Antibody Kinetics Research Articles

SARS-CoV-2-infection- and vaccine-induced antibody responses are long lasting with an initial waning phase followed by a stabilization phase

It is thought that mRNA-based vaccine-induced immunity to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) wanes quickly, based mostly on short-term studies. Here, we analyzed the kinetics and durability of the humoral responses to SARS-CoV-2 infection and vaccination using >8,000 longitudinal samples collected over a 3-year period in New York City. Upon primary immunization, participants with pre-existing immunity mounted higher antibody responses faster and achieved higher steady-state antibody titers than naive individuals. Antibody kinetics were characterized by two phases: an initial rapid decay, followed by a stabilization phase with very slow decay. Booster vaccination equalized the differences in antibody concentration between participants with and without hybrid immunity, but the peak antibody titers decreased with each successive antigen exposure. Breakthrough infections increased antibodies to similar titers as an additional vaccine dose in naive individuals. Our study provides strong evidence that SARS-CoV-2 antibody responses are long lasting, with initial waning followed by stabilization.

SARS-CoV-2 Antibody Kinetics in Unvaccinated Hospitalized Children With COVID-19.

Antibody levels decline a few months post-acute COVID-19, but humoral memory persists in adults. Age and disease severity may affect antibody responses. This study aims to evaluate the presence and durability of antibody responses in children with COVID-19. A prospective, single-center study, involving unvaccinated children 0-16 years of age who were hospitalized with COVID-19 between October 2020 and December 2021, was conducted. Serological testing for anti-Spike severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) IgG and neutralizing antibodies was performed at diagnosis and at 1-, 3-, 6- and 12-months post-infection. A total of 65 immunocompetent children were enrolled [mean age (±SD): 6.7 (±6.4) years; males: 56.9%]. At 3 months, 40/44 (91%) children were seropositive; seropositivity persisted in 22/26 (85%) children at 6 months and in 10/12 (83%) children at 12 months. There was no evidence that age was modifying the prediction of variance of SARS-CoV-2 IgG levels. In contrast, SARS-CoV-2 IgG levels varied with time and disease severity. The association with time was non-linear, so that with increasing time there was a significant reduction in SARS-CoV-2 IgG levels [coef, 0.044 (95% confidence interval {CI}: 0.061-0.028), P < 0.001]. For each increment of time, the higher disease severity group was associated with 0.9 lower SARS-CoV-2 IgG levels. Everyone varied from the average effect of time with an SD of 0.01, suggesting that individuals may have different trajectories across time. Disease severity, but not age, influences antibody titers among children hospitalized with COVID-19. SARS-CoV-2 infection induces durable seroconversion in these children with detectable IgG levels at 1 year after infection.

Investigating the Seroconversion Patterns of Specific Antibodies Against Various Antigens of SARS-CoV-2 in Hospitalized COVID-19 Patients and Vaccinated Individuals

Background: Inducing a humoral response to SARS-CoV-2 may partially control virus dissemination. However, there is a lack of consistency in the reported kinetics of IgM and IgG responses to SARS-CoV-2. Additionally, the humoral response to SARS-CoV-2 may differ from that elicited by vaccination. Therefore, we were motivated to evaluate the kinetics of antibodies against SARS-CoV-2 in both infected and vaccinated individuals. Objectives: This study aimed to investigate the seroconversion patterns of specific antibodies against various antigens of SARS-CoV-2 in hospitalized COVID-19 patients and vaccinated individuals, focusing specifically on comparing the humoral responses elicited by infection and vaccination. Methods: Serial blood and swab samples were collected from 134 COVID-19 patients at six time points following admission. Real-time RT-PCR specific for SARS-CoV-2, as well as anti-SARS-CoV-2 IgM and IgG, were tested using ELISA. Additionally, 141 serum samples were obtained from vaccinated individuals. Anti-SARS-CoV-2 spike and RBD IgGs, along with neutralizing antibodies (NAs), were assessed using ELISA in both the vaccinated group and 96 COVID-19 patients. Results: Anti-SARS-CoV-2 IgM was found positive in 23.3% of patients at 0 - 7 days after symptom onset, with seropositivity increasing to 71.7% at 15 - 21 days. Subsequently, IgM positivity gradually decreased to 62.7% at &gt; 28 days post-symptom onset. Meanwhile, anti-SARS-CoV-2 IgG was positive in 28.3% of patients at 0 -7 days, rising to 83.7% at 22 - 28 days after symptom onset, and remained constant thereafter. Anti-spike and RBD IgGs, along with NAs, were detected in 89.7%, 87.4%, and 87.9% of vaccinated individuals, respectively, and in 37.5%, 32.3%, and 32.3% of COVID-19 patients, respectively. There was a significant correlation between anti-spike IgG and anti-RBD IgG levels and NAs in both COVID-19-infected and vaccinated individuals. The mean concentrations of anti-spike and RBD IgGs were higher in vaccinated individuals with a history of COVID-19 infection compared to those without prior infection. Conclusions: The antibody profile for IgM and IgG against SARS-CoV-2 suggests that as time passes after the onset of disease symptoms, the seropositivity in COVID-19 patients increases. Furthermore, antibodies against SARS-CoV-2 are produced more efficiently through COVID-19 vaccination than natural infection.

