Circular RNA vaccines against SARS-CoV-2 and emerging variants.

As the emerging variants of SARS-CoV-2 continue to drive the worldwide pandemic, there is a constant demand for vaccines that offer more effective and broad-spectrum protection. Here, we report a circular RNA (circRNA) vaccine that elicited potent neutralizing antibodies and T cell responses by expressing the trimeric RBD of the spike protein, providing robust protection against SARS-CoV-2 in both mice and rhesus macaques. Notably, the circRNA vaccine enabled higher and more durable antigen production than the 1mΨ-modified mRNA vaccine and elicited a higher proportion of neutralizing antibodies and distinct Th1-skewed immune responses. Importantly, we found that the circRNARBD-Omicron vaccine induced effective neutralizing antibodies against the Omicron but not the Delta variant. In contrast, the circRNARBD-Delta vaccine protected against both Delta and Omicron or functioned as a booster after two doses of either native- or Delta-specific vaccination, making it a favorable choice against the current variants of concern (VOCs) of SARS-CoV-2.

Protective prototype-Beta and Delta-Omicron chimeric RBD-dimer vaccines against SARS-CoV-2.

Breakthrough infections by SARS-CoV-2 variants become the global challenge for pandemic control. Previously, we developed the protein subunit vaccine ZF2001 based on the dimeric receptor-binding domain (RBD) of prototype SARS-CoV-2. Here, we developed a chimeric RBD-dimer vaccine approach to adapt SARS-CoV-2 variants. A prototype-Beta chimeric RBD-dimer was first designed to adapt the resistant Beta variant. Compared with its homotypic forms, the chimeric vaccine elicited broader sera neutralization of variants and conferred better protection in mice. The protection of the chimeric vaccine was further verified in macaques. This approach was generalized to develop Delta-Omicron chimeric RBD-dimer to adapt the currently prevalent variants. Again, the chimeric vaccine elicited broader sera neutralization of SARS-CoV-2 variants and conferred better protection against challenge by either Delta or Omicron SARS-CoV-2 in mice. The chimeric approach is applicable for rapid updating of immunogens, and our data supported the use of variant-adapted multivalent vaccine against circulating and emerging variants.

N4BP1 mediates RAM domain-dependent notch signaling turnover during neocortical development.

Notch signaling pathway activity, particularly fluctuations in the biologically active effector fragment NICD, is required for rapid and efficient dynamic regulation of proper fate decisions in stem cells. In this study, we identified NEDD4-binding protein 1 (N4BP1), which is highly expressed in the developing mouse cerebral cortex, as a negative modulator of Notch signaling dynamics in neural progenitor cells. Intriguingly, N4BP1 regulated NICD stability specifically after Notch1 S3 cleavage through ubiquitin-mediated degradation that depended on its RAM domain, not its PEST domain, as had been extensively and previously described. The CoCUN domain in N4BP1, particularly the "Phe-Pro" motif (862/863 amino acid), was indispensable for mediating NICD degradation. The Ring family E3 ligase Trim21 was, in contrast to other NEDD4 family members, required for N4BP1-regulated NICD degradation. Overexpression of N4BP1 in cortical neural progenitors promoted neural stem cell differentiation, whereas neural progenitor cells lacking N4BP1 were sensitized to Notch signaling, resulting in the maintenance of stem-like properties in neural progenitor cells and lower production of cortical neurons.

Human transferrin receptor can mediate SARS-CoV-2 infection.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has been detected in almost all organs of coronavirus disease-19 patients, although some organs do not express angiotensin-converting enzyme-2 (ACE2), a known receptor of SARS-CoV-2, implying the presence of alternative receptors and/or co-receptors. Here, we show that the ubiquitously distributed human transferrin receptor (TfR), which binds to diferric transferrin to traffic between membrane and endosome for the iron delivery cycle, can ACE2-independently mediate SARS-CoV-2 infection. Human, not mouse TfR, interacts with Spike protein with a high affinity (KD ~2.95 nM) to mediate SARS-CoV-2 endocytosis. TfR knock-down (TfR-deficiency is lethal) and overexpression inhibit and promote SARS-CoV-2 infection, respectively. Humanized TfR expression enables SARS-CoV-2 infection in baby hamster kidney cells and C57 mice, which are known to be insusceptible to the virus infection. Soluble TfR, Tf, designed peptides blocking TfR-Spike interaction and anti-TfR antibody show significant anti-COVID-19 effects in cell and monkey models. Collectively, this report indicates that TfR is a receptor/co-receptor of SARS-CoV-2 mediating SARS-CoV-2 entry and infectivity by likely using the TfR trafficking pathway.

