Cell fixation and chromatin sonication were optimised for each cell line in order to obtain enrichment of DNA fragments between 200-500bp. Chromatin was pre-cleared with BSA saturated Protein A sepharose (Thermo Scientific). A fraction of the chromatin was then incubated overnight at 4°C with the appropriate antibody (in duplicate) and then immunoprecipitated with BSA saturated Protein A sepharose (Thermo Scientific) for 4 hours at 4°C. Following washing to remove aspecificity, each IP was eluted from the Protein A sepharose overnight. DNA was then purified with standard phenol/chloroform extraction and quantified using Quant-iT™ Picogreen® dsDNA Broad-Range Assay Kit (Life Technologies™). IRF4, PU.1 and SPIB CHIP-seq libraries from OCI-LY3, OCI-LY10 and H929 were generated using the Illumina ChIP-seq Sample Prep Kit (Illumina®) according to manufacturer’s instructions. The BATF and the SPIB knockdown libraries were generated using the Microplex Library Preparation™ Kit (Diagenode) following manufacturer's instructions, and size selected using Agencourt® AMPure® XP beads (Beckman Coulter®).