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Department of Demyelinating Disease and Aging, National Institute of Neuroscience, National Center of Neurology and Psychiatry, Tokyo, Japan
| Abstract |
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82) of expanded
clones defined by single-strand conformation polymorphism clonotype. To
estimate the Ag specificities of dominant clonotypes in the activated T
cells, these samples were examined in parallel with Th1 T cell clones
specific for myelin basic protein or proteolipid protein (PLP) derived
from the same patients. Analysis of two patients demonstrated that the
dominant clonotypes would contain those specific for myelin basic
protein or PLP. Although the majority of the clonotypes could be
detected only transiently, a PLP95116-specific clonotype was found to
persist for over 1 yr. Thus, single-strand conformation polymorphism
clonotype analysis allows us to monitor the kinetics of given T cell
clones in vivo and could provide useful information for designing
clonotype (Id)-specific manipulation of human diseases such as
MS. | Introduction |
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In the present study, we addressed the questions for autoimmune T cell expansion in MS by using a novel technique relying on the single-strand conformation polymorphism (SSCP) of TCR messenger signals. The SSCP-based clonality analysis (9, 10), referred to also as SSCP clonotype analysis, depends on the fact that a single strand of the nucleotide chains would form a unique conformation according to its sequence and migrate to its own position during electrophoresis in the SSCP gel (11). As such, when cDNAs of TCR ß-chains from a given sample are amplified by RT-PCR, denatured, and electrophoresed, the TCR message of clonally expanded T cells (clonotype) can be visualized as a distinct band, while those from minor clones are erased in the background smear (Reviewed in 10 . While SSCP clonotype analysis of freshly isolated PBMC or biopsy samples provides basic information for T cell clonality in vivo (9, 10, 12, 13, 14, 15), comparison of accumulated T cell clones in different samples is also informative because of the reproducible mobility of each clonotype. As reported in a recent study (16), parallel examination of T cell clones with defined Ag specificities could lead to identification of Ag specificities of accumulated clonotypes in vivo. However, because of limited availability of T cell clones specific for target autoantigens, the feasibility of this strategy has not been formally proven in the field of autoimmune disease research. Owing to a panel of T cell clones specific for putative encephalitogenic epitopes, the present study could provide definitive evidence for expansion and activation of autoimmune T cells reactive to defined epitopes of MBP or PLP in MS. Furthermore, we obtained insights into the dynamics of the autoimmune T cell clones and its relative dominance during clinical course.
| Materials and Methods |
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All patients except for one (patient TN with acute MS) had definite MS fulfilling the diagnostic criteria proposed by Poser et al. (17). The diagnosis was further assisted by magnetic resonance imaging in all. Clonal expansion of MBP or PLP peptide-specific T cells was investigated in two relapsing/remitting MS patients (patient OK: 54-yr-old female, DRB1*1501/1502 and patient SK: 45-yr-old male, DRB1*1502/1403) and one secondary progressive MS (patient IS: 30-yr-old female, DR1/DRB1*0410). HLA-DR types were determined by a hybridization protection assay using acridinium-ester-labeled DNA probes (18) or by a standard serological typing. None of the patients received immunosuppressive agents during the period of study.
T cell clones and lines (TCCL)
A panel of CD4+ TCR
ß+ T cell clones
and lines (TCCL) (Table I
) had previously
been established from PBMC by our modification of the "split-well"
technique (19, 20). All the TCCLs (here we use "TCCL" as an
operational term representing an independently established long-term
culture composed of mono- or oligoclonal T cells) were restricted by
HLA-DR in the recognition of MBP or PLP peptide as revealed by
proliferation assays with DR-specific blocking Abs or with
DR-transfected L cells as APCs (20). They were characterized as
Th1-type T cells based on their ability to produce IFN-
but not IL-4
in response to Ag (our unpublished data). Although there was no
particular bias in the use of either MBP82102, PLP95116, 105124,
118139, or 139155 peptide for generation of TCCL, our TCCL panel
was biased for PLP95116-specific TCCLs, a majority of which were
derived from OK bearing DR2 haplotype. This is consistent with our
previous work showing that PLP95116 is an HLA-DR2-associated epitope
in MS (20). SSCP analysis had revealed monoclonal or oligoclonal
compositions of the TCCLs and characterized the Vß gene use of each
clonotype in TCCL (Table I
).
