47 Background: The greatest challenge in cancer immunotherapy is to identify efficient predictive biomarkers to select patients for treatment. Though tumor cell membrane PD-L1 has been most anticipated, tumor cell membrane PD-L1 does not correlate with higher response rates and predict for clinical benefit. Subsequently studies showed that the prognostic value of tumor cell membrane PD-L1 in cancer patients remains controversial. In addition to membrane-associated PD-L1, tumor cell also secreted extracellular soluble PD-L1 in the microenvironment. However, even if extracellular soluble PD-L1 was detected, it did not solve the problem mentioned above. In the present study, we discovered another form of PD-L1 in extracellular microenvironment in cancer cells, that is exosomal PD-L1. However, the predictive role and the effect of tumor-derived exosomal PD-L1 is unclear. Methods: We evaluated the prognostic value of exosomal PD-L1 in the plasma of gastric cancer patients by ELISA and the effect of exosomal PD-L1-derived from gastric cancer cell lines by Western blot and Flow cytometry analysis. Results: Exosomal PD-L1 was detected in plasma samples from 69 gastric cancer patients, and exosomal PD-L1 content was significantly associated with T stage (P = 0.012). Overall Survival was significantly lower in the high exosomal PD-L1 group (p = 0.021). Additionally, gastric cancer cells also secreted exosomal PD-L1, with the amounts positively associated with PD-L1 amounts in the corresponding gastric cancer cell lines. Besides, exosomal PD-L1 was more stable and showed stronger immunosuppressive effects in the microenvironment compared with soluble PD-L1. Conclusions: Exosomal PD-L1 might predict the survival in gastric cancer, and induces higher T-cell apoptosis levels compared with soluble PD-L1.
Tropomyosin-related receptor kinase B at the invasive front and tumour cell dedifferentiation in gastric cancer