ORIGINAL ARTICLE
Hematopoietic progenitor cell mobilization and harvesting in children
with malignancies: do the advantages ofpegfilgrastim really translate
into clinical benefit?
E Merlin
1,2,3, S Zohar
4, C Je´roˆme
5, R Veyrat-Masson
3,6, G Marceau
3,6, C Paillard
1,2,3, A Auvrignon
7,
P Le Moine
8, V Gandemer
9, V Sapin
3,6, P Halle
1,2,3, N Boiret-Dupre´
3,6, S Chevret
4, F Deme´ocq
1,2,3,
C Dubray
1,2,3and J Kanold
1,2,31CHU Clermont-Ferrand, Centre Re´gional de Cance´rologie et The´rapie Cellulaire Pe´diatrique, Hoˆtel-Dieu, Clermont-Ferrand, France; 2Inserm, CIC501, Clermont-Ferrand, France;3Clermont Universite´, Univ Clermont1, Faculte´ de Me´decine, Clermont-Ferrand, France; 4U717 Inserm, De´partement de Biostatistiques et Informatique Me´dicale, Hoˆpital Saint-Louis, Paris, France;5Institut Cance´rologique de la
Loire, Service de Pe´diatrie, St Etienne, France;6CHU Clermont-Ferrand, Laboratoires d’He´matologie et de Biochimie, Hoˆtel-Dieu,
Clermont-Ferrand, France;7
Hoˆpital Trousseau, Service d’He´matologie et d’Oncologie Pe´diatrique, Paris, France;8
Hoˆpital des Enfants, Unite´ d’He´mato-Oncologie, Brest, France and9
CHU Rennes, He´matologie Pe´diatrique, Rennes, France
Our purpose was to assess success rates in children of achieving optimal hematopoietic progenitor cells (HPCs) harvest after mobilization with 300lg/kg pegfilgrastim. Between January 2005 and January 2007, 26 children with solid malignancies who were referred for HPC collection were consecutively included. Hematopoietic progenitor cell mobilization consisted ofone s.c. injection of300lg/kg body weight (BW) ofpegfilgrastim. The success criterion was defined as at least 5 106 CD34þ cells/kg during the first standard apheresis (less than 3 blood volumes processed (BVP)). After 26 inclusions, the Bayesian analysis gave a mean estimated success rate of 60.7% (95% credibility interval: 42.0–78.0%). The first apheresis allowed the collection of8.3 106 CD34þ cells/kg BW (range 0.6–37.8), with a median of2.8 BVP (range 1.4–3.0). Overall, the median ofCD34þ cells collected was 12.4 106/kg (range 2.7–37.8). The cumu-lative dose ofanthracyclin was the only variable associated with the total number ofCD34þ collected cells (Po0.05). Mobilization was clinically well tolerated in 20 patients. No drug-related adverse events ofgrade X3 occurred. We conclude that a single injection of 300lg/kg pegfilgrastim in the hematological steady state is an efficient and well-tolerated method of HPC mobilization in children with solid malignancies.
Bone Marrow Transplantation (2009) 43, 919–925; doi:10.1038/bmt.2008.412; published online 22 December 2008 Keywords: children; mobilization; G-CSF
Introduction
Mobilization of hematopoieticprogenitor cells (HPCs) with G-CSF alone in the hematological steady state offers notable advantages of ease of planning, patient comfort and a reduced number of hospital visits and blood tests. To date, G-CSF at 10 mg/kg/d remains the standard regimen in children, although recent data suggest that increasing and splitting the dosage of G-CSF into twice-daily doses is more efficient.1 However, this strategy requires more s.c. injections and does not allow the collection of an optimal number of HPCs in a single apheresis for all children.2In our experience,1,3 an optimal graft (containing at least 5 106 CD34þ cells/kg) was achieved after 4 days of mobilization and with one apheresis (including large volume) in 48/120 patients (40%, 95% confidence interval (CI): 31–49) after mobilization with G-CSF at 10 mg/kg/d for 4 days (four injections) and in 17/32 patients (53%, 95% CI: 36–71) after twice-daily dosage (2 12 mg/kg/d) for 4 days (eight injections). With this last regimen, despite the use of large-volume apheresis, two other teams failed to achieve this optimal value in a single apheresis in more than 50% of children.2,4 Thus, finding more efficient well-tolerated strategies remains desirable.
