a, Scheme for mixed cell assay. HeLa cells were lifted and labelled with CellTracker Deep Red, then mixed in a 1:1 ratio with Jurkat cells. The mixed cell sample was stained with either 10 nM ctx or ctx-M6Pn conjugate, followed by anti-human 488, then subjected to live-cell flow cytometry. b, Cell surface CI-M6PR levels on HeLa cells (CIM6PR+EGFR+) and Jurkat cells (CIM6PR+EGFR−) were measured by live-cell flow cytometry. HeLa and Jurkat cells exhibited similar levels of cell-surface CI-M6PR. c, Ctx and ctx-M6Pn exhibit equivalent binding to HeLa cells, and ctx-M6Pn exhibits minimal increased binding to Jurkat cells relative to ctx. Data are representative of two independent experiments (b) or two experimental replicates (c).