An agonist murine monoclonal antibody to the human c-Mpl receptor stimulates megakaryocytopoiesis.
Thrombopoietin (TPO) is a hematopoietic growth factor that stimulates megakaryocytopoiesis and platelet production in vivo and promotes the development of identifiable megakaryocytes in vitro. We have developed a murine monoclonal antibody, BAH-1, raised against human megakaryocytic cells, which specifically recognizes the c-Mpl receptor and shows agonist activity by stimulating megakaryocytopoiesis in vitro. BAH-1 antibody specifically binds to platelets and to recombinant c-Mpl with high affinity. Similar to TPO, BAH-1 alone supported the formation of colony-forming unit-megakaryocyte (CFU-MK) colonies. The combination of BAH-1 plus interleukin-3 or of BAH-1 plus human TPO significantly increased the number of human CFU-MK colonies. In addition, BAH-1 monoclonal antibody stimulated the proliferation and maturation of primary bone marrow megakaryocytes in a dynamic heterogeneous liquid culture system. Individual large megakaryocytes as well as small megakaryocytic cells were observed in cultures of CD34(+) CD41(+) cells in the presence of BAH-1 antibodies. Similar to TPO, BAH-1 antibody induced a significant response of murine immature megakaryocytes as observed by an increase in the detectable numbers of acetylcholinesterase-positive megakaryocytes. No effects of BAH-1 antibody were observed on colony-forming unit-granulocyte-macrophage, burst-forming unit-erythroid, or colony-forming unit-erythroid colonies. In vivo studies showed that BAH-1, alone or in combination with TPO, expands the numbers of megakaryocytic progenitor cells in myelosuppressed mice. This antibody should prove useful in understanding the structure-function aspects of the c-Mpl receptor as well as in evaluating the effects of the sustained activation of this receptor in preclinical models of severe thrombocytopenia.
Deng
B
B
Divisions of Experimental Medicine and Hematology/Oncology, Beth Israel Deaconess Medical Center, Harvard Institutes of Medicine, Boston, MA and Genentech Inc, South San Francisco, CA, USA.
Banu
N
N
Malloy
B
B
Hass
P
P
Wang
J F
JF
Cavacini
L
L
Eaton
D
D
Avraham
H
H
D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry / Q000494:pharmacology* / Q000502:physiology; D001853:Bone Marrow / Q000187:drug effects / Q000276:immunology; D003114:Colony-Forming Units Assay; D005260:Female; D006410:Hematopoiesis / Q000187:drug effects / Q000276:immunology*; D006801:Humans; D008533:Megakaryocytes / Q000187:drug effects / Q000276:immunology*; D051379:Mice; D008807:Mice, Inbred BALB C; D009363:Neoplasm Proteins; D011518:Proto-Oncogene Proteins / Q000819:agonists* / Q000276:immunology* / Q000494:pharmacology; D018121:Receptors, Cytokine; D053628:Receptors, Thrombopoietin; D013926:Thrombopoietin / Q000378:metabolism* / Q000494:pharmacology
D000911:Antibodies, Monoclonal; D009363:Neoplasm Proteins; D011518:Proto-Oncogene Proteins; D018121:Receptors, Cytokine; D053628:Receptors, Thrombopoietin; C082218:MPL protein, human; D013926:Thrombopoietin