Priming CD45RA⁺T-cell subset in the presence of Jagged-1 induces alloantigen hyporesponsiveness. Primary MLR cultures consisted of CD45RA⁺ CD4⁺ and/or CD45RA⁺ CD8⁺ T-cell responders and control or Jagged-1-transduced EBV-LCL stimulator cells. (A) The proliferative responses were determined by ³H incorporation at day 5 of the cultures. Results show the means ±SD of triplicates studied in each experiment for a P value for the effect of Jagged-1 of P < .001 for CD4, P = .557 for CD8, and P = .001 for unseparated T cells. A further 9 experiments revealed an identical pattern of results for an overall P value of .00114 for unseparated cells. (B) Specific lysis of target cells after a day-7 MLC, against which the responder cells were generated, is shown. Moreover, when CD4⁺ T cells either from the control culture (^*) or from the Jagged-1 culture (^**) were added to CD8⁺ T cells primed with control LCLs at a 1:1 ratio, no cytotoxic effect was observed. These experiments used PHA-blasts (^***) from the same donor as additional target cells as well as EBV-LCLs from a fully mismatched third party (pyramid-stacked ^*). These cells acted as specific killing controls.