Induced heterogeneous differentiation of CD4+T cells with respect to a pair of master regulators (X and Y). a. Diversity of cell phenotypes during induced differentiation. In the undifferentiated cell, the expression level of both X and Y are low. When the cell is differentiated, three possible functional phenotypes can be obtained: X single-positive cell, Y single-positive cell and double-positive cell. b. Three types of induced heterogeneous differentiation. In a differentiation event, a group of naive cells can be differentiated into two types of single-positive cells (Type 1), one type of single-positive cell and DP cell (Type 2) or all three functional phenotypes (Type 3).