Bivalent single domain antibody constructs for effective neutralization of Venezuelan equine encephalitis

Venezuelan equine encephalitis virus (VEEV) is a mosquito borne alphavirus which leads to high viremia in equines followed by lethal encephalitis and lateral spread to humans. In addition to naturally occurring outbreaks, VEEV is a potential biothreat agent with no approved human vaccine or therapeutic currently available. Single domain antibodies (sdAb), also known as nanobodies, have the potential to be effective therapeutic agents. Using an immune phage display library derived from a llama immunized with an equine vaccine that included inactivated VEEV, five sdAb sequence families were identified that showed varying ability to neutralize VEEV. One of the sequence families had been identified previously in selections against chikungunya virus, a related alphavirus of public health concern. A key advantage of sdAb is the ability to optimize properties such as neutralization capacity through protein engineering. Neutralization of VEEV was improved by two orders of magnitude by genetically linking sdAb. One of the bivalent constructs showed effective neutralization of both VEEV and chikungunya virus. Several of the bivalent constructs neutralized VEEV in cell-based assays with reductions in the number of plaques by 50% at protein concentrations of 1 ng/mL or lower, making future evaluation of their therapeutic potential compelling.

SARS-CoV-2 induces a durable and antigen specific humoral immunity after asymptomatic to mild COVID-19 infection

Current SARS-CoV-2 serological assays generate discrepant results, and the longitudinal characteristics of antibodies targeting various antigens after asymptomatic to mild COVID-19 are yet to be established. This longitudinal cohort study including 1965 healthcare workers, of which 381 participants exhibited antibodies against the SARS-CoV-2 spike antigen at study inclusion, reveal that these antibodies remain detectable in most participants, 96%, at least four months post infection, despite having had no or mild symptoms. Virus neutralization capacity was confirmed by microneutralization assay in 91% of study participants at least four months post infection. Contrary to antibodies targeting the spike protein, antibodies against the nucleocapsid protein were only detected in 80% of previously anti-nucleocapsid IgG positive healthcare workers. Both anti-spike and anti-nucleocapsid IgG levels were significantly higher in previously hospitalized COVID-19 patients four months post infection than in healthcare workers four months post infection (p = 2*10−23 and 2*10−13 respectively). Although the magnitude of humoral response was associated with disease severity, our findings support a durable and functional humoral response after SARS-CoV-2 infection even after no or mild symptoms. We further demonstrate differences in antibody kinetics depending on the antigen, arguing against the use of the nucleocapsid protein as target antigen in population-based SARS-CoV-2 serological surveys.

SARS-CoV-2 Humoral and Cellular Immune Responses in COVID-19 Convalescent Individuals With HIV

Background SARS-CoV-2-specific immune response features in people with HIV infection (PWH) remain to be fully elucidated. We aimed to evaluate the impact of HIV over humoral and cellular responses in COVID-19 convalescent PWH. Methods Blood samples from 29 PWH with preserved CD4+T-cell counts on ART and 29 HIV-negative (HIVneg) donors were included. SARS-CoV-2-specific IgG levels and IgG titers were determined by ELISA. Antibody neutralization capacity was evaluated against the reference B1 strain SARS-CoV-2. IFN-γ-secreting cells were detected by ELISpot using SARS-CoV-2 Spike, RBD, or Nucleocapsid protein or overlapping peptide pools. Frequency and phenotype of T, B and NK cells and levels of soluble cytokines and chemokines were assessed by flow cytometry. Results SARS-CoV-2-specific antibodies were detected on 65.5% of PWH and 79.3% of HIVneg individuals, with no differences in serum IgG levels and anti-SARS-CoV-2 neutralizing antibodies. All donors exhibited SARS-CoV-2-specific cellular immunity, including those with undetectable antibody responses. PWH showed diminished percentages of antibody-secreting cells compared to HIVneg cohort, with similar B cell proportions between groups. PWH presented an increment in T follicular helper (Tfh, CD4+CXCR5+) percentage, which negatively correlated with IgG titers. Additionally, CD4+PD1+ and CD8+HLA-DR+ cell frequencies were augmented in PWH. Moreover, PWH presented a high proportion of CD95+, CD25+, NKp46+, HLA-DR+, and CD38+/HLA-DR+ NK cells. Both groups displayed similar Tregs frequency, effector/memory, and T-helper profile for CD4TL, exhaustion and memory phenotypes for CD8TL and subtle differences in classical monocytes. Profile of circulating cytokines and chemokines was significantly different between both groups. Magnitude of IFN-γ responses to S or N proteins, and RBD was lower in PWH compared to HIVneg donors. Correlation analysis of immune and clinical parameters showed a distinct immune landscape in the PWH group. Conclusions PWH showed a distinctive immune profile although severity of COVID-19 was not exacerbated. PWH with conserved CD4+T-cell counts exerted both humoral and cellular responses against SARS-CoV-2. Even though cellular response was lower compared to HIVneg individuals, PWH achieved similar antibody responses with a high neutralization capacity. These data reinforce the impact of ART, not only in controlling HIV but also other infections.

