T lymphocytes expand in vivo in patients who receive Cy/Flu/DLI. Peripheral blood mononuclear cells were collected from the DLI donor and from patients prior to initiating chemotherapy (pre-DLI) and 14 days, 28 days, 2 months, and 3 months after Cy/Flu/DLI therapy. (A) The absolute lymphocyte counts (ALCs) from the clinical complete blood count were used to calculate absolute CD4⁺ and CD8⁺ counts at all time points. (B) Cells were stained for the intracellular Ki-67 antigen as a marker for proliferating T cells. Results are shown as the percentage Ki-67-positive cells gated on CD3⁺, CD3⁺/CD4⁺, and CD3⁺/CD8⁺ cells. Error bars indicate SEM.