Drug resistance associated properties of blasts subpopulations with different CD34 expression in childhood acute lymphoblastic leukemia (ALL)
Aim: The objective of this study was to investigate expression of drug resistance associated genes in CD34+ and CD34- leukemic subpopulations in childhood acute lymphoblastic leukemia (ALL). Methods: ALL samples with heterogeneous CD34 expression were separated into CD34-positive and CD34-negative s...
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| Опубліковано в: : | Experimental Oncology |
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| Дата: | 2011 |
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Інститут експериментальної патології, онкології і радіобіології ім. Р.Є. Кавецького НАН України
2011
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| Цитувати: | Drug resistance associated properties of blasts subpopulations with different CD34 expression in childhood acute lymphoblastic leukemia (ALL) / T.V. Shman, U.U. Fedasenka, V.P. Savitski, A.M. Kustanovich, O.V. Aleinikova // Experimental Oncology. — 2011. — Т. 33, № 3. — С. 145-149. — Бібліогр.: 35 назв. — англ. |
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Shman, T.V. Fedasenka, U.U. Savitski, V.P. Kustanovich, A.M. Aleinikova, O.V. 2018-06-19T11:00:30Z 2018-06-19T11:00:30Z 2011 Drug resistance associated properties of blasts subpopulations with different CD34 expression in childhood acute lymphoblastic leukemia (ALL) / T.V. Shman, U.U. Fedasenka, V.P. Savitski, A.M. Kustanovich, O.V. Aleinikova // Experimental Oncology. — 2011. — Т. 33, № 3. — С. 145-149. — Бібліогр.: 35 назв. — англ. 1812-9269 https://nasplib.isofts.kiev.ua/handle/123456789/138658 Aim: The objective of this study was to investigate expression of drug resistance associated genes in CD34+ and CD34- leukemic subpopulations in childhood acute lymphoblastic leukemia (ALL). Methods: ALL samples with heterogeneous CD34 expression were separated into CD34-positive and CD34-negative subpopulations and mRNA levels of MDR1, LRP , BCRP and BCL-2 genes were compared. Results: BCL-2 gene expression levels did not differ significantly between CD34+ vs CD34− subpopulations in most analyzed ALL cases. Oppositely, MDR1 gene had >two-fold differences in expression levels between subpopulations in the majority of ALL cases. In T-lineage ALL CD34− fractions had increased level of BCRP and LRP genes in comparison with CD34+ ones whereas in most of B-lineage ALL expression of these genes did not differ. Conclusion: It was not found the unique pattern of resistance related genes expression in CD34+ vs CD34− subpopulations. However, in majority of studied pediatric ALL cases with CD34 heterogeneous expression one of subpopulations (positive or negative) could have an advantage for survival through elevated expression of drug resistance related genes. We would like to thank T. Savitskaya, R. Utskevich, A. Valochnik for data on cytogenetics and fusion genes expression. en Інститут експериментальної патології, онкології і радіобіології ім. Р.Є. Кавецького НАН України Experimental Oncology Original contributions Drug resistance associated properties of blasts subpopulations with different CD34 expression in childhood acute lymphoblastic leukemia (ALL) Article published earlier |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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| title |
Drug resistance associated properties of blasts subpopulations with different CD34 expression in childhood acute lymphoblastic leukemia (ALL) |
| spellingShingle |
Drug resistance associated properties of blasts subpopulations with different CD34 expression in childhood acute lymphoblastic leukemia (ALL) Shman, T.V. Fedasenka, U.U. Savitski, V.P. Kustanovich, A.M. Aleinikova, O.V. Original contributions |
| title_short |
Drug resistance associated properties of blasts subpopulations with different CD34 expression in childhood acute lymphoblastic leukemia (ALL) |
| title_full |
Drug resistance associated properties of blasts subpopulations with different CD34 expression in childhood acute lymphoblastic leukemia (ALL) |
| title_fullStr |
Drug resistance associated properties of blasts subpopulations with different CD34 expression in childhood acute lymphoblastic leukemia (ALL) |
| title_full_unstemmed |
Drug resistance associated properties of blasts subpopulations with different CD34 expression in childhood acute lymphoblastic leukemia (ALL) |
| title_sort |
drug resistance associated properties of blasts subpopulations with different cd34 expression in childhood acute lymphoblastic leukemia (all) |
