Simultaneous assessment of PD-L1 and IRF1 expression on breast cancer circulating tumor cells
PD-L1 staining on its own cannot separate a tumor cell responding to interferon-gamma from one expressing PD-L1 for another reason; this AACR 2018 poster reports a 6-marker assay that reads PD-L1 together with its upstream regulator IRF1 on the same breast cancer circulating tumor cell.
Presented by RareCyte and University of Washington.
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- A 6-marker panel places PD-L1 and nuclear IRF1 on the same circulating tumor cell. Buffy coat was separated from 7.5 mL of blood by AccuCyte, stained for pan-cytokeratin, EpCAM, CD45, PD-L1, IRF1 and a nuclear dye, then scanned on CyteFinder, with CTCs identified by cytokeratin and/or EpCAM positivity and negative CD45 staining.
- Two CTC models separate interferon-gamma-driven PD-L1 from PD-L1 expressed without it. A549 cells cultured overnight with 10 ng/mL interferon-gamma showed PD-L1 staining and strong nuclear IRF1, while unstimulated MDA-MB-231 cells showed high PD-L1 with low to absent nuclear IRF1 — a pattern that may identify PD-L1 expression not driven by interferon-gamma signaling.
- In patient CTCs, high-PD-L1 cells carried 2.7-fold more nuclear IRF1 than low-PD-L1 cells. With the PD-L1 threshold set at the upper 95% confidence interval of unstimulated A549 cells, high-PD-L1 CTCs from two breast cancer patients had a mean 2.7-fold higher nuclear IRF1 mean fluorescence intensity than low-PD-L1 CTCs, ranging from 1.4 to 3.3; the poster presents this simultaneous readout as feasible for non-invasive assessment.
