Five specimens of normal mammary tissue and 53 primary breast carcinoma lesions were tested for expression of HLA antigens and components of the antigen-processing machinery by immunohistochemical staining. The expression of transporter associated with antigen processing (TAP) 1, TAP2, and HLA class I antigens in breast carcinoma lesions was significantly associated with tumor grading. Like normal mammary tissue, the 16 low-grade (G1) breast carcinoma lesions showed strong staining for TAP1, TAP2, and HLA class I antigens. In contrast, only 12 (32%) of 37 high-grade (G2 and G3) breast carcinoma lesions displayed the normal staining pattern. In 14 (38%) of 37 high-grade lesions, HLA class I antigen down-regulation was observed without loss of low molecular mass polypeptide and/or TAP staining. Congruent down-regulation of HLA class I antigen and TAP1 or TAP2 was found in 8 (22%) of 37 high-grade lesions. Complete loss of HLA class I antigens, TAP1, and TAP2 was observed in 3 (8%) of 37 high-grade lesions. No lesion was negative for TAP1 and/or TAP2 staining while positive for HLA class I antigen staining. These data demonstrate an association of HLA class I antigen and TAP down-regulation with tumor progression in breast carcinoma. This association suggests that loss of HLA and/or TAP may represent an escape from the host's immune pressure or may reflect the accumulation of abnormalities associated with neoplastic progression. This accumulation of defects in antigen processing and presentation may in turn be responsible for reduced recognition of malignant cells by putative clinically relevant tumor-specific T cells.
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