Harnessing the Immunomodulatory Properties of Bacterial Ghosts to Boost the Anti-mycobacterial Protective Immunity

Abstract

Tuberculosis (TB) pathogenesis is characterized by inadequate immune cell activation and delayed T cell response in the host. Recent immunotherapeutic efforts have been directed at stimulating innate immunity and enhancing interactions between antigen presenting cells and T cells subsets to improve the protective immunity against TB. In this study, we investigated the immunostimulatory properties of bacterial ghosts (BG) as a novel approach to potentiate the host immunity against mycobacterial infection. BG are intact cytoplasm-free Escherichia coli envelopes and have been developed as bacterial vaccines and adjuvant/delivery system in cancer immunotherapy. However, BG have yet to be exploited as immunopotentiators in the context of infectious diseases. Here, we showed that BG are potent inducers of dendritic cells (DC), which led to enhanced T cell proliferation and differentiation into effector cells. BG also induced macrophage activation, which was associated with enhanced nitric oxide production, a key anti-mycobacterial weapon. We further demonstrated that the immunostimulatory capability of BG far exceeds that of LPS and involves both TLR4-dependent and independent pathways. Consistently, BG treatment, but not LPS treatment, reduced the bacterial burden in infected mice, which correlated with increased influx of innate and adaptive effector immune cells and increased production of key cytokines in the lungs. Finally and importantly, enhanced bacilli killing was seen in mice co-administered with BG and second-line TB drugs bedaquiline and delamanid. Overall, this work paves the way for BG as potent immunostimulators that may be harnessed to improve mycobacteria killing at the site of infection.

Bacterial Ghosts-Based Vaccine and Drug Delivery Systems

“…Bedaquiline/delamanid@BGs stimulate the immune system to kill bacteria and treat tuberculosis [88] mice pBV220-E CIP ECN CIP@BGs is used to destroy Staphylococcus aureus in macrophages [89] macrophage RAW264.7/ mice pBV220-E ZOL/5-FU ECN ZOL/5-FU@BGs promote macrophage polarization and kill tumor [5] mice…”

“…They stimulate innate immunity to enhance interactions between APCs and T cells, promoting inflammation [94]. Lim et al delivered bedaquinoline and delamani, second-line tuberculosis drugs, to the lungs of mice via Mycobacterium bovis BGs [88]. The drugs effectively killed the bacteria and significantly increased the number of innate immune cells (neutrophils, macrophages, and DCs), adaptive immune cells (CD4 effector cells), and levels of Th1 cytokines (TNFα, IFNγ and IL-12p70).…”

“…Given the tumor microenvironment, it is more flexible to use environment-induced promoters such as hypoxic promoters and temperature-controlled promoters to induce site-specific lysis of tumortargeted bacteria. Overall, BG-based delivery systems are potential chemotherapeutic strategies [88].…”

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

“…However, the detailed mechanism of how BSGs increases cytokines in macrophages has not yet been elucidated, further research is needed in future. Furthermore, it is interesting to note that B. subtilis elicits an inflammatory response different from that of its diverse BGs produced by different chemical treatments (Hajam et al 2017 ; Amara et al 2013 ; Lim et al 2019 ); therefore, future research in this field should be carried out.…”

A Novel and Efficient High-Yield Method for Preparing Bacterial Ghosts

“…On one hand, the multi-antigenic structure of BGs can effectively stimulate cellular and humoral immunity to prevent pathogenic bacterial infection [3] and serve as a new type of vaccine [4]. On the other hand, BGs have been shown to be effective biological carriers [5] to deliver drugs [6] or antigens [7] to antigen-presenting cells (APCs) such as B cells, dendritic cells (DCs), and macrophages [8]. BGs have a wide application prospect in health medicine and great research value.…”