Abnormal dendritic cell differentiation and accumulation of immunosuppressive myeloid cells in cancer is one of the major factors of tumor nonresponsiveness. We have previously shown that hyperactivation of the Janus-activated kinase 2/signal transducers and activators of transcription 3 (JAK2/STAT3) induced by tumor-derived factors (TDF) is responsible for abnormal dendritic cell differentiation. Here, using a novel selective inhibitor of JAK2/STAT3 JSI-124, we investigated the possibility of pharmacologic regulation of dendritic cell differentiation in cancer. Our experiments in vitro have shown that JSI-124 overcomes the differentiation block induced by TDF and promotes the differentiation of mature dendritic cells and macrophages. JSI-124 significantly reduced the presence of immature myeloid cells in vivo and promoted accumulation of mature dendritic cells. In addition to a direct antitumor effect in several animal models, JSI-124 significantly enhanced the effect of cancer immunotherapy. This indicates that pharmacologic inhibition of the JAK2/STAT3 pathway can be an important new therapeutic strategy to enhance antitumor activity of cancer immunotherapy.
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