PDCD1 and neoplasm: performed a meta‐analysis and identified both CXCL13 and CCR5 as key determinants of T cell responsiveness to ICIs.[91] Together, these studies establish PD‐1 (PDCD1) and CXCL13 as core biomarkers of tumor‐reactive T cells (Figure 1), offering clinically actionable tools for patient stratification and ICI response prediction in oncology.