Bacterial ghosts as adjuvants: mechanisms and potential

Peptides with Antimicrobial Activity in the Saliva of the Malaria Vector Anopheles coluzzii

Mosquito saliva plays a crucial physiological role in both sugar and blood feeding by helping sugar digestion and exerting antihemostatic functions. During meal acquisition, mosquitoes are exposed to the internalization of external microbes. Since mosquitoes reingest significant amounts of saliva during feeding, we hypothesized that salivary antimicrobial components may participate in the protection of mouthparts, the crop, and the gut by inhibiting bacterial growth. To identify novel potential antimicrobials from mosquito saliva, we selected 11 candidates from Anopheles coluzzii salivary transcriptomic datasets and obtained them either using a cell-free transcription/translation expression system or, when feasible, via chemical synthesis. Hyp6.2 and hyp13, which were predicted to be produced as propeptides and cleaved in shorter mature forms, showed the most interesting results in bacterial growth inhibition assays. Hyp6.2 (putative mature form, 35 amino acid residues) significantly inhibited the growth of Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli and Serratia marcescens) bacteria. Hyp13 (short form, 19 amino acid residues) dose-dependently inhibited E. coli and S. marcescens growth, inducing membrane disruption in both Gram-positive and Gram-negative bacteria as indicated with scanning electron microscopy. In conclusion, we identified two A. coluzzii salivary peptides inhibiting Gram-positive and Gram-negative bacteria growth and possibly contributing to the protection of mosquito mouthparts and digestive tracts from microbial infection during and/or after feeding.

Globally occurring pelagiphage infections create ribosome-deprived cells

Phages play an essential role in controlling bacterial populations. Those infecting Pelagibacterales (SAR11), the dominant bacteria in surface oceans, have been studied in silico and by cultivation attempts. However, little is known about the quantity of phage-infected cells in the environment. Using fluorescence in situ hybridization techniques, we here show pelagiphage-infected SAR11 cells across multiple global ecosystems and present evidence for tight community control of pelagiphages on the SAR11 hosts in a case study. Up to 19% of SAR11 cells were phage-infected during a phytoplankton bloom, coinciding with a ~90% reduction in SAR11 cell abundance within 5 days. Frequently, a fraction of the infected SAR11 cells were devoid of detectable ribosomes, which appear to be a yet undescribed possible stage during pelagiphage infection. We dubbed such cells zombies and propose, among other possible explanations, a mechanism in which ribosomal RNA is used as a resource for the synthesis of new phage genomes. On a global scale, we detected phage-infected SAR11 and zombie cells in the Atlantic, Pacific, and Southern Oceans. Our findings illuminate the important impact of pelagiphages on SAR11 populations and unveil the presence of ribosome-deprived zombie cells as part of the infection cycle.

Comparison of the immune effects of the Chlamydia abortus MOMP antigen displayed in different parts of bacterial ghosts

Bacterial ghosts (BGs) are promising vaccine platforms owing to their high adjuvant properties and delivery efficiency. Heterologous antigens can be anchored to different parts of BGs using genetic engineering strategies to prepare vaccines. However, several key issues need to be resolved, including the efficient preparation of BGs and determining the optimal anchoring position of exogenous antigens in the BGs. Here, we prepared an efficient temperature-controlled lysis system using lysis gene E of phage PhiX174 and used the major outer membrane protein (MOMP) of Chlamydia abortus (C. abortus) as a model antigen to explore the optimal display location of exogenous antigens in BGs. We demonstrated that the constructed recombinant temperature-controlled lysis plasmid can still stably inhibit E gene expression at 37°C, and the lysis efficiency of E. coli can reach above 99.9%. Four recombinant MOMP Escherichia coli (E. coli) ghost vaccines were constructed using different anchor sequences. These vaccines all induced strong specific antibody responses and secrete high levels of IFN-γ in immunized mice and significantly increased the clearance of C. abortus in a mouse infection model. Notably, the strongest immune effect was observed when MOMP was displayed on the surface of E. coli ghosts (rECG-InpN-M), which resulted in the clearance of C. abortus in mice 6 days earlier than that with the recombinant MOMP vaccine. Altogether, we constructed an efficient BG temperature-controlled lysis system and provided a feasible strategy for developing a BG delivery platform with enhanced immune effects.

Bacteria-Based Nanoprobes for Cancer Therapy

Surgical removal together with chemotherapy and radiotherapy has used to be the pillars of cancer treatment. Although these traditional methods are still considered as the first-line or standard treatments, non-operative situation, systemic toxicity or resistance severely weakened the therapeutic effect. More recently, synthetic biological nanocarriers elicited substantial interest and exhibited promising potential for combating cancer. In particular, bacteria and their derivatives are omnipotent to realize intrinsic tumor targeting and inhibit tumor growth with anti-cancer agents secreted and immune response. They are frequently employed in synergistic bacteria-mediated anticancer treatments to strengthen the effectiveness of anti-cancer treatment. In this review, we elaborate on the development, mechanism and advantage of bacterial therapy against cancer and then systematically introduce the bacteria-based nanoprobes against cancer and the recent achievements in synergistic treatment strategies and clinical trials. We also discuss the advantages as well as the limitations of these bacteria-based nanoprobes, especially the questions that hinder their application in human, exhibiting this novel anti-cancer endeavor comprehensively.

Graphene oxide as novel vaccine adjuvant

To improve antigen immunogenicity and promote long-lasting immunity, vaccine formulations have been appropriately supplemented with adjuvants. Graphene has been found to enhance the presentation of antigens to CD8+ T cells, as well as stimulating innate immune responses and inflammatory factors. Its properties, such as large surface area, water stability, and high aspect ratio, make it a suitable candidate for delivering biological substances. Graphene-based nanomaterials have recently attracted significant attention as a new type of vaccine adjuvants due to their potential role in the activation of immune responses. Due to the limited functionality of some approved human adjuvants for use, the development of new all-purpose adjuvants is urgently required. Research on the immunological and biomedical use of graphene oxide (GO) indicates that these nanocarriers possess excellent physicochemical properties, acceptable biocompatibility, and a high capacity for drug loading. Graphene-based nanocarriers also could improve the function of some immune cells such as dendritic cells and macrophages through specific signaling pathways. However, GO injection can lead to significant oxidative stress and inflammation. Various surface functionalization protocols have been employed to reduce possible adverse effects of GO, such as aggregation of GO in biological liquids and induce cell death. Furthermore, these modifications enhance the properties of functionalized-GO's qualities, making it an excellent carrier and adjuvant. Shedding light on different physicochemical and structural properties of GO and its derivatives has led to their application in various therapeutic and drug delivery fields. In this review, we have endeavored to elaborate on different aspects of GO.

Advancements in Vaccine Adjuvants: The Journey from Alum to Nano Formulations

Vaccination is a groundbreaking approach in preventing and controlling infectious diseases. However, the effectiveness of vaccines can be greatly enhanced by the inclusion of adjuvants, which are substances that potentiate and modulate the immune response. This review is based on extensive searches in reputable databases such as Web of Science, PubMed, EMBASE, Scopus, and Google Scholar. The goal of this review is to provide a thorough analysis of the advances in the field of adjuvant research, to trace the evolution, and to understand the effects of the various adjuvants. Historically, alum was the pioneer in the field of adjuvants because it was the first to be approved for use in humans. It served as the foundation for subsequent research and innovation in the field. As science progressed, research shifted to identifying and exploiting the potential of newer adjuvants. One important area of interest is nano formulations. These advanced adjuvants have special properties that can be tailored to enhance the immune response to vaccines. The transition from traditional alum-based adjuvants to nano formulations is indicative of the dynamism and potential of vaccine research. Innovations in adjuvant research, particularly the development of nano formulations, are a promising step toward improving vaccine efficacy and safety. These advances have the potential to redefine the boundaries of vaccination and potentially expand the range of diseases that can be addressed with this approach. There is an optimistic view of the future in which improved vaccine formulations will contribute significantly to improving global health outcomes.