The pathogenicity of SARS-CoV-2 in hACE2 transgenic mice.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the cause of coronavirus disease 2019 (COVID-19), which has become a public health emergency of international concern1. Angiotensin-converting enzyme 2 (ACE2) is the cell-entry receptor for severe acute respiratory syndrome coronavirus (SARS-CoV)2. Here we infected transgenic mice that express human ACE2 (hereafter, hACE2 mice) with SARS-CoV-2 and studied the pathogenicity of the virus. We observed weight loss as well as virus replication in the lungs of hACE2 mice infected with SARS-CoV-2. The typical histopathology was interstitial pneumonia with infiltration of considerable numbers of macrophages and lymphocytes into the alveolar interstitium, and the accumulation of macrophages in alveolar cavities. We observed viral antigens in bronchial epithelial cells, macrophages and alveolar epithelia. These phenomena were not found in wild-type mice infected with SARS-CoV-2. Notably, we have confirmed the pathogenicity of SARS-CoV-2 in hACE2 mice. This mouse model of SARS-CoV-2 infection will be valuable for evaluating antiviral therapeutic agents and vaccines, as well as understanding the pathogenesis of COVID-19.

MOV10 recruits DCP2 to decap human LINE-1 RNA by forming large cytoplasmic granules with phase separation properties.

Long interspersed element 1 (LINE-1) is the only active autonomous mobile element in the human genome. Its transposition can exert deleterious effects on the structure and function of the host genome and cause sporadic genetic diseases. Tight control of LINE-1 mobilization by the host is crucial for genetic stability. In this study, we report that MOV10 recruits the main decapping enzyme DCP2 to LINE-1 RNA and forms a complex of MOV10, DCP2, and LINE-1 RNP, exhibiting liquid-liquid phase separation (LLPS) properties. DCP2 cooperates with MOV10 to decap LINE-1 RNA, which causes degradation of LINE-1 RNA and thus reduces LINE-1 retrotransposition. We here identify DCP2 as one of the key effector proteins determining LINE-1 replication, and elucidate an LLPS mechanism that facilitates the anti-LINE-1 action of MOV10 and DCP2.

Analysis of the aging-related biomarker in a nonhuman primate model using multilayer omics.

BACKGROUND: Aging is a prominent risk factor for diverse diseases; therefore, an in-depth understanding of its physiological mechanisms is required. Nonhuman primates, which share the closest genetic relationship with humans, serve as an ideal model for exploring the complex aging process. However, the potential of the nonhuman primate animal model in the screening of human aging markers is still not fully exploited. Multiomics analysis of nonhuman primate peripheral blood offers a promising approach to evaluate new therapies and biomarkers. This study explores aging-related biomarker through multilayer omics, including transcriptomics (mRNA, lncRNA, and circRNA) and proteomics (serum and serum-derived exosomes) in rhesus monkeys (Macaca mulatta). RESULTS: Our findings reveal that, unlike mRNAs and circRNAs, highly expressed lncRNAs are abundant during the key aging period and are associated with cancer pathways. Comparative analysis highlighted exosomal proteins contain more types of proteins than serum proteins, indicating that serum-derived exosomes primarily regulate aging through metabolic pathways. Finally, eight candidate aging biomarkers were identified, which may serve as blood-based indicators for detecting age-related brain changes. CONCLUSIONS: Our results provide a comprehensive understanding of nonhuman primate blood transcriptomes and proteomes, offering novel insights into the aging mechanisms for preventing or treating age-related diseases.

Glioma induces atypical depression-like behaviors in mice through the 5-HT and glutamatergic synapse pathways.

