Generation of a novel chimeric PALFn antigen of Bacillus anthracis and its immunological characterization in mouse model

Anthrax Vaccines in the 21st Century

Vaccination against Bacillus anthracis is the best preventive measure against the development of deadly anthrax disease in the event of exposure to anthrax either as a bioweapon or in its naturally occurring form. Anthrax vaccines, however, have historically been plagued with controversy, particularly related to their safety. Fortunately, recent improvements in anthrax vaccines have been shown to confer protection with reduced short-term safety concerns, although questions about long-term safety remain. Here, we (a) review recent and ongoing advances in anthrax vaccine development, (b) emphasize the need for thorough characterization of current (and future) vaccines, (c) bring to focus the importance of host immunogenetics as the ultimate determinant of successful antibody production and protection, and (d) discuss the need for the systematic, active, and targeted monitoring of vaccine recipients for possible Chronic Multisymptom Illness (CMI).

Efficacy assessment of a triple anthrax chimeric antigen as a vaccine candidate in guinea pigs: challenge test with Bacillus anthracis 17 JB strain spores

CONTEXT

Bacillus anthracis secretes a tripartite toxin comprising protective antigen (PA), edema factor (EF), and lethal factor (LF). The human anthrax vaccine is mainly composed of the anthrax protective antigen (PA). Considerable efforts are being directed towards improving the efficacy of vaccines because the use of commercial anthrax vaccines (human/veterinary) is associated with several limitations.

OBJECTIVE

In this study, a triple chimeric antigen referred to as ELP (gene accession no: MT590758) comprising highly immunogenic domains of PA, LF, and EF was designed, constructed, and assessed for the immunization capacity against anthrax in a guinea pig model.

MATERIALS AND METHODS

Immunization was carried out considering antigen titration and immunization protocol. The immunoprotective efficacy of the ELP was evaluated in guinea pigs and compared with the potency of veterinary anthrax vaccine using a challenge test with B. anthracis 17JB strain spores.

RESULTS

The results demonstrated that the ELP antigen induced strong humoral responses. The T-cell response of the ELP was found to be similar to PA, and showed that the ELP could protect 100%, 100%, 100%, 80% and 60% of the animals from 50, 70, 90, 100 and 120 times the minimum lethal dose (MLD, equal 5 × 10⁵ spore/ml), respectively, which killed control animals within 48 h.

DISCUSSION AND CONCLUSIONS

It is concluded that the ELP antigen has the necessary requirement for proper immunization against anthrax and it can be used to develop an effective recombinant vaccine candidate against anthrax.

A novel role of the miR-152-3p/ERRFI1/STAT3 pathway modulates the apoptosis and inflammatory response after acute kidney injury

Acute kidney injury (AKI) is one of the most common and serious complications in the development of sepsis. Many microRNAs are closely related to the occurrence, development, and prognosis of sepsis AKI (but the effect and mechanism of miR-152-3p in it is unclear). Meanwhile, the ERBB receptor feedback inhibitor 1 (ERRFI1) has a negative regulatory effect on signal transducer and activator of transcription 3 (STAT3) phosphorylation on uterine epithelial cells. But, the relationship between miR-152-3p and renal function, inflammatory factors, prognosis in AKI, and the mechanism is not clear. Analyzing sepsis-induced AKI rats and the cell model, our results revealed that miR-152-3p was upregulated in septic AKI patients and positively correlated with serum creatinine, urea nitrogen, interleukin 1β (IL-1β) and tumor necrosis factor α (TNF-α). Downregulation of miR-152-3p with the inhibitor could dramatically attenuate caspase-3, bromodeoxyuridine and IL-1β, and TNF-α in the AKI rats' model. Furthermore, downregulation of miR-152-3p attenuated lipopolysaccharide-induced apoptosis and inflammatory response in HK-2 and HEK293 cells. To further explore the mechanisms, we found ERRFI1 was appreciably downregulated and STAT3 was upregulated in AKI, whereas ERRFI1 was radically upregulated and STAT3 was greatly downregulated after the addition of miR-152-3p inhibitor, no matter in vivo or in vitro. Summarily, our study confirmed that miR-152-3p could promote the expression of STAT3 by targeting ERRFI1, aggravate cell apoptosis and inflammatory response, and thereby aggravate kidney injury in sepsis AKI.

Development of a novel chimeric PA-LF antigen of Bacillus anthracis, its immunological characterization and evaluation as a future vaccine candidate in mouse model

Tremendous efforts are being made to develop an anthrax vaccine with long term protection. The main component of traditional anthrax vaccine is protective antigen (PA) with the trace amount of other proteins and bacterial components. In this study, we developed a recombinant PA-LF chimera antigen of Bacillus anthracis by fusing the PA domain 2-4 with lethal factor (LF) domain 1 and evaluated its protective potential against B. anthracis in mouse model. The anti-PA-LF chimera serum reacted with both PA and LF antigen, individually. The chimera elicited a strong antibody titer in mice with predominance of IgG1 isotype followed by IgG2b, IgG2a and IgG3. Cytokines were assessed in splenocytes of immunized mice and a significant up-regulation in the expression of IL-4, IL-10, IFN-γ and TNF-α was observed. The PA-LF chimera immunized mice exhibited 80% survival after challenge with virulent spores of B. anthracis. Pathological studies showed normal architecture in vital organs (spleen, lung, liver and kidney) of recovered immunized mice on 20 DPI after spore challenge. These findings suggested that PA-LF chimera of B. anthracis elicited good humoral as well as cell mediated immune response in mice, and thus, can be a potent vaccine candidate against anthrax.

Vaccines against anthrax based on recombinant protective antigen: problems and solutions

Introduction: Anthrax is a dangerous bio-terror agent because Bacillus anthracis spores are highly resilient and can be easily aerosolized and disseminated. There is a threat of deliberate use of anthrax spores aerosol that could lead to serious fatal diseases outbreaks. Existing control measures against inhalation form of the disease are limited. All of this has provided an impetus to the development of new generation vaccines. Areas сovered: This review is devoted to challenges and achievements in the design of vaccines based on the anthrax recombinant protective antigen (rPA). Scientific databases have been searched, focusing on causes of PA instability and solutions to this problem, including new approaches of rPA expression, novel rPA-based vaccines formulations as well as the simultaneous usage of PA with other anthrax antigens. Expert opinion: PA is a central anthrax toxin component, playing a key role in the defense against encapsulated and unencapsulated strains. Subunit rPA-based vaccines have a good safety and protective profile. However, there are problems of PA instability that are greatly enhanced when using aluminum adjuvants. New adjuvant compositions, dry formulations and resistant to proteolysis and deamidation mutant PA forms can help to handle this issue. Devising a modern anthrax vaccine requires huge efforts.

Development of a novel multiepitope chimeric vaccine against anthrax

Bacillus anthracis (BA), the etiological agent of anthrax, secretes protective antigen (PA), lethal factor (LF), and edema factor (EF) as major virulence mediators. Amongst these, PA-based vaccines are most effective for providing immunity against BA, but their low shelf life limits their usage. Previous studies showed that B-cell epitopes, ID II and ID III present in PA domain IV possess higher toxin neutralization activity and elicit higher antibody titer than ID I. Moreover, N-terminal region of both LF and EF harbors PA-binding sites which share 100% identity with each other. Here, in this study, we have developed an epitope-based chimeric vaccine (ID-LFn) comprising ID II-ID III region of PA and N-terminal region of LF. We have also evaluated its protective efficacy as well as stability and found it to be more stable than PA-based vaccine. Binding reactivities of ID-LFn with anti-PA/LF/EF antibodies were determined by ELISA. The stability of chimeric vaccine was assessed using circular dichroism spectroscopy. ID-LFn response was characterized by toxin neutralization, lymphocyte proliferation isotyping and cytokine profiling. The protective efficacy was analyzed by challenging ID-LFn-immunized mice with B. anthracis (pXO1⁺ and pXO2⁺). ID-LFn was found to be significantly stable as compared to PA. Anti-ID-LFn antibodies recognized PA, LF as well as EF. The T-cell response and the protective efficacy of ID-LFn were found to be almost similar to PA. ID-LFn exhibits equal protective efficacy in mice and possesses more stability as compared to PA along with the capability of recognizing PA, LF and EF at the same time. Thus, it can be considered as an improved vaccine against anthrax with better shelf life. ID-LFn, a novel multiepitope chimeric anthrax vaccine: ID-LFn comprises of immunodominant epitopes of domain 4 of PA and N-terminal homologous stretch of LF and EF. The administration of this protein as a vaccine provides protection against anthrax.

Anthrax lethal toxin (LeTx) neutralization by PA domain specific antisera

Anthrax associated causalities in humans and animals are implicated mainly due to the action of two exotoxins that are secreted by the bacterium Bacillus antharcis during the infection. These exotoxins comprise of three protein components namely protective antigen (PA), lethal factor (LF) and edema factor (EF). The protective antigen is the common toxin component required to form both lethal toxin (LeTx) and edema toxin (EdTx). The LeTx is formed, when PA combines with LF and EdTx is formed when PA combines with EF. Therapeutic interventions aiming to neutralize these key effectors of anthrax pathology would therefore, provide an effective means to counter the toxicity imposed by the anthrax toxins on the host. The present work describes the lethal toxin neutralization potential of polyclonal antisera developed against the individual domains of the protective antigen component of the anthrax toxin. The individual domains were produced as recombinant proteins in E. coli and validated with peptide mass fingerprinting by MALDI-TOF analysis and corresponding mice polyclonal antisera by western blotting. Each domain specific antibody titre and isotype was ascertained by ELISA. The isotyping revealed the predominance of IgG1 isotype. The toxin neutralizing potential of these domain specific antisera were evaluated by in-vitro cell viability MTT assay, employing J774.1 mouse macrophage cell line against LeTx (0.25 μg ml^-1 PA and 0.125 μg ml^-1 LF concentrations). Among the four domain specific antisera, the antiserum against PA domain IV could neutralize LeTx with high efficiency. No significant neutralization of LeTx was observed with other domain specific antibodies. Results indicate that antibodies to r-PA domain IV could be explored further as therapeutic anti toxin molecule along with appropriate antibiotic regimens against anthrax.