Tumor-targeted therapy with BRAF-inhibitor recruits activated dendritic cells to promote tumor immunity in melanoma

• Published in: Journal for immunotherapy of cancer 2024-04, Vol.12 (4), p.e008606
• Main Authors: Hornsteiner, Florian, Vierthaler, Janine, Strandt, Helen, Resag, Antonia, Fu, Zhe, Ausserhofer, Markus, Tripp, Christoph H, Dieckmann, Sophie, Kanduth, Markus, Farrand, Kathryn, Bregar, Sarah, Nemati, Niloofar, Hermann-Kleiter, Natascha, Seretis, Athanasios, Morla, Sudhir, Mullins, David, Finotello, Francesca, Trajanoski, Zlatko, Wollmann, Guido, Ronchese, Franca, Schmitz, Marc, Hermans, Ian F, Stoitzner, Patrizia
• Format: Article
• Language: English
• Subjects: Animals; Antigens; Antigens, Neoplasm; CD8-Positive T-Lymphocytes; Cell death; Clinical/translational cancer immunotherapy; Cytokines; Dendritic Cells; Genes; Humans; Immune modulatory; Immunotherapy; Kinases; Lymphatic system; Lymphocytes; Melanoma; Melanoma - metabolism; Mice; Mutation; Myeloid cells; Proteins; Proto-Oncogene Proteins B-raf - genetics; Recruitment; Sarcoma; Signal transduction; Skin Cancer; Tumor immunity; Tumor Microenvironment; Tumor-targeted therapy; Tumors
• ISSN: 2051-1426; 2051-1426
• DOI: 10.1136/jitc-2023-008606

BackgroundTumor-targeted therapy causes impressive tumor regression, but the emergence of resistance limits long-term survival benefits in patients. Little information is available on the role of the myeloid cell network, especially dendritic cells (DC) during tumor-targeted therapy.MethodsHere, we investigated therapy-mediated immunological alterations in the tumor microenvironment (TME) and tumor-draining lymph nodes (LN) in the D4M.3A preclinical melanoma mouse model (harboring the V-Raf murine sarcoma viral oncogene homolog B (BRAF)V600E mutation) by using high-dimensional multicolor flow cytometry in combination with multiplex immunohistochemistry. This was complemented with RNA sequencing and cytokine quantification to characterize the immune status of the tumors. The importance of T cells during tumor-targeted therapy was investigated by depleting CD4+ or CD8+ T cells in tumor-bearing mice. Tumor antigen-specific T-cell responses were characterized by performing in vivo T-cell proliferation assays and the contribution of conventional type 1 DC (cDC1) to T-cell immunity during tumor-targeted therapy was assessed using Batf3−/− mice lacking cDC1.ResultsOur findings reveal that BRAF-inhibitor therapy increased tumor immunogenicity, reflected by an upregulation of genes associated with immune activation. The T cell-inflamed TME contained higher numbers of activated cDC1 and cDC2 but also inflammatory CCR2-expressing monocytes. At the same time, tumor-targeted therapy enhanced the frequency of migratory, activated DC subsets in tumor-draining LN. Even more, we identified a cDC2 population expressing the Fc gamma receptor I (FcγRI)/CD64 in tumors and LN that displayed high levels of CD40 and CCR7 indicating involvement in T cell-mediated tumor immunity. The importance of cDC2 is underlined by just a partial loss of therapy response in a cDC1-deficient mouse model. Both CD4+ and CD8+ T cells were essential for therapy response as their respective depletion impaired therapy success. On resistance development, the tumors reverted to an immunologically inert state with a loss of DC and inflammatory monocytes together with the accumulation of regulatory T cells. Moreover, tumor antigen-specific CD8+ T cells were compromised in proliferation and interferon-γ-production.ConclusionOur results give novel insights into the remodeling of the myeloid landscape by tumor-targeted therapy. We demonstrate that the transient immunogenic tumor milieu contains more activate