IFN-γ protects short-term ovarian carcinoma cell lines from CTL lysis via a CD94/NKG2A-dependent mechanism

Abstract

IFN-gamma regulates the immunogenicity of target cells by increasing their expression of HLA class I molecules. This facilitates the T cell receptor-mediated recognition by CD8(+) T cells but decreases target cell sensitivity to lysis by NK cells due to engagement of inhibitory NK receptors. In this study, short-term tumor cell lines from patients with advanced ovarian carcinomas were established. We demonstrate the paradoxical finding that IFN-gamma treatment of these short-term ovarian carcinoma cell lines (OVACs) resulted in resistance of tumor cells to lysis by peptide- and allospecific CD8(+) T cells. Blocking experiments revealed that this phenomenon was dependent on enhanced inhibitory signalling via CD94/NKG2A receptors expressed on the effector cells. This was associated with increased expression of HLA-E mRNA and HLA-G at the protein level in IFN-gamma-treated OVACs. Furthermore, pulsing of untreated OVACs with the leader sequence peptide of HLA-G protected these cells from lysis by CTLs, thus mimicking the inhibitory effect of IFN-gamma. This study provides evidence that CD94/NKG2A receptors play an important role in regulating T cell activity against tumors and shows that IFN-gamma modulation of target cells may shift the balance of triggering and inhibitory signals to T cells, turning off their cytolytic activity.

Switch ofHLA-G alternative splicing in a melanoma cell line causes loss of HLA-G1 expression and sensitivity to NK lysis

“…This data is in agreement with previous reports showing a downregulation of HLA-G1 cell-surface expression upon in vitro culture of renal carcinoma cell lines 16 and short-term ovarian carcinoma cell lines. 18 Interestingly, we found that loss of HLA-G1 mRNA in melanoma cells is associated with a selective switch in HLA-G alternative splicing toward HLA-G2 expression. This process is of particular interest since it abrogates the role of HLA-G1 in tumor escape from NK lysis.…”

“…cDNA were prepared from 1-5 lg of total RNA using Ready To Go TM kit and oligo (dT) [12][13][14][15][16][17][18] , according to the manufacturer's recommendations. For HLA-G1 to -G5 transcript detection, PCR amplification and hybridization of the PCR products were performed as previously described.…”

“…To date, only a few tumor cell lines, other than choriocarcinoma cell lines, have been found to express cell-surface HLA-G: 4 renal carcinoma cell lines, 9,16,17 4 glioma cell lines 13 and 9 short-term ovarian carcinoma cell lines. 18 This observation may be due to the loss of HLA-G expression during long-term cell culture. Supporting this hypothesis, we show here that a melanoma cell line named Fon, which was derived from an HLA-G-positive surgically removed primitive melanoma lesion, 19,20 lost its constitutive HLA-G surface expression upon long-term in vitro propagation.…”

Primary Human Tumor Cells Expressing CD155 Impair Tumor Targeting by Down-Regulating DNAM-1 on NK Cells

“…Blood from healthy donors was obtained from the Blood Centre at the Karolinska University Hospital. Lymphocytes were enriched by density gradient centrifugation (Ficoll-Hypaque; Amersham Biosciences) as previously described (26). Cells were frozen in 10% DMSO (Sigma-Aldrich) and 90% heat-inactivated FBS (Invitrogen) and stored in liquid nitrogen.…”

Activating NK‐cell receptors co‐stimulate CD4+CD28− T cells in patients with rheumatoid arthritis

“…Furthermore, expression of activating killer cell Ig-like receptors (KIR) on CD4 1 T cells has been associated with severe disease manifestations in RA patients [17]. Inhibitory receptors, however, seem to shut of the activation program in a more dominant fashion leading to abrogation of TCR signaling cascades [18,19]. The expression of inhibitory receptors has also been suggested to protect differentiated cells from activation-induced cell death, thereby taking part in the formation and survival of memory T cells [20].…”