Reduction of Granulocyte-Colony Stimulating Factor Requirement in the Course of Long-Term Treatment for More Than 5 Years in Congenital Neutropenia Patients Harbouring ELANE Mutations

Congenital neutropenias include a heterogeneous group of diseases characterized by a decrease in circulating neutrophils and different underlying germ-line gene mutations. Since 1988 recombinant human G-CSF is available for the treatment of severe chronic neutropenia patients. In phase I/II/III studies in patients with severe congenital and cyclic neutropenia, treatment with recombinant human granulocyte colony-stimulating factor (r-metHuG-CSF) resulted in a rise in the absolute neutrophil counts (ANC) and a reduction in infections. The Severe Chronic Neutropenia International Registry collects clinical information on patients suffering from severe chronic neutropenia since 1994. 312 of 379 CN and 65 of 79 CyN patients receive long-term G-CSF treatment for a median duration of 8,26 years in CN and 9,37 in CyN. Median G-CSF doses vary by neutropenia subtype and gene mutation. Patients with congenital neutropenia revealing ELANE mutations require the highest G-CSF doses compared to other subtypes (median G-CSF dose 5 µg/kg/day in 88 patients). SCNIR follow-up data suggest that pediatric ELANE-CN patients were maintained at a particular G-CSF dose per kg body weight for longer than expected by the gain of body weight. We therefore analysed the reported yearly G-CSF doses in all treated ELANE-CN patients to evaluate the dose trend:

From 88 G-CSF treated patients with ELANE-CN we excluded 16 patients with nonresponse (ANC remained below 0.5 x 10⁹ /L) and partial response (ANC remained between 0.5 and 0.99 x 10⁹ /L). Since the gain of body weight is highest during the first 5 years of life with and 10-fold increase we divided G-CSF good responders by age at G-CSF initiation (0-5 years vs above 6 years) and compared G-CSF doses at the end of the dose finding period with the last dose reported. 51 of the remaining 72 patients started G-CSF treatment between the first and 5^th year of life with a median G-CSF treatment duration of 9.76 years. 37 of the 51 patients were treated for at least 5 years. In 21 of the 72 patients G-CSF treatment was initiated after their 10^thbirthday with a median follow up of 20.45 years. 19 of the 21 patients were treated for at least 5 years. All patients with a treatment duration of less than 5 years were excluded from further analysis.

In ELANE-CN patients with treatment start at an age of 0-5 years the mean G-CSF dose decreased significantly from 13.47 µg/kg/day at the time of ANC-response to 7.96 µg/kg/day at the last report (median G-CSF dose decreased from 6.85 µg/kg/day to 4.42 µg/kg/day) during a treatment duration of at least 5 years.

In summary, a significant decrease in the individual G-CSF doses could be observed in ELANE-CN patients who started G-CSF treatment during the first five years of their lives suggesting an age dependent alleviation of the severity of the disease as judged by the response to G-CSF.