T Cell subsets for therapy-unconventional CD1d-restricted natural killer T cells

Unconventional T cells, including gamma delta (γδ) T cells, mucosal-associated invariant T (MAIT) cells, and CD1d-restricted natural killer T (NKT) cells, comprise a unique component of the immune system. These cells play critical roles in host defense, immune regulation, and disease pathogenesis. In particular, invariant NKT (iNKT) cells have emerged as key immunological orchestrators that bridge innate and adaptive immunity by rapidly recognizing lipid antigens presented by CD1d molecules. This chapter provides a comprehensive overview of iNKT cell biology, including their development, phenotypic and functional heterogeneity, and activation mechanisms. It discusses the role of iNKT cells in pathological conditions in detail. Their ability to directly kill tumor cells, as well as their potential to orchestrate the immune response, opens up new possibilities for anti-cancer therapy. Their contribution to immune response regulation and tolerance highlights their critical role in infectious diseases and transplantation. The chapter summarizes current clinical approaches aimed at harnessing iNKT cells, including in vivo activation strategies, adoptive transfer of ex vivo-expanded cells, and developing chimeric antigen receptor (CAR)-engineered iNKT cells. These emerging therapies have advantages over conventional CAR-T approaches, such as reduced toxicity and the potential for allogeneic use. Finally, the chapter discusses the role of type II NKT cells and their cross-regulatory interactions with iNKT cells. Overall, CD1d-restricted NKT cells are a promising target for next-generation immunotherapies. However, further mechanistic and clinical studies are needed to realize their full therapeutic potential.