IL21 and cancer: In addition, TIL activity and proliferation can be further enhanced through the use of cytokine combinations, particularly interleukin-2 (IL-2), interleukin-15 (IL-15), and interleukin-21 (IL-21), which promote T-cell expansion and survival Among these, IL-15 and IL-21 are gaining attention in cancer immunotherapy due to their pivotal roles in supporting the ex vivo expansion of TILs (21–23).