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For analysis of activated T cells, PBMC were doubly stained with
anti-CD25-FITC (anti-IL-2 receptor
-chain) and
anti-CD3-phycoerythrin (PE) mAbs (Becton Dickinson, Mountain
View, CA). The CD3+CD25+ fraction was collected
by a standard sorting method using a FACSort flow cytometer (Becton
Dickinson). CD4+ cells were isolated by a magnetic cell
sorter MACS (Miltenyi Biotec, Auburn, CA) after labeling with
anti-CD4 mAb (PharMingen, San Diego, CA).
SSCP clonotype analysis
SSCP clonotype analysis was performed in essentially the same
condition as described by Yamamoto et al. (9, 10). In brief, mRNA was
isolated from PBMC, CD3+CD25+ cells,
cerebrospinal fluid (CSF), or TCCL with QuickPrep Micro mRNA
Purification Kit (Pharmacia Biotech, Uppsala, Sweden) and converted to
cDNA by using First-Strand cDNA Synthesis Kit (Pharmacia Biotech). One
microliter of the diluted cDNA reaction was then individually mixed
with a set of a Vß-specific sense primer and the Cß antisense
primer (30 pmol for each) (21). PCR was performed in 50-µl reactions
containing 5 µl of 10x ExTaqBuffer (Takara, Tokyo, Japan), 4 µl of
dNTPs, and 2.5 units of ExTaq DNA polymerase (Takara) for 35 cycles
(94°C for 30 s, 60°C for 30 s, and 72°C for 1 min),
unless otherwise stated. The amplified sample was diluted in a
denaturing solution (95% formamide/10 mM EDTA/0.1% bromophenol
blue/0.1% xylencyanol) and incubated at 90°C for 2 min for
heat denaturation. The sample was then loaded onto a nondenaturing 4%
polyacrylamide gel containing 10% glycerol. After electrophoresis, the
DNA was transferred to Immobilon-S (Millipore Intertech, Bedford, MA)
and hybridized with a biotinylated Cß-specific sense probe (10). The
hybridized anti-sense DNAs were visualized by subsequent incubation
with streptavidin, biotinylated alkaline phosphatase, and a
chemiluminescent substrate system (Phototope Detection Kit, New England
Biolabs, Beverly, MA). To explore Ag specificities of clonotypes found
in the blood and CSF samples, the cDNA derived from MBP- or
PLP-specific TCCL was run on the adjacent lane as a probe. When we
found identical band pairs between the paired samples, electrophoresis
was performed at least two more times, varying the sample dilution
and/or time for electrophoresis. Only when the migration positions of
the corresponding clonotypes were identical in the additional
experiments (80
90% in the cases), the two clonotypes were regarded
as being identical.
TCR DNA sequencing
In brief, we cut out a small area of the SSCP gel corresponding to the band and then extracted the TCR clonotype message as previously described (14). The extract was submitted to a second amplification by PCR with a corresponding Vß (21) and an internal Cß primer (GCGACCTCGGGTGGGAAC). The PCR products were ligated to M13 mp19 vector arms obtained through SmaI digestion. Phages were grown on XL-1 Blue Escherichia coli cells (Stratagene, La Jolla, CA), and recombinants were selected by hybridization with a Cß probe (21). The single-strand DNA was isolated from the positive plaques, and sequencing reactions were induced with BucaBEST Dideoxy Sequencing Kit (Takara) after priming with M13-47 primer.
| Results and Discussion |
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In preparatory experiments, eleven PBMC samples from healthy
subjects (HS) and 21 from MS were examined by SSCP clonotype analysis.
In accordance with previous studies (9, 10, 12, 13), the samples from
HS showed a smear pattern or demarcated variable numbers of bands on
the smear backgrounds (Fig. 1
A). While samples from MS in
remission were not significantly different from HS samples, MS in
relapse tended to demarcate higher numbers of bands than HS or MS in
remission (Fig. 1
B). However, there were remarkable
individual differences (data not shown), and the SSCP profile in a
given subject correlated poorly with the clinical state. Then we
examined three PBMC samples from patient OK and two PBMC from patient
SK in parallel with all the PLP-reactive TCCLs derived from
the patients shown in Tables I and II.
