A vaccine targeting the RBD of the S protein of SARS-CoV-2 induces protective immunity.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes a respiratory disease called coronavirus disease 2019 (COVID-19), the spread of which has led to a pandemic. An effective preventive vaccine against this virus is urgently needed. As an essential step during infection, SARS-CoV-2 uses the receptor-binding domain (RBD) of the spike protein to engage with the receptor angiotensin-converting enzyme 2 (ACE2) on host cells1,2. Here we show that a recombinant vaccine that comprises residues 319-545 of the RBD of the spike protein induces a potent functional antibody response in immunized mice, rabbits and non-human primates (Macaca mulatta) as early as 7 or 14 days after the injection of a single vaccine dose. The sera from the immunized animals blocked the binding of the RBD to ACE2, which is expressed on the cell surface, and neutralized infection with a SARS-CoV-2 pseudovirus and live SARS-CoV-2 in vitro. Notably, vaccination also provided protection in non-human primates to an in vivo challenge with SARS-CoV-2. We found increased levels of RBD-specific antibodies in the sera of patients with COVID-19. We show that several immune pathways and CD4 T lymphocytes are involved in the induction of the vaccine antibody response. Our findings highlight the importance of the RBD domain in the design of SARS-CoV-2 vaccines and provide a rationale for the development of a protective vaccine through the induction of antibodies against the RBD domain.

Research progress in spike mutations of SARS-CoV-2 variants and vaccine development.

The coronavirus disease 2019 (COVID-19) pandemic can hardly end with the emergence of different variants over time. In the past 2 years, several variants of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), such as the Delta and Omicron variants, have emerged with higher transmissibility, immune evasion and drug resistance, leading to higher morbidity and mortality in the population. The prevalent variants of concern (VOCs) share several mutations on the spike that can affect virus characteristics, including transmissibility, antigenicity, and immune evasion. Increasing evidence has demonstrated that the neutralization capacity of sera from COVID-19 convalescent or vaccinated individuals is decreased against SARS-CoV-2 variants. Moreover, the vaccine effectiveness of current COVID-19 vaccines against SARS-CoV-2 VOCs is not as high as that against wild-type SARS-CoV-2. Therefore, more attention might be paid to how the mutations impact vaccine effectiveness. In this review, we summarized the current studies on the mutations of the SARS-CoV-2 spike, particularly of the receptor binding domain, to elaborate on how the mutations impact the infectivity, transmissibility and immune evasion of the virus. The effects of mutations in the SARS-CoV-2 spike on the current therapeutics were highlighted, and potential strategies for future vaccine development were suggested.

Lymph-Node-Targeted Cholesterolized TLR7 Agonist Liposomes Provoke a Safe and Durable Antitumor Response.

Toll-like receptor (TLR) agonists as the potent stimulants of an innate immune system hold promises for applications in anticancer immunotherapy. However, most of them are limited in the clinical translation due to the uncontrolled systemic inflammatory response. In the current study, 1V209, a small molecule TLR7 agonist, was conjugated with cholesterol (1V209-Cho) and prepared into liposomes (1V209-Cho-Lip). 1V209-Cho-Lip exerted minimal toxic effects and enhanced the transportation ability in lymph nodes (LNs) compared with 1V209. 1V209-Cho-Lip treatment inhibited tumor progression in CT26 colorectal cancer, 4T1 breast cancer, and Pan02 pancreatic ductal cancer models through inducing effective DC activation and eliciting CD8+ T cell responses. Furthermore, 1V209-Cho-Lip induced tumor-specific memory immunity to inhibit cancer recurrence and metastasis. These results indicate that cholesterol conjugation with 1V209 is an effective approach to target lymph nodes and to reduce the adverse effects. This work provides a rational basis for the distribution optimization of TLR agonists for potential clinical use.

Targeting Myeloid-Derived Suppressor Cells for Premetastatic Niche Disruption After Tumor Resection.

