Fig. 1

Healthy volunteer spiking experiments for (A) PD-L1, (B) PD-L2, (C) B7-H3, and (D) CTLA-4 checkpoint ligands on CTCs. Cell lines known to be positive or negative for expression of each immune checkpoint biomarker were spiked into healthy volunteer whole blood. Control samples were spiked with approximately 500 cells (variation due to random error). Each panel shows unspiked, negative and positive control cells captured from these spiking experiments, with total # of CTCs captured below. Panels of CTCs depicted below are the raw CTC output from Cellearch – from left to right, merged image of captured cell, cytokeratin (CK) stain, the DAPI nuclear stain, CD45 (leukocyte marker, negative in tumor cells), and the checkpoint ligand of interest