The present invention provides a means to be used for a new immunotherapy of cancer or infection utilizing activation of dendritic cell (DC) by innate immunity, namely, a method of preparing a cell co-expressing a target antigen and CD1d and having an ability to activate immunity against the target antigen, comprising the following steps (a) and (b): (a) a step of transfecting an mRNA encoding the target antigen into a CD1d-expressing cell to give a cell co-expressing the target antigen and CDld and (b) a step of treating the cell obtained in step (a) with a CD1d ligand in a culture medium.
