Spike Receptor-binding Domain Research Articles

Comprehensive deep mutational scanning reveals the pH induced stability and binding differences between SARS-CoV-2 spike RBD and human ACE2

The SARS-CoV-2 spike (S) glycoprotein with its mobile receptor-binding domain (RBD), binds to the human ACE2 receptor and thus facilitates virus entry through low-pH-endosomal pathways. The high degree of SARS-CoV-2 mutability has raised concern among scientists and medical professionals because it created doubt about the effectiveness of drugs and vaccinations designed specifically for COVID-19. In this study, we used computational saturation mutagenesis approach, including structure-based free energy calculations to analyse the effects of the missense mutations on the SARS-CoV-2 S-RBD stability and the S-RBD binding affinity with ACE2 at three different pH (pH 4.5, pH 6.5, and pH 7.4). A total of 3705 mutations in the S-RBD protein were analyzed, and we discovered that most of these mutations destabilize the RBD protein. Specifically, residues G404, G431, G447, A475, and G526 were important for RBD protein stability. In addition, RBD residues Y449, Y489, Y495, Q498, and N487 were critical for the RBD-ACE2 interaction. Next, we found that the distribution of the mean stability changes and mean binding energy changes of RBD due to mutations at both serological and endosomal pH correlated well, indicating the similar effects of mutations. Overall, this computational analysis is useful for understanding the effects of missense mutations in SARS-CoV-2 pathogenesis at different pH. Communicated by Ramaswamy H. Sarma

A Novel Fusion Protein System for the Production of Nanobodies and the SARS-CoV-2 Spike RBD in a Bacterial System

Antibodies are key proteins of the immune system, and they are widely used for both research and theragnostic applications. Among them, camelid immunoglobulins (IgG) differ from the canonical human IgG molecules, as their light chains are completely missing; thus, they have only variable domains on their heavy chains (VHHs). A single VHH domain, often called a nanobody, has favorable structural, biophysical, and functional features compared to canonical antibodies. Therefore, robust and efficient production protocols relying on recombinant technologies are in high demand. Here, by utilizing ecotin, an Escherichia coli protein, as a fusion partner, we present a bacterial expression system that allows an easy, fast, and cost-effective way to prepare nanobodies. Ecotin was used here as a periplasmic translocator and a passive refolding chaperone, which allowed us to reach high-yield production of nanobodies. We also present a new, easily applicable prokaryotic expression and purification method of the receptor-binding domain (RBD) of the SARS-CoV-2 S protein for interaction assays. We demonstrate using ECD spectroscopy that the bacterially produced RBD is well-folded. The bacterially produced nanobody was shown to bind strongly to the recombinant RBD, with a Kd of 10 nM. The simple methods presented here could facilitate rapid interaction measurements in the event of the appearance of additional SARS-CoV-2 variants.

Heterologous SARS-CoV-2 spike protein booster elicits durable and broad antibody responses against the receptor-binding domain

The immunogenicity of mRNA vaccines has not been well studied when compared to different vaccine modalities in the context of additional boosters. Here we show that longitudinal analysis reveals more sustained SARS-CoV-2 spike receptor-binding domain (RBD)-binding IgG titers with the breadth to antigenically distinct variants by the S-268019-b spike protein booster compared to the BNT162b2 mRNA homologous booster. The durability and breadth of RBD-angiotensin-converting enzyme 2 (ACE2) binding inhibitory antibodies are pronounced in the group without systemic adverse events (AEs) after the S-268019-b booster, leading to the elevated neutralizing activities against Omicron BA.1 and BA.5 variants in the stratified group. In contrast, BNT162b2 homologous booster elicited antibodies to spike N-terminal domain in proportion to the AE scores. High-dimensional immune profiling identifies early CD16+ natural killer cell dynamics with CCR3 upregulation, as one of the correlates for the distinct anti-RBD antibody responses by the S-268019-b booster. Our results illustrate the combinational effects of heterologous booster on the immune dynamics and the durability and breadth of recalled anti-RBD antibody responses against emerging virus variants.

