IL21 and neoplasm: Enhanced Tfh function, indicated by the increased frequencies of Tfhem cells, may support malignant B cells to survive and growth via Tfh effector molecules such as CD40L and IL‐21.12 Th1 cells promote CD8+ T cell to differentiate into effectors which can gradually acquire the state of exhaustion by the chronic stimulation of malignant B cells.18 Furthermore, since IFN‐γ produced by Th1 cells can upregulate PD‐L1 expression on tumour cells,16 it is conceivable that the excessive Th1 differentiation may also render the risk of CD8+ T‐cell exhaustion through the PD‐1‐PD‐L1 interactions.