Description of a novel multiplex avidity assay for evaluating HPV antibodies

Microarray-Based Avidity Assay for Assessment of Thyroid Autoantibodies

Background/Objectives: The aim of this study was to evaluate the avidity of thyroid autoantibodies (Abs) in sera of patients with autoimmune thyroid disease (AITD) and thyroid autoantibody carriers without diagnosed AITD. Methods: A hydrogel microarray-based multiplex assay with the chaotrope destruction stage was developed to measure the avidity of thyroid disease-associated autoantibodies, including those targeting thyroperoxidase (TPO), thyroglobulin (Tg), and other minor antigens. Results: Evaluation of the assay in three independent cohorts of patients, totaling 266 individuals with and without AITD, demonstrated the heterogeneous avidity of autoantibodies to thyroid proteins. For the confirmation study, the median avidity index (AI) for AbTg was 29.9% in healthy autoantibody carriers, 52.6% for AITD patients, and 92.7% for type 1 diabetes (T1D) thyroid autoantibody carriers. The median AI for AbTPO was 39.9% in healthy carriers, 73.4% in AITD patients, 83.2% in T1D thyroid autoantibody carriers, and 98.5% in AITD patients with thyroid neoplasm. In patients with Hashimoto's thyroiditis and known disease duration, changes in the avidity maturation of AbTPO over time were demonstrated. Conclusions: Longitudinal studies of TPO- and/or Tg-positive healthy individuals (with an interval of 1-2 years between visits) are needed to evaluate the maturation of autoantibody avidity during the asymptomatic phase and to assess the potential of autoantibody avidity as a prognostic marker for disease development.

Antibody Avidity Maturation Following Booster Vaccination with an Intranasal Adenovirus Salnavac Vaccine

BACKGROUND

The COVID-19 pandemic has led to the rapid development of new vaccines and methods of testing vaccine-induced immunity. Despite the extensive research that has been conducted on the level of specific antibodies, less attention has been paid to studying the avidity of these antibodies. The avidity of serum antibodies is associated with a vaccine showing high effectiveness and reflects the process of affinity maturation. In the context of vaccines against SARS-CoV-2, only a limited number of studies have investigated the avidity of antibodies, often solely focusing on the wild-type virus following vaccination. This study provides new insights into the avidity of serum antibodies following adenovirus-based boosters. We focused on the effects of an intranasal Salnavac booster, which is compared, using a single analytical platform, to an intramuscular Sputnik V.

METHODS

The avidity of RBD-specific IgGs and IgAs was investigated through ELISA using urea and biolayer interferometry.

RESULTS

The results demonstrated the similar avidities of serum antibodies, which were induced by both vaccines for six months post-booster. However, an increase in antibody avidity was observed for the wild-type and Delta variants, but not for the BA.4/5 variant.

CONCLUSIONS

Collectively, our data provide the insights into antibody avidity maturation after the adenovirus-based vaccines against SARS-CoV-2.

The quantity and quality of anti-SARS-CoV-2 antibodies show contrariwise association with COVID-19 severity: lessons learned from IgG avidity

Gaining more appreciation on the protective/damaging aspects of anti-SARS-CoV-2 immunity associated with disease severity is of great importance. This study aimed to evaluate the avidity of serum IgG antibodies against SARS-CoV-2 spike (S) and nucleocapsid (N) in hospitalized symptomatic COVID-19 patients and asymptomatic RT-PCR-confirmed SARS-CoV-2 carriers as well as to compare antibody avidities with respect to vaccination status, vaccination dose and reinfection status. Serum levels of anti-S and anti-N IgG were determined using specific ELISA kits. Antibody avidity was determined by urea dissociation assay and expressed as avidity index (AI) value. Despite higher IgG levels in the symptomatic group, AI values of both anti-S and anti-N IgG were significantly lower in this group compared to asymptomatic individuals. In both groups, anti-S AI values were elevated in one-dose and two-dose vaccinees versus unvaccinated subjects, although significant differences were only detected in the symptomatic group. However, anti-N avidity showed no significant difference between the vaccinated and unvaccinated subgroups. Almost all vaccinated patients of different subgroups (based on vaccine type) had higher anti-S IgG avidity, while the statistical significance was detected only between those receiving Sinopharm compared to the unvaccinated subgroup. Also, statistically significant differences in antibody AIs were only found between primarily infected individuals of the two groups. Our findings indicate a key role for anti-SARS-CoV-2 IgG avidity in protection from symptomatic COVID-19 and calls for the incorporation of antibody avidity measurement into the current diagnostic tests to predict effective immunity toward SARS-CoV-2 infection or even for prognostic purposes.

