Tumor cells of wild-type mice express antigenic peptides derived from novel proteins on the cell surface in association with MHC class I molecules. These cells are therefore recognized and killed by CTLs and tumors do not progress. In contrast; the presentation of antigenic peptides and/or MHC class I molecules is impaired in LMP2-/- tumor cells as a result of a defect in proteasomal function. These LMP2-/- tumor cells are therefore not attacked by CTLs, but may be recognized and killed by NK cells.
