Here, we investigated the HLA-G/ILT2 checkpoint in clear-cell renal-cell carcinoma (ccRCC) patients and focused on tumor-infiltrating CD8<sup>+</sup> T lymphocytes (TIL) expressing the HLA-G receptor ILT2.
In addition, qPCR analyses and immunohistochemical staining revealed an inverse, expression of miR-628-5p, but not of miR-548q to the HLA-G protein in primary RCC lesions and cell lines.
IHC data showed that HLA-G was observed in 49.5% of clear cell, 50% of either chromophobe or collecting duct RCC lesions but undetectable in papillary RCC and tumor-negative renal tissues.
A 5'-aza-2-deoxycytidine (5-Aza-dC)-mediated demethylation of the HLA-G promoter DNA resulted in an enhanced HLA-G expression in four of six RCC cell lines, whereas a de novo induction of HLA-G was only observed in one HLA-G(-) RCC cell line on treatment with 5-Aza-dC.
Silencing of HLA-G expression in RCC is often associated with methylation of the HLA-G promoter which could be reverted by the treatment with demethylating agents.
These results provide evidence for the heterogeneity of major histocompatibility complex expression patterns in renal carcinoma and support the hypothesis that specific mechanisms underlying the malignant transformation into clear cell renal carcinoma up-regulate expression of HLA-G and to a lesser extent HLA class II molecule expression.
Thus, aberrant HLA-G expression is found at a relatively high frequency in RCC and might participate in evasion of these tumor cells from immunosurveillance.
As several studies suggest that HLA-G displays various functional features that allow down-modulation of immune response in vitro, we propose that selective in vivo expression of HLA-G may participate in the impairment of antitumor immunity in RCC.