IL-21-producing CD8+ T cells in polyp tissues, which co-expressed CXCR5, PD-1 and ICOS, displayed Tfh cell functionality by promoting IgG production in isolated polyp B cells, and the percentages of IL-21-producing CD8+ T cells were found to be associated with both the CT and endoscopic scores of NP patients. The gene discussed is CD8A; the disease is polyp.