Background: The presence of tumor infiltrating lymphocytes (TIL) in renal cell carcinomas (RCC) is thought to reflect a host-mediated immune response against the tumor and the Fas/Fas ligand--based lytic pathway is a major mechanism of T lymphocyte--mediated cytotoxicity. The aim of the present study was to investigate the expression of Fas and Fas ligand (FasL) in freshly-isolated pure TIL as compared to autologous peripheral blood lymphocytes (PBL), in order to determine their activation status.
Materials and methods: The mRNA expression of Fas and FasL was compared in freshly-isolated CD3(+)-, CD4(+)- and CD8(+)-TIL and matched autologous CD3(+)-, CD4(+)- and CD8(+)-PBL. The TIL were isolated from mechanically disaggregated tumor material and PBL from peripheral blood by gradient centrifugation and subsequent selection with magnetic beads. In these pure lymphocyte preparations the constitutive expression of Fas and FasL was determined by using a semiquantitative PCR-assisted mRNA amplification assay.
Results: In the CD3(+)-TIL of 20 patients with RCC (group 1), mRNA levels of FasL were significantly higher than in the matched autologous CD3(+)-PBL (p < or = 0.01) whereas Fas expression was not different in both populations. In a second group of 20 patients (group 2), we found a significantly higher expression of FasL in the CD8(+)-TIL compared to the CD8(+)-PBL (p < or = 0.001) and also in the CD4(+)-TIL compared to the CD4(+)-PBL (p < or = 0.001).
Conclusion: The higher expression of FasL in the TIL compared to autologous PBL reflects an in vivo activation and lytic potency of the lymphocytes in the tumor surrounding.