N-terminus of Flagellin Fused to an Antigen Improves Vaccine Efficacy against Pasteurella multocida Infection in Chickens

Engineered bacteria in tumor immunotherapy

As the limitations of cancer immunotherapy become increasingly apparent, there is considerable anticipation regarding the utilization of biological tools to enhance treatment efficacy, particularly bacteria and their derivatives. Leveraging advances in genetic and synthetic biology technologies, engineered bacteria now play important roles far beyond those of conventional immunoregulatory agents, and they could function as tumor-targeting vehicles and in situ pharmaceutical factories. In recent years, these engineered bacteria play a role in almost every aspect of immunotherapy. It is nothing short of impressive to keep seeing different strain of bacteria modified in diverse ways for unique immunological enhancement. In this review, we have scrutinized the intricate interplay between the immune system and these engineered bacteria. These interactions generate strategies that can directly or indirectly optimize immunotherapy and even modulate the effects of combination therapies. Collectively, these engineered bacteria present a promising novel therapeutic strategy that promises to change the current landscape of immunotherapy.

Advancing PEDV Vaccination: Comparison between Inactivated and Flagellin N-Terminus-Adjuvanted Subunit Vaccines

Vaccinations can serve as an important preventive measure against the porcine epidemic diarrhea (PED) virus that currently threatens the swine industry. This study focuses on the development of a fusion protein vaccine, FliC99-mCOE, which combines the N-terminus of flagellin (FliC99) with a modified core neutralizing epitope (mCOE) of PEDV. In silico immunoinformatic analysis confirmed the construct's non-toxic, non-allergenic, and highly antigenic nature. Molecular docking and molecular dynamics (MD) simulations demonstrated FliC99-mCOE's strong binding to the TLR-5 immunological receptor. Repeated exposure simulations and immunological simulations suggested enhanced cell-mediated immunity. Both FliC99-mCOE and an inactivated PEDV vaccine were produced and tested in mice. The results from cell proliferation, ELISA, and neutralization assays indicated that FliC99-mCOE effectively stimulated cellular immunity and neutralized PEDV. We conclude that the FliC99-mCOE fusion protein may serve as a promising vaccine candidate against PEDV.

Self-Assembling Nanovaccine Fused with Flagellin Enhances Protective Effect against Foot-and-Mouth Disease Virus

Nanovaccines based on self-assembling nanoparticles (NPs) can show conformational epitopes of antigens and they have high immunogenicity. In addition, flagellin, as a biological immune enhancer, can be fused with an antigen to considerably enhance the immune effect of antigens. In improving the immunogenicity and stability of a foot-and-mouth disease virus (FMDV) antigen, novel FMDV NP antigens were prepared by covalently coupling the VP1 protein and truncated flagellin containing only N-terminus D0 and D1 (N-terminal aa 1-99, nFLiC) with self-assembling NPs (i301). The results showed that the fusion proteins VP1-i301 and VP1-i301-nFLiC can assemble into NPs with high thermal tolerance and stability, obtain high cell uptake efficiency, and upregulate marker molecules and immune-stimulating cytokines in vitro. In addition, compared with monomeric VP1 antigen, high-level cytokines were stimulated with VP1-i301 and VP1-i301-nFLiC nanovaccines in guinea pigs, to provide clinical protection against viral infection comparable to an inactivated vaccine. This study provides new insight for the development of a novel FMD vaccine.

Recombinant-attenuated Salmonella enterica serovar Choleraesuis vector expressing the PlpE protein of Pasteurella multocida protects mice from lethal challenge

BACKGROUND

Bacterial surface proteins play key roles in pathogenicity and often contribute to microbial adhesion and invasion. Pasteurella lipoprotein E (PlpE), a Pasteurella multocida (P. multocida) surface protein, has recently been identified as a potential vaccine candidate. Live attenuated Salmonella strains have a number of potential advantages as vaccine vectors, including immunization with live vector can mimic natural infections by organisms, lead to the induction of mucosal, humoral, and cellular immune responses. In this study, a previously constructed recombinant attenuated Salmonella Choleraesuis (S. Choleraesuis) vector rSC0016 was used to synthesize and secrete the surface protein PlpE of P. multocida to form the vaccine candidate rSC0016(pS-PlpE). Subsequently, the immunogenicity of S. Choleraesuis rSC0016(pS-PlpE) as an oral vaccine to induce protective immunity against P. multocida in mice was evaluated.

