C-Phycocyanin and Phycocyanobilin as a Novel Adjuvant in Hepatitis B Vaccine

Vaccine adjuvants are components that enhance immune responses to an antigen. Given the importance of adjuvants, research on novel adjuvants with higher efficacy and fewer adverse effects remains crucial. Spirulina (Arthrospira sp.), an aqueous, photosynthetic, filamentous, spiral, multicellular microalga also classified as a cyanobacterium, is well known for its high protein content, vitamins, essential fatty acids, and amino acids. C-phycocyanin (C-PC) is one of the most significant proteins in Spirulina.

This study aimed to investigate the adjuvant capabilities of three Spirulina-derived substances-Spirulina extract, C-phycocyanin (C-PC), and phycocyanobilin (PCB)-in conjunction with the Hepatitis B surface antigen (HBsAg).

Vaccine groups received the vaccine and adjuvants three times at two-week intervals, administered either orally or by injection in encapsulated or naked forms. To use the injectable form while preventing antigenic effects from the C-PC protein portion, the PCB portion was isolated and used as an injectable adjuvant.

The highest levels of interferon gamma (IFN-γ) and interleukin 4 (IL-4) stimulation were observed in the naked PCB form with the vaccine. In both oral and injectable forms of PCB and C-PC, results indicated an increased expression of Hepatitis B surface antibodies (HBsAb) in response to the antigen. The absence of a significant difference between C-PC and Spirulina extract in oral form suggested that the adjuvant effect of this microalga was primarily due to the C-PC compound. Additionally, the injectable form of PCB led to the highest HBsAb expression level. This enhancement of the humoral immune response indicated that these compounds have potential as adjuvants in both oral and injectable forms.

These findings suggest the potential for improved Hepatitis B vaccine efficacy with this novel adjuvant, paving the way for further evaluation with other vaccines.