Background:Alemtuzumab has been used in organ transplantation and a variety of hematologic malignancies (especially for the treatment of B-cell chronic lymphocytic leukemia).However,serious infectious complications frequently occur after treatment.The reason for increased infections postalemtuzumab treatment is unknown at this stage.We explore the effect ofalemtuzumab on intestinal intraepithelial lymphocytes (IELs) and intestinal barrier function in cynomolgus model to explain the reason of infection following alemtuzumab treatment.Methods:Twelve male cynomolguses were randomly assigned to either a treatment or control group.The treatment group received alemtuzumab (3 mg/kg,intravenous injection) while the control group received the same volume of physiological saline.Intestinal IELs were isolated from the control group and the treatment group (on day 9,35,and 70 after treatment) for counting and flow cytometric analysis.Moreover,intestinal permeability was monitored by enzymatic spectrophotometric technique and enzyme-linked immunosorbent assay.Results:The numbers of IELs were decreased significantly on day 9 after treatment compared with the control group (0.35 ± 0.07 x 108 and 1.35 ± 0.09 × 108,respectively; P ＜ 0.05) and were not fully restored until day 70 after treatment.There were significant differences among four groups considering IELs subtypes.In addition,the proportion ofapoptotic IELs after alemtuzumab treatment was significantly higher than in the control group (22.01 ± 3.67 and 6.01 ± 1.42,respectively; P ＜ 0.05).Moreover,the concentration of D-lactate and endotoxin was also increased significantly on day 9 after treatment.Conclusions:Alemtuzumab treatment depletes lymphocytes in the peripheral blood and intestine of cynomolgus model.The induction of apoptosis is an important mechanism of lymphocyte depletion after alemtuzumab treatment.Notably,intestinal barrier function may be disrupted after alemtuzumab treatment.