Fusion expression and immunogenicity of Bordetella pertussis PTS1-FHA protein: implications for the vaccine development

The Effect of Tryptophan-to-Tyrosine Mutation at Position 61 of the Nonstructural Protein of Severe Fever with Thrombocytopenia Syndrome Virus on Viral Replication through Autophagosome Modulation

In our prior investigations, we elucidated the role of the tryptophan-to-tyrosine substitution at the 61st position in the nonstructural protein NSsW61Y in diminishing the interaction between nonstructural proteins (NSs) and nucleoprotein (NP), impeding viral replication. In this study, we focused on the involvement of NSs in replication via the modulation of autophagosomes. Initially, we examined the impact of NP expression levels, a marker for replication, upon the infection of HeLa cells with severe fever thrombocytopenia syndrome virus (SFTSV), with or without the inhibition of NP binding. Western blot analysis revealed a reduction in NP levels in NSsW61Y-expressing conditions. Furthermore, the expression levels of the canonical autophagosome markers p62 and LC3 decreased in HeLa cells expressing NSsW61Y, revealing the involvement of individual viral proteins on autophagy. Subsequent experiments confirmed that NSsW61Y perturbs autophagy flux, as evidenced by reduced levels of LC3B and p62 upon treatment with chloroquine, an inhibitor of autophagosome-lysosome fusion. LysoTracker staining demonstrated a decrease in lysosomes in cells expressing the NS mutant compared to those expressing wild-type NS. We further explored the mTOR-associated regulatory pathway, a key regulator affected by NS mutant expression. The observed inhibition of replication could be linked to conformational changes in the NSs, impairing their binding to NP and altering mTOR regulation, a crucial upstream signaling component in autophagy. These findings illuminate the intricate interplay between NSsW61Y and the suppression of host autophagy machinery, which is crucial for the generation of autophagosomes to facilitate viral replication.

An mRNA-Based Multiple Antigenic Gene Expression System Delivered by Engineered Salmonella for Severe Fever with Thrombocytopenia Syndrome and Assessment of Its Immunogenicity and Protection Using a Human DC-SIGN-Transduced Mouse Model

Currently, there are no commercial vaccines or therapeutics against severe fever with thrombocytopenia syndrome (SFTS) virus. This study explored an engineered Salmonella as a vaccine carrier to deliver a eukaryotic self-mRNA replicating vector, pJHL204. This vector expresses multiple SFTS virus antigenic genes for the nucleocapsid protein (NP), glycoprotein precursor (Gn/Gc), and nonstructural protein (NS) to induce host immune responses. The engineered constructs were designed and validated through 3D structure modeling. Western blot and qRT-PCR analyses of transformed HEK293T cells confirmed the delivery and expression of the vaccine antigens. Significantly, mice immunized with these constructs demonstrated a cell-mediated and humoral response as balanced Th1/Th2 immunity. The JOL2424 and JOL2425 delivering NP and Gn/Gc generated strong immunoglobulin IgG and IgM antibodies and high neutralizing titers. To further examine the immunogenicity and protection, we utilized a human DC-SIGN receptor transduced mouse model for SFTS virus infection by an adeno-associated viral vector system. Among the SFTSV antigen constructs, the construct with full-length NP and Gn/Gc and the construct with NP and selected Gn/Gc epitopes induced robust cellular and humoral immune responses. These were followed by adequate protection based on viral titer reduction and reduced histopathological lesions in the spleen and liver. In conclusion, these data indicate that recombinant attenuated Salmonella JOL2424 and JOL2425 delivering NP and Gn/Gc antigens of SFTSV are promising vaccine candidates that induce strong humoral and cellular immune responses and protection against SFTSV. Moreover, the data proved that the hDC-SIGN transduced mice as a worthy tool for immunogenicity study for SFTSV.