Superior immunity that allows neutralization of all SARS-CoV-2 variants of concern develops in COVID-19 convalescents and naïve individuals after three vaccinations

Infection-neutralizing antibody responses after SARS-CoV-2 infection or COVID-19 vaccination are an essential part of antiviral immunity. This immune protection is challenged by the occurrence of SARS-CoV-2 variants of concern (VoCs) with immune escape properties, such as omicron (B.1.1.529) that is rapidly spreading worldwide. Here, we report neutralizing antibody dynamics in a longitudinal cohort of COVID-19 convalescent and naïve individuals vaccinated with mRNA BNT162b2 by quantifying anti-SARS-CoV-2-spike antibodies and determining their avidity and neutralization capacity. A superior infection-neutralizing capacity against all VoCs, including omicron, developed by either two vaccinations of convalescents, or a third vaccination or breakthrough infection of twice-vaccinated naïve individuals. These three consecutive spike antigen exposures resulted in an increasing neutralization capacity per anti-spike antibody unit and were paralleled by stepwise increases in antibody avidity. In conclusion, an infection/vaccination-induced hybrid immunity or a triple immunization induces high-quality antibodies resulting in superior neutralization capacity against VoCs, including omicron.

Human Milk SARS-CoV-2 Antibodies up to 6 Months After Vaccination

BACKGROUND: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)–specific antibodies have been detected in human milk up to 6 weeks post–coronavirus disease 2019 (COVID-19) vaccination. We evaluated SARS-CoV-2-specific antibodies, neutralization activity, effect of pasteurization, and persistence through 6 months after vaccination. METHODS: This prospective longitudinal study enrolled 30 pregnant or lactating women. SARS-CoV-2 antibodies and neutralization capacity were analyzed using an enzyme-linked immunosorbent assay compared at prevaccination and 1, 3, and 6 months postvaccination, and through Holder pasteurization. RESULTS: Human milk SARS-CoV-2-specific IgG levels peaked at 1 month postvaccination and persisted above prevaccination levels for at least 6 months (P = .005). SARS-CoV-2-specific IgA was detected at 1 and 3 months (both P < .001) but waned by 6 months compared with baseline (P = .07). Milk SARS-CoV-2-specific IgG and IgA correlated with serum IgG at the same time point (R2 = 0.37, P < .001 and R2 = 0.19, P < .001). Neutralization activity was seen in 83.3%, 70.4%, and 25.0% of milk samples at 1, 3, and 6 months postvaccination. Neutralization most strongly correlated with SARS-CoV-2-specific IgG (R2 = 0.57, P < .001). Pre- and postpasteurization samples showed similar IgG (0.84 vs 1.07, P = .36) and neutralizing activity (57.7% vs 58.7% inhibition, P = .27), but lower IgM and IgA levels postpasteurization (0.09 vs 0.06, P = .004 and 0.21 vs 0.18, P = .043). CONCLUSIONS: The data suggest that human milk SARS-CoV-2-specific antibodies may be available to milk-fed infants for up to 6 months. In addition, donor milk from vaccinated mothers retain IgG and neutralizing activity.

Longitudinal dynamics of SARS-CoV-2-specific cellular and humoral immunity after natural infection or BNT162b2 vaccination

The timing of the development of specific adaptive immunity after natural SARS-CoV-2 infection, and its relevance in clinical outcome, has not been characterized in depth. Description of the long-term maintenance of both cellular and humoral responses elicited by real-world anti-SARS-CoV-2 vaccination is still scarce. Here we aimed to understand the development of optimal protective responses after SARS-CoV-2 infection and vaccination. We performed an early, longitudinal study of S1-, M- and N-specific IFN-γ and IL-2 T cell immunity and anti-S total and neutralizing antibodies in 88 mild, moderate or severe acute COVID-19 patients. Moreover, SARS-CoV-2-specific adaptive immunity was also analysed in 234 COVID-19 recovered subjects, 28 uninfected BNT162b2-vaccinees and 30 uninfected healthy controls. Upon natural infection, cellular and humoral responses were early and coordinated in mild patients, while weak and inconsistent in severe patients. The S1-specific cellular response measured at hospital arrival was an independent predictive factor against severity. In COVID-19 recovered patients, four to seven months post-infection, cellular immunity was maintained but antibodies and neutralization capacity declined. Finally, a robust Th1-driven immune response was developed in uninfected BNT162b2-vaccinees. Three months post-vaccination, the cellular response was comparable, while the humoral response was consistently stronger, to that measured in COVID-19 recovered patients. Thus, measurement of both humoral and cellular responses provides information on prognosis and protection from infection, which may add value for individual and public health recommendations.