| author |
Shman, T.V. Fedasenka, U.U. Savitski, V.P. Kustanovich, A.M. Aleinikova, O.V. |
| author_facet |
Shman, T.V. Fedasenka, U.U. Savitski, V.P. Kustanovich, A.M. Aleinikova, O.V. |
| topic |
Original contributions |
| topic_facet |
Original contributions |
| publishDate |
2011 |
| language |
English |
| container_title |
Experimental Oncology |
| publisher |
Інститут експериментальної патології, онкології і радіобіології ім. Р.Є. Кавецького НАН України |
| format |
Article |
| description |
Aim: The objective of this study was to investigate expression of drug resistance associated genes in CD34+ and CD34- leukemic subpopulations in childhood acute lymphoblastic leukemia (ALL). Methods: ALL samples with heterogeneous CD34 expression were separated into CD34-positive and CD34-negative subpopulations and mRNA levels of MDR1, LRP , BCRP and BCL-2 genes were compared. Results: BCL-2 gene expression levels did not differ significantly between CD34+ vs CD34− subpopulations in most analyzed ALL cases. Oppositely, MDR1 gene had >two-fold differences in expression levels between subpopulations in the majority of ALL cases. In T-lineage ALL CD34− fractions had increased level of BCRP and LRP genes in comparison with CD34+ ones whereas in most of B-lineage ALL expression of these genes did not differ. Conclusion: It was not found the unique pattern of resistance related genes expression in CD34+ vs CD34− subpopulations. However, in majority of studied pediatric ALL cases with CD34 heterogeneous expression one of subpopulations (positive or negative) could have an advantage for survival through elevated expression of drug resistance related genes.
|
| issn |
1812-9269 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/138658 |
| citation_txt |
Drug resistance associated properties of blasts subpopulations with different CD34 expression in childhood acute lymphoblastic leukemia (ALL) / T.V. Shman, U.U. Fedasenka, V.P. Savitski, A.M. Kustanovich, O.V. Aleinikova // Experimental Oncology. — 2011. — Т. 33, № 3. — С. 145-149. — Бібліогр.: 35 назв. — англ. |
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| fulltext |
Experimental Oncology 33, 145–149, 2011 (September) 145
DRUG RESISTANCE ASSOCIATED PROPERTIES OF BLASTS
SUBPOPULATIONS WITH DIFFERENT CD34 EXPRESSION
IN CHILDHOOD ACUTE LYMPHOBLASTIC LEUKEMIA (ALL)
T.V. Shman*, U.U. Fedasenka, V.P. Savitski, A.М. Kustanovich, O.V. Aleinikova
Belarusian Research Center for Pediatric Oncology and Hematology, Minsk, Belarus
Aim: The objective of this study was to investigate expression of drug resistance associated genes in CD34+ and CD34- leukemic
subpopulations in childhood acute lymphoblastic leukemia (ALL). Methods: ALL samples with heterogeneous CD34 expression were
separated into CD34-positive and CD34-negative subpopulations and mRNA levels of MDR1, LRP , BCRP and BCL-2 genes were
compared. Results: BCL-2 gene expression levels did not differ significantly between CD34+ vs CD34− subpopulations in most
analyzed ALL cases. Oppositely, MDR1 gene had >two-fold differences in expression levels between subpopulations in the major-
ity of ALL cases. In T-lineage ALL CD34− fractions had increased level of BCRP and LRP genes in comparison with CD34+
ones whereas in most of B-lineage ALL expression of these genes did not differ. Conclusion: It was not found the unique pattern
of resistance related genes expression in CD34+ vs CD34− subpopulations. However, in majority of studied pediatric ALL cases
with CD34 heterogeneous expression one of subpopulations (positive or negative) could have an advantage for survival through
elevated expression of drug resistance related genes.
Key Words: acute lymphoblastic leukemia, CD34 heterogeneity, BCL-2, MDR1, LRP, BCRP.
In spite of substantial improvement in treatment
of childhood acute leukemia that has been achieved
during the past decades, a relapse still proves
to be a major obstacle on the way to a prolonged
complete remission [1]. Patients diagnosed with acute
lymphoblastic leukemia (ALL) and receiving treatment
in accordance with current protocols still face an ap-
proximately 20% chance of a relapse [2–5].
Minimal residual disease (MRD) monitoring
provides important information for early prediction
of a recurrence of the illness, however immunopheno-
typic modulation (shifts in immunophenotypic markers
of leukemic cells during treatment and at relapse) and
presence of several immunophenotypic subpopula-
tions provide additional difficulties for clinicians [6–7].