The Mathematical Modeling of the Host-Virus Interaction in Dengue Virus Infection: A Quantitative Study.

Infectious diseases, such as Dengue fever, pose a significant public health threat. Developing a reliable mathematical model plays a crucial role in quantitatively elucidating the kinetic characteristics of antibody-virus interactions. By integrating previous models and incorporating the antibody dynamic theory, we have constructed a novel and robust model that can accurately simulate the dynamics of antibodies and viruses based on a comprehensive understanding of immunology principles. It explicitly formulates the viral clearance effect of antibodies, along with the positive feedback stimulation of virus-antibody complexes on antibody regeneration. In addition to providing quantitative insights into the dynamics of antibodies and viruses, the model exhibits a high degree of accuracy in capturing the kinetics of viruses and antibodies in Dengue fever patients. This model offers a valuable solution to modeling the differences between primary and secondary Dengue infections concerning IgM/IgG antibodies. Furthermore, it demonstrates that a faster removal rate of antibody-virus complexes might lead to a higher peak viral loading and worse clinical symptom. Moreover, it provides a reasonable explanation for the antibody-dependent enhancement of heterogeneous Dengue infections. Ultimately, this model serves as a foundation for constructing an optimal mathematical model to combat various infectious diseases in the future.

COVID-19 Seropositivity Among Adults of Tribal Origin Attending a Primary Care Centre in Wayanad Kerala- A Cross Sectional Study

Introduction: Coronavirus Disease-2019 (COVID-19) is a highly contagious viral illness caused by Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2). Serological surveys help in understanding the burden of past infections. The World Health Organisation (WHO) suggests the need for populationbased sero-epidemiological investigations to acquire data for implementing containment measures. The tribal population, being the most marginalised and vulnerable section, is at a higher risk for COVID-19. However, there is limited literature regarding the seroprevalence of COVID-19 among the tribal population in our country. Aim: To assess the COVID-19 seropositivity, associated factors, and knowledge among adults of tribal origin attending a primary care centre in Wayanad, Kerala. Materials and Methods: A cross-sectional study was conducted among 279 adults of tribal origin, aged between 18 and 95 years, attending a primary tribal healthcare centre at Amrita Institute of Medical Sciences, Kochi, Kerala, India, from August 2021 to October 2021. A semistructured questionnaire was used to collect socio-demographic details, history of COVID-19 infection, vaccination status, and participants’ knowledge and awareness about COVID-19. Antibody presence was tested using the WANTAI test kit. Data analysis was performed using Statistical Package for Social Sciences(SPSS) version 21.0 A multivariable logistic regression was conducted following univariate analysis to identify independent factors associated with COVID-19 seropositivity. Results: The mean age of the study population was 45.34±15.86 years. Among the 279 participants, the proportion of seropositivity to COVID-19 antibodies was found to be 245 (87.8%) with a 95% confidence interval (CI) of 83.98 to 91.62. Regarding knowledge and awareness related to COVID-19, 186 (66.7%) participants were not aware of the common symptoms of COVID19. Individuals aged above 60 years had a five times higher probability of having COVID-19 antibodies compared to those aged 30 years or younger (adjusted odds ratio (aOR) 4.71, 95% CI 0.111 to 20.025). Those who had received atleast one dose of the vaccine were nine times more likely to have seropositivity (aOR 8.58, 95% CI 1.390 to 53.028). Conclusion: The seropositivity of COVID-19 was high at 87.8%. Older people and vaccinated individuals were more likely to be seropositive. Therefore, it is necessary to strengthen vaccination efforts among all age groups. Continued sero-surveillance and vaccination surveys need to be conducted to gain more insights into the antibody kinetics of this novel pathogen.