Development and evaluation of a mouse model susceptible to severe fever with thrombocytopenia syndrome virus by rAAV-based exogenous human DC-SIGN expression

Experimental animal model is indispensable to evaluate the prophylactic and therapeutic candidates against severe fever with thrombocytopenia syndrome virus (SFTSV). To develop a suitable mouse model for SFTSV infection, we delivered human dendritic cell-specific ICAM-3-grabbing non-integrin (hDC-SIGN) by adeno-associated virus (AAV2) and validated its susceptibility for SFTSV infection. Western blot and RT-PCR assays confirmed the expression of hDC-SIGN in transduced cell lines and a significantly increased viral infectivity was observed in cells expressing hDC-SIGN. The C57BL/6 mice transduced with AAV2 exhibited a stable hDC-SIGN expression in the organs for 7 days. Upon SFTSV challenge with 1 × 10⁵ FAID₅₀, the mice transduced with rAAV-hDC-SIGN showed a 12.5% mortality and reduced platelet and white blood cell count in accordance with higher viral titer than control group. Liver and spleen samples collected from the transduced mice had pathological signs similar to the IFNAR^-/- mice with severe SFTSV infection. Collectively, the rAAV-hDC-SIGN transduced mouse model can be used as an accessible and promising tool for studying the SFTSV pathogenesis and pre-clinical evaluation of vaccines and therapeutics against the SFTSV infection.

Highly feasible immunoprotective multicistronic SARS-CoV-2 vaccine candidate blending novel eukaryotic expression and Salmonella bactofection

Introduction

The emergence of SARS-CoV-2 variants has raised concerns on future vaccine efficacy as most vaccines target only the spike protein. Hence, vaccines targeting multiple SARS-CoV-2 proteins will offer broader protection and improve our preparedness to combat the pandemic.

Objectives

The study aimed to develop a novel vaccine strategy by combining a eukaryotic vector expressing multiple SARS-CoV-2 genes and Salmonella-mediated in vivo DNA delivery.

Methods

The eukaryotic vector was designed to function as a DNA-launched RNA replicon in a self-replicating and self-amplifying mRNA mechanism. By exploiting the self-cleaving peptide, P2A, we fused four SARS-CoV-2 targets, including receptor-binding domain (RBD), heptad repeat domain (HR), membrane protein (M) and epitopes of nsp13, in a single open reading frame. Western blot and immunofluorescence assays were used to determine protein expression. In mice, the vaccine's safety and immunogenicity were investigated.

Results

Western blot analysis revealed co-expression all four proteins from the vaccine construct, confirming the efficiency of Salmonella-mediated gene delivery and protein expression. The vaccine candidate was safe and elicited robust antigen-specific antibody titers in mice, and a recall response from splenocytes revealed induction of strong cell-mediated immunity. Flow cytometry demonstrated an increase in sub-populations of CD4+ and CD8+ T cells with the highest CD4+ and CD8+ T cells recorded for HR and RBD, respectively. Overall, humoral and cellular immune response data suggested the induction of both Th1 and Th2 immunity with polarization towards an antiviral Th1 response. We recorded a potent SARS-CoV-2 neutralizing antibody titers in the immunized mice sera.

Conclusions

The Salmonella bactofection ensured optimum in vivo gene delivery, and through a P2A-enabled efficient multicistronic expression, the vaccine candidate elicited potent anti-SARS-CoV-2 immune responses. These findings provide important insight into development of an effective multivalent vaccine to combat SARS-CoV-2 and its variants.