CD34 is a stage-specific antigen that is expressed
on human hematopoietic stem and progenitor cells
whose expression decreases with differentiation of the
cell. CD34 marker is broadly used in ALL diagnostics
and MRD monitoring [8–9]. However, it has been dem-
onstrated significant reduction of CD34 expression
during induction therapy in childhood ALL [10]. Those
phenotypic changes could be a result of drug exposure
or caused by a clonal selection during chemotherapy.
In this study we tried to elucidate if immunopheno-
typically heterogeneous subpopulations of leukemic
cells differed in expression of drug resistance related
genes in childhood ALL. Previously, some properties
of CD34+ vs CD34− leukemic subpopulations were in-
vestigated in acute myeloid leukemia (AML) samples.
It was found that predominantly CD34+ fractions were
more resistant to apoptosis, had increased expression
levels of antiapoptotic and drug resistance associated
genes/proteins compared to a corresponding CD34−
one [11–13]. Although other authors stated that during
chemotherapy CD34+ leukemic cells depleted more
rapidly than CD34− cells [14]. Therefore, the absence
of publications about “resistance associated” proper-
ties of CD34+/CD34− leukemic fractions in ALL provides
an interesting field for investigations in this area.
With regard to the facts mentioned above we stud-
ied bone marrow samples taken at diagnosis of child-
hood T- and B-lineage ALL. For an in-depth study, all
samples with heterogeneous CD34 expression were
separated into CD34-positive and negative subpopula-
tions and mRNA levels of multidrug resistance genes,
antiapoptotic gene BCL-2 were compared.
MATERIALS AND METHODS
Patients. 17 children at the median age of 10 years
(range, 1–18) with ALL were taken in this study. 11 pa-
tients were diagnosed as pro-B, common or pre-B ALL
(B-cell precursor ALL, BCP-ALL), 6 patients were
pro-/pre-T, cortical or mature T-ALL (T-lineage ALL,
T-ALL). Heterogeneous CD34 expression and suffi-
cient quantity of leukemic cells were the main criteria
for choosing samples. ALL population was considered
as heterogeneous when quantity of CD34 positive cells
was between 10–90%.
This investigation was approved by the local Insti-
tutional Ethic Committee. Characteristics of patients
are listed in Table 1.
Cell preparation. Leukemic cells of all used
samples were isolated from bone marrow by gradi-
ent density centrifugation. Information about pattern
of antigens expression was obtained from standard
three-color immunophenotyping procedure.
Cell sorting. Leukemic cells were separated into
CD34+ and CD34− fractions after CD34 PE labeling
(Becton Dickinson, San Jose, CA, USA). Additional
Received: June 27, 2011.
*Correspondence: Email — t_shman@yahoo.com
Fax: 375 (0) 17 265 42 22,
Abbreviations used: ALL — acute lymphoblastic leukemia; AML —
acute myeloid leukemia; BCP-ALL — B-cell precursor acute lym-
phoblastic leukemia; MRD — minimal residual disease.
Exp Oncol 2011
33, 3, 145–149
146 Experimental Oncology 33, 145–149, 2011 (September)
labeling and gating according to CD45 FITC fluores-
cence were used to exclude normal cells contamina-
tion. Dead cells were excluded using forward and side
scatter gating. The purity of sorted subpopulations was
always more than 98%. Gating strategy was performed
as described previously [15]. Leukemic cells sorting
were carried out using FACSVantage SE (BD).
Real-Time PCR. Total RNA from sorted cells was
extracted using Gen Elute Mammalian Total RNA
Miniprep Kit (Sigma-Aldrich, St Louis, MO, USA).
According to manufacturer’s protocol after first step
(cell lysing) samples were stored at -70 °C. When
needed, samples were thawed and RNA was extracted.
Quantity and quality of obtained total RNA were de-
fined by spectrophotometry using Gene Quant RNA/
DNA Calculator (GE Healthcare). Reaction of reverse
transcription was carried out immediately after RNA
extraction using Advantage RT-for-PCR Kit (BD) ac-
cording to the manufacturer’s protocol.
cDNA from one extraction from IM-9 cell line
was used as a standard and a calibrator for analy-
zing BCL-2, MDR1, LRP and BCRP gene expression
in leukemic bone marrow blasts where all these genes
expressed at levels comparable with those in the cell
line. Normal gene GUS was used as a loading control
gene [16].