Transmission of SARS-CoV-2 Omicron Variant under a Dynamic Clearance Strategy in Shandong, China.

SARS-CoV-2 Omicron caused a large wave of COVID-19 cases in China in spring 2022. Shandong was one of the most affected regions during this epidemic yet was also among those areas that were able to quickly contain the transmission. We aimed to investigate the origin, genetic diversity, and transmission patterns of the Omicron epidemic in Shandong under a dynamic clearance strategy. We generated 1,149 Omicron sequences, performed phylogenetic analysis, and interpreted results in the context of available epidemiological information. We observed that there were multiple introductions of distinct Omicron sublineages into Shandong from foreign countries and other regions in China, while a small number of introductions led to majority of local cases. We found evidence suggesting that some local clusters were potentially associated with foreign imported cases. Superspreading events and cryptic transmissions contributed to the rapid spread of this epidemic. We identified a BA.1.1 genome with the R493Q reversion mutation in the spike receptor binding domain, potentially associated with an escape from vaccine and Omicron infection elicited neutralizing immunity. Our findings illustrated how the dynamic clearance strategy constrained this epidemic's size, duration, and geographical distribution. IMPORTANCE Starting in March 2022, the Omicron epidemic caused a large wave of COVID-19 cases in China. Shandong was one of the most affected regions during this epidemic but was also among those areas that were able to quickly contain the transmission. We investigated the origin, genetic diversity, and transmission patterns of Omicron epidemic in Shandong under a dynamic clearance strategy. We found that there were multiple introductions of distinct Omicron sublineages into Shandong from foreign countries and other regions in China, while a small number of introductions led to most local cases. We found evidence suggesting that some local clusters were associated with foreign imported cases. Superspreading events and cryptic transmissions contributed to the rapid spread of this epidemic. Our study illustrated the transmission patterns of Omicron epidemic in Shandong and provided a looking glass onto this epidemic in China.

Humoral immune response to SARS-CoV-2 in pregnant and nonpregnant women following infection

Immune changes that occur during pregnancy may place pregnant women at an increased risk for severe disease following viral infections like SARS-CoV-2. Whether these immunologic changes modify the immune response to SARS-CoV-2 infection during pregnancy is not well understood. This study aimed to compare the humoral immune response to SARS-CoV-2 infection in pregnant and nonpregnant women. The immune response following vaccination for SARS-CoV-2 was also explored. In this cohort study, 24 serum samples from 20 patients infected with SARS-CoV-2 during pregnancy were matched by number of days after a positive test with 46 samples from 40 nonpregnant women of reproductive age. Samples from 9 patients who were vaccinated during pregnancy were also examined. Immunoglobulin G and immunoglobulin M levels were measured. Trends in the log antibody levels over time and mean antibody levels were assessed using generalized estimating equations. The median number of days from first positive test to sampling was 6.5 in the pregnant group (range, 3-97) and 6.0 among nonpregnant participants (range, 2-97). No significant differences in demographic or sampling characteristics were noted between the groups. No differences in immunoglobulin G or immunoglobulin M levels over time or mean antibody levels were noted among pregnant and nonpregnant participants following SARS-CoV-2 infection for any of the SARS-CoV-2 antigen targets examined (spike, spike receptor-binding domain, spike N-terminal domain, and nucleocapsid). Participants who were vaccinated during pregnancy had higher immunoglobulin G levels than pregnant patients who tested positive for all SARS-CoV-2 targets except nucleocapsid antibodies (all P<.001) and had lower immunoglobulin M spike (P<.05) and receptor-binding domain (P<.01) antibody levels. This study suggests that the humoral response following SARS-CoV-2 infection does not seem to differ between pregnant women and their nonpregnant counterparts. These findings should reassure patients and healthcare providers that pregnant patients seem to mount a nondifferential immune response to SARS-CoV-2.

