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Blood, Vol. 91 No. 12 (June 15), 1998:
pp. 4472-4479
Fetal Hemoglobin and F-Cell Responses to Long-Term Hydroxyurea
Treatment in Young Sickle Cell Patients
By
Micheline Maier-Redelsperger,
Mariane de Montalembert,
Antoine Flahault,
Maria Grazia Neonato,
Rolande Ducrocq,
Marie-Pierre Masson,
Robert Girot, and
Jacques Elion for the French Study Group
on Sickle Cell Disease
From the Service d'Hématologie Biologique, Hôpital
Tenon, Paris, France; Unité INSERM U 458, Hôpital Robert
Debré, Paris, France; the Centre de Transfusion Sanguine,
Hôpital Necker-Enfants Malades, Paris, France; and Unité
INSERM 444, Hôpital Saint Antoine, Paris, France.
 |
ABSTRACT |
We have studied the cellular and molecular responses to long-term
hydroxyurea (HU) treatment in 29 severely affected young patients with
sickle cell disease (mean age, 10.9 ± 4.1 years). Patients received
HU at 20 mg/kg/d on 4 consecutive days per week initially, with a
monthly escalated dose avoiding marrow-toxicity (mean steady-state
dose, 34.2 ± 4.6 mg/kg/d) for 12 to 36 months (mean duration, 22 months). The studied parameters were hemoglobin F (HbF), F
reticulocytes (F retics), F cells, the amount of HbF per F cell (F/F
cell), polymer tendency at 40% and 70% oxygen saturation, and
hemolysis. Initial HbF (Fi) was dispersed (from 0.85% to 13.9%). HbF
increased in all patients but 1. HbF at maximal response (Fmax) reached
a sustained level varying from a 1.5-fold to a 16-fold Fi after a
variable delay (6 to 24 months). Fmax was not related to HU dosage, but
 F (Fmax  Fi) was strongly correlated to MCV (MCVmax MCVi).
HbF increase resulted from the increase of both F cells and F/F cell.
In this rather short series, Fi and Fmax were not significantly
associated with age, gender, or  -globin haplotype. Neither Fmax nor
F was related to bone marrow reserve, as measured by baseline
reticulocyte or neutrophil counts. However, Fmax was highly dependent
on Fi. When patients are individualized into three groups according to
Fmax (group 1, Fmax >20% [12 patients]; group 2, 10% < Fmax < 20% [11 patients]; group 3, Fmax <10% [5 patients]), Fi is
significantly different between groups, being the highest in group 1. In addition, the best responders (group 1) were significantly different
from patients in the two other groups with higher levels of total
hemoglobin, decreased bilirubin, and decreased polymer tendency.
| |
INTRODUCTION |
SICKLING OF RED BLOOD cells in sickle
cell disease (SCD) is the consequence of a single amino acid
substitution in the -globin chain (6Glu Val) that is
responsible for the polymerization of the abnormal hemoglobin S (HbS)
upon deoxygenation.1-3 The extent of polymer formation at
any oxygen saturation is primarily dependent on the total intracellular
hemoglobin concentration and on the respective percentages of S and
non-S hemoglobins within the cell.4,5 Non-S hemoglobins,
such as hemoglobins A (HbA), A2 (HbA2), or F (HbF), influence the
polymerization process, because they reduce the intracellular HbS
concentration and because mixed hybrids with HbS and HbF (or A2) do not
enter the polymer.5-9 This last property makes HbF the most
potent inhibitor of deoxyHbS polymerization.
