MPL and Thrombocytopenia: Interestingly, while THPO can stimulate human and mouse HSC expansion, knockout mice for either Thpo or Mpl show an approximately sevenfold decrease in transplantable HSCs, but do maintain relatively normal cellularity in the bone marrow and with the exception of the thrombocytopenia, there are no other peripheral blood abnormalities present (Solar et al, 1998).