Fuente: WIPO "tomato" Provided herein are single chain trimer proteins engineered to have altered CD8 binding affinities. Because of these altered affinities, the recombinant proteins are particularly useful for eliciting immunogenic responses otherwise difficult to induce. Also provided are recombinant polypeptides encoding the single chain trimer proteins, cells and vaccines or other pharmaceutical compositions including the single chain trimer proteins, and treatment methods using the single chain trimer proteins, recombinant polypeptides, cells, and pharmaceutical compositions.