RESULTS

After immunization, the recombinant attenuated S. Choleraesuis vector can efficiently delivered P. multocida PlpE protein in vivo and induced a specific immune response against this heterologous antigen in mice. In addition, compared with the inactivated vaccine, empty vector (rSC0016(pYA3493)) and PBS immunized groups, the rSC0016(pS-PlpE) vaccine candidate group induced higher antigen-specific mucosal, humoral and mixed Th1/Th2 cellular immune responses. After intraperitoneal challenge, the rSC0016(pS-PlpE) immunized group had a markedly enhanced survival rate (80%), a better protection efficiency than 60% of the inactivated vaccine group, and significantly reduced tissue damage.

CONCLUSIONS

In conclusion, our study found that the rSC0016(pS-PlpE) vaccine candidate provided good protection against challenge with wild-type P. multocida serotype A in a mouse infection model, and may potentially be considered for use as a universal vaccine against multiple serotypes of P. multocida in livestock, including pigs.

Cloning, DNA sequence, and expression of flagellins from high and low virulence strains of Edwardsiella tarda and their macrophage-stimulating activities

Edwardsiella tarda is a causative pathogen of edwardsiellosis in fish. Our previous studies on high (NUF251) and low (NUF194) virulent strains of E. tarda demonstrated that NUF251 strain induced significantly higher levels of NO and TNF-α from fish and mouse macrophages than NUF194 strain. Subsequent studies suggested that a flagellin-like protein secreted from E. tarda might be a responsible factor for the macrophage-stimulating activities. To evaluate the activities of flagellins of E. tarda, in this study, the flagellin genes of NUF251 and NUF194 strains were isolated by PCR and cloned into pQE-30 and pCold I expression vectors, and then the recombinant flagellins of two strains were overexpressed in E. coli JM109 and pG-Tf/BL21, respectively. The molecular weight of the purified recombinant flagellins of NUF251 and NUF194 strains were estimated to be 45 kDa and 37 kDa, respectively on SDS-PAGE analysis. Referring the three-dimensional structure of Salmonella flagellin, which has been reported to have 4 domains (D0, D1, D2, and D3), high sequence homology between two flagellins of E. tarda was observed at conservative domain (D0 and D1) regions, whereas the sequences equivalent to D2 and D3 domains were different, and even equivalent to 57 amino acids were deleted in NUF194. Both recombinant flagellins induced NO production, mRNA expression level of inducible NO synthase (iNOS), and intercellular ROS production in mouse macrophage cell line RAW264.7 cells. Also, the secretion of TNF-α and its mRNA expression level were increased by treatment of both recombinant flagellins. These results indicate that the recombinant flagellins from different virulent E. tarda strains can stimulate macrophages with nearly equal levels as judged by the parameters tested, even though they are differences in the structure and molecular weight, suggesting that conservative D0 and D1 domains are sufficient structural elements for the recombinant flagellins to induce a certain level of macrophage-stimulation in vitro. Further studies are necessary focusing on the role of D2 and D3 domain regions of the recombinant flagellins as macrophage-stimulating agent as well as their influence on host immune system in vivo.

Flagellin Improves the Immune Response of an Infectious Bursal Disease Virus (IBDV) Subunit Vaccine

Flagellin activates the immune system through Toll-like receptor 5 (TLR5) and can work as an adjuvant for subunit vaccines. In this study, we tested the adjuvancy of two different N-terminal fragments of flagellin, (1) FliC99, residues 1–99, and (2) FliC176, residues 1–176, to incorporate larger areas of the hotspot region for potentially higher levels of TLR5 activation and immune response. A truncated version of the VP2 protein (name tVP2, residues 199–356) of the Infectious bursal disease virus (IBDV) was genetically linked to the flagellin constructs, and the immune response was evaluated in chickens. Results showed that both chimeric antigen–adjuvant constructs increased humoral (total IgG titers), cellular and cytokine immune response (IL-4, IFN-γ). The resulting antibody also successfully neutralized IBDV. We conclude that the N-terminus of flagellin can act as an immune activator to enhance vaccine efficacy.

