HLA expression in cancer: implications for T cell-based immunotherapy

HLA class I expression is altered in a significant fraction of the tumor ty pes reviewed here. reflecting either immune pressure or, simply. the accumu lation of pathological changes and alterations. However, in all tumor types analyzed, a majority of the tumors express HLA class 1, with a general ten dency for the more severe alterations to be found in later-stage and less d ifferentiated tumors. These results are encouraging for the development of specific immunotherapies, especially considering that (1) the relatively lo w sensitivity of immunohistochemical techniques might underestimate HLA exp ression in tumors, (2) class I expression can be induced in tumor cells as a result of local inflammation and lymphokine release, and (3) class I-nega tive cells would be predicted to be sensitive to lysis by natural killer ce lls.