A phase 1 study to address the safety and efficacy of granulocyte colony‐stimulating factor for the mobilization of hematopoietic progenitor cells in active rheumatoid arthritis

Objective . To examine the safety and efficacy of granulocyte colony‐stimulating factor (G‐CSF) alone for the mobilization of peripheral blood progenitor cells in patients with resistant active rheumatoid arthritis (RA). Methods . Five patients with resistant active RA were studied. A dose of 5 μg/kg of G‐CSF (Filgrastim) was given subcutaneously each day for 5 days, and the number of stem cells mobilized into the peripheral blood was assessed by daily CD34 counts. RA disease activity was assessed by standard clinical methods. Results . The absolute numbers of peripheral blood CD34+ cells peaked on day 4, with a mean value of 0.025 × 10 9 /liter (range 0.013–0.048 × 10 9 /liter). There was no significant change in disease activity during the study or in the month following therapy. Conclusion . Using G‐CSF alone, CD34+ progenitor peripheral blood cells were mobilized in numbers suitable for leukopheresis. G‐CSF therapy was welltolerated in patients with active RA, and was not associated with a flare during treatment or in the month following treatment.