Direct Cloning of Bacterial Surface Polysaccharide Gene Cluster for One-Step Production of Glycoconjugate Vaccine

Genetic engineering of E. coli K-12 for heterologous carbohydrate antigen production

BACKGROUND

Carbohydrate-based vaccines have made a remarkable impact on public health over the past three decades. Efficient production of carbohydrate antigens is a crucial prerequisite for the development of such vaccines. The enzymes involved in the synthesis of bacterial surface carbohydrate antigens are usually encoded by large, uninterrupted gene clusters. Non-pathogenic E. coli glycoengineering starts with the genetic manipulation of these clusters. Heterologous gene cluster recombination through an expression plasmid has several drawbacks, including continuous antibiotic selection pressure, genetic instability, and metabolic burdens. In contrast, chromosome-level gene cluster expression can minimize the metabolic effects on the host and reduce industrial costs.

RESULTS

In this study, we employed the suicide vector-mediated allelic exchange method to directly replace the native polysaccharide gene clusters in E. coli with heterologous ones. Unlike previously strategies, this method does not rely on I-SceI endonuclease or CRISPR/Cas system to release the linearized DNA insert and λ-red recombinase to promote its homologous recombination. Meanwhile, the vectors could be conveniently constructed by assembling multiple large DNA fragments in order in vitro. The scarless chromosomal insertions were confirmed by whole-genome sequencing and the polysaccharide phenotypes of all glycoengineered E. coli mutants were evaluated through growth curves, silver staining, western blot, and flow cytometry. The data indicated that there was no obvious metabolic burden associated with the insertion of large gene clusters into the E. coli W3110 O-antigen locus, and the glycoengineered E. coli can produce LPS with a recovery rate around 1% of the bacterial dry weight. Moreover, the immunogenicity of the heterologously expressed carbohydrate antigens was analyzed by mice immunization experiments. The ELISA data demonstrated the successful induction of anti-polysaccharide IgM or IgG antibodies.

CONCLUSIONS

We have provided a convenient and reliable genomic glycoengineering method to produce efficacious, durable, and cost-effective carbohydrate antigens in non-pathogenic E. coli. Non-pathogenic E. coli glycoengineering has great potential for the highly efficient synthesis of heterologous polysaccharides and can serve as a versatile platform to produce next-generation biomedical agents, including glycoconjugate vaccines, glycoengineered minicells or outer membrane vesicles (OMVs), polysaccharide-based diagnostic reagents, and more.

A Bioconjugate Vaccine Against Extra-Intestinal Pathogenic Escherichia coli (ExPEC)

Background: Extra-intestinal pathogenic Escherichia coli (ExPEC) represents a major global public health challenge due to its ability to cause diverse clinical infections, including urinary tract infections, bacteremia, neonatal meningitis, and sepsis. The growing prevalence of multidrug-resistant (MDR) ExPEC strains, which rapidly erode antibiotic efficacy, underscores vaccine development as a critical priority. Bioconjugate vaccines have emerged as a promising approach to mitigate ExPEC-associated infections. Methods and Results: In this study, we utilized protein glycan coupling technology (PGCT) based on oligosaccharyltransferase (OST) PglL to engineer a tetravalent bioconjugate vaccine targeting four predominant ExPEC serotypes (O1, O2, O6, and O25). We conducted a series of experiments to demonstrate the efficacy of the conjugate vaccine in eliciting humoral immune responses and inducing the production of specific antibodies against Escherichia coli O1, O2, O6, or O25 serotypes. Conclusions: This work establishes the first application of the O-linked PGCT system for engineering bioconjugate vaccines against ExPEC infections.

Direct cloning strategies for large genomic fragments: A review

Mining large-scale functional regions of the genome helps to understand the essence of cellular life. The rapid accumulation of genomic information provides a wealth of material for genomic functional, evolutionary, and structural research. DNA cloning technology is an important tool for understanding, analyzing, and manipulating the genetic code of organisms. As synthetic biologists engineer greater and broader genetic pathways and expand their research into new organisms, efficient tools capable of manipulating large-scale DNA will offer momentum to the ability to design, modify, and construct engineering life. In this review, we discuss the recent advances in the field of direct cloning of large genomic fragments, particularly of 50-150 kb genomic fragments. We specifically introduce the technological advances in the targeted release and capture steps of these cloning strategies. Additionally, the applications of large fragment cloning in functional genomics and natural product mining are also summarized. Finally, we further discuss the challenges and prospects for these technologies in the future.

Genomics and pathotypes of the many faces of Escherichia coli

Escherichia coli is the most researched microbial organism in the world. Its varied impact on human health, consisting of commensalism, gastrointestinal disease, or extraintestinal pathologies, has generated a separation of the species into at least eleven pathotypes (also known as pathovars). These are broadly split into two groups, intestinal pathogenic E. coli (InPEC) and extraintestinal pathogenic E. coli (ExPEC). However, components of E. coli's infinite open accessory genome are horizontally transferred with substantial frequency, creating pathogenic hybrid strains that defy a clear pathotype designation. Here, we take a birds-eye view of the E. coli species, characterizing it from historical, clinical, and genetic perspectives. We examine the wide spectrum of human disease caused by E. coli, the genome content of the bacterium, and its propensity to acquire, exchange, and maintain antibiotic resistance genes and virulence traits. Our portrayal of the species also discusses elements that have shaped its overall population structure and summarizes the current state of vaccine development targeted at the most frequent E. coli pathovars. In our conclusions, we advocate streamlining efforts for clinical reporting of ExPEC, and emphasize the pathogenic potential that exists throughout the entire species.