Pegfilgrastim is a PEG-conjugated form of r-metHuG-CSF (recombinant methionyl human G-r-metHuG-CSF, filgrastim, Amgen, Thousand Oaks, CA, USA) with an increased serum half-life (from 4 up to 33 h) due to decreased renal elimination. Early studies in healthy donors and adult patients showed that pegfilgrastim mobilized HPC effi-ciently, with the notable advantage of only a single dose administration being necessary instead of multiple s.c. injections.5–7In children, the data on pegfilgrastim are very limited and refer to the prevention and treatment of chemotherapy-induced neutropenia and chemo-induced stem cell mobilization.8–11
The objective of this phase IIA study was to evaluate the percentage of children achieving steady-state mobilization
Received 31 July 2008; revised 6 October 2008; accepted 11 November 2008; published online 22 December 2008
Correspondence: Dr J Kanold, Centre Re´gional de Cance´rologie et The´rapie Cellulaire Pe´diatrique, Hoˆtel Dieu, CHU, BP 69, 11, boulevard Le´on-Malfreyt, Clermont-Ferrand 63003, France.
E-mail: jkanold@chu-clermontferrand.fr
&2009 Macmillan Publishers Limited All rights reserved 0268-3369/09$32.00 www.nature.com/bmt
of HPCs using pegfilgrastim, that is, an optimal harvest of 5 106 CD34þ cells/kg in one standard apheresis (p3 blood volumes processed (BVP)) after a single injection of 300 mg/kg pegfilgrastim.
Patients and methods Patients
Children with solid malignancies who were referred to our center for HPC collection for autologous BMT were consecutively invited to enter this phase IIA open-label, single-center prospective study (clinical trials NCT 00695370). Pre-collection treatments and subsequent trans-plants were carried out in the original hospitals. Entry criteria were: age 0–18 years, solid malignancy, Lansky score 470%, more than 17 days since the beginning of the last chemotherapy cycle and an ANC 41 109/l with no administration of any hematopoieticgrowth factor in the previous 8 days. Exclusion criteria were clinical or biological conditions precluding the mobilization or collection procedure. The study protocol was approved by the Comite´ pour la Protection des Personnes (CPP Sud Est 6), the Institutional Review Board of Auvergne. Informed written consent was obtained from all the children’s parents and, where possible, from the children themselves before their enrollment.
Mobilization and collection regimens
Hematopoietic progenitor cell mobilization consisted of one s.c. injection of 300 mg/kg body weight (BW) of pegfilgrastim (Amgen) without exceeding 12 mg. The choice of the dose was based on data published earlier regarding non-conjugated and pegylated G-CSF.5 To date, the standard regimen of non-conjugated G-CSF for post-chemotherapy mobilization is 5 mg/kg/d. In the steady state, this dose is suboptimal and the standard dose is 10 mg/kg/d. Moreover, a benefit in increasing the dose up to 24 mg/kg/d has been strongly suggested in children. As far as pegfilgrastim is concerned, after chemotherapy the dose of 100 mg/kg has been proposed on the basis of several studies showing that a dose of 100 mg/kg of pegfilgrastim is comparable to a daily administration of 5 mg/kg filgrastim in terms of neutrophil recovery.12 Hence, in the steady state, there is a rationale for increasing this dose in order to target stem cell mobilization. In healthy volunteers, pharmacokinetic studies have shown that the dose of 300 mg/kg is well tolerated and more efficient than 100 mg/kg for CD34þ cell mobilization.5 We therefore assumed that increasing the dose of pegfilgrastim would be safe and more efficient in children with malignancies, as in healthy adults.
Apheresis was started at day 3 after pegfilgrastim administration if a value of 20 CD34þ /ml cells was present in the blood, or as soon as the level exceeded 10 CD34þ cells/ml blood after day 3. Apheresis was continued daily for up to four consecutive collections until the required number of cells (set by each patient’s own clinician) was achieved. Apheresis was performed using a Cobe Spectra separator (Gambro BCT, Bourg-la-Reine, France) as described
elsewhere.13 The patient’s total blood volume was calcu-lated as follows: 80 ml/kg in children aged less than 2 years and 75 ml/kg in older ones.
