Functional Investigation of Fas Ligand Expressions in Human Non-Small Cell Lung Cancer Cells and Its Clinical Implications

Abstract

The purpose of this study is to investigate whether Fas ligand is functionally expressed in human lung cancer cells and to verify our hypothesis that specific inhibition of cancer-expressed FasL can improve the cellular immunity against cancer cells. The primary lung cancer cells (PLCCs) and autologous tumor-infiltrating lymphocytes (TILs) were separated from the surgical tissue samples. Western blot and immunofluorescence flow cytometry were used to detect the expressions of FasL. The FasL-specific small interfering (si)RNA was used to downregulate the expression of FasL, and a neutralizing mAb was used to block the ligation between FasL and Fas. Cancer cells and immune cells were alternatively selected as the effector cells or the target cells according to the different purposes. Cytotoxicity and apoptosis assays were used to detect the growth inhibition and apoptosis. The A549 cells and Jurkat T cells were co-cultured to study whether there is a counterattack against T cells. The PLCCs were co-cultured with autologous TILs to study whether specific blockage of cancer-expressed FasL can improve the TILs' cytotoxicity. The FasL is functionally expressed in human lung cells and can facilitate cancer cells to counterattack immune cells. Activated immune cells are more vulnerable to counterattack. Targeting A549-expressed FasL by siRNA could significantly abrogate counterattack while blockade of PLCCs-expressed FasL by a neutralizing mAb could enhance TILs' cytotoxicity. The improvement of cellular immunity against lung cancer depends on both activation and protection of immune cells. The specific inhibition of cancer-expressed FasL is effective in protecting immune cells, thus making FasL a new therapeutic target for cancer treatment.