Antibody Avidity and Neutralizing Response against SARS-CoV-2 Omicron Variant after Infection or Vaccination

Background

The recently emerged SARS-CoV-2 Omicron variant exhibits several mutations on the spike protein, enabling it to escape the immunity elicited by natural infection or vaccines. Avidity is the strength of binding between an antibody and its specific epitope. The SARS-CoV-2 spike protein binds to its cellular receptor with high affinity and is the primary target of neutralizing antibodies. Therefore, protective antibodies should show high avidity. This study aimed at investigating the avidity of receptor-binding domain (RBD) binding antibodies and their neutralizing activity against the Omicron variant in SARS-CoV-2 infected patients and vaccinees.

Methods

Samples were collected from 42 SARS-CoV-2 infected patients during the first pandemic wave, 50 subjects who received 2 doses of mRNA vaccine before the Omicron wave, 44 subjects who received 3 doses of mRNA vaccine, and 35 subjects who received heterologous vaccination (2 doses of adenovirus-based vaccine plus mRNA vaccine) during the Omicron wave. Samples were tested for the avidity of RBD-binding IgG and neutralizing antibodies against the wild-type SARS-CoV-2 virus and the Omicron variant.

Results

In patients, RBD-binding IgG titers against the wild-type virus increased with time, but remained low. High neutralizing titers against the wild-type virus were not matched by high avidity or neutralizing activity against the Omicron variant. Vaccinees showed higher avidity than patients. Two vaccine doses elicited the production of neutralizing antibodies, but low avidity for the wild-type virus; antibody levels against the Omicron variant were even lower. Conversely, 3 doses of vaccine elicited high avidity and high neutralizing antibodies against both the wild-type virus and the Omicron variant.

Conclusions

Repeated vaccination increases antibody avidity against the spike protein of the Omicron variant, suggesting that antibodies with high avidity and high neutralizing potential increase cross-protection against variants that carry several mutations on the RBD.

Modified ELISA for antibody avidity evaluation: The need for standardization

Antibody avidity is an important parameter to evaluate immune response, being useful to evaluate vaccine responses and helping to distinguish acute and latent infection. The antibody avidity can be measured by different methods, yet the most common is a modified ELISA. The utilization of commercial kits or in-house methods to evaluate antibody avidity have been adopted more and more, although the lack of standardization between different assays may generate a lot of variation in the process, making it hard to compare the results generated.

Delayed dosing intervals for quadrivalent human papillomavirus vaccine do not reduce antibody avidity

The quadrivalent HPV vaccine (4vHPV) was originally recommended as a three-dose series (0/2/6 months), though delays in completing the series frequently occur. We previously found delayed dosing in girls resulted in similar or higher antibody titers compared to on-time dosing. Archived sera from 262 healthy females aged 9–18 recruited from pediatric clinics were tested to determine if delayed dosing intervals affected antibody avidity. Avidity index (AI; ratio of IgG Ab bound in the treated and untreated sample) was determined pre- and post-dose 3 4vHPV for each participant using a modified multiplex ELISA. Data were grouped by dosing intervals: (1) on-time dose 2 and 3, (2) delayed dose 2 and on-time dose 3, (3) on-time dose 2 and delayed dose 3, (4) delayed dose 2 and 3. Overall, mean AI was highest for HPV16 and lowest for HPV6. As expected, AI did not differ between groups 1 & 3 or groups 2 & 4 pre-dose 3, however, for most types mean AI was significantly higher both pre- and post-dose 3 for groups with delayed dose 2. For all types, mean AI was higher post-dose 3 in all delayed dosing groups compared to group 1. One month post-dose 3, there was a positive but weak correlation between AIs and antibody titer for HPV 6 (ρ = 0.25, p = .0001), HPV 11 (ρ = 0.14, p = .0370), HPV 16 (ρ = 0.11, p = .0934), and HPV 18 (ρ = 0.37, p < .0001). Our findings suggest longer intervals between doses result in higher antibody avidity, providing further evidence that delayed dosing of 4vHPV does not hinder the immune response.

