Despite their small numbers (~0.001-1% in blood), invariant natural killer T (iNKT) cells in humans have been suggested to play important roles regulating multiple diseases including infections, allergies, cancer and autoimmunity. Like all other immune cells, iNKT cells are derived from the blood stem cells living in the bone marrow of adult humans. Successful clinical interventions with iNKT cells have been greatly hindered by our limited knowledge on how these cells are produced by blood stem cells, largely due to the lack of tools and track these cells in humans. Our project proposes to overcome this research bottleneck by transplanting human blood stem cells into a mouse and genetically engineer these cells to develop into human iNKT cells. This “humanized” mouse model will allow us to directly track the differentiation of human blood stem cells into iNKT cells in a living animal. In this reporting period, we have demonstrated the feasibility of this model system, and have successfully generated stem cell-engineered human iNKT cells. In the coming year, we plan to use this established model system to address some critical unanswered questions for iNKT cell development, and explore the therapeutic potential of stem-cell based iNKT cell therapies.