SARS-CoV-2 S1 Subunit Booster Vaccination Elicits Robust Humoral Immune Responses in Aged Mice

Currently approved COVID-19 vaccines prevent symptomatic infection, hospitalization, and death of the disease. However, the emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants raises concerns of reduced vaccine effectiveness and increased risk of infection. Repeated homologous booster in elderly individuals and immunocompromised patients is considered to solve severe form of disease caused by new SARS-CoV-2 variants but cannot protect completely against breakthrough infection. In our previous study we assessed the immunogenicity of an adenovirus-based vaccine expressing SARS-CoV-2-S1 (Ad5.S1) in mice, resulting in that a single immunization with Ad5.S1, via subcutaneously injection or intranasal delivery, induced robust humoral and cellular immune responses [1]. As a follow up study, here we showed that vaccinated mice had high titers of anti-S1 antibodies at one year after vaccination compared to PBS immunized mice. Furthermore, one booster dose of non-adjuvanted recombinant S1Beta (rS1Beta) subunit vaccine was effective in stimulating strong long-lived S1-specific immune responses and inducing significantly high neutralizing antibodies against the Wuhan, Beta, and Delta strain with 3.6- to 19.5-fold change increases. Importantly, the booster dose elicits cross-reactive antibody responses resulting in ACE2 binding inhibition against spike of SARS-CoV-2 variants (Wuhan, Alpha, Beta, Gamma, Delta, Zeta, Kappa, New York, India) as early as two-week post-boost injection, persisting over 28 weeks after a booster vaccination. Interestingly, levels of neutralizing antibodies were correlated with not only level of S1-binding IgG but also level of ACE2 inhibition in the before- and after-booster serum samples. Our findings show that S1 recombinant protein subunit vaccine candidate as a booster has potential to offer cross-neutralization against broad variants, and has important implications for vaccine control of new emerging breakthrough SARS-CoV-2 variants in elderly individuals primed with adenovirus-based vaccine like AZD1222 and Ad26.COV2.S.

Adenovirus-Vectored SARS-CoV-2 Vaccine Expressing S1-N Fusion Protein

Additional COVID-19 vaccines that are safe, easy to manufacture, and immunogenic are needed for global vaccine equity. Here, we developed a recombinant type 5 adenovirus vector encoding for the SARS-CoV-2-S1 subunit antigen and nucleocapsid as a fusion protein (Ad5.SARS-CoV-2-S1N) delivered to BALB/c mice through multiple vaccine administration routes. A single subcutaneous (S.C.) immunization with Ad5.SARS-CoV-2-S1N induced a similar humoral response, along with a significantly higher S1-specific cellular response, as a recombinant type 5 adenovirus vector encoding for S1 alone (Ad5.SARS-CoV-2-S1). Immunogenicity was improved by homologous prime boost strategies, using either S.C. or intranasal (I.N.) delivery of Ad5.SARS-CoV-2-S1N, and further improved through heterologous prime boost, with traditional intramuscular (I.M.) injection, using subunit recombinant S1 protein. Priming with low dose (1x1010 v.p.) of Ad5.SARS-CoV-2-S1N and boosting with either wildtype recombinant rS1 or B.1.351 recombinant rS1 induced a robust neutralizing response, that was sustained against immune evasive Beta and Gamma SARS-CoV-2 variants, along with a long-lived plasma cell response in the bone marrow 29 weeks post vaccination. This novel Ad5-vectored SARS-CoV-2 vaccine candidate showed promising immunogenicity in mice and supports the further development of COVID-19 based vaccines incorporating the nucleoprotein as a target antigen.

