CXCL13 and neoplasm: While clonally expanded T cells are presumed to be more functionally active, the antigens targeted by such active T cells are not necessarily tumor antigens.[34] Thus, we differentiated tumor‐reactive T cells from bystander T cells using the CXCL13 biomarker.[21] Evidently, the potential tumor‐reactive T cells were predominantly cytotoxic T cells, Tex cells, and cycling Tex cells that received recruitment and antigen presentation signals (Figure 5H).