Synthesis and Evaluation of a QS-17/18-Based Vaccine Adjuvant

We have synthesized a QS-17/18 analogue (<b>7</b>) and evaluated its adjuvant activity in the formulation with rHagB antigen. Compound <b>7</b> and QS-21 analogues <b>5</b> and <b>6</b> are presumably the major components of GPI-0100, a widely used complex mixture of semisynthetic derivatives of Quillaja saponaria (QS) Molina saponins. The QS-17/18 analogue <b>7</b> shows an adjuvant activity profile similar to that of GPI-0100, potentiating mixed Th-1/Th-2 immune responses, which is different from those of QS-21 analogues <b>5</b> and <b>6</b> that probably only induce a Th2-like immunity. The combination of QS-17/18 and QS-21 analogues does not show a synergistic effect. These results suggest that QS-17/18 analogue <b>7</b> might be the active component of GPI-0100 responsible for its immunostimulant property. Therefore, compound <b>7</b> can not only be a structurally defined alternative to GPI-0100 but also provide a valuable clue for rational design of new QS-based vaccine adjuvants with better adjuvant properties.