Surgical resection is a common therapeutic option for primary solid tumors. However, high cancer recurrence and metastatic rates after resection are the main cause of cancer related mortalities. This implies the existence of a "fertile soil" following surgery that facilitates colonization by circulating cancer cells. Myeloid-derived suppressor cells (MDSCs) are essential for premetastatic niche formation, and may persist in distant organs for up to 2 weeks after surgery. These postsurgical persistent lung MDSCs exhibit stronger immunosuppression compared with presurgical MDSCs, suggesting that surgery enhances MDSC function. Surgical stress and trauma trigger the secretion of systemic inflammatory cytokines, which enhance MDSC mobilization and proliferation. Additionally, damage associated molecular patterns (DAMPs) directly activate MDSCs through pattern recognition receptor-mediated signals. Surgery also increases vascular permeability, induces an increase in lysyl oxidase and extracellular matrix remodeling in lungs, that enhances MDSC mobilization. Postsurgical therapies that inhibit the induction of premetastatic niches by MDSCs promote the long-term survival of patients. Cyclooxygenase-2 inhibitors and ß-blockade, or their combination, may minimize the impact of surgical stress on MDSCs. Anti-DAMPs and associated inflammatory signaling inhibitors also are potential therapies. Existing therapies under tumor-bearing conditions, such as MDSCs depletion with low-dose chemotherapy or tyrosine kinase inhibitors, MDSCs differentiation using all-trans retinoic acid, and STAT3 inhibition merit clinical evaluation during the perioperative period. In addition, combining low-dose epigenetic drugs with chemokine receptors, reversing immunosuppression through the Enhanced Recovery After Surgery protocol, repairing vascular leakage, or inhibiting extracellular matrix remodeling also may enhance the long-term survival of curative resection patients.

Patient-Derived Tumor Xenografts Plus Ex Vivo Models Enable Drug Validation for Tenosynovial Giant Cell Tumors.

INTRODUCTION: Tenosynovial giant cell tumor (TGCT) is a locally aggressive tumor with colony-stimulating factor 1 receptor (CSF1R) signal expression. However, there is a lack of better in vivo and ex vivo models for TGCT. This study aims to establish a favorable preclinical translational platform, which would enable the validation of efficient and personalized therapeutic candidates for TGCT. PATIENTS AND METHODS: Histological analyses were performed for the included patients. Fresh TGCT tumors were collected and sliced into 1.0-3.0 mm3 sections using a sterilized razor blade. The tumor grafts were surgically implanted into subrenal capsules of athymic mice to establish patient-derived tumor xenograft (PDTX) mouse models. Histological and response patterns to CSF1R inhibitors evaluations were analyzed. In addition, ex vivo cultures of patient-derived explants (PDEs) with endpoint analysis were used to validate TGCT graft response patterns to CSF1R inhibitors. RESULTS: The TGCT tumor grafts that were implanted into athymic mice subrenal capsules maintained their original morphological and histological features. The "take" rate of this model was 95% (19/20). Administration of CSF1R inhibitors (PLX3397, and a novel candidate, WXFL11420306) to TGCT-PDTX mice was shown to reduce tumor size while inducing intratumoral apoptosis. In addition, the CSF1R inhibitors suppressed circulating nonspecific monocyte levels and CD163-positive cells within tumors. These response patterns of engrafts to PDTX were validated by ex vivo PDE cultures. CONCLUSIONS: Subrenal capsule supports the growth of TGCT tumor grafts, maintaining their original morphology and histology. This TGCT-PDTX model plus ex vivo explant cultures is a potential preclinical translational platform for locally aggressive tumors, such as TGCT.

Cisplatin-induced oxPAPC release enhances MDSCs infiltration into LL2 tumour tissues through MCP-1/CCL2 and LTB4/LTB4R pathways.

Lung cancer is the leading global cause of cancer-related death, however, resistance to chemotherapy drugs remains a huge barrier to effective treatment. The elevated recruitment of myeloid derived suppressor cells (MDSCs) to tumour after chemotherapy has been linked to resistance of chemotherapy drugs. Nevertheless, the specific mechanism remains unclear. oxPAPC is a bioactive principal component of minimally modified low-density lipoproteins and regulates inflammatory response. In this work, we found that cisplatin, oxaliplatin and ADM all increased oxPAPC release in tumour. Treating macrophages with oxPAPC in vitro stimulated the secretion of MCP-1 and LTB4, which strongly induced monocytes and neutrophils chemotaxis, respectively. Injection of oxPAPC in vivo significantly upregulated the percentage of MDSCs in tumour microenvironment (TME) of wild-type LL2 tumour-bearing mice, but not CCL2-/- mice and LTB4R-/- mice. Critically, oxPAPC acted as a pro-tumor factor in LL2 tumour model. Indeed, cisplatin increased oxPAPC level in tumour tissues of WT mice, CCL2-/- and LTB4R-/- mice, but caused increased infiltration of Ly6Chigh monocytes and neutrophils only in WT LL2-bearing mice. Collectively, our work demonstrates cisplatin treatment induces an overproduction of oxPAPC and thus recruits MDSCs infiltration to promote the tumour growth through the MCP-1/CCL2 and LTB4/LTB4R pathways, which may restrict the effect of multiple chemotherapy. This provides evidence for a potential strategy to enhance the efficacy of multiple chemotherapeutic drugs in the treatment of lung cancer by targeting oxPAPC.

