γδ T cells and their roles in immunotherapy: a narrative review

Objective: In order to understand the activation mechanism of γδ T cells and their role in tumor immunity and autoimmune diseases. Background: γδ T cells are a conserved population of natural lymphocytes with a variety of structural and functional heterogeneities, accounting for approximately 0.5% to 10% of total peripheral blood lymphocytes in healthy adults. As a “bridge” between innate and acquired immunity, they have an important role in tumor surveillance. Methods: γδ T cells are considered to be effective anti-tumor effector cells, which can kill tumor cells through direct and indirect methods; γδ T cells can secrete a variety of cytokines, such as tumor necrosis factor α (TNF- α ), γ -interferon (IFN- γ ), perforin, etc., thus, they own the ability to kill tumor cells directly, and can also regulate other innate and adaptive immune cells, and then achieve the purpose of indirectly killing tumor cells, thereby establishing anti-tumor immunity. A unique feature of γδ T cells is that they recognize antigens in a non-major histocompatibility complex (MHC)-restricted manner, and they have strong cytotoxicity to a variety of cancer cells, which make them have important clinical application value. Conclusions: In this review, we provide an overview of the activation mechanisms of γδ T cells and their role in tumor immunity and autoimmune diseases. These studies provide insights into γδ T cell function to facilitate more targeted approaches for tumor therapy.