Diagnosis of Imported Dengue and Zika Virus Infections in Italy from November 2015 to November 2022: Laboratory Surveillance Data from a National Reference Laboratory.

Dengue (DENV) and Zika (ZIKV) viruses are mosquito-borne human pathogens. In Italy, the presence of the competent vector Aedes albopictus increases the risk of autochthonous transmission, and a national plan for arboviruses prevention, surveillance, and response (PNA 2020-2025) is in place. The results of laboratory diagnosis of both viruses by the National Reference Laboratory for arboviruses (NRLA) from November 2015 to November 2022 are presented. Samples from 655 suspected cases were tested by both molecular and serological assays. Virus and antibody kinetics, cross-reactivity, and diagnostic performance of IgM ELISA systems were analysed. Of 524 cases tested for DENV, 146 were classified as confirmed, 7 as probable, while 371 were excluded. Of 619 cases tested for ZIKV, 44 were classified as confirmed, while 492 were excluded. All cases were imported. Overall, 75.3% (110/146) of DENV and 50% (22/44) of ZIKV cases were confirmed through direct virus detection methods. High percentages of cross reactivity were observed between the two viruses. The median lag time from symptoms onset to sample collection was 7 days for both DENV molecular (range 0-20) and NS1 ELISA (range 0-48) tests, with high percentages of positivity also after 7 days (39% and 67%, respectively). For ZIKV, the median lag time was 5 days (range 0-22), with 16% positivity after 7 days. Diagnostic performance was assessed with negative predictive values ranging from 92% to 95% for the anti-DENV systems, and of 97% for the ZIKV one. Lower positive predictive values were seen in the tested population (DENV: 55% to 91%, ZIKV: 50%). DENV and ZIKV diagnosis by molecular test is the gold standard, but sample collection time is a limitation. Serological tests, including Plaque Reduction Neutralization Test, are thus necessary. Co-circulation and cross-reactivity between the two viruses increase diagnostic difficulty. Continuous evaluation of diagnostic strategies is essential to improve laboratory testing.

Antibody Profiling: Kinetics with Native Biomarkers for Diagnostic Assay and Drug Developments.

Despite remarkable progress in applied Surface Plasmon Resonance (SPR)-based methods, concise monitoring of kinetic properties for native biomarkers from patient samples is still lacking. Not only are low concentrations of native targets in patient samples, often in the pM range, a limiting and challenging factor, but body fluids as complex matrices furthermore complicate measurements. The here-described method enables the determination of kinetic constants and resulting affinities for native antigens from patients' cerebrospinal fluid (CSF) and sera binding to antibodies. Using a significantly extended target-enrichment step, we modified a common sandwich-assay protocol, based on a primary and secondary antibody. We successfully analyze antibody kinetics of native targets from a variety of origins, with consistent results, independent of their source. Moreover, native neurofilament light chain (NFL) was investigated as an exemplary biomarker. Obtained data reveal antibodies recognizing recombinant NFL with high affinities, while showing no, or only significantly weakened binding to native NFL. The indicated differences for recombinant vs. native material demonstrate another beneficial application. Our assay is highly suitable for gaining valuable insights into characteristics of native biomarkers, thus impacting on the binder development of diagnostic reagents or pharmaceutical drugs.

Screening, Expression and Identification of Nanobody Against Monkeypox Virus A35R.

