The myeloid cell type I IFN system promotes antitumor immunity over pro-tumoral inflammation in cancer T-cell therapy

Objectives: Type I interferons are evolutionally conserved cytokines, with broad antimicrobial and immunoregulatory functions. Despite well-characterised role in spontaneous cancer immunosurveillance, the function of type I IFNs in cancer immunotherapy remains incompletely understood.

Methods: We utilised genetic mouse models to explore the role of the type I IFN system in CD8⁺ T-cell immunotherapy targeting the melanocytic lineage antigen gp100.

Results: The therapeutic efficacy of adoptively transferred T cells was found to depend on a functional type I IFN system in myeloid immune cells. Compromised type I IFN signalling in myeloid immune cells did not prevent expansion, tumor infiltration or effector function of melanoma-specific Pmel-1 CD8⁺ T cells. However, melanomas growing in globally (Ifnar1^-/-) or conditionally (Ifnar1^ΔLysM) type I IFN system-deficient mice displayed increased myeloid infiltration, hypoxia and melanoma cell dedifferentiation. Mechanistically, hypoxia was found to induce dedifferentiation and loss of the gp100 target antigen in melanoma cells and type I IFN could directly inhibit the inflammatory activation of myeloid cells. Unexpectedly, the immunotherapy induced significant reduction in tumor blood vessel density and whereas host type I IFN system was not required for the vasculosculpting, it promoted vessel permeability.

Conclusion: Our results substantiate a complex and plastic phenotypic interconnection between melanoma and myeloid cells in the context of T-cell immunotherapy. Type I IFN signalling in myeloid cells was identified as a key regulator of the balance between antitumor immunity and disease-promoting inflammation, thus supporting the development of novel combinatorial immunotherapies targeting this immune cell compartment.