Accordingly, many approaches to develop therapies for SCD10
have focused on preventing polymerization by the use of pharmacological agents that increase the production of HbF.11 Among the
various drugs proposed within the last years to improve the clinical
course of SCD, hydroxyurea (HU)12 seems to be the most
effective and has now been tried in large multicentric series of adult
patients.13 After a double-blind trial enrolling 299 adults
patients, it appeared that HU significantly reduced the frequency of
painful crises, acute chest syndrome episodes, and blood transfusion
requirements. These promising results in adult patients, associated
with the absence of toxic effects or malignancies observed during
long-term HU administration in a series of young patients with cyanotic congenital heart disease,14 encouraged us to investigate
this treatment in young SCD patients. We present here data concerning a
phase II therapeutic assay performed over 3 years in a cohort of 29 young SCD patients to appreciate if HU could stimulate HbF production
without inducing clinical or hematological toxicity. This cohort
included a large majority of children and teenagers belonging to a
first generation of African immigrants, usually of homogeneous ethnic
background. Beside the clinical follow-up, which supported the efficacy
of HU in reducing painful events,15 attention was focused
on the evolution of HbF expression and the related cellular parameters,
F reticulocytes (F retics) and F cells, measured at 3-month intervals,
and the expected effects of those variables on polymer formation and
rate of hemolysis. In addition, we studied different factors that might
predict the response to HU to guide this therapy.
| |
MATERIALS AND METHODS |
Patients
Twenty-nine young homozygous SCD patients (21 males and 8 females) were
selected for this study from the clinics of centers belonging to the
French Study Group on Sickle Cell Disease. The age range was 4 to 19 years (mean age, 10.9 ± 4.1 years). One child was less than 5 years
of age, 10 were between 5 and 10 years of age, 10 were between 10 and
15 years of age, and 8 were more than 15 years of age. Diagnosis of SCD
was established for each individual on the basis of hemoglobin
electrophoresis and family studies. To be eligible, patients had to
have reported at least three painful crises necessitating an
hospitalization in the precedent year. Exclusion criteria were renal
insufficiency (creatinine clearance <120 mL/min/1.73 m2),
hepatic insufficiency (ALAT >5N, or chronic hepatic disease), iron
deficiency or current iron supplementation, hypersplenism, human
immunodeficiency virus infection, or a past history of frequent and
severe infections. Patients for whom a monthly follow-up seemed difficult to ensure were excluded. The necessity to avoid pregnancy was
explained to older girls, and contraceptive pills were prescribed when
necessary. The storage of frozen sperm was proposed to mature boys.
Patients were treated with HU for 12 to 36 months (mean duration of the
treatment, 22 months) according to a previously published
protocol16: 20 mg/kg/d on 4 consecutive days per week
initially, with a monthly increase of 5 mg/kg/d in absence of
myelotoxicity (maximum, 40 mg/kg/d). Myelotoxicity was defined as a
20% decrease in hemoglobin levels, less than 2.5 × 109 neutrophils/L, less than 150 × 109
platelets/L, or less than 100 × 109 reticulocytes/L.
Temporary cessation of treatment was prescribed if reticulocytes
decreased below 50 × 109/L, neutrophils below 1.5 × 109/L, or platelets below 100 × 109/L, until normalization of the parameters occurred.
Stopping treatment was prescribed if the ALAT value had increased
twofold or if the creatinine value was more than 30% of the initial
value. The protocol was approved by the Ethics Committee of the
Hôpital Necker-Enfants Malades. Fully informed parents had to
give their written consent. The patients were regularly observed and
blood samples were obtained before the administration of HU and every
month during the treatment to supervise the good tolerance to the
treatment.
Laboratory Studies
The quarterly biological follow-up included a complete blood count and
the determination of the erythrocyte indices using the H*1 hematology
analyzer (Bayer Corp, Tarrytown, NY), a reticulocyte count performed
after methylene blue supravital stain, and the determination of HbF, F
retics, and F cells.