Immunity to SARS-CoV-2 up to 15 months after infection

BackgroundInformation concerning the longevity of immunity to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) following natural infection may have considerable implications for durability of immunity induced by vaccines. Here, we monitored the SARS-CoV-2 specific immune response in convalescent coronavirus disease-2019 (COVID-19) patients up to 15 months after symptoms onset. MethodsThe levels of anti-spike and anti-receptor binding domain antibodies and neutralizing activities were tested in a total of 188 samples from 136 convalescent patients who experience mild to critical COVID-19. Specific memory B and T cell responses were measured in 76 peripheral blood mononuclear cell samples collected from 54 patients. Twenty-three vaccinated individuals were included for comparison. FindingsFollowing a peak at day 15-28 post-infection, the IgG antibody response and plasma neutralizing titers gradually decreased over time but stabilized after 6 months. Plasma neutralizing activity against G614 was still detected in 87% of the patients at 6-15 months. Compared to G614, the median neutralizing titers against Beta, Gamma and Delta variants in plasma collected at early (15-103 days) and late (9-15 month) convalescence were 16- and 8-fold lower, respectively. SARS-CoV-2-specific memory B and T cells reached a peak at 3-6 months and persisted in the majority of patients up to 15 months although a significant decrease in specific T cells was observed between 6 and 15 months. ConclusionThe data suggest that antiviral specific immunity especially memory B cells in COVID-19 convalescent patients is long-lasting, but some variants of concern, including the fast-spreading Delta variant, may at least partially escape the neutralizing activity of plasma antibodies. FundingEU-ATAC consortium, the Italian Ministry of Health, the Swedish Research Council, SciLifeLab, and KAW.

SARS-CoV-2 vaccine breakthrough infections are asymptomatic or mildly symptomatic and are infrequently transmitted.

Vaccine breakthrough SARS-CoV-2 infection has been monitored in 3720 healthcare workers receiving 2 doses of BNT162b2. SARS-CoV-2 infection is detected in 33 subjects, with a 100-day cumulative incidence of 0.93%. Vaccine protection against acquisition of SARS-CoV-2 infection is 83% (95%CI: 58-93%) in the overall population and 93% (95%CI: 69-99%) in SARS-CoV-2-experienced subjects, when compared with a non-vaccinated control group from the same Institution, in which SARS-CoV-2 infection occurs in 20/346 subjects (100-day cumulative incidence: 5.78%). The infection is symptomatic in 16 (48%) vaccinated subjects vs 17 (85%) controls (p=0.001). All analyzed patients, in whom the amount of viral RNA was sufficient for genome sequencing, results infected by the alpha variant. Antibody and T-cell responses are not reduced in subjects with breakthrough infection. Evidence of virus transmission, determined by contact tracing, is observed in two (6.1%) cases. This real-world data support the protective effect of BNT162b2 vaccine. A triple antigenic exposure, such as two-dose vaccine schedule in experienced subjects, may confer a higher protection.

Bispecific antibody prevents SARS-CoV-2 escape and protects mice from disease

Neutralizing antibodies targeting the receptor binding domain (RBD) of the SARS-CoV-2 Spike (S) are among the most promising approaches against coronavirus disease 2019 (COVID-19)1,2. We developed a bispecific, IgG1-like molecule (CoV-X2) based on two antibodies derived from COVID-19 convalescent donors, C121 and C1353. CoV-X2 simultaneously binds two independent sites on the RBD and, unlike its parental antibodies, prevents detectable S binding to Angiotensin-Converting Enzyme 2 (ACE2), the virus cellular receptor. Furthermore, CoV-X2 neutralizes SARS-CoV-2 and its variants of concern, as well as the escape mutants generated by the parental monoclonals. In a novel animal model of SARS-CoV-2 infection with lung inflammation, CoV-X2 protects mice from disease and suppresses viral escape. Thus, simultaneous targeting of non-overlapping RBD epitopes by IgG-like bispecific antibodies is feasible and effective, combining into a single molecule the advantages of antibody cocktails.

Neutrophil extracellular traps induce the epithelial-mesenchymal transition: implications in post-COVID-19 fibrosis

The release of neutrophil extracellular traps (NETs), a process termed NETosis, avoids pathogen spread but may cause tissue injury. NETs have been found in severe COVID-19 patients, but their role in disease development is still unknown. The aim of this study is to assess the capacity of NETs to drive epithelial-mesenchymal transition (EMT) of lung epithelial cells and to analyze the involvement of NETs in COVID-19. Neutrophils activated with PMA (PMA-Neu), a stimulus known to induce NETs formation, induce both EMT and cell death in the lung epithelial cell line, A549. Notably, NETs isolated from PMA-Neu induce EMT without cell damage. Bronchoalveolar lavage fluid of severe COVID-19 patients showed high concentration of NETs. Thus, we tested in an in vitro alveolar model the hypothesis that virus-induced NET may drive EMT. Co-culturing A549 at air-liquid interface with alveolar macrophages, neutrophils and SARS-CoV2, we demonstrated a significant induction of the EMT in A549 together with high concentration of NETs, IL8 and IL1{beta}, best-known inducers of NETosis. Lung tissues of COVID-19 deceased patients showed that epithelial cells are characterized by increased mesenchymal markers. These results show for the first time that NETosis plays a major role in triggering lung fibrosis in COVID-19 patients.