Is There a Difference in Immune Response to SARS-CoV-2 Vaccination between Liver and Lung Transplant Patients with Cystic Fibrosis?

People with Cystic Fibrosis (CF), especially solid organ transplant recipients, have been prioritized in the SARS-CoV-2 vaccination program. This study assesses antibody response of patients with CF who have undergone liver (CF-LI) or lung (CF-LU) transplantation, and compares results to published data of patients with solid organ transplantation without CF as underlying disease. Antibodies against the spike receptor-binding domain were measured within the routine visits at the CF Centre in Innsbruck, Austria, after the second and third doses of SARS-CoV-2 mRNA vaccines. We report on 13 adult CF patients who are recipients of solid organ transplant, including five CF-LI and eight CF-LU. Overall, 69% had measurable antibody response after two, and 83% after three doses of SARS-CoV-2 vaccines. In CF-LI, positive serological response amounted to 100% after two and three doses, while CF-LU showed only a 50% and a 71% response rate, respectively. Clear differences are seen between the CF-LI and CF-LU groups in our cohort, with worse response rate for lung transplant recipients. Immune response between CF-LI and CF-LU, therefore, must be considered in a differentiated manner, and the importance of booster vaccination is once more emphasized with these data.

Repurposing 1,2,4-oxadiazoles as SARS-CoV-2 PLpro inhibitors and investigation of their possible viral entry blockade potential

Although vaccines are obviously mitigating the COVID-19 pandemic diffusion, efficient complementary antiviral agents are urgently needed to combat SARS-CoV-2. The viral papain-like protease (PLpro) is a promising therapeutic target being one of only two essential proteases crucial for viral replication. Nevertheless, it dysregulates the host immune sensing response. Here we report repositioning of the privileged 1,2,4-oxadiazole scaffold as promising SARS-CoV-2 PLpro inhibitor with potential viral entry inhibition profile. The design strategy relied on mimicking the general structural features of the lead benzamide PLpro inhibitor GRL0617 with isosteric replacement of its pharmacophoric amide backbone by 1,2,4-oxadiazole core. Inspired by the multitarget antiviral agents, the substitution pattern was rationalized to tune the scaffold's potency against other additional viral targets, especially the spike receptor binding domain (RBD) that is responsible for the viral invasion. The Adopted facial synthetic protocol allowed easy access to various rationally substituted derivatives. Among the evaluated series, the 2-[5-(pyridin-4-yl)-1,2,4-oxadiazol-3-yl]aniline (5) displayed the most balanced dual inhibitory potential against SARS-CoV-2 PLpro (IC50=7.197 μM) and spike protein RBD (IC50 = 8.673 μM), with acceptable ligand efficiency metrics, practical LogP (3.8) and safety profile on Wi-38 (CC50 = 51.78 μM) and LT-A549 (CC50 = 45.77 μM) lung cells. Docking simulations declared the possible structural determinants of activities and enriched the SAR data for further optimization studies.

MXene-Based Aptameric Fluorosensor for Sensitive and Rapid Detection of COVID-19.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-caused COVID-19 pandemic has rapidly escalated into the largest global health emergency, which pushes to develop detection kits for the detection of COVID-19 with high sensitivity, specificity, and fast analysis. Here, aptamer-functionalized MXene nanosheet is demonstrated as a novel bionanosensor that detects COVID-19. Upon binding to the spike receptor binding domain of SARS-CoV-2, the aptamer probe is released from MXene surface restoring the quenched fluorescence. The performances of the fluorosensor are evaluated using antigen protein, cultured virus, and swab specimens from COVID-19 patients. It is evidenced that this sensor can detect SARS-CoV-2 spike protein at final concentration of 38.9fgmL-1 and SARS-CoV-2 pseudovirus (limit of detection: 7.2 copies) within 30min. Its application for clinical samples analysis is also demonstrated successfully. This work offers an effective sensing platform for sensitive and rapid detection of COVID-19 with high specificity.

