All-trans retinoic acid and rapamycin synergize with transforming growth factor-β1 to induce regulatory T cells but confer different migratory capacities

TLDR

Tregs are essential for immune homeostasis, but expanding them from peripheral blood while preserving suppressive function is difficult, and TGF‑β alone does not reliably generate stable Tregs, although TGF‑β plus retinoic acid has been well described, whereas the properties of TGF‑β plus rapamycin‑induced Tregs remain unclear. This study aims to evaluate whether ATRA or rapamycin can synergize with TGF‑β to induce stable, functional Tregs from non‑Tregs. The authors generated iTregs by treating cells with TGF‑β together with either ATRA or rapamycin, then characterized their phenotype, suppressive function, and migratory properties. They found that rapamycin‑induced Tregs differ in phenotype and exhibit reduced in vivo homing compared to RA‑induced and TGF‑β‑only iTregs, leading to diminished therapeutic efficacy in a mouse colitis model.

Abstract

Tregs play important roles in maintaining immune homeostasis, and thus, therapies based on Treg are promising candidates for the treatment for a variety of immune-mediated disorders. These therapies, however, face the significant challenge of obtaining adequate numbers of Tregs from peripheral blood that maintains suppressive function following extensive expansion. Inducing Tregs from non-Tregs offers a viable alternative. Different methods to induce Tregs have been proposed and involve mainly treating cells with TGF-β-iTreg. However, use of TGF-β alone is not sufficient to induce stable Tregs. ATRA or rapa has been shown to synergize with TGF-β to induce stable Tregs. Whereas TGF-β plus RA-iTregs have been well-described in the literature, the phenotype, function, and migratory characteristics of TGF-β plus rapa-iTreg have yet to be elucidated. Herein, we describe the phenotype and function of mouse rapa-iTreg and reveal that these cells differ in their in vivo homing capacity when compared with mouse RA-iTreg and mouse TGF-β-iTreg. This difference in migratory activity significantly affects the therapeutic capacity of each subset in a mouse model of colitis. We also describe the characteristics of iTreg generated in the presence of TGF-β, RA, and rapa.