pH-Sensitive branched β-glucan-modified liposomes for activation of antigen presenting cells and induction of antitumor immunity.

Induction of cellular immunity is important for effective cancer immunotherapy. Although various antigen carriers for cancer immunotherapy have been developed to date, balancing efficient antigen delivery to antigen presenting cells (APCs) and their activation via innate immune receptors, both of which are crucially important for the induction of strong cellular immunity, remains challenging. For this study, branched β-glucan was selected as an intrinsically immunity-stimulating and biocompatible material. It was engineered to develop multifunctional liposomal cancer vaccines capable of efficient interactions with APCs and subsequent activation of the cells. Hydroxy groups of branched β-glucan (Aquaβ) were modified with 3-methylglutaric acid ester and decyl groups, respectively, to provide pH-sensitivity and anchoring capability to the liposomal membrane. The modification efficiency of Aquaβ derivatives to the liposomes was significantly high compared with linear β-glucan (curdlan) derivatives. Aquaβ derivative-modified liposomes released their contents in response to weakly acidic pH. As a model antigenic protein, ovalbumin (OVA)-loaded liposomes modified with Aquaβ derivatives interacted efficiently with dendritic cells, and induced inflammatory cytokine secretion from the cells. Subcutaneous administration of Aquaβ derivative-modified liposomes suppressed the growth of the E.G7-OVA tumor significantly compared with curdlan derivative-modified liposomes. Aquaβ derivative-modified liposomes induced the increase of CD8+ T cells, and polarized macrophages to the antitumor M1-phenotype within the tumor microenvironment. Therefore, pH-sensitive Aquaβ derivatives can be promising materials for liposomal antigen delivery systems to induce antitumor immune responses efficiently.