Figure 5

Pluripotent cells can be killed by CTLs despite very low expression of MHC class I molecules. (A) The means of relative lysis ± SD of maGSC and ESC lines by CTLs are shown as determined in three independent experiments. The target cells were pulsed with the SIINFEKL peptide (0.5 μg/ml) and exposed to CTLs derived from TCR-transgenic OT-I mice. For normalization between experiments, the mean percentage of specific lysis of RMA cells (serving as positive control) at the highest effector to target ratio (10:1) was adjusted to 100% in each test and the relative lysis of the various target cells at different effector to target ratios was calculated. (B) The means of relative lysis ± SD of iPSCs and F9 teratocarcinoma cells by CTLs are shown as determined in three independent experiments. The target cells were pulsed with the SIINFEKL peptide (0.5 μg/ml) and exposed to CTLs derived from TCR-transgenic OT-I mice. The relative lysis was calculated as described above. YAC-1 cells (H2^a) served as a negative control. (C) The target cells were tested in each experiment for MHC class I expression (H2K^b and H2D^b) by flow cytometry. Representative individual histograms are shown. (D) The mean percentages of positive cells + SD (staining with MHC class I mAbs minus isotype control) and the MFI + SD are given for the three experiments.