MBTPS1 and lymphopenia: Such conditional Sphk deletion resulted in an intrathymic accumulation of mature thymocytes and an accompanying peripheral T‐cell lymphopenia, both of which are indicative of disrupted thymocyte egress and thus highlights the crucial role of thymic mesenchyme in regulating T‐cell egress via the S1P pathway.71 In addition to thymic pericytes, additional nonepithelial stromal populations have been shown to regulate S1P‐dependent egress through the positive influence of S1P levels.