HbF was quantified by a high performance ion-exchange liquid
chromatography (HPLC) procedure.17 F retics and F cells
were determined by an immunofluorescent assay, as previously
described.18 The amount of HbF per F cell (F/F cell) was
calculated using the following ratio: (mean cell hemoglobin content × HbF)/F cells. The tendency of F cells and non-F cells toward
intracellular polymerization was calculated from the total
intracellular hemoglobin concentration and the percentages of HbS, HbF,
and HbA2 at 40% and 70% oxygen saturation values, which correspond to
the physiologically relevant region of oxygen
saturation.19-21 Total bilirubin was measured. The
-globin gene cluster haplotype and the  -gene number were assessed
once during the initial weeks according to previously reported
methods.22
Statistical Analysis
Because the sample size was too small to apply parametric tests,
nonparametric statistical procedures were used, allowing us to compare
groups of patients without any assumption on the distribution of
variables. Comparisons of parameters, before HU and at the time of HbF
maximal response, were performed by using the Wilcoxon signed test,
with a level of significance (P) set at .05 (two-tailed
formulation). Comparisons between more than two groups of patients,
either at baseline or at the time of HbF maximal response, were
performed by using the Kruskal-Wallis test, with a level of
significance (P) set at .05 (two-tailed formulation). Comparisons between males and females for pretreatment HbF and maximal
HbF were performed using the Mann-Whitney test. Different factors
reported to be important in determining HbF levels were analyzed by
simple linear regression. Regression coefficients and P values
are provided in the Results.
| |
RESULTS |
Patients
Follow-up varied from 12 to 36 months (mean duration, 22 months). Four
cessations of treatment were observed. HU was discontinued in 2 children considered to have failed to respond to treatment: in the
first case after 6 months and in the second case after 2 years,
although improvement had been initially observed. One child moved from
the area. A girl developed a systemic lupus syndrome 1 year after
having been included in the protocol and HU therapy was stopped. In our
series, 20 patients were homozygous for one of the three common
-globin haplotypes (Senegal [n = 3], CAR or Bantu [n = 8], and
Benin [n = 9]), 3 were heterozygous CAR-Benin, 1 was atypical, and 5 were undetermined. Determination of -globin genotype was performed
in 19 patients: 14 had 4 -genes, 4 had 3 -genes, and 1 had 2 -genes. Based on the initial F retics, 6 of the 8 girls could be
classified as LL for the X-linked FCP locus23; only 1 was
HL and 1 was HH. Initial F retics were available for 11 boys, and all
were L.
Hematological Data
Table 1 shows the mean hematological
response of the cohort before HU, yearly during the treatment, and at
the time of HbF maximal response. At that time, an increase in
hemoglobin level of more than 1 g/dL was observed in 11 patients.
Overall, the increase of the mean hemoglobin level was significant,
from 8.4 ± 1.2 before HU to 8.9 ± 1.1 g/dL (P = .03). This increase was associated with an increase in the mean cell
volume (MCV) from 84.5 ± 10.1 to 101.4 ± 13.4 fL (P < .001). MCV values were not correlated to HU dosage. The reticulocyte
count decreased significantly from 417 ± 214 to 229 ± 129 × 109/L (P < .001). A significant decrease
was observed in the neutrophil count from 7.2 ± 2.9 to 4.2 ± 2.6 × 109/L (P < .0005). The platelet count
also decreased from 393 ± 170 to 340 ± 114 × 109/L, but this decrease was not significant.
HbF Production
Variations in HbF.
Table 1 summarizes the mean HbF response of the cohort before HU,
yearly during the treatment, and at the time of HbF maximal response.
Initial HbF levels (Fi) before treatment were dispersed (from 0.85% to
13.9%). Fi values were highly correlated to MCV (r = .57, P = .002). Female patients (n = 8) had a higher mean Fi than
males (n = 21: 6.1% ± 5.1% v 3.5% ± 2.1%), but this
difference was not significant. Mean Fi values for Senegalese, Benin,
and CAR homozygous patients were 5.5% ± 0.8%, 3.3% ± 1.6%,
and 4.3% ± 4.1%, respectively, but these differences were not
significant. In this series, Fi was not correlated to age.
An increase in HbF was consistently observed in all the patients except
1 (treatment was stopped for this patient). The variations of HbF
percentages are presented in Fig 1.
Individual data for all the patients are represented in Fig 1A, which
shows the great variability of response from patient to patient. To
better illustrate the various types of response described below, eight
of these curves were selected and are shown in Fig 1B.
