As COVID-19 continues to spread rapidly worldwide and variants continue to emerge, the development and deployment of safe and effective vaccines are urgently needed. Here, we developed an mRNA vaccine based on the trimeric receptor-binding domain (RBD) of the SARS-CoV-2 spike (S) protein fused to ferritin-formed nanoparticles (TF-RBD). Compared to the trimeric form of the RBD mRNA vaccine (T-RBD), TF-RBD delivered intramuscularly elicited robust and durable humoral immunity as well as a Th1-biased cellular response. After further challenge with live SARS-CoV-2, immunization with a two-shot low-dose regimen of TF-RBD provided adequate protection in hACE2-transduced mice. In addition, the mRNA template of TF-RBD was easily and quickly engineered into a variant vaccine to address SARS-CoV-2 mutations. The TF-RBD multivalent vaccine produced broad-spectrum neutralizing antibodies against Alpha (B.1.1.7) and Beta (B.1.351) variants. This mRNA vaccine based on the encoded self-assembled nanoparticle-based trimer RBD provides a reference for the design of mRNA vaccines targeting SARS-CoV-2.

RIG-I is a key cytosolic pattern recognition receptor that interacts with MAVS to induce type I interferons (IFNs) against RNA virus infection. In this study, we found that cyclophilin A (CypA), a peptidyl-prolyl cis/trans isomerase, functioned as a critical positive regulator of RIG-I-mediated antiviral immune responses. Deficiency of CypA impaired RIG-I-mediated type I IFN production and promoted viral replication in human cells and mice. Upon Sendai virus infection, CypA increased the interaction between RIG-I and its E3 ubiquitin ligase TRIM25, leading to enhanced TRIM25-mediated K63-linked ubiquitination of RIG-I that facilitated recruitment of RIG-I to MAVS. In addition, CypA and TRIM25 competitively interacted with MAVS, thereby inhibiting TRIM25-induced K48-linked ubiquitination of MAVS. Taken together, our findings reveal an essential role of CypA in boosting RIG-I-mediated antiviral immune responses by controlling the ubiquitination of RIG-I and MAVS.

Aa: amino acid; ATF6: activating transcription factor 6; ATG5: autophagy related 5; CCPG1: cell cycle progression 1; CFTR: CF transmembrane conductance regulator; cGAMP: cyclic GMP-AMP; CGAS: cyclic GMP-AMP synthase; CHX: cycloheximide; Co-IP: co-immunoprecipitation; CQ: chloroquine; EIF2A/eIF2α: eukaryotic translation initiation factor 2A; EIF2AK3/PERK: eukaryotic translation initiation factor 2 alpha kinase 3; ER: endoplasmic reticulum; ERN1/IRE1: endoplasmic reticulum to nucleus signaling 1; GFP: green fluorescent protein; HSPA5/GRP78: heat shock protein family A (Hsp70) member 5; HSV-1: herpes simplex virus type 1; IFIT1: interferon induced protein with tetratricopeptide repeats 1; IFNB1/IFN-β: interferon beta 1; IRF3: interferon regulatory factor 3; ISG15: ISG15 ubiquitin like modifier; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MAP3K7/TAK1: mitogen-activated protein kinase kinase kinase 7; MAVS: mitochondrial antiviral signaling protein; MOI: multiplicity of infection; NFKB/NF-κB: nuclear factor kappa B; NSP6: non-structural protein 6; Δ106-108: deletion of amino acids 106-108 in NSP6 of SARS-CoV-2; Δ105-107: deletion of amino acids 105-107 in NSP6 of SARS-CoV-2; RETREG1/FAM134B: reticulophagy regulator 1; RIGI/DDX58: RNA sensor RIG-I; SQSTM1/p62: sequestosome 1; STING1: stimulator of interferon response cGAMP interactor 1; TBK1: TANK binding kinase 1.

Naproxen is a non-steroidal anti-inflammatory drug that has previously been shown to exert antiviral activity against influenza A virus by inhibiting nucleoprotein (NP) binding to RNA. Here, we show that naproxen is a potential broad, multi-mechanistic anti-influenza virus therapeutic, as it inhibits influenza B virus replication both in vivo and in vitro. The anti-influenza B virus activity of naproxen is more efficient than that of the commonly used neuraminidase inhibitor oseltamivir in mice. Furthermore, the NP of influenza B virus (BNP) has a higher binding affinity to naproxen than influenza A virus NP (ANP). Specifically, naproxen targets the NP at residues F209 (BNP) and Y148 (ANP). This interaction antagonizes the nuclear export of NP normally mediated by the host export protein CRM1. This study reveals a crucial mechanism of broad-spectrum anti-influenza virus activity of naproxen, suggesting that the existing drug naproxen may be used as an anti-influenza drug.

The importance of enhancing influenza resistance in domestic flocks is quite clear both scientifically and economically. Chicken is very susceptible to influenza virus. It has been reported that human cellular cyclophilin A (CypA) impaired influenza virus infection in 293T cells. Whether chicken CypA (chCypA) inhibits influenza virus replication is not known. The molecular mechanism of resistance in chicken to influenza virus remains to be studied.

Background: H9N2 influenza A viruses have undergone extensive reassortments in different host species, and could lead to the epidemics or pandemics with the potential emergence of novel viruses. Methods: To understand the genetic and pathogenic features of early and current circulating H9N2 viruses, 15 representative H9N2 viruses isolated from diseased chickens in northern China between 1998 and 2010 were characterized and compared with all Chinese H9N2 viruses available in the NCBI database. Then, the representative viruses of different genotypes were selected to study the pathogenicity in mice with the aim to investigate the adaptation and the potential pathogenicity of the novel H9N2 reassortants to mammals. Results: Our results demonstrated that most of the 15 isolates were reassortants and generated four novel genotypes (B62-B65), which incorporated the gene segments from Eurasian H9N2 lineage, North American H9N2 branch, and H5N1 viruses. It was noteworthy that the newly identified genotype B65 has been prevalent in China since 2007, and more importantly, different H9N2 influenza viruses displayed a diverse pathogenicity to mice. The isolates of the 2008-2010 epidemic (genotypes B55 and B65) were lowly infectious, while two representative viruses of genotypes B0 and G2 isolated from the late 1990s were highly pathogenic to mice. In addition, Ck/SD/LY-1/08 (genotype 63, containing H5N1-like NP and PA genes) was able to replicate well in mouse lungs with high virus titers but caused mild clinical signs. Conclusion: Several lines of evidence indicated that the H9N2 influenza viruses constantly change their genetics and pathogenicity. Thus, the genetic evolution of H9N2 viruses and their pathogenicity to mammals should be closely monitored to prevent the emergence of novel pandemic viruses.