Glioma patients often undertake psychiatric disorders such as depression and anxiety. There are several clinical epidemiological studies on glioma-associated depression, but basic research and corresponding animal experiments are still lacking. Here, we observed that glioma-bearing mice exhibited atypical depression-like behaviors in orthotopic glioma mouse models. The concentrations of monoamine neurotransmitters were detected by enzyme-linked immunosorbent assay (ELISA), revealing a decrease in 5-hydroxytryptamine (5-HT) levels in para-glioma tissues. The related gene expression levels also altered, detected by quantitative RT-PCR. Then, we developed a glioma-depression comorbidity mouse model. Through sucrose preference test (SPT), forced swimming test (FST), tail suspension test (TST) and other tests, we found that the occurrence of glioma could lead to changes in depression-like behaviors in a chronic unpredictable mild stress (CUMS) mouse model. The results of RNA sequencing (RNA-seq) indicated that the altered expression of glutamatergic synapse related genes in the paratumor tissues might be one of the main molecular features of the comorbidity model. Our findings suggested that the presence of glioma caused and altered depression-like behaviors, which was potentially related to the 5-HT and glutamatergic synapse pathways.

iPLA2ß loss leads to age-related cognitive decline and neuroinflammation by disrupting neuronal mitophagy.

BACKGROUND: During brain aging, disturbances in neuronal phospholipid metabolism result in impaired cognitive function and dysregulation of neurological processes. Mutations in iPLA2ß are associated with neurodegenerative conditions that significantly impact brain phospholipids. iPLA2ß deficiency exacerbates mitochondrial dysfunction and abnormal mitochondrial accumulation. We hypothesized that iPLA2ß contributes to age-related cognitive decline by disrupting neuronal mitophagy. METHODOLOGY: We used aged wild-type (WT) mice and iPLA2ß-/- mice as natural aging models to assess cognitive performance, iPLA2ß expression in the cortex, levels of chemokines and inflammatory cytokines, and mitochondrial dysfunction, with a specific focus on mitophagy and the mitochondrial phospholipid profile. To further elucidate the role of iPLA2ß, we employed adeno-associated virus (AAV)-mediated iPLA2ß overexpression in aged mice and re-evaluated these parameters. RESULTS: Our findings revealed a significant reduction in iPLA2ß levels in the prefrontal cortex of aged brains. Notably, iPLA2ß-deficient mice exhibited impaired learning and memory. Loss of iPLA2ß in the PFC of aged mice led to increased levels of chemokines and inflammatory cytokines. This damage was associated with altered mitochondrial morphology, reduced ATP levels due to dysregulation of the parkin-independent mitophagy pathway, and changes in the mitochondrial phospholipid profile. AAV-mediated overexpression of iPLA2ß alleviated age-related parkin-independent mitophagy pathway dysregulation in primary neurons and the PFC of aged mice, reduced inflammation, and improved cognitive function. CONCLUSIONS: Our study suggests that age-related iPLA2ß loss in the PFC leads to cognitive decline through the disruption of mitophagy. These findings highlight the potential of targeting iPLA2ß to ameliorate age-related neurocognitive disorders.

Indispensable role of Nectin-like 4 in regulating synapse-related molecules, synaptic structure, and individual behavior.

Nectin-like family members (Necls) are involved in synaptic organization. In contrast to that of Necl-2/CADM1/SynCAM1, which is critical in synaptic events, investigation of Necl-4/CADM4/SynCAM4 in synapses has largely lagged behind given the particularity of homophilic self-interactions compared to interactions with other Necls. We sought to further understand the role of Necl-4 in synapses and found that knockout of Necl-4 led to aberrant expression levels of proteins mediating synaptic function in cortex homogenates and augmented accumulation of ionotropic glutamate receptor in postsynaptic density fractions, although a compensatory effect of Necl-1 on the expression levels existed. Concurrently, we also found increased synaptic clefts in the cortex and simplified dendritic morphology of primary cultured cortical neurons. Experiments on individual behaviors suggested that compared to their wild-type littermates, Necl-4-KO mice exhibited impaired acquisition of spatial memory and working memory and enhanced behavioral despair and anxiety-like behavior. These findings suggest that Necl-4 mediates synaptic function and related behaviors through an indispensable role and offer a new perspective about collaboration and specialization among Necls.

Polypyrimidine Tract-Binding Protein Enhances Zika Virus Translation by Binding to the 5'UTR of Internal Ribosomal Entry Site.