The monkeypox (Mpox) virus epidemic presents a significant risk to global public health security. A35R, a crucial constituent of EEV, plays a pivotal role in virus transmission, serves as a vital target for vaccine development, and has potential for serological detection. Currently, there is a dearth of research on nanobodies targeting A35R. The purpose of this study is to identify specific nanobodies target A35R, so as to provide new antibody candidates for Mpox vaccine development and diagnostic kit development. Three nanobodies specific to the monkeypox virus protein A35R were screened from a naïve phage display library. After four rounds of panning, positive phage clones were identified by enzyme-linked immunosorbent assay (ELISA). Further, the nanobody fusion protein was constructed in pNFCG1-IgG1-Fc vector and expressed in HEK293F cells and purified by affinity chromatography. The specificity and affinity of the nanobodies were identified by ELISA. The binding kinetics of the VHH antibody to A35R were assessed via employment of a bio-layer interferometry (BLI) apparatus, thereby determining the nanobodies affinity. The three purified nanobodies showed specific high-affinity binding MPXV A35R, of them, VHH-1 had the best antigen binding affinity (EC50 = 0.010 ug/mL). In addition, VHH-1 on Protein A biosensor can bind Mpox virus A35R, with an affinity constant of 54 nM as determined in BLI assay. In sum, we has obtained three nanobody strains against Mpox virus A35R with significant affinity and specificity, therefore laying an essential foundation for further research as well as the applications of diagnostic and therapeutic tools of Mpox virus.

Tafasitamab in Combination with a CD20xCD3 Bispecific T-Cell Engager Significantly Prolongs Survival in Preclinical Lymphoma Models

R-CHOP remains the standard of care for newly diagnosed DLBCL patients. However, 30-40% of patients are refractory or relapse after initial response to the immunochemotherapy, indicating a high-unmet medical need for these patients. Tafasitamab is a CD19-targeting, Fc-modified humanized monoclonal antibody mediating antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP) and direct cytotoxicity. Tafasitamab was granted accelerated approval by the FDA in 2020 and conditional marketing authorization by the EMA in 2021 for the treatment of transplant-ineligible adult patients with relapsed or refractory (R/R) DLBCL in combination with the immunomodulatory drug lenalidomide. CD20xCD3 T-cell engagers are currently under clinical investigation or recently received FDA approval in 2L+ DLBCL (Thieblemont 2023; Dickinson 2022). CD19- and CD20-targeting antibodies might complement each other, as I) CD19 could compensate for CD20-low/ -negative settings and vice versa and II) monoclonal antibodies and T-cell engagers combine powerful and distinct immune pathways holding great potential to increase responses in patients who may need additional therapeutic options. The aim of this study was to investigate the combination of tafasitamab and MOR212, a proprietary proof-of-concept CD20xCD3 T-cell engaging antibody, in preclinical models of lymphoma. First, MOR212 was characterized in vitro and in vivo to ensure comparability with other CD20xCD3 bispecific antibodies (comp1-3) currently under clinical investigation. In in vitro cytotoxicity assays, MOR212 demonstrated similar (comp1-2), or improved (comp3) cytotoxicity (MOR212 vs comp1 and 2 p&amp;gt;0.05 vs comp3 p=0.03; exemplary data for EC50 in SU-DHL-4 cells; n=6), cytokine secretion (MOR212 vs comp1-3 p&amp;gt;0.05; exemplary data for EC50 TNFα; n=4) and T-cell activation (MOR212 vs comp1 p=0.05; vs comp2 p&amp;gt;0.05 vs comp3 p=0.003; exemplary data for % CD69 on CD8 T-cells; n=6) in cell lines expressing different levels of CD20. In a lymphoma in vivo model co-engrafted with human T-cells, MOR212 prolonged progression-free survival of mice to a similar extent as two comparator molecules that were tested head-to-head (MOR212 vs comp1 and 3 p&amp;gt;0.05;) at a dose of 0.1 mg/kg. Next, we investigated the combination of tafasitamab and MOR212 in vitro. Due to the differential killing kinetics of a monoclonal antibody and a T-cell engager, we made use of a real time live-cell imaging assay. Lymphoma cells were co-cultured with healthy donor peripheral blood mononuclear cells (PBMCs) and tafasitamab and MOR212 were added in different concentration combinations. Tumor cell killing was monitored every 3 hours for 72 hours and revealed improved target cell killing by the combination of both compounds (signal/background caspase 3/7 staining at 48h: MOR212 24.2 vs tafasitamab 28.2 vs MOR212+tafasitamab 111.5; n=1). To confirm these findings in vivo, we used human CD34+ engrafted NCG mice with a huIL15 boost allowing for the development of human T-cells as well as NK-cells, as essential effector cells for the combination of both compounds. Raji lymphoma cells were engrafted and treatment with the single or combination therapy was started once tumors reached a pulpable size. Combination of tafasitamab and MOR212 significantly improved progression-free survival in animals compared to monotherapy treatment (tafasitamab+MOR212 vs tafasitamab only p=0.0002 and MOR212 only p=0.0098). In addition, the combined treatment regimen appeared to be safe in mice as no side effects on both body weight loss and clinical score were recorded throughout the entire observation period. Our findings prove that the combination of tafasitamab and a CD20xCD3 T-cell engaging antibody significantly increases tumor cell eradication both in vitro and in vivo and lay the ground to potentially translate the results into improved outcome for patients with aggressive lymphoma in future clinical trials.