In Vivo Validation of Novel Synthetic tbp1 Peptide-Based Vaccine Candidates against Haemophilus influenzae Strains in BALB/c Mice

Haemophilus influenzae is a Gram-negative bacterium characterized as a small, nonmotile, facultative anaerobic coccobacillus. It is a common cause of a variety of invasive and non-invasive infections. Among six serotypes (a-f), H. influenzae type b (Hib) is the most familiar and predominant mostly in children and immunocompromised individuals. Following Hib vaccination, infections due to other serotypes have increased in number, and currently, there is no suitable effective vaccine to induce cross-strain protective antibody responses. The current study was aimed to validate the capability of two 20-mer highly conserved synthetic tbp1 (transferrin-binding protein 1) peptide-based vaccine candidates (tbp1-E1 and tbp1-E2) predicted using in silico approaches to induce immune responses against H. influenzae strains. Cytokine induction ability, immune simulations, and molecular dynamics (MD) simulations were performed to confirm the candidacy of epitopic docked complexes. Synthetic peptide vaccine formulations in combination with two different adjuvants, BGs (Bacterial Ghosts) and CFA/IFA (complete/incomplete Freund's adjuvant), were used in BALB/c mouse groups in three booster shots at two-week intervals. An indirect ELISA was performed to determine endpoint antibody titers using the Student's t-distribution method. The results revealed that the synergistic use of both peptides in combination with BG adjuvants produced better results. Significant differences in absorbance values were observed in comparison to the rest of the peptide-adjuvant combinations. The findings of this study indicate that these tbp1 peptide-based vaccine candidates may present a preliminary set of peptides for the development of an effective cross-strain vaccine against H. influenzae in the future due to their highly conserved nature.

Weissella koreensis and Pediococcus pentosaceus bacterial ghosts induce inflammatory responses as immunostimulants

In this study, bacterial ghosts (BGs) were generated from Weissella koreensis LKS42 (WKorGs) and Pediococcus pentosacues KA94 (PPGs) by chemically inducing lysis using substances such as hydrochloric acid (HCl), sulfuric acid (H2SO4), nitric acid (HNO3), acetic acid (CH3COOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), sodium carbonate (Na2CO3), n-butanol, and C6H8O7. HCl-induced WKorGs and PPGs exhibited complete removal of DNA and displayed transverse membrane dissolution tunnel structures under scanning electron microscopy (SEM). Cell viability assays showed high viability of RAW 264.7 cells exposed to HCl-induced WKorGs and PPGs. Additionally, treatment with HCl-induced WKorGs and PPGs elevated mRNA levels of pro-inflammatory cytokines (IL-1β, IL-6, TNF-α, iNOS) and the anti-inflammatory cytokine IL-10 in RAW 264.7 cells. These findings suggest that HCl-induced WKorGs and PPGs have the potential to be used as inactivated bacterial immunostimulants, highlighting their promising applications in immunization and immunotherapy.

Vaccination with bacterial ghosts of Streptococcus iniae and Lactococcus garvieae originated from outbreak of marine fish streptococcosis, induce potential protection against the disease in Nile tilapia, Oreochromis niloticus (Linnaeus, 1758)

Streptococcosis is an important bacterial disease affects fresh, brackish and marine fish. The disease caused annual severe economic losses in Egyptian Mari-culture. S. iniae and L. garvieae usually the main causative agents isolated. The presented study conducted to prepare bacterial ghost vaccine (BGV) candidates from isolated strains of marine streptococcosis outbreaks using NaOH chemical approach. Selected strains confirmed as pathogenic for Nile tilapia, therefore the fish selected as an experimental model. In such respect, the re-isolated S. iniae and L. garvieae were used for ghost preparations, BGVs evaluation and fish challenges. Apart of four, three fish groups namely, A, B, C designated for BGVs evaluations, while the fourth one (D) designated as control. Vaccination experiments performed via intra-peritoneal injection with 0.1 mL (1.5 × 108 CFU/mL/fish) of their corresponding BGVs twice with 2 weeks' interval; however, control fish received 0.1 mL of fish saline instead. Blood, serum, and tissue samples collected from all groups at 2 and 4 weeks post immunization (PI) for estimation of hematological, innate, and specific immune parameters. At the end, all remained fish challenged with appropriated pathogen (s) and the relative percentage of survival (RPS) calculated. Three BGVs generated namely, SiG, in addition to, novel contributions of LgG and SiLgG. Ghosts were corresponding to S. iniae, L. garvieae and their both ghost mixtures, respectively. Fish groups immunized with prepared BGVs revealed variable significant increases in PCV, GLB, PP, SOD, CAT, C5, IL-β1, LZM, specific antibody titers and CD4 expression 2 and 4 weeks PI. MDA decreased in all vaccinated groups that was significantly with group C. Expression of MHC-II showed elevations 2 weeks PI, however, it significantly decreased at 4 weeks. The RPS recorded 90, 88.89 and 95.46% in immunized groups A, B and C, respectively. At all levels tested, obtained results proposed SiG, LgG and SiLgG as innovative vaccine candidates, which can protect cultured fish from being attacked by S. iniae, and/or L. garvieae.

Production of highly immunogenic and safe Triton X-100 produced bacterial ghost vaccine against Shigella flexneri 2b serotype

BACKGROUND

Bacterial ghost cells (BGCs) are cells were drained of their genetic and cytoplasmic components. This work aimed to develop vaccine candidates against the Shigella flexneri (S. flexneri) 2b serotype using the BGCs approach. For the first time, (S. flexneri) 2b serotype BGCs vaccine was prepared by incubation with Triton X-100 (TX100) for only 12 h. Its safety and immunogenicity were compared to another vaccine produced using a previously used surfactant, namely Tween 80 (TW80). Scanning electron microscopy (SEM), cellular DNA, protein contents measurements, and ghost cell re-cultivation were used to confirm the successful generation of the BGCs. Immunogenicity was assessed through mice's intraperitoneal (IP) immunization followed by infection with S. flexneri ATCC 12022. Finally, histopathological examination was carried out.

RESULTS

Viable colony forming units (CFUs) of S. flexneri were counted from stool samples as well as homogenized colon tissues of the non-immunized challenged group. Immunized mice sera showed a significant increase in serum bactericidal activity of both preparations (TX100 = 40% and TW80 = 56%) compared to the non-immunized challenged group (positive control). The IgG levels of the bacterial ghost-vaccinated groups were four and three times greater for the TX100 and TW80 ghost vaccines, respectively, compared to that of the positive control; both bacterial ghost vaccines (BGVs) were safe and effective, according to the results of the safety check tests and histopathological analysis.

CONCLUSIONS

When comparing the BGVs prepared using TX100 and TW80 methods, the use of TX100 as a new chemical treating agent for BGC production attained robust results in terms of shorter incubation time with the targeted cells and a strong immune response against S. flexneri 2b serotype ATCC 12022 in the IP challenge test. However, a clinical study is needed to confirm the efficacy and total safety of this novel vaccine.

