A multi-epitope protein vaccine encapsulated in alginate nanoparticles as a candidate vaccine against Shigella sonnei

Abstract

Shigellosis, caused by the Gram-negative bacterium Shigella, is a major global health challenge. Despite extensive research over the past two decades, no commercial vaccine is available to prevent Shigella infection. Developing multi-epitope vaccines offers a promising and innovative approach to tackling infectious diseases. In this study, we produced a multi-epitope vaccine candidate using E. coli BL21 (DE3) plysS bacteria and purified the vaccine protein with Ni-NTA affinity chromatography. We then prepared alginate nanoparticles containing the vaccine protein, with a particle size of 122 ± 6 nm, PDI 0.17, SPAN 0.83, and zeta potential of -27 ± 2 mV. Successful protein loading was confirmed through nanodrop and ATR-FTIR analyses. To evaluate the immunogenicity of the encapsulated vaccine, mice were orally vaccinated, and their serum was analyzed for IgG, IL-4, and IFN-γ levels cytokines. The results showed a significant increase in IgG level in the vaccinated group compared to controls. Additionally, the vaccinated group exhibited a notable increase in IL-4 and IFN-γ cytokines, indicating a robust Th-cell-mediated immune response essential for combating Shigella. Our nano-vaccine demonstrated high efficacy in activating both humoral and cellular immunity, effectively protecting against the bacteria. The alginate-based oral vaccine candidate thus emerges as a promising strategy for developing a multi-epitope vaccine candidate against Shigella.

Keywords: Alginate nanoparticles; Multi-epitope; Oral vaccination; Shigellosis; Vaccine.

Fig. 1

Designed vaccine construct including adjuvant (D0 and D1 domains of flagellin in N and C terminal), selected Helper T cell Lymphocytes (HTL) epitopes from Ipa B, Omp A, and Ipa D antigens which connected by suitable amino acid linkers.

Fig. 2

Evaluation of the recombinant vaccine candidate expression. Lane M shows protein marker, and Lane C shows control before induction with IPTG. Lanes 1–3 show protein expression 4, 6, and 8 h after induction with a concentration of 1 mM IPTG, respectively. Lane 4 shows a purified vaccine candidate. As shown in the figure, the highest level of protein expression was observed within 8 h after induction with IPTG.

Fig. 3

DLS analyses of A: free alginate nanoparticles and B: alginate nanoparticles containing vaccine candidate.

Fig. 4

Zeta potential profiles of A: free alginate nanoparticles, B: alginate nanoparticles containing vaccine candidate, and C: pure vaccine candidate.

Fig. 5

ATR-FTIR of A: pure Alginate, B: free alginate nanoparticles, and C: alginate nanoparticles containing vaccine candidate.

Fig. 6

Determination of IgG titer. (A) control group receiving PBS, (B) control group receiving free alginate nanoparticles, (C) group receiving pure vaccine candidate, and (D) group receiving alginate nanoparticles containing vaccine candidate (nano-vaccine). A significant difference in the total IgG level was detected in the group receiving the nano-vaccine compared to the control groups. Also, the group that received the nano-vaccine indicated a significant increase in the total IgG level compared to the group that received the pure vaccine candidate (P value < 0.0001).

Fig. 7

Level of IFN-γ (A) and interleukin 4 cytokines (B). Significant differences were detected between the test group (nano-vaccine (NV)) and the control groups (PBS, nano, and vaccine candidate) (P value < 0.0001). The difference between induced (in) and uninduced (un) in each group of mice is due to the activation of the immune response, specifically by the vaccine antigen.

Fig. 8

Body weight changes were monitored at (0–3 days) post infection time. A significant decrease in the average of weight of mice in the control groups was observed in comparison to the test group. Statistical analysis was performed with Two-way ANOVA (** P value = 0.003).

Fig. 9

Investigative the consistency of feces after exposure Shigella sonnei ATCC − 9290 to displays that the the test group (Nano-vaccine) maintained normal fecal consistency (A), while control groups developed diarrhea (B-D).