OBJECTIVES: To identify the 5' untranslated region of Zika virus (ZIKV 5'UTR) RNA-binding proteins and to investigate the impact of the binding protein on the activity of internal ribosomal entry site (IRES) located in ZIKV 5'UTR and virus production. METHODS: Interacting proteins in U251 cells were captured using tRSA-tagged ZIKV 5'UTR RNA and tRSA-ZIKV 5'UTR RNA-binding proteins were visualized by SDS-PAGE silver staining. Subsequently, liquid chromatography-tandem mass spectrometry (LC-MS/MS), bioinformatics analysis, and Western blot were used to identify the candidate proteins binding to ZIKV 5'UTR. Dicistronic expression assay and plaque forming assay were performed to analyze the effect of the binding protein on ZIKV IRES activity and ZIKV production, respecitvely. RESULTS: tRSA RNA pull-down assay, LC-MS/MS, and Western blot analysis showed that polypyrimidine tract-binding protein (PTB) bound to the ZIKV 5'UTR. Furthermore, dual luciferase reporter assay revealed that overexpression of PTB significantly enhanced the IRES activity of ZIKV (t = 10.220, P < 0.001), while PTB knockdown had the opposite effect (t = 4.897, P < 0.01). Additionally, virus plaque forming assay demonstrated that up-regulation of PTB expression significantly enhanced viral titer (t = 6.400, P < 0.01), whereas reducing PTB expression level weakened virus infectivity (t = 5.055, P < 0.01). CONCLUSIONS: PTB positively interacts with the ZIKV 5'UTR and enhances IRES activity and virus production.

NECL2 regulates blood-testis barrier dynamics in mouse testes.

The adhesion protein nectin-like molecule 2 (NECL2) is involved in spermatogenesis and participates in the connections between Sertoli cells and germ cells. Necl2 deficiency leads to infertility in male mice. We found that NECL2 is relatively highly expressed on the cell membranes of preleptotene spermatocytes. It is known that preleptotene spermatocytes pass through the blood-testis barrier (BTB) from the base of the seminiferous tubules to the lumen to complete meiosis. We hypothesized that the NECL2 protein on the surfaces of preleptotene spermatocytes has an effect on the BTB when crossing the barrier. Our results showed that Necl2 deficiency caused the levels of proteins in the BTB to be abnormal, such as those of Claudin 3, claudin 11, and Connexin43. NECL2 interacted and colocalized with adhesion proteins forming the BTB, such as Connexin43, Occludin, and N-cadherin. NECL2 regulated BTB dynamics when preleptotene spermatocytes passed through the barrier, and Necl2 deficiency caused BTB damage. Necl2 deletion significantly affected the testicular transcriptome, especially the expression of spermatogenesis-related genes. These results suggest that before meiosis and spermatid development occur, BTB dynamics regulated by NECL2 are necessary for spermatogenesis.

Single-cell transcriptome atlas reveals protective characteristics of COVID-19 mRNA vaccine.

Messenger RNA (mRNA) vaccines are promising alternatives to conventional vaccines in many aspects. We previously developed a lipopolyplex (LPP)-based mRNA vaccine (SW0123) that demonstrated robust immunogenicity and strong protective capacity against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection in mice and rhesus macaques. However, the immune profiles and mechanisms of pulmonary protection induced by SW0123 remain unclear. Through high-resolution single-cell analysis, we found that SW0123 vaccination effectively suppressed SARS-CoV-2-induced inflammatory responses by inhibiting the recruitment of proinflammatory macrophages and increasing the frequency of polymorphonuclear myeloid-derived suppressor cells. In addition, the apoptotic process in both lung epithelial and endothelial cells was significantly inhibited, which was proposed to be one major mechanism contributing to vaccine-induced lung protection. Cell-cell interaction in the lung compartment was also altered by vaccination. These data collectively unravel the mechanisms by which the SW0123 protects against lung damage caused by SARS-CoV-2 infection.

SARS-CoV-2 Omicron (B.1.1.529) infection in rhesus macaques, hamsters, and BALB/c mice with severe lung histopathological damage.

