Blood, 1 October 2001, Vol. 98, No. 7, pp. 2272-2274
BRIEF REPORT
Presence of N regions in the clonotypic DJ rearrangements of the
immunoglobulin heavy-chain genes indicates an exquisitely short latency
in t(4;11)-positive infant acute lymphoblastic leukemia
Karin Fasching,
Simon Panzer,
Oskar A. Haas,
Arndt Borkhardt,
Rolf Marschalek,
Frank Griesinger, and
E. Renate Panzer-Grümayer
From the Children's Cancer Research Institute, St Anna
Kinderspital, and Clinic for Blood Group Serology, University of
Vienna, Austria; the Department of Pediatric Hematology/Oncology,
Justus Liebig Universität, Giessen, Institute of Pharmaceutical
Biology, University of Frankfurt; and the Department of
Hematology/Oncology, University of Göttingen, Germany
 |
Abstract |
Childhood acute lymphoblastic leukemia (ALL) is frequently
initiated in utero at a time of developmentally regulated insertion of
N regions into the DJH rearrangements of immunoglobulin
heavy-chain (IgH) genes. Here it is shown that N regions
are present in the clonotypic DJH rearrangements in 11 of
12 infant ALLs with t(4;11). These data are compared with the 122 previously published DJH sequences and were found to have a
pattern similar to that of ALL in children older than 3 years at
diagnosis but were unlike that in children younger than 3 years who
predominantly lack N regions. These findings, therefore, indicate that
t(4;11)-positive infant ALL is initiated later in fetal development
than most B-cell precursor ALL from children younger than 3 years and
that they have a shorter latency period already in utero.
(Blood. 2001;98:2272-2274)
© 2001 by The American Society of Hematology.
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Introduction |
Childhood acute lymphoblastic leukemia (ALL) is a
heterogeneous group of leukemias with a predominance of the B-cell
precursor (BCP) phenotype. A minority of these leukemias is associated
with a translocation involving the mixed-lineage leukemia
(MLL) gene on chromosome 11q23 that is fused, in 50% of
patients, to the AF4 gene on chromosome 4q21.1
The chromosomal translocation t(4;11)(q21;q23) occurs mostly in infant
ALL and confers a dismal prognosis in this age group, whereas in older
children and adults the prognosis does not differ from t(4;11)-negative
cases.2,3 Differences in the chromosomal breakpoints of
the MLL gene between infants and children or adults with
t(4;11) ALL suggest different mechanisms for the development of these
instances of ALL4 and, thus, their different
biologic functions.
Greaves5 proposed a 2-step model for the development of
ALL with an initiating event in utero, followed by a second mutation leading to overt leukemia. Indeed, leukemia-specific chromosomal translocations and clonotypic antigen-receptor gene rearrangements at
birth recently confirmed the initiation of childhood ALL in utero.6-9 Thus, depending on the time of clinical
manifestation, the latency period varies among the different types of
leukemia. In contrast to leukemias with long latency periods for which
a chromosomal translocation and additional postnatal mutations are required,9 the extremely short latency periods in infant
ALL (with MLL rearrangements) suggest only limited further
mutagenic requirements.1 It seems likely that not only
postnatal but also prenatal development of the disease is rapid.
Assuming that the gene fusion resulting from t(4;11) in infant ALL is
indeed an initiating event, its origin must be restricted to a period
between the beginning of B lymphopoiesis in the fetal liver
ie, the
6th gestational week10and possibly a few months before
the diagnosis of leukemia.11 This translocation is assumed to occur in a cell that has already started to rearrange its
IgH genes. The time period of these rearrangement processes
during fetal development can be determined by the presence or absence of N regions between the DJH joinings. The addition of N
nucleotides requires terminal deoxynucleotidyl transferase (TdT) that
is not initially present in fetal lymphopoiesis but that has been
observed by the end of the first trimester of
gestation.12-14
We therefore used the leukemia clone-specific junctional regions of
DJH rearrangements to determine the time point of a first mutation in utero in t(4;11) ALL in infancy. We show the presence of N
regions between the DJH joinings in 11 of 12 infant ALLs with t(4;11) indicating their initiation at a later time during fetal
development than most other leukemias that become apparent during the
first 3 years of life.
| |
Study design |
The occurrence of t(4;11) ALL was analyzed in 13 infants.
Inclusion criteria were patient age younger than 1 year at diagnosis and the presence of at least one clonotypic IgH
rearrangement (Figure 1). All leukemias
had a pro B phenotype with frequent coexpression of myeloid markers.
The local institutional ethical committee approved the study, and
informed consent was obtained from the parents.
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| Figure 1.
Nucleotide sequence of IgH rearrangements in t(4;11) infant
ALL.
