A phase 2 randomized trial with autologous polyclonal expanded regulatory T cells in children with new-onset type 1 diabetes

CD4 + CD25 hi CD127 lo/− FOXP3 + regulatory T cells (T regs ) play a key role in preventing autoimmunity. In autoimmune type 1 diabetes (T1D), adoptive transfer of autologous polyclonal T regs has been shown to be safe in adults in phase 1 clinical trials. We explored factors contributing to efficacy of autologous polyclonal expanded T regs (expT regs ) in a randomized phase 2 multi-center, double-blind, clinical trial (Sanford/Lisata Therapeutics T-Rex phase 2 trial, ClinicalTrials.gov NCT02691247). One hundred ten treated children and adolescents with new-onset T1D were randomized 1:1:1 to high-dose (20 × 10 6 cells/kilogram) or low-dose (1 × 10 6 cells/kilogram) treatments or to matching placebo. Cytometry as well as bulk and single-cell RNA sequencing were performed on selected expT regs and peripheral blood samples from participants. The single doses of expT regs were safe but did not prevent decline in residual β cell function over 1 year compared to placebo ( P = 0.94 low dose, P = 0.21 high dose), regardless of age or baseline C-peptide. ExpT regs were highly activated and suppressive in vitro. A transient increase of activated memory T regs was detectable 1 week after infusion in the high-dose cohort, suggesting effective transfer of expT regs . However, the in vitro fold expansion of expT regs varied across participants, even when accounting for age, and lower fold expansion and its associated gene signature were linked with better C-peptide preservation regardless of T reg dose. These results suggest that a single dose of polyclonal expT regs does not alter progression in T1D; instead, T reg quality may be an important factor.