[Study on blocking the tumor immune escape by Fas ligand pathway]

The expression of Fas ligand (FasL) on the membrane of many kinds of leukemia or solid tumor cells played an important role in the immune escape of tumor cells. This study was aimed to know if the soluble Fas (sFas), expressed by adenovirus, could block the immune escape of tumor cells by FasL pathway. The two recombinant adenoviral vectors, AdsFas with murine soluble Fas gene and AdEGFP with enhanced GFP protein gene, were constructed by homologous recombination between two plasmids in Escherichia coli with the AdEasy adenovirus vector system. The viruses were propagated and purified by two times ultracentrifugation. Their titres were detected by plaque assays. The expressed protein was evaluated by Western blot analysis. Then the tumor EL4 cells were infected with AdsFas and AdEGFP respectively. The apoptosis ratio of the target cells-YAC-1 cells induced by EL4 cells was respectively detected by (3)H-thymidine ((3)H-TdR) labeling. The results showed that the recombinant adenoviral vectors AdsFas and AdEGFP were successfully obtained. The titres of viruses purified by two times ultracentrifugation were up to 10(11) pfu/ml by plaque assays. The sFas protein was highly expressed in the target cells by Western blot analysis. After the EL4 cells were transfected with the adenoviruses AdsFas, the apoptosis rate of YAC-1 cells in the sFas transfection group (respectively 6%, 7% and 9% when the effector:target (E:T) was 3:1, 10:1 and 30:1) was obviously lower than that in the control group (respectively 28%, 37% and 45%), P < 0.01. But when the EL4 cells were transfected with AdEGFP, the apoptosis rate of YAC-1 cells (respectively 30%, 36% and 48%) was similar to the control group, P > 0.05. In conclusion, the transfer of sFas by adenovirus could inhibit the apoptosis of Fas(+) cells-YAC-1 cells induced by tumor EL4 cells. It showed that the transduction of sFas could block the effect of the immune escape of EL4 cells through FasL in vitro. These results thus provide a new direction to find a way to treat tumors.