A Comprehensive Review on Bacterial Vaccines Combating Antimicrobial Resistance in Poultry

Bacterial vaccines have become a crucial tool in combating antimicrobial resistance (AMR) in poultry. The overuse and misuse of antibiotics in poultry farming have led to the development of AMR, which is a growing public health concern. Bacterial vaccines are alternative methods for controlling bacterial diseases in poultry, reducing the need for antibiotics and improving animal welfare. These vaccines come in different forms including live attenuated, killed, and recombinant vaccines, and they work by stimulating the immune system to produce a specific response to the target bacteria. There are many advantages to using bacterial vaccines in poultry, including reduced use of antibiotics, improved animal welfare, and increased profitability. However, there are also limitations such as vaccine efficacy and availability. The use of bacterial vaccines in poultry is regulated by various governmental bodies and there are economic considerations to be taken into account, including costs and return on investment. The future prospects for bacterial vaccines in poultry are promising, with advancements in genetic engineering and vaccine formulation, and they have the potential to improve the sustainability of the poultry industry. In conclusion, bacterial vaccines are essential in combating AMR in poultry and represent a crucial step towards a more sustainable and responsible approach to poultry farming.

Use of adjuvant ISA VG 71 to produce neutralizing egg yolk antibodies against bothropic venom

The use of egg yolk antibodies-IgY technology-represents an alternative to the production of mammalian immunoglobulins and has several advantages regarding animal welfare and lower costs of production. The use of adjuvants to achieve the hyperimmunization of laying hens plays a key role in the success of the production of high levels of the antibodies. In the present work, two different adjuvant systems (Freund's adjuvants and Montanide^TM ISA 71 VG) were compared to produce IgY anti-Bothrops alternatus. For the first immunization, formalin-inactivated Salmonella was added to Montanide^TM ISA 71 VG to emulate Freund's complete adjuvant which includes a mycobacteria antigen. After eight immunizations, IgY produced by using either adjuvant was able to neutralize the lethal activity of the venom in a mouse model, but differences were found regarding the recognition of components of the venom between the two adjuvants tested. Overall, Montanide^TM adjuvant used in this work could be a good alternative choice to produce antibodies capable of neutralizing the lethality of complex antigens. This adjuvant is commercially available and used in the formulation of several poultry vaccines and could be used for the IgY technology instead of traditional immunomodulators such as Freund's adjuvants. Key points • IgY extracts recognized major components of the venom.• Avidity indexes of the IgY extracts increased after the successive immunizations.• IgY obtained by two adjuvant systems neutralized the lethal activity of the venom.

Non-antibiotic prevention and treatment against Acinetobacter baumannii infection: Are vaccines and adjuvants effective strategies?

Acinetobacter baumannii (A. baumannii) is a Gram-negative opportunistic pathogen widely attached to the surface of medical instruments, making it one of the most common pathogens of nosocomial infection, and often leading to cross-infection and co-infection. Due to the extensive antibiotic and pan-resistance, A. baumannii infection is facing fewer treatment options in the clinic. Therefore, the prevention and treatment of A. baumannii infection have become a tricky global problem. The requirement for research and development of the new strategy is urgent. Now, non-antibiotic treatment strategies are urgently needed. This review describes the research on A. baumannii vaccines and antibacterial adjuvants, discusses the advantages and disadvantages of different candidate vaccines tested in vitro and in vivo, especially subunit protein vaccines, and shows the antibacterial efficacy of adjuvant drugs in monotherapy.

Production of Lactobacillus plantarum ghosts by conditional expression of a prophage-encoded holin

Bacterial ghosts (BGs) are nonviable empty bacterial cell envelopes with intact cellular morphology and native surface structure. BGs made from pathogenic bacteria are used for biomedical and pharmaceutical applications. However, incomplete pathogenic cell inactivation during BG preparation raises safety concerns that could limit the intended use. Therefore, safer bacterial cell types are needed for BG production. Here, we produced BGs from the food-grade Gram-positive bacterium Lactobacillus plantarum TBRC 2-4 by conditional expression of a prophage-encoded holin (LpHo). LpHo expression was regulated using the pheromone-inducible pSIP system and LpHo was localized to the cell membrane. Upon LpHo induction, a significant growth retardation and a drastic decrease in cell viability were observed. LpHo-induced cells also showed membrane pores by scanning electron microscopy, membrane depolarization by flow cytometry, and release of nucleic acid contents in the cell culture supernatant, consistent with the role of LpHo as a pore-forming protein and L. plantarum ghost formation. The holin-induced L. plantarum BG platform could be developed as a safer alternative vehicle for the delivery of biomolecules.

Production and Characterization of Bacterial Ghost Vaccine against Neisseria meningitidis

Bacterial ghosts (BGS) are empty non-living envelopes produced either genetically or chemically. This study investigated a novel chemical protocol for the production of Neisseria meningitidis ghost vaccine using tween 80 followed by a pH reduction with lactic acid. For our vaccine candidate, both safety and immunogenicity aspects were evaluated. The ghost pellets showed no sign of growth upon cultivation. BGS were visualized by scanning electron microscopy, illustrating the formation of trans-membrane tunnels with maintained cell morphology. Gel electrophoresis showed no distinctive bands of the cytoplasmic proteins and DNA, assuring the formation of ghost cells. In animal model, humoral immune response significantly increased when compared to commercial vaccine (p < 0.01). Moreover, serum bactericidal assay (SBA) recorded 94.67% inhibition compared to 64% only for the commercial vaccine after three vaccination doses. In conclusion, this is the first N. meningitidis ghost vaccine candidate, proven to be effective, economic, and with significant humoral response and efficient SBA values; however, clinical studies should be performed.

Screening the potential part of the G protein antigen is an achievable strategy to improve the immune effect of DNA vaccine against MSRV infection

DNA vaccines, as an effective prophylactic technology to induce both humoral and cellular immune responses, have already been widely studied to prevent and control viral and bacterial infections in aquaculture. To find a more effective and safer way to control Micropterus salmoides rhabdovirus (MSRV) infection in largemouth bass, two different DNA vaccines expressing partial (pcDNA3.1-G2) and full-length (pcDNA3.1-G) of the MSRV G protein were developed and injected intramuscularly with different doses. The immune effect was comprehensively compared and evaluated by detecting immune-related parameters including serum antibody levels, immune-related physiological indexes, immune-related gene expression and relative survival rates in this study. The results showed that compared with the pcDNA3.1-G vaccine, the pcDNA3.1-G2 vaccine induced higher serum antibody levels, a lower nonspecific immune response in serum (ACP, SOD and T-AOC activities), higher immune-related gene expression and a higher relative survival rate. Moreover, the immune effect of pcDNA3.1-G2-vaccinated fish showed gradually higher with the increasing pcDNA3.1-G2 concentration, especially in pcDNA3.1-G2 (10μg/per fish) group, the relative survival rate reached to 82.5%, which was significant higher (p < 0.05) than pcDNA3.1-G (10μg/per fish) group. This study indicated that screening the potential core part of an antigen is an achievable strategy to improve the immunogenicity and immunoprotective effect of DNA vaccine.

