Abstract: Objective To explore the change and significance of FOXP3⁺Treg within peripheral blood mononudear cells(PBMC),which stimulated by CD28 monoclonal antibody in tumor patients.Methods Ascites induced immune and pro-law chromatography for purification and preparation of the monoclonal antibody,Ficoll density gradient centrifugation to obtain peripheral blood PBMC,and/or stimulated by CD28 monoclonal antibody 10μg/mL after co-culture by immunofluorescence and flow cytometry analysis of FOXP3⁺ Treg,as well as the expression of FOXP3⁺Fas⁺Treg and FOXP3⁺ FasL⁺Treg.Results Immunofluorescence and flow cytometry showed that the peripheral blood of tumor patients with FOXP3⁺Treg expression ratio(6.208±2.754)%,while the control group(2.653±0.638)%.FOXP3+FasL+Treg cells activated by CD28 monoclonal antibody for the FasL expression(7.252± 2.23)%,and healthy control group(7.96± 2.938)% Before and after activation the ratio of FOXP3⁺Fas⁺Treg(1.467± 0.590)%,(3.692± 1.822)%.Conclusion The ratio of FOXP3⁺Treg within PBMC in tumor patients decreased(P＜0.01)after stimulating by CD28 monoclonal antibody which suggested the patients immune function recover and improve.