Colony-stimulating factor-1 receptor inhibition combined with paclitaxel exerts effective antitumor effects in the treatment of ovarian cancer.

Ovarian cancer is the tumor with the highest mortality among gynecological malignancies. Studies have confirmed that paclitaxel chemoresistance is associated with increased infiltration of tumor-associated macrophages (TAMs) in the microenvironment. Colony-stimulating factor 1 (CSF-1) receptor (CSF-1R) plays a key role in regulating the number and differentiation of macrophages in certain solid tumors. There are few reports on the effects of targeted inhibition of CSF-1R in combination with chemotherapy on ovarian cancer and the tumor microenvironment. Here, we explored the antitumor efficacy and possible mechanisms of the CSF - 1R inhibitor pexidartinib (PLX3397) when combined with the first-line chemotherapeutic agent paclitaxel in the treatment of ovarian cancer. We found that CSF-1R is highly expressed in ovarian cancer cells and correlates with poor prognosis. Treatment by PLX3397 in combination with paclitaxel significantly inhibited the growth of ovarian cancer both in vitro and in vivo. Blockade of CSF-1R altered the macrophage phenotype and reprogrammed the immunosuppressive cell population in the tumor microenvironment.

Intranasal boosting with RBD-HR protein vaccine elicits robust mucosal and systemic immune responses.

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants has decreased the efficacy of SARS-CoV-2 vaccines in containing coronavirus disease 2019 (COVID-19) over time, and booster vaccination strategies are urgently necessitated to achieve sufficient protection. Intranasal immunization can improve mucosal immunity, offering protection against the infection and sustaining the spread of SARS-CoV-2. In this study, an intranasal booster of the RBD-HR vaccine after two doses of the mRNA vaccine significantly increased the levels of specific binding antibodies in serum, nasal lavage fluid, and bronchoalveolar lavage fluid compared with only two doses of mRNA vaccine. After intranasal boosting with the RBD-HR vaccine, the levels of serum neutralizing antibodies against prototype and variant strains of SARS-CoV-2 pseudoviruses were markedly higher than those in mice receiving mRNA vaccine alone, and intranasal boosting with the RBD-HR vaccine also inhibited the binding of RBD to hACE2 receptors. Furthermore, the heterologous intranasal immunization regimen promoted extensive memory T cell responses and activated CD103+ dendritic cells in the respiratory mucosa, and potently enhanced the formation of T follicular helper cells and germinal center B cells in vital immune organs, including mediastinal lymph nodes, inguinal lymph nodes, and spleen. Collectively, these data infer that heterologous intranasal boosting with the RBD-HR vaccine elicited broad protective immunity against SARS-CoV-2 both locally and systemically.

A chimeric adenovirus-vectored vaccine based on Beta spike and Delta RBD confers a broad-spectrum neutralization against Omicron-included SARS-CoV-2 variants.

Urgent research into innovative severe acute respiratory coronavirus-2 (SARS-CoV-2) vaccines that may successfully prevent various emerging emerged variants, particularly the Omicron variant and its subvariants, is necessary. Here, we designed a chimeric adenovirus-vectored vaccine named Ad5-Beta/Delta. This vaccine was created by incorporating the receptor-binding domain from the Delta variant, which has the L452R and T478K mutations, into the complete spike protein of the Beta variant. Both intramuscular (IM) and intranasal (IN) vaccination with Ad5-Beta/Deta vaccine induced robust broad-spectrum neutralization against Omicron BA.5-included variants. IN immunization with Ad5-Beta/Delta vaccine exhibited superior mucosal immunity, manifested by higher secretory IgA antibodies and more tissue-resident memory T cells (TRM) in respiratory tract. The combination of IM and IN delivery of the Ad5-Beta/Delta vaccine was capable of synergically eliciting stronger systemic and mucosal immune responses. Furthermore, the Ad5-Beta/Delta vaccination demonstrated more effective boosting implications after two dosages of mRNA or subunit recombinant protein vaccine, indicating its capacity for utilization as a booster shot in the heterologous vaccination. These outcomes quantified Ad5-Beta/Delta vaccine as a favorable vaccine can provide protective immunity versus SARS-CoV-2 pre-Omicron variants of concern and BA.5-included Omicron subvariants.

