In vivo efficacy of anti-MPL agonist antibody in promoting primary human hematopoietic cells.

In a previous study, we generated novel antithrombopoietin receptor agonist antibodies as therapeutic candidates. In this report, we investigated the in vivo effects of one of these antibodies, MA01G4344U, on primary human hematopoietic cells using xenotransplantation. NOD/Shi-scid, IL-2Rgamma(null) (NOG) mice were pretreated by total-body irradiation and received a transplant of human cord blood-derived CD34(+) cells. Weekly intraperitoneal injection of MA01G4344U (100 microg/mouse per week) or Peg-rhMGDF (5 microg/mouse per week) or phosphate-buffered saline (PBS) was performed. Human cells in peripheral blood were analyzed by flow cytometry and bone marrow cells were analyzed by flow cytometry and colony assay. MA01G4344U successfully increased the number of human CD41(+) platelets and human CD45(+) cells in peripheral blood. In the bone marrow, MA01G4344U increased the number of human CD45(+)/CD34(+) cells, which resulted in more multilineage progenitor cells. The efficacy of MA01G4344U in promoting primary human hematopoietic cells in vivo suggests its therapeutic potential for thrombocytopenic and pancytopenic disorders.