PS-1145 inhibits alloreactive T-cell responses in vitro but is less potent than bortezomib. B10.BR T cells (1 × 10⁵/well) were cultured with B6 CD11c⁺ dendritic cells (5 × 10⁴) in a standard mixed lymphocyte culture for 5 days. (A) Replicate wells were cultured alone (□) or in the presence of 5-fold μM dilutions of bortezomib (▪) or PS-1145 (▨) for 5 days. Cells were pulsed with ³H-Tdr for the last 18 hours of culture, and the percentages of incorporated radioactivity were determined. (B-C) B10.BR T cells (1 × 10⁵/well) were cultured with B6 CD11c⁺ dendritic cells (5 × 10⁴) alone or with bortezomib (0.32 μM) or PS-1145 (8 μM) for 5 days. Bortezomib and PS-1145 were added to microwells on days 0, 1, or 2 after culture initiation. Cells were pulsed with ³H-Tdr for the last 18 hours of culture and the percentages of incorporated radioactivity were determined (B); in separate experiments, supernatants were collected and tested for the presence of IFN-γ (C). Data are presented as the mean ± SEM from triplicate control wells. Data shown are from 1 of 3 experiments that produced similar results. (D) B10.BR T cells were cultured with B6 CD11c⁺ dendritic cells alone or with bortezomib (0.32 μM) or PS-1145 (8 μM). Cells were harvested and pooled from triplicate microwells after 3 or 4 days and were surface stained for CD4 or CD8 and annexin V. Data are presented as the mean ± SEM. Data shown are cumulative results of 4 experiments.