Polyspecific tumor vaccination should offer broad control of tumor cells and reduce the risk of emergence of immune escape variants. Here, we evaluated the capacity of a polypeptide composed of optimized cryptic peptides derived from three different universal tumor antigens (TERT988Y, HER-2/neu402Y and MAGE-A248V9) to induce a polyspecific CD8 cell response both in vivo in HHD mice and in vitro in humans. A mixture of TERT988Y, HER-2/neu402Y and MAGE-A248V9 peptides failed to induce a trispecific response. In contrast, a polypeptide composed of the three peptides stimulated a trispecific immune response. Interestingly, the capacity of the polypeptide to induce a trispecific response depended on its internal organization. Six different polypeptide variants corresponding to all possible combinations of the three peptides were tested. Only one variant, named Poly-6, elicited an immune response simultaneously targeting all three peptides.