Proliferation of ALPS DNT cells can be induced by costimulatory signals in vitro. Sorted DNT cells (A, B) or CD4⁺ T cells (B) from patients with ALPS or healthy controls were labeled with CFSE and stimulated with PHA, anti-CD3, anti-CD3/CD28, and allogeneic DC in the presence of IL-2. Cell proliferation was determined on day 6, dead cells were excluded by 7AAD staining. (A) Histograms show 1 representative experiment, (B) graphs represent cumulative data (mean ± SD) of 5 patients with ALPS and healthy controls. *P < .05 (Mann-Whitney U test).