Comparative study of subcutaneous, intramuscular, and oral administration of bovine pathogenic Escherichia coli bacterial ghost vaccine in mice

Escherichia coli is one of the most common bacterial pathogens in cattle. Prophylactic vaccines are considered promising strategies with the potential to reduce the incidence of colibacillosis. Some studies suggested that bacterial ghosts may serve as a novel approach for preventing bacterial infections. However, the roles of administration route on vaccine immunogenicity and efficacy have not been investigated. In this study, the efficacy of vaccination via different immune routes in generating humoral and cellular immune response was compared through subcutaneous (SC), intramuscular (IM), and oral (O) administration in female BALB/c mice with bacterial ghosts prepared using wild type Escherichia coli isolates CE9, while phosphate buffer saline (PBS) and inactivated vaccines containing aluminum adjuvants (Killed) were used as control. Our results showed that the plasmid pBV220-E-aa-SNA containing E. coli was efficiently cleaved at 42°C with 94.8% positive ratio as assessed by colony counts. Transmission electron microscopy (TEM) confirmed bacteria retained intact surface structure while devoid of cytoplasmic component. We found that total IgG titers in killed, IM and SC groups showed significant increase on 7, 14, 21 and 28 days post-immunization. The IgA level of the IM group was higher than that of all other groups on the 28th day. Meanwhile, four experimental groups showed a significant difference in IgA levels compared with PBS control. In the IM group, an increase in the relative percentages of CD3+CD4+ T cells was accompanied by an increase in the relative percentages of splenic CD3+CD8+ T cells. In comparison with the inactivated vaccine, intramuscular CE9 ghosts immunization elicited higher levels of IL-1β, IL-2, IL-6 and IL-12. Subcutaneous and intramuscular immunizations were significantly associated with improved survival in comparison with oral route, traditional vaccine and the control. Pathologic assessment revealed that less severe tissue damage and inflammation were found in lung, kidney, and intestine of IM group compared with other groups. The results above demonstrate that immunization of Escherichia coli CE9 ghosts via intramuscular injection elicits a more robust antigen-specific immune response in mice to prevent the Escherichia coli infection.

Bacteria-Templated and Dual Enzyme-Powered Microcapsule Motors To Promote Thrombus Penetration and Thrombolytic Efficacy

Antithrombotic therapy is confronted with short half-lives of thrombolytic agents and high bleeding risks. Challenges remain in the development of drug delivery systems for thorough destruction of thrombi and timely restoration of blood flow while minimizing side effects. Herein, polydopamine capsule-like micromotors with urokinase (uPA) loadings and Arg-Gly-Asp (RGD) grafts (r-u@PCM) were constructed using rod-shaped bacteria as the template, and one single opening was created on each capsule through bacterial ghost (BG) formation. Glucose oxidase and catalase were encapsulated in the large cavity of microcapsules, and their successive oxidation of glucose produced O₂ bubbles, which ejected out through the single opening to propel the motion of r-u@PCM. In vitro targeting testing of r-u@PCM shows significant higher accumulations on the activated platelets than those without RGD grafts (u@PCM, 7 folds) or without enzyme loadings (r-u@PC, 11 folds). Compared with the major distribution of r-u@PC on the clot surface, r-u@PCM efficiently penetrates into clots with dense fibrin networks, and near-infrared (NIR) irradiation (r-u@PCM/NIR) promotes thrombus infiltration through increasing uPA release and thermolysis of the networks. Pharmacokinetic study shows that the loading of uPA in r-u@PCM extends the terminal half-life from 24 min to 5.5 h and the bioavailability increased 13 times. In a hindlimb venous thrombosis model, r-u@PCM/NIR treatment promotes uPA accumulations in thrombi and disrupts all the thrombi after 8 h with a full recovery of blood flows. Effective thrombolysis is also achieved even after reducing the uPA dose 5 times. Thus, this is the first attempt to fabricate rod-shaped microcapsule motors through a biologically derived method, including bacterial templating and BG formation-induced opening generation. r-u@PCM/NIR treatment promotes thrombolysis through the photothermal effect, self-propelled infiltration into thrombi, and accelerated local release of uPA, providing a prerequisite for reducing uPA dose and bleeding side effects.

Recent Update on Bacteria as a Delivery Carrier in Cancer Therapy: From Evil to Allies

Cancer is associated with a comprehensive burden that significantly affects patient’s quality of life. Even though patients’ disease condition is improving following conventional therapies, researchers are studying alternative tools that can penetrate solid tumours to deliver the therapeutics due to issues of developing resistance by the cancer cells. Treating cancer is not the only the goal in cancer therapy; it also includes protecting non-cancerous cells from the toxic effects of anti-cancer agents. Thus, various advanced techniques, such as cell-based drug delivery, bacteria-mediated therapy, and nanoparticles, are devised for site-specific delivery of drugs. One of the novel methods that can be targeted to deliver anti-cancer agents is by utilising genetically modified non-pathogenic bacterial species. This is due to the ability of bacterial species to multiply selectively or non-selectively on tumour cells, resulting in biofilms that leads to disruption of metastasis process. In preclinical studies, this technology has shown significant results in terms of efficacy, and some are currently under investigation. Therefore, researchers have conducted studies on bacteria transporting the anti-cancer drug to targeted tumours. Alternatively, bacterial ghosts and bacterial spores are utilised to deliver anti-cancer drugs. Although in vivo studies of bacteria-mediated cancer therapy have shown successful outcome, further research on bacteria, specifically their targeting mechanism, is required to establish a complete clinical approach in cancer treatment. This review has focused on the up-to-date understanding of bacteria as a therapeutic carrier in the treatment of cancer as an emerging field.

Development and optimization of Lysis gene E as a counter-selection marker with high stringency

BACKGROUND

Seamless modification of bacterial chromosomes is widely performed in both theoretical and practical research. For this purpose, excellent counter-selection marker genes with high stringency are needed.

MAIN METHODS AND MAJOR RESULTS

The lysis gene E was first constructed under the control of the P_L promoter and the cI857 repressor. At 42°C, it could effectively kill Escherichia coli and seamless modification in this bacterium using E as a counter-selection marker was successfully conducted. It also works in another gram-negative strain, Serratia marcescens, under the control of the Arac/P_BAD regulatory system. By combining lysis gene E and kil, the counter-selection frequencies of the P_L -kil-sd-E cassette in E. coli reached 4.9 × 10^-8 and 3.2 × 10^-8 at two test loci, which are very close to frequencies observed with the best counter-selection systems reported, the inducible toxin systems. Under the control of the Arac/P_BAD , the counter-selection frequency of P_BAD -kil-sd-E in S. marcescens reached the level of 10^-7 at four test loci. By expressing the araC gene from plasmid pKDsg-ack, 5- to 17-fold improvements in counter-selection stringency were observed at these loci. A surprisingly low counter-selection frequency of 4.9 × 10^-9 was obtained at the marR-1 locus, which reflects the highest stringency for a counter-selection cassette reported thus far. Similarly, at the araB locus of E. coli, the counter-selection frequency of P_BAD -kil-sd-E was 3 × 10^-9 after introducing plasmid pKDsg-ack.

CONCLUSIONS AND IMPLICATIONS

We have developed and optimized a new universal counter-selection marker based on lysis gene E. The best counter-selection stringency of this new marker exceeds the inducible toxin system several fold. Our work can also provide inspiration for improving counter-selection stringency based on existing markers. This article is protected by copyright. All rights reserved.

Bacteria and bacterial derivatives as delivery carriers for immunotherapy

There is growing interest in the role of microorganisms in human health and disease, with evidence showing that new types of biotherapy using engineered bacterial therapeutics, including bacterial derivatives, can address specific mechanisms of disease. The complex interactions between microorganisms and metabolic/immunologic pathways underlie many diseases with unmet medical needs, suggesting that targeting these interactions may improve patient treatment. Using tools from synthetic biology and chemical engineering, non-pathogenic bacteria or bacterial products can be programmed and designed to sense and respond to environmental signals to deliver therapeutic effectors. This review describes current progress in biotherapy using live bacteria and their derivatives to achieve therapeutic benefits against various diseases.

