Virus-specific T cells play essential roles in protection against multiple virus infections, including SARS-CoV and MERS-CoV. While SARS-CoV-2–specific T cells have been identified in COVID-19 patients, their role in the protection of SARS-CoV-2–infected mice is not established. Here, using mice sensitized for infection with SARS-CoV-2 by transduction with an adenovirus expressing the human receptor (Ad5-hACE2), we identified SARS-CoV-2–specific T cell epitopes recognized by CD4+ and CD8+ T cells in BALB/c and C57BL/6 mice. Virus-specific T cells were polyfunctional and were able to lyse target cells in vivo. Further, type I interferon pathway was proved to be critical for generating optimal antiviral T cell responses after SARS-CoV-2 infection. T cell vaccination alone partially protected SARS-CoV-2–infected mice from severe disease. In addition, the results demonstrated cross-reactive T cell responses between SARS-CoV and SARS-CoV-2, but not MERS-CoV, in mice. Understanding the role of the T cell response will guide immunopathogenesis studies of COVID-19 and vaccine design and validation.

Influenza A virus (IAV) remains a major threat to global public health because of its capacity for antigenic drift, reassortment, zoonotic transmission, and pandemic emergence. Viral transcription and genome replication are carried out by the influenza virus RNA-dependent RNA polymerase (FluPol), a heterotrimeric complex composed of polymerase basic protein 1 (PB1), polymerase basic protein 2 (PB2), and polymerase acidic protein (PA), which functions together with nucleoprotein (NP) within viral ribonucleoprotein complexes (vRNPs). FluPol activity is regulated not only by viral determinants and host cofactors but also by diverse post-translational modifications. Among these, ubiquitination has emerged as a particularly versatile regulatory mechanism because it can control protein stability, polymerase assembly, subunit interactions, conformational dynamics, NP–RNA interactions, and innate immune signaling. Depending on the modified substrate, ubiquitin linkage type, acceptor residue, and responsible E3 ligase or deubiquitinase, ubiquitination may either restrict IAV replication or be exploited by the virus to enhance polymerase function and vRNP activity. This review summarizes recent advances in ubiquitination-mediated regulation of FluPol and NP, focusing on the responsible E3 ubiquitin ligases, deubiquitinases, ubiquitination sites, ubiquitin-chain types, and host restriction mechanisms. We further discuss the crosstalk between ubiquitination and other post-translational modifications, highlight unresolved mechanistic questions, and evaluate the therapeutic potential and challenges of targeting ubiquitin-dependent pathways for antiviral intervention. Collectively, this review provides a conceptual framework for understanding how ubiquitination shapes IAV replication and identifies E3 ligases and DUBs as potential targets for host-directed antiviral strategies.

Coronavirus infections pose a significant threat to both human and animal health, causing widespread morbidity, mortality, and substantial economic losses. While vaccines are crucial for prevention, their efficacy is often limited by the high mutation rate of these viruses. This underscores the urgent need for anti-coronavirus drugs, particularly broad-spectrum antiviral agents. In this study, we demonstrated for the first time that Biochanin A (BCA), a bioactive isoflavonoid found in legumes, exhibits broad-spectrum antiviral activity against coronaviruses. BCA potently inhibits porcine epidemic diarrhea virus (PEDV), as well as human coronaviruses HCoV-OC43 and HCoV-229E in vitro, with EC₅₀ values of 6.90, 2.80 and 15.4 μM, respectively. In a lethal mouse model of HCoV-OC43-induced encephalitis, oral administration of BCA (40–60 mg/kg) significantly improved animal survival and reduced cerebral viral loads. Mechanistic studies revealed that BCA upregulates the AMPK/Nrf2 signaling pathway, thereby increasing expression of the glutamate-cysteine ligase catalytic subunit (GCLC) and enhancing glutathione (GSH) biosynthesis. Our findings identify BCA as a promising host-directed antiviral agent and highlight its therapeutic potential against coronavirus infections.

Influenza viruses continue to pose a significant threat to human and animal health. However, the limited number of licensed antivirals is increasingly compromised by drug resistance driven by high mutation rates. This highlights the urgent need for broad-spectrum therapeutics with novel mechanisms of action. Nanobodies, a new generation of antibody drugs, have great potential in the treatment of influenza virus infections. Neuraminidase (NA) mediates the sialic acid cleavage required for viral release, and its genetic drift is generally slower than that of hemagglutinin (HA) in influenza viruses, making it an attractive target for broad-spectrum antiviral and vaccine development. To construct a phage display nanobody library targeting NA, an alpaca was immunized with the NA protein of the H9N2 influenza virus. A specific nanobody, designated F4, was subsequently screened from the immune library. The nanobody was engineered into an Fc-fused nanobody, F4-Fc, which exhibited inhibitory activity against multiple influenza A and B viruses in vitro and provided robust prophylactic and therapeutic protection against influenza A and influenza B virus infections in vivo . Mechanistically, F4-Fc inhibits NA enzymatic activity and mediates antibody-dependent cellular cytotoxicity. In conclusion, F4-Fc demonstrates prophylactic and therapeutic efficacy against influenza A and B viruses, representing a promising antiviral drug candidate for influenza virus infection. IMPORTANCE: Influenza viruses seriously threaten human and animal health, and drugs are crucial for controlling influenza outbreaks. However, the limited variety of existing anti-influenza virus medicines and the high mutation rate of the virus have led to the continuous emergence of drug-resistant strains. Neuraminidase (NA) is a critical surface glycoprotein that exhibits slower antigenic drift than hemagglutinin (HA), making it an attractive target for cross-protective antiviral development. However, broadly active NA-targeting nanobodies, particularly those effective against both influenza A and B viruses, remain limited. Here, we constructed an Fc-fused F4 nanobody (F4-Fc) targeting neuraminidases from multiple influenza A and B viruses and demonstrated its antiviral efficacy in vitro and protective activity in vivo , highlighting its potential as a promising strategy for the prevention and treatment of influenza virus infection.