Expression of CXC chemokine IP-10 in testicular germ cell tumours

Tumour-infiltrating T lymphocytes (TILs) possess discrepant properties ranging from anti- to protumour activities. Understanding precisely which mechanisms navigating T lymphocytes into the tumour site will help to further the anti-tumour or to disrupt the pro-tumour activities of TILs. The present study asked what enables TILs to migrate into testicular germ cell tumours (TGCTs). TILs were characterized and the expression of a large panel of T-lymphocyte-attracting chemokines was investigated in 21 TGCT cases. Flow cytometry revealed that approximately 80% of TGCT-infiltrating T lymphocytes express CXCR3, a receptor for the chemokine interferon-inducible protein-10 (IP-10). RT-PCR and immunohistochemistry indicated that IP-10 was the only chemokine investigated which was constantly expressed in TGCT. As IP-10 was found to be expressed by endothelial cells of TGCT-associated blood vessels, the question arose whether the IP-10-regulating cytokine interferon-gamma (IFNgamma) is produced by tumour cells and if so, whether tumour-derived IFNgamma can induce IP-10 in endothelial cells. Applying in situ hybridization, IFNgamma transcripts were found in neoplastic germ cells. Analyses of two TGCT cell lines indicated that the tumour cells not only express IFNgamma mRNA, but also produce and secrete IFNgamma protein; tumour-derived IFNgamma provokes IP-10 expression and secretion by endothelial cells in vitro, as assessed by PCR and ELISA. Together, the data suggest that neoplastic germ cells secret IFNgamma and thereby stimulate tumour-associated endothelial cells to express IP-10, which contributes to the recruitment of CXCR3+ T lymphocytes to the site of TGCTs.