 Later on, they are fully committed to the T cell lineage- when thymocytes expressing Notch1 receptors engage thymic stromal cells expressing Notch1 ligands, the thymocytes become finally committed to the T-cell lineage.See Gallery Image "Double Negatives"

With the commitment to the T cell lineage, begins a very complex process known as TcR gene rearrangement.This creates an enormous diversity of T cells bearing antigen receptors.