The rapid rise of SARS-CoV-2 Omicron subvariants with immune evasion properties: XBB.1.5 and BQ.1.1 subvariants.

As the fifth variant of concern of the SARS-CoV-2 virus, the Omicron variant (B.1.1.529) has quickly become the dominant type among the previous circulating variants worldwide. During the Omicron wave, several subvariants have emerged, with some exhibiting greater infectivity and immune evasion, accounting for their fast spread across many countries. Recently, two Omicron subvariants, BQ.1 and XBB lineages, including BQ.1.1, XBB.1, and XBB.1.5, have become a global public health issue given their ability to escape from therapeutic monoclonal antibodies and herd immunity induced by prior coronavirus disease 2019 (COVID-19) vaccines, boosters, and infection. In this respect, XBB.1.5, which has been established to harbor a rare mutation F486P, demonstrates superior transmissibility and immune escape ability compared to other subvariants and has emerged as the dominant strain in several countries. This review provides a comprehensive overview of the epidemiological features, spike mutations, and immune evasion of BQ.1 and XBB lineages. We expounded on the mechanisms underlying mutations and immune escape from neutralizing antibodies from vaccinated or convalescent COVID-19 individuals and therapeutic monoclonal antibodies (mAbs) and proposed strategies for prevention against BQ.1 and XBB sublineages.

JMJD6 in tumor-associated macrophage regulates macrophage polarization and cancer progression via STAT3/IL-10 axis.

The tumor-associated macrophage (TAM) is the most abundant group of immune cells in the tumor microenvironment (TME), which plays a critical role in the regulation of tumor progression and treatment resistance. Based on different polarization status, TAMs may also induce antitumor immune responses or immunosuppression. The present study identified JMJD6 (Jumonji domain-containing 6) as a novel modulator of TAM activation, the upregulation of which was associated with the immunosuppressive activities of TAMs. JMJD6 deficiency attenuated the growth of both Lewis lung carcinoma (LLC) tumors and B16F10 melanomas by reversing M2-like activation of macrophages, and sensitized tumors to immune checkpoint blockades (ICBs). Moreover, the JMJD6-induced inhibition of M2 polarization was potentially mediated by the STAT3/IL-10 signaling. These findings highlight the regulatory activities of JMJD6 in TAM polarization, and the therapeutic potential of JMJD6/STAT3/IL-10 axis blockades to enhance the efficacy of ICBs in cancer treatment.

A recombinant spike-XBB.1.5 protein vaccine induces broad-spectrum immune responses against XBB.1.5-included Omicron variants of SARS-CoV-2.

The XBB.1.5 subvariant has drawn great attention owing to its exceptionality in immune evasion and transmissibility. Therefore, it is essential to develop a universally protective coronavirus disease 2019 vaccine against various strains of Omicron, especially XBB.1.5. In this study, we evaluated and compared the immune responses induced by six different spike protein vaccines targeting the ancestral or various Omicron strains of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in mice. We found that spike-wild-type immunization induced high titers of neutralizing antibodies (NAbs) against ancestral SARS-CoV-2. However, its activity in neutralizing Omicron subvariants decreased sharply as the number of mutations in receptor-binding domain (RBD) of these viruses increased. Spike-BA.5, spike-BF.7, and spike-BQ.1.1 vaccines induced strong NAbs against BA.5, BF.7, BQ.1, and BQ.1.1 viruses but were poor in protecting against XBB and XBB.1.5, which have more RBD mutations. In sharp contrast, spike-XBB.1.5 vaccination can activate strong and broadly protective immune responses against XBB.1.5 and other common subvariants of Omicron. By performing correlation analysis, we found that the NAbs titers were negatively correlated with the number of RBD mutations in the Omicron subvariants. Vaccines with more RBD mutations can effectively overcome the immune resistance caused by the accumulation of RBD mutations, making spike-XBB.1.5 the most promising vaccine candidate against universal Omicron variants.

TFAM deficiency in dendritic cells leads to mitochondrial dysfunction and enhanced antitumor immunity through cGAS-STING pathway.

