Effects of Endothelial Progenitor Cell on Immune Reconstitution in Mice Undergoing Allo-geneic Bone Marrow Transplantation After BU/CY Pretreatment

Abstract

Objective To study the effects of endothelial progenitor cell (EPC) on immune reconstitution in mice undergoing allo-geneic bone marrow transplantation after busulfan/cyclophosphamide (BU/CY) pretreatment.Methods Fifty eight healthly SPF male BALB/c mice aged (8-10) weeks and weighted (22-24)g were randomly divided into control group (n=9),which injected with 0.2 mL phosphate buffer solution (PBS) ; BU/CY pretreatment group (n=9),which treated with BU/CY from day-7 to day -2 and injected with 0.2 mL PBS; bone marrow cells transplantation (BMT) group (n=20),which injected with donor derived bone marrow cells after BU/CY pretreatment; EPCs combined with BMT (EPC) group (n=20),which injected with donor derived bone marrow cells and EPCs after BU/CY pretreatment.The number of progenitor B (ProB) cells (CD19+ c-kit+ IgM-) in the bone marrow and the percentages of CD4+,CD8+,double positive (DP),double negative(DN)T cells in the thymus and the percentages of CD4+,CD8+ T cells and B cells in the spleen were detected by flow cytometry.The morphology of immune organs was observed by the light microscope to evaluate the repair of tissues and injured endothelial cells.Results The number of ProB cells in BMT group and EPC group increased continuously after transplantation,and compared with the BMT group (0.14 × 106),the EPC group (0.83×106) increased significantly on day 14 (x2 =7.2,P＜0.05).The percentage of DP cells in the thymus reached the highest peak on day 21,and increased significantly in the EPC group (0.58％) compared with the BMT group (0.39％) (x2 =6.49,P＜0.05).After transplantation,the percentage of CD4+ T cells in the spleen also had gradual increase,and the EPC group (3.64 ％) increased significantly compared with the BMT group (2.47％) (x2 =7.2,P＜0.05) on day 28;The percentage of CD8+ T cells in the spleen peaked on day 21,with the EPC group (3.64％) increased significantly compared with the BMT group (3.21％) (x2 =5.42,P＜ 0.05).The histopathological examination revealed that the repair of damaged tissue in the central and periphery immune organs and the increase of parenchymal cell number accelerated in the EPC group compared with the BMT group,the immunohistochemical staining of the spleen sinusoids also revealed a faster recovery of the integrity of endothelial cells in the EPC group than the BMT group.Conclusions EPC infusion along with bone marrow cells could repair injured blood vessels,accelerate the repair of damaged immune organs,and promote the process of immune reconstruction after allo-HSCT. Key words: bone marrow transplantation; EPC; immune reconstitution; repair