Histological Type, Cytotoxic T Cells and Macrophages in the Tumor Microenvironment Affect the PD-L1 Status of Gastric Cancer

Abstract

Gastric cancer (GC) therapies include gastrectomy and chemoradiotherapy. The tumor immune microenvironment (TME) has implications for potential immunotherapy. We analyzed the expression of PD-L1, CD8, CTLA-4 and IFN-γ in the tumor and regional lymph node (LN) of patients with GC and compared it with clinical and pathological data. Paraffin blocks were collected from 97 patients undergoing gastrectomy/lymphadenectomy for GC. Double immunohistochemistry was performed for CD8 and PD-L1 and double immunofluorescence for CTLA-4 and IFN-γ. Statistical significance was set at p < 0.05. PD-L1 expression in tumor cells was associated with intestinal GC type (p = 0.046), the density of macrophages and CD8 + T cells (p < 0.001, both). The median number of CD8+ T cells was higher in PD-L1-positive than in -negative tumors. A cut-off of 28.5 CD8 + T cells in one high-magnification field predicted PD-L1-positive tumors (AUROC 0.797, sensitivity 74.2%, specificity 77.3%). IFN-γ expression in tumor cells was found in 37 GCs and was positively associated with CTLA4+ lymphocytes in the LN (p = 0.027) and CTLA4+/IFN-γ+ in tumors and the LN (all p < 0.001). The median overall survival (OS) was 17 months. In the group of deceased patients, IFN-γ expression in metastases correlated with lower OS (RHO = −0.314, p = 0.008). PD-L1 expression in tumor cells correlated with CD8 + T cells and macrophages in the TME and IFN-γ expression with suppressive CTLA4+/IFNγ+ immune cells in the TME and LN.

TAMs and PD-1 Networking in Gastric Cancer: A Review of the Literature

“…The flow diagram, illustrating the final selection process for eligible articles, is shown in Figure 2 . Seven studies investigated the correlation between the existence of TAMs and the expression of PD-L1 in GC cells [ 39 , 40 , 41 , 42 , 43 , 44 , 45 ], and three studies explored the prognosis of patients with GC expressing high levels of PD-1+ TAMs [ 46 , 47 , 48 ]. Due to the significant heterogeneity of the sample across the scrutinized studies, it was not possible to perform a cumulative statistical analysis of pooled available evidence.…”

“…In Table 2 and Table 3 , the methods of analysis used for the expression of PD-L1 in GC specimens are presented for each article. Specifically, after the initial processing of the slides, they were incubated with a primary antibody, PD-L1, with an anti-human PD-L1 monoclonal antibody [ 3 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 ]. In Ubukata et al’s.…”

“…In Ivanovic et al’s study, the presence of PD-L1-positive tumor cells was categorized into four groups: negative (0), low (1–10%), moderate (11–49%) and strong (≥50%). Additionally, the PD-L1 status of GC was considered positive if ≥1% of tumor cells expressed PD-L1 [ 45 ].…”

“…Conversely, low PD-L1 expression in GC is associated with reduced infiltration of TAMs. Whether these small differences in TAM expression may play a crucial role in immunotargeting/immunoescaping and whether they might influence immunotherapy outcomes remains a subject of research, as no prospective randomized clinical data are currently available [ 39 , 40 , 41 , 42 , 43 , 44 , 45 ].…”

“…Finally, Ivanovi et al’s study identified a link between the presence of PD-L1 expression in tumor cells and the infiltration of macrophages. To be more precise, the proportion of macrophages within PD-L1-positive GC instances was found to be 2.6 times greater compared to the levels observed in PD-L1 negative cases [ 45 ].…”