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| Fig 1.
HbF response during treatment with HU. Data for all the
patients (A). Data for 8 selected patients representative of the
various types of response to HU (B).
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At the time of the patients' HbF maximal response, HbF reached an
absolute level (Fmax) varying from 3.3% to 36.2% (patient no. 1 in
Fig 1B reached an Fmax of 34.7%). From patient to patient, this
represented a variable increase of Fi, from 1.5-fold (patient no. 3 in
Fig 1B) to 16-fold (patient no. 5 in Fig 1B). Eighteen patients
achieved at least a twofold increase of Fi at 3 months and 8 patients
at 6 months. Two patients achieved a twofold increase after 6 months,
with their HbF increase being 1.5- and 1.8-fold, respectively, at 6 months (patient no. 3 in Fig 1B). The delay to reach Fmax was variable,
from 6 months (patients no. 7 and 4 in Fig 1B) to 18 months (patient
no. 2 in Fig 1B) and even 24 months (1 case) of treatment. For that
matter, patients no. 7 and 8 are interesting to compare, because they
reached the same sustained Fmax value, but at very different times (6 and 15 months, respectively). In some cases, HbF values reached a
plateau after 6 months (patient no. 7 in Fig 1B) or were still
increasing after 12 months (patient no. 2 in Fig 1B). The slope of HbF
increase was not predictive of Fmax (see patients no. 6 and 7) and was not correlated to age. Once the peak of maximal HbF value was reached,
most of the time, HbF stabilized at a lower level, except for 5 patients for whom the maximal HbF value was sustained (patients no. 8, 7, 4, 3, and 2 in Fig 1B).
Fmax was not correlated to the maximum HU dosage, but it was correlated
to MCVmax (r = .56, P = .002). Similarly,  F (Fmax Fi) was strongly correlated to MCV (MCVmax MCVi)
(r = .62, P = .0007). Fmax was not related to
reticulocyte, neutrophil, or platelet initial values, but it was highly
correlated to initial F retics (r = .63, P = .003). It
was not correlated to age, gender, or -globin haplotypes. Because
the vast majority of the patients belonged to the L (boys) or LL
(girls) phenotype concerning the FCP locus, no conclusion can be drawn
from our series as to the potential influence of this locus on HbF
response. Similarly, the number of patients for whom the -globin
gene status was determined was too small to conclude on its eventual
influence.
We chose arbitrarily 10% and 20% Fmax levels to individualize three
groups of patients: group 1, whose Fmax were greater than 20%; group
2, whose Fmax were greater than 10% but lower than 20%; and group 3, whose Fmax remained less than 10%. HbF variation from Fi to Fmax for
each individual in these three groups is shown in
Fig 2. Noticeably, the 20% level (group 1)
was reached by 12 patients in a delay varying from 6 to 15 months. Nine
of them had a pretreatment HbF value greater than 4%. The 10% level
(group 2) was reached by 11 patients. Five patients did not reach the 10% level (group 3) and 4 of them had an initial HbF value less than
2%. Comparisons between the three groups were performed for all the
parameters that were found to be significantly different before HU and
at the time of Fmax on the whole cohort analysis (Table 2). Pretreatment hemoglobin levels,
MCV values, and reticulocyte counts were not significantly different
from one group to another. However, Fi values were significantly
different between the three groups (P = .005). At the time of
HbF maximal response, significant differences were observed between the
three groups for hemoglobin levels (P = .004) and MCV values
(P = .03). From pretreatment to the time of HbF maximal
response, the reticulocyte count decreased by 55%, 37%, and 25% for
groups 1, 2, and 3, respectively, but these differences are not
significant. Within each group, significant variations were observed
from pretreatment to the time of HbF maximal response for total
hemoglobin, MCV, reticulocytes, and HbF for group 1; MCV,
reticulocytes, and HbF for group 2; and MCV and HbF for group 3 (see
Table 2 for details). Considering the whole series, the average
bilirubin level decreased from a pretreatment value of 40.4 ± 24.8 mg/L to 33.3 ± 20.2 mg/L at the time of HbF maximal response
(P = .07). But when this parameter was analyzed within each of
the three groups, a significant decrease was only observed for group 1 (Table 2).
