Delineating The Immunometabolism Of Human Invariant Natural Killer T Cells
Invariant natural killer T (iNKT) cells comprise a unique subset of T lymphocytes that possess innate-like functional features and are primed for activation. iNKT cells exert robust anti-tumor cytotoxicity through both direct mechanisms and by modulation of other immune populations. However, the use of these cells for immunotherapies has been quite limited, remaining in early clinical stages. This is largely due to our limited understanding of basic cellular properties of iNKT cells that may influence their ability to survive and maintain effector functions within the harsh, nutrient-poor solid tumor microenvironment (TME). In conventional T cells (TCONV), naïve, effector, and memory differentiation states are characterized by unique metabolic properties and bioenergetic demands that support their dynamic functions. In TCONV, cellular metabolism is tightly linked to effector functions and their ability to adapt to the nutrient-poor TME. In contrast, the bioenergetic requirements of iNKT cells – particularly those of human iNKT cells – at baseline and upon stimulation are not well understood; neither is how these requirements affect cytokine production or anti-tumor effector functions. Thus, the focus of this thesis work was to characterize the immunometabolism of iNKT cells and investigated whether this differs from TCONV. Using transcriptional profiling, nutrient depletion studies, flow-based metabolic dyes, and Seahorse flux metabolic assays to measure real-time activity, we discover novel immunometabolic features of human iNKT cells. Unlike TCONV, human iNKT cells were not dependent upon glucose or glutamine for cytokine production and cytotoxicity upon stimulation. We also found that stimulated human iNKT cells appeared to be less glycolytic than TCONV and predominantly utilize fatty acid oxidation (FAO). Notably, this memory-like metabolism of iNKT cells may predict better adaptability to the TME long-term. Future studies are needed to further probe the immunometabolic features of different phenotypic and functional subsets of iNKT cells, as well as intratumoral iNKT cells. Importantly, our findings suggest that iNKT cell-based immunotherapeutic strategies could co-opt these unique features of iNKT cells to improve their efficacy and longevity of anti-tumor responses, a critical need for the field of cancer immunotherapy.