This preliminary analysis showed the presence of a Vß14 clonotype of
TCCL 118.19 in one of the three samples from patient OK and a Vß20
clonotype in TCCL 105.18 in one of the two samples from patient SK
(data not shown), indicating that Ag specificities of clonally expanded
T cells could be determined by this method. However, seeing that
distinct clonotypes could hardly be demonstrated in samples obtained
from MS in remission, we speculated that only a small proportion of
expanded clones in blood may be visualized by this method. Next we
examined the activated T cell population expressing both CD3 and CD25
(IL-2R
-chain) (Fig. 2
). Notably,
analysis of this population was found to demarcate much higher numbers
of distinct clonotypes on the SSCP gels as compared with unseparated
PBMC (Fig. 3
). Based on this interesting
observation, we presume that the mixture of heterogeneous
CD25- population may lower the efficiency in detecting
clonal accumulations of CD25+ T cells. Because of technical
merits to detect higher number of bands and as activated T cells should
play critical roles in vivo, we decided to use the
CD3+CD25+ population in following studies.
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Collectively, five CD3+CD25+ samples from
HS and 10 samples from MS were investigated by the SSCP technique
(Table III
). The results showed a
tendency that the samples from MS demarcate a lower number of
clonotypes that are characterized by more limited use of Vß genes as
compared with HS. However, the proportion of
CD3+CD25+ cells among total lymphocytes was not
significantly different between MS and HS (Table III
). An extreme end
of the spectrum was seen in the first sample obtained from patient IS
with secondary progressive MS, demarcating only
20 bands with biased
TCR usage for Vß6 and Vß14 (Fig. 4
A) and in patient TN, who has
recently developed an acute episode of probable MS. Although less
remarkable, samples from relapsing/remitting MS (patient OK) also
showed similar profiles characterized by fewer bands and biased Vß
use (Fig. 5
, A and B). These results
suggest a narrowing of activated T cell repertoire in association with
development of MS. Although the underlying mechanism is unclear, we may
speculate that T cell recognition targets in MS may tend to be shifted
from those for regulatory cells (such as TCR peptides) to a limited
epitopes for self-destructive T cells.
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Identification of MBP- or PLP-reactive T cells among CD3+CD25+ population
We next analyzed 7 of the 10 samples from MS (2 from patient IS
and 5 from patient OK) together with the patient-derived TCCLs listed
in Table I
. The results showed evidence for transient or persistent
expansion of MBP- or PLP-specific clonotypes in MS (Table IV
and Fig. 6
). A most remarkable observation was
that two of the dominant clonotypes in the first sample of patient IS
(Jan 97) would correspond to those specific for MBP82102 (indicated
by arrow a and b in Fig. 4
A), implying that a few
MBP-specific T cells could play overwhelming roles in certain phases of
MS. Together with the fact that the expanded clones are activated in
vivo and the corresponding clones belong to Th1 T cells, we speculate
that, if a few pathogenic clones can be deleted by anti-clonotype
vaccine, it may greatly reduce the clinical activity of this patient in
the active phase. It was also striking that a most prominent clonotype
in a sample of patient OK corresponded to that of PLP95116-specific T
cell clone 2BA205 (Fig. 5
A). SSCP analysis and TCR
sequencing (Fig. 7
) revealed the presence
of the 2BA205 clonotype in all the samples, indicating that 2BA205
clone is probably in a continuously activated state in the peripheral
circulation (Table IV
). Although previous studies suggested the
presence of persistent MBP-specific clones (6, 7), it remained elusive
whether they were continuously or periodically activated, since the
interval of sampling was quite long (1 yr). This is the most convincing
proof that myelin-specific T cell clones could exist in a persistently
activated state. In contrast, the Vß15+ clonotype of
118.23 was found only in a single relapse, and the Vß8+
clonotype of 118.19 was found only once during remission (Table IV
),
although these clonotypes are specific for the same PLP epitope. This
does not only imply that the kinetics of autoimmune T cell clones are
quite heterogeneous but indicates that different mechanisms may be
involved for triggering each of these clones with the same epitope
specificities. It is tempting to speculate that exogenous superantigens
or viral-derived peptides may be involved because they could
differentially activate T cells with the same specificity.