Diagnostic challenges and antibody kinetics in a paediatric traveller with scrub typhus.

Diagnosing scrub typhus in travellers is challenging due to symptom similarities with other travel-related illnesses and limited early diagnostic tools. We present a distinctive case of scrub typhus in a child traveller, providing a comprehensive account of the case, the diagnostic challenges encountered, laboratory findings, and the dynamics of antibodies.

A longitudinal study of Middle East respiratory syndrome coronavirus (MERS-CoV) in dromedary camels

BackgroundMiddle East respiratory syndrome coronavirus (MERS-CoV) was identified in humans in 2012. Since then, 2605 cases and 937 associated deaths have been reported globally. Camels are the natural host for MERS-CoV and camel to human transmission has been documented. The relationship between MERS-CoV shedding and presence of neutralizing antibodies in camels is critical to inform surveillance and control, including future deployment of camel vaccines. However, it remains poorly understood. The longitudinal study conducted in a closed camel herd in Egypt between December 2019 and March 2020 helped to characterize the kinetics of MERS-CoV neutralizing antibodies and its relation with viral shedding.ResultsDuring the 100-day longitudinal study, 27 out of 54 camels (50%) consistently tested negative for presence of antibodies against MERS-CoV, 19 (35.2%) tested positive and 8 (14.8%) had both, positive and negative test results. Fourteen events that could be interpreted as serological indication of probable infection (two seroconversions and twelve instances of positive camels more than doubling their optical density ratio (OD ratio) in consecutive samples) were identified. Observed times between the identified events provided strong evidence (p = 0.002) against the null hypothesis that they occurred with constant rate during the study, as opposed to clustering at certain points in time. A generalized additive model showed that optical density ratio (OD ratio) is positively associated with being an adult and varies across individual camels and days, peaking at around days 20 and 90 of the study. Despite serological indication of probable virus circulation and intense repeated sampling, none of the tested nasal swab samples were positive for MERS-CoV RNA, suggesting that, if the identified serological responses are the result of virus circulation, the virus may be present in nasal tissue of infected camels during a very narrow time window.ConclusionsLongitudinal testing of a closed camel herd with past history of MERS-CoV infection is compatible with the virus continuing to circulate in the herd despite lack of contact with other camels. It is likely that episodes of MERS-CoV infection in camels can take place with minimal presence of the virus in their nasal tissues, which has important implications for future surveillance and control of MERS-CoV in camel herds and prevention of its zoonotic transmission.

Fractional Dosing of Yellow Fever Live Attenuated 17D Vaccine: A Perspective.

Yellow fever virus (YFV) is a mosquito-borne flavivirus that causes over 109,000 severe infections and over 51,000 deaths annually in endemic areas of sub-Saharan Africa and tropical South America. The virus has a transmission cycle involving mosquitoes and humans or non-human primates (NHPs) as the vertebrate hosts. Although yellow fever (YF) is prevented by a live attenuated vaccine (strain 17D), recent epidemics in Angola, the Democratic Republic of the Congo (DRC), and Brazil put great pressure on vaccine stockpiles. This resulted in the World Health Organization (WHO) and Pan American Health Organization (PAHO) implementing, on an emergency basis only, off-label dose-sparing techniques and policies during 2016-2018 to protect as many people in DRC and Brazil as possible from disease during unexpected large outbreaks of YF. Subsequently non-inferiority studies involving full doses compared to fractional doses indicated promising results, leading some policy-makers and scientists to consider utilizing YF vaccine fractional doses in non-emergency scenarios. Although the additional data on the immunogenicity and safety of fractional doses are promising, there are several questions and considerations that remain regarding the use of fractional doses, including differences in the initial antibody kinetics, differences in the immune response in certain populations, and durability of the immune response to fractional doses compared to full doses. Until the remaining knowledge gaps are addressed, full doses instead of fractional doses should continue to be used unless there are insufficient doses of the vaccine available to control outbreaks of YF.

