PDCD1 and B-cell chronic lymphocytic leukemia: Likewise, it has been reported that CTLs in CLL upregulate the expression of different co‐inhibitory receptors, including PD‐1, CD160, TIGIT, and 2B4 (CD244), resulting in their cytotoxic and proliferative impairment while retaining their ability to produce cytokines [14, 15].