Third-party CD4⁺ iNKT cells promote an expansion of donor Tregs. (A) Relative and absolute numbers of donor Tregs from spleens of BALB/c recipient mice at day +10. Error bars indicate SEM. Pooled data from 2 independent experiments with 6 mice per group are shown. (B) Representative dot plots gated on live Thy1.1⁺CD4⁺ donor T cells re-isolated at day +10 from BALB/c recipient spleens. Shown is 1 of 2 independent experiments. (C) BALB/c recipient mice received Tcons from FoxP3^DTR/GFP/luc C57BL/6 albino mice with and without CD4⁺ iNKT cells from FVB/N third-party mice. Bioluminescence signals derive from luc⁺FoxP3⁺ donor T cells. Shown is 1 of 2 independent experiments with 5 mice per group, as well as a representative bioluminescence image from one untreated FoxP3^DTR/GFP/luc C57BL/6 albino mouse. The † indicates that all animals from the respective group died or needed to be euthanized. ***P ≤ .001. SSA, side scatter area.