Expression and shedding of MHC class I-related chain (MIC) A and B molecules in human carcinoma cell lines

The interaction of the MHC class 1-related chain molecules (MIC) A and B with the corresponding Natural Killer Group 2D receptor elicits cytotoxicity of Natural Killer cells and T cell subsets. Albeit absent in normal tissue, these molecules are constitutively expressed on transformed cells and play an important role in tumor immunosurveillance. Consequently, the ectodomain shedding of MICA and MICB is regarded as an important mechanism of the immune escape of cancer cells. However, the proteolytic machinery responsible for the shedding of endogenous MICA/MICB from tumors has not been well defined. In this study, we analyzed different human tumor entities including mammary, pancreatic and prostate carcinomas for the expression and shedding of endogenous MICA and MICB molecules. Flow cytometry and ELISA revealed that all the tested cells constitutively expressed MICA and MICB on the cell surface and also released NKG2D ligands into the supernatant. Inhibitor studies showed that metalloproteases are responsible for both the constitutive and phorbolester-induced generation of soluble MICA/B, whereas aspartate, cysteine and serine proteases are not involved in this process. Consequently, the inhibition of metalloproteases reduced the level of released MICA/B and increased cell surface expression. In the prostate carcinoma cell line PC-3, MICA was not shed at all, despite expression of these molecules on the cell surface. Genotyping of this cell line showed that the reason for this discrepancy was the expression of the truncated allelic variant, MICA*008:01, indicating an allele-specific regulation of this process. Studies employing RNA interference not only revealed a prominent role of a disintegrin and metalloprotease (ADAM) 10 and 17 in the shedding of NKG2D ligands but also a differential susceptibility of MICA to the proteolytic activity of ADAM10/17. Altogether, inhibition of shedding responsible proteases lowers the release of tumor-promoting soluble MICA/B and increases the cell surface density of these molecules and in that way presumably also the immunogenic potential of tumors. The detailed analysis of the proteolytic machinery responsible for the shedding of NKG2D ligands such as MICA/B from tumor cells might open the field for new strategies in tumor therapy

Histone Deacetylase Inhibitor Modulates NKG2D Receptor Expression and Memory Phenotype of Human Gamma/Delta T Cells Upon Interaction With Tumor Cells

The functional plasticity and anti-tumor potential of human γδ T cells have been widely studied. However, the epigenetic regulation of γδ T-cell/tumor cell interactions has been poorly investigated. In the present study, we show that treatment with the histone deacetylase inhibitor Valproic acid (VPA) significantly enhanced the expression and/or release of the NKG2D ligands MICA, MICB and ULBP-2, but not ULBP-1 in the pancreatic carcinoma cell line Panc89 and the prostate carcinoma cell line PC-3. Under in vitro tumor co-culture conditions, the expression of full length and the truncated form of the NKG2D receptor in γδ T cells was significantly downregulated. Furthermore, using a newly established flow cytometry-based method to analyze histone acetylation (H3K9ac) in γδ T cells, we showed constitutive H3K9aclow and inducible H3K9achigh expression in Vδ2 T cells. The detailed analysis of H3K9aclow Vδ2 T cells revealed a significant reversion of TEMRA to TEM phenotype during in vitro co-culture with pancreatic ductal adenocarcinoma cells. Our study uncovers novel mechanisms of how epigenetic modifiers modulate γδ T-cell differentiation during interaction with tumor cells. This information is important when considering combination therapy of VPA with the γδ T-cell-based immunotherapy for the treatment of certain types of cancer

The Serine Protease CD26/DPP4 in Non-Transformed and Malignant T Cells

CD26/Dipeptidylpeptidase 4 is a transmembrane serine protease that cleaves off N-terminal dipeptides. CD26/DPP4 is expressed on several immune cell types including T and NK cells, dendritic cells, and activated B cells. A catalytically active soluble form of CD26/DPP4 can be released from the plasma membrane. Given its wide array of substrates and interaction partners CD26/DPP4 has been implicated in numerous biological processes and effects can be dependent or independent of its enzymatic activity and are exerted by the transmembrane protein and/or the soluble form. CD26/DPP4 has been implicated in the modulation of T-cell activation and proliferation and CD26/DPP4-positive T cells are characterized by remarkable anti-tumor properties rendering them interesting candidates for T cell-based immunotherapies. Moreover, especially in cutaneous T-cell lymphoma CD26/DPP4 expression patterns emerged as an established marker for diagnosis and treatment monitoring. Surprisingly, besides a profound knowledge on substrates, interaction partners, and associated signal transduction pathways, the precise role of CD26/DPP4 for T cell-based immune responses is only partially understood