Assessing the post hoc effectiveness of tixagevimab-cilgavimab for prevention of SARS-CoV-2 infections in solid organ transplant recipients.

Tixagevimab-cilgavimab (Tix-Cil) was authorized for prophylaxis against COVID-19 in immunocompromised patients from December 2021 through January 2023. Real-world effectiveness for solid organ transplant (SOT) recipients has been unclear. We enrolled 911 SOT recipients into a longitudinal COVID-19 serology study, of whom 381 (42%) received ≥1 dose of Tix-Cil. We collected and analyzed data on incident SARS-CoV-2 infections and antibody kinetics for all patients from January 2022 to March 2023, including periods dominated by Omicron BA and BQ subvariants. Over 253 ± 131 days of follow-up, there were 324 new-onset SARS-CoV-2 infections: 117 (31%) in Tix-Cil treated and 207 (39%) in Tix-Cil untreated patients (p = .012). In analyses adjusting for demographic, clinical, and COVID-19 exposure factors, any Tix-Cil treatment was associated with lower infection risk (OR 0.52, 95% CI 0.27-0.96, p = .039) throughout the surveillance period including when more resistant BQ.1 and BQ.1.1 subvariants had emerged (12/1/2022 onwards). Among treated patients, receiving a Tix-Cil dose was associated with substantial and sustained increase in anti-spike IgG antibody and angiotensin-converting enzyme 2 binding inhibition levels (Abbott Architect assay) that together also demonstrated association with lower infection risk (p = .042). During the full surveillance period, the frequency of infections requiring hospitalization was low overall (N = 26, 2.9% of the total cohort) and not significantly different between Tix-Cil recipients (N = 12, 3.2% of treated patients) and non-Tix-Cil recipients (N = 14, 2.6% of untreated patients) with unadjusted p = .31 for between-group difference. In a large cohort of SOT recipients, we found that Tix-Cil reduced infection risk even amidst emergent Omicron subvariants. Additionally, the extent of measurable humoral response to Tix-Cil may indicate relative effectiveness. Pre-exposure monoclonal antibody therapy may represent a strategy that will continue to offer clinical benefit for immunocompromised persons who are known to derive limited protection from vaccinations.

WITHDRAWN: Development of a double-antigen sandwich ELISA for African swine fever virus antibody detection based on K205R protein

African swine fever (ASF) is a highly fatal infectious disease that affects swine caused by the African swine fever virus (ASFV) and poses a significant threat to the swine industry, and its effective diagnosis is crucial due to the current lack of commercially available vaccine for disease prevention and control. In this regard, the K205R protein is a suitable diagnostic antigen for enzyme-linked immunosorbent assay (ELISA) owing to its continuous expression throughout all ASFV replication stages, high immunogenicity, and sequence conservation. The double-antigen sandwich ELISA (DAgS-ELISA) is capable of detecting all immunoglobulins present in the serum, and outperforms alternative methods by enabling earlier antibody detection. Therefore, in this study, the K205R protein was prokaryotically expressed, and the K205R protein digested His-tag was labeled with horseradish peroxidase (HRP) and named K205R-HRP. The DAgS-ELISA was conducted using a combination of digested His-tag proteins and K205R-HRP. This method exhibits exceptional properties, including high sensitivity and no cross-reactivity with other porcine antibodies, with both the intra- and inter-assay coefficients of variation (CV) below 10 %. Antibody kinetics experiments have demonstrated that this method is capable of detecting antibodies as early as 7 to 9 days post-infection, which is a significant improvement compared to the commercial kit that can only detect antibodies from 11 to 13 days post-infection. In 120 clinical serum tests, the Kappa value between the DAgS-ELISA and the commercial kit was 0.96 (almost perfect). Owing to its high sensitivity, impressive repeatability, and strong specificity, this method enables earlier antibody detection and is suitable for ASFV antibody testing.

