Monocytes acquire a tumor-associated IL1B program upon encountering patient-derived colon cancer organoids

Tumor-associated macrophages (TAMs) and monocytes that accumulate in colorectal cancer (CRC) play a crucial role in shaping the tumor microenvironment (TME) and anti-tumor immune responses. Although TAMs have been linked to both pro- and anti-tumor functions, our understanding of the cues instructing their heterogeneous phenotypes and function in cancer patients remains limited. Here, we established co-cultures comprising primary human monocytes and patient-derived organoids (PDOs) from patients with microsatellite-stable CRC to emulate myeloid/tumor cell interactions <i>in vitro</i>. Upon encountering PDOs, monocytes acquire phenotypic changes that are distinct from those induced by typical polarization protocols. Single-cell RNA sequencing revealed that PDO-exposed monocytes transcriptionally resembled IL1B-programmed monocytes previously identified in the tumor tissues of CRC patients. This phenotype emerged independently of tumor mutational profiles or consensus molecular subtypes. Mechanistically, soluble PDO-derived mediators induced the production of CXCL2, CXCL5 and CXCL7 chemokines, whereas the phagocytic uptake of tumor debris impaired the MHC class II-mediated antigen presentation capabilities of monocytes in co-culture. In addition, our <i>in vitro</i> system allowed functional assessment of PDO-exposed monocytes demonstrating a compromised capacity to mount an inflammatory response upon TLR stimulation. Together, PDO-monocyte co-cultures offer a platform to dissect the interplay between cancer cells and monocytes, and advance our understanding of myeloid plasticity and function in cancer patients.