Rapid and Broad Immune Efficacy of a Recombinant Five-Antigen Vaccine against Staphylococcus Aureus Infection in Animal Models

Staphylococcus aureus (S. aureus) is a leading cause of both healthcare-and community-associated infections globally, which result in severe disease and readily developing antibiotic resistance. Developing an efficacious vaccine against S. aureus is urgently required. In the present study, we selected five conserved antigens, including the secreted factors α-hemolysin (Hla), staphylococcal enterotoxin B (SEB) and the three surface proteins staphylococcal protein A (SpA), iron surface determinant B N2 domain (IsdB-N2) and manganese transport protein C (MntC). They were all well-characterized virulence factor of S. aureus and developed a recombinant five-antigen S. aureus vaccine (rFSAV), rFSAV provided consistent protection in S. aureus lethal sepsis and pneumonia mouse models, and it showed broad immune protection when challenged with a panel of epidemiologically relevant S. aureus strains. Meanwhile, rFSAV immunized mice were able to induce comprehensive cellular and humoral immune responses to reduce bacterial loads, inflammatory cytokine expression, inflammatory cell infiltration and decrease pathology after challenge with a sub-lethal dose of S. aureus. Moreover, the importance of specific antibodies in protection was demonstrated by antibody function tests in vitro and in vivo. Altogether, our data demonstrate that rFSAV is a potentially promising vaccine candidate for defensing against S. aureus infection.

Subcutaneous administration of a fusion protein composed of pertussis toxin and filamentous hemagglutinin from Bordetella pertussis induces mucosal and systemic immune responses

Objective(s):

After decades of containment, pertussis disease, caused by Bordetella pertussis seems to be re-emerging and still remains a major cause of reported vaccine-preventable deaths worldwide. The current licensed whole-cell vaccines display reactogenicity while acellular vaccines are expensive and do not induce Th1-type immune responses that are required for optimum protection against the disease. Thus, there is an urgent need to develop new vaccines and the recombinant technology seems to be the method of choice for this purpose. The present study was an attempt to develop a new, simplified, cost-effective and well-defined vaccine against Bordetella pertussis, with capacity to induce a Th1 response.

Materials and Methods:

A fusion DNA fragment encoding the N-terminal region of pertussis toxin S1 subunit and filamentous hemagglutinin type 1 immunodominant domain was constructed and the corresponding fusion protein (F1S1) was produced in Escherichia coli. F1S1 in conjunction with imiquimod was administered by subcutaneous (SC) and intranasal (IN) routes to BALB/c mice.

Results:

This vaccine formulation could elicit high levels of IFN-γ, serum IgG (with higher IgG2a/IgG1 ratio) and lung IgA after the SC and, to a lesser extent, following the IN administration.

Conclusion:

Our results indicate that the above-mentioned important proteins of B. pertussis could be successfully produced in E. coli as a single fusion protein. Furthermore, this protein could induce proper systemic and mucosal immune responses after administration via SC or IN routes.

Protective Efficacy of the Trivalent Pseudomonas aeruginosa Vaccine Candidate PcrV-OprI-Hcp1 in Murine Pneumonia and Burn Models

Pseudomonas aeruginosa is a formidable pathogen that is responsible for a diverse spectrum of human infectious diseases, resulting in considerable annual mortality rates. Because of biofilm formation and its ability of rapidly acquires of resistance to many antibiotics, P. aeruginosa related infections are difficult to treat, and therefore, developing an effective vaccine is the most promising method for combating infection. In the present study, we designed a novel trivalent vaccine, PcrV_28-294-OprI_25-83-Hcp1_1-162 (POH), and evaluated its protective efficacy in murine pneumonia and burn models. POH existed as a dimer in solution, it induced better protection efficacy in P. aeruginosa lethal pneumonia and murine burn models than single components alone when formulated with Al(OH)₃ adjuvant, and it showed broad immune protection against several clinical isolates of P. aeruginosa. Immunization with POH induced strong immune responses and resulted in reduced bacterial loads, decreased pathology, inflammatory cytokine expression and inflammatory cell infiltration. Furthermore, in vitro opsonophagocytic killing assay and passive immunization studies indicated that the protective efficacy mediated by POH vaccination was largely attributed to POH-specific antibodies. Taken together, these data provided evidence that POH is a potentially promising vaccine candidate for combating P. aeruginosa infection in pneumonia and burn infections.

