Costimulatory Requirements for the Expansion of Human T Regulatory Cells

Abstract

We used cell‐based artificial APCs (aAPC) to explore the costimulatory requirements to expand functional T regulatory cells (Treg) enriched from human peripheral blood. Only CD28 costimulation maintained high levels of FoxP3 expression and suppressive function in enriched T regulatory cultures. Interestingly, CD4 T cells grown in the presence of CD28 costimulation and rapamycin displayed significant in vitro suppressive activity. However, when these cells were evaluated for suppressive activity in vivo, only the cultures that were initially enriched for Tregs suppressed. We investigated whether additional costimulatory pathways could augment CD28's ability to promote further Treg expansion in rapamycin. In a minority of donors OX40 costimulation was able to augment Treg expansion and maintain function; however, in the majority of donors these cultures often lost suppressive function. In contrast, we found that re‐stimulation of the Treg cultures after 8–10 days of culture with CD28 costimulation alone resulted in 1000 fold expansion of Treg in less than 3 weeks. These highly expanded Tregs retained potent in vitro and in vivo suppressive function. These studies indicate the optimal costimulatory requirements to expand Tregs differ from T effector cells and establish the feasibility of using expanded Tregs for adoptive T cell therapy.The project is supported by JDRF for Cell Therapy grant.