Stem Cell Engineered Invariant Natural Killer T Cells for Cancer Immunotherapy
Cancer immunotherapy is a rapidly developing field that has already shown to be of great clinical value as evidenced by the success of engineered T cell therapies, such as chimeric antigen receptor (CAR) therapies in treating B cell leukemia and T cell receptor (TCR) therapies in treating melanoma, and by checkpoint inhibitor therapies, such as PD-1 and CTLA-4 antibodies, in treating a variety of cancers. This dissertation seeks to add to this growing knowledge base and carve out a niche in the discipline by utilizing a unique combination of immune cell type and method of delivery; a hematopoietic stem cell (HSC) can be genetically engineered using a viral vector in order to generate invariant natural killer T (iNKT) cells in vivo.
Several cancer immunotherapy clinical trials have already utilized iNKT cells either by infusion after expansion ex vivo and/or activation of the cells in vivo by dendritic cells loaded with the synthetic ligand α-Galactosylceramide (α-GalCer). These trials have demonstrated that the treatments are well tolerated, and while some have shown promising anti-tumor immunity, most have yielded unsatisfactory results. This lack of clinical efficacy has been attributed to the cells’ very low and highly variable number in humans (0.001-1% in peripheral blood) and their rapid depletion after stimulation.
Many cancer immunotherapy treatments trend towards a phase of promising tumor regression followed by a disheartening cancer relapse. This may be due to several factors, but a major contributor specific to cancer immunotherapy is thought to be exhaustion of the therapeutic cells by the ex vivo expansion protocol. This protocol drives the therapeutic cells to expand and differentiate into terminally differentiated effector cells. While these effector cells have increased killing efficacy, it comes at the expense of a decreased life span and regeneration. This would explain the initial regression mediated by the effector cells, followed by a relapse when the cells become exhausted. This issue can be addressed by utilizing viral vectors to genetically engineer hematopoietic stem cells to continually generate new therapeutic cells in vivo.
This dissertation lays the foundation for combining the genetic engineering of HSCs by viral transduction to generate iNKT cells to be used for cancer immunotherapy. Proof-of-principle experiments in mice and an expansion to the use of the humanized mouse model provided the necessary knowledge and tools for further development to be pursued. Ongoing and future studies aim to demonstrate anti-cancer efficacy in humanized mouse models in order to collect data for an application to utilize these HSC-engineered iNKT cells in a cancer immunotherapy clinical trial.