Natural Killer T (NKT) cells are distinct innate lymphocytes that recognize lipid antigens in the context of nonpolymorphic molecule CD1d. Multiple myeloma (MM) is a hematologic malignancy wherein malignant plasma cells express CD1d and are sensitive to lysis by NKT cells. Progressive malignancy in MM is characterized by NKT cell dysfunction. Several studies have tried to harness the anti-tumor properties of NKT cells in MM to mediate tumor regression. NKT cells are also attractive targets for approaches at immune redirection in MM with chimeric-antigen receptor NKT (CAR-NKT) and bispecific antibodies. In addition to the commonly studied invariant-NKT (iNKT) cells, MM patients often also exhibit alterations in type-II NKT cells and their ligands. In patients and mouse models with Gaucher disease (GD), an inherited lipid-storage disorder with markedly increased risk for MM, distinct type-II NKT cells exhibit a T-follicular helper (NKT-TFH) phenotype and provide help to lipid-specific B cells. Chronic immune activation in this setting eventually sets the stage for malignancy, which can be targeted in both mouse models and GD patients by reducing the underlying antigen. NKT cells are thus integrally linked to MM pathogenesis and an attractive target for MM immunotherapy.
