THPO and Thrombocytopenia: While the patients in the AMGen clinical trials responded to MGDF with substantial thrombocytosis (e.g., 3-fold increased platelet counts in normal volunteers), and subsequent apheresis yielded impressive platelet collections, following the multiple dosing regimen, a number of the platelet donors began developing severe thrombocytopenia due to the development of anti-MGDF antibodies that cross reacted with the recipients’ endogenous thrombopoietin [67,68].