Antibody Responses to 3rd Dose mRNA Vaccines in Nursing Home and Assisted Living Residents

A comparison of SARS-CoV-2 wild-type and the beta variant virus neutralization capacity between 2 and 3 mRNA vaccine series in nursing home residents, and between nursing home and assisted living residents strongly supports 3rd dose vaccine recommendations, and equivalent polices for nursing homes and assisted living settings. Findings suggest that residents mount a robust humoral response to a 3rd mRNA vaccination, and have greater neuralization capacity compared to a 2 dose series.

SARS-CoV-2 B.1.1.529 variant (Omicron) evades neutralization by sera from vaccinated and convalescent individuals

Recently, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant B.1.1.529 (Omicron) has been described.Here, we analyze titers of neutralizing antibodies of sera from convalescent or vaccinated individuals against the new B.1.1.529 variant and compared them with titers against other Variants of Concern (B.1.1.7, B.1.351, B.1617.2) using replication competent SARS-CoV-2 variants.We found that sera from vaccinated individuals neutralized the B.1.1.529 variant to a much lesser extent than any other variant analyzed. Neutralization capacity against B.1.1.529 was maintained best against sera from super immune individuals (infected and vaccinated or vaccinated and infected).

A novel bacterial protease inhibitor adjuvant in RBD-based COVID-19 vaccine formulations increases neutralizing antibodies, specific germinal center B cells and confers protection against SARS-CoV-2 infection.

In this work we evaluated recombinant receptor binding domain (RBD) based vaccine formulation prototypes with potential for further clinical development. We assessed different formulations containing RBD plus Alum, AddaS03, AddaVax or the combination of Alum and U-Omp19: a novel Brucella spp. protease inhibitor vaccine adjuvant. Results show that the vaccine formulation composed of U-Omp19 and Alum as adjuvants have a better performance: it significantly increased mucosal and systemic neutralizing antibodies in comparison to antigen plus Alum, AddaVax or AddaS03. Antibodies induced with the formulation containing U-Omp19 not only increased their neutralization capacity against the wild-type virus but also cross neutralized alpha, lambda and gamma variants with similar potency. Also, addition of U-Omp19 to vaccine formulation increased the frequency of RBD-specific geminal center B cells and plasmablasts. Additionally, U-Omp19+Alum formulation induced RBD-specific Th1 and CD8+ T cell responses in spleens and lungs. Finally, this vaccine formulation conferred protection against an intranasal SARS-CoV-2 challenge of K18-hACE2 mice.

High seroconversion rate and SARS-CoV-2 Delta neutralization in PLWHIV vaccinated with BNT162b2

ObjectivesTo assess the humoral and cellular responses against SARS-CoV-2 Delta variant after BNT162b2 vaccination in PLWHIV.DesignMulticenter cohort study of PLWHIV, with a CD4 cell count <500/mm3 and a viral load <50 copies/ml on stable antiretroviral therapy for at least 3 months.MethodsAnti-SARS-CoV-2 Receptor Binding Domain IgG antibodies (anti-RBD IgG) were quantified and their neutralization capacity was evaluated using an ELISA (GenScript) and a virus neutralization test (VNT), against historical strain, Beta and Delta variants before vaccination (day 0) and one month after a complete vaccination schedule (M1).Results97 patients were enrolled in the study: 85 received 2 vaccine doses (11 previous COVID-19 and 1 premature exit). The seroconversion rate in anti-RBD IgG was 97% CI95[90%; 100%] at M1. Median (IQR) anti-RBD IgG titer was 0.97 (0.97-5.3) BAU/ml at D0 and 1219 (602-1929) at M1. Neutralizing antibodies (NAbs) capacity improved between D0 (15% CI95[8%; 23%]) and M1 (94% CI95[87%; 98%]) with the GenScript assay (p<0.0001). At M1, NAbs against historical strain, Beta and Delta variants were present in 82%, 77% and 84% patients respectively. The seroconversion rate and median anti-RBD IgG were 91% and 852 BAU/ml in patients with CD4<250/mm3 (n=13) and 98% and 1270 BAU/ml in patients with CD4>250/mm3 (n=64) (p=0.3994). 73% of patients with CD4<250 had NAbs and 97% of those with CD4>250 (p=0.0130). The NAbs against Beta variant was elicited in 50% in CD4<250 and in 81% in CD4>250 (p=0.0292). No change in CD4+ or CD8+ T cells count was observed while a decrease of CD19+ B cells count was observed (208 ±124 cells/mm3 at D0 vs 188 ±112 cells/mm3 at M1, p<0.01). No notable adverse effects or COVID-19 were reported.ConclusionsThese results show a high seroconversion rate with a Delta neutralization in PLWHIV patients after a complete BNT162b2 vaccination schedule.