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| Fig 2.
HbF response (from initial HbF to maximal HbF) in
patients divided in three groups, according to a 10% and 20% maximal
HbF level.
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Variations in cellular parameters.
Table 1 shows the mean values of F cells, F/F cell, and F retics before
HU, yearly during treatment, and at the time of HbF maximal response.
An increase of these parameters was constant, but it was very variable
from patient to patient both in terms of kinetics and of the maximal
levels achieved. F cells exhibited a 1.2- to 5.1-fold increase of the
pretreatment value and F retics a 1.5- to 7.4-fold increase. Reaching a
plateau at 6 months was frequent but not constant. Statistical analysis
showed that HbF levels were highly correlated to both F cells
(r = .95, P < .0001) and F/F cells (r = .77, P < .0001) before treatment and also at the time of HbF
maximal response with a similar level of significance. Considering F
cells, the highest values at the time of HbF maximal response were
observed for the patients with the lowest pretreatment values of F
cells (Fig 3). Variations in cellular
parameters were studied according to the -globin haplotypes. The
values were higher in Senegalese patients as compared with CAR and
Benin patients, but in a nonsignificant way (data not shown).
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| Fig 3.
Fold-increase of F cell percentages at the time of HbF
maximal response as a function of initial values of F cells (F cells at
HbF maximal response/initial F cells).
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The study of the cellular parameters before HU and at the time of HbF
maximal response were studied in the three groups defined above (Table
2). Because these groups have been defined on the value of Fmax, F
cells, F/F cell, and F retics were understandably different between the
three groups at the time of maximal HbF response. But a significant
difference in the values of these three parameters was also observed
between the groups before treatment, in agreement with the difference
in Fi. Within each group, significant variations were observed from
pretreatment to the time of HbF maximal response for F retics, F cells,
and F/F cell for groups 1 and 2, but not for group 3 (see Table 2 for
details).
Polymer Formation at Different Oxygen Saturations
In the F-cell population, the rate of polymer tendency
decreased significantly during the treatment in all cases (except 1; Table 2). At 40% oxygen saturation, calculated values were 0.28 ± 0.07 (0.16 to 0.42) and 0.20 ± 0.04 (0.13 to 0.30) before HU and at
the time of HbF maximal response respectively (P < .0003). At
70% oxygen saturation, calculated values were 0.05 ± 0.05 (0.00 to 0.17) and 0.01 ± 0.02 (0.00 to 0.07) before HU and at
the time of HbF maximal response, respectively (P < .003).
Considering groups 1, 2, and 3, neither pretreatment values nor values
at the time of HbF maximal response were significantly different from
one group to another (Table 2). A decrease in polymer tendency at 40%
and 70% oxygen saturation during treatment occurred for all three
groups of patients, but the decrease was significant only for group 1 (P = .01 and P = .02). In the non-F-cell
population, no variation of polymer tendency was observed as predicted
from the lack of changes in HbF levels.
| |
DISCUSSION |
Contrasting with the large body of data concerning the use of HU in
adult patients, including the multicentric series,13 only a
few pediatric trials have been reported to date in the United
States,24 Belgium,25 and France,15
respectively. These reports deal mostly with global HbF response,
clinical benefit, and tolerance. We report data here concerning the
cellular and molecular parameters of the response to HU, including
variations of F retics, F cells, F/F cell, and polymer tendency in the
F-cell population, in 29 patients of the French cohort.
Two parameters can be used to describe HbF response: (1) the rate of
HbF increase and (2) the maximal value achieved. We find that both
parameters are highly variable; thus, their accurate evaluation depends
both on the size of the series and on the duration of follow-up. Here,
29 young patients have been observed for periods varying from 12 to 36 months (average, 22 months), as compared with 6 months of follow-up of
25 patients in the Belgian series25 and a 6 to 39 months
(average, 24 months) of follow-up of 13 patients in the American
series.24 We find that the maximal level of HbF is not
reached at 6 months for 68% of the children and only after 12 months
for 14% of them. In addition, we find that the HbF value at 6 months
is not predictive of the maximal achieved value.
