Doctor of Philosophy
Microbiology and Immunology
Invariant natural killer T (iNKT) cells are a unique unconventional T cell subset that recognize glycolipids presented by CD1d expressing cells. The prototypical glycolipid agonist of iNKT cells, α-Galactosylceramide (α-GalCer), can induce the rapid release of an arsenal of cytotoxic effector molecules and enormous amounts of immunomodulatory cytokines as early as two hours after activation. In addition to α-GalCer, various glycolipid agonists are available that allow for specific, in vivo targeting of iNKT cells, and can exert divergent T-helper (TH)1 and/or TH2 immune responses. Therefore, the type of response instigated by iNKT cells can profoundly influence the nature of downstream immune response pathways. Sepsis and cancer are two distinct, detrimental pathologies where dysregulated immune responses play a key role in the pathogenesis and disease progression. The extent to which iNKT cells contribute to the pathology of sepsis and cancer has not been fully explored. Furthermore, whether iNKT cells can be targeted by glycolipid immunotherapy to mitigate disease progression has yet to be fully elucidated. In this thesis, the immunomodulatory capacity of iNKT cells were manipulated to skew the host immune response towards a protective phenotype. Firstly, using the surgical cecal ligation and puncture model on C57BL/6 (B6) mice to induce polymicrobial sepsis, iNKT cells were activated with a two-pronged glycolipid immunotherapy. I found that glycolipid treatment conferred significant improvements in sepsis morbidity and mortality. Moreover, glycolipid treatments induced an alteration in the cytokine milieu, restored immunocompetence and NK cell cytotoxicity in septic survivors when compared to vehicle treated controls. Secondly, I discovered a tumoricidal population known as, precursors to mature NK (pre-mNK) cells, that robustly expanded in the liver of naïve B6 mice, upon α-GalCer injection. Notably, in situ expansion of resident hepatic pre-mNK cells was found to be dependent on IL-12 and IL-18 signaling. Moreover, α-GalCer-expanded pre-mNK cells were found to mediate cytotoxicity via the granzyme/perforin pathway and significantly contributed to the anti-metastatic activity of NK cells in vivo. Collectively, the findings reported in this thesis show novel mechanisms by which glycolipid therapies can exploit the immunomodulatory potentials of iNKT cells to ameliorate immunopathologies in sepsis and cancer.
Summary for Lay Audience
Invariant natural killer T (iNKT) cells are a special group of immune cells that recognize sugar coated fat compounds known as glycolipids. The most commonly used glycolipid to study iNKT cells is α-Galactosylceramide (α-GalCer). Upon activation with α-GalCer, iNKT cells rapidly produce numerous small proteins that can have significant impact on shaping the course of the overall immune response. Although sepsis and cancer are two distinct diseases, they are both affected by a severe dysfunctional immune response that can exacerbate disease progression. The functional role of iNKT cells in sepsis and cancer is not fully known. Considering the dysfunctional immune response invariably found in sepsis and cancer, whether iNKT cells can be targeted by glycolipids, like α-GalCer, to steer the overall immune response towards normalcy is unknown. In this thesis, glycolipids were used to target iNKT cells in live mice to improve disease outcomes in sepsis and cancer. First, using a surgical mouse model of sepsis, I found that glycolipid treated mice had greater survival than untreated mice. In addition, I found that glycolipid activated iNKT cells were able to steer the immune response to produce vastly different proteins in the blood and restore immune cell function in septic mice. Second, using a different mouse model, I discovered another population known as precursors to mature NK (pre-mNK) cells that vastly increased in number in the liver when injected with α-GalCer. This expansion was a result of cell division of pre-existing pre-mNK cells in the liver instead of newly recruited pre-mNK cells. I uncovered that pre-mNK cell expansion was dependent on two soluble proteins, IL-12 and IL-18, which was caused by α-GalCer injection. In terms of function, pre-mNK cells were found to efficiently kill cancer cells and contribute to the overall anti-cancer response in live mice. Taken together, these findings reveal new ways glycolipids can be used to target iNKT cells to impact the immune response to improve outcomes in sepsis and cancer.
Choi, Joshua, "Exploiting the immunomodulatory potentials of iNKT cells in sepsis and cancer." (2020). Electronic Thesis and Dissertation Repository. 7312.