Tumor-associated macrophage functional heterogeneity is driven by niche diversity in breast cancer

The concept of macrophage niches has redefined the classification of macrophages, moving beyond ontogeny and function to encompass the mutually beneficial loop of signals in a given tissue environment. As such, tissue-resident macrophages adapt to local environmental signals within and between tissues to acquire specific functional adaptations. Neoplastic transition transforms the tissue environment, which then raises the question as to how existing macrophage subsets and their niche contribute to the tumor-associated macrophage (TAM) compartment. By combining single cell RNA sequencing and 2-photon imaging, we discovered that considerable TAM heterogeneity in mammary breast tumor is driven by niches that exist prior to tumor development, macrophage localization within the tumor and the stage of tumor malignancy. The differentiation of TAM subsets was associated with distinct signaling paths, homing and transcription factor signatures. We find similar functional heterogeneity in human breast TAMs. In overview, we show that specific niches within the tumor rather than defined activation states (e.g. the M1/M2 dichotomy) are the major drivers of TAM plasticity and heterogeneity. The distinctions created by this analysis show how treatments of different tumor indications should propose targeting specific TAMs at this niche/pathway level. Overall design: 3 sorted tumor samples from a pool of 4 mice(spontaneous tumors; bulk myeloid, cd11b-hi-enriched, and cd11b-lo-enriched) 1 sorted tumor samples from a pool of 5 mice(orthotopically injected tumors; bulk myeloid)