Platelets upregulate tumor cell PD-L1 in a coculture system. (A) Scheme of platelet and tumor cell coculture system. (B) Flow cytometric analysis of tumor cell-surface PD-L1 median fluorescence intensity (MFI) on MDA-MB-468 cells (left panel, n = 7-10) and A549 cells (right panel, n = 9) cocultured with platelets (+platelets) or coculture treated with 100 μM aspirin or 1 μM ticagrelor. (C) Relative levels of PD-L1 in coculture to tumor cell monoculture for MDA-MB-468 and A549 cells. n = 7. (D) Flow cytometric analysis of tumor cell-surface PD-L1 levels following tumor cell monoculture, cocultured with platelets, or cocultured with platelets physically separated by transwells. Left panel: MDA-MB-468 (n = 7); right panel: A549 (n = 6). (E) PDL1 gene expression in tumor cells either as monoculture or cocultured with platelets. Normalized to glyceraldehyde-3-phosphate dehydrogenase. Left panel: MDA-MB-468 (n = 4); right panel: A549 (n = 7). Lines connect the data points are from an individual healthy donor. Paired t test was used for testing data with 2 groups. One-way analysis of variance (with Tukey correction was used for testing data with 3 or more groups. ∗P < .05, ∗∗P < .01, ∗∗∗P < .001. ns, not significant; RT-qPCR, reverse transcription quantitative polymerase chain reaction.