Potent enhancement of cellular and humoral immune responses against recombinant hepatitis B antigens using AS02A adjuvant in healthy adults

Recombinant subunit protein vaccines generally elicit good humoral immune responses, weak helper T cell responses and no cytotoxic T cell responses. Certain adjuvants are known to enhance humoral and cellular immune responses.This study evaluated the humoral, CD4+ T helper and CTL responses induced by the recombinant SL* protein adjuvanted with AS02A in comparison with non-adjuvanted SL* in PBS in two groups of 15 healthy adult volunteers. The AS02A adjuvant contains monophosphoryl lipid A (MPL), QS21 and an oil in water emulsion. The adjuvanted vaccine induced fast and vigorous humoral and helper T cell responses of the Th1 type. Using a pool of overlapping 20mer peptides a cytotoxic response was detected in 6 out of 14 HLA-A2-positive (+) and HLA-A2-negative (−) recipients of the adjuvanted vaccine. All HLA-A2-positive subjects in the adjuvanted group and up to 30% of the subjects in the SL* PBS group displayed a CTL response against selected HLA-A2-restricted CD8+ T cell epitopes. The non-adjuvanted vaccine induced a very weak antibody response and no helper T cell responses. Local and general reactions were more frequently reported by AS02A recipients than in the non-adjuvanted group but the safety profile was considered acceptable. AS02A can be considered as a useful adjuvant that strongly enhances the cellular and humoral responses of subunit protein vaccines.