Vaccine-induced SARS-CoV-2 antibody response: the comparability of S1-specific binding assays depends on epitope and isotype discrimination.

Quantification of the SARS-CoV-2-specific immune response by serological immunoassays is critical for the management of the COVID-19 pandemic. In particular, neutralizing antibody titers to the viral spike (S) protein have been proposed as a correlate of protection (CoP). The WHO established the First International Standard (WHO IS) for anti-SARS-CoV-2 immunoglobulin (Ig) (NIBSC 20/136) to harmonize binding assays with the same antigen specificity by assigning the same unitage in binding antibody units (BAU)/ml. In this study, we analyzed the S1-specific antibody response in a cohort of healthcare workers in Germany (n = 76) during a three-dose vaccination course over 8.5 months. Subjects received either heterologous or homologous prime-boost vaccination with ChAdOx1 nCoV-19 (AstraZeneca) and BNT162b2 (Pfizer-BioNTech) or three doses of BNT162b2. Antibodies were quantified using three anti-S1 binding assays (ELISA, ECLIA, and PETIA) harmonized to the WHO IS. Serum levels of neutralizing antibodies were determined using a surrogate virus neutralization test (sVNT). Binding assays were compared using Spearman's rank correlation and Passing-Bablok regression. All assays showed good correlation and similar antibody kinetics correlating with neutralizing potential. However, the assays show large proportional differences in BAU/ml. ECLIA and PETIA, which detect total antibodies against the receptor- binding domain (RBD) within the S1 subunit, interact similarly with the convalescent plasma-derived WHO IS but differently with vaccine serum, indicating a high sensitivity to the IgG/IgM/IgA ratio. All three binding assays allow monitoring of the antibody response in COVID-19-vaccinated individuals. However, the assay-specific differences hinder the definition of a common protective threshold in BAU/ml. Our results highlight the need for the thoughtful use of conversion factors and consideration of method-specific differences. To improve the management of future pandemics and harmonize total antibody assays, we should strive for reference material with a well-characterized Ig isotype composition.

The impact of IdeS (imlifidase) on allo-specific, xeno-reactive, and protective antibodies in a sensitized rhesus macaque model.

Highly sensitized patients face many barriers to kidney transplantation, including higher rates of antibody-mediated rejection after HLA-incompatible transplant. IdeS, an endopeptidase that cleaves IgG nonspecifically, has been trialed as desensitization prior to kidney transplant, and successfully cleaves donor-specific antibody (DSA), albeit with rebound. IdeS was generated and tested (2mg/kg, IV) in two naïve and four allosensitized nonhuman primates (NHP). Peripheral blood samples were collected at regular intervals following IdeS administration. Total IgG, total IgM, and anti-CMV antibodies were quantified with ELISA, and donor-specific antibody (DSA) and anti-pig antibodies were evaluated using flow cytometric crossmatch. B cell populations were assessed using flow cytometry. IdeS successfully cleaved rhesus IgG in vitro. In allosensitized NHP, robust reduction of total, DSA, anti-pig, and anti-CMV IgG was observed within one day following IdeS administration. Rapid rebound of all IgG antibody populations was observed, with antibody levels returning to baseline around day 14 post-infusion. Total IgM level was not affected by IdeS. Interestingly, a comparable reduction in antibody populations was observed after the second dose of IdeS. However, we have not observed any significant modulation of B cell subpopulations after IdeS. This study evaluated efficacy of IdeS in the allosensitized NHP in IgG with various specificities, mirroring antibody kinetics in human patients. The efficacy of IdeS on preexisting anti-pig antibodies may be useful in clinical xenotransplantation. However, given the limitation of IdeS on its durability as a monotherapy, optimization of IdeS with other agents targeting the humoral response is further needed.

Neutralizing Antibody Levels as a Correlate of Protection Against SARS-CoV-2 Infection: AModeling Analysis.

