Can Adjuvant Combination Boost Immune Response?

An effective adjuvant can deliver the antigen to APCs in its native form, stimulate the secretion of the correct cytokines, and activate effective humoral and cell-mediated immune responses. Due to the difficulty of finding a substance that can perform all these functions, there is intensive research on the possibility of incorporating different adjuvants into a single vaccine formulation and their potential synergistic effects. Various combinations of adjuvants are at different stages of clinical trials in human vaccines against infectious diseases and cancer. The results obtained from these studies indicate that adjuvant combination may increase the efficacy of animal vaccines.

FCA’s success in producing high antibody titers has prompted many researchers to combine emulsions and bacteria derived components into a single vaccine formulation. Several research groups have evaluated the combination of O/W or W/O/W emulsions with bacterial CpG motifs as adjuvant systems in avian influenza and FMD vaccines. A mixture of CpG ODNs and emulsions can induce higher levels of neutralizing antibodies than these adjuvants. Emulsions provide sustained release of antigen and CpG ODNs, while the latter can activate IFN-y secreting lymphocytes. The combination of inactivated spores of Bacillus atrophaeus and Q. saponins enhanced antibody responses to rabies virus in a murine model compared vaccine groups formulated only with spors or saponins. The combination of saponins and emulsions has also been shown to improve the efficacy of FMD vaccines. QS-21 accelerated the formation of anti-FMDV neutralizing antibodies in cows immunized with W/O/W emulsion adjuvant vaccine. In an experiment with mice vaccinated against FMD, the combination of saponins and emulsion induced higher titers of IgG1, IgG2a, IgG2b and IgG3 antibodies.

Although several promising adjuvant combinations have been tested in vitro, further research is needed to confirm their safety and efficacy in large animals. Besides, the impact of combining different adjuvants on production costs must be thoroughly evaluated before they can be applied to make commercial animal vaccines.