PDCD1 and colorectal carcinoma: showed that PD‐1 blockade in mismatch repair‐deficient CRC reduces CD4+ regulatory T (Tregs) cells and increases CD20+ B cells, which are linked to a higher abundance of CD8+ effector‐memory T (Tem) cells in patients who achieved a pathological complete response (pCR) to anti‐PD‐1 therapy.[149] Collectively, these studies indicate that B cells not only function as predictive biomarkers for favorable responses to ICIs but also play a direct mechanistic role in enhancing immunotherapy efficacy.