BACKGROUND: Mitochondrial transcription factor A (TFAM) is a transcription factor that maintains mitochondrial DNA (mtDNA) stabilization and initiates mtDNA replication. However, little is known about the immune regulation function and TFAM expression in immune cells in the tumors. METHODS: Mouse tumor models were applied to analyze the effect of TFAM deficiency in myeloid cell lineage on tumor progression and tumor microenvironment (TME) modification. In vitro, primary mouse bone marrow-derived dendritic cells (BMDCs) were used in the investigation of the altered function and the activated pathway. OVA was used as the model antigen to validate the activation of immune responses in vivo. STING inhibitors were used to confirm the STING activation provoked by Tfam deficient in DCs. RESULTS: The deletion of TFAM in DCs led to mitochondrial dysfunction and mtDNA cytosolic leakage resulting in the cGAS-STING pathway activation in DCs, which contributed to the enhanced antigen presentation. The deletion of TFAM in DCs has interestingly reversed the immune suppressive TME and inhibited tumor growth and metastasis in tumor models. CONCLUSIONS: We have revealed that TFAM knockout in DCs ameliorated immune-suppressive microenvironment in tumors through STING pathway. Our work suggests that specific TFAM knockout in DCs might be a compelling strategy for designing novel immunotherapy methods in the future.

Surgical Treatment of Osteosarcoma Induced Distant Pre-Metastatic Niche in Lung to Facilitate the Colonization of Circulating Tumor Cells.

Recently, the major challenge in treating osteosarcoma patients is the metastatic disease, most commonly in the lungs. However, the underlying mechanism of recurrence and metastasis of osteosarcoma after surgical resection of primary tumor remains unclear. This study aims to investigate whether the pulmonary metastases characteristic of osteosarcoma is associated with surgical treatment and whether surgery contributes to the formation of pre-metastatic niche in the distant lung tissue. In the current study, the authors observe the presence of circulating tumor cells in patients undergoing surgical resection of osteosarcoma which is correlated to tumor recurrence. The pulmonary infiltrations of neutrophils and Gr-1+ myeloid cells are characterized to form a pre-metastatic niche upon the exposure of circulating tumor cells after surgical resection. It is found that mitochondrial damage-associated molecular patterns released from surgical resection contribute to the formation of pre-metastatic niche in lung through IL-1ß secretion. This study reveals that surgical management for osteosarcoma, irrespective of the primary tumor, might promote the formation of postoperative pre-metastatic niche in lung which is with important implications for developing rational therapies during peri-operative period.

Trimeric protein vaccine based on Beta variant elicits robust immune response against BA.4/5-included SARS-CoV-2 Omicron variants.

The current Coronavirus Disease 2019 (COVID-19) pandemic, induced by newly emerging severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron variants, posed great threats to global public health security. There is an urgent need to design effective next­generation vaccines against Omicron lineages. Here, we investigated the immunogenic capacity of the vaccine candidate based on the receptor binding domain (RBD). An RBDß-HR self-assembled trimer vaccine including RBD of Beta variant (containing K417, E484 and N501) and heptad repeat (HR) subunits was developed using an insect cell expression platform. Sera obtained from immunized mice effectively blocked RBD-human angiotensin-converting enzyme 2 (hACE2) binding for different viral variants, showing robust inhibitory activity. In addition, RBDß-HR/trimer vaccine durably exhibited high titers of specific binding antibodies and high levels of cross-protective neutralizing antibodies against newly emerging Omicron lineages, as well as other major variants including Alpha, Beta, and Delta. Consistently, the vaccine also promoted a broad and potent cellular immune response involving the participation of T follicular helper (Tfh) cells, germinal center (GC) B cells, activated T cells, effector memory T cells, and central memory T cells, which are critical facets of protective immunity. These results demonstrated that RBDß-HR/trimer vaccine candidates provided an attractive next-generation vaccine strategy against Omicron variants in the global effort to halt the spread of SARS-CoV-2.

Prospect of acromegaly therapy: molecular mechanism of clinical drugs octreotide and paltusotine.

Somatostatin receptor 2 (SSTR2) is highly expressed in neuroendocrine tumors and represents as a therapeutic target. Several peptide analogs mimicking the endogenous ligand somatostatin are available for clinical use, but poor therapeutic effects occur in a subset of patients, which may be correlated with subtype selectivity or cell surface expression. Here, we clarify the signal bias profiles of the first-generation peptide drug octreotide and a new-generation small molecule paltusotine by evaluating their pharmacological characteristics. We then perform cryo-electron microscopy analysis of SSTR2-Gi complexes to determine how the drugs activate SSTR2 in a selective manner. In this work, we decipher the mechanism of ligand recognition, subtype selectivity and signal bias property of SSTR2 sensing octreotide and paltusotine, which may aid in designing therapeutic drugs with specific pharmacological profiles against neuroendocrine tumors.

