CD4 and gastric cancer: Studies have shown that the CD4 + /CD8 + ratio is significantly decreased in patients with some cancers (such as breast cancer, gastric cancer, and lung cancer) (Wang et al., 2013; Dias Rodrigues et al., 2017; Liu, 2022), HIV (Castilho et al., 2019), and neuromyelitis optica spectrum disorders (Yang et al., 2021), indicating that the immune function of patients may be reduced.