The Regulation On Hematopoietic Reconstitution By CD4(+)T Cytotoxic Cells In Bone Marrow Of Mice

Background:Due to their self-renewal and multipotent differentiaon, two unique features, hematopoietic stem cells(HSCs) can reconstitute hematopoietic tissue in HLA matched recipients upon transplantation for life-time. HSC transplantation therapy is one of the most effective means of treating reflactory hematopoietic diseases such as bone marrow failure and leukemia; however such treatment is limited by the shortage of HSC resources. In vitro HSC expansion(to increase HSC resources) and promoting engraftment capacity of HSCs(in order to best use of the limited HSC resource) during transplantation are two most effective ways to solve this problem.HSC activity is tightly controlled by specific bone marrow niche, a specific microenvironment which is composed of non-hematopoietic cells(such as mesenchymal stromal cells and endothelial cells) and hematopoietic cells(including granulocytes, monocytes,lymphocytes and megakaryocytes). Niche cells regulate HSC self-renewal, proliferation, survival and differentiation by directly interaction and/or producing hematopoietic regulatory factors(such as G-CSF, GM-CSF, IL-3, SCF, EPO, TPO, Fit, etc.), development-associated factors(e.g., Wnt, TGFβ and Notch ligand) and inflammatory molecules(such as IL6, TNFα and IFNα / γ, etc.). The factors secreted by bone marrow niche cells increased significantly during hematopoietic damages or inflammatory reactions, to induce the activation of HSCs in order to meet the increased demond for blood cells of our body. Among them, many of the inflammatory molecules are secreted by lymphocytes located in the bone marrow, spleen and other tissues. However the role of lymphocytes in hematopoietic regenration has not been well studied.T lymphocytes are composed of CD4+ helper T(Th1/Th2) cells, Th17 inflammatory T cells, Treg cells and CD8+ cytotoxic cells(Tc). Th1 and Th2 cells regulate the activity of CD8+ Tc-mediated cellular immune reaction and B lymphocytes-mediated humoral immune response through the secretion of inflammatory cytokines such as TNFα, IFNγ and IL4. In addition to CD4, Treg cells also express CD25, Foxd3, T-bet, GATA3 or RORγ, which inhibit both T and B cell-mediated immune response. It was found that Treg cells might be also involved in regulation of hematopoiesis by protecting HSCs from the attack from other immune cells. Nevertheless, the role of T cells in hematopoietic regulation has not been completely uncovered.5-Fu(5-fluorouracil) is a chemotherapy drug that is commonly used in clinical for cancer treatment. It can activate HSC and hematopoietic regeneration by killing the proliferative hematopoietic progenitor cells. Such damage-induced bone marrow regeneration provides a useful model system to study the hematopoietic regulatory cells and factors in bone marrow niche.Aim:Determine the role of role of CD4+ T lymphocytes on hematopoietic regeneration by using 5-Fu-induced bone marrow damage and hemetopoitic repairing model.Method:1). Examine the dynamic changes of CD4+ T lymphocytes during the process of 5-Fu-induced bone marrow damage and hematopoietic recovery by using antibody staining and flow-cytometric analysis; 2) Study the effects of CD4+ T cell depletion on the hematopoietic recovery after 5-Fu treatment by anti-CD4 antibody injection followed by phenotype analysis.Result:1) Both CD4+ and CD8+ T lymphocytes seem more resistant to 5Fu treatment which comparaed to other hematopoietic cells. The numbers of CD4+ and CD8+ T lymphocytes are relatively consistent during the hematopoietic repairing process. As a consequence, the percentages of CD4+ and CD8+ T lymphocytes were increased at the early several days and reached to top at 6 days. 2) Depletion of CD4+ T cells by anti-CD4 antibody injection delayed the recovery of both HSC and MPP when compared to control antibody injection group. 3) The condition medium of CD4+ T lymphocytes culture promotes survival of HSPC in vitro, suggesting CD4+ T cells enhance hematopoietic repair through secreting factors.Conclusion : During damage-induced hematopoietic repairing process, The dynamic changes of CD4+ T lymphocytes are correlated to and involve in hematopoietic repairing process by secreting factors.