Intranasal Boosting with Spike Fc-RBD of Wild-Type SARS-CoV-2 Induces Neutralizing Antibodies against Omicron Subvariants and Reduces Viral Load in the Nasal Turbinate of Mice.

The emergence of new immune-evasive severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants and subvariants outpaces the development of vaccines specific against the dominant circulating strains. In terms of the only accepted immune correlate of protection, the inactivated whole-virion vaccine using wild-type SARS-CoV-2 spike induces a much lower serum neutralizing antibody titre against the Omicron subvariants. Since the inactivated vaccine given intramuscularly is one of the most commonly used coronavirus disease 2019 (COVID-19) vaccines in developing regions, we tested the hypothesis that intranasal boosting after intramuscular priming would provide a broader level of protection. Here, we showed that one or two intranasal boosts with the Fc-linked trimeric spike receptor-binding domain from wild-type SARS-CoV-2 can induce significantly higher serum neutralizing antibodies against wild-type SARS-CoV-2 and the Omicron subvariants, including BA.5.2 and XBB.1, with a lower titre in the bronchoalveolar lavage of vaccinated Balb/c mice than vaccination with four intramuscular doses of inactivated whole virion vaccine. The intranasally vaccinated K18-hACE2-transgenic mice also had a significantly lower nasal turbinate viral load, suggesting a better protection of the upper airway, which is the predilected site of infection by Omicron subvariants. This intramuscular priming and intranasal boosting approach that achieves broader cross-protection against Omicron variants and subvariants may lengthen the interval required for changing the vaccine immunogen from months to years.

SIM imaging resolves endocytosis of SARS-CoV-2 spike RBD in living cells

It is urgent to understand the infection mechanism of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) for the prevention and treatment of COVID-19. The infection of SARS-CoV-2 starts when the receptor-binding domain (RBD) of viral spike protein binds to angiotensin-converting enzyme 2 (ACE2) of the host cell, but the endocytosis details after this binding are not clear. Here, RBD and ACE2 were genetically coded and labeled with organic dyes to track RBD endocytosis in living cells. The photostable dyes enable long-term structured illumination microscopy (SIM) imaging and to quantify RBD-ACE2 binding (RAB) by the intensity ratio of RBD/ACE2 fluorescence. We resolved RAB endocytosis in living cells, including RBD-ACE2 recognition, cofactor-regulated membrane internalization, RAB-bearing vesicle formation and transport, RAB degradation, and downregulation of ACE2. The RAB was found to activate the RBD internalization. After vesicles were transported and matured within cells, RAB was finally degraded after being taken up by lysosomes. This strategy is a promising tool to understand the infection mechanism of SARS-CoV-2.

Design of a stabilized RBD enables potently neutralizing SARS-CoV-2 single-component nanoparticle vaccines

Waning immunity and emerging variants necessitate continued vaccination against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Improvements in vaccine safety, tolerability, and ease of manufacturing would benefit these efforts. Here, we develop a potent and easily manufactured nanoparticle vaccine displaying the spike receptor-binding domain (RBD). Computational design to stabilize the RBD, eliminate glycosylation, and focus the immune response to neutralizing epitopes results in an RBD immunogen that resolves issues hindering the efficient nanoparticle display of the native RBD. This non-glycosylated RBD can be genetically fused to diverse single-component nanoparticle platforms, maximizing manufacturing ease and flexibility. All engineered RBD nanoparticles elicit potently neutralizing antibodies in mice that far exceed monomeric RBDs. A 60-copy particle (noNAG-RBD-E2p) also elicits potently neutralizing antibodies in non-human primates. The neutralizing antibody titers elicited by noNAG-RBD-E2p are comparable to a benchmark stabilized spike antigen and reach levels against Omicron BA.5 that suggest that it would provide protection against emerging variants.

