RAPAMYCIN EXPANDS AND CONFERS RESISTANCE TO APOPTOSIS

The immunosuppressive drug Rapamycin (RAPA) has been shown to promote expansion ofCD4+ IL-10+ natural human regulatory T cells (nTreg) in vitro and in vivo. RAPA effects on inducible Treg (Trl) are unknown, and this study explores in vitro responses ofTrl to this drug. CD4+CD25neg T cells isolated from PBMC of normal donors were used to generate Trl cells. Expanded Trl cells were tested for surface markers, expression of survival proteins, resistance to apoptosis and the ability to suppress proliferation of autologous CD4+CD25neg responder T cells (RC) in functional assays. RAPA was found to promote the generation of human Trl cells from autologous CD4+CD25neg precursors in peripheral blood. Trl cells + RAPA mediated higher suppression (p<O.OI) ofRC proliferation than Trl cells cultured without RAPA. Trl cells + RAPA also expressed higher levels of FasL and granzyme B (p<0.002), produced more IL-10 and TGF-pl and were more resistant to activation-induced cell death (p<0.02). RAPA up-regulated expression of the Bcl-2 family anti-apoptotic proteins in Trl. In addition, stimulation of Trl by LPS + RAPA resulted in increased proliferation and resistance to apoptosis. RAPA favors in vitro generation of inducible human Treg (Trl) from CD4+CD25neg precursor cells and significantly enhances their survival and suppressor functions. A growing body of evidence suggests tha