Hacking Commensal Bacteria to Consolidate the Adaptive Mucosal Immune Response in the Gut–Lung Axis: Future Possibilities for SARS-CoV-2 Protection

Infectious diseases caused by mucosal pathogens significantly increase mortality and morbidity. Thus, the possibility to target these pathogens at their primary entry points can consolidate protective immunity. Regarding SARS-CoV-2 infection, it has been observed that the upper respiratory mucosa is highly affected and that dysregulation of resident microbiota in the gut–lung axis plays a crucial role in determining symptom severity. Thus, understanding the possibility of eliciting various mucosal and adaptive immune responses allows us to effectively design bacterial mucosal vaccine vectors. Such design requires rationally selecting resident bacterial candidates as potential host carriers, evaluating effective carrier proteins for stimulating an immune response, and combining these two to improve antigenic display and immunogenicity. This review investigated mucosal vaccine vectors from 2015 to present, where a few have started to utilize Salmonella and lactic acid bacteria (LAB) to display SARS-CoV-2 Spike S proteins or fragments. Although current literature is still lacking for its studies beyond in vitro or in vivo efficiency, decades of research into these vectors show promising results. Here, we discuss the mucosal immune systems focusing on the gut–lung axis microbiome and offer new insight into the potential use of alpha streptococci in the upper respiratory tract as a vaccine carrier.

Hydrochloric acid-treated Bacillus subtilis ghosts induce IL-1 beta, IL-6, and TNF-alpha in murine macrophage

Background

Bacterial ghosts (BGs) are empty cell envelopes commonly generated using Gram-negative bacteria; they represent a potential platform for efficient adjuvant and vaccine delivery systems. However, the efficient production of BGs from bacteria in a short period of time is challenging.

Objective

The purpose of this study was to investigate the possibility of producing BGs in the Gram-positive Bacillus subtilis using various chemicals, and the potential application of BGs as a novel immunomodulatory agent.

Results

In this study, Bacillus subtilis ghosts (BSGs) were generated, for the first time to the best of our knowledge, using the minimum inhibitory concentration (MIC) of hydrochloric acid (HCl; 6.25 mg/mL), sulfuric acid (H₂SO₄; 3.125 mg/mL), and nitric acid (HNO₃; 6.25 mg/mL). Among the BSGs generated using these chemicals, HCl-induced BSGs were completely DNA-free as confirmed by real-time polymerase chain reaction. Scanning electron microscopy showed the formation of transmembrane lysis tunnel structures in HCl-induced BSGs. Murine macrophages exposed to the HCl-induced BSGs at a concentration of 1 × 10⁵ CFU/mL showed a cell viability of 97.8%. Additionally, HCl-induced BSGs upregulated the expression of pro-inflammatory cytokines including interleukin (IL)-1β, tumor necrosis factor alpha, and IL-6. Furthermore, we found differences in the protein expression profiles between intact live bacteria and BSGs using two-dimensional electrophoresis coupled with peptide mass fingerprinting/matrix-assisted laser desorption/ionization-time of flight mass spectrometry analysis.

Conclusion

These data suggest that the HCl-induced BSGs may be potentially safe and effective candidates for inactivated bacterial vaccines and/or immunostimulants.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13273-022-00221-5.

Adjuvants: Engineering Protective Immune Responses in Human and Veterinary Vaccines

Adjuvants are key components of many vaccines, used to enhance the level and breadth of the immune response to a target antigen, thereby enhancing protection from the associated disease. In recent years, advances in our understanding of the innate and adaptive immune systems have allowed for the development of a number of novel adjuvants with differing mechanisms of action. Herein, we review adjuvants currently approved for human and veterinary use, describing their use and proposed mechanisms of action. In addition, we will discuss additional promising adjuvants currently undergoing preclinical and/or clinical testing.

Vaccination with a Brucella ghost developed through a double inactivation strategy provides protection in Guinea pigs and cattle

Vaccination can prevent and control animal brucellosis. Currently, live attenuated vaccines are extensively used to prevent Brucella infection. However, traditional vaccines such as live attenuated vaccines are associated with biological safety risks for both humans and animals. The bacterial ghost (BG) is a new form of vaccine with great prospects. However, bacterial cells cannot be completely inactivated by biological lysis, conferring a safety risk associated with the vaccine. In this study, we developed a Brucella abortus A19 bacterial ghost (A19BG) through a double inactivation strategy with sequential biological lysis and hydrogen peroxide treatment. This strategy resulted in 100% inactivation of Brucella, such that viable bacterial cells were not detected even at an ultrahigh concentration of 10¹⁰ colony-forming units/mL. Furthermore, A19BG had a typical BG morphology and good genetic stability. Moreover, it did not induce adverse reactions in guinea pigs. The levels of antibodies, interferon-γ, interleukin-4, and CD4⁺ T cells in guinea pigs inoculated with the A19BG vaccine were similar to those inoculated with the existing A19 vaccine. Immunization with A19BG conferred a similar level of protection with that of A19 against Brucella melitensis M28 in both guinea pigs and cattle. In conclusion, the combination of biological lysis and H₂O₂-mediated inactivation is a safe and effective strategy that can serve as a reference for the preparation of BG vaccines.

Bacteria from Infectious Particles to Cell Based Anticancer Targeted Drug Delivery Systems

Bacterial ghosts (BGs) are empty cell envelopes of nonliving evacuated bacterial cells. They are free from their cytoplasmic contents; however, they sustain their cellular 3D morphology and antigenic structures, counting on bioadhesive properties. Lately, they have been tested as an advanced drug delivery system (DDS) for different materials like DNA, peptides, or drugs, either single components or combinations. Different studies have revealed that, BG DDS were paid the greatest attention in recent years. The current review explores the impact of BGs on the field of drug delivery and drug targeting. BGs have a varied area of applications, including vaccine and tumor therapy. Moreover, the use of BGs, their synthesis, their uniqueness as a delivery system and application principles in cancer are discussed. Furthermore, the safety issues of BGs and stability aspects of using ghost bacteria as delivery systems are discussed. Future perspective efforts that must be followed for this important system to continue to grow are important and promising.

Bacterial Ghosts-Based Vaccine and Drug Delivery Systems

Bacterial ghosts (BGs) are empty bacterial envelopes of Gram-negative bacteria produced by controlled expressions of cloned gene E, forming a lysis tunnel structure within the envelope of the living bacteria. Globally, BGs have been used as vaccine delivery systems and vaccine adjuvants. There is an increasing interest in the development of novel delivery systems that are based on BGs for biomedical applications. Due to intact reservation of bacterial cell membranes, BGs have an inherent immunogenicity, which enables targeted drug delivery and controlled release. As carrier vehicles, BGs protect drugs from interference by external factors. In recent years, there has been an increasing interest in BG-based delivery systems against tumors, inflammation, and infection, among others. Herein, we reviewed the preparation methods for BGs, interactions between BGs and the host, and further highlighted research progress in BG development.

The effect of ultrasound treatment in combination with nisin on the inactivation of Listeria innocua and Escherichia coli

Ultrasound, alone or in combination with natural antimicrobials, is a novel food processing technology of interest to replace traditional food decontamination methods, as it is milder than classical sterilisation (heat treatment) and maintains desirable sensory characteristics. However, ultrasound efficacy can be affected by food structure/composition, as well as the order in which combined treatments are applied. More specifically, treatments which target different cell components could result in enhanced inactivation if applied in the appropriate order. The microbial properties i.e. Gram positive/Gram negative can also impact the treatment efficacy. This work presents a systematic study of the combined effect of ultrasound and nisin on the inactivation of the bacteria Listeria innocua (Gram positive) and Escherichia coli (Gram negative), at a range of cavitation conditions (44, 500, 1000 kHz). The order of treatment application was varied, and the impact of system structure was also investigated by varying the concentration of Xanthan gum used to create the food model systems (0 - 0.5% w/v). Microbial inactivation kinetics were monitored, and advanced microscopy and flow cytometry techniques were utilised to quantify the impact of treatment on a cellular level. Ultrasound was shown to be effective against E. coli at 500 kHz only, with L. innocua demonstrating resistance to all frequencies studied. Enhanced inactivation of E. coli was observed for the combination of nisin and ultrasound at 500 kHz, but only when nisin was applied before ultrasound treatment. The system structure negatively impacted the inactivation efficacy. The combined effect of ultrasound and nisin on E. coli was attributed to short-lived destabilisation of the outer membrane as a result of sonication, allowing nisin to penetrate the cytoplasmic membrane and facilitate cell inactivation.