Evaluation and comparison of four quantitative SARS-CoV-2 serological assays in COVID-19 patients and immunized healthy individuals, cancer patients, and patients with immunosuppressive therapy

BackgroundSemi-quantitative and quantitative immunoassays are the most commonly used methodology to evaluate immunity post immunization. Objectives: To compare four quantitative SARS-CoV-2 serological assays in COVID-19 patients and immunized healthy individuals, cancer patients, and patients with immunosuppressive therapy. Study design: 210 serological samples from COVID-19 infection and vaccination cohorts were used to create a serological sample repository. Serological methods from four manufacturers, namely Euroimmun, Roche, Abbott, and DiaSorin, were evaluated for quantitative, semi-quantitative, and qualitative antibody measurements. All four methods measure IgG antibodies against the SARS-CoV-2 spike receptor–binding domain and report the results in Binding Antibody Unit/mL (BAU/mL). A Total Error Allowable (TEa) of ±25% was chosen as the criteria to determine whether two methods are clinically equivalent quantitatively. Semi-quantitative results (titers) were derived using numeric antibody concentration divided by the cut-off value for each method. Results: All paired quantitative comparisons demonstrated unacceptable performance. With ±25% as TEa, the best agreement was 74 (35.2% out of 210 samples) between Euroimmun and DiaSorin, whereas the lowest agreement was 11 (5.2% out of 210 samples) between Euroimmun and Roche. Antibody titers amongst all four methods were significantly different (p < 0.001). The highest titer difference from the same sample is between Roche and DiaSorin with a 1392-fold difference. On qualitative comparison, none of the paired comparison showed acceptable comparison (p < 0.001). Conclusions: Poor correlation exists between four evaluated assays, quantitatively, semi-quantitatively, and qualitatively. Further harmonization of assays is required to achieve comparable measurements.

Sensitivity-enhanced nanoplasmonic biosensor using direct immobilization of two engineered nanobodies for SARS-CoV-2 spike receptor-binding domain detection

Sensitive, rapid, and easy-to-implement biosensors are critical in responding to highly contagious and fast-spreading severe acute respiratory syndrome coronavirus (SARS-CoV-2) mutations, enabling early infection screening for appropriate isolation and treatment measures to prevent the spread of the virus. Based on the sensing principle of localized surface plasmon resonance (LSPR) and nanobody immunological techniques, an enhanced sensitivity nanoplasmonic biosensor was developed to quantify the SARS-CoV-2 spike receptor-binding domain (RBD) in serum within 30 min. The lowest concentration in the linear range can be detected down to 0.01 ng/mL by direct immobilization of two engineered nanobodies. Both the sensor fabrication process and immune strategy are facile and inexpensive, with the potential for large-scale application. The designed nanoplasmonic biosensor achieved excellent specificity and sensitivity for SARS-CoV-2 spike RBD, providing a potential option for accurate early screening of the novel coronavirus disease 2019 (COVID-19).

Virus-like Particles of Nodavirus Displaying the Receptor Binding Domain of SARS-CoV-2 Spike Protein: A Potential VLP-Based COVID-19 Vaccine.

Since the outbreak of the coronavirus disease 2019 (COVID-19), various vaccines have been developed for emergency use. The efficacy of the initial vaccines based on the ancestral strain of severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) has become a point of contention due to the emergence of new variants of concern (VOCs). Therefore, continuous innovation of new vaccines is required to target upcoming VOCs. The receptor binding domain (RBD) of the virus spike (S) glycoprotein has been extensively used in vaccine development due to its role in host cell attachment and penetration. In this study, the RBDs of the Beta (β) and Delta (δ) variants were fused to the truncated Macrobrachium rosenbergii nodavirus capsid protein without the protruding domain (CΔ116-MrNV-CP). Immunization of BALB/c mice with the virus-like particles (VLPs) self-assembled from the recombinant CP showed that, with AddaVax as an adjuvant, a significantly high level of humoral response was elicited. Specifically, mice injected with equimolar of adjuvanted CΔ116-MrNV-CP fused with the RBD of the β- and δ-variants increased T helper (Th) cell production with a CD8+/CD4+ ratio of 0.42. This formulation also induced proliferation of macrophages and lymphocytes. Overall, this study demonstrated that the nodavirus truncated CP fused with the SARS-CoV-2 RBD has potential to be developed as a VLP-based COVID-19 vaccine.

