Polypeptides, such as a multi-valent polypeptide designated svD2, useful in pharmaceutical compositions for stimulation of the adaptive arm of the immune system. svD2 demonstrated in vivo activity in a syngeneic mouse model. svD2 is biologically active at nanomolar concentrations. These properties are believed to result as a consequence of the ability of svD2 to cross-link cell-surface receptors.
