Therapeutic Use of Recombinant Human G-CSF (rhG-CSF) in a Canine Model of Sublethal and Lethal Whole-body Irradiation

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Abstract
The short biologic half-life of the peripheral neutrophil (PMN) requires an active granulopoietic response to replenish functional PMNs and to maintain a competent host defence in irradiated animals. Recombinant human G-CSF (rhG-CSF) was studied for its ability to modulate haemopoiesis in normal dogs as well as to decrease therapeutically the severity and duration of neutropenia in sublethally and lethally irradiated dogs. For the normal dog, subcutaneous administration of rhG-CSF induced neutrophilia within hours after the first injection; total PMNs continued to increase (with plateau phases) to mean peak values of 1000 per cent of baseline at the end of the treatment period (12-14 days). Bone-marrow-derived granulocyte-macrophage colony-forming cells (GM-CFC) increased significantly during treatment. For a sublethal 200 cGy dose, treatment with rhG-CSF for 14 consecutive days decreased the severity and shortened the duration of neutropenia and thrombocytopenia. The radiation-induced lethality of 60 per cent after a dose of 350 cGy was associated with marrow-derived GM-CFC survival of 1 per cent. Treatment with rhG-CSF markedly reduced the lethality associated with exposure to 350 cGy of radiation to zero. White blood cell (WBC) and platelet recovery kinetics were correlated with degree of marrow damage. The rhG-CSF reduced the severity and duration of neutropenia. Control animals required antibiotic therapy (WBC less than 1000 mm3) for a total of 16 days versus 3 days for rhG-CSF-treated dogs. The duration of thrombocytopenia was reduced, although the severity of depletion was unchanged with treatment. These data indicate that in the lethally irradiated dog, effective cytokine therapy with rhG-CSF will increase survival through the induction of earlier recovery of neutrophils and platelets.

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