Protective Efficacy and Mechanism of Passive Immunization with Polyclonal Antibodies in a Sepsis Model of Staphylococcus aureus Infection

Staphylococcus aureus (S. aureus) is an opportunistic bacterial pathogen responsible for a diverse spectrum of human diseases, resulting in considerable yearly mortality rates. Due to its rapid acquisition of antibiotic resistance, it becomes increasingly difficult to cure S. aureus infections with conventional antibiotics. Immunotherapy represents a promising alternative strategy to prevent and/or treat the infection. In the present study, passive immunization with polyclonal antibodies targeting three possible S. aureus antigens, Hla, SEB and MntC (termed "SAvac-pcAb") after challenge with lethal dose of S. aureus resulted in reduced bacterial loads, inflammatory cell infiltration and decreased pathology, and was able to provide nearly complete protection in a murine sepsis model. In vitro studies confirmed the direct interaction of SAvac-pcAb with S. aureus bacteria. Additional studies validated that SAvac-pcAb contained both opsonic and neutralizing antibodies that contributed to its protective efficacy. The former mediated opsonophagocytosis in a neutrophil-dependent manner, while the later inhibited the biological functions of Hla and SEB, two major virulence factors secreted by S. aureus. Critically, we demonstrated that SAvac-pcAb was cross-reactive with different clinical strains of S. aureus. These results confirmed the efficacy for treatment of S. aureus infection by passive immunization as an important therapeutic option.

Immunization with Heat Shock Protein A and γ-Glutamyl Transpeptidase Induces Reduction on the Helicobacter pylori Colonization in Mice

The human gastric pathogen Helicobacter pylori (H. pylori) is a successful colonizer of the stomach. H. pylori infection strongly correlates with the development and progression of chronic gastritis, peptic ulcer disease, and gastric malignances. Vaccination is a promising strategy for preventing H. pylori infection. In this study, we evaluated the candidate antigens heat shock protein A (HspA) and H. pylori γ-glutamyl transpeptidase (GGT) for their effectiveness in development of subunit vaccines against H. pylori infection. rHspA, rGGT, and rHspA-GGT, a fusion protein based on HspA and GGT, were constructed and separately expressed in Escherichia coli and purified. Mice were then immunized intranasally with these proteins, with or without adjuvant. Immunized mice exhibited reduced bacterial colonization in stomach. The highest reduction in bacterial colonization was seen in mice immunized with the fusion protein rHspA-GGT when paired with the mucosal adjuvant LTB. Protection against H. pylori colonization was mediated by a strong systemic and localized humoral immune response, as well as a balanced Th1/Th2 cytokine response. In addition, immunofluorescence microscopy confirmed that rHspA-GGT specific rabbit antibodies were able to directly bind H. pylori in vitro. These results suggest antibodies are essential to the protective immunity associated with rHspA-GGT immunization. In summary, our results suggest HspA and GGT are promising vaccine candidates for protection against H. pylori infection.

Protection against Escherichia coli O157:H7 challenge by immunization of mice with purified Tir proteins

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 infections cause serious public health problems worldwide. The translocation intimin receptor (Tir) is responsible for adhesion and attaching and effacing lesions. In the current study, we used a mitomycin-treated mouse model to evaluate the efficacy of subcutaneous vs intranasal administration of the recombinant Tir as vaccine. Following immunization, mice were infected with E. coli O157:H7 and faces were monitored for shedding. Mice immunized intrasally with purified Tir proteins produced higher IgG and IgA titers in serum and feces, resulting in significant reductions in fecal shedding of EHEC O157 and higher a survival rate (92.9%), compared with subcutaneous or control immunizations. These results demonstrate the potential for the use of Tir proteins in mucosal vaccine formulations to prevent colonization and shedding of E. coli O157:H7. Therefore, purified Tir protects mice against EHEC challenge after intranasal immunization and is worth further clinical development as a vaccine candidate.