Technical Articles

This article systematically elaborates on the molecular characteristics and biological functions of interleukin-21 (IL-21), focusing on its structural features as a member of the IL-15/IL-21 family and its mechanism of activating the JAK-STAT signaling pathway through the IL-21R/γc receptor complex. It also analyzes its pivotal role in regulating the functions of CD8+ T cells, NK cells, and CD4+ T cell subsets.

IL-21 protein belongs to the IL-2 cytokine superfamily and is primarily produced by CD4-positive T cells. It can also be partially secreted by natural killer T cells, follicular helper T cells, and CD8-positive T cells, with some lymphoid hematopoietic cells capable of producing it in small amounts.

The lack of functional tumor-infiltrating lymphocytes in the tumor microenvironment is a significant reason for the suboptimal efficacy of tumor immunotherapy. Even in tumor tissues rich in tumor-infiltrating lymphocytes, the presence of dysfunctional PD-1-positive Tim-3-positive CD8-positive T cells remains a major indicator of poor prognosis in cancer patients.