Once the peak of maximal HbF value is reached, HbF stabilized at a
slightly lower level, except for 5 patients for whom the maximal HbF
value was sustained. The plateauing of HbF at 2 or 3 years of HU
contrasts with Steinberg's observation in adults,26 who
shows that only half of patients have a sustained increase of HbF after
2 years of HU treatment. Whether HbF response under HU is better in
children than in adults is an hypothesis that may be suggested on
another issue: a fourfold increase of HbF level is observed in the two
series that include the youngest children (Ferster's series [children
2 to 22 years of age]25 and our series [children 4 to 19 years of age]), whereas a twofold increase is only observed in
Scott's series, which includes older children (children 10 to 17 years
of age).24 Furthermore, a negative relationship was found
between the age and the slope of HbF increase in de Montalembert's
series,15 which includes the patients of the series studied
here and also 6 additional children, most of them very young. However,
comparison between series is difficult, because we used a different
drug dosing than Scott and Ferster. We can nevertheless observe that
our mean steady state dose was 34.2 ± 4.6 mg/kg administered 4 days/wk, equivalent to a weekly dose of about 136 mg/kg and thus very
close to the steady-state weekly doses administered by Ferster (140 to
175 mg/kg) and Scott (160 mg/kg). Still, it is important to consider that HbF response to the treatment was highly variable. At the time of
HbF maximal response, HbF increased 1.5- to 16-fold. We found no
correlation between HU dosages and maximal HbF values. However, F
(Fmax Fi) was strongly correlated to MCV (MCVmax MCVi), which might be a better index of the overall pharmacological effect of the HU treatment.
Alternatively, response variability might be related to other factors
such as genetic background23,26 or bone marrow reserve. Females values were higher than males values, but in a nonsignificant way. The patients with SCD observed in France include a large majority
of children belonging to a first generation of African immigrants,
usually of homogeneous ethnic background and indeed most of our
patients were homozygous for 1 of the 3 common -globin haplotypes.
Thus, it constitutes a population of choice to investigate a potential
effect of the haplotype. In this series, we found that neither initial
nor maximal HbF was correlated with -globin haplotype. This may be
in contradiction with some results of the literature,27 but
the size of the series might be too small, most particularly for
patients with the Senegal haplotype. Similarly, our series is not large
enough to evaluate an eventual effect of the -globin gene status on
the response to HU. We did not find any correlation between F (Fmax Fi) and baseline reticulocyte or neutrophil counts, which have
been proposed to reflect the bone marrow reserve, ie, the capacity of
the marrow to withstand moderate doses of HU with acceptable
myelotoxicity.27 The number of myelotoxic episodes in our
series was clearly lower than that reported in Steinberg's
series.27 It was actually limited to three episodes defined
according to our criteria15: one was a neutropenic episode
(neutrophils, 1.3 × 109/L), one a thrombopenia
(platelets, 90 × 109/L), and the third one a
reticulopenia (reticulocytes, 80 × 109/L). This may
be related either to the modified schedule of administration that we
used (4 days/wk instead of daily) or to a better hematological tolerance of the drug in children. In this short pediatric series, there was no correlation between myelotoxic events and HbF increase, suggesting that perhaps marrow reserve does not influence HbF response
in children.