Persistence of SARS-CoV-2 specific B- and T-cell responses in convalescent COVID-19 patients 6-8 months after the infection

BackgroundThe longevity of the immune response against SARS-CoV-2 is currently debated. We thus profiled the serum anti-SARS-CoV-2 antibody levels and virus specific memory B- and T-cell responses over time in convalescent COVID-19 patients. MethodsA cohort of COVID-19 patients from the Lombardy region in Italy who experienced mild to critical disease and Swedish volunteers with mild symptoms, were tested for the presence of elevated anti-spike and anti-receptor binding domain antibody levels over a period of eight months. In addition, specific memory B- and T-cell responses were tested in selected patient samples. ResultsAnti-SARS-CoV-2 antibodies were present in 85% samples collected within 4 weeks after onset of symptoms in COVID-19 patients. Levels of specific IgM or IgA antibodies declined after 1 month while levels of specific IgG antibodies remained stable up to 6 months after diagnosis. Anti-SARS-CoV-2 IgG antibodies were still present, though at a significantly lower level, in 80% samples collected at 6-8 months after symptom onset. SARS-CoV-2-specific memory B- and T-cell responses were developed in vast majority of the patients tested, regardless of disease severity, and remained detectable up to 6-8 months after infection. ConclusionsAlthough the serum levels of anti-SARS-CoV-2 IgG antibodies started to decline, virus-specific T and/or memory B cell responses increased with time and maintained during the study period (6-8 months after infection). FundingEuropean Unions Horizon 2020 research and innovation programme (ATAC), the Italian Ministry of Health, CIMED, the Swedish Research Council and the China Scholarship Council.

Broncho-alveolar inflammation in COVID-19 patients: a correlation with clinical outcome

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) rapidly reached pandemic proportions. We conducted a prospective study to assess deep lung inflammatory status in patients with moderate to severe COVID-19. Diagnostic bronchoalveolar lavage (BAL) was performed in 33 adult patients with SARS-CoV-2 infection by real-time PCR on nasopharyngeal swab admitted to the Intensive care unit (ICU) (n=28) and to the Intermediate Medicine Ward (IMW) (n=5). We analyze the differential cell count, ultrastructure of cells and Interleukin(IL)6, 8 and 10 levels. ICU patients showed a marked increase in neutrophils (72%, 60-81), lower lymphocyte (8%, 4-12) and macrophages fractions (17%, 11-27) compared to IMW patients (3%, 2-17, 15%, 6-26 and 74%, 58-90, respectively) (p<0.01). Ultrastructural study from ICU patients showed viral-like particles in cytopathic mononuclear cells however extensive cytopathic damage in all cell lineages. Immunostaining with anti-viral capsid and spike antibodies specifically immunoreacted with BAL cells, mostly cytopathic ones. IL6 and IL8 were significantly higher in ICU patients than in IMW (IL6 p<0.01, IL8 p<0.0001), and also in patients who did not survive (IL6 p < 0.05, IL8 p = 0.05 vs. survivors). IL10 did not show a significant variation between groups. Dividing patients by treatment received, lower BAL concentrations of IL6 were found in patients treated with steroids as compared to those treated with tocilizumab (p<0.1) or antivirals (p<0.05). Alveolitis, associated with COVID-19, is mainly sustained by innate effectors which showed features of extensive activation. The burden of pro-inflammatory cytokines IL6 and IL8 in the broncho-alveolar environment is associated with clinical outcome.

Clinical And Analytical Performance Of An Automated Serological Test That Identifies S1/S2 Neutralizing IgG In Covid-19 Patients Semiquantitatively.