Evaluation during the study
All clinical and biological data were recorded by the same investigator, with particular attention being paid to previously reported adverse events related to filgrastim or pegfilgrastim administration.14 Evaluation comprised pa-tient history, physical examination, complete blood count with differential reticulocytes and highly fluorescent re-ticulocytes, complete blood chemistry, lacticodehydrogen-ase, uricemia and liver functional tests on day 0 and from day 2 to day 11. For the first 13 patients, G-CSF serum concentration was measured (ELISA, Quantikine Human G-CSF Immunoassay Kit, R&D Systems, Inc., Minneapo-lis, MN, USA).15 In accordance with French recomme-ndations, abdominal ultrasonography was planned in cases of hyperleukocytosis 470 109/l or clinical splenomegaly. In the case of symptomatic hyperleukocytosis or clinically threatening splenomegaly, an anticipated leukapheresis was planned. The CD34þ cell count was determined as prescribed by the International Society for Hematotherapy and Graft Engineering guidelines.16Functional assessment of HPC was carried out as described earlier.17After SCT, neutrophil engraftment was defined as achieved on the first of three consecutive days with a neutrophil count X0.5 109/l after the post transplant nadir. Plt engraft-ment was defined as occurring on the first of five consecutive days with a plt count X20 109/l without plt transfusions.
Statistical design and analysis
The aim of this trial was to assess the success rate in patients of achieving an optimal HPC harvest defined as at least 5 106 CD34þ cells/kg during the first standard apheresis (less than 3 BVP). The primary motivation for this sequential Bayesian strategy18,19 was to provide a formal means of summarizing patient outcome by a single binary event (success or failure). It allowed continuous monitoring of outcomes throughout the trial, and thus was expected to be more efficient in protecting patients from ineffective treatment.20 We used our experience with mobilization of HPCs in children by using an informative opinion before the beginning of the trial, which was formalized as a prior distribution of the success rate centered on 30%. As the patient outcomes in the trial were recorded, the subsequent distribution of the outcome probability under experimental treatment was computed by applying Bayes’ theorem, which yielded a mean estimated success rate with a 95% credibility interval (measure of Bayesian precision). Also, on the basis of this subsequent distribution, early stopping criteria were calculated to allow early termination of the trial: (i) stop for inefficacy if the estimated success rate was unacceptably low compared with the expected rate of 0.3, or (ii) stop for futility if the expected gain from further inclusions in the reliability of the estimated success rate was low (p0.05).
Univariate and multivariate analyses were performed to identify independent predictors of the day on which
mobilization kinetics peaked. In the univariate analysis, the variables considered were age, height, body mass index, body area, plt count on day 0, neutrophil blood count on day 0, previous radiotherapy and prior anthracyclin administration. Owing to the small sample size, only the two most significant variables in the univariate analysis were considered in the multiple analysis model.
Statistical analyses were performed using R software (version 2.4, The R Development Core Team). P-values o0.05 were considered significant.
Results
Patient characteristics
Between 1 January 2006 and 1 January 2008, 33 children were consecutively referred to our center for HPC collection. Four declined to enter the study. Three received pegfilgrastim before achieving 1 109/l ANC after che-motherapy and were not included. The characteristics of the 26 patients included are shown in Table 1.
Mobilization and collection
Sixteen of twenty-six patients met the success criterion. This means that X5 106CD34þ cells/kg were collected in the first three BVP (representing one standard apheresis). After 26 inclusions, the Bayesian analysis gave a mean estimated success rate of 60.7% (95% credibility interval: 42.0– 78.0%). The stopping criterion associated with inefficacy was not met, the probability that the success rate was lower than 30% after 26 inclusions being estimated at 0.0005. The predictive probability of observing two or more successes in the next five patients was 90%. Finally, the stopping criterion based on no significant gain (o0.05) from the next five inclusions, taking into account the width of the
credibility interval (the precision), recommended stopping after the inclusion of 26 patients.
Blood and graft compositions are shown in Table 2. The first apheresis allowed the collection of 8.3 106CD34þ cells/kg BW (range 0.6–37.8) in a median of 2.8 BVP (range 1.4–3.0). The median value of CD34þ cells collected in one BVP was 3.0 106CD34þ cells/kg BW (range 0.4–14.3). Overall, the median number of CD34þ cells collected/kg was 12.4 106 (range 2.7–37.8). The cumulative dose of anthracyclin was the only parameter associated with the total number of CD34þ cells collected (Po0.05).