Heterologous vaccination with subunit protein vaccine induces a superior neutralizing capacity against BA.4/5-included SARS-CoV-2 variants than homologous vaccination of mRNA vaccine.

BA.4 and BA.5 (BA.4/5), the subvariants of Omicron, are more transmissible than BA.1 with more robust immune evasion capability because of its unique spike protein mutations. In light of such situation, the vaccination against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is in desperate need of the third booster. It has been reported that heterologous boosters might produce more effective immunity against wild-type SARS-CoV-2 and the variants. Additionally, the third heterologous protein subunit booster should be considered potentially. In the present study, we prepared a Delta full-length spike protein sequence-based mRNA vaccine as the "priming" shot and developed a recombinant trimeric receptor-binding domain (RBD) protein vaccine referred to as RBD-HR/trimer as a third heterologous booster. Compared to the homologous mRNA group, the heterologous group (RBD-HR/trimer vaccine primed with two mRNA vaccines) induced higher neutralizing antibody titers against BA.4/5-included SARS-CoV-2 variants. In addition, heterologous vaccination exhibited stronger cellular immune response and long-lasting memory response than the homologous mRNA vaccine. In conclusion, a third heterologous boosting with RBD-HR/trimer following two-dose mRNA priming vaccination should be a superior strategy than a third homologous mRNA vaccine. The RBD-HR/trimer vaccine becomes an appropriate candidate for a booster immune injection.

Low levels of neutralizing antibodies against XBB Omicron subvariants after BA.5 infection.

The COVID-19 response strategies in Chinese mainland were recently adjusted due to the reduced pathogenicity and enhanced infectivity of Omicron subvariants. In Chengdu, China, an infection wave was predominantly induced by the BA.5 subvariant. It is crucial to determine whether the hybrid anti-SARS-CoV-2 immunity following BA.5 infection, coupled with a variety of immune background, is sufficient to shape the immune responses against newly emerged Omicron subvariants, especially for XBB lineages. To investigate this, we collected serum and nasal swab samples from 108 participants who had been infected in this BA.5 infection wave, and evaluated the neutralization against pseudoviruses. Our results showed that convalescent sera from individuals, regardless of vaccination history, had remarkably compromised neutralization capacities against the newly emerged XBB and XBB.1.5 subvariants. Although post-vaccination with BA.5 breakthrough infection slightly elevated plasma neutralizing antibodies against a part of pseudoviruses, the neutralization activities were remarkably impaired by XBB lineages. Furthermore, we analyzed the impacts of the number of vaccinations, age, and sex on the humoral and cellular immune response after BA.5 infection. Our findings suggest that the neutralization against XBB lineages that elicited by current hybrid immunity after BA.5 infection, are remained at low levels, indicating an urgent need for the development of next-generation of COVID-19 vaccines that designed based on the XBB sub-lineages and other future variants.

Cationic crosslinked carbon dots-adjuvanted intranasal vaccine induces protective immunity against Omicron-included SARS-CoV-2 variants.

Mucosal immunity plays a significant role in the first-line defense against viruses transmitted and infected through the respiratory system, such as SARS-CoV-2. However, the lack of effective and safe adjuvants currently limits the development of COVID-19 mucosal vaccines. In the current study, we prepare an intranasal vaccine containing cationic crosslinked carbon dots (CCD) and a SARS-CoV-2 antigen, RBD-HR with spontaneous antigen particlization. Intranasal immunization with CCD/RBD-HR induces high levels of antibodies with broad-spectrum neutralization against authentic viruses/pseudoviruses of Omicron-included variants and protects immunized female BALB/c mice from Omicron infection. Despite strong systemic cellular immune response stimulation, the intranasal CCD/RBD-HR vaccine also induces potent mucosal immunity as determined by the generation of tissue-resident T cells in the lungs and airway. Moreover, CCD/RBD-HR not only activates professional antigen-presenting cells (APCs), dendritic cells, but also effectively targets nasal epithelial cells, promotes antigen binding via sialic acid, and surprisingly provokes the antigen-presenting of nasal epithelial cells. We demonstrate that CCD is a promising intranasal vaccine adjuvant for provoking strong mucosal immunity and might be a candidate adjuvant for intranasal vaccine development for many types of infectious diseases, including COVID-19.