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

CD4+CD25hiCD127lo/-FOXP3+ regulatory T cells (Tregs) play a key role in preventing autoimmunity. In autoimmune type 1 diabetes (T1D), adoptive transfer of autologous polyclonal Tregs has been shown to be safe in adults in Phase I clinical trials. We explored factors contributing to efficacy of autologous polyclonal expanded Tregs (expTregs) in a randomized Phase II multi-center, double-blind, clinical trial in 110 treated children and adolescents with new-onset T1D (Sanford/Lisata Therapeutics T-Rex Phase II trial) randomized 1:1:1 to high- (24*10^6 cells/kg) or low- (1*10^6 cells/kg) dose treatments or to matching placebo. Cytometry, bulk and single-cell RNA-sequencing were performed on selected expTregs and peripheral blood samples from participants. The single doses of expTregs were safe but did not prevent the decline in residual beta cell function over one year compared to placebo (P = 0.94 low dose, P = 0.21 high dose), regardless of age or baseline C-peptide. ExpTregs were highly activated and suppressive in vitro. A transient increase of activated memory Tregs was detectable one week after infusion in the high dose cohort suggesting effective transfer of expTregs. However, in vitro fold expansion of expTregs 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 Treg dose. These results suggest that a single dose of polyclonal expTregs does not alter progression in T1D; instead, Treg quality may be an important factor.