Although anti-severe acute respiratory syndrome-coronavirus 2 antibody kinetics have been described in large populations of vaccinated individuals, we still poorly understand how they evolve during a natural infection and how this impacts viral clearance. For that purpose, we analyzed the kinetics of both viral load and neutralizing antibody levels in a prospective cohort of individuals during acute infection with alpha variant. Using a mathematical model, we show that the progressive increase in neutralizing antibodies leads to a shortening of the half-life of both infected cells and infectious viral particles. We estimated that the neutralizing activity reached 90% of its maximal level within 11 days after symptom onset and could reduce the half-life of both infected cells and circulating virus by a 6-fold factor, thus playing a key role to achieve rapid viral clearance. Using this model, we conducted a simulation study to predict in a more general context the protection conferred by pre-existing neutralization titers, due to either vaccination or prior infection. We predicted that a neutralizing activity, as measured by 50% effective dose > 103 , could reduce by 46% the risk of having viral load detectable by standard polymerase chain reaction assays and by 98% the risk of having viral load above the threshold of infectiousness. Our model shows that neutralizing activity could be used to define correlates of protection against infection and transmission.

Twenty-Month Monitoring of Humoral Immune Response to BNT162b2 Vaccine: Antibody Kinetics, Breakthrough Infections, and Adverse Effects.

Vaccination is one of the most effective life-saving medical interventions, and the introduction of SARS-CoV-2 vaccines was intended to prevent the serious implications of COVID-19. The objectives of the study were (i) to observe the humoral immune response to the BNT162b2 vaccine and SARS-CoV-2 infection (mainly breakthrough infections), (ii) to demonstrate the persistence of anti-SARS-CoV-2 antibodies over time in relation to the number of received vaccine doses and the course of infection, and (iii) to determine the adverse effects after primary vaccine doses. To assess the humoral response, IgG and IgA anti-S1 antibodies were quantified by ELISA assays. In total, the tests were carried out seven times in almost two years. We demonstrated strong immunogenicity (compared to levels before primary vaccination, 150- and 20-fold increases in IgG and IgA, respectively) of the BNT162b2 vaccine. Over time, we observed a systematic decline in antibody levels, which may have contributed to breakthrough infections. Although they caused seroconversion similar to the booster, antibody levels in such patients fell more rapidly than after re-vaccination. On the other hand, in individuals who did not receive booster(s) and who did not present breakthrough infection, anti-SARS-CoV-2 antibodies returned to pre-vaccination levels after 20 months. The most commonly recognized adverse effects were injection site redness and swelling. Vaccination is highly effective in preventing the most severe outcomes of COVID-19 and should be performed regardless of prior infection. Booster doses significantly enhance anti-SARS-CoV-2 antibody levels and, in contrast to those obtained by breakthrough infection, they remain longer.

Bartonella infections are prevalent in rodents despite efficient immune responses

BackgroundPathogens face strong selection from host immune responses, yet many host populations support pervasive pathogen populations. We investigated this puzzle in a model system of Bartonella and rodents from Israel’s northwestern Negev Desert. We chose to study this system because, in this region, 75–100% of rodents are infected with Bartonella at any given time, despite an efficient immunological response. In this region, Bartonella species circulate in three rodent species, and we tested the hypothesis that at least one of these hosts exhibits a waning immune response to Bartonella, which allows reinfections.MethodsWe inoculated captive animals of all three rodent species with the same Bartonella strain, and we quantified the bacterial dynamics and Bartonella-specific immunoglobulin G antibody kinetics over a period of 139 days after the primary inoculation, and then for 60 days following reinoculation with the same strain.ResultsContrary to our hypothesis, we found a strong, long-lasting immunoglobulin G antibody response, with protective immunological memory in all three rodent species. That response prevented reinfection upon exposure of the rodents to the same Bartonella strain.ConclusionsThis study constitutes an initial step toward understanding how the interplay between traits of Bartonella and their hosts influences the epidemiological dynamics of these pathogens in nature.Graphical

P-378 Longitudinal antibody and T-cell kinetics over four doses of COVID-19 vaccination and predictors of poor response in patients with multiple myeloma

P-378 Longitudinal antibody and T-cell kinetics over four doses of COVID-19 vaccination and predictors of poor response in patients with multiple myeloma