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.

Switching constant domains enhances agonist activities of antibodies to a thrombopoietin receptor.

We enhanced the activities of two agonist antibodies specific for the thrombopoietin receptor (c-MPL) by switching domains within their constant regions to those of different antibody isotypes. Our results suggest the importance of the hinge region in modulating agonist activity. The antibodies' thrombopoietin-like activity in vitro and in vivo, as well as the desirable pharmacokinetic profile conferred by retaining the whole-IgG structure, suggests that they provide a valuable option for treating thrombocytopenia.