Ten patients did not meet the success criterion. A graft of 2.7 106CD34þ cells/kg was collected in one apheresis in a very low-weight child (6.2 kgs), and the clinician considered a second apheresis unnecessary. Nine patients needed a second (n¼ 7) or supplementary (n ¼ 2) apheresis to achieve the optimal graft of 5 106CD34þ cells/kg; six of them achieved this objective. Three heavily pre-treated patients had a final graft of less than 5 106CD34
þ cells/ kg (2.8, 3.7 and 4.3 106CD34þ cells/kg, respectively, in three, three and four apheresis).
Kinetics of mobilization
The kinetics of mobilization are shown in Figure 1. In all the patients, the CD34þ level rose from day 2 (31/ml
Table 1 Patient characteristics at mobilization (n¼ 26) Characteristic Quantity
No. of patients 26
Age (years), median (range) 7.1 (1.6–16) Weight (kg), median (range) 19.3 (6–78) No. of chemotherapy cycles, median (range) 3.5 (2–10) Previous radiotherapy 6 Diagnosis Neuroblastoma 7 Nephroblastoma 1 CNS 8 HD/NHL 3/2 Sarcoma/other 3/2
No. of weeks from diagnosis, median (range) 16 (6–332) Disease status
CR1/PR1/NR1 3/14/3
1st relapse/CR2/PR2 3/2/2
PR3 1
BM involvement at diagnosis 7 Abbreviations: CNS¼ central nervous system; HD ¼ Hodgkin’s disease; NHL¼ non-Hodgkin’s lymphoma; NR ¼ non-response.
All patients were treated according to the protocols of the SIOP/SFCE (French Society of Pediatric Oncology) between 2002 and 2007.
Table 2 Characteristics of the hematopoietic progenitor cells mobilization and harvest
Characteristic Median
Pre-apheresis blood count
WBC 109/l, median (range) 39 (9.0–114)
Mononuclear cells (%), median (range) 15 (6–37) Plt count 109/l, median (range) 186 (24–342)
CD34+ blood count 106
/l, median (range) 68 (10–353) Hemoglobin count (g/l), median (range) 12.1 (9–13.7) CFU-GM 103
/ml, median (range) 19.5 (2.4–39.0) BFU-E 103/ml, median (range) 18.1 (3.8–32.9)
First apheresis
No. BVP, median (range) 2.8 (1.4–3.0) Progenitor cells collected
CD34+ 106/kg, median (range) 8.3 (0.6–37.8)
CD34+/kg/BVP 106
/kg, median (range) 3.0 (0.4–14.3) CD34+/l processed 106, median (range) 37 (5–181)
CFU-GM 105
/kg, median (range) 17.5 (2–59.5) BFU-E 105/kg, median (range) 16.3 (1.1–56.9)
Graft composition
Plt count 109/l, median (range) 1235 (172–8381)
Leucocytes 109
/l median (range) 198 (39–527) Monocytes % median (range) 35 (11–71) Lymphocytes % median (range) 21 (4–59) Collection efficiency % median (range) 53 (30–92) No. of children with X5 106CD34+/kg (%) 16/26
Overall collection CD34+ cells 106
/kg, median (range) 12.4 (2.7–37.8) No. of apheresis, median (range) 2 (1–4) No. of BVP, median (range) 3.6 (2–9) No. of children with X5 106CD34+/kg (%) 22/26
CD34+/kg/BVP 106/kg, median (range) 3.2 (0.4–14)
Abbreviations: BVP¼ blood volume processed.
Collection efficacy (CE) was calculated as follows: CE¼ total CD34 þ cell count in apheresis product/(pre-apheresis blood CD34þ cell count processed blood volume).
E Merlin et al
blood, range 2–149) to day 3 (80/ml, range 6–353), with a median peak value of circulating CD34þ cells ranging from 15 to 777/ml, (median 80/ml, mean 135/ml). At day 3, six patients had less than 20 CD34þ cells/ml blood, whereas at day 4 all patients had at least 10 CD34þ cells/ml blood. The peak was observed on day 3 in 10/26 patients, and later in 16/26 patients (on day 4 in 13 patients and on day 5 in 3 patients). In univariate analysis, the day of the peak tended to be influenced by age (P¼ 0.06), height (P¼ 0.06), body mass index (P ¼ 0.05), body area (P¼ 0.05) and plt count on day 0 (P ¼ 0.06), but not by absolute neutrophil blood count on day 0 or prior anthracyclin administration.
