Invariant natural killer T (iNKT) cells are robust cytotoxic effectors and immune modulators, which makes them ideal candidates for cancer immunotherapy. However, the use of iNKTs for cellular therapy against cancer has been limited due to their transient response in pre-clinical trials. Although TCR-CD1d interactions are generally required for iNKT cell cytotoxicity, the receptors and signaling mechanisms that co-operate with the TCR to promote maximal anti-tumor responses are poorly understood. Therefore, elucidating the mechanisms that regulate anti-tumor responses is critical for the development of effective iNKT-based therapies. Our efforts have shown that 2B4, a SLAM receptor, when expressed on iNKTs reduces their cytotoxic response against lymphoma cells. Surprisingly, 2B4 is not expressed on resting iNKTs but gets rapidly upregulated via stimulation through the TCR. 2B4 has two isoforms, which are splice variants of each other, of which the inhibitory long form is predominantly expressed in activated iNKTs. Our data show that 2B4 is a checkpoint molecule and has an inhibitory role in iNKT cell cytotoxicity. Indeed, when we overexpressed 2B4 in an iNKT cell hybridoma, the killing capacity of the iNKT cell line was abrogated. Moreover, 2B4 can be converted to a potent activating receptor by swapping its intracellular domains with proline motifs, which drastically augments tumor cell lysis. Taken together, this study highlights the important role of 2B4 in iNKT cell cytolysis and broadens the knowledge of immunoregulatory receptors in iNKT cells for future applications in cancer therapy.
Read
