The HLA crossroad in tumor immunology

It is generally accepted that human and experimental tumor cells can lose m ajor histocompatibility complex (MHC) class I molecules. These human leukoc yte antigen (HLA) losses are detected when the primary tumor breaks the bas al membrane, invades the surrounding tissues, and starts to metastasize. Th ese altered HLA class I phenotypes probably constitute the major tumor esca pe mechanism facing anti-tumor T-cell mediated responses. Thus, it is impor tant to characterize these phenotypes in clinical tumor samples, analyze th e mechanism(s) responsible for them, and counsel patients before and during peptide anti-cancer immunotherapy. The present paper summarizes the most r elevant altered HLA class I phenotypes found in human tumor samples, indica tes their frequency, and outlines the mechanisms implicated. This review al so points out that the natural killer (NK) escape mechanism of HLA class I deficient cancer cells is yet to be defined. Knowledge accumulated to date reveals that HLA class I molecules are an important crossroad in tumor immu nology. Human Immunology 61, 65-73 (2000). (C) American Society for Histoco mpatibility and Immunogenetics, 2000. Published by Elsevier Science Inc.