We evaluated expression levels of experimental
genes using real-time PCR (iCycler, BioRad). For
calculating relative expression levels standard curves
method was used. Each standard curve was gener-
ated according to four points of 10-fold dilutions
of cDNA obtained from IM-9 cell line. Amplifications
were carried out in a total volume of 25 μl containing
cDNA, Platinum Quantitative PCR SuperMix-UDG
(Invitrogene, Carlsbad, CA, USA, final concentration
of MgCl2 was raised to 4mM), 300nM of forward and
reverse primer, and 200nM of TaqMan probe. The
following primers were used (5' to 3'): BCL-2 forward
primer: TTG GCC CCC GTT GCT T, reverse primer: CGG
TTG TCG TAC CCC GTT CTC, TaqMan probe: FAM AGC
GTG CGC CAT CCT TCC CAG BHQ1; MDR1 forward
primer: AGG AAG ACA TGA CCA GGT ATG C, reverse
primer: CCA ACA TCG TGC ACA TCA AAC, TaqMan
probe: FAM CCT GGC AGC TGG AAG ACA AAT ACA
CAA BHQ1; LRP forward primer: CAG CTG GCC ATC
GAG ATC A, reverse primer: TCC AGT CTC TGA GCC
TCA TGC, TaqMan probe: FAM CAA CTC CCA GGA AGC
GGC GGC BHQ1; BCRP forward primer: TGG CTG TCA
TGG CTT CAG TA, reverse primer: GCC ACG TGA TTC
TTC CAC AA, TaqMan probe: FAM AGC AGG GCA TCG
AGC TCT CAC CCT G BHQ1.
Quantitative analysis of TEL-AML1 fusion gene
expression in CD34+ and CD34- leukemic fractions
was estimated with DNA-standards (Ipsogen, France)
according to protocol of Gabert J. et al. [17] and nor-
malized to GUS expression [16].
Statistical analysis. Student’s test for paired
samples was applied to determine significance of dif-
ferences between CD34+ and CD34- populations.
RESULTS
Bone marrow leukemic samples with heteroge-
neous expression of CD34 were separated into CD34+
and CD34− fractions by fluorescent activated cell
sorting. Characteristics of patients included in this
investigation are listed in Table1. Median values
of CD34 positive leukemic cells for all selected patients
was 50 % (from 14 to 80 %).
Table 1. Patient Characteristics
Patient
№ Age ALL CD34,
% Heterogeneous markers Fusion
gene
1 2 BCP 70 CD45, CD13 Negative
2 <1 BCP 48 CD15 MLL-AF1p
3 5 BCP 58 CD5, CD117 Negative
4 8 BCP 50 CD20, CD33 Negative
5 16 BCP 22 CD33, CD11b Negative
6 2 BCP 33 CD45, CD10, CD19 TEL-AML1
7 2 BCP 34 CD45, CD20, CD15 TEL-AML1
8 6 BCP 59 DR, CD20, CD13, CD10, CD15 TEL-AML1
9 15 ВCP, relapse 46 DR Negative
10 3 BCP 70 CD20 TEL-AML1
11 15 BCP 46 DR, CD20,CD15 MLL-AF4
12 15 Т, relapse 80 CD13, CD11b Negative
13 15 Т 14 CD8, CD13, TdT SIL-TAL
14 13 Т 58 CD1a Negative
15 16 Т 67 CD4 Negative
16 14 Т 54 CD8, CD3, CD13, CD10,
CD117, CD1a, TdT
Negative
17 10 Т 47 CD4, CD3, CD117, CD33,
CD11b, TdT,
Negative
Previously we described apoptosis and prolifera-
tions differences in small groups of childhood ALL and
AML samples [15]. Here expression levels of BCL-2,
MDR1, LRP and BCRP genes were analyzed in CD34+/
CD34− subpopulations of childhood ALL. Differences
in expression level of genes between studied subpopu-
lations in ≥two-fold we considered as significant when
differences <two-fold were accounted as insignificant.
In general, in BCP-ALL group we found no evident
trend to higher expression levels of any studied genes
in CD34+ or CD34− fractions. In particular, BCL-2 gene
expression levels to be higher in CD34+ cells vs CD34−
cells only in 1 out of 11 samples (patient 1). Whereas
in 2 out of 11 samples (patients 7, 8) expression lev-
els of BCL-2 were higher in CD34− cells, and in eight
samples (73%) we found expression levels of this
gene in CD34+ and CD34− subpopulations to be not
significantly different (Fig. 1, a).
