Recent scRNA-seq research on tumor samples and adjacent non-tumor samples from nine untreated non-metastatic GC patients revealed that CD8+ T cells exhibited no significant increase of exhaustion levels and expressed low levels of exhaustion markers, including PDCD1, cytotoxic T-lymphocyte antigen 4 (CTLA-4), HAVCR2, LAG-3, and TIGIT (T-cell immunoreceptor with immunoglobulin and ITIM domains), which may partly explain the limited benefit of immunotherapy among GC patients (95). This evidence concerns the gene PDCD1 and gastric cancer.