Encapsulation in liposomal nanoparticles enhances the immunostimulatory, adjuvant and anti-tumor activity of subcutaneously administered CpG ODN

Abstract

Immunostimulatory oligodeoxynucleotides (ODN) containing cytosine-guanine (CpG) motifs are powerful stimulators of innate as well as adaptive immune responses, exerting their activity through triggering of the Toll-like receptor 9. We have previously shown that encapsulation in liposomal nanoparticles (LN) enhances the immunostimulatory activity of CpG ODN (LN-CpG ODN) (Mui et al. in J Pharmacol Exp Ther 298:1185, 2001). In this work we investigate the effect of encapsulation on the immunopotency of subcutaneously (s.c.) administered CpG ODN with regard to activation of innate immune cells as well as its ability to act as a vaccine adjuvant with tumor-associated antigens (TAAs) to induce antigen (Ag)-specific, adaptive responses and anti-tumor activity in murine models. It is shown that encapsulation specifically targets CpG ODN for uptake by immune cells. This may provide the basis, at least in part, for the significantly enhanced immunostimulatory activity of LN-CpG ODN, inducing potent innate (as judged by immune cell activation and plasma cytokine/chemokine levels) and adaptive, Ag-specific (as judged by MHC tetramer positive T lymphocytes, IFN-gamma secretion and cytotoxicity) immune responses. Finally, in efficacy studies, it is shown that liposomal encapsulation enhances the ability of CpG ODN to adjuvanate adaptive immune responses against co-administered TAAs after s.c. immunization, inducing effective anti-tumor activity against both model and syngeneic tumor Ags in murine tumor models of thymoma and melanoma.

Enhancing Efficacy of Anticancer Vaccines by Targeted Delivery to Tumor-Draining Lymph Nodes

“…Compared with current published studies, our TRP-2-based therapeutic nanoparticle vaccine is very potent at the low doses used for antigen and adjuvant (18,39,40). Similarly, other studies have shown improved therapeutic outcomes by either conjugating the adjuvant or the antigen onto or into delivery systems, such as poly(lactideco-glycolide) particles and liposomes, but, to our knowledge, this is the first study to show enhanced co-uptake of both adjuvant and antigen by LN-resident APCs after nanoparticle conjugation (14)(15)(16)(17)(18)(19). Furthermore, it has been shown recently that encapsulating antigens or TLR agonists in nanoparticles enhanced humoral responses compared with immunization with soluble antigen or adjuvant (41,42).…”

“…S5). Furthermore, efficient LN targeting by nanoparticles and conjugation of CpG onto nanoparticles allowed a very low dose of CpG (1 mg/ mouse) to be effective, while typically much higher doses of free CpG (8-100 mg) are needed for effective adjuvant function (14)(15)(16)18). Our results showed that the vaccine-induced local immune response in the tdLN translated to greater tumor reduction than the one elicited in a non-tdLN.…”

“…17, 31, 38). Our nanoparticles were in the range of 30 nm, thus smaller than particles used in many vaccination studies, hence affording enhanced lymphatic drainage and targeting of the skin-draining LNs (14)(15)(16)(17)(18)(19).…”

“…Strategies based on delivering adjuvants or antigens carried by nanoparticles or liposomes have led to improved targeting of LNs, activation of LN-resident DCs, and enhanced induction of antigen-specific CD8 þ T cells, hence better protection in tumor challenge studies (14)(15)(16)(17)(18)(19). Ultrasmall, functionalizable nanoparticles (NP) developed in our laboratory effectively target DCs in skin-draining LNs upon intradermal delivery (20,21).…”

Liposome Formulations of Hydrophobic Drugs

“…Vaccine delivery systems are generally composed of particles of comparable dimensions to pathogens as bacteria and viruses (e.g. liposomes, microemulsions, immunostimulatory complexes and other nano-or microparticle systems) (8)(9)(10)(11).…”