Monocytes acquire a tumor-associated IL1B program upon encountering patient-derived colon cancer organoids
Tumor-associated monocytes and macrophages (TAM) accumulate in colorectal cancer (CRC) and play an active role in shaping the tumor microenvironment (TME). While they have been linked to both pro- and anti-tumor functions, understanding the cues that instruct the phenotype of individual subsets as well as their functional impact on the TME remains challenging. In this study, we established co-cultures comprising primary human monocytes and patient-derived organoids (PDOs) from CRC tumors to emulate myeloid cell/carcinoma interactions in vitro that drive tumor-associated monocyte  programming. Upon encountering PDOs, monocytes acquired a complex phenotype not reflected by classical TAM markers or polarization protocols. Single-cell RNA sequencing revealed that PDO-exposed monocyte transcriptionally resembled IL1B-programmed monocytes previously identified in CRC patients. This phenotype emerged independently of the tumors' mutational profiles or CMS type. Mechanistically, soluble PDO-derived mediators induced the production of chemotactic CXCL2, CXCL5 and CXCL7, while phagocytic uptake of tumor debry limited the MHC class II-mediated antigen presentation capabilities of monocytes in co-culture. Additionally, our in vitro system allowed the functional assessment of PDO-exposed monocytes demonstrating a compromised capacity to mount an inflammatory response upon TLR stimulation. Together, our PDO–monocyte co-cultures offer a tractable, human-specific model system to study the interplay between epithelial cancer cells and monocytes, and advance our understanding of myeloid plasticity and function in cancer patients. Overall design: Single-cell RNA sequencing of CD45+ sorted monocytes after four days of monoculture or co-culture with PDO19 or PDO30