Extracellular disintegration of viral proteins as an innovative strategy for developing broad-spectrum antivirals against coronavirus

The coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has claimed millions of lives worldwide, not to mention innumerable losses in the global economy and disruptions in social relationships. Unfortunately, state-of-the-art treatments still lag behind the fast emergence of new variants of concern. The key to resolve this issue is to develop broad-spectrum antivirals with innovative antiviral mechanisms in which coronaviruses are deactivated regardless of their variant development. Herein, we report a new antiviral strategy involving extracellular disintegration of viral proteins that are indispensable for viral infection with hyperanion-grafted enediyne molecules. The sulfate groups ensure low cellular permeability and rather low cytotoxicity of the molecules, while the core enediyne generates reactive radical species and causes significant damage to the spike (S) protein of coronavirus. The enediyne compounds exhibit antiviral activity at micromolar to nanomolar concentrations, and the selectivity index of up to 20,000 against four kinds of human coronaviruses, including the SARS-CoV-2 omicron variant, suggesting the high potential of this new strategy in combating the COVID-19 pandemic.

Potent synthetic nanobodies against SARS-CoV-2 and molecular basis for neutralization

SARS-CoV-2, the causative agent of COVID-191, recognizes host cells by attaching its receptor-binding domain (RBD) to the host receptor ACE22-7. Neutralizing antibodies that block RBD-ACE2 interaction have been a major focus for therapeutic development8-18. Llama-derived single-domain antibodies (nanobodies, [~]15 kDa) offer advantages including ease of production and possibility for direct delivery to the lungs by nebulization19, which are attractive features for bio-drugs against the global respiratory disease. Here, we generated 99 synthetic nanobodies (sybodies) by in vitro selection using three libraries. The best sybody, MR3 bound to RBD with high affinity (KD = 1.0 nM) and showed high neutralization activity against SARS-CoV-2 pseudoviruses (IC50 = 0.40 g mL-1). Structural, biochemical, and biological characterization of sybodies suggest a common neutralizing mechanism, in which the RBD-ACE2 interaction is competitively inhibited by sybodies. Various forms of sybodies with improved potency were generated by structure-based design, biparatopic construction, and divalent engineering. Among these, a divalent MR3 conjugated with the albumin-binding domain for prolonged half-life displayed highest potency (IC50 = 12 ng mL-1) and protected mice from live SARS-CoV-2 challenge. Our results pave the way to the development of therapeutic nanobodies against COVID-19 and present a strategy for rapid responses for future outbreaks.

The recombinant N-terminal domain of spike proteins is a potential vaccine against Middle East respiratory syndrome coronavirus (MERS-CoV) infection.

The persistent public health threat of infection with the Middle East respiratory syndrome coronavirus (MERS-CoV) highlights the need for an effective MERS-CoV vaccine. Previous studies have focused mainly on the receptor-binding domain (RBD) on the spike protein of MERS-CoV. Herein, we investigated the immunogenicity and protective potential of the recombinant N-terminal domain (rNTD) of spike proteins as a vaccine candidate. BALB/c mice vaccinated with 5 or 10µg of rNTD protein demonstrated a significant humoral immune response (serum IgG and neutralizing activity). Additionally, according to the enzyme-linked immunospot, intracellular cytokine staining, and cytometric bead array assays, significant and functional T-cell immunity was induced by 10µg of the rNTD vaccination with aluminum and CpG adjuvant. Furthermore, rNTD-immunized mice showed reduced lung abnormalities in a MERS-CoV-challenge mouse model transfected with an adenoviral vector expressing human DPP4, showing protection consistent with that found with rRBD vaccination. These data show that rNTD induced potent cellular immunity and antigen-specific neutralizing antibodies in mice and that it demonstrated protective capacity against a viral challenge, indicating that rNTD is a vaccine candidate against MERS-CoV infection.

Cross protective immune responses in mice elicited by prime-boost strategy with a recombinant DNA vaccine and adenoviral 5-based vaccine expressing structural antigens of hepatitis C virus / 中华微生物学和免疫学杂志