BACKGROUNDIn the Covid-19 pandemic, highly selective serological testing is essential to define exposure to SARS-CoV-2 virus. Many tests have been developed, yet with variable speed to first result, and of unknown quality, particularly when considering the prediction of neutralizing capacity. OBJECTIVES/METHODSThe LIAISON(R) SARS-CoV-2 S1/S2 IgG assay was designed to measure antibodies against the SARS-CoV-2 native S1/S2 proteins in a standardized automated chemiluminescent assay. Clinical and analytical performance of the test were validated in an observational study using residual samples (>1500) with positive or negative Covid-19 diagnosis. RESULTSThe LIAISON(R) SARS-CoV-2 S1/S2 IgG assay proved highly selective and specific, and offers semiquantitative measures of serum or plasma levels of anti-S1/S2 IgG with neutralizing activity. The diagnostic sensitivity was 91.3% and 95.7% at >5 or [≥]15 days from diagnosis respectively, and 100% when assessed against a neutralizing assay. The specificity ranged between 97% and 98.5%. The average imprecision of the assay was <5 % coefficient of variation. Assay performance at 2 different cut-offs was evaluated to optimize predictive values in settings with different % disease prevalence. CONCLUSIONS. The automated LIAISON(R) SARS-CoV-2 S1/S2 IgG assay brings efficient, sensitive, specific, and precise serological testing to the laboratory, with the capacity to test large amounts of samples per day: first results are available within 35 minutes with a throughput of 170 tests/hour. The test also provides a semiquantitative measure to identify samples with neutralizing antibodies, useful also for a large scale screening of convalescent plasma for safe therapeutic use. IMPORTANCEWith the worldwide advance of the COVID-19 pandemic, efficient, reliable and accessible diagnostic tools are needed to support public health officials and healthcare providers in their efforts to deliver optimal medical care, and articulate sound demographic policy. DiaSorin has developed an automated serology based assay for the measurement of IgG specific to SARS CoV-2 Spike protein, and tested its clinical performance in collaboration with Italian health care professionals who provided access to large numbers of samples from infected and non-infected individuals. The assay delivers excellent sensitivity and specificity, and is able to identify samples with high levels of neutralizing antibodies. This will provide guidance in assessing the true immune status of subjects, as well as meeting the pressing need to screen donors for high titer convalescent sera for subsequent therapeutic and prophylactic use.

Mortality reduction in 46 severe Covid-19 patients treated with hyperimmune plasma. A proof of concept single arm multicenter interventional trial

BACKGROUNDHyperimmune plasma from Covid-19 convalescent is a potential treatment for severe Covid-19. METHODSWe conducted a multicenter one arm proof of concept interventional study. Patients with Covid-19 disease with moderate-to-severe Acute Respiratory Distress Syndrome, elevated C-reactive Protein and need for mechanical ventilation and/or CPAP were enrolled. One to three 250-300 ml unit of hyperimmune plasma (neutralizing antibodies titer [≥]1:160) were administered. Primary outcome was 7-days hospital mortality. Secondary outcomes were PaO2/FiO2, laboratory and radiologic changes, as well as weaning from mechanical ventilation and safety. RESULTSThe study observed 46 patients from March, 25 to April, 21 2020. Patients were aged 63, 61% male, 30 on CPAP and 7 intubated. PaO2/FiO2 was 128 (SD 47). Symptoms and ARDS duration were 14 (SD 7) and 6 days (SD 3). Three patients (6.5%) died within 7 days. The upper one-sided 90%CI was 13.9%, allowing to reject the null hypothesis of a 15% mortality. PaO2/FiO2 increased by 112 units (95%CI 82 to142) in survivors, the chest radiogram severity decreased in 23% (95%CI 5% to 42%); CRP, Ferritin and LDH decreased by 60, 36 and 20% respectively. Weaning from CPAP was obtained in 26/30 patients and 3/7 were extubated. Five serious adverse events occurred in 4 patients (2 likely, 2 possible treatment related). CONCLUSIONSHyperimmune plasma in Covid-19 shows promising benefits, to be confirmed in a randomized controlled trial. This proof of concept study could open to future developments including hyperimmune plasma banking, development of standardized pharmaceutical products and monoclonal antibodies.