Trimming of the rearranged segments is indicated by the numbers of
nucleotides. N nucleotides between DD segments are shown in
italics; shaded areas indicate sequence homology between 2 rearrangements.
|
|
DNA was extracted from cells by standard procedures.15
Amplification of the ret-oncogen confirmed the integrity of DNA in all
samples. Clonal IgH rearrangements were determined by
VH-family-specific and JH consensus primers
for the amplification of V(D)JH rearrangements and of
primer sets for the amplification of all incomplete DJH rearrangements, as described previously.16,17 Amplified
products were sequenced directly, and involved gene segments were
identified by BLAST sequence similarity searches
(http://www.ncbi.nlm.nih.gov/BLAST/) and by comparison with published
sequences of all known human immunoglobulin genes
(http://www.ebi.acc.uk), allowing the assignment of nucleotides to
either the V, D, and J regions or to the P and N regions by exclusion.
| |
Results and discussion |
We identified 16 IgH rearrangements in 13 infants with
t(4;11) ALL (Figure 1A). Ten leukemias had 1 rearrangement, and 3 leukemias (patients 4, 8, 10) had 2 rearrangements. We considered only
1 of the 2 rearrangements (in patients 4 and 10) because they had identical DJH regions. We excluded the DJH
rearrangement in patient 1 because the sequence between DH
and JH was homologous to the J1 pseudogene. Thus, 13 unique
rearrangements were analyzed for the inclusion of N regions. We
observed in patient 4 a D-D fusion, but only the DH
gene segment most proximal to the JH segment was included
in the analysis. As depicted in Figure 1, only 1 of the 13 unique
sequences lacked N regions at the DJH junction. The results
from this study are compared with those from 122 previously published
cases (Table 1). It appears that the lack
of N regions in t(4;11) infant ALL is less common than in children with
ALL who are younger than 3 years at diagnosis but that they are about as common as in children older than 3 years.15,18,19
Figure 1 illustrates the use of DH and JH
families, similar to that reported previously.16,18,19
The data from this study indicate that most DJH regions
from infant ALL with t(4;11) contain N nucleotides that developed at a
time of TdT activity; hence, they were more mature than those without N
regions. Interestingly, other leukemias, diagnosed in children before
the age of 3, do not have N regions in their DJH junctions15,18,19 and thus have a longer latency period
than the t(4;11) infant leukemias. There are 2 groups of BCP ALL that have N regions in their clonotypic DJH junctions, namely
t(4;11) infant ALL with a manifestation mostly in the first year of
life and other leukemias with a clinical manifestation after the 3rd year of life.18,19 Both rearrange their DJH
segments at a similar time during gestational development. It is
obvious, however, that t(4;11) ALL has a remarkably shorter latency
than the others.
We propose a model for the relation between the time of initiation of
the leukemia, characterized by the clonotypic DJH
rearrangements, and the age of the children at clinical manifestation
of BCP ALL (Figure 2). IgH
rearrangements that lack N regions occur during a narrow time
windowthe first weeks of B lymphopoiesis in fetal liver that is TdT
negative. Transformed cells with such rearrangements most likely
acquire additional mutations, leading to leukemias during the first 3 years of life. IgH rearrangements with the addition of N
nucleotides in the DJH junction occur later in gestation, when TdT has already been activated. These leukemias become clinically apparent during the first year of life if a t(4;11) chromosomal translocation started leukemogenesis or, in its absence, after the 3rd
year of life. Alternatively, the t(4;11) translocation arises in a
TdT-negative primitive cell without IgH rearrangements. This target cell may represent a B-plus myeloid lymphoid stem cell, as
described by Cumano et al20 in mouse fetal liver, which would be unique in specific stages of in utero hematopoiesis. The N
region-positive DJH rearrangement may be a later addition during progression to leukemia. Then, unrelated rearrangements are
expected, such as in t(9;22) B lymphoid blast crisis of chronic myeloid leukemia.16 However, in our series, no leukemia
had multiple unrelated IgH rearrangements, but 2 leukemias
had related rearrangements. In addition, the target cell for the
t(4;11) translocation may be a rare progenitor with TdT expression at
earlier stages of fetal lymphopoiesis than common B precursor cells. No
such cells have been identified thus far in humans.
It is assumed that a chromosomal translocation is an initiating event
in leukemogenesis,9,21 which can be induced by apoptotic stimuli that lead to the generation of gene fusions in B precursor cells, thus rescuing a cell programmed to die.22 This
assumption is supported by the findings that most IgH
rearrangements in ALL are either incomplete or not potentially
productive,16 underlining the immaturity of these cells,
which would not survive without a transformation. It is further
hypothesized that additional mutations are required for the development
of leukemia. However, our findings support the hypothesis that the
t(4;11) is either sufficient for leukemogenesis or provokes efficiently
further changes that lead eventually to leukemia in
infancy.1,11
| |
Acknowledgment |
This article is dedicated to Helmut Gadner for his 60th birthday.
| |
Footnotes |
Submitted March 2, 2001; accepted May 29, 2001.
Supported in part by the Österreichische Kinderkrebshilfe and by
a grant from the Deutsche Krebshilfe (Bo 10-124.3).
The publication costs of this
article were defrayed in part by
page charge payment. Therefore,
and solely to indicate this fact,
this article is hereby marked
"advertisement"
in accordance with 18 U.S.C.
section 1734.
Reprints: E. Renate Panzer-Grümayer, Children's
Cancer Research Institute, St Anna Kinderspital, Kinderspitalgasse 6, A-1090 Vienna, Austria; e-mail: panzer{at}ccri.univie.ac.at.
| |
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Top
Abstract
Introduction
and N+ BCP leukemias in childhood.
