Abstract
In recent years, immunotherapy for advanced melanoma has been gaining increased attention. The efficacy of anti-cytotoxic T-lymphocyte antigen 4 antibodies, anti-programmed cell death 1 antibodies, and the BRAF(V600E) kinase inhibitor has been proven in metastatic melanoma. At the same time, adoptive cell transfer has significant effects against metastatic melanoma; however, it is difficult to apply on a broad scale because of the problems related to cell preparation. To overcome these problems, we developed immune cell therapy using induced pluripotent stem (iPS) cells. The benefit of our method is that a large number of cells can be readily obtained. We focused on macrophages for immune cell therapy because macrophage infiltration is frequently observed in solid cancers. In this study, the efficacy of human iPS cell-derived myeloid cell lines (iPS-ML) genetically modified to express type I IFNs against human melanoma cells was examined. The morphology, phagocytic ability, and surface markers of iPS-ML were similar to those of macrophages. The iPS-ML that express type I IFNs (iPS-ML-IFN) showed significant effects in inhibiting the growth of disseminated human melanoma cells in SCID mice. The infiltration of iPS-ML into the tumor nests was confirmed immunohistologically. The iPS-ML-IFNs increased the expression of CD169, a marker of M1 macrophages that can activate antitumor immunity. The iPS-ML-IFNs could infiltrate into tumor tissue and exert anticancer effects in the local tumor tissue. In conclusion, this method will provide a new therapeutic modality for metastatic melanoma.