First, we explored single cell RNA sequencing data derived from tumor biopsies of patients with metastatic melanoma.21 We were able to identify the myeloid cells similar to the cluster of monocytes/macrophages as identified in the original publication (figure 4A; online supplementary figure 4A).21 Subsequently, using hierarchical clustering, we could define monocytes, macrophage and moDCs by expression of CSF1R, CLEC10A, MARCO, APOE, CD14, CD163, CD1C, MAFB and CIITA genes (figure 4B; online supplementary figure 4B). Here, APOE is linked to metastatic melanoma.