Down regulation of stem cell colony formation by purified CD8 lymphocytes and CD8 conditioned medium: potential importance for bone marrow transplantation in leukemia.
A methodology for selection of the CD8 cell subset from the peripheral blood and bone marrow mononuclear cells was developed using anti-T8 (CD8) antibody and magnetic microspheres coated with anti-mouse IgG. Following optimization of antibody:cell binding ratio and microsphere:cell ratios, CD8(+)-cells in the peripheral blood and bone marrow were effectively removed, with an overall final recovery of 34.9% +/- 8.6%, and 56% +/- 8.5% respectively with complete recovery of stem cells and very little contamination with effector cells. CD8(+)-depleted cell preparations demonstrated a 3-4 fold increase in CFU-C and CFU-E colony formation over non-depleted preparations when stimulated with G-CSF, GM-CSF or IL-3 and erythropoietin. The largest increase in colony formation was evident when IL-3 was used to stimulate colony formation. Purified autologous CD8+ T-cells or culture supernatant from in vitro cultures of purified autologous CD8+ T-cells added back to CD8 depleted preparations, induced 20%-90% suppression of CFU-C and CFU-E colony formation in a dose dependent manner. Colony formation by CD34+ cells, purified by anti CD34 antibodies and magnetic microspheres, were also inhibited by either pure CD8(+)-cell populations or CD8-culture supernatant. Preliminary fractionation studies indicate that the inhibitory factor is a protein of > 50 kd. In contrast, when purified autologous CD4+ cells were added to purified CD34+ stem cells, an increase (< 50%) in colony formation was observed. These results, taken together, suggest that CD8+ T-cells are negative effectors of normal hematopoiesis whereas CD4+ T-cells function as positive effectors.
Gazitt
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Department of Pediatric Hematology-Oncology, University of Florida, Gainesville.
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Y J
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D000818:Animals; D015703:Antigens, CD / Q000502:physiology; D018952:Antigens, CD34; D016026:Bone Marrow Transplantation; D016827:CD8 Antigens / Q000502:physiology*; D017077:Culture Media, Conditioned; D015536:Down-Regulation; D006412:Hematopoietic Stem Cells / Q000502:physiology*; D006801:Humans; D007938:Leukemia / Q000601:surgery*; D013552:Swine; D013601:T-Lymphocytes / Q000502:physiology*
D015703:Antigens, CD; D018952:Antigens, CD34; D016827:CD8 Antigens; D017077:Culture Media, Conditioned