Short in vivo circulation is a major hindrance to the widespread adoption of protein therapeutics. Protein nanocapsules generated by encapsulating proteins with a thin layer of phosphorylcholine-based polymer via a two-step encapsulation process exhibited significantly prolonged plasma half-life. Furthermore, by constructing nanocapsules with similar sizes but different surface charges and chemistry, we demonstrated a generic strategy for prolonging the plasma half-life of therapeutic proteins. In an in vitro experiment, four types of bovine serum albumin (BSA) nanocapsules were incubated with fetal bovine serum (FBS) in phosphate buffer saline (PBS); the cell uptake by HeLa cells was monitored to systematically evaluate the characteristics of the surface chemistry during circulation. Single positron emission tomography–computed tomography (SPECT) was employed to allow real-time observation of the BSA nanoparticle distribution in vivo, as well as quantification of the plasma concentration after intravenous administration. This study offers a practical method for translating a broad range of proteins for clinical use.

Protein therapy, wherein therapeutic proteins are delivered to treat disorders, is considered the safest and most direct approach for treating diseases. However, its applications are highly limited by the paucity of efficient strategies for delivering proteins and the rapid clearance of therapeutic proteins in vivo after their administration. Here, we demonstrate a novel strategy that can significantly prolong the circulation time of therapeutic proteins as well as minimize their immunogenicity. This is achieved by encapsulating individual protein molecules with a thin layer of crosslinked phosphorylcholine polymer that resists protein adsorption. Through extensive cellular studies, we demonstrate that the crosslinked phosphorylcholine polymer shell effectively prevents the encapsulated protein from being phagocytosed by macrophages, which play an essential role in the clearance of nanoparticles in vivo. Moreover, the polymer shell prevents the encapsulated protein from being identified by immune cells. As a result, immune responses against the therapeutic protein are effectively suppressed. This work describes a feasible method to prolong the circulation time and reduce the immunogenicity of therapeutic proteins, which may promote the development and application of novel protein therapies in the treatment of diverse diseases.