The median total white blood count rose to a maximum level on day 3 (39.3 109/l, range 9.0–113.8) and decreased to normal on day 11 (6.79 109/l, range 5.3–14.2). The absolute and relative peaks of lymphocytes (1.95 109/ l¼ 4% of leukocytes), monocytes (4.02 109/l¼ 7% of leukocytes) and highly fluorescent reticulocytes
(21 109/l¼ 11% of reticulocytes) were observed on day 3. Reduced plt counts occurred in 16/26 patients before the first apheresis (median 9%, max 41% compared with day 0), but they never required transfusion. After mobilization and collection, the start of the following chemotherapy cycle was on day 35 (range 31–42) of the previous cycle. To assess whether the mobilization could affect hematological toxicity of the ensuing chemotherapy round, we looked at the duration of chemo-induced neutropenia after the prior and subsequent rounds for the 12 patients who received similar courses before and after mobilization. Subsequently, there was a 2-day increase in the chemo-induced neutropenia duration (o0.5 109/l) compared with similar earlier cycles (Po0.05).
Safety
Mobilization was clinically well tolerated in 20 patients. No drug-related adverse events of grade X3 occurred. Eleven adverse events of gradep2 occurred in eight patients: mild fever (4), nausea or anorexia (3), myalgias (1) and mild bone pains (1). Two patients showed asymptomatic splenomegaly (2 cm). No patient had symptomatic hyper-leukocytosis; two patients had a peak of leukocytes higher than 100 109/l on day 2 (127 and 110 109/l, respectively) that returned to normal levels by day 10. All patients had increased plasma levels of lacticodehydrogenases, from 1.3 to 3.1 times the normal upper limit. Five patients had asymptomatichyperuricemia, up to 520 mmol/l (normal: o300 mmol/l).
Pharmacokinetics
The pharmacokinetic study was performed on the first 13 patients (Figure 2) and then stopped because of logistical issues. On day 0, G-CSF serum concentrations were undetectable in all but one patient (endogenous secretion). The maximal serum concentrations ranged from 172 to 1410 ng/ml on day 2 (median 724, mean 738). On day 7, G-CSF serum concentrations were undetectable in all patients. Serum G-CSF level on day 2 correlated with the CD34þ cell peak level (R2¼ 0.535, Po0.005).
Hematopoietic engraftment kinetics after high-dose chemotherapy and SCT
At the time of writing this paper, 21 procedures of myeloablative regimen followed by HPC reinfusion had 0 20 40 60 80 100 120 0 20 40 60 80 100 120 0 10 20 30 40 50 60 70 0 2 4 6 8 10 12 14 16 18 WBC ANC Monocytes Lymphocytes 0 5 10 15 20 25 30 35 Day of mobilization Monocytes -lymphocytes (x 10 9 /l) CD34 HFR BFU-E CFU-GM WBC –ANC (x 10 9/l) CD34/µl x10 3/ml HFR x 10 9 /ll 0 1 2 3 4 5 6 7 8 9 10 11 0 1 2 3 4 5 6 7 8 9 10 11 0 1 2 3 4 5 6 7 8 9 10 11
Figure 1 Kinetics of differential blood count and hematopoietic pro-genitor cell mobilization induced by pegfilgrastim in the hematological steady state. Twenty-six children with solid malignancies received one s.c. injection of 300 mg/kg pegfilgrastim on day 0 for mobilization. Data are shown as median±25th percentile. HFR: highly fluorescent reticulocytes; BFU-E: burst-forming erythroid; CFU-GM: colony-forming unit-granulocyte-macrophage. 400 0 200 600 800 1000 1200 1400 Day of mobilization Serum G-CSF (ng/ml) 0 2 3 4 5 6 7 9
Figure 2 G-CSF serum concentrations during mobilization (n¼ 13 patients). All patients received 300 mg/kg pegfilgrastim on day 0, in hematological steady state. Data are shown as mean±s.d.
been performed. The number of CD34þ cells reinfused was 4.5 106 CD34þ cells/kg BW (1.2–12.9). Four patients received a CD34þ immuno-selected graft. Nine of the twenty-one children received non-conjugated G-CSF from day 1 post-reinfusion to neutrophil recovery. The total ANC recovered by day 11 (median, range 9–22) and plt recovery was achieved by day 15 (median, range 8–49). Long-term data were available for six patients (median follow-up 440 days, range 75–797). The hematological values of these children are shown in Table 3.
