Lack of efficacy of thrombopoietin and granulocyte colony-stimulating factor after high dose total-body irradiation and autologous stem cell or bone marrow transplantation in rhesus monkeys.

The efficacy of recombinant human thrombopoietin (TPO) and recombinant human granulocyte colony stimulating factor (G-CSF) in stimulating platelet and neutrophil recovery was evaluated in a placebo-controlled study involving transplantation of limited numbers (1-3 x 10(4)/kg) of highly purified autologous stem cells (CD34++/RhLA-DR[dull]) into rhesus monkeys after the animals were subjected to 8 Gy of total body irradiation (TBI) (x-rays). The grafts shortened profound TBI-induced pancytopenia from 5 to 6 weeks to 3 weeks. Daily subcutaneous (sc) injection of TPO (10 microg/kg/day, days 1-21 after TBI) did not stimulate platelet regeneration after transplantation either alone or in combination with G-CSF (5 microg/kg/day sc, days 1-21 after TBI). G-CSF treatment failed to prevent neutropenia in the monkeys and did not stimulate recovery to normal neutrophil levels. Simultaneous administration of TPO and G-CSF did not influence the observed recovery patterns. To test the hypothesis that the limited number of cells transplanted or the subset chosen was responsible for the lack of effectiveness of TPO, three additional monkeys were transplanted with 10(7)/kg unfractionated autologous bone marrow cells. Two of these animals received TPO and the other served as a control. In this setting, as well, TPO treatment did not prevent thrombocytopenia. This study demonstrates that treatment with TPO does not accelerate platelet reconstitution from transplanted stem cells after high-dose TBI. These findings contrast with the rapid TPO-stimulated platelet recovery in myelosuppression induced by 5 Gy of TBI in rhesus monkeys; we conclude from this that the clinical effectiveness of the TPO response depends on the availability of TPO target cells in the first week after TBI, that is, before endogenous TPO levels reach the saturation point. In addition, protracted isolated thrombocytopenia was observed in two G-CSF-treated monkeys, one of which also received TPO. Furthermore, TPO treatment for 7 days in the 6th week after TBI during severe thrombocytopenia in one monkey produced prompt clinical improvement and an increase in platelet counts.