Mouse serum

Cells were first stained with Live/Dead Aqua (Thermo Fisher Scientific) in PBS for 10 min at 4 °C. Then, cells were stained in PBS containing 0.5% human AB serum and 2 mM EDTA with anti-CD1a APC and anti-CD16 FITC for 30 min on ice. After washing, cells were fixed with paraformaldehyde 4% in PBS for 20 min at room temperature and permeabilized with Permeabilization Buffer (Fixation/Permeablization Kit, BD Biosciences) containing Fc block (Human TruStain FcX, BioLegend) and mouse serum (BioLegend) for 30 min on ice. Cells were then incubated with the primary antibody in permeabilization buffer, rabbit anti-ETV6/Tel (Novus Biologicals, NBP1-80695, dilution 1:1,000) or rabbit anti-ETV3 (Atlas Antibodies, HPA004794, dilution 1:1,000), at 4 µg ml⁻¹ for 1 h at room temperature. Finally, cells were incubated with the secondary antibody anti-rabbit immunglobulin G (H + L) Alexa Fluor-594 (Molecular Probes, catalog no. A-11037, dilution 1:500) for 1 h at room temperature and then resuspended in staining buffer containing DAPI (Thermo Fisher Scientific, 50 ng ml⁻¹). Samples were acquired in an Amnis ImageStream instrument (Luminex). Data were analyzed using the IDEAS software to obtain the similarity score between DAPI and Alexa Fluor-594 channels. Finally, data were exported to FlowJo for quantification and visualization.

PBMCs were isolated from the buffy coats of anonymous human healthy donors using Ficoll‐Paque Premium (GE Healthcare). PBMCs were treated with the supernatant collected from THLE‐3 cells expressing Birc5 or control vector for 5 days. For flow cytometry analysis, cells were collected and washed and incubated with mouse serum (BioLegend) for 10 min at 4°C to block Fcγ receptors. Then, the cells were stained by anti‐human myeloid markers CD11b, CD14, CD33 and HLA‐DR, followed by flow cytometry analysis. Flow cytometry data were acquired using the CytoFLEX (BECKMAN COULTER), and the percentages of proliferating cells were analyzed by FlowJo software 10 (Tree Star, Inc.).