Discussion
Although the optimization of HPC mobilization is parti-cularly desirable in children, little research has been performed in this field. Here, we report the first published data on HPC mobilization by pegfilgrastim in children with malignancies in the hematological steady state. With non-conjugated G-CSF, dose increase and splitting have been suggested to provide better mobilization compared with the standard regimen of non-conjugated G-CSF at 10 mg/kg/d.2,4 However, in these series, the success criterion of 5 106 CD34þ cells/kg BW was met ino50% of patients, despite the use of large-volume aphereses. This can be compared with our results (60.7% of success, credibility interval 42–78%). Furthermore, with the high dose of pegfilgrastim, all our patients reached the level of 10 CD34þ cells/ml blood (including heavily pre-treated patients), and none was denied apheresis because of insufficient mobilization. This was not the case in our experience of G-CSF at 2 12 mg/kg/d, wherein 2/32 patients failed to achieve this threshold level. Although this difference is not significant, this could suggest that high-dose pegfilgrastim may be of benefit in heavily pre-treated patients. With pegfilgrastim, the optimal graft of 5 106 CD34
þ cells/kg was finally obtained in 22/26 patients. A graft of 10 106 CD34þ cells/kg was collected from 17/26 patients, with 9/26 achieving this level with a single leukapheresis (p3 BVP). Hence, many arguments strongly suggest that one injection of 300 mg/kg pegfilgrastim is at least as efficient as non-conjugated G-CSF for HPC mobilization in the hemato-logical steady state.
This high efficiency is probably due to the fact that the serum G-CSF rises quickly and markedly after the injection, and remains elevated up to the third day.5 BM
stimulation is immediately maximal, as shown by the fact that the ANC does not increase between day 2 and day 3. As a result, the kinetics of pegfilgrastim-induced CD34þ cell mobilization look slightly different. Although with one daily dose of conventional G-CSF the peak number of peripheral blood CD34þ cells occurs at day 4 or day 5,3 the maximum cell concentration after pegfilgrastim admin-istration was reached on day 3 or day 4. As apheresis was started on day 3 for 21 patients, these data do not necessarily reflect the natural mobilization kinetics and have to be considered cautiously. To determine the natural kinetics of mobilization in children with malignancies would imply mobilization without performing an apheresis, and this would be considered unethical. Thus, the kinetics we describe represent the actual clinical situation but not the true natural kinetics of mobilization, as healthy volunteers were used. After the peak level of PBPC is achieved, the cell concentration decreases gradually up to day 5. Hence, in practice, we chose to plan the first apheresis on day 3 if a value of 20 CD34þ /ml cells were present in the blood, which allowed a second worthwhile leukapheresis on day 4 when the blood level of CD34þ cell was still high, if necessary.
In healthy volunteers and donors, in contrast to post-chemotherapy mobilization,12 pegfilgrastim efficacy is strongly dose-dependent in terms of CD34þ cell mobiliza-tion.5,21 In patients with malignancy, the drawback to increasing the dose of pegfilgrastim is that it leads to sustained BM stimulation, which could delay chemother-apy. In adults, high serum concentrations of G-CSF up to 12 days after a pegfilgrastim injection have been reported in the context of the reduction of chemotherapy-induced neutropenia.22Consequently, there is a significant risk that cycling cells may be exposed to chemotherapy, resulting in secondary neutropenia. The situation is quite different in the context of the hematological steady state. As pegfil-grastim is essentially metabolized by polynuclear cells, a high ANC provides a faster decrease in this exposure.5In our patients, G-CSF serum concentrations declined dra-matically after the third day following injection, and were undetectable by day 7. It is of note that we found a slight increase in chemo-induced neutropenia duration after mobilization. As the benefit of avoiding a few s.c. injections could be questioned if this led to prolonged neutropenia, it is important to determine whether this increase exists with high doses of unconjugated G-CSF.
Table 3 Long-term hematological follow-up after myeloablative regimen and stem cell reinfusion
Characteristic 6 months 12 months 18 months
No. of evaluable patients 6a 5a 3a
WBC 109
/l, median (range) 4.7 (2.9–12.9) 4.1 (2.7–14.1) 6.6 (2.9–7.8) ANC 109/l, median (range) 3.2 (1.7–10.6) 2.4 (1.4–6.5) 4.8 (1.7–6.3)
Lymphocytes 109
/l, median (range) 0.62 (0.54–1.03) 0.94 (0.54–5.96) 0.97 (0.67–1.05) Monocytes 109/l, median (range) 0.50 (0.24–1.03) 0.65 (0.27–1.27) 0.49 (0.34–0.66)
Hb g/100 ml, median (range) 10.9 (10.3–12.3) 12.1 (8.5–13.6) 11.7 (10.3–14.7) MCV fl, median (range) 90 (89–104) 90 (88–92) 90 (89–92) Plts 109/l, median (range) 130 (65–250) 131 (83–175) 130 (91–175)
Abbreviations: MCV¼ mean corpuscular volume.
a
One patient received craniospinal radiotherapy after BMT.
