The recognition of antigens by T cell receptors triggers a series of biological responses by T cells. However, T cell receptors are innately cross-reactive and the collection of T cell receptor repertoire needs to cover a large diverse range of antigens. It has been challenging to understand the relationship between T cell receptor repertoire and antigen repertoire. Recently, Jiang lab has developed several technologies to perform high-throughput and high-dimensional profiling of T cells with a focus of T cell antigen specificity and cross-reactivity. In this talk, she will introduce these technologies and give examples on how they use these technologies to understand the functions of the T cells in several human diseases, which could provide important insights to T cell biology and guide T cell based therapeutic development.