Immaturities in NB hematopoiesis include defects in both myelopoiesis and thrombopoiesis. 25% of babies admitted to the NICU experience thrombocytopenia(Castle et al, J Peds 108:1986), and it is a risk factor for neonatal morbidity and mortality (Andrews et al, J Peds 110:1987). TPO and rhG-CSF have been shown to be potent stimulators of thrombopoiesis and myelopoiesis, respectively. (Blood 86:(10), 1995) The present study investigates the effects of TPO alone and in combination with rhG-CSF in modulating NB rat hematopoiesis. NB Sprague Dawley rats (24-36 hrs, n=16/tx) were given SC TPO (10 μg/kg, (provided by Genentech), rhG-CSF (100μg/kg) (provided by Amgen), TPO + rhG-CSF (same doses) or PBS/HSA × 14 days. CBC and PLT were obtained on alternate days from d 0-20. Random animals (n=3/tx) were sacrificed on d 14 for bone marrow CFU-GM, MEG and proliferation studies. TPO alone or + rhG-CSF had no effect on HCT or RBC. However, significant increases in ANC (/mm3) were seen with TPO alone vs PBS/HSA beginning on d 2 (1386 ± 101.3 vs 1057.0 ± 68.6, p< 0.05), d 8 (1032.8 ± 96.3 vs 509.0 ± 62.7, p< 0.05), d 14 (1490.4 ± 233.6 vs 835.2 ± 72.3, p< 0.05). A significant increase in ANC (/mm3)was also seen with TPO + rhG-CSF vs rhG-CSF alone beginning on d 4 (2486.0 ± 256.1 vs 1714.4 ± 342.8, p< 0.01), d 8 (2207.2 ± 218.2 vs 1476.0 ± 179.1, p< 0.001), d 14(2124.0 ± 150.2 vs 1175.2 ± 169.2, p< 0.01). Significant increases in PLT (K/mm3) were seen with TPO alone d 4-18 with no effect seen with rhG-CSF alone. However, a significant abrogation of PLT was seen with TPO + rhG-CSF vs TPO alone beginning on d 8 (1674.4 ± 235.5 vs 2188 ± 148.1, p < 0.05), d 14 (2466.0 ± 330.8 vs 2980.8± 100.9, p < 0.05). Significant increases were seen in CFU-Meg and GM with TPO alone & TPO+ rhG-CSF vs C (colonies/2×105c) (MEG: 23.3 ± 1.0, 20.33 ± 3.8 vs 6.0 ± 1.0, p< 0.05) (GM: 144.0 ± 4.51, 106.7 ± 15.4 vs 84.3 ± 6.5, p< 0.01). Megakaryocyte proliferation was increased in TPO alone & TPO + rhG-CSF vs PBS/HSA (%C) (250.1 ± 44.3 & 246.8±21.1 vs 100, p< 0.05). These data suggests that TPO induces myeloid and megakaryocytic progenitor cells, and increases neutrophil and platelet production in the NB rat. However, the addition of rhG-CSF abrogates the TPO effect on platelet production. Further studies are required to determine the clinical implications of the combination of TPO + rhG-CSF in the treatment of neonatal thrombocytopenia and neutropenia.
