Immune Cell Infiltration and the Expression of PD-1 and PD-L1 in Primary PDGFRA-Mutant Gastrointestinal Stromal Tumors

Purpose To characterize the immune cell profile and expression of PD-1, PD-L1, and IDO in PDGFRA-mutant gastrointestinal stromal tumors (GISTs). Methods The clinicopathological data of PDGFRA-mutant GIST patients who received surgical resection in Zhongshan Hospital between January 2013 and August 2019 were reviewed retrospectively. The specimens of tissue chips were detected for immune cell infiltration and the expression of PD-1, PD-L1, and IDO by immunohistochemical staining. Results CD3 + , CD8 + , and CD68 + cells were the main infiltrating immune cells in the 42 patients included in this study. In addition, CD4 + , CD56 + , Foxp3 + , and CD20 + cells were also observed. A higher CD8 + T cell count was associated with smaller tumor size and PDGFRA D842V mutation ( P = 0.047, P = 0.005). A higher CD3 + and CD68 + cell count was associated with a higher mitotic index ( P = 0.022, P = 0.006). CD4 + and CD20 + cell count was associated with tumor morphology ( P = 0.002, P = 0.045). PD-1 expression was present in 37 (88%) samples. Eighteen samples were positive for PD-L1 expression, and it was higher in small vs . large tumors ( P = 0.012) and epithelioid and mixed cell type vs. spindle cell type GISTs ( P = 0.046). IDO expression was positive in all 42 patients. The number of CD4 + cells was significantly greater in the specimens with high IDO expression ( P = 0.012). Conclusion There were abundant infiltrating immune cells in PDGFRA-mutant GISTs. PD-L1 expression was negatively associated with tumor size. The immunotherapy targeting PD-1/PD-L1 checkpoint and IDO may be valuable.