Classical HLA class I antigen downregulation and abnormal HLA-G expression in ovarian cancer

Objective: To elucidate the potential role of HLA-G and classical HLA class I molecules in ovarian cancer, we researched their patterns of expression in benign and malignant ovarian tumors. Methods: In 10 benign and 33 malignant ovarian tumor tissues, HLA-G expression was determined both at the mRNA level by reverse transcriptase-polymerase chain reaction and immunohistochemical staining. The expression of classical HLA class I heavy chains were determined immunohistochemically. Results: Immunohistochemical analysis revealed the expression of HLA-G molecules in 27 of the 33 (81.8%) ovarian cancers but in none of the benign ovarian tumors. Classical HLA class I antigen expression was down-regulated in 25 out of the 33 (75.8%) ovarian cancers and in only 1 of the 10 benign ovarian tumors. HLA-G expression and classical HLA class I antigen downregulation were related to disease stage (Spearman's rho = 0.468, P = 0.001; Spearman's rho = -0.392, P = 0.005). Conclusion: Our results reveal that abnormal expression of HLA-G and down-regulation of classical HLA class I antigen in ovarian cancer may be one of the mechanisms by which cancer cells may escape host's immune system.