Inhibition of Hsp90 function with 17-DMAG predominantly induces apoptosis in alloreactive, proliferating T cells in MLRs. (A) CFSE^dim proliferating T cells in MLRs show up-regulation of the T-cell activation marker CD25. (B) CD25-positive activated T cells and CD25-negative resting cells of a mixed lymphocyte reaction were separated with microbeads, and the levels of Hsp90α and Hsp90β were determined by Western blot. (C) A mixed lymphocyte reaction was pulsed with 17-DMAG 4 days after culture initiation, and apoptosis was determined by annexin V staining 40 hours after inhibitor treatment. (D) CFSE dilution after 4 days in MLRs either left untreated or treated with the Hsp90 inhibitor 17-DMAG. (E) Summary of depletion efficacy in 9 experiments: proliferative fraction of MLRs with and without 17-DMAG after stimulation with allogeneic DC. The displayed P value was obtained using a 2-tailed paired t test.