Treg suppressive capacity is only modestly impaired by umbralisib treatment. (A) Naive CD4⁺ T cells were isolated from normal donor PBMCs and cultured under Treg-polarizing conditions for 5 days. Tregs were washed and pretreated with PI3K inhibitors (1 μM, 24 hours) and then washed and cocultured with autologous CellTrace Violet–labeled responder T cells. Cell division was assessed by dilution of CellTrace Violet in responder cells 5 days after beginning coculture. Line graphs depict division of responder T cells from 1 representative donor. (B) Box and whisker plots show quantification of suppression assay (n = 6) as mean + standard deviation. *P < .05, **P < .005, ***P < .0005, ordinary 1-way ANOVA.