Since the first SARS-CoV-2 outbreak in late 2019, the SARS-CoV-2 genome has harbored multiple mutations, especially spike protein mutations. The currently fast-spreading Omicron variant that manifests without symptoms or with upper respiratory diseases has been recognized as a serious global public health problem. However, its pathological mechanism is largely unknown. In this work, rhesus macaques, hamsters, and BALB/C mice were employed as animal models to explore the pathogenesis of Omicron (B.1.1.529). Notably, Omicron (B.1.1.529) infected the nasal turbinates, tracheae, bronchi, and lungs of hamsters and BALB/C mice with higher viral loads than in those of rhesus macaques. Severe histopathological damage and inflammatory responses were observed in the lungs of Omicron (B.1.1.529)-infected animals. In addition, viral replication was found in multiple extrapulmonary organs. Results indicated that hamsters and BALB/c mice are potential animal models for studies on the development of drugs/vaccines and therapies for Omicron (B.1.1.529).

Comparison of the Spatiotemporal Expression Patterns of Three Cre Lines, Emx1IRES-Cre, D6-Cre and hGFAP-Cre, Commonly Used in Neocortical Development Research.

Emx1IRES-Cre, D6-Cre and hGFAP-Cre are commonly used to conditionally manipulate gene expression or lineage tracing because of their specificity in the dorsal telencephalon during early neurogenesis as previously described. However, the spatiotemporal differences in Cre recombinase activity would lead to divergent phenotypes. Here, we compared the patterns of Cre activity in the early embryos among the three lines by mating with reporter mice. The activities of Emx1IRES-Cre, D6-Cre and hGFAP-Cre were observed in the dorsal telencephalon, starting from approximately embryonic day 9.5, 11.5 and 12.5, respectively. Although all the three lines have activity in radial glial cells, Emx1IRES-Cre fully covers the dorsal and medial telencephalon, including the archicortex and cortical hem. D6-Cre is highly restricted to the dorsal telencephalon with anterior-low to posterior-high gradients, partially covers the hippocampus, and absent in the cortical hem. Moreover, both Emx1IRES-Cre and hGFAP-Cre exhibit Cre activity outside the dorsal neocortex. Meanwhile, we used the three Cre lines to mediate Dicer knockout and observed inconsistent phenotypes, including discrepancies in radial glial cell number, survival and neurogenesis in the neocortex and hippocampus. Together we proved differences in Cre activity can perturb the resultant phenotypes, which aid researchers in appropriate experimental design.

The Gastrointestinal Tract Is an Alternative Route for SARS-CoV-2 Infection in a Nonhuman Primate Model.

BACKGROUND & AIMS: Gastrointestinal (GI) manifestations have been increasingly reported in patients with coronavirus disease 2019 (COVID-19). However, the roles of the GI tract in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection are not fully understood. We investigated how the GI tract is involved in SARS-CoV-2 infection to elucidate the pathogenesis of COVID-19. METHODS: Our previously established nonhuman primate (NHP) model of COVID-19 was modified in this study to test our hypothesis. Rhesus monkeys were infected with an intragastric or intranasal challenge with SARS-CoV-2. Clinical signs were recorded after infection. Viral genomic RNA was quantified by quantitative reverse transcription polymerase chain reaction. Host responses to SARS-CoV-2 infection were evaluated by examining inflammatory cytokines, macrophages, histopathology, and mucin barrier integrity. RESULTS: Intranasal inoculation with SARS-CoV-2 led to infections and pathologic changes not only in respiratory tissues but also in digestive tissues. Expectedly, intragastric inoculation with SARS-CoV-2 resulted in the productive infection of digestive tissues and inflammation in both the lung and digestive tissues. Inflammatory cytokines were induced by both types of inoculation with SARS-CoV-2, consistent with the increased expression of CD68. Immunohistochemistry and Alcian blue/periodic acid-Schiff staining showed decreased Ki67, increased cleaved caspase 3, and decreased numbers of mucin-containing goblet cells, suggesting that the inflammation induced by these 2 types of inoculation with SARS-CoV-2 impaired the GI barrier and caused severe infections. CONCLUSIONS: Both intranasal and intragastric inoculation with SARS-CoV-2 caused pneumonia and GI dysfunction in our rhesus monkey model. Inflammatory cytokines are possible connections for the pathogenesis of SARS-CoV-2 between the respiratory and digestive systems.

Herbal inhibitors of SARS-CoV-2 Mpro effectively ameliorate acute lung injury in mice.

