A 55-year-old woman with small cell carcinoma of the lung is admitted to the hospital to undergo chemotherapy. Six days after treatment is started, she develops a temperature of 38°C (100.4°F). Physical examination shows no other abnormalities. Laboratory studies show a leukocyte count of 100/mm3 (5% segmented neutrophils and 95% lymphocytes). Which of the following is the most appropriate pharmacotherapy to increase this patient's leukocyte count?

A) Granulocyte-macrophage colony-stimulating factor (GM-CSF)
B) Granulocyte colony-stimulating factor (G-CSF)
C) Erythropoietin
D) Interleukin-2 (IL-2)