*4.5. Future Progress of Cancer Immunotherapy Using TCLs*

The study of the relationship between cancer and immune responses has increased rapidly over the last few decades, among which TCLs have demonstrated their utility to elicit sustained CTL responses and vaccine effectiveness in cancer therapy. Moreover, since TCLs do not induce a strong enough CTL response against cancer, additional immune agonists or adjuvants have been utilized in combination, as previously described [149]. A series of delivery platforms described in this review possess the necessary functionalities, including an effective cargo protective carrier, immune agonistic property, and/or adjuvant efficacy. However, it should be also considered that there might be a possible risk of overreaction, such as cytokine storm activation, during periods of high immune activity [150]. Therefore, in order to develop more effective strategies in TCL delivery, the optimization for clinical safety, and the combination with an additional immune agonist or adjuvant, is necessary for inducing selective activation of T cells to respond to specific tumor antigens, rather than broad activation of various immune cells, which could cause deleterious side effects [151]. It should be also emphasized that there is still work to be done in developing combination therapy and optimizing vaccine platforms before TCL-based treatment becomes a viable immune modulatory and therapeutic strategy [152].