Signal sequence contributes to the immunogenicity of Pasteurella multocida lipoprotein E

Recombinant Pasterurella multocida lipoprotein E (PlpE) has been shown to protect against fowl cholera. This study aimed to determine if the signal sequence may contribute to the antigenicity and protective efficacy of recombinant PlpE. A small antigenic domain of PlpE (termed truncated PlpE, tPlpE) was constructed with (SP-tPlpE) or without (tPlpE) the signal sequence and evaluated in vitro and in vivo. In vitro, the HEK-Bule hTLR2 Cells were used to evaluate the activation of NF-kB in the test associated with the stimulation of the SP-tPlpE and tPlpE proteins. When chickens were immunized, compared to the tPlpE vaccine group, the SP-tPlpE group showed higher antibody levels and enhanced CD4⁺ T cell response. In a challenge test, the SP-tPlpE group showed a survival rate of 87.5% (n = 8), compared to 25% for the tPlpE group. It is confirmed that the inclusion of the native signal sequence enhanced protective efficacy against fowl cholera and may act as a vaccine adjuvant. The short SP-tPlpE construct is amenable to further vaccine engineering and has potential to be developed as a fowl cholera vaccine.

N-terminus of flagellin enhances vaccine efficacy against Actinobacillus pleuropneumoniae

BACKGROUND

Flagellin elicits potent immune response and may serve as a vaccine adjuvant. We previously reported that the N-terminus of flagellin (residues 1-99, nFliC) is sufficient for vaccine efficacy enhancement against Pasteurella multocida challenge in chickens. In this study, we futher tested the adjuvancy of nFliC in a subunit vaccine against the pig pathogen Actinobacillus pleuropneumoniae in a mice model. For vaccine formulation, the antigen ApxIIPF (the pore-forming region of the exotoxin ApxII) was combined with nFliC, either through genetic fusion or simple admixture.

RESULTS

Immune analysis showed that nFliC, introduced through genetic fusion or admixture, enhanced both humoral (antibody levels) and cellular (T cell response and cytokine production) immunity. In a challenge test, nFliC increased vaccine protective efficacy to 60-80%, vs. 20% for the antigen-only group. Further analysis showed that, even without a supplemental adjuvant such as mineral salt or oil emulsion, genetically linked nFliC still provided significant immune enhancement.

CONCLUSIONS

We conclude that nFliC is a versatile and potent adjuvant for vaccine formulation.

Development of a Subunit Vaccine against Duck Hepatitis A Virus Serotype 3

In this study, we sought to develop a subunit vaccine against the increasingly prevalent Duck hepatitis A virus serotype 3 (DHAV-3). The VP1 protein of DHAV-3 and a truncated version containing the C-terminal region of VP1, termed VP1-C, were expressed recombinantly in Escherichia coli as vaccine antigens. For enhanced immune response, a truncated version of flagellin, nFliC, was included as vaccine adjuvant. Ducklings were vaccinated once for immune response analysis and challenge test. Results showed that VP1-C elicited a higher level of virus-specific antibody response and neutralization titer than VP1. The addition of nFliC further enhanced the antibody response. In terms of cellular immune response, the VP1-C + nFliC vaccine elicited the highest level of T cell proliferation among the vaccine formulations tested. Examination of the cytokine expression profile showed that peripheral blood mononuclear cells from the VP1-C + nFliC vaccine group expressed the highest levels of pro-inflammatory (IL-6) and TH-1 type (IL-12 and IFN-γ) cytokines. Finally, in a DHAV-3 challenge test, the VP1-C + nFliC vaccine provided a 75% protection rate (n = 8), in contrast to 25% for the VP1 vaccine. In conclusion, E. coli-expressed VP1-C has been shown to be a promising antigen when combined with nFliC and may be further developed as a single-dose subunit vaccine against DHAV-3.

