Posttransplantation immune reconstitution measured by lymphocyte subsets. Mean (A) CD4⁺ lymphocyte, NK cell, and (B) CD8⁺ lymphocyte counts after HLA-haploidentical HCT in patients receiving a conditioning therapy containing reduced-dose busulfan, fludarabine, and ATG. Data from patients who survived at least 6 months without progression/recurrence of underlying disease were analyzed, including data obtained from 48 patients before conditioning therapy and at 1, 2, and 3 months after HCT; and from 44 and 27 patients at 6 and 12 months, respectively. Among the lymphocyte subsets, NK-cell counts recovered earliest, exceeding pretransplantation counts at 1 month, with > 90% of patients maintaining NK-cell counts > 100/μL beginning 3 months after HCT. CD8⁺ lymphocyte counts exceeded pretransplantation levels at 2 months, and > 90% of patients maintained counts > 200/μL beginning 3 months after HCT. CD4⁺ lymphocyte counts recovered more slowly, with only approximately half of all patients showing CD4⁺ lymphocyte counts > 200/μL at 2 to 6 months. However, 12 months after HCT, however, 24 of 27 patients (89%) had CD4⁺ lymphocyte counts more than 200/μL. Error bars represent ± 1 SD.