Abstract
As the focus has shifted from traditional killed or live, attenuated vaccines toward subunit vaccines, improvements in vaccine safety have been confronted with low immunogenicity of protein antigens. This issue has been addressed by synthesizing and designing a wide variety of antigen carriers and adjuvants, such as Toll-like receptor agonists (e.g., MPLA, CpG). Studies have focused on optimizing adjuvants for improved cellular trafficking, cytosolic availability, and improved antigen presentation. In this work, we describe the design of novel amphiphilic pentablock copolymer (PBC) adjuvants that exhibit high biocompatibility and reversible pH- and temperature-sensitive micelle formation. We demonstrate improved humoral immunity in mice in response to single-dose immunization with PBC micelle adjuvants compared with soluble antigen alone. With the motive of exploring the mechanism of action of these PBC micelles, we studied intracellular trafficking of these PBC micelles with a model antigen and demonstrated that the PBC micelles associate with the antigen and enhance its cytosolic delivery to antigen-presenting cells. We posit that these PBC micelles operate via immune-enhancing mechanisms that are different from that of traditional Toll-like receptor activating adjuvants. The metabolic profile of antigen-presenting cells stimulated with traditional adjuvants and the PBC micelles also suggests distinct mechanisms of action. A key finding from this study is the low production of nitric oxide and reactive oxygen species by antigen-presenting cells when stimulated by PBC micelle adjuvants in sharp contrast to TLR adjuvants. Together, these studies provide a basis for rationally developing novel vaccine adjuvants that are safe, that induce low inflammation, and that can efficiently deliver antigen to the cytosol.