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. 2021 Feb 18;5(4):1069–1080. doi: 10.1182/bloodadvances.2019001110

Figure 3.

Figure 3.

PD-1 blockade enhances NK cell killing of PD-L1–expressing targets, and PD-L1 overexpression suppresses NK function. (A-B) Purified NK cells from peripheral blood of healthy donors were cocultured with CellTrace-labeled K562 (A) or THP-1 (B) in the presence or absence of PD-1 blocking antibodies. (C-E) Visualization of killed targets is shown 24 hours after coculture with THP-1 cells without blockade (C), with pembrolizumab (D), or pembrolizumab scFv (E). Target cell killing was identified by CellTrace and activated caspase-3 and caspase-7 positivity. The killing assay was carried out in an IncuCyte Zoom (IncuCyte) for 48 hours with images taken every 30 minutes (n = 3). Magnification ×4. (F) K562 and K.PD-L1 cells were stained for PD-L1. (G) K562 and K.PD-L1 cells were cocultured for 4 hours with purified NK cells from healthy donors for 4 hours and stained for CD107a (n = 6). Error bars indicate the mean ± SEM. *P < .05; **P < .01; ***P < .001. NT, no treatment.