Through the support of the CIRM we have initiated our efforts to differentiate and grow thymic epithelial cells from human embryonic stem cells. Over the last year we have been culturing human ES cells under different conditions and have examined marker expression in the cells for similarity to thymic epithelium. We have made significant progress, with a number of known markers being upregulated in our cells. We plan to continue similar efforts over the next year and expand our experiments to test whether these cells can induce immune tolerance. These findings are critical for the CIRM in that they may be an important way to keep the immune system in check and prevent immune rejection when ES cell derived material is transplanted.