Production and characterisation of a SARS-CoV-2 S-protein RBD homodimer with increased avidity for specific antibodies

Monitoring of the proportion of immune individuals and the effectiveness of vaccination in a population involves evaluation of several important parameters, including the level of virus-neutralising antibodies. In order to combat the COVID-19 pandemic, it is essential to develop approaches to detecting SARS-CoV-2 neutralising antibodies by safe, simple and rapid methods that do not require live viruses. To develop a test system for enzyme-linked immunosorbent assay (ELISA) that detects potential neutralising antibodies, it is necessary to obtain a highly purified recombinant receptor-binding domain (RBD) of the spike (S) protein with high avidity for specific antibodies.The aim of the study was to obtain and characterise a SARS-CoV-2 S-protein RBD homodimer and a recombinant RBD-expressing cell line, as well as to create an ELISA system for detecting potential neutralising antibodies.Materials and methods: the genetic construct was designed in silico. To generate a stable producer cell line, the authors transfected CHO-S cells, subjected them to antibiotic pressure, and selected the optimal clone. To isolate monomeric and homodimeric RBD forms, the authors purified the recombinant RBD by chromatographic methods. Further, they analysed the activity of the RBD forms by Western blotting, bio-layer interferometry, and indirect ELISA. The analysis involved mono clonal antibodies GamXRH19, GamP2C5, and h6g3, as well as serum samples from volunteers vaccinated with Gam-COVID-Vac (Sputnik V) and unvaccinated ones.Results: the authors produced the CHO-S cell line for stable expression of the recombinant SARS-CoV-2 S-protein RBD. The study demonstrated the recombinant RBD’s ability to homodimerise after fed-batch cultivation of the cell line for more than 7 days due to the presence of unpaired cysteines. The purified recombinant RBD yield from culture broth was 30–50 mg/L. Monomeric and homodimeric RBD forms were separated using gel-filtration chromatography and characterised by their ability to interact with specific monoclonal antibodies, as well as with serum samples from vaccinated volunteers. The homodimeric recombinant RBD showed increased avidity for both monoclonal and immune sera antibodies.Conclusions: the homodimeric recombinant RBD may be more preferable for the analysis of levels of antibodies to the receptor-binding domain of the SARS-CoV-2 S protein

Получение и характеристика гомодимерной формы RBD S-белка SARS-CoV-2, обладающей повышенной авидностью к специфическим антителам

