Implementing Photodynamic Therapy to Activate the IFN-1 Pathway in Melanoma Cells: A Protocol for Inducing Immunogenic Cell Death and Enhancing Dendritic Cell Maturation.

This chapter outlines a detailed protocol for employing photodynamic therapy (PDT) to induce immunogenic cell death (ICD) in melanoma cells, specifically targeting the type-I-interferons (IFN-1) signaling pathway. Recent studies have highlighted the role of IFN-1 in the immune response against cancer, acting as novel damage-associated molecular patterns (DAMPs) that bridge innate and adaptive immunity. Our approach utilizes methyl-aminolevulinate (Me-ALA) to induce the production of endogenous photosensitizer protoporphyrin IX (PpIX), which preferentially accumulates in the endoplasmic reticulum (ER). Activation of PpIX through visible light irradiation triggers oxidative stress-induced apoptotic cell death. This chapter provides a step-by-step guide to replicate these conditions, which have been shown to significantly upregulate IFN-α/β transcripts in B16-OVA melanoma cells, leading to enhanced expression of GMP-AMP synthase (cGAS) and interferon-stimulated genes (ISGs) like CXCL10, MX1, and ISG15. We further discuss the consequential IFN-1-dependent-phenotypic maturation of monocyte-derived dendritic cells (DCs), evidenced by increased expression of co-stimulatory molecules such as CD80 and MHC-II and enhanced tumor-directed chemotaxis. By detailing the protocol for this novel application of PDT, this chapter aims to facilitate its integration into immunotherapy regimens, providing a comprehensive toolkit for researchers and clinicians aiming to harness the antitumor potential of the IFN-1 pathway.