AIM: To study the role of immature dendritic cells (imDCs) on immune tolerance in rat penetrating keratoplasty (PKP) in high-risk eyes and to investigate the mechanism of immune hyporesponsiveness induced by donor-derived imDCs.METHODS:Seventy-five SD rats (recipient) and 39 Wistar rats (donor) were randomly divided into 3 groups:control, imDC and mature dendritic cell (mDC) group respectively. Using a model of orthotopic corneal transplantation in which allografts were placed in neovascularized high-risk eyes of recipient rat. Corneal neovascularization was induced by alkaline burn in the central cornea of recipient rat. Recipients in imDC group or mDC group were injected donor bone marrow-derived imDCs or mDCs of 1×10⁶ respectively 1 week before corneal transplantation via tail vein. Control rat received the same volume of PBS. In each group, 16 recipients were kept for determination of survival time and other 9 recipients were executed on day 3, 7 and 14 after transplantation. Cornea was harvested for hematoxylin-eosin staining and acute rejection evaluation, Western blot was used to detect the expression level of Foxp3.RESULTS: The mean survival time of imDC group was significantly longer than that of control and mDC groups (all P<0.05). The expression level of Foxp3 on CD4⁺CD25⁺T cells of imDC group (2.24±0.18) was significantly higher than that in the control (1.68±0.09) and mDC groups (1.46±0.13) (all P<0.05).CONCLUSION: Donor-derived imDC is an effective treatment in inducing immune hyporesponsiveness in rat PKP. The mechanism of immune tolerance induced by imDC might be inhibit T lymphocytes responsiveness by regulatory T cells.