PLA-PEG as a delivery system for a Chlamydia Trachomatis subunit vaccine

Chlamydia trachomatis is the leading cause of bacterial sexually transmitted infections (STIs) but as yet there is no available vaccine to combat this infection. Different strategies have been employed to meet this challenge, and one such strategy is the development of a Chlamydia vaccine using nanoparticle-delivery systems. Previously we reported the successful encapsulation and characterization of a model protein, bovine serum albumin (BSA) in poly (lactic acid)-b-Poly (ethylene glycol) (PLA-PEG) nanoparticles. Here we encapsulated a peptide derivative of C. trachomatis major outer membrane protein (MOMP), (named M278) in PLA-PEG and characterized it in vitro followed by immunogenicity studies in vivo. We hypothesize that M278 encapsulated in PLA-PEG will provide for its slow controlled release and thus enhance its capacity to induce immune responses in mice. M278 was encapsulated in PLA-PEG by the double emulsion method (water/oil/water). Scanning Electron microscopy (SEM) analyses revealed PLA-PEG-M278 to be coagulated particles and in the conformation of what have been referred to as a PEGylated "brush" with rough outer surfaces. The zetasizer measurement showed the sizes of the PLA-PEG-PBS and PLA-PEG-M278 to be ~ 200-272 nm. These findings demonstrate that the encapsulation process had little effect on changing the properties and size of the nanoparticles, which are essential for maintaining the integrity and delivery potential of the particles. The protein encapsulation efficiency of PLA-PEG-M278 was ~ 60%, while the in vitro release study showed a slow and continuous release of the M278 protein from PLA-PEG nanoparticles. Three groups of BALB/c mice (PLA-PEG-PBS, PLA-PEG-M278 and M278), received three immunizations at two-week intervals and two weeks after the last immunization sera were collected for systemic antibody analyses. PLA-PEG-M278 immunized mice produced higher IgG and IgG 1 M278-specific antibodies as compared to the M278 immunized mice. Our data indicates the successful encapsulation and characterization of M278 in PLA-PEG and, more importantly, that PLA-PEG enhanced the capacity of M278 to induce antibody responses in mice. These findings suggest that the PLA-PEG-M278 holds considerable promise as a nanovaccine against C. trachomatis, and warrants efficacy studies in mice.