Disclosed are cells and methods for treating or preventing tumor formation or infections with pathogens in a patient. The cells of the invention are antigen-presenting cells (e.g., dendritic cells or macrophage) that have been loaded with RNA derived from tumors or pathogens. By administering the RNA-loaded antigen-presenting cells to a patient, tumor formation or pathogen infections can be treated or prevented. Alternatively, the RNA-loaded cells can be used as stimulator cells in the ex vivo expansion of CTL. Such CTL can then be used in a variation of conventional adoptive immunotherapy techniques.