|
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A previous study by Masuko et al. reported that clonal persistence revealed by the SSCP was highly restricted to CD8+ population in healthy individuals who had been infected with a common pathogen (12). In contrast, expansion of CD4+ T cells tended to be transient. Furthermore, since rodent encephalitogenic T cells are CD4+ (22), a theoretical possibility remained that 2BA205 clonotype detected in the CD3+CD25+ population might be expressed by another T cell clone expressing CD8. We therefore separated the PBMC into CD4+/CD4- fractions by magnetic sorting and examined which of the fractions would contain the TCR message of 2BA205. The results demonstrate that 2BA205 clonotype is specifically found in the CD4+ fraction but not in the CD4- fraction (not shown). This further supports that the in vivo expanded clone is identical to the PLP-specific 2BA205 clone.
Evidence for presence of autoimmune T cells in CSF
Finally, we analyzed two CSF samples from patients OK and IS. As
shown in Table IV
, two MBP-specific clonotypes and three PLP-specific
clonotypes including 2BA205 were detected in the CSF samples of
patients IS and OK, respectively (Fig. 8
). Except for 2BA205, the clonotypes
detected in the CSF were not found in the
CD3+CD25+ T cells obtained at the same time.
However, a MBP82102-specific clonotype of 4SC5 was found in the
CD3+CD25+ T cells sampled 5 mo previously,
indicating dynamic shift of some autoimmune T cell clones from blood to
CSF-central nervous system compartment. These results indicate that the
MBP- or PLP-reactive clones could cross the blood-brain barrier and
possibly infiltrate the site of inflammation.
|
Clonal expansion of autoimmune T cells was previously estimated in MS by using limiting dilution analysis (6) or the RT-PCR assay measuring mRNA transcripts encoding TCR chains of MBP-reactive clones (7). These techniques are useful for exquisite analysis of limited populations defined by either Ag specificity (6) or by T cell clonotype (7). However, they do not estimate the significance of examined populations in the total repertoire. In addition, while limiting dilution analysis assays are influenced by multiple factors inherent in in vitro manipulation (7), the PCR assay could handle only a limited number of clones. In contrast, the SSCP analysis (9, 10) figures out the overall profile of dominant clonotypes without depending on in vitro culture. Owing to this technical advantage and the availability of T cell clones specific for putative encephalitogenic peptide, we were able to identify the presence of autoimmune T cells in the activated T cell population of blood and CSF in two patients with MS. Although care should be taken in its use for quantitative estimation, the SSCP analysis is a most reliable and efficient tool for identifying and tracking Ag-specific T cells in human diseases such as MS. Our results revealed that only a small proportion of clonotypes from in vitro established clones can be detected in a series of activated T cell populations in vivo. We assume that the in vivo detected clones might have been involved in the pathology of MS at the time of sampling, while the other clones had played a role previously or may be unrelated to disease as being derived from the naive T cell pool. Such information on in vivo expanded and activated clones might prove truly useful for designing "individually tailored" clonotype-specific treatment for autoimmune diseases in the future.
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| Acknowledgments |
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| Footnotes |
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2 Address correspondence and reprint requests to Dr. Takashi Yamamura, Department of Demyelinating Disease and Aging, National Institute of Neuroscience, NCNP, 41-1 Ogawahigashi, Kodaira, Tokyo 187-0031, Japan. E-mail address: ![]()
3 Abbreviations used in this paper: MS, multiple sclerosis; CSF, cerebrospinal fluid; HS, healthy subject; MBP, myelin basic protein; PLP, proteolipid protein; SSCP, single-strand conformation polymorphism; TCCL, T cell clones and lines. ![]()
Received for publication August 17, 1998. Accepted for publication October 26, 1998.
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