B2M and renal cell carcinoma: Due to the monospecificity of the mAb TFL-033 recognizing only β2-m and peptide-free intracellular heavy chains (HC) HLA-E monomers [24] this mAb was used to determine HLA-E expression in untreated and IFN-γ-treated RCC cell lines and as negative control in IFN-γ insensitive HEK293T cells.