Higher expression levels of MDR1 gene in CD34+
vs CD34− cells was registered in 3 out of 11 samples
(patients 3, 4, 6). However, in 4 out of 11 samples
we registered lower expression level of MDR1 in CD34+
fraction. In four samples (36%) expression levels
of MDR1 gene did not exceed two-fold difference
(Fig. 1, B).
BCRP expression levels in CD34+ cells was higher
in 1 out of 11 samples (patient 1); in 2 out of 11 samples
(patient 2, 3) its expression in CD34+ subpopula-
tion was lower; and eight samples (73%) we found
no difference (figure 1C). For all BCP-ALL patients
expression levels of LRP gene did not exceed two-fold
difference between CD34+ and CD34− subpopulations
(figure 1D).
In T-ALL group differences in genes expression
between CD34+ and CD34− subpopulations are rep-
Experimental Oncology 33, 145–149, 2011 (September) 147
resented in Fig. 2. Antiapoptotic gene BCL-2 in 1 out
of 6 samples (patient 17) had >two-fold higher ex-
pression in CD34− than CD34+ fraction while in other
five samples we found negligible difference between
fractions (figure 2a).
0
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Fig. 1. Expression levels of BCL-2 (a), MDR1 (b), BCRP (c) and
LRP (d) genes in CD34+ and CD34- leukemic subpopulations
in BCP-ALL
100
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CD34+ CD34-
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Fig. 2. Expression levels of BCL-2 (a), MDR1 (b), BCRP (c) and
LRP (d) genes in CD34+ and CD34- leukemic subpopulations
in T-ALL
Expression levels of MDR1 gene in samples
from T-ALL group were significantly higher compar-
ing to BCP-ALL group. For T-ALL samples median
values of MDR1 expression for CD34+ and CD34−
were 60.4 (range, 13.2–2384.0) and 117.2 (range,
6.3–967.2) arbitrary units respectively, while it were
2.7 (range, 0.16–15.3) and 3.6(range, 0.06–26.4) for
CD34+ and CD34− subpopulations for BCP-ALL cases.
In 3 out of 6 samples (patients 12, 13, 15) MDR1 gene
was expressed at higher levels in CD34+ cells than
in CD34− cells and in 2 samples (patients 14, 16) it was
expressed at lower levels in CD34+ cells; one sample
had no two-fold difference.
Interestingly, for all T-ALL cases LRP gene was
expressed in higher level in CD34− leukemic fractions
than CD34+ ones. For patients 13, 14 and 16 differenc-
es in LRP expression levels between CD34− vs CD34+
were 2.7, 3.9 and 2.3 fold respectively. BCRP gene
levels were higher in CD34− cells than CD34+ cells
in 5 out of 6 samples, for three of them differences
between CD34+ vs CD34− cells were >two-fold.
Then we supposed that genetic alterations in leu-
kemic cells could lead to a specific pattern of expres-
sion of investigated genes in CD34+ vs CD34− leuke-
mic fractions. TEL-AML1 fusion gene was detected
in four leukemic samples. It was found out that for all
four samples CD34+ leukemic fractions had higher
level of TEL-AML1 expression, however parameters
of genes expression were revealed in a variable extent
(from no difference to > two fold difference) in CD34+/
CD34− leukemic subpopulations.
DISCUSSION
Currently it is evident that tumor tissues are com-
posed of heterogeneous combinations of cells with
different phenotypic characteristics, proliferation
potentials, self-renewal ability, etc. [18]. In this work
we made an attempt to investigate biologic proper-
ties of CD34− and CD34+ leukemic cells with respect
to a more “resistant phenotype” and a better chance
of surviving during chemotherapy.
Apoptosis is an important mechanism that regu-
lates survival of leukemic cells. It was described that
an intact apoptosis signaling was important for effi-
cient induction and maintenance of remission in child-
hood precursor B-cell ALL [19]; a relapse in childhood
ALL was associated with decreased BAX/BCL-2 ratio
and loss of spontaneous caspase-3 processing in vivo
[20]. BCL-2 protein plays a critical role in inhibiting
anticancer drug-induced apoptosis, constitutive over-
expression of BCL-2 is one of mechanisms of drug
resistance in cancer [21]. Previously we described
a decreased ability to apoptosis of CD34+ leukemic
cells than CD34− fraction [15]. Such difference in apop-
tosis levels between subpopulations can be a result
of different expression of BCL-2 gene. However, here
our data did not reveal any considerable difference
in BCL-2 gene expression between CD34+ vs CD34−
fractions for BCP-ALL and for T-ALL.
