Key words: Rapamycin, Regulatory T cells, Corneal transplantCorneal disease, one of the leading causes of blindness in China, 1 requires a corneal transplant to restore visual function in most cases. 2 Although immune privilege of corneal allografts endows a high success rate of corneal transplant than other solid-organ transplants, immunologic rejection remains a major cause of graft failure after corneal transplant. 3,4 Regulatory CD4 + CD25 + Foxp3 + T cells (Treg), an important regulator in maintaining immune homeostasis, play a crucial role in autoimmune diseases and tumors, and protect individuals from graft rejection. 5 However, Treg cells are present in low numbers under normal conditions, reported to be 5% to 10% of CD4 + T cells in mice and human blood, and have an anergic phenotype. 6 Therefore, enhancement of activated Treg cells may protect individuals from autoimmune diseases and graft rejection, just as previous studies have revealed. [7][8][9][10] Rapamycin, a novel macrolide immunosuppressive drug, has been reported to prevent clinical allograft rejections including corneal allografts. 11 Moreover, rapamycin allows expansion of CD4 + CD25 + Foxp3 + Treg in vitro and in vivo, 12-14 and CD4 + CD25 + Foxp3 + Treg converted by rapamycin has more-potent regulatory abilities. 15 It has been shown that adoptive transfer of CD4 + CD25 + Foxp3 + Treg expanded by rapamycin in vitro is capable of artIClE