Furthermore, in STAD, the increased expression of C3, CR4, and C5aR1 was positively correlated with Tregs (FOXP3, CCR8, TGFβ1, and STAT5B) and T cell exhaustion (TIM-3, LAG3, CTLA4, and PD-1) (Table 2, Figure 6). Here, PDCD1 is linked to gastric adenocarcinoma.