PRT-treated platelets induce only weak activation of blood T cells and inhibit T-cell responses to subsequent untreated platelets. The responses of T cells were examined from blood at days 2, 4, 7, and 14. (A) Cells were gated on CD3⁺/CD19⁻, followed by CD4⁺ or CD8⁺ events. (B) CD4⁺ and CD8⁺ T cells were then evaluated for frequency of CD25⁺, CD44⁺, and ICOS⁺/CD28⁺. (C) Heat map shows fold changes in frequencies of each group compared with the nontransfused group for CD4⁺ T cells (top) or CD8⁺ T cells (bottom) (out of total CD3⁺ events) or CD4⁺ CD25⁺ events (out of total CD4⁺ events). CD8⁺ T cells did not meet threshold of 100 positive events for CD25 and were therefore excluded (X). (D-E) Frequencies of CD44⁺ (D) or ICOS⁺/CD28⁺ (E) out of total CD4⁺ or CD8⁺ T-cell events, respectively. Notation indicates significance between groups. Data are combined from 3 independent experiments (n = 3 per group), and bars indicate mean and standard deviation. *P < .05, **P < .01, ****P < .0001.