Hellmich et al. [14] reported that recombinant human granulocyte colony-stimulating factor (rHuG-CSF) could be safely used in 6 patients with granulomatosis with polyangiitis (previously Wegener’s granulomatosis), all PR3 antibody positive, to treat severe neutropenia (absolute neutrophil count < 1,000/μL) after being treated with cyclophosphamide without causing disease flare. Here, CSF2 is linked to neutropenia.