Enhanced mucosal immune responses and reduced viral load in the respiratory tract of ferrets to intranasal lipid nanoparticle-based SARS-CoV-2 proteins and mRNA vaccines

BackgroundUnlike the injectable vaccines, intranasal lipid nanoparticle (NP)-based adjuvanted vaccine is promising to protect against local infection and viral transmission. Infection of ferrets with SARS-CoV-2 results in typical respiratory disease and pathology akin to in humans, suggesting that the ferret model may be ideal for intranasal vaccine studies.ResultsWe developed SARS-CoV-2 subunit vaccine containing both Spike receptor binding domain (S-RBD) and Nucleocapsid (N) proteins (NP-COVID-Proteins) or their mRNA (NP-COVID-mRNA) and NP-monosodium urate adjuvant. Both the candidate vaccines in intranasal vaccinated aged ferrets substantially reduced the replicating virus in the entire respiratory tract. Specifically, the NP-COVID-Proteins vaccine did relatively better in clearing the virus from the nasal passage early post challenge infection. The immune gene expression in NP-COVID-Proteins vaccinates indicated increased levels of mRNA of IFNα, MCP1 and IL-4 in lungs and nasal turbinates, and IFNγ and IL-2 in lungs; while proinflammatory mediators IL-1β and IL-8 mRNA levels in lungs were downregulated. In NP-COVID-Proteins vaccinated ferrets S-RBD and N protein specific IgG antibodies in the serum were substantially increased at both day post challenge (DPC) 7 and DPC 14, while the virus neutralizing antibody titers were relatively better induced by mRNA versus the proteins-based vaccine. In conclusion, intranasal NP-COVID-Proteins vaccine induced balanced Th1 and Th2 immune responses in the respiratory tract, while NP-COVID-mRNA vaccine primarily elicited antibody responses.ConclusionsIntranasal NP-COVID-Proteins vaccine may be an ideal candidate to elicit increased breadth of immunity against SARS-CoV-2 variants.

The SpACE-CCM: A facile and versatile cell culture medium-based biosensor for detection of SARS-CoV-2 spike-ACE2 interaction

The COVID-19 pandemic is an ongoing global public health threat. COVID-19 is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, and binding of the SARS-CoV-2 spike to its receptor, angiotensin-converting enzyme 2 (ACE2), on host cells is critical for viral infection. Here, we developed a luminescent biosensor that readily detects interactions of the spike receptor-binding domain (RBD) and ACE2 in cell culture medium (‘SpACE-CCM’), which was based on bimolecular complementation of the split nanoluciferase-fused spike RBD and ectodomain of ACE2 and further engineered to be efficiently secreted from cells by adding a heterologous secretory signal peptide (SSP). Screening of various SSPs identified ‘interferon-α+alanine-aspartate’ as the SSP that induced the highest activity. The SpACE-CCM biosensor was validated by observing a marked reduction of the activity caused by interaction-defective mutations or in the presence of neutralizing antibodies, recombinant decoy proteins, or peptides. Importantly, the SpACE-CCM biosensor responded well in assay-validating conditions compared with conventional cell lysate-based NanoLuc Binary Technology, indicating its advantage. We further demonstrated the biosensor's versatility by quantitatively detecting neutralizing activity in blood samples from COVID-19 patients and vaccinated individuals, discovering a small molecule interfering with the spike RBD-ACE2 interaction through high-throughput screening, and assessing the cross-reactivity of neutralizing antibodies against SARS-CoV-2 variants. Because the SpACE-CCM is a facile and rapid one-step reaction biosensor that aptly recapitulates the native spike-ACE2 interaction, it would be advantageous in many experimental and clinical applications associated with this interaction.

