Melanoma cell states shape spatial tumor-immune ecosystems to dictate the efficacy of anti-PD1 immunotherapy.

backgroundMelanoma shows one of the highest response rates to immune checkpoint inhibitors (ICIs), yet nearly half of patients experience primary or acquired resistance. While immune contexture strongly influences therapeutic efficacy, tumor cell-intrinsic features are increasingly recognized as key regulators of antitumor immunity. In particular, intratumoral heterogeneity driven by melanoma cell plasticity underlies diverse immune escape mechanisms. How this plasticity shapes ICI outcomes in patients remains poorly defined.

methodsTumor cell states and immune contexture were assessed in 57 primary cutaneous melanomas from stage III patients, collected prior to adjuvant anti-programmed cell death protein-1 (anti-PD-1) therapy and stratified according to 2-year relapse status (33 relapse-free, 24 relapsed). Whole slide multiplex immunofluorescence was combined with spatial transcriptomics (Visium, n=4) to investigate the spatial architecture of melanoma cell states, T cells, tumor-associated macrophages (TAMs), dendritic cell subsets, and tertiary lymphoid structures.

resultsUnsupervised clustering of melanoma cells identified distinct phenotypic states that formed spatially restricted homotypic patches. From these data, we defined a melanoma plasticity ratio (undifferentiated/differentiated tumor patches), which was significantly associated with reduced relapse-free survival. Integrated immune analyses recapitulated prognostically distinct immunotypes, with macrophage subsets displaying striking spatial compartmentalization. Antitumoral macrophages preferentially infiltrated differentiated melanoma regions, while protumoral macrophages localized to undifferentiated patches. Spatial transcriptomics confirmed that melanoma cell states tightly shape the neighboring immune microenvironment, with macrophages emerging as pivotal players. Their polarization was further influenced by tumor-derived signals in addition to microenvironmental cues (interferon-gamma, hypoxia). Entropy-based integration of melanoma cell states, TAMs, and T cell subsets uncovered two dominant spatial ecosystems with opposing associations to ICI efficacy. Ecosystems enriched in differentiated melanoma cells, programmed death-ligand 1 (PD-L1)

conclusionsOur study uncovers how cancer cell plasticity shapes spatially organized tumor-immune ecosystems that critically modulate adjuvant ICI efficacy in melanoma. These findings highlight melanoma cell plasticity as a key driver of immune evasion via macrophages reprogramming, through targetable interactions that may represent novel therapeutic avenues to enhance ICI efficacy.