Migratory properties of ex vivo expanded regulatory T cells: Influence of all-trans retinoic acid and rapamycin

Adoptively transferred regulatory T-cells represent a promising therapeutic approach for tolerance induction in autoimmunity and transplantation medicine. However, a major hurdle for clinical application is the manufacturing of sufficient Treg cell numbers with respect to the low frequency of naturally occurring Tregs in the peripheral blood. Therefore, ex vivo large-scale expansion is mandatory for most of the clinical conditions. Besides the Treg cell number other parameters of the cell product are of high relevance for safe and efficient clinical Treg cell application like Treg cell purity, suppressive capacity and genetic stability of the Treg cell phenotype. Moreover, migratory properties of ex vivo expanded Tregs should be defined very clearly in order to predict their migration to secondary lymphoid organs as sites of antigen-specific activation, in vivo proliferation and subsequent trafficking to affected target organs. Therefore, we studied different cell culture conditions for Treg large-cell expansion using all-trans retinoic acid (ATRA) and/or rapamycin (Rapa) with focus on their migratory properties. The tested culture conditions revealed comparable chemokine receptor expression profiles (CXCR3, CCR4, CCR6, CCR7) and functional migration capabilities (IP10 and CCL19) with respect to Th1 and Th2 inflammatory conditions. However, the most striking difference was detected for the expansion capacity, suppressive potency and genetic stability likely predisposing large-scale expansion with ATRA and/or Rapa for therapeutic intervention in acute GvHD and without supplementation for chronic GvHD.