Long-term culture of triple-negative thymocytes.

The role of the thymic microenvironment in regulating events that occur subsequent to the acquisition of CD4, CD8, and the TCR, such as positive and negative selection, has been studied extensively. However, comparatively less is known about how thymic stromal cells regulate growth and differentiation within the CD4-CD8-TCR- triple negative (TN) cell compartment. Long-term culture systems have played a pivotal role in the understanding of microenvironmental regulation of myelopoiesis and B lymphopoiesis, but establishment of comparable cultures for T lineage cells has proved challenging. This report describes a culture system in which a thymic stromal cell line preferentially supports the long-term growth of TN thymocytes. In addition to demonstrating that TN cells have a considerable proliferative potential, the results provide insights into the effects of IL-7 on the growth and/or survival of TN cells and its role in regulating TCR gene rearrangements. The ability of the cultured TN cells to mature into CD4- and/or CD8-expressing thymocytes, some of which express TCR-alpha beta, suggests that the system will be valuable for the identification of microenvironmental stimuli that regulate the maturation of TN cells.