The immunogenic potential of bacterial flagella for Salmonella‐mediated tumor therapy

Abstract

Genetically engineered Salmonella Typhimurium are potent vectors for prophylactic and therapeutic measures against pathogens as well as cancer. This is based on the potent adjuvanticity that supports strong immune responses. The physiology of Salmonella is well understood. It simplifies engineering of both enhanced immune-stimulatory properties as well as safety features, thus, resulting in an appropriate balance between attenuation and efficacy for clinical applications. A major virulence factor of Salmonella is the flagellum. It is also a strong pathogen-associated molecular pattern recognized by extracellular and intracellular receptors of immune cells of the host. At the same time, it represents a serious metabolic burden. Accordingly, the bacteria evolved tight regulatory mechanisms that control flagella synthesis in vivo. Here, we systematically investigated the immunogenicity and adjuvant properties of various flagella mutants of Salmonella in vitro and in a mouse cancer model in vivo. We found that mutants lacking the flagellum-specific ATPase FliHIJ or the inner membrane ring FliF displayed the greatest stimulatory capacity and strongest antitumor effects, while remaining safe in vivo. Scanning electron microscopy revealed the presence of outer membrane vesicles in the ΔfliF and ΔfliHIJ mutants. Finally, the combination of the ΔfliF and ΔfliHIJ mutations with our previously described attenuated and immunogenic background strain SF102 displayed strong efficacy against the highly resistant cancer cell line RenCa. We thus conclude that manipulating flagella biosynthesis has great potential for the construction of highly efficacious and versatile Salmonella vector strains.S.W. and M.E. contributed equally to this work Additional Supporting Information may be found in the online version of this article.

Can SARS-CoV-2 Virus Use Multiple Receptors to Enter Host Cells?

“…TLR activating ligands have previously been used, as immunogenic adjuvants during vaccine development, to enhance vaccine efficacy and facilitate production of a tailored and robust immune responses [145,146]. Flagellin (a microtubule-based structural whip-like filament that enables locomotion in motile Gram-negative and positive bacteria [147]) is a potent immunomodulatory agent [148,149], which has been utilized as an adjuvant component in vaccine formulation due to its ability to influence pathogenic virulence [150,151]. Flagellin exclusively interacts with TLR5, and results in subsequent NF-kB driven inflammation, through recruitment of MyD88 [59,60].…”

Perspectives on Oncolytic Salmonella in Cancer Immunotherapy—A Promising Strategy

“…Salmonella secreting flagellin B inhibits tumor growth by regulating TME via TLR5 and shifts macrophages from M2-like suppressive activities to M1 phenotypes in the microenvironment. Besides, flagellin diminished the numbers of T reg cells in the TME ( 46 , 47 ). Binder et al (2016).…”

“…In addition to destroying the microenvironment required for tumor growth, Salmonella can also kill tumor cells by secreting or inducing antitumor agents. As the pathogen-associated molecular patterns (PAMPs) of Salmonella , LPS and flagella have been shown antitumor activities in many studies, whose elimination accounts for a loss of therapeutic potency ( 43 – 47 ). LPS from Salmonella can increase TNF-α and the tumor specific response of CD8 + T cells ( 45 ).…”

“…When flagellin affects tumors, TLR4 and TLR5 were shown to play important role in this process using mouse models ( 43 , 44 ). An engineered flagellum of Salmonella has been shown to exert strong antitumor effect ( 47 ). Salmonella can also inhibit tumors through producing NO in TME, where nitrate reductase secreted by Salmonella converts nitrates and nitrites into NO ( 48 , 49 ).…”

A Review of Human Coronaviruses’ Receptors: The Host-Cell Targets for the Crown Bearing Viruses

“…During vaccine development and to enhance the vaccine efficacy by tailoring the immune responses, a potent immunomodulatory agent called flagellin, which is a structural whip-like filament dependent on microtubules, has been used as an adjuvant component [196,197] due to its ability to influence pathogenic virulence to enable locomotion in motile Gram-negative and positive bacteria [165,198]. The interaction of flagellin with TLR5 leads to subsequent NF-kβ motivated inflammation through enrolment of MyD88 and has been shown to be an effective immunomodulatory agent [157,158,[199][200][201]. The use of flagellin to target TLR5 in the creation of vaccines against viral infections has been studied.…”