Biomarkers of immunogenic stress in metastases from melanoma patients: Correlations with the immune infiltrate

Melanoma is known to be under latent immunosurveillance. Here, we studied four biomarkers of immunogenic cell stress and death (microtubule-associated proteins 1A/1B light chain 3B (MAP-LC3B, best known as LC3B)-positive puncta in the cytoplasm as a sign of autophagy; presence of nuclear HMGB1; phosphorylation of eIF2α; increase in ploidy) in melanoma cells, in tissue microarrays (TMA) from metastases from 147 melanoma patients. These biomarkers of immunogenicity were correlated with the density of immune cells infiltrating the metastases and expressing CD3, CD4+, CD8+, CD20, CD45, CD56, CD138, CD163, DC-LAMP or FOXP3. LC3B puncta positively correlated with the infiltration of metastases by CD163+ macrophages, while expression of HMGB1 correlated with infiltration by FOXP3+ regulatory T cells and CD56+ lymphocytes. eIF2α phosphorylation was associated with an augmentation of nuclear diameters, reflecting an increase in ploidy. Interestingly, therapeutic vaccination led to a reduction of eIF2α phosphorylation suggestive of immunoselection against cells bearing this sign of endoplasmic reticulum (ER) stress. None of the stress/death-related biomarkers had a significant prognostic impact, contrasting with the major prognostic effect of the ratio of cytotoxic T lymphocytes (CTL) over immunosuppressive FOXP3+ and CD163+ cells. Altogether, these results support the idea of a mutual dialog between, on one hand, melanoma cells with their cell-intrinsic stress pathways and, on the other hand, immune effectors. Future work is required to understand the detailed mechanisms of this interaction.