Macrophages are cells of the innate immune system fundamental to support normal haematopoiesis, fight infection, anti-cancer immunity and tumour progression. However, the function of macrophages in myeloid leukaemias remain largely unknown, due to difficulties in isolating non-transformed cells from the malignant ones. Here we use a state-of-the-art chimeric mouse of chronic myeloid leukaemia (CML) to study in the impact of the dysregulated bone marrow (BM) microenvironment on bystander macrophages. Utilising single cell RNA sequencing (scRNA seq) of Philadelphia chromosome (Ph) negative macrophages and secretome proteomics of murine c-kit+ stem/progenitor cells we have uncovered that macrophages exposed to a CML environment are altered transcriptionally and have reduced phagocytic function