However, we found a clear relation between Fmax and Fi. Indeed, when we
divide the patients in three groups according to the Fmax levels, based
on the assumption that this parameter is the most relevant to the
expected clinical benefit,28-32 then all the Fi-related
parameters in the three groups are significantly different. In
contrast, these three groups are indistinguishable on the bases of
initial hematological and hemolysis parameters. This finding also
contrasts with Steinberg's observation in adults,27 who found no association between HbF response and baseline HbF levels. At
the time of HbF maximal response, group 1 (that with the maximal response, HbF >20%) is clearly singled out. All the HbF-related parameters are at the highest, including F retics. As a result, polymer
tendency is reduced and so is total bilirubin. In accordance, total Hb
is increased and reticulocyte count is low. This decrease in polymer
tendency agrees with Bridges's results that HU increases HbS
polymerization delay time.33
We find that Fi were correlated to the two parameters F cells and F/F
cell. In agreement with the data of Charache et al,34 we
find that HbF increase during HU treatment resulted both from the
increase of F cells and F/F cell and thus might proceed from cellular
as well as molecular mechanisms. When the factor of increase of F cells
from the initial value is determined at the time of the patients' HbF
maximal response, we find that the highest values are achieved for the
patients exhibiting the lowest pretreatment values of F cells. This
observation contrasts with our result that the best responders (group
1) are those with the highest Fi. However, this finding may be an
indirect effect of the sensitivity of the method of detection. Indeed,
when scoring F cells, cells containing amounts of HbF just below the
threshold of detection are naturally scored with non-F cells and minor
variations in HbF production during treatment may be sufficient to
shift the distribution of these cells across the
threshold.35,36In conclusion, our data tend to support the
fact that response to HU treatment in young patients is better than in
adults, because we observed only one nonresponder. It results in a HbF
level that is sustained at a level slightly lower than the HbF maximal
value. We find that the HbF response in children is dependent on the initial HbF value but not, as observed in the adults, on the bone marrow reserve. The best responders form a group that distinguishes clearly from the others, with higher Hb levels, decreased bilirubin, and decreased polymer tendency. Our study was focused on the parameters of HbF response to HU treatment. Given the fact that HU clearly has
pleiotropic effects, other parameters will have to be studied before a
clear correlation could be established between the clinical and
biological response to treatment. These additional factors will be
likely to provide further insights into the polygenic modulation of HU
response and to generate more definitive predictive markers of the
robustness of the response and of the ultimate clinical utility.
| |
FOOTNOTES |
Submitted August 12, 1997;
accepted February 6, 1998.
Supported in part by Grants No. 494011 from the Institut National de la
Santé et de la Recherche Médicale (INSERM), Grant No.
950075 from the Délégation à la Recherche Clinique de
l'Assistance Publique-Hôpitaux de Paris, and Grant No.
TS3*-CT93-0244 from the European Union.
Address reprint requests to Micheline Maier-Redelsperger,
Service d'Hématologie Biologique, Hôpital
Tenon, 4, rue de la Chine, 75970 Paris Cedex 20, France.
The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" is accordance with 18 U.S.C. section 1734 solely to indicate this fact.
| |
ACKNOWLEDGMENT |
The authors thank Dr Dominique Labie for her critical reading of this
manuscript and her constant support.
| |
APPENDIX |
Investigators of the French Study Group on Sickle Cell Disease: F. Bernaudin, Service de Pédiatrie, Centre Hospitalier
Intercommunal, Créteil; M. Belloy and M. Benkerrou, Centre de la
Drépanocytose, Hôpital Robert Debré, Paris; R. Mardini and N. Philippe, Service d'Hématologie, Hôpital
Debrousse, Lyon; M. Hunault, Service d'Hématologie,
Hôpital Hotel Dieu, Paris; F. Gouraud, Service d'Hématologie, Hôpital Trousseau, Paris; T. Cynober,
Laboratoire d'Hématologie, Hôpital Bicêtre, Le
Kremlin Bicêtre; D. Bachir, Centre de la Drépanocytose,
Hôpital Henri Mondor, Créteil; J. Vedrenne, Service de
Pédiatrie, Centre Hospitalier, Fontainebleau; J. Lorilloux,
Service de Pédiatrie, Hôpital Delafontaine, Saint Denis; C. Olivier, Service de Pédiatrie, Hôpital Louis Mourier, Colombes.
| |
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Abstract
Introduction
Abstract