The recombinant form we previously tested resembles the naturally cleaved lipoprotein commencing with a cysteine but lacking lipid modification. A synthetic lipid (DHPPA-Mal) was designed for conjugation of this protein via its N-terminal cysteine to the maleimide headgroup. DHPPA-Mal was first formulated with liposomes to produce MalLipo; then, CD0873 was conjugated to headgroups protruding from the outer envelope to generate CD0873-MalLipo. The immunogenicity of CD0873-MalLipo was compared to CD0873 in hamsters. Intestinal sIgA and CD0873-specific serum IgG were induced in all vaccinated animals; however, neutralising activity was greatest for the CD0873-MalLipo group. Our data hold great promise for development of a novel oral vaccine platform driving intestinal and systemic immune responses.