Objective To investigate the development strategy of novel T cell based vaccine against HCV infection.Methods BALB/c mice were primed with pSCK-based DNA vaccine and boosted with type 5 adenoviral vector-based vaccine, which expressed the structural proteins ( Core, E1 and E2) de-rived from a Chinese HCV patient (genotype 1b, Hebei strain).Enzyme linked immunospot assay (ELIS-POT) and intracellular cytokine staining ( ICS) were used to analyze the elicited antigen-specific immune re-sponses and the efficacy of cross-protection.Results Immunization of mice with the prime-boost vaccination strategy elicited stronger T cell immune responses against multiple HCV antigens than using the DNA vac-cines alone, especially the IFN-γ-secreting T cell responses against E1 protein as indicated by ELISPOT as-say.ICS data indicated that the prime-boost regimen elicited more TNF-α-producing CD4+and IFN-γ-produ-cing CD8+T cells against E1 protein and high levels of IFN-γ-producing CD4+and CD8+T cells against E2 protein in comparison with immunization with DNA vaccines.Moreover, the prime-boost vaccination was ca-pable of eliciting effective cross-protection in a surrogate challenge model based on a recombinant heterolo-gous HCV (JFH1, 2a) vaccinia virus.Conclusion The prime-boost vaccination using DNA and rAd5-based vaccine expressing HCV structural antigens induced significant cellular immune response and cross-protection in mice, suggesting the possibility of using it as a promising T cell based vaccine against HCV in-fection.

Prokaryotic expression and characterization of receptor binding domain protein of the Middle East respiratory syndrome coronavirus / 中华微生物学和免疫学杂志

Objective To express the receptor binding domain (RBD) protein of the Middle East respiratory syndrome coronavirus (MERS-CoV) and to characterize the antigenicity of the purified recombi-nant protein. Methods The codon-optimized gene encoding the RBD protein of MERS-CoV was synthesized and then cloned into the pET30a ( +) vector to construct the recombinant expression plasmid. The trans-formed E. coli BL21 (DE3) strains carrying expression plasmid were induced by IPTG under different condi-tions. The expressed products were purified by using nickel affinity chromatography and further analyzed by SDS-PAGE and Western blot assay. Indirect ELISA was performed to analyze the antigenicity and specificity of RBD proteins expressed in prokaryotic expression systems in human serological test. Results The recom-binant RBD proteins were mainly expressed as conclusion body in an optimal induction condition of 37℃ and 0. 5 mmol/ L IPTG for 4 h. The high purified recombinant RBD proteins were obtained through denaturation and renaturation with a relative molecular mass of about 29×103 . Results of the Western blot assay showed that the recombinant RBD proteins could have specific reaction with the serum samples collected form mice with MERS-CoV infection. Indirect ELISA revealed that the RBD proteins expressed in the prokaryotic ex-pression system showed better sensitivity and specificity in the detection of antibodies against MERS-CoV in human serum samples. Conclusion This study reported the prokaryotic expression and purification of RBD protein of MERS-CoV for the first time, which might pave the way for further investigation on immunological detection of MERS-CoV and development of vaccines against MERS-CoV infection.

Screening of mouse-derived monoclonal antibodies against the receptor binding domain of Middle East respiratory syndrome coronavirus (MERS-CoV) spike protein / 中华微生物学和免疫学杂志

Objective To prepare and screen out monoclonal antibodies against the receptor bind-ing domain (RBD) of Middle East respiratory syndrome coronavirus ( MERS-CoV) spike ( S) protein in mice. Methods The RBD of MERS-CoV S protein expressed in the insect-baculovirus system was purified and then used to immunize the female BALB/ c mice. The spleen cells collected from the mice were fused with myeloma Sp2 / 0 cells. The positive hybridoma cells were obtained by using limited dilution method. Enzyme-linked immunosorbent assay ( ELISA), Western blot assay and neutralization test based on the MERS-CoV pseudovirus were performed for further screening and identification. Results Twelve strains of hybridoma cells that produced the monoclonal antibodies against RBD of MERS-CoV S protein were screened out. All of the 12 monoclonal antibodies (McAbs) could have specific reaction with the RBD of MERS-CoV S protein as indicated by the results of ELISA. Of the 12 McAbs, two were identified as the immunoglobulin M (IgM) isotype and the rest were IgG1 isotype by using double antibodies sandwich ELISA. Four McAbs including 1F1, 2E4, 3C3 and 3E6 were identified as having neutralizing activity by the neutralization test based on MERS-CoV pseudovirus. Results of the Western blot assay showed that the four McAbs (1F1, 2E4, 3C3 and 3E6) could have specific reaction with the RBD of MERS-CoV S protein, but no cross-reac-tion with that of SARS-CoV S protein. Conclusion Twelve mouse-derived McAbs against the RBD of MERS-CoV S protein were obtained. The prepared hybridoma cells showed the characteristics of high speci-ficity and stability in antibody secretion. Four out of the 12 McAbs were proved to have neutralizing activity.

