TGF-β in uveal melanoma

Uveal melanoma is the most common primary ocular cancer among adults and patients with distant metastases seldom survive longer than a year. Melanomas of the eye have the advantage of growing in the special environment of an immune privileged site and it has long been shown, that the special immunosuppressive properties of the intraocular microenvironment are strongly mediated by cytokines, especially transforming growth factor-beta (TGF-beta). Here, we sought to investigate the presence of TGF-β in surgically removed uveal melanoma specimens using immunohistochemical methods to verify possible autocrine mechanisms. Immunocytochemistry for pan-TGF-β and TGF-β₂ was performed on 13 melanoma specimens using an alkaline phosphatase labeling procedure. Melanocytic origin of the tumors was confirmed by HMB-45 staining. All tissue samples exhibited positive staining using either pan-TGF-β or TGF-β₂ antibody regardless of cell-type, size of the tumor, or tumor location. The intensity of staining did not vary significantly within a given tumor. All tumors stained positive against the HMB-45 antibody. Many cytokines have been found to act on melanoma tumors. The presence of the TGF-β₂ isoform in all specimens points to progressive tumor-growth as has been shown for melanomas of the skin. Based on our immunohistochemical findings and the immunosuppressive properties of TGF-β, we suppose that ocular melanomas should be able to create their own immunosuppressive environment even in the uvea, which might be a non-privileged site.