The Role of Flagellin B in Vibrio anguillarum-Induced Intestinal Immunity and Functional Domain Identification

Vibrio anguillarum, an opportunistic pathogen of aquatic animals, moves using a filament comprised of polymerised flagellin proteins. Flagellins are essential virulence factors for V. anguillarum infection. Herein, we investigated the effects of flagellins (flaA, flaB, flaC, flaD and flaE) on cell apoptosis, TLR5 expression, and production of IL-8 and TNF-α. FlaB exhibited the strongest immunostimulation effects. To explore the functions of flaB in infection, we constructed a flaB deletion mutant using a two-step recombination method, and in vitro experiments showed a significant decrease in the expression of TLR5 and inflammatory cytokines compared with wild-type cells. However in the in vivo study, expression of inflammatory cytokines and intestinal mucosal structure showed no significant differences between groups. Additionally, flaB induced a significant increase in TLR5 expression based on microscopy analysis of fluorescently labelled TLR5, indicating interactions between the two proteins, which was confirmed by native PAGE and yeast two-hybrid assay. Molecular simulation of interactions between flaB and TLR5 was performed to identify the residues involved in binding, revealing two binding sites. Then, based on molecular dynamics simulations, we carried out thirteen site-directed mutations occurring at the amino acid sites of Q57, N83, N87, R91, D94, E122, D152, N312, R313, N320, L97, H316, I324 in binding regions of flaB protein by TLR5, respectively. Surface plasmon resonance (SPR) was employed to compare the affinities of flaB mutants for TLR5, and D152, D94, I324, N87, R313, N320 and H316 were found to mediate interactions between flaB and TLR5. Our comprehensive and systematic analysis of V. anguillarum flagellins establishes the groundwork for future design of flagellin-based vaccines.

Glycyrrhiza polysaccharides can improve and prolong the response of chickens to the Newcastle disease vaccine

Licorice is a medicinal and food plant widely used to treat diseases and produce food additives, because of its unique chemical constituents like polysaccharides, flavones, and saponins. Glycyrrhiza Polysaccharides (GPS-1) are water-soluble neutral polysaccharides extracted from licorice. Currently, GPS-1 is administrated to chickens by gavage every d for 14 d to observe the impact of GPS-1 on the Newcastle disease vaccine. To determine the immunity of these chickens to NDV, blood serum levels of hemagglutinin-inhibition (HI) antibody, and immunoglobulins IgA and IgG were measured. Meanwhile, the expression levels of cytokines IL-2, IL-4, IL-17, and IFN-γ were measured to evaluate the degree of immune booster activity. The chickens' spleen and peripheral blood lymphocytes displayed a significant increase in the proportion of CD4+ and CD8+ T cells after booster treatments with GPS-1. The results indicated that GPS-1 had a significant, dose-dependent, immune-boosting effect which could enhance NDV vaccine immunity in chickens.

Macrophage Activation Assays to Evaluate the Immunostimulatory Capacity of Avibacterium paragallinarum in A Multivalent Poultry Vaccine

High-quality vaccines are crucial to prevent infectious disease outbreaks in the poultry industry. In vivo vaccination tests are routinely used to test poultry vaccines for their potency, i.e., their capacity to induce protection against the targeted diseases. A better understanding of how poultry vaccines activate immune cells will facilitate the replacement of in vivo potency tests for in vitro assays. Using the chicken macrophage-like HD11 cell line as a model to evaluate innate immune responses, the current explorative study addresses the immunostimulatory capacity of an inactivated multivalent vaccine for infectious bronchitis, Newcastle disease, egg-drop syndrome, and infectious coryza. The vaccine stimulated HD11 cells to produce nitric oxide and to express pro-inflammatory cytokines IL-1β, TNF, and IL-12p40, chemokines CXCLi1 and CXCLi2, and the anti-inflammatory cytokine IL-10, but only when inactivated Avibacterium paragallinarum, the causative agent of infectious coryza, was present. Lipopolysaccharides from Avibacterium paragallinarum were crucial for the production of nitric oxide and expression of IL-1β and CXCLi1. The described immune parameters demonstrate the capacity of this multivalent vaccine to activate innate immune cells and may in the future, combined with antigen quantification methods, contribute to vaccine quality testing in vitro, hence the replacement of current in vivo vaccination tests.