CXCR5 and Tumor Lysis Syndrome: In the NPC microenvironment, CXCL13 is mainly produced by CD4+ helper T cells and PD-1+ exhausted T cells, suggesting that exhausted T cells might remain beneficial to the immune modulation via the recruitment of CXCR5+ B cells (only plasma B cells are CXCR5-) and TLS development (23).