Cohort-specific serological recognition of SARS-CoV-2 variant RBD antigens

Background: Estimating the response of different cohorts (e.g. vaccinated or critically ill) to new SARS-CoV-2 variants is important to customize measures of control. Thus, our goal was to evaluate binding of antibodies from sera of infected and vaccinated people to different antigens expressed by SARS-CoV-2 variants. Methods: We compared sera from vaccinated donors with sera from four patient/donor cohorts: critically ill patients admitted to an intensive care unit (split in sera collected between 2 and 7 days after admission and more than ten days later), a NIBSC/WHO reference panel of SARS-CoV-2 positive individuals, and ambulatory or hospitalized (but not critically ill) positive donors. Samples were tested with an anti-SARS-CoV-2 IgG serological assay designed with microplates coated with a SARS-CoV-2 RBD recombinant antigen. The same sample sets were also tested with microplates coated with antigens harbouring RBD mutations present in eleven of the most widespread variants. Results: Sera from vaccinated individuals exhibited higher antibody binding (P<0.001) than sera from infected (but not critically ill) individuals when tested against the WT and each of 11 variants' RBD. The optical density generated by sera from non-critically ill convalescence individuals upon binding to variant's antigens was different (P<0.05) from that of the WT in some variants-noteworthy, Beta, Gamma, Delta, and Delta Plus variants. Conclusions: Understanding differences in binding and neutralizing antibody titers against WT vs variant RBD antigens from different donor cohorts can help design variant-specific immunoassays and complement other diagnostic and clinical data to evaluate the epidemiology of new variants. Key Words: COVID-19; SARS-CoV-2 vaccine; SARS-CoV-2 variants; RBD mutations; antibody specificity; critically ill, immunoassays, serology.

Obtaining Specific Hybridomas for Ki-67 Protein Immunodetection

BACKGROUND: Active proliferation is specific property of a tumor cells. However, the cost of the analysis is high due to commercial anti-Ki-67 mAbs used as the main immunoreagent for reliable identification of proliferating cells. In this study, recombinant protein was used to obtain specific mAbs for Ki-67 biomarker immunodetection.METHODS: Codon optimized fragment of ki-67 gene was cloned into the pET28c(+)vector. The recombinant protein was purified by immobilized metal affinity chromatography (IMAC) and confirmed by liquid chromatography–mass spectrometry (LC-MS)/MS. Hybridoma cells were obtained by fusing myeloma cells with mouse spleen cells immunized with recombinant antigen. The specificity and activity of mAbs was determined by enzyme-linked immunosorbent assay (ELISA), Western blot and immunocytochemistry.RESULTS: The pET-28c(+)/ki-67 plasmid, which encodes 355 amino acid protein, was obtained. Analysis by LC-MS/MS of the recombinant antigen showed that 77.5% of the amino-acid sequence belonged to Ki-67 protein. Recombinant fragment of Ki-67 protein was used to obtain specific hybridoma strains. ELISA and Western blot demonstrated high affinity and the specificity of obtained mAbs against Ki-67 protein. Newly generated anti-Ki67 mAbs detected target protein in proliferating cells of MCF-7 cell line by immunocytochemistry.CONCLUSION: Newly developed mAbs are potentially useful as an immunodiagnostic tool for assessing the proliferative activity of breast tumor cells using immunocytochemistry.KEYWORDS: breast cancer, Ki-67, monoclonal antibodies, nuclear antigen, recombinant antigen, tumor cells

Radiolabeling Strategies of Nanobodies for Imaging Applications

Nanobodies are small recombinant antigen-binding fragments derived from camelid heavy-chain only antibodies. Due to their compact structure, pharmacokinetics of nanobodies are favorable compared to full-size antibodies, allowing rapid accumulation to their targets after intravenous administration, while unbound molecules are quickly cleared from the circulation. In consequence, high signal-to-background ratios can be achieved, rendering radiolabeled nanobodies high-potential candidates for imaging applications in oncology, immunology and specific diseases, for instance in the cardiovascular system. In this review, a comprehensive overview of central aspects of nanobody functionalization and radiolabeling strategies is provided.

