Design of a novel vaccine nanotechnology-based delivery system comprising CpGODN-protein conjugate anchored to liposomes.

Although the well-known Toll like receptor 9 (TLR9) agonist CpGODN has shown promising results as vaccine adjuvant in preclinical and clinical studies, its in vivo stability and potential systemic toxicity remain a concern. In an effort to circumvent these issues, different strategies have been employed to increase its stability, localise action and reduce dosage. These include conjugation of CpGODN with proteins or encapsulation/adsorption of CpGODN into/onto liposomes, and have resulted in enhanced immunopotency compared to co-administration of free CpGODN and antigen. Here, we designed a novel delivery system of CpGODN based on its conjugation to serve as anchor for liposomes. Thiol-maleimide chemistry was utilised to covalently ligate the Group B Streptococcus (GBS) GBS67 protein antigen with the CpGODN TLR9 agonist. This treatment did not alter protein's ability to be recognised by specific antibodies or the CpGODN to function as a TLR9 agonist. Due to its negative charge, the protein conjugate readily electrostatically bound cationic liposomes composed of 1, 2-distearoyl-sn-glycero-3-phosphocholine (DSPC), cholesterol and dimethyldioctadecylammonium bromide (DDA). The novel cationic liposomes-protein conjugate complex (GBS67-CpGODN+L) shared similar vesicle characteristics (size and charge) compared to free liposomes but exhibited different structure and morphology. Following intramuscular immunisation, GBS67-CpGODN+L formed a vaccine depot at the injection site and induced a remarkable increase of functional immune responses against GBS compared to the simple co-administration of GBS67, CpGODN and liposomes. This work demonstrates that the conjugation of CpGODN to GBS67 in conjunction with adsorption on cationic liposomes, can promote co-delivery leading to the induction of a multifaceted immune response at low antigen and CpGODN doses. Our findings highlight the potential for harnessing the immunostimulatory properties of different adjuvants to develop more effective nanostructure-based vaccine platforms.
Competing Interests: Declaration of Competing Interest GB, IP, FC, MRR, DO, UD and RA are employees of the GSK group of companies. RA and DO are owners of GSK stocks. Other authors declare no conflict of interest.
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