CE¼ total CD34 þ cell count in apheresis product/(pre-apheresis blood CD34 þ cell count processed blood volume).
E Merlin et al
Owing to the small size of the pediatricpopulation, and as the outcome is achieved soon after inclusion, the sequential Bayesian approach offered the best means of conducting this phase IIA trial in a reasonable time. We determined the prior distribution of the success rate, centered on 30%, based on our experience and on two historical cohorts of children who received non-conjugated G-CSF at 10 mg/kg/d or at 2 12 mg/kg/d for mobilization. In these cohorts, the success rates were 48/120 (40%, 95% CI 31–49%) and 17/32 (53%, 95% CI 36–70%), respec-tively. If another threshold had been chosen, the trial would not have been interrupted, and the retrospective response means for prior means of 40 and 50% would have been 60.8% (42.1–78%) and 61.1% (42.1–78.2%), respectively. If 10 additional patients had been included in the trial, the probability of observing more than four responses would have been 81%, and the probability of observing more than five responses would have been 63.6%. Using these predictive probabilities to calculate a stopping rule for futility of further inclusions allowed us to recommend trial cessation after 26 patients. However, we acknowledge that it is a small sample and that larger comparative studies are needed.
Moreover, the small size of our study requires that the short- and long-term safety of receiving such a high dose of hematopoietic growth factor be confirmed. If any adverse event arises after pegfilgrastim injection, it is impossible to stop the mobilization process, in particular, in cases of hyperleukocytosis. We would like to point out that in our series two patients had 4100 109/l leukocytes. Although none of them showed clinical symptoms, this could be a concern and larger studies in the future should address this possible serious side effect. In our experience of children who received G-CSF at 10 or 20 mg/kg/d, no such increase was reported.23However, these levels were observed with G-CSF administered at 2 12 mg/kg/d.4Splenicrupture has been reported in adults as a potential adverse event following pegfilgrastim injection,24but some similar events were reported earlier with non-conjugated G-CSF.25 The long-term risk of myelodysplasia or selection of a clone has been shown after intensive chemotherapy in ALL, G-CSF being an independent risk factor.26In the context of solid tumors, the role of G-CSF remains unclear. In mobiliza-tion, this theoretical risk could be amplified by the increased dosage of G-CSF, but this remains hypothetical. Given these results, we have adopted this scheme of HPC mobilization in a situation in which a large quantity of cells is required, or in heavily pretreated patients, and provided that the next treatment can be slightly delayed. One approach to reducing this delay could consist of injecting a reduced dose of pegfilgrastim earlier after prior che-motherapy, and adjusting the dose on the ANC. Also, the simplicity of using pegfilgrastim allows the individuali-zation of treatment, with the possibility of a non-conjugated G-CSF boost if necessary.
In conclusion, this study shows that a single injection of 300 mg/kg pegfilgrastim in the hematological steady state is an efficient, well-tolerated method of HPC mobilization in children. Given the small and heterogeneous patient cohort and the lack of an appropriate control, we cannot state that pegfilgrastim is more efficient than unconjugated G-CSF.
However, the combination of predictable mobilization kinetics, a good acceptance profile and an efficacy that appears at least as good as with unconjugated G-CSF, offer several interests for the HPC mobilization process in children. This justifies large randomized clinical trials to investigate whether the use of pegfilgrastim will translate into clinical benefit for children with cancer. Our data may aid the design of such studies.
Acknowledgements
This work was supported by the Comite´ De´partemental du Puy-de-Doˆme de la Ligue Nationale Contre le Cancer. We thank C Cailliot (Amgen, France) for his advice, and the nursing staff of the Unite´ Bioclinique de The´rapie Cellulaire: Annick Collard, Raymond Eglizot, Vale´rie Herve´, Caroline Lallemand and Anne Laverroux for their excellent assistance in collections and children’s care.
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E Merlin et al
