Depletion of alloreactive T cells by anti-CD25 immunotoxin. (A) FACS analysis showing increased expression of CD25 (y axis) on CD3/4/8⁺ T cells after activation with HLA-mismatched LCLs and effective depletion of CD3⁺/CD25⁺, CD4⁺/CD25⁺, and CD8⁺/CD25⁺ cells following treatment with anti-CD25 immunotoxin. The figure shows a representative FACS analysis from 6 different donor-recipient pairs. The percentage of double-positive cells is indicated. (B) Primary mixed lymphocyte reaction showing a mean 15-fold decrease in proliferation in response to HLA-mismatched LCL stimulators after treatment with anti-CD25 immunotoxin (IT). Results are the mean ± SD of 5 haplo-identical donor-patient pairs each assayed in triplicate.