Semisynthetic Glycoconjugate Vaccine Candidates against Escherichia coli O25B Induce Functional IgG Antibodies in Mice

Extraintestinal pathogenic Escherichia coli (ExPEC) is a major health concern due to emerging antibiotic resistance. Along with O1A, O2, and O6A, E. coli O25B is a major serotype within the ExPEC group, which expresses a unique O-antigen. Clinical studies with a glycoconjugate vaccine of the above-mentioned O-types revealed O25B as the least immunogenic component, inducing relatively weak IgG titers. To evaluate the immunological properties of semisynthetic glycoconjugate vaccine candidates against E. coli O25B, we here report the chemical synthesis of an initial set of five O25B glycan antigens differing in length, from one to three repeat units, and frameshifts of the repeat unit. The oligosaccharide antigens were conjugated to the carrier protein CRM₁₉₇. The resulting semisynthetic glycoconjugates induced functional IgG antibodies in mice with opsonophagocytic activity against E. coli O25B. Three of the oligosaccharide-CRM₁₉₇ conjugates elicited functional IgGs in the same order of magnitude as a conventional CRM₁₉₇ glycoconjugate prepared with native O25B O-antigen and therefore represent promising vaccine candidates for further investigation. Binding studies with two monoclonal antibodies (mAbs) revealed nanomolar anti-O25B IgG responses with nanomolar K _D values and with varying binding epitopes. The immunogenicity and mAb binding data now allow for the rational design of additional synthetic antigens for future preclinical studies, with expected further improvements in the functional antibody responses. Moreover, acetylation of a rhamnose residue was shown to be likely dispensable for immunogenicity, as a deacylated antigen was able to elicit strong functional IgG responses. Our findings strongly support the feasibility of a semisynthetic glycoconjugate vaccine against E. coli O25B.

Sonic hedgehog signaling pathway in Myelodysplastic Syndrome: Abnormal activation and jervine intervention

OBJECTIVE

This study aims to investigate the roles of Sonic hedgehog (Shh) signaling pathway in the occurrence and progression of Myelodysplastic Syndrome (MDS) and further evaluate using jervine as therapeutic strategy for MDS by inhibiting Shh pathway.

METHODS

CD34+ cells from the bone marrow of 53 MDS patients were counted by flow cytometry and isolated by magnetic bead sorting. Shh, Smo, Ptch-1 and Gli-1 (involved in Shh pathway) in CD34+ cells were examined by RT-qPCR. Besides, the relationship between Shh pathway-related genes and the clinical features or prognosis of MDS were analyzed. Further, the effects of jervine on MUTZ-1 cells regarding their proliferation, apoptosis and cell cycle as well as Shh pathway-related gene and protein expression were analyzed.

RESULTS

Gene expression level of Shh, Gli-1 and Smo was significantly increased in MDS patients. Herein, Smo and Gli-1 were correlated with chromosome karyotype classification and IPSS. MDS patients with high expression of Smo or Gli-1 had a poor prognosis. Jervine inhibited gene and protein expression of Shh, Smo, Ptch-1 and Gli-1. Besides, jervine suppressed the proliferation and promoted the apoptosis of MUTZ-1 cells, as well as inhibited the transition of cells from G1 to S phase.

CONCLUSION

Shh signaling pathway of MDS patients is abnormally activated and participated in the occurrence and progression of MDS. Jervine intervention is a potential therapeutic strategy for MDS.

Glycoconjugate vaccines: current approaches towards faster vaccine design

Introduction: Over the last decades, glycoconjugate vaccines have been proven to be a successful strategy to prevent infectious diseases. Many diseases remain to be controlled, especially in developing countries, and emerging antibiotic-resistant bacteria present an alarming public-health threat. The increasing complexity of future vaccines, and the need to accelerate development processes have triggered the development of faster approaches to glycoconjugate vaccines design. Areas covered: This review provides an overview of recent progress in glycoconjugation technologies toward faster vaccine design. Expert opinion: Among the different emerging approaches, glycoengineering has the potential to combine glycan assembly and conjugation to carrier systems (such as proteins or outer membrane vesicles) in one step, resulting in a simplified manufacturing process and fewer analytical controls. Chemical and enzymatic strategies, and their automation can facilitate glycoepitope identification for vaccine design. Other approaches, such as the liposomal encapsulation of polysaccharides, potentially enable fast and easy combination of numerous antigens in the same formulation. Additional progress is envisaged in the near future, and some of these systems still need to be further validated in humans. In parallel, new strategies are needed to accelerate the vaccine development process, including the associated clinical trials, up to vaccine release onto the market.