Assessing the efficacy of mammalian target of rapamycin inhibitors by phosphorylation of p70S6K in CD4-positive cells of liver transplant patients.

The activity of p70S6 kinase located downstream of the mammalian target of rapamycin (mTOR) pathway is sensitive to mTOR inhibitors. However, the methods of assessing p70S6 kinase activity are still unclear. This study aimed to investigate p70S6 kinase activity in CD4-positive cells of liver transplant patients.Liver transplant patients treated with mTOR inhibitors were recruited from Beijing Chaoyang Hospital between October 2014 and October 2016. The influence of mycophenolic acid (MPA) derivatives and prednisone on p70S6 kinase phosphorylation in CD4-positive cells was examined in liver transplant patients and healthy controls (HCs). The phosphorylation of p70S6K in CD4 + CD25 regulatory T cells (Treg cells) and CD4 + CD25- T effector cells was analyzed by phospho-flow cytometry.The phospho-flow technique detected a significant loss of p70S6 kinase phosphorylation in CD4-positive cells of patients treated with mTOR inhibitors compared with HCs. MPA derivatives and prednisone did not affect p70S6 kinase phosphorylation significantly. No significant difference in p70S6 kinase phosphorylation was observed when the whole blood was stored within 3 hours at room temperature. The phosphorylation of p70S6K was significantly lower in CD4 + CD25 Treg cells than in CD4 + CD25-T effector cells in HCs. After liver transplant patients were treated with mTOR inhibitors, p70S6K phosphorylation was more reduced in CD4 + CD25-T effector cells than in CD4 + CD25 Treg cells.The presence of phosphorylation of p70S6 kinase in CD4-positive cells was reduced in liver transplant patients who were treated by mTOR inhibitors.