Computational pipeline provides mechanistic understanding of Omicron variant of concern neutralizing engineered ACE2 receptor traps

The SARS-CoV-2 Omicron variant, with 15 mutations in Spike receptor-binding domain (Spike-RBD), renders virtually all clinical monoclonal antibodies against WT SARS-CoV-2 ineffective. We recently engineered theSARS-CoV-2 host entry receptor, ACE2, to tightly bind WT-RBD and prevent viral entry into host cells ("receptor traps"). Here we determine cryo-EM structures of our receptor traps in complex with stabilized Spike ectodomain. We develop a multi-model pipeline combining Rosetta protein modeling software and cryo-EM to allow interface energy calculations even at limited resolution and identify interface side chains that allow for high-affinity interactions between our ACE2 receptor traps and Spike-RBD. Our structural analysis provides a mechanistic rationale for the high-affinity (0.53-4.2nM) binding of our ACE2 receptor traps to Omicron-RBD confirmed with biolayer interferometry measurements. Finally, we show that ACE2 receptor traps potently neutralize Omicron and Delta pseudotyped viruses, providing alternative therapeutic routes to combat this evolving virus.

COVID-19 Vaccine Response in People with Multiple Sclerosis Treated with Dimethyl Fumarate, Diroximel Fumarate, Natalizumab, Ocrelizumab, or Interferon Beta Therapy.

Some multiple sclerosis (MS) disease-modifying therapies (DMTs) impair responses to vaccines, emphasizing the importance of understanding COVID-19 vaccine immune responses in people with MS (PwMS) receiving different DMTs. This prospective, open-label observational study enrolled 45 participants treated with natalizumab (n = 12), ocrelizumab (n = 16), fumarates (dimethyl fumarate or diroximel fumarate, n = 11), or interferonbeta (n = 6); ages 18-65years inclusive; stable on DMT for at least 6months. Responder rates, anti-SARS-CoV-2 spike receptor-binding domain IgG (anti-RBD) geometric mean titers (GMTs), antigen-specific Tcells, and vaccination-related adverse events were evaluated at baseline and 8, 24, 36, and 48weeks after first mRNA-1273 (Moderna) dose. At 8weeks post vaccination, all natalizumab-, fumarate-, and interferonbeta-treated participants generated detectable anti-RBD IgG titers, compared to only 25% of the ocrelizumab cohort. At 24 and 36weeks post vaccination, natalizumab-, fumarate-, and interferonbeta-treated participants continued to demonstrate detectable anti-RBD IgG titers, whereas participants receiving ocrelizumab did not. Anti-RBD GMTs decreased 81.5% between 8 and 24weeks post vaccination for the non-ocrelizumab-treated participants, with no significant difference between groups. At 36weeks post vaccination, ocrelizumab-treated participants had higher proportions of spike-specific Tcells compared to other treatment groups. Vaccine-associated side effects were highest in the ocrelizumab arm for most symptoms. These results suggest that humoral response to mRNA-1273 COVID-19 vaccine is preserved and similar in PwMS treated with natalizumab, fumarate, and interferonbeta, but muted with ocrelizumab. All DMTs had preserved Tcell response, including the ocrelizumab cohort, which also had a greater risk of vaccine-related side effects.

Persistent memory despite rapid contraction of circulating T Cell responses to SARS-CoV-2 mRNA vaccination.