Antigenic Characterization of ORF2 and ORF3 Proteins of Hepatitis E Virus (HEV)

To evaluate the antigenic properties of Hepatitis E Virus (HEV) Open Reading Frame 2 and 3 (ORF2 and ORF3) codified proteins, we expressed different portions of ORF2 and the entire ORF3 in E. coli, a truncated ORF2, was also expressed in baculovirus. A panel of 37 monoclonal antibodies (MAbs) was raised against ORF2 (1–660 amino acids) and MAbs were mapped and characterized using the ORF2 expressed portions. Selected HEV positive and negative swine sera were used to evaluate ORF2 and ORF3 antigens’ immunogenicity. The MAbs were clustered in six groups identifying six antigenic regions along the ORF2. Only MAbs binding to the sixth ORF2 antigenic region (394–608 aa) were found to compete with HEV positive sera and efficiently catch the recombinant antigen expressed in baculovirus. The ORF2 portion from 394–608 aa demonstrated to include most immunogenic epitopes with 85% of HEV positive swine sera reacting against the region from 461–544 aa. Only 5% of the selected HEV sera reacted against the ORF3 antigen.

Spatial Distribution and Burden of Emerging Arboviruses in French Guiana

Despite the health, social and economic impact of arboviruses in French Guiana, very little is known about the extent to which infection burden is shared between individuals. We conducted a large multiplexed serological survey among 2697 individuals from June to October 2017. All serum samples were tested for IgG antibodies against DENV, CHIKV, ZIKV and MAYV using a recombinant antigen-based microsphere immunoassay with a subset further evaluated through anti-ZIKV microneutralization tests. The overall DENV seroprevalence was estimated at 73.1% (70.6–75.4) in the whole territory with estimations by serotype at 68.9% for DENV-1, 38.8% for DENV-2, 42.3% for DENV-3, and 56.1% for DENV-4. The overall seroprevalence of CHIKV, ZIKV and MAYV antibodies was 20.3% (17.7–23.1), 23.3% (20.9–25.9) and 3.3% (2.7–4.1), respectively. We provide a consistent overview of the burden of emerging arboviruses in French Guiana, with useful findings for risk mapping, future prevention and control programs. The majority of the population remains susceptible to CHIKV and ZIKV, which could potentially facilitate the risk of further re-emergences. Our results underscore the need to strengthen MAYV surveillance in order to rapidly detect any substantial changes in MAYV circulation patterns.

Development of rSs-NIE-1 and rSs-IR Recombinant Antigen-Based Immunoblot for Detection of Antibody to Strongyloides stercoralis

Strongyloides stercoralis is a soil-transmitted nematode that can cause life-threatening conditions in immunocompromised persons. In the United States, strongyloidiasis should be considered mainly in immigrants, refugees, or travelers. The confirmatory laboratory diagnosis is usually performed by detecting larvae from the stool, duodenal material, and sputum. In persons who are immunocompromised with severe strongyloidiasis, adult worms and eggs can be detected from duodenal material. For serological diagnosis, most assays use crude antigens to detect anti-S. stercoralis IgG. Recently, recombinant proteins such as rSs-NIE-1 and rSs-IR have been used to detect IgG antibodies. We used rSs-NIE-1 and rSs-IR recombinant antigens to develop a biplex Western blot assay to detect the IgG4 antibody in individuals with strongyloidiasis. The sensitivities of rSs-NIE-1 and rSs-IR were 97.4% and 90.8%, respectively, whereas the specificities were 97.6% and 98%, respectively. In conclusion, the biplex rSs-NIE-1 and rSs-IR immunoblot performs well in detecting IgG4 antibody in S. stercoralis-infected persons.