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*
Laboratory of Medical Virology, The Rockefeller University, New York, NY 10021;
Department of Medicine, North Shore University Hospital, Manhasset, NY 11030; and
Third Department of Internal Medicine and
§
Department of Virology, Faculty of Medicine, Kagoshima University, Kagoshima, Japan
| Abstract |
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| Introduction |
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| Materials and Methods |
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Four HTLV-I ACs, five patients with HAM, and one patient with ATL were examined. Uninfected controls were 60 normal individuals who were analyzed in a previous study using the identical multiplex PCR assay under identical conditions (17). Three clinically asymptomatic individuals with HTLV-II served as additional control subjects. These were two males, age 46 and 58, and one female, age 53.
HLA typing
HLA Ags were determined serologically by the standard National
Institutes of Health microcytotoxicity test using sera that were
standardized to the criteria and nomenclature of the 11th International
Histocompatibility Workshop (14). Further HLA DNA typing of HLA class
II DRB1* and DQB1* alleles were conducted by the PCR/RFLP method (15, 16). The results are shown in Table I
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PBMCs were obtained by centrifugation over Ficoll-Hypaque. Cells were washed twice in RPMI 1640 with 1% FCS and resuspended in PBS with 1% FCS at a concentration of 10 x 106 cells/ml. Positive selection for CD8+ T cells was conducted by incubating the PBMC with anti-CD8 immunomagnetic beads (Dynal, Great Neck, NY) for 30 min at 4°C on a rotating shaker, as recommended by the manufacturer. The unbound cells were then incubated with anti-CD4 immunomagnetic beads for selection of CD4+ T cells. The cells bound to the beads were placed directly into RNAzolB (Biotex, Houston, TX) for isolation of total RNA.
Multiplex PCR assay for CDR3 length of TCR BV-chains
Total RNA (2 µg) from the selected T cell populations was used
for the first-strand cDNA synthesis using a TCR B-chain C region
primer, 3CB3 (see Table II
). The cDNA
synthesis was performed with Moloney murine leukemia virus
reverse transcriptase in buffer supplied by manufacturer (Life
Technologies, Gaithersburg, MD) at 42°C for 1 h in a total
volume of 120 µl. Specific primers used in RT-PCR for CDR3 of TCR
BV-chains are shown in Table II
. Specific combinations of two or three
Vß (BV)-specific forward primers (20 pmol each) were used for each
multiplex PCR. Each reaction also contained 20 pmol of a reverse primer
specific for the C region (3CB1), out of which 3 pmol were end labeled
with 32P using T4 kinase (Life Technologies). The BV primer
combinations were selected on the basis of the location of each BV
specific primer with respect to the end of the BV region. The 12
different reaction sets were as follows; A, TCRBV1, 18, 23; B,
BV2 4, 8; C, BV3, 13S1; D, BV5S2, 5S1; E, BV6, 20; F, BV7, 22; G, BV9,
16; H, BV11, 12; I, BV15, 13S2; J, BV14, 17; K, BV19, 24; and L, BV10,
21. A representative multiplex PCR assay is shown in Fig. 1
. A total of 10 µl of the cDNA was
used for each PCR. Conditions for the PCR were as follow: After initial
denaturation at 94°C for 5 min, 35 cycles were conducted in a DNA
thermocycler (model 9600; Perkin-Elmer, Norwalk, CT) Each cycle
consisted of denaturation at 94°C for 30 s, annealing at 55°C
for 30 s, and extension at 72°C for 1 min. PCR buffer conditions
were 10 mM Tris-HCl (pH 8.3), 2 mM MgCl2, and 50 mM KCL,
with 20 pmol of each primer in a 100-µl reaction volume. After 35
cycles, an additional extension at 72°C for 10 min was conducted.
Five microliters of the amplified products were loaded on a standard
6% polyacrylamide sequencing gel. Bands (spaced 3 bp apart) were
visualized after overnight exposure to Kodak AR film (Rochester, NY).
The radioactive bands were also analyzed and quantitated using a
PhosphorImager (PhosphorