T-cell chimerism and immune reconstitution. (A) Infusion of ex vivo-activated donor T cells on days 28, 56, and 112 was associated with a prompt increase in the percentage of donor CD4⁺ and CD8⁺ T cells in the peripheral blood of recipients. Six months after transplantation, all 13 patients who could be evaluated showed complete donor T-cell chimerism. Compared with a historical cohort of patients who did not receive prophylactic donor T-cell infusion after T cell–depleted SCT (B), the increase in donor T-cell chimerism to levels > 50% had occurred > 3 months earlier. (C) The absolute count of lymphocyte subsets. CD4⁺ T-cell numbers remained less than 200/μL within the first 12 months after transplantation, whereas CD8⁺ T cells dominated during that period. CD19⁺ B cells reached normal levels as soon as 3 months after transplantation, whereas CD3⁻/CD56⁺ NK cells peaked 2 months after transplantation and slowly declined for further 10 months.