Cellobiose-coated poly(lactide-co-glycolide) particles loaded with diphtheria toxoid for per os immunization.

Aim: To evaluate the dose-dependent immunogenic properties of poly(lactide-co-glycolide) (PLGA) particles coated with cellobiose as antigen carriers for oral immunization.

Methods: Two types of PLGA-cellobiose particles (PLGA-cellobiose-1, ~ 0.8 μm and PLGA-cellobiose-2, ~ 1.2 μm) containing non-toxic recombinant subunit B (SbB) of diphtheria toxin fused with enhanced green fluorescent protein were characterized in vitro for their size, shape, antigen loading, and ability to induce phagocytosis. Different doses of antigen, immobilized on the particles (2.5 μg, 25 μg, 250 μg, and 2500 μg per 1 kg of body weight), were administered per os 3 times with intervals of 2 weeks to BALB/c female mice. The antigen-specific IgG and IgA antibodies were estimated in serum by ELISA.

Results: After the first immunization, increase in concentration of blood antitoxic antibodies was detected. Antigen dose 250 μg/kg was the most immunogenic for IgG antibodies induction for both types of PLGA-cellobiose particles. Antigen doses 25 μg/kg and 2.5 μg/kg were the most immunogenic for IgA antibodies induction by PLGA-cellobiose 1 and 2 particles, respectively. The second and the third treatment had no significant effect on the immune response or even reduced it, which could be explained by immune tolerance induction by the antigens delivered per os.

Conclusion: Our results suggest that the correct dose of PLGA-cellobiose particles loaded with antigen could significantly increase the humoral immune response against the introduced antigen already after the first immunization. Thus, PLGA particles can be considered as a potent component of oral vaccines.