Pristine mesoporous carbon hollow spheres as safe adjuvants induce excellent Th2-biased immune response

The development of a safe and effective adjuvant that amplifies the immune response to an antigen is important for vaccine delivery. In this study, we developed pristine mesoporous carbon hollow spheres as high-capacity vaccine protein nanocarriers and safe adjuvants for boosting the immune response. Mono-dispersed invaginated mesostructured hollow carbon spheres (IMHCSs) have an average particle size of ~200 nm, large pore size of 15 nm, and high pore volume of 2.85 cm³·g^-1. IMHCSs exhibited a very high loading capacity (1, 040 μg·mg^-1) towards ovalbumin (OVA, a model antigen), controlled OVA release behavior, excellent safety profile to normal cells, and high antigen delivery efficacy towards macrophages. In vivo immunization studies in mice demonstrated that OVA-loaded IMHCSs induced a 3-fold higher IgG response compared to a traditional adjuvant QuilA used in veterinary vaccine research. OVA delivered by IMHCSs induced a higher IgG1 concentration than IgG2a, indicating a T-helper 2 (Th2)-polarized response. Interferon-γ and interleukin-4 concentration analysis revealed both T-helper 1 (Th1) and Th2 immune responses induced by OVA-loaded IMHCSs. IMHCSs are safer adjuvants than QuilA. Our study revealed that pure IMHCSs without further functionalization can be used as a safe adjuvant for promoting Th2-biased immune responses for vaccine delivery.