Tumoral Interferon Beta Induces an Immune-Stimulatory Phenotype in Tumor-Associated Macrophages in Melanoma Brain Metastases

Type I interferons (IFNs) are immune-stimulatory cytokines involved in antiviral and antitumor immune responses. They enhance the efficacy of immunogenic anticancer therapies by activating both innate and adaptive intratumoral immune cell populations. Macrophages are one of the most abundant innate immune cells in the immune microenvironment of melanoma brain metastases (MBMs) and can exert potent immune-suppressive functions. Here, we investigate the potential of tumoral type I IFNs to re-polarize tumor-associated macrophages (TAMs) in a murine melanoma mouse model. We describe a pro-inflammatory and M1-like TAM phenotype induced by tumoral IFNβ and identify a myeloid type I interferon-response signature associated with a high M1/M2 TAM ratio and an increased overall survival in previously irradiated patients with MBMs. We provide evidence that tumoral IFNβ supports an effective antitumor immune response by re-educating immune-regulatory TAMs. These findings uncover type I interferon-dependent therapies as a potential macrophage-targeting therapeutic approach and provide a rationale for combining radiotherapy with concomitant immunotherapy to improve treatment response in patients with MBM. To investigate the effects of tumoral IFNβ on the phenotype of M2-like TAMs in a murine MBM model, we generated bone marrow-derived macrophages (BMDMs) and polarized them into a M2-like polarization state (n=3 mice per condition). M2-like BMDMs were treated with cell culture supernatant containing tumoral IFNβ from Dox-treated YUMM5.2 Ifnb1eGFP cells, recombinant IFNβ, cell culture supernatant from Doxycycline (Dox)-treated YUMM5.2 eGFP control cells or left untreated. Cell culture supernatant was obtained from the YUMM5.2 cell line which was transduced with a lentiviral vector containing a tetracycline response promotor followed by the Ifnb1 and eGFP (or only the eGFP gene as control) allowing Dox-dependent tumoral IFNβ secretion. After 72h, we performed bulk RNA sequencing analysis of the BMDMs (4 conditions, 3 biological replicates each).