cancer cells outcompete macrophages for microenvironmental zinc to drive immunotherapy resistance.

Approximately 50% of cancers exhibit decreased expression ( ), which is linked to immune checkpoint blockade (ICB) resistance. While is traditionally recognized as a tumor suppressor and cell cycle regulator, we have previously put forth a new paradigm demonstrating its role in intracellular metabolic reprogramming. Whether the metabolic derangement due to loss alters metabolites within the tumor microenvironment (TME) and how that affects the immune compartment and ICB response has never been investigated. Here we found that cancer cells reorganize zinc compartmentalization by upregulating the zinc importer SLC39A9 in the plasma membrane, leading to intracellular zinc accumulation in cancer cells and concurrent zinc depletion in the TME. This competition for zinc results in zinc-starved macrophages, leading to reduced phagocytic activity. Remarkably, restoring zinc levels in the TME through a dietary intervention re-educates macrophages to a pro-phagocytic phenotype, sensitizing tumors to ICB. Unexpectedly, T cells are not required for this response. Clinically, macrophages from cancer patients have decreased zinc signatures, corresponding to reduced phagocytosis signatures. Moreover, patients with low circulating zinc levels have reduced time-to-event outcomes compared to those with higher zinc levels. Our work reveals a previously unrecognized mechanism through which cancer cells outcompete macrophages for zinc, directly disrupting their function and ICB efficacy.