STRUCTURAL AND FUNCTIONAL-ANALYSIS OF BETA-2-MICROGLOBULIN ABNORMALITIES IN HUMAN LUNG AND BREAST-CANCER

The escape of tumor cells from immune recognition is a central problem in tumor immunology. Here, we examined the functional role of somatic beta 2-microglobulin (beta 2m) gene mutations in human lung and breas t cancers. Using single-strand conformational polymorphism (SSCP) anal ysis and DNA sequencing, we found mutations in the beta 2m gene in 2 o f 110 tested lung, colon and breast tumors and tumor cell lines. No mu tations were identified in 63 breast cancer tumors, in B-lymphoblastoi d cell lines or normal tissues from these or other patients. In these cell lines, beta 2m protein was undetectable by Western blot analysis and there was no MHC class I on their cell surface even after treatmen t with interferon-gamma. Transfection of these tumor cell lines with t he beta 2m gene, but not addition of purified beta 2m protein restored MHC expression without addition of exogenous peptides, indicating tha t endogenous beta 2m expression is necessary for proper intracellular MHC assembly and stabilization by endogeneous peptides. Mutation in be ta 2m caused cell line H2009 to be resistant to specific lysis by infl uenza virus-specific CTL from HLA matched donors, and transfection of the beta 2m gene restored this killing. A small cell lung cancer cell line with low class expression and with a normal beta 2m genomic seque nce nonetheless also demonstrated increased class I expression after t ransfection of the beta 2m expression vector alone, indicating that th e availability of beta 2m may be rate limiting for MHC assembly in thi s line. Our results indicate that somatic mutations or selective loss of expression of the beta 2m gene in human lung cancer is rare, but ca n cause defective MHC class I expression and function allowing these c ells to escape recognition by cytotoxic T cells. (C) 1996 Wiley-Liss, Inc.