Multidrug resistance phenotype is usually associ-
ated with efflux of anticancer agents from cells leading
to a decreased drug accumulation. The role of MDR1,
BCRP, LRP genes / proteins in drug resistance in leu-
kemia has been studied for years, however, the prog-
nostic role of these proteins in childhood ALL remains
controversial [22–25].
Earlier, associations between expression of drug
resistance associated genes/proteins, antiapop-
totic BCL-2 and CD34 expression were frequently
described for AML patients [26–29]. However, these
correlations were found rarely in ALL samples [23,
148 Experimental Oncology 33, 145–149, 2011 (September)
30–31]. Our results demonstrated that in the majority
of B-lineage ALL cases CD34+/CD34− leukemic frac-
tions did not differ in expression of BCRP and LRP
genes. On the other hand, for all analyzed T-lineage
ALL samples CD34- leukemic fractions had increased
level of BCRP (from 1.2 to 8.1 fold) and LRP (from
1.2 to 3.9 fold) genes in comparison with CD34+.
In the majority of patients with BCP- (7/11) and T-ALL
(5/6) expression of MDR1 gene had >two-fold differ-
ence between subpopulations, however increased
MDR1 gene expression was detected in CD34+ as well
as in CD34− subpopulations. However recently it was
described that expression of CD34 was associated
with elevated MDR1 and MRP1 mRNA expression
levels, but not LRP in pediatric T-ALL [32].
Investigations of drug resistance properties of sub-
populations became especially interesting in the light
of new data that in childhood ALL blasts at all stages
of immunophenotypic maturation have stem cell
properties (ability to engraft and reconstitute leukemia
in NOD/SCID mice) [33]. Normal hematopoietic and
leukemic stem cells possess several characteristics
that protect them from potential insults through the
expression of ATP-associated transporters [34–35].
Therefore, we summarized all data comparing genes
expression levels in CD34+ vs CD34− leukemic fractions
obtained from children with BCP-ALL and T-ALL. Con-
ditionally we admit that if leukemic subpopulation
(CD34+ or CD34−) had > two fold higher level at least
of one of analyzed genes it means that this subpopu-
lation possess “resistant” properties. Thus, we sepa-
rated all analyzed cases into groups with “resistant”
CD34+ cells, “resistant” CD34− cells, a group of cases
with both subpopulations showed signs of a “resistant”
phenotype and a group that showed no difference
between two subpopulations (Table 2).
Table 2. Comparison of “resistant” properties CD34+ vs CD34− leukemic
subpopulations
BCP-ALL
n=11
T-lineage ALL
n=6
Only CD34+ subpopulation had resis-
tant properties
Patients 1, 4, 6 Patient 15
Only CD34− subpopulation had resis-
tant properties
Patients 2, 7, 8,
9, 10, 11
Patients 14,
16, 17
CD34+ and CD34− subpopulations had
resistant properties
Patient 3 Patients 12, 13
No difference between CD34+ and
CD34− subpopulations
Patient 5 0
According to our assumption, it was found that
both studied subpopulations showed indications
of a resistant phenotype. Among of all analyzed cases
only one sample (5.9%) revealed no difference in re-
sistance associated features between cells with high
and low CD34 expression. In 3 out of 17 cases (17.6%)
both subpopulations displayed signs of a “resistant”
phenotype. Surprisingly, only in 4 out of 17 ALL cases
(23,5%) CD34+ cells had more pronounced resistance
properties. Finally, in 9 out of 17 cases (52,9 %) CD34−
subpopulation had properties of a resistant phenotype.
In conclusion, it was not found the unique pat-
tern of resistance related genes expression in CD34+
vs CD34− subpopulations however, in majority of stud-
ied pediatric ALL cases with CD34 heterogeneous ex-
pression one of subpopulations (positive or negative)
could have an advantage for survival through elevated
expression of drug resistance related genes. Further
investigation is required to elucidate reasons and pat-
terns of such distinctions between subpopulations.
ACKNOWLEDGMENTS
We would like to thank T. Savitskaya, R. Utskevich,
A. Valochnik for data on cytogenetics and fusion genes
expression.
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