Immune mechanisms for response and angiogenesis in metastatic melanoma

Abstract

Despite the success of immune checkpoint inhibitors, metastatic melanoma remains a major therapeutic challenge due to limited or temporary responses. Improving clinical outcomes requires a dual approach: firstly, to better understand the immune-related adverse events (irAE) that signal effective anti-tumor immunity and secondly, targeting resilient melanoma biology, specifically alternative vascularization that evades current conventional therapies. Focusing on cutaneous melanoma, this thesis examined the association between irAEs and overall survival (OS), explored the immune mechanisms underlying ICI-associated sarcoidosis, an irAE linked to exceptional anti-tumor responses, and investigated the occurrence of an understudied form of blood vessel formation, intussusceptive angiogenesis, in which a vessel divides into two through the insertion of tissue pillars. In Paper I, a retrospective cohort of PD-1 treated melanoma patients, showed that patients who developed irAE had significantly longer OS than those without irAE. Survival benefits were specific to certain irAE types, with rheumatic, endocrine and ICI-sarcoidosis irAE being associated with improved OS, whereas hepatitis, nephritis and pneumonitis offered no survival advantage. Beneficial irAE also associated with lower corticosteroid doses, but not with duration or time of initiation of corticosteroids. Paper II investigated immune mechanisms behind ICIsarcoidosis, a rare irAE with mild symptoms and exceptional anti-tumor responses. Immune profiling with flow cytometry, proteomics and single cell RNA sequencing, revealed expansion of non-classical monocytes in active ICI-sarcoidosis, but no T-cell or inflammatory protein patterns were notable in blood. Tissue biopsies revealed granulomas dominated with non-classical macrophages with enhanced antigen presentation and interferon signaling, while macrophages and CD4+T cells were found in the granuloma core, collectively indicating effective antigen presentation to CD4+ T cells. Paper III demonstrated that intussusceptive angiogenesis occurs in human melanoma metastases and is promoted by inflammation and metalloproteinases (MMP), with MMP inhibition in co-cultures reducing pillar formation. The studies included in this thesis demonstrate that not all irAEs are equivalent; rather, some are associated with improved survival, suggesting that distinct immune patterns may reflect effective anti-tumor responses. In ICI-associated sarcoidosis, exceptional responses appear to be driven by enhanced antigen presentation by non-classical monocytes rather than by effective T-cell– mediated cytotoxicity. In addition, this thesis provides evidence that intussusceptive angiogenesis occurs in melanoma metastases and is promoted by MMPs. These findings suggest that antiangiogenic therapy should target multiple modes of vascularization, with MMP inhibition representing a potential strategy to block IA.