Monitoring of the proportion of immune individuals and the effectiveness of vaccination in a population involves evaluation of several important parameters, including the level of virus-neutralising antibodies. In order to combat the COVID-19 pandemic, it is essential to develop approaches to detecting SARS-CoV-2 neutralising antibodies by safe, simple and rapid methods that do not require live viruses. To develop a test system for enzyme-linked immunosorbent assay (ELISA) that detects potential neutralising antibodies, it is necessary to obtain a highly purified recombinant receptor-binding domain (RBD) of the spike (S) protein with high avidity for specific antibodies. The aim of the study w as t o obtain and characterise a SARSCoV-2 S-protein RBD homodimer and a recombinant RBD-expressing cell line, as well as to create an ELISA system for detecting potential neutralising antibodies. Materials and methods: the genetic construct was designed in silico. To generate a stable producer cell line, the authors transfected CHO-S cells, subjected them to antibiotic pressure, and selected the optimal clone. To isolate monomeric and homodimeric RBD forms, the authors purified the recombinant RBD by chromatographic methods. Further, they analysed the activity of the RBD forms by Western blotting, bio-layer interferometry, and indirect ELISA. The analysis involved monoclonal antibodies GamXRH19, GamP2C5, and h6g3, as well as serum samples from volunteers vaccinated with Gam-COVID-Vac (Sputnik V) and unvaccinated ones. Results: the authors produced the CHO-S cell line for stable expression of the recombinant SARS-CoV-2 S-protein RBD. The study demonstrated the recombinant RBD’s ability to homodimerise after fed-batch cultivation of the cell line for more than 7 days due to the presence of unpaired cysteines. The purified recombinant RBD yield from culture broth was 30–50 mg/L. Monomeric and homodimeric RBD forms were separated using gel-filtration chromatography and characterised by their ability to interact with specific monoclonal antibodies, as well as with serum samples from vaccinated volunteers. The homodimeric recombinant RBD showed increased avidity for both monoclonal and immune sera antibodies. Conclusions: the homodimeric recombinant RBD may be more preferable for the analysis of levels of antibodies to the receptor-binding domain of the SARS-CoV-2 S protein.Важным параметром, оцениваемым при мониторинге иммунной прослойки у населения и эффективности вакцинации населения, является уровень вируснейтрализующих антител. Разработка подхода к выявлению вируснейтрализующих антител к вирусу SARS-CoV-2 с помощью безопасного, простого и быстрого метода, не требующего использования живых вирусов, имеет большое значение для борьбы с пандемией COVID-19. Для разработки тест-систем для проведения иммуноферментного анализа (ИФА), детектирующих потенциально вируснейтрализующие антитела, необходимо получение высокоочищенного рекомбинантного рецептор-связывающего домена (RBD) S-белка, обладающего высокой авидностью к специфическим антителам. Цель работы: получение и характеристика гомодимерной формы RBD S-белка вируса SARS-CoV-2, а также клеточной линии, продуцирующей рекомбинантный RBD, для создания ИФА тест-системы для выявления потенциально вируснейтрализующих антител. Материалы и методы: дизайн генетической конструкции проводили in silico. Стабильную клеточную линию получали при помощи трансфекции клеток CHO-S, селекции на антибиотике и отбора оптимального клона. Рекомбинантный RBD очищали с использованием хроматографических методов, получали мономерную и гомодимерную формы RBD. Активность полученных форм анализировали с использованием методов Вестерн-блот, биослойной интерферометрии и непрямго ИФА. Для анализа использовали моноклональные антитела GamXRH19, GamP2C5 и h6g3, а также образцы сывороток крови добровольцев, вакцинированных препаратом Гам-КОВИД-Вак, и невакцинированных добровольцев. Результаты: получена клеточная линия CHO-S, стабильно продуцирующая рекомбинантный RBD S-белка вируса SARS-CoV-2. Показано, что при культивировании данной клеточной линии в режиме fed-batch более 7 суток рекомбинантный RBD способен образовывать гомодимеры за счет наличия неспаренных цистеинов. Количественный выход очищенного рекомбинантного RBD из культуральной жидкости составил 30–50 мг/л. Мономерная и гомодимерная формы RBD были разделены при помощи гель-фильтрации и охарактеризованы по способности взаимодействовать со специфическими моноклональными антителами, а также сыворотками крови от вакцинированных добровольцев. Продемонстрировано, что именно гомодимерная форма рекомбинантного RBD обладает повышенной авидностью к моноклональным антителам и антителам в сыворотке крови вакцинированных. Выводы: гомодимерная форма рекомбинантного RBD может являться более предпочтительной для анализа уровня антител к рецептор-связывающему домену S-белка вируса SARS-CoV-2

rAAV expressing recombinant antibody for emergency prevention and long-term prophylaxis of COVID-19

