We analyzed the expression of HLA class I antigens in 78 tumor tissue samples obtained from patients diagnosed as having colorectal carcinomas. A broad panel of mAbs defining HLA monomorphic, locus-specific and allele-specific determinants was used. In addition, an antibody defining HLA-C locus-specific determinant (L31) was also tested. Previous reports on these tumors indicated HLA class I losses of 30 to 40%. At least 73% of the patients in the present study had a detectable HLA class I alteration. These altered HLA phenotypes were classified as total HLA loss (18%) (phenotype I); HLA-A locus-specific loss (9%) (phenotype IIIa); HLA-B locus-specific loss (8%) (phenotype IIIb); HLA-A and B locus losses (2%) and HLA allelic losses (36%) (phenotype IV). We found no HLA-C locus losses. Autologous peripheral blood lymphocyte HLA class I typing was always necessary to define phenotype IV. We also studied the CD3 zeta chain in tumor tissues to correlate possible changes in the CD3 signal transduction pathway with HLA alterations. The CD3 ratio was frequently altered, but this alteration could not be correlated with tumor HLA phenotypes. The high frequency of HLA class I losses in colorectal carcinomas suggests that this finding is a widespread phenomenon and may be required to escape T-cell recognition. It remains to be determined whether HLA expression is "normal" in the rest of the 27% of our patients.
Beta2 microglobulin mutations are an important mechanism for HLA class I total loss, (phenotype No. I) and have been described in colon carcinomas, melanomas and lymphomas. We describe a new beta2 microglobulin mutation detected in the melanoma cell line GR-34. The new mutation reported here was identified as a deletion of 4 bases (TTCT) in the highly repetitive sequence CTCTCTCTTTCT located in the leader sequence of the beta2 microglobulin gene at codon 15-16 of exon 1. The mutation produces a frameshift in the open reading frame sequence with the appearance of a stop codon at position 42. We also demonstrate that the second beta2 microglobulin gene is deleted. Comparisons with beta2 microglobulin mutations in other tumor cell lines suggest a mutation hot spot in exon 1.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.