SELECTIVE MANIPULATION OF THE HUMAN T-CELL RECEPTOR REPERTOIRE EXPRESSED BY THYMOCYTES IN ORGAN-CULTURE

A recently described organ culture system for human thymocytes is shown to support the generation of a diverse T-cell receptor repertoire in vitro: thymocytes of the alpha-beta-lineage, including representatives of the V-beta-families 5.2/5.3, 6.7, and 8, accounted for the majority of T-cell receptor-positive cells throughout a 3-week culture period. Thymocytes bearing gamma-delta-receptors were also identified, particularly among the CD4 CD8 double-negative subset. The T-cell receptor repertoire expressed in organ culture responded to experimental manipulation with staphylococcal enterotoxins. Staphylococcal enterotoxin D (a powerful activator of human peripheral T cells expressing V-beta-5.2/5.3 receptors) caused a marked reduction of V-beta-5.2/5.3 expression, as determined with the V-beta-specific antibody 42/1C1. Evidence is presented that this loss of V-beta-5.2/5.3 expression resulted from the selective deletion of activated thymocytes by apoptosis, in concert with T-cell receptor modulation. These effects of staphylococcal enterotoxin D were specific (since staphylococcal enterotoxin E did not influence V-beta-5.2/5.3 expression) and V-beta-selective (since expression of V-beta-6.7 remained unaffected by staphylococcal enterotoxin D). On the basis of these observations, we suggest that thymic organ culture provides a powerful approach to study the generation of the human T-cell repertoire.