Immunogenicity of HPV prophylactic vaccines: Serology assays and their use in HPV vaccine evaluation and development

When administered as standard three-dose schedules, the licensed HPV prophylactic vaccines have demonstrated extraordinary immunogenicity and efficacy. We summarize the immunogenicity of these licensed vaccines and the most commonly used serology assays, with a focus on key considerations for one-dose vaccine schedules. Although immune correlates of protection against infection are not entirely clear, both preclinical and clinical evidence point to neutralizing antibodies as the principal mechanism of protection. Thus, immunogenicity assessments in vaccine trials have focused on measurements of antibody responses to the vaccine. Non-inferiority of antibody responses after two doses of HPV vaccines separated by 6 months has been demonstrated and this evidence supported the recent WHO recommendations for two-dose vaccination schedules in both boys and girls 9-14 years of age. There is also some evidence suggesting that one dose of HPV vaccines may provide protection similar to the currently recommended two-dose regimens but robust data on efficacy and immunogenicity of one-dose vaccine schedules are lacking. In addition, immunogenicity has been assessed and reported using different methods, precluding direct comparison of results between different studies and vaccines. New head-to-head vaccine trials evaluating one-dose immunogenicity and efficacy have been initiated and an increase in the number of trials relying on immunobridging is anticipated. Therefore, standardized measurement and reporting of immunogenicity for the up to nine HPV types targeted by the current vaccines is now critical. Building on previous HPV serology assay standardization and harmonization efforts initiated by the WHO HPV LabNet in 2006, new secondary standards, critical reference reagents and testing guidelines will be generated as part of a new partnership to facilitate harmonization of the immunogenicity testing in new HPV vaccine trials.

Mapping Protective Regions on a Three-Dimensional Model of the Moraxella catarrhalis Vaccine Antigen Oligopeptide Permease A

A vaccine against Moraxella catarrhalis would reduce tremendous morbidity, mortality, and financial burden by preventing otitis media in children and exacerbations of chronic obstructive pulmonary disease (COPD) in adults. Oligopeptide permease A (OppA) is a candidate vaccine antigen that is (i) a nutritional virulence factor expressed on the bacterial cell surface during infection, (ii) widely conserved among strains, (iii) highly immunogenic, and (iv) a protective antigen based on its capacity to induce protective responses in immunized animals. In the present study, we show that the antibodies to OppA following vaccination mediate accelerated clearance in animals after pulmonary challenge. To identify regions of OppA that bind protective antibodies, truncated constructs of OppA were engineered and studied to map regions of OppA with surface-accessible epitopes that bind high-avidity antibodies following vaccination. Protective epitopes were located in the N and C termini of the protein. Immunization of mice with constructs corresponding to these regions (T5 and T8) induced protective responses. Studies of overlapping peptide libraries of constructs T5 and T8 with OppA immune serum identified two discrete regions on each construct. These potentially protective regions were mapped on a three-dimensional computational model of OppA, where regions with solvent-accessible amino acids were identified as three potentially protective epitopes. In all, these studies revealed two regions with three specific epitopes in OppA that induce potentially protective antibody responses following vaccination. Detection of antibodies to these regions could serve to guide vaccine formulation and as a diagnostic tool for monitoring development of protective responses during clinical trials.