LETTER TO THE EDITOR Safety of stem cell mobilization in donors with sickle cell trait Bone Marrow Transplantation (2015) 50, 310–311; doi:10.1038/ bmt.2014.252; published online 3 November 2014 High WBC plays a major role in the pathogenesis of many of the complications seen in patients with sickle cell disease (SCD). 1 Individuals with Sickle cell trait may develop SCD-related complications in conditions of severe stress. 2 G-CSF increases the WBC and may contribute to some of the complications in individuals with sickle cell trait when used in stem cell mobilization. To the best of our knowledge, only one small study 3 assessed the safety of the mobilization of stem cells in individuals with sickle cell trait. Herein, we aimed to compare mobilization adverse events between donors with and without sickle cell trait. Consecutive donors for BMT in our center, Sultan Qaboos University Hospital during the period January 2007–March 2013 were reviewed for inclusion. Donors with evidence of sickle cell trait in the pre-donation hemoglobin electrophoresis or HPLC were included in this study. Twelve donors with sickle cell trait were found. Similar numbers of age and gender matched controls with normal HPLC were selected. We used filgrastim 10 μg/kg subcutaneously daily for 6 days for the mobilization of stem cells. The PBSC were collected on day 6 two hours after the last dose of G-CSF on the day of mobilization. In our center, the target count used is 6 × 10 6 CD34+ cells per kg recipient. This is a retrospective matched case control study comparing the stem cell mobilization adverse events between donors with sickle cell trait defined as cases and age and gender matched donors without sickle cell trait defined as controls. Data were collected through computer review of donors’ records. Variables collected included: age, gender, weight, WBC count, platelet count, hemoglobin level and CMV status. The adjudication of adverse events was assigned retrospectively based on the physicians and nursing notes in the electronic health records. Continuous variables are presented as means with ± s.d. or medians and ranges if not normally distributed. Categorical variables are presented as frequencies and proportions. Continuous variables were compared using paired t-test or Mann–Whitney test if not normally distributed. Categorical variables were compared using McNemar test. All statistical tests were two sided with an alpha error threshold of 0.05. All statistical analyses were done using STATA 11 software (StataCorp. 2011. Stata Statistical Software: Release 11. StataCorp LP, College Station, TX, USA). The study was reviewed and approved by the ethics board committee of Sultan Qaboos University Hospital. There were 12 eligible donors with sickle cell trait. A similar number of donors negative for sickle cell trait were selected as controls. There are no statistically significant differences between the two groups in the baseline clinical and laboratory variables (Table 1). The mean age for the sickle cell trait donor group was 17 ± 9.1 years compared with 19 ± 8.6 years in the control group. Only one donor was positive for CMV. The mean hemoglobin level and platelet count for sickle cell trait group were 13 ± 1.4 g/dL and 301 × 10 9 /L (±96) while for non-sickle cell trait group, they were 13 ± 1.5 g/dL, 320 × 10 9 /L (±58). There was no statistically significant difference in the rates of bone pain, headache, myalgia and paresthesia between the sickle cell trait and non-sickle cell trait groups (Table 2). In the sickle cell trait group, three donors had headache, one had bone pain and one had paresthesia. In the non-sickle cell trait group, two had headache, two had bone pain and one had myalgia. No donor in our study had chest pain, seizure, bleeding, nausea and vomiting, transfusion, infection, splenic rupture and carpal-tunnel syndrome and no deaths were reported. The mean CD34+ cell counts were 98.2 × 10 6 /L (±87.1) in the sickle cell trait group and 81.87 × 10 6 /L (±78.7) in the non-sickle cell trait control group (P = 0.81). The CD34 positive cells per kg recipient was 6.5 × 10 6 (±1.8) in the sickle cell trait group and 7.4 × 10 6 (±2.2) in the control group with no statistically significant difference (P = 0.382). Our matched case control study demonstrated the low rates of adverse events in donors with sickle cell trait undergoing high- dose G-CSF mobilization and peripheral stem cell collection. There was no difference in the rate of adverse events between the sickle cell trait and non-sickle cell trait groups and no death was reported in the study. The results are similar to the study reported by Kang et al. 3 and in another study, 4 where 10 patients with SCD were transplanted and no adverse events were observed in donors with sickle cell trait. The rate of adverse events related to PBSC mobilization was very low in our study and a number of other studies. 5 The process is very safe and findings from large registries of unrelated donors suggest the same. 5 Nevertheless, some rare complications can be serious, like seizure, splenic rupture and line thrombosis for healthy volunteer donors. Table 1. Baseline characteristics of study subjects with and without sickle cell trait Variable Sickle cell trait subjects Control subjects P-value Age, years 17.08 (9.09) 19.41 (8.63) 0.056 Gender, M/F 6/6 6/6 Weight, kg 57.93 (34.54) 63.31 (30.03) 0.548 CMV status 1/11 0/12 0.317 White cell count, 10 9 /L 6.33 (2.04) 6.03 (2.24) 0.609 Hemoglobin, g/dL 13.23 (1.39) 13.29 (1.50) 0.900 Platelet count, 10 9 /L 301.25 (95.73) 320.08 (57.60) 0.534 Abbreviation: CMV = cytomegalo virus. Values are given as mean (s.d.). Table 2. Comparison of adverse events between the sickle cell trait and non- sickle cell trait donor groups Variable Sickle cell trait group Control group P-value Nausea and vomiting 0 0 a Bone pain 1 2 0.56 Chest pain 0 0 a Bleeding 0 0 a Splenic rupture 0 0 a Seizures 0 0 a Infection 0 0 a Transfusion 0 0 a Carpal-tunnel 0 0 a Parasethsia 1 0 0.32 Headache 3 2 0.65 Myalgia 0 1 0.32 a Could not be estimated. 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