IntroductionNumerous agents for prophylaxis of SARS-CoV-2-induced diseases are currently registered for the clinical use. Formation of the immunity happens within several weeks following vaccine administration which is their key disadvantage. In contrast, drugs based on monoclonal antibodies, enable rapid passive immunization and therefore can be used for emergency pre- and post-exposure prophylaxis of COVID-19. However rapid elimination of antibody-based drugs from the circulation limits their usage for prolonged pre-exposure prophylaxis.MethodsIn current work we developed a recombinant adeno-associated viral vector (rAAV), expressing a SARS-CoV-2 spike receptor-binding domain (RBD)-specific antibody P2C5 fused with a human IgG1 Fc fragment (P2C5-Fc) using methods of molecular biotechnology and bioprocessing.Results and discussionsA P2C5-Fc antibody expressed by a proposed rAAV (rAAV-P2C5-Fc) was shown to circulate within more than 300 days in blood of transduced mice and protect animals from lethal SARS-CoV-2 virus (B.1.1.1 and Omicron BA.5 variants) lethal dose of 105 TCID50. In addition, rAAV-P2C5-Fc demonstrated 100% protective activity as emergency prevention and long-term prophylaxis, respectively. It was also demonstrated that high titers of neutralizing antibodies to the SARS-CoV-2 virus were detected in the blood serum of animals that received rAAV-P2C5-Fc for more than 10 months from the moment of administration.Our data therefore indicate applicability of an rAAV for passive immunization and induction of a rapid long-term protection against various SARS-CoV-2 variants

Safety and immunogenicity of rAd26 and rAd5 vector-based heterologous prime-boost COVID-19 vaccine against SARS-CoV-2 in healthy adolescents: an open-label, non-randomized, multicenter, phase 1/2, dose-escalation study

To protect young individuals against SARS-CoV-2 infection, we conducted an open-label, prospective, non-randomised dose-escalation Phase 1/2 clinical trial to evaluate the immunogenicity and safety of the prime-boost “Sputnik V” vaccine administered at 1/10 and 1/5 doses to adolescents aged 12–17 years. The study began with the vaccination of the older cohort (15-to-17-year-old participants) with the lower (1/10) dose of vaccine and then expanded to the whole group (12-to-17-year-old participants). Next, 1/5 dose was used according to the same scheme. Both doses were well tolerated by all age groups. No serious or severe adverse events were detected. Most of the solicited adverse reactions were mild. No significant differences in total frequencies of adverse events were registered between low and high doses in age-pooled groups (69.6% versus 66.7%). In contrast, the 1/5 dose induced significantly higher humoral and T cell-mediated immune responses than the 1/10 dose. The 1/5 vaccine dose elicited higher antigen-binding (both S and RBD-specific) as well as virus-neutralising antibody titres at the maximum of response (day 42), also resulting in a statistically significant difference at a distanced timepoint (day 180) compared to the 1/10 vaccine dose. Higher dose resulted in increased cross-neutralization of Delta and Omicron variants.;Clinical Trial RegistrationClinicalTrials.gov, NCT04954092, LP-007632

DataSheet_1_Estimation of anti-orthopoxvirus immunity in Moscow residents and potential risks of spreading Monkeypox virus.docx

WHO has declared the outbreak of monkeypox as a public health emergency of international concern. In less than three months, monkeypox was detected in more than 30 000 people and spread to more than 80 countries around the world. It is believed that the immunity formed to smallpox vaccine can protect from monkeypox infection with high efficiency. The widespread use of Vaccinia virus has not been carried out since the 1980s, which raises the question of the level of residual immunity among the population and the identification of groups requiring priority vaccination. We conducted a cross-sectional serological study of remaining immunity among Moscow residents. To do this, a collection of blood serum samples of age group over 30 years old was formed, an in-house ELISA test system was developed, and a virus neutralization protocol was set up. Serum samples were examined for the presence of IgG antibodies against Vaccinia virus (n=2908), as well as for the ability to neutralize plaque formation with a Vaccinia virus MNIIVP-10 strain (n=299). The results indicate the presence of neutralizing antibody titer of 1/20 or more in 33.3 to 53.2% of people older than 45 years. Among people 30-45 years old who probably have not been vaccinated, the proportion with virus neutralizing antibodies ranged from 3.2 to 6.7%. Despite the higher level of antibodies in age group older than 66 years, the proportion of positive samples in this group was slightly lower than in people aged 46-65 years. The results indicate the priority of vaccination in groups younger than 45, and possibly older than 66 years to ensure the protection of the population in case of spread of monkeypox among Moscow residents. The herd immunity level needed to stop the circulation of the virus should be at least 50.25 – 65.28%.</p