Coronavirus disease 2019, a newly emerging serious infectious disease, has spread worldwide. To date, effective drugs against the disease are limited. Traditional Chinese medicine was commonly used in treating COVID-19 patients in China. Here we tried to identify herbal effective lipid compounds from the lipid library of 92 heat-clearing and detoxication Chinese herbs. Through virtual screening, enzymatic activity and inhibition assays, and surface plasmon resonance tests, we identified lipid compounds targeting the main protease (Mpro ) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and verified their functions. Here, we found that natural lipid compounds LPC (14:0/0:0) and LPC (16:0/0:0) could target SARS-CoV-2 Mpro , recover cell death induced by SARS-CoV-2, and ameliorate acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) induced by bacterial lipopolysaccharides and virus poly (I:C) mimics in vivo and in vitro. Our results suggest that LPC (14:0/0:0) and LPC (16:0/0:0) might be potential pan remedy against ARDS.

Zbed3 Is Indispensable for Wnt Signaling Regulation of Cortical Layers Formation in Developing Brain.

Wnt/ß-catenin signaling plays multiple important roles during mammalian brain development, and it regulates the proliferation and differentiation of neural progenitors in a context-dependent manner and affects neocortex layer formation. However, the specific role of Wnt/ß-catenin in neuronal layer fate determination in the neocortex is still unclear. Here, we report that Zbed3, which is a positive regulator of Wnt/ß-catenin signaling, colocalizes with ß-catenin at the endfeet of radial glia in the ventricular zone of embryo mouse neocortex. Overexpression and knockdown of Zbed3 increased and decreased the activity of Wnt/ß-catenin signaling in the neocortex, respectively. Interestingly, knockdown of Zbed3 in vivo could significantly shift neuronal fates from deep layers to upper layers but is not required for the proliferation and differentiation of neural progenitors. Overexpression of Zbed3 led to increased generation of deep-layer neurons without impairing cell cycle exit of neural progenitors. More importantly, knockdown of Zbed3 could effectively block the effects of the ectopic expression of stabilized ß-catenin on neocortex layer formation. Hence, our results demonstrate that Zbed3 is indispensable for Wnt/ß-catenin signaling regulating neuronal layer fates in the developing brain.

Structure of the heterophilic interaction between the nectin-like 4 and nectin-like 1 molecules.

Nectin-like (Necl) molecules are Ca2+-independent Ig-like transmembrane cell adhesion molecules that participate in junctions between different cell types. The specific cell-cell adhesions mediated by Necl proteins are important in neural development and have been implicated in neurodegenerative diseases. Here, we present the crystal structure of the mouse Necl-4 full ectodomain and the structure of the heterophilic Necl ectodomain complex formed by the mNecl-4 and mNecl-1 ectodomains. We demonstrate that, while the ectodomain of mNecl-4 is monomeric, it forms a stable heterodimer with Ig1 of mNecl-1, with an affinity significantly higher than that observed for self-dimerization of the mNecl-1 ectodomain. We validated our structural characterizations by performing a surface plasmon resonance assay and an Fc fusion protein binding assay in mouse primary dorsal root ganglia neurites and Schwann cells and identified a selection of residues important for heterophilic interactions. Finally, we proposed a model of Necl binding specificity that involves an induced-fit conformational change at the dimerization interface.

RBD-Modified Bacterial Vesicles Elicited Potential Protective Immunity against SARS-CoV-2.

The disease caused by SARS-CoV-2 infection threatens human health. In this study, we used high-pressure homogenization technology not only to efficiently drive the bacterial membrane to produce artificial vesicles but also to force the fusion protein ClyA-receptor binding domain (RBD) to pass through gaps in the bacterial membrane to increase the contact between ClyA-RBD and the membrane. Therefore, the load of ClyA-RBD on the membrane is substantially increased. Using this technology, we constructed a "ring-like" bacterial biomimetic vesicle (BBV) loaded with polymerized RBD (RBD-BBV). RBD-BBVs injected subcutaneously can accumulate in lymph nodes, promote antigen uptake and processing, and elicit SARS-CoV-2-specific humoral and cellular immune responses in mice. In conclusion, we evaluated the potential of this novel bacterial vesicle as a vaccine delivery system and provided a new idea for the development of SARS-CoV-2 vaccines.