While antibodies raised by SARS-CoV-2 mRNA vaccines have had compromised efficacy to prevent breakthrough infections due to both limited durability and spike sequence variation, the vaccines have remained highly protective against severe illness. This protection is mediated through cellular immunity, particularly CD8+ T cells, and lasts at least a few months. Although several studies have documented rapidly waning levels of vaccine-elicited antibodies, the kinetics of T cell responses have not been well defined. Interferon (IFN)-γ enzyme-linked immunosorbent spot (ELISpot) assay and intracellular cytokine staining (ICS) were utilized to assess cellular immune responses (in isolated CD8+ T cells or whole peripheral blood mononuclear cells, PBMCs) to pooled peptides spanning spike. ELISA was performed to quantitate serum antibodies against the spike receptor binding domain (RBD). In two persons receiving primary vaccination, tightly serially evaluated frequencies of anti-spike CD8+ T cells using ELISpot assays revealed strikingly short-lived responses, peaking after about 10 days and becoming undetectable by about 20 days after each dose. This pattern was also observed in cross-sectional analyses of persons after the first and second doses during primary vaccination with mRNA vaccines. In contrast, cross-sectional analysis of COVID-19-recovered persons using the same assay showed persisting responses in most persons through 45 days after symptom onset. Cross-sectional analysis using IFN-γ ICS of PBMCs from persons 13 to 235 days after mRNA vaccination also demonstrated undetectable CD8+ T cells against spike soon after vaccination, and extended the observation to include CD4+ T cells. However, ICS analyses of the same PBMCs after culturing with the mRNA-1273 vaccine in vitro showed CD4+ and CD8+ T cell responses that were readily detectable in most persons out to 235 days after vaccination. Overall, we find that detection of spike-targeted responses from mRNA vaccines using typical IFN-γ assays is remarkably transient, which may be a function of the mRNA vaccine platform and an intrinsic property of the spike protein as an immune target. However, robust memory, as demonstrated by capacity for rapid expansion of T cells responding to spike, is maintained at least several months after vaccination. This is consistent with the clinical observation of vaccine protection from severe illness lasting months. The level of such memory responsiveness required for clinical protection remains to be defined.

Baculovirus displaying SARS-CoV-2 spike RBD promotes neutralizing antibody production in a mouse model

BackgroundThere is always a need for a safe and efficient vaccine platform, especially when facing a pandemic such as COVID-19. Most of the SARS-CoV-2-based vaccines are based on the full spike protein, which is presented as a trimerized protein, and many viral vector vaccines express the spike protein into the host cells and do not display it on virus surfaces. However, the spike receptor-binding domain (RBD)-based vaccines are efficient and are currently under investigation and clinical trials. MethodologyIn this study, we are testing the efficacy of the RBD displayed on a baculovirus as a mean to formulate a safe and stable carrier to induce the immune system against SARS-CoV-2. Therefore, two pseudotyped baculoviruses were constructed to display the RBD, AcRBD-sfGFP-64, and AcRBD-sfGFP-V, using two different displaying strategies based on gp64 and VSV-G envelope glycoproteins, from Autographa californica multiple nucleopolyhedrovirus (AcMNPV) and vesicular stomatitis virus (VSV), respectively. BALB/C mice were immunized with the pseudotyped baculoviruses in a dose-optimized manner. Dot blot and Western blot were used to screen and validate the polyclonal antibodies’ specificity to the SARS-CoV-2 RBD. A plaque reduction neutralization test (PRNT) was used to measure the sera neutralization capacity against a SARS-CoV-2 wild-type isolate from Egypt. ELISA was used to quantify certain cytokines for the assessment of the immune response. ResultThe outcome of our investigation showed that the monomeric RBD proteins were properly displayed on baculovirus and efficiently triggered the mouse immune system. The produced sera efficiently neutralized about 50% of SARS-CoV-2 in more than 100-fold serum dilution. The immunized mice showed a significant increase (p<0.01) in the levels of IL-2 and IFN-γ and a significant decrease (p<0.01) and (p<0.001) in the levels of IL-4 and IL-10, respectively, which suggest that AcRBD-sfGFP-64 and AcRBD-sfGFP-V induce Th1 cellular immune response. ConclusionThe produced recombinant viruses can induce the immune response without adjuvant, which needs dose optimization and further stability tests. Neutralizing antibodies were induced without affecting the health of immunized mice. Th1 response can be attainable through the system, which is of great benefit in SARS CoV-2 infection and the system can be tested for future applications including vaccine development and polyclonal antibody production.