Establishment of an inactivated viral particle-based ELISA for the detection of anti-MERS-CoV anti-bodies / 中华微生物学和免疫学杂志

Objective To establish an inactivated viral particle-based ELISA for the detection of antibodies against Middle East respiratory syndrome coronavirus (MERS-CoV) in serum samples collected from a MERS-CoV associated case. Methods Serum samples were collected from 10 newborns and 40 healthy adults. A viral particle-based ELISA was established by using the inactivated MERS-CoV virions as antigen. The levels of IgM and IgG antibodies in the serum samples were detected by the established ELISA and the cut-off values for positive detection were determined. Then the inactivated MERS-CoV virion-based ELISA was used to detect the antibodies against MERS-CoV in 5 serum samples collected from the first im-ported MERS case in China. Results The cut-off values of IgM and IgG antibodies in serum samples for ELISA were determined to be A450 readings of 0. 32 and 0. 42, respectively. The titers of IgM and IgG anti-bodies in serum samples collected at early admission to hospital from the first imported MERS case in China were both 1 ︰ 40. Seroconversion occurred 2 weeks after his admission to hospital with the titers of IgM and IgG reaching to 1 ︰ 320. Conclusion The inactivated MERS-CoV virion-based ELISA was established successfully and could be used for the detection of serum antibodies (IgG and IgM) in MERS associated cases.

Bioinformatics-based Design of Peptide Vaccine Candidates Targeting Spike Protein of MERS-CoV and Immunity analysis in Mice / 病毒学报

Middle East respiratory syndrome coronavirus (MERS-CoV) was identified as a novel human coronavirus and posed great threat to public health world wide,which calls for the development of effective and safe vaccine urgently. In the study, peptide epitopes tagrgeting spike antigen were predicted based on bioinformatics methods. Nine polypeptides with high scores were synthesized and linked to keyhole limpet hemocyanin (KLH). Female BALB/C mice were immunized with individual polypeptide-KLH, and the total IgG was detected by ELISA as well as the cellular mediated immunity (CMI) was analyzed using ELIs-pot assay. The results showed that an individual peptide of YVDVGPDSVKSACIEVDIQQTFFDKTWPRPIDVSKADGI could induce the highest level of total IgG as well as CMI (high frequency of IFN-γ secretion) against MERS-CoV antigen in mice. Our study identified a promising peptide vaccine candidate against MERS-CoV and provided an experimental support for bioinformatics-based design of peptide vaccine.

Characterizaiton of virus-like particles prepared by Bac-to-Bac system co-expressing HA and M1 ;protein of highly pathogenic avian influenza H5N1 / 中华微生物学和免疫学杂志

Objective To express and characterize the virus-like particles( VLPs) of H5 subtype containing of hemagglutinin ( HA ) and matrix 1 ( M1 ) protein by using Baculovirus-insect cells .Methods Full length genes encoding HA protein from the A/Indonesia/05/2005(H5N1) strain and the M1 protein from the A/Anhui/01/2005 ( H5N1 ) strain were cloned into a baculovirus expression vector to construct pFBD-M1-HA.The expression of HA and M1 proteins were detected by Western blot and indirect immunoflu-orescence after the transfection of Spodoptra frugiperda (Sf9) insect cells with recombinant baculovirus.Pu-rified VLPs were analyzed by SDS-PAGE and visualized with transmission electron microscope.The biologi-cal activity of purified VLPs was detected by hemagglutination test.Results The HA and M1 proteins of H5 subtype expressed by baculovirus-insect cells could be self-assembled into the functional mature VLPs.The hemagglutination titer of VLPs was as high as 1024 HAU/50μl.Conclusion The H5 subtype VLPs as pre-pared in this study would pave a way for the development of a candidate recombinant A ( H5) vaccine.

Clinical and Biological Character in Mouse Models for Middle East Respiratory Syndrome Generated by Transduction with Different Doses of DPP4 Molecule / 病毒学报

In this study, we evaluated the difference ot biological characteristics in the MERS-CoV infected mice model in prior to transduction with different dosage of human DPP4. Firstly, we transduced different dosage of DPP4 (high or low) into mice, and then challenged them with MERS-CoV in order to establish the model. After establishment of mice model, we observed the clinical signs of disease, virus replication, immunopathogenesis and antibody response. The results indicated that the infected mice showed typical pneumonia, virus replication, histological lesions, and neutralizing antibody production. Moreover, the high dosage group was superior to the low dosage group. Fourteen days after infection, the specific antibody to virus structural protein and neutralizing antibody were analyzed, the high dosage group induced higher level antibody. In summary, the MERS-CoV infected mice model were established prior transduction with DPP4, and the level of DPP4 influenced the clinical signs of disease, virus replication and antibody response in this model.