Bacterial Ghosts Are an Efficient Delivery System for DNA Vaccines

Abstract

Mass implementation of DNA vaccines is hindered by the requirement of high plasmid dosages and poor immunogenicity. We evaluated the capacity of Mannheimia haemolytica ghosts as delivery system for DNA vaccines. In vitro studies showed that bacterial ghosts loaded with a plasmid carrying the green fluorescent protein-encoding gene (pEGFP-N1) are efficiently taken up by APC, thereby leading to high transfection rates (52–60%). Vaccination studies demonstrated that ghost-mediated delivery by intradermal or i.m. route of a eukaryotic expression plasmid containing the gene coding for β-galactosidase under the control of the CMV immediate early gene promoter (pCMVβ) stimulates more efficient Ag-specific humoral and cellular (CD4+ and CD8+) immune responses than naked DNA in BALB/c mice. The use of ghosts also allows modulating the major Th response from a mixed Th1/Th2 to a more dominant Th2 pattern. Intravenous immunization with dendritic cells loaded ex vivo with pCMVβ-containing ghosts also resulted in the elicitation of β-galactosidase-specific responses. This suggests that dendritic cells play an important role in the stimulation of immune responses when bacterial ghosts are used as a DNA delivery system. Bacterial ghosts not only target the DNA vaccine construct to APC, but also provide a strong danger signal, acting as natural adjuvants, thereby promoting efficient maturation and activation of dendritic cells. Thus, bacterial ghosts constitute a promising technology platform for the development of more efficient DNA vaccines.

The bacterial ghost platform system

“…Beta-galactosidase-specific immune response was detected after intravenous immunization of mice with autologous dendritic cells (DCs) transfected ex vivo with pCMVbeta-loaded BGs. 32 An increase of IFN-gamma producing AG-specific CD8 + T cells was observed in animals vaccinated with DNA loaded BGs in response to restimulation by APCs pulsed with peptide containing the immunodominant MHC class I epitope. BGs enhanced expression of MHC class I molecules and costimulatory molecules on DCs.…”

“…The use of BGs as candidate vaccines and advanced drug carriers can be found in several recent reviews. 24,27,29,[32][33][34][35][36] …”

“…Importantly, no cytotoxic impact was observed on target cells. 32,71,74,75 Intradermal and intramuscular immunization of Balb/c mice with BGs loaded with pCMV encoding beta-galactosidase stimulated more efficient humoral and cellular AG-specific immune responses than naked DNA. Beta-galactosidase-specific immune response was detected after intravenous immunization of mice with autologous dendritic cells (DCs) transfected ex vivo with pCMVbeta-loaded BGs.…”

“…BGs enhanced expression of MHC class I molecules and costimulatory molecules on DCs. 32 Cross-presentation of AGs delivered to DCs by BGs could activate both CD4 + and CD8 + T cells and stimulates the immune system to enhance immune response against AGs expressed by target cells. Bacterial LPS enhances maturation of DCs, affects endosomal acidification of DCs and also improves cross-presentation of AGs.…”

Development of aChlamydia trachomatisbacterial ghost vaccine to fight human blindness

“…It was also found that the Th2 (humoral) immune response against the DNA encoded antigen was stronger than the Th1 (cellular) response, which is rather unusual for DNA vaccines, and can most likely be attributed to the delivery and BG induced signaling. 77 A more sophisticated and recently developed version of loading BG with DNA uses the specific interaction of an inner membrane anchored DNA binding protein with the corresponding operator region on target plasmid. This allows a one step DNA loading and BG formation process.…”