BDCA1+ cDC2s, BDCA2+ pDCs and BDCA3+ cDC1s reveal distinct pathophysiologic features and impact on clinical outcomes in melanoma patients.

OBJECTIVES: Dendritic cells play a pivotal but still enigmatic role in the control of tumor development. Composed of specialised subsets (cDC1s, cDC2s, pDCs), DCs are critical in triggering and shaping antitumor immune responses. Yet, tumors exploit plasticity of DCs to subvert their functions and escape from immune control. This challenging controversy prompted us to explore the pathophysiological role of cDCs and pDCs in melanoma, where their precise and coordinated involvement remains to be deciphered. METHODS: We investigated in melanoma patients the phenotypic and functional features of circulating and tumor-infiltrating BDCA1+ cDC2s, BDCA2+ pDCs and BDCA3+ cDC1s and assessed their clinical impact. RESULTS: Principal component analyses (PCA) based on phenotypic or functional parameters of DC subsets revealed intra-group clustering, highlighting specific features of DCs in blood and tumor infiltrate of patients compared to healthy donors. DC subsets exhibited perturbed frequencies in the circulation and actively infiltrated the tumor site, while harbouring a higher activation status. Whereas cDC2s and pDCs displayed an altered functionality in response to TLR triggering, circulating and tumor-infiltrating cDC1s preserved potent competences associated with improved prognosis. Notably, the proportion of circulating cDC1s predicted the clinical outcome of melanoma patients. CONCLUSION: Such understanding uncovers critical and distinct impact of each DC subset on clinical outcomes and unveils fine-tuning of interconnections between DCs in melanoma. Elucidating the mechanisms of DC subversion by tumors could help designing new therapeutic strategies exploiting the potentialities of these powerful immune players and their cross-talks, while counteracting their skewing by tumors, to achieve immune control and clinical success.