Treg depletion leads to NK-cell persistence and expansion that correlates with remission. (A) Successful in vivo donor NK cell expansion was observed in 80% of patients with Treg depletion (shown as percentage of PB lymphocytes; n = 6) compared with 0% in patients with high levels of Tregs (n = 9). (B) Rates of complete remission in patients with or without detectable donor NK cells in PB at day 7. (C) PB flow cytometry plot of selected subjects who demonstrated in vivo NK expansion at days 7 and 14.