Bacteria biohybrid oral vaccines for colorectal cancer treatment reduce tumor growth and increase immune infiltration

Bacteria biohybrid-based vaccine delivery systems, which integrate a vaccine carrier with live non-pathogenic bacteria, are hypothesized to have improved immunostimulating potential. The aim of this study was to develop oral bacteria biohybrid-based vaccines to treat a mouse model of colorectal cancer. E. coli were combined with tumor antigen- and adjuvant-containing emulsions or liposomes. Emulsion and liposome biohybrid vaccines demonstrated in vitro and in vivo therapeutic potential. Bacteria biohybrid vaccines significantly increased the expression of CD40⁺, CD80⁺ and CD86⁺ on murine bone marrow-derived dendritic cells. Mice vaccinated with emulsion biohybrid vaccines had an increased CD8⁺ T cell infiltration into tumors and developed three-fold smaller tumors compared to the mice that received emulsion vaccine without E. coli.

Bio-Nanocarriers for Lung Cancer Management: Befriending the Barriers

Lung cancer is a complex thoracic malignancy developing consequential to aberrations in a myriad of molecular and biomolecular signaling pathways. It is one of the most lethal forms of cancers accounting to almost 1.8 million new annual incidences, bearing overall mortality to incidence ratio of 0.87. The dismal prognostic scenario at advanced stages of the disease and metastatic/resistant tumor cell populations stresses the requisite of advanced translational interdisciplinary interventions such as bionanotechnology. This review article deliberates insights and apprehensions on the recent prologue of nanobioengineering and bionanotechnology as an approach for the clinical management of lung cancer. The role of nanobioengineered (bio-nano) tools like bio-nanocarriers and nanobiodevices in secondary prophylaxis, diagnosis, therapeutics, and theranostics for lung cancer management has been discussed. Bioengineered, bioinspired, and biomimetic bio-nanotools of considerate translational value have been reviewed. Perspectives on existent oncostrategies, their critical comparison with bio-nanocarriers, and issues hampering their clinical bench side to bed transformation have also been summarized.

Bacteria-Inspired Nanomedicine

The natural world has provided a host of materials and inspiration for the field of nanomedicine. By taking design cues from naturally occurring systems, the nanoengineering of advanced biomimetic platforms has significantly accelerated over the past decade. In particular, the biomimicry of bacteria, with their motility, taxis, immunomodulation, and overall dynamic host interactions, has elicited substantial interest and opened up exciting avenues of research. More recently, advancements in genetic engineering have given way to more complex and elegant systems with tunable control characteristics. Furthermore, bacterial derivatives such as membrane ghosts, extracellular vesicles, spores, and toxins have proven advantageous for use in nanotherapeutic applications, as they preserve many of the features from the original bacteria while also offering distinct advantages. Overall, bacteria-inspired nanomedicines can be employed in a range of therapeutic settings, from payload delivery to immunotherapy, and have proven successful in combatting both cancer and infectious disease.

Long noncoding RNAs in bacterial infection

Infectious and inflammatory diseases remain major causes of mortality and morbidity worldwide. To combat bacterial infections, the mammalian immune system employs a myriad of regulators, which secure the effective initiation of inflammatory responses while preventing pathologies due to overshooting immunity. Recently, the human genome has been shown to be pervasively transcribed and to generate thousands of still poorly characterized long noncoding RNAs (lncRNAs). A growing body of literature suggests that lncRNAs play important roles in the regulatory circuitries controlling innate and adaptive immune responses to bacterial pathogens. This review provides an overview of the roles of lncRNAs in the interaction of human and rodent host cells with bacterial pathogens. Further decoding of the lncRNA networks that underlie pathological inflammation and immune subversion could provide new insights into the host cell mechanisms and microbial strategies that determine the outcome of bacterial infections. This article is categorized under: RNA in Disease and Development > RNA in Disease RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications.

Research Advances on Tilapia Streptococcosis

Streptococcus agalactiae, often referred to as group B streptococci (GBS), is a severe pathogen that can infect humans as well as other animals, including tilapia, which is extremely popular in commercial aquaculture. This pathogen causes enormous pecuniary loss, and typical symptoms of streptococcosis—the disease caused by S. agalactiae—include abnormal behavior, exophthalmos, and meningitis, among others. Multiple studies have examined virulence factors associated with S. agalactiae infection, and vaccines were explored, including studies of subunit vaccines. Known virulence factors include capsular polysaccharide (CPS), hemolysin, Christie-Atkins-Munch-Peterson (CAMP) factor, hyaluronidase (HAase), superoxide dismutase (SOD), and serine-threonine protein kinase (STPK), and effective vaccine antigens reported to date include GapA, Sip, OCT, PGK, FbsA, and EF-Tu. In this review, I summarize findings from several studies about the etiology, pathology, virulence factors, and vaccine prospects for S. agalactiae. I end by considering which research areas are likely to yield success in the prevention and treatment of tilapia streptococcosis.

Immunization of chicken with flagellin adjuvanted Salmonella enteritidis bacterial ghosts confers complete protection against chicken salmonellosis

The present study describes the generation of Salmonella enteritidis (SE) ghosts with a surface decorated Salmonella Typhimurium (ST) flagellin (FliC) antigen for immune enhancement and strain-specific protection. The ghosts were generated by biological means using pJHL184::fliC temperature inducible plasmid where the lysis occurs by phage PhiX174 lysis gene E expression. Being an inactivated strain, no environmental contamination was observed by fecal shedding upon inoculation into the chicken. To test the protective immune responses, ghost vaccination was conducted via the intramuscular route using chicken as the model organism. The development of antigen-specific humoral, cell-mediated, and protective immune responses was assessed. Compared to vector alone and phosphate-buffered saline (PBS) control groups, pJHL184::fliC ghost could generate significantly high antigen-specific IgY and cell-mediated immune (CMI) responses measured by a peripheral blood mononuclear cell proliferation, flow cytometer, and cytokine responses elicited by stimulated splenic T-cells (P < 0.05). The adjuvant effect induced by FliC was demonstrated by elicitation of Toll-like receptor 5 (TLR5). To test the protection efficacy, chickens were challenged with both SE and ST wild type (WT) strains, and the protection efficacy was assessed by determining the presence of challenging strains in the spleen and liver, and by assessing the histopathological alterations. Complete clearance of the challenged strain and least inflammatory signs were evident in the SE ghosts vaccinated group compared to the vector and PBS control. The elimination of both SE and ST in chicken organs ensures the intramuscular immunization of the present SE ghost vaccine can reduce SE and ST contamination levels in chicken that can be beneficial to prevent enteric infections in humans.

Minicircle Biopharmaceuticals–An Overview of Purification Strategies

Minicircles are non-viral delivery vectors with promising features for biopharmaceutical applications. These vectors are plasmid-derived circular DNA molecules that are obtained in vivo in Escherichia coli by the intramolecular recombination of a parental plasmid, which generates a minicircle containing the eukaryotic therapeutic cassette of interest and a miniplasmid containing the prokaryotic backbone. The production process results thus in a complex mixture, which hinders the isolation of minicircle molecules from other DNA molecules. Several strategies have been proposed over the years to meet the challenge of purifying and obtaining high quality minicircles in compliance with the regulatory guidelines for therapeutic use. In minicircle purification, the characteristics of the strain and parental plasmid used have a high impact and strongly affect the purification strategy that can be applied. This review summarizes the different methods developed so far, focusing not only on the purification method itself but also on its dependence on the upstream production strategy used.

Design, development, and evaluation of the efficacy of a nucleic acid-free version of a bacterial ghost candidate vaccine against avian pathogenic E. coli (APEC) O78:K80 serotype

One of the major bacterial infectious diseases in the poultry industry is avian pathogenic Escherichia coli (APEC), which causes colibacillosis in chickens. To develop a novel nucleic acid-free bacterial ghost (BG) vaccine against the O78:K80 serotype of APEC, in this study we constructed a plasmid that harbored E-lysis and S nuclease (SNUC). Following the expression, the O78:K80 bacteria lost all of their cytoplasmic content and nucleic acids by enzymatic digestion. The functionality of these two proteins in the production procedure of bacterial ghosts was confirmed by monitoring the number of colonies, scanning electron microscopy imaging, gel electrophoresis of genomic DNA, and qPCR on the plasmid content of bacterial ghosts. The protective efficacy of the ghost vaccine generated from O78:K80 serotype of APEC was tested in chickens by injection and inhalation routes and compared with that in chickens that received the injection of a killed vaccine. The O78:K80 BG vaccine candidate, used as injection and inhalation, in comparison with the killed vaccine, triggered higher proinflammatory cytokine expression including IL-6, IL-1β, and TNFSF15; a higher level of antibody-dependent humoral (IgY and IgA) and cellular immune responses (IFNγ and lymphocyte proliferation); and lower lesion scores. According to the results of this study, we suggest that the bacterial ghost technology has the potential to be applied for the development of novel vaccines against avian colibacillosis. This technology provides an effective and reliable approach to make multivalent vaccines for more prevalent APEC strains involved in the establishment of this infectious disease in the poultry industry.

Recombinant Vibrio parahaemolyticus ghosts protect zebrafish against infection by Vibrio species

Aquatic animals are frequently threated by bacterial pathogens. The most economic and efficient protection against bacterial infection are through vaccine immunization. The various serotypes of the pathogens, such as Vibrios, hurdle the development of the vaccines, especially polyvalent vaccines. Here, we demonstrate that recombinant bacterial ghost is a good candidate for multivalent vaccine. By expressing PhiX174 gene E alone or co-expressing the gene E with two genes encoding outer membrane proteins (VP1667 and VP2369) in V. parahaemolyticus, we generated the recombinant V. parahaemolyticus ghosts VPG and rVPGs respectively. Fish immunized with either VPG or rVPG showed increased survival against the infection by either V. parahaemolyticus or V. alginolyticus, with a better protective effect by immunization with rVPG. Our furthermore studies show that rVPG stimulates stronger innate immune responses by increasing the expression of tnfα, il1β, il6, il8 and il10 as well as that of c3b, lyz, and tlr5, the key players linking the innate and adaptive immune responses upon microbial stimulation. In summary, VPG and rVPG can protect zebrafish against the infection from at least two Vibrio species, suggesting its potential value for further aquaculture vaccines development.

The potential use of theranostic bacteria in cancer

Conventional chemotherapy approaches have not been fully successful in the treatment of cancer, due to limitations imposed by the pathophysiology of solid tumors, leading to nonspecific drug uptake by healthy cells, poor bioavailability, and toxicity. Thus, novel therapeutic modalities for more efficient cancer treatment are urgently required. Living bacteria can be used as a theranostic approach for the simultaneous diagnosis and therapy of tumors. Herein, we summarize the currently available literature focused on the advantages and challenges for the use of theranostic bacteria in cancer therapy.

New technologies in developing recombinant-attenuated bacteria for cancer therapy

Cancer has always been a global problem, with more cases of cancer patients being diagnosed every year. Conventional cancer treatments, including radiotherapy, chemotherapy, and surgery, are still unable to bypass their obvious limitations, and developing effective targeted therapies is still required. More than one century ago, the doctor William B. Coley discovered that cancer patients had tumor regression by injection of Streptococcus bacteria. The studies of cancer therapy using bacterial microorganisms are now very widespread. In particular, the facultative anaerobic bacteria Salmonella typhimurium is widely investigated as it can selectively colonize different types of tumors, locally deliver various antitumor drugs, and inhibit tumor growth. The exciting antitumor efficacy and safety observed in animal tumor models prompted the well-known attenuated Salmonella bacterial strain VNP20009 to be tested in human clinical trials in the early 21st century. Regrettably, no patients showed significant therapeutic effects and even bacterial colonization in tumor tissue was undetectable in most patients. Salmonella bacteria are still considered as a promising agent or vehicle for cancer therapy. Recent efforts have been focused on the generation of attenuated bacterial strains with higher targeting for tumor tissue, and optimization of the delivery of therapeutic antitumor cargoes into the tumor microenvironment. This review will summarize new technologies or approaches that may improve bacteria-mediated cancer therapy.

An update on dengue vaccine development, challenges, and future perspectives

INTRODUCTION

From both a public health and economic perspective, vaccination is arguably the most effective approach to combat endemic and pandemic infectious diseases. Dengue affects more than 100 countries in the tropical and subtropical world, with 100-400 million infections every year. In the wake of the recent setback faced by Dengvaxia, the only FDA-approved dengue vaccine, safer and more effective dengue vaccines candidates are moving along the clinical pipeline.

AREA COVERED

This review provides an update of the latest outcomes of dengue vaccine clinical trials. In the light of recent progress made in our understanding of dengue pathogenesis and immune correlates of protection, novel vaccine strategies have emerged with promising second-generation dengue vaccine candidates. Finally, the authors discuss the dengue-specific challenges that remain to be addressed and overcome.

EXPERT OPINION

The authors propose to explore various adjuvants and delivery systems that may help improve the design of safe, effective, and affordable vaccines against dengue. They also challenge the concept of a 'universal' dengue vaccine as increasing evidence support that DENV strains have evolved different virulence mechanisms.

Potential of Bacteriocins from Lactobacillus taiwanensis for Producing Bacterial Ghosts as a Next Generation Vaccine

Bacteriocins are functionally diverse toxins produced by most microbes and are potent antimicrobial peptides (AMPs) for bacterial ghosts as next generation vaccines. Here, we first report that the AMPs secreted from Lactobacillus taiwanensis effectively form ghosts of pathogenic bacteria and are identified as diverse bacteriocins, including novel ones. In detail, a cell-free supernatant from L. taiwanensis exhibited antimicrobial activities against pathogenic bacteria and was observed to effectively cause cellular lysis through pore formation in the bacterial membrane using scanning electron microscopy (SEM). The treatment of the cell-free supernatant with proteinase K or EDTA proved that the antimicrobial activity is mediated by AMPs, and the purification of AMPs using Sep-Pak columns indicated that the cell-free supernatant includes various amphipathic peptides responsible for the antimicrobial activity. Furthermore, the whole-genome sequencing of L. taiwanensis revealed that the strain has diverse bacteriocins, confirmed experimentally to function as AMPs, and among them are three novel bacteriocins, designated as Tan 1, Tan 2, and Tan 3. We also confirmed, using SEM, that Tan 2 effectively produces bacterial ghosts. Therefore, our data suggest that the bacteriocins from L. taiwanensis are potentially useful as a critical component for the preparation of bacterial ghosts.

The development of ghost vaccines trials

INTRODUCTION

Bacterial ghosts are intact bacterial cell envelopes that are emptied of their content by gentle biological or chemical poring methods. Ghost techniques increase the safety of the killed vaccines, while maintaining their antigenicity due to mild preparation procedures. Moreover, ghost-platforms may express and/or carry several antigens or plasmid-DNA encoding for protein epitopes.

AREAS COVERED

In this review, the development in ghost-vaccine production over the last 30 years is classified and discussed. The different applications of ghost-vaccines, how they trigger the immune system, their advantages and limitations are displayed. The phage-mediated lysis, molecular manipulation of the lysis-genes, and the biotechnological production of ghosts are described. The trials are classified according to the pattern of lysis and to the type of bacteria. Further subdivision includes chronological ordered application of the ghost as alternative-killed vaccine, recombinant antigen platform, plasmid DNA carrier, adjuvants, and dendritic cell inducer. Particular trials for specific pathogens or from distinct research schools are gathered.

EXPERT OPINION

Ghosts are highly qualified to act as immune-presenting platforms that express and/or carry several recombinant and DNA vaccines, as well as, being efficient alternative-killed vaccines. The coming years will show more molecular advances to develop ghost-production and to express more antigens.

Bacteriosomes as a Promising Tool in Biomedical Applications: Immunotherapy and Drug Delivery

Bacteriosomes are a member of cell-derived vesicles that are proposed as promising tools in diagnosis, therapy, and drug delivery. These vesicles could be derived from a virus, bacterial cells, and animal cells. Biotechnology techniques were used in bioengineering of cell-derived vesicles in vitro, and in vivo. Bacterial vesicles such as bacterial cells, bacterial ghost, or bacteriosomes are vesicular structures derived from bacteria produced by manipulation of bacterial cells by chemical agents or gene-mediated lysis. Subsequently, bacterial vesicles (bacteriosomes) are non-living, non-denatured bacterial cell envelopes free of the cytoplasm and genetic materials. Gram-negative and Gram-positive bacteria are exploited in the production of bacteriosomes. Bacteriosomes have instinct organs, tissues, cells, as well as subcellular tropism. Moreover, bacteriosomes might be used as immunotherapy and/or drug delivery shuttles. They could act as cargoes for the delivery of small drugs, large therapeutics, and nanoparticles to the specific location. Furthermore, bacteriosomes have nature endosomal escaping ability, hence they could traffic different bio-membranes by endocytosis mechanisms. Therefore, bacterial-derived vesicles could be used in therapy and development of an innovative drug delivery systems. Consequently, utilizing bacteriosomes as drug cargoes enhances the delivery and efficacy of administered therapeutic agents. This review highlighted bacteriosomes in terms of source, engineering, characterization, applications, and limitations.

Salmonella Enteritidis ghost vaccine carrying the hemagglutinin globular head (HA1) domain from H1N1 virus protects against salmonellosis and influenza in chickens

This study evaluated the attenuated Salmonella Enteritidis (SE) ghost strain JOL2114 (Δlon ΔcpxR Δasd), which displays on the bacterial surface the H1N1 hemagglutinin globular head portion (HA1; amino acid residues 63-286) on the bacterial surface for protective efficacy against Salmonella and H1N1 challenge in the chicken model, as the birds are the predominant reservoirs for both diseases. The ghost system enhanced the lysis process by converging two lysis processes found in bacteriophages: bacteriophage PhiX174 lysis gene E and holin-endolysin genes found in bacteriophage λ, complemented with accessory lysis-related proteins Rz/Rz1. The present lysis machinery resulted in complete lysis of host-attenuated SE strains in about 24 hrs of incubation under a non-permissible temperature of 42 °C in the absence of L-arabinose, an antisense inducer that blocks lysis gene expression during the growth phase. SE ghost JOL2114 surface display of HA1 was confirmed by Western blot analysis resulting in an immune-reactive band of 31 kDa in size. Chicken immunization via intramuscular and oral routes yielded both SE and HA1 antigen-specific immune responses. Protective humoral and cell-mediated immune responses were effectively elicited against both Salmonella and influenza challenge. This efficient strategy of ghost generation employs a dual system of phage lysis for biological generation of SE ghosts that preserves the surface antigenic architecture, offering a rapid and effective way to generate vaccines that could be deployed in urgent circumstances to protect against both Salmonella and influenza infection.

Treatment Strategies for Infections With Shiga Toxin-Producing Escherichia coli

Infections with Shiga toxin-producing Escherichia coli (STEC) cause outbreaks of severe diarrheal disease in children and the elderly around the world. The severe complications associated with toxin production and release range from bloody diarrhea and hemorrhagic colitis to hemolytic-uremic syndrome, kidney failure, and neurological issues. As the use of antibiotics for treatment of the infection has long been controversial due to reports that antibiotics may increase the production of Shiga toxin, the recommended therapy today is mainly supportive. In recent years, a variety of alternative treatment approaches such as monoclonal antibodies or antisera directed against Shiga toxin, toxin receptor analogs, and several vaccination strategies have been developed and evaluated in vitro and in animal models. A few strategies have progressed to the clinical trial phase. Here, we review the current understanding of and the progress made in the development of treatment options against STEC infections and discuss their potential.

Research progress and clinical prospect of immunocytotherapy for the treatment of hepatocellular carcinoma

As a common malignant tumor, hepatocellular carcinoma (HCC) has high fatality rate due to its strong metastasis and high degree of malignancy. Current treatment strategies adopted in clinical practice were still conventional surgery, assisted with interventional therapy, radiotherapy and chemotherapy. However these treatments have limited effects with high recurrence rate. Current research progress of immunocytotherapy has shown that tumor cells can be directly identified and killed by stimulating the immune function and enhancing the anti-tumor immunity in tumor microenvironment. Targeted immunotherapeutics have therefore become the hope of conquering cancer in the future. It can kill tumor cells without damaging the body's immune system and function, restore and strengthen the body's natural anti-tumor immune system. It can reduce the toxic side effects of radiotherapy and chemotherapy, reduce the recurrence rate and prolong the survival period of patients with HCC. Currently, the immune cells widely studied are mainly as follows: Dendritic cells (DC), Cytokine-induced killer (CIK), DC-CIK, Chimeric antigen receptor T cells (CAR-T), Tumor infiltrating lymphocyte (TIL) and Natural killer cell (NK). Immunocytotherapy is a long-term treatment method, some studies have combined traditional therapy with immunocytotherapy and achieved significant effects, providing experimental basis for the application of immunocytotherapy. However, there are still some difficulties in the clinical application of immune cells. In this article, we discuss the application of immunocytotherapy in the clinical treatment of HCC, their effectiveness either alone or in combination with conventional therapies, and how future immunocytotherapeutics can be further improved from investigations in tumour immunology.

Current knowledge about interactions between avian dendritic cells and poultry pathogens

In poultry production conditions today, birds are surrounded by viral, bacterial, and parasitic agents. DCs are the main antigen-presenting cells located in tissues of the body, and their role involves recognizing antigen structures, engulfing and processing them, and subsequently presenting antigen peptides on their surface by major histocompatibility complex, where T cells and B cells are stimulated and can begin appropriate cellular and antibody immune response. This unique function indicates that these cells can be used in producing vaccines, but first it is necessary to culture DCs in vitro to identify the principles of their interactions with pathogens. The following review summarizes our current knowledge about avian dendritic cells and their interactions with pathogens. It provides a basis for future studies of these unique cells and their use in vaccine development.