Objective:To study the in vitro effect of adipose stromal stem cells(ASC) on phenotype and secretion of cytokines of allogenetic T lymphocytes,and to elucidate the possible roles of ASC for immunomodulation.Methods:ASC was isolated and cultured.The supernatant of ASC and ASC itself were co-cultured with allogenetic T lymphocytes.MTT assays were used to detect the proliferative rates of T cells.Annexin-Ⅴ/PI staining was used to detect apoptotic rates,and flow cytometry to detect the proportion of CD4+CD25+ cells.ELISA was used to detect the secretion of IL-10 and TGF-?1.Reverse transcription-polymerase chain reaction(RT-PCR) was used to detect the expressing level of Foxp3 gene.Results:The supernatant of ASC had no deep impact on the proliferation and apoptosis of T lymphocytes.ASC had the direct inhibitory effect on growth of T lymphocytes,while the stem cells did not affect apoptosis.Both the supernatant of ASC and ASC itself increased the proportion of CD4+CD25+ cells in T lymphocytes,and increasd the level of IL-10 and TGF-?1.They could also up-regulate expressing level of Foxp3 in T cells.Conclusion:ASC can affect the function of T lymphocytes via cell-to-cell contact and secretion of cytokines.By these ways ASC exhibits negative immunomodulation and plays an important role in inducing immune tolerance.