Differential RNA expression of immune-related genes and tumor cell proximity from intratumoral M1 macrophages in acral lentiginous melanomas treated with PD-1 blockade

Immune checkpoint inhibitors (ICIs) offer improved survival for patients with advanced malignant melanomas. However, only a subset of these patients exhibit an objective response rate of 10–40 % with ICIs. We aimed to ascertain the effects of RNA signatures and the spatial distribution of immune cells on the treatment outcomes of patients with malignant melanomas undergoing ICI therapy. Clinical data were retrospectively collected from ICI-treated patients with malignant melanoma; RNA expression profiles were examined via next-generation sequencing, whereas the composition, density, and spatial distribution of immune cells were determined via multiplex immunohistochemistry. Patients with poor and good responses to ICIs showed significant differences in mRNA expression profiles. Different spatial distributions of T-cells, macrophages, and NK cells as well as RNA signatures of immune-related genes were found to be closely related to therapeutic outcomes in ICI-treated patients with malignant melanomas. The spatial distributions of PD-1+ T-cells and activated M1 macrophages showed a significant correlation with favorable responses to ICIs. Our findings highlight the clinical relevance of the spatial proximity of immune cell subsets in the treatment outcomes of metastatic malignant melanoma.