Minghua Li

Background/Objectives: Despite the gradual waning of global interest in SARS-CoV-2, the continued evolution and emergence of viral variants underscore the need for broadly protective vaccines. Vaccines targeting the highly mutable S1 subunit of the spike protein have shown limited breadth of protection, whereas conserved regions within the S2 fusion machinery remain critical targets for the development of vaccines effective against future variants. This study evaluated two mRNA-lipid nanoparticle (mRNA-LNP) vaccines encoding HR121, a conserved HR1-HR2-HR1 fusion-intermediate immunogen, in comparison with a recombinant HR121 protein vaccine. Methods: Two mRNA vaccine candidates, TM-HR121 and Fc-HR121, were designed to present HR121 through distinct antigen presentation strategies by incorporating a transmembrane anchor or an IgG Fc domain, respectively. Immunogenicity and protective efficacy were assessed in New Zealand White rabbits, BALB/c mice, and Golden Syrian hamsters. Results: Both mRNA vaccines elicited robust HR121-specific binding antibody responses and broad neutralizing activity against seven SARS-CoV-2 pseudoviruses in rabbits. In mice, the mRNA vaccines induced higher peak IgG titers, a more balanced IgG1/IgG2a profile, stronger antigen-specific IFN-γ responses, and enhanced T-cell responses compared with the recombinant protein vaccine, while maintaining detectable IL-4 responses. In hamsters, immunization with the HR121 mRNA vaccines significantly reduced lung viral RNA levels and attenuated pulmonary pathology and nucleocapsid antigen expression following authentic SARS-CoV-2 challenge. Conclusions: HR121-based mRNA-LNP vaccines successfully elicited cross-variant humoral and cellular immune responses and conferred protective efficacy in small-animal models. These findings support HR121 mRNA-LNP vaccines as a promising strategy for the development of broadly protective coronavirus vaccines targeting conserved S2 fusion epitopes.

Viral infectious diseases pose a persistent challenge to global livestock production, animal welfare, and food security, emphasizing the critical role of early host defense mechanisms in limiting viral replication and transmission. As frontline sensors of infection, pattern recognition receptors (PRRs) detect viral nucleic acids and trigger antiviral innate immune responses via coordinated downstream signaling. This review summarizes the functions of three major PRR families, Toll-like receptors (TLRs), RIG-I-like receptors (RLRs), and the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway, emphasizing their involvement in detecting viral agents and activating downstream pathways, including NF-κB and IRF3/7. Particular attention is given to how these receptors function in pigs and poultry, highlighting their immune responses to economically significant viruses such as porcine reproductive and respiratory syndrome virus (PRRSV), African swine fever virus (ASFV), avian influenza virus (AIV), and Newcastle disease virus (NDV). The mechanisms by which PRRs activate interferon-mediated immune responses, as well as viral strategies to evade detection, are systematically discussed. Additionally, the review explores recent advances in understanding PRR signaling specificity across species, and their potential applications in vaccine adjuvant design or antiviral drug development are also reviewed. By integrating these insights, this work provides a theoretical foundation for improving disease prevention and control in livestock production.

Severe fever with thrombocytopenia syndrome virus (SFTSV), an emerging tick-borne phlebovirus, poses a growing public health threat, with no approved vaccines or targeted therapies. Its genetic diversity and rapid reassortment have hindered the development of broadly effective interventions. Here, we isolated and characterized broadly neutralizing camelid nanobodies generated by a heterologous immunization strategy. These nanobodies exhibited cross-subtype neutralization and conferred protection against disease in humanized and lethal murine models of SFTSV infection. Structural analysis revealed binding to distinct, nonoverlapping epitopes on the viral glycoprotein complex. A rationally designed cocktail leveraging this epitope diversity achieved complete viral inhibition through synergistic mechanisms. In both murine and immunocompetent ferret models, the cocktail enabled efficient viral clearance and full protection against lethal challenge. These results demonstrate the therapeutic potential of nanobody cocktails for SFTSV infection and establish a generalizable framework for nanobody-based countermeasures against genetically variable emerging viruses, including other members of the Bunyavirales order.

Development of potent and broad‐spectrum drugs against severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) remains one of the top priorities, especially in the cases of the emergence of mutant viruses and inability of current vaccines to prevent viral transmission. In this study, we have generated a novel membrane fusion‐inhibitory lipopeptide IPB29, which is currently under clinical trials; herein, we report its design strategy and preclinical data. First, we surprisingly found that IPB29 with a rigid linker between the peptide sequence and lipid molecule had greatly improved α‐helical structure and antiviral activity. Second, IPB29 potently inhibited a large panel of SARS‐CoV‐2 variants including the previously and currently circulating viruses, such as Omicron XBB.5.1 and EG.5.1. Third, IPB29 could also cross‐neutralize the bat‐ and pangolin‐isolated SARS‐CoV‐2‐related CoVs (RatG13, PCoV‐GD, and PCoV‐GX) and other human CoVs (SARS‐CoV, MERS‐CoV, HCoV‐NL63, and HCoV‐229E). Fourth, IPB29 administrated as an inhalation solution (IPB29‐IS) in Syrian hamsters exhibited high therapeutic and preventive efficacies against SARS‐CoV‐2 Delta or Omicron variant. Fifth, the pharmacokinetic profiles and safety pharmacology of IPB29‐IS were extensively characterized, providing data to support its evaluation in humans. In conclusion, our studies have demonstrated a novel design strategy for viral fusion inhibitors and offered an ideal drug candidate against SARS‐CoV‐2 and other coronaviruses.

Determining the quantity of active virus is the most important basis to judge the risk of virus infection, which usually relies on the virus median tissue culture infectious dose (TCID₅₀) assay performed in a biosafety level 3 laboratory within 5–7 days. We have developed a culture-free method for rapid and accurate quantification of active severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) by targeting subgenomic RNA (sgRNA) based on reverse transcription digital PCR (RT-dPCR). The dynamic range of quantitative assays for sgRNA-N and sgRNA-E by RT-dPCR was investigated, and the result showed that the limits of detection (LoD) and quantification (LoQ) were 2 copies/reaction and 10 copies/reaction, respectively. The delta strain (NMDC60042793) of SARS-CoV-2 was cultured at an average titer of 10^6.13 TCID₅₀/mL and used to evaluate the developed quantification method. Copy number concentrations of the cultured SARS-CoV-2 sgRNA and genomic RNA (gRNA) gave excellent linearity (R² = 0.9999) with SARS-CoV-2 titers in the range from 500 to 10⁵ TCID₅₀/mL. Validation of 63 positive clinical samples further proves that the quantification of sgRNA-N by RT-dPCR is more sensitive for active virus quantitative detection. It is notable that we can infer the active virus titer through quantification of SARS-CoV-2 sgRNA based on the linear relationship in a biosafety level 2 laboratory within 3 h. It can be used to timely and effectively identify infectious patients and reduce unnecessary isolation especially when a large number of COVID-19 infected people impose a burden on medical resources. Graphical abstract

Background: Ending the global COVID-19 pandemic requires efficacious therapies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Nevertheless, the emerging Omicron sublineages largely escaped the neutralization of current authorized monoclonal antibody therapies. Here we report a tetravalent bispecific antibody ISH0339, as a potential candidate for long-term and broad protection against COVID-19.Methods: We report here the making of ISH0339, a novel tetravalent bispecific antibody composed of a pair of non-competing neutralizing antibodies that binds specifically to two different neutralizing epitopes of SARS-CoV-2 receptor-binding domain (RBD) and contains an engineered Fc region for prolonged antibody half-life. We describe the preclinical characterization of ISH0339 and discuss its potential as a novel agent for both prophylactic and therapeutic purposes against SARS-CoV-2 infection.Results: ISH0339 bound to SARS-CoV-2 RBD specifically with high affinity and potently blocked the binding of RBD to the host receptor hACE2. ISH0339 demonstrated greater binding, blocking and neutralizing efficiency than its parental monoclonal antibodies, and retained neutralizing ability to all tested SARS-CoV-2 variants of concern. Single dosing of ISH0339 showed potent neutralizing activity for treatment via intravenous injection and for prophylaxis via nasal spray. Preclinical studies following single dosing of ISH0339 showed favorable pharmacokinetics and well-tolerated toxicology profile.Conclusion: ISH0339 has demonstrated a favorable safety profile and potent anti-SARS-CoV-2 activities against all current variants of concern. Furthermore, prophylactic and therapeutic application of ISH0339 significantly reduced the viral titer in lungs. Investigational New Drug studies to evaluate the safety, tolerability and preliminary efficacy of ISH0339 for both prophylactic and therapeutic purposes against SARS-CoV-2 infection have been filed.

The continuously arising of SARS-CoV-2 variants has been posting a great threat to public health safety globally, from B.1.17 (Alpha), B.1.351 (Beta), P.1 (Gamma), B.1.617.2 (Delta) to B.1.1.529 (Omicron). The emerging or re-emerging of the SARS-CoV-2 variants of concern is calling for the constant monitoring of their epidemics, pathogenicity and immune escape. In this study, we aimed to characterize replication and pathogenicity of the Alpha and Delta variant strains isolated from patients infected in Laos. The amino acid mutations within the spike fragment of the isolates were determined via sequencing. The more efficient replication of the Alpha and Delta isolates was documented than the prototyped SARS-CoV-2 in Calu-3 and Caco-2 ​cells, while such features were not observed in Huh-7, Vero E6 and HPA-3 ​cells. We utilized both animal models of human ACE2 (hACE2) transgenic mice and hamsters to evaluate the pathogenesis of the isolates. The Alpha and Delta can replicate well in multiple organs and cause moderate to severe lung pathology in these animals. In conclusion, the spike protein of the isolated Alpha and Delta variant strains was characterized, and the replication and pathogenicity of the strains in the cells and animal models were also evaluated.