Birch pollen epitope-specific immune responses in the presence of Tregitopes. Coculture of PBMC with Bet v 1 allergen with either hTregitope 289 or hTregitope 167 leads to a Th2 to Th1/TReg shift. PBMC from three birch tree-pollen-allergic subjects were costimulated with Bet v 1_141-155 peptide with or without hTregitope. A. Ten to 14 day Tregitope costimulation led Bet v 1_141-155 tetramer positive CD4⁺ cells to decrease Th2-associated surface markers and to increase regulatory-associated surface markers GITR and CTLA4 (average of donors I, II, and III). B. Coincubation also led to a decrease of Bet v 1_141-155 tetramer–positive CD4⁺ cells secreting IL-5 (left axis) and a modest increase in Bet v 1_141-155 tetramer–positive CD4⁺ cells secreting IL-10 (right axis). C. PBMC from Donor I were tested under prolonged culture for 30 days; under these conditions, coculture with Tregitope 167 led to a reduction in the number of Bet v 1_141-155–specific cells secreting IL-5 and to an increase in Bet v 1_141-155–specific cells that were Th0 (neither IL-5– nor IFN-γ–secreting, 42%) or Th1 (IFN-γ–secreting, 44%). Numbers in boxes are the percentage of cells in the respective quadrant.