EDITORIALS EXPRESSION OF HLA CLASS I ANTIGENS IN HUMAN TUMORS AND THEIR INVOLVEMENT IN TUMOR GROWTH ° CATERINA SALERNO, TIZIANA CREPALDI, PAOLA SAVOIA, PATRICIA RICHIARDI Dipartimento di C-enetica, Biologia e Chimica Medica, Universitg* degli Studi di Torino e Centro CNR Immunogenetica ed Istocompatibilit~, Torino The altered expression of class I major histocompatibility complex (MHC) antigens has been shown to be one of the most important factors for the oncogenicity of neoplastic cells in many mouse tumor systems 5, 7,10.11,14. These membrane molecules restrict recognition of tumor antigens by the cytotoxic T lymphocytes (CTLs) of the immune system 57,58 and hence their in vivo destruc- tion of tumor cells 46,48. The earliest results were obtained on virus-induced tumors. Rat cells trans- formed by the highly oncogenic type 12 adenovirus and transplanted to a syngeneic host displayed high degree of malignancy associated with heavy re- duction in class I H-2 antigens, whereas cells transformed with adenovirus 5 were poorly oncogenic and expressed normal class I MHC antigen levels ~1. Reduced expression of class I antigens has also been observed in spontaneous mouse tumors such as leukemias and sarcomas 11,19,4°. Reversion to the benign phenotype has been obtained by transfection with H-2 genes, which restores normal tumor cell MHC antigen levels 17, 41, 47, 5~ and normal sensitivity to CTLs. Loss of class I andgens is therefore one of the mechanisms through which tumors are able to elude the host immune system and continue to grow. In human tumors a reduction in HLA-A,B,C andgens has been demonstrated for many neoplasias including choriocarcinoma TM, teratocarcinoma 1, skin carci- noma 15, neuroblastoma 2°, small-cell lung carcinoma (SCLC) 6, colorectal ~4, 29. 50, laryngeaP, 24 and breast ~ carcinomas, melanoma 4, 25, ~s, 39. 51 and lymphoma 28. I n Key-words: Cytotoxicity; HLA class I antigens; Human tumors; Immune surveillance; Major histocompati- bility complex; Tumor growth. • This work was supported in part by Consiglio Nazionale delle Ricerche (CNR), Roma, Italy, Progetto Finalizzato 'Biotecnologie e Biostrumentazione" T. Crepaldi was supported by a fellowship of 'Comi- tato Gigi Ghirotti'. Accepted for publication on February 8, 1990. Res. Clin. Lab. 20, 85-93, 1990. 85