Confocal microscopy showed that Vγ2Vδ2 TCR underwent aggregating or capping during the in vivo clonal expansion of Vγ2Vδ2 T cells after the phosphoantigen treatment. (A,B) The increased mean numbers of Vγ2Vδ2 T cells in the blood of 3 monkeys after HMBPP/IL-2 treatment (A) and 2 monkeys after Picostim/IL2 treatment (B). Almost all expanded γδ T cells were Vγ2Vδ2 T cells coexpressing both Vγ2 and Vδ2. (C,D) Representative confocal microscopic data that show the formation of aggregating and capping TCR on the clonally expanded Vγ2Vδ2 T cells at days 4 and 7 after HMBPP/IL-2 (C) or Picostim/IL-2 (D) treatment. In both panels C and D, the left panel shows fluorescence images and the right panel shows differential interference contrast. All clonally expanded Vγ2Vδ2 T cells examined on days 4 and 7 after the treatment exhibited indistinguishable large TCR aggregates or capped dots, sustained for 1 to 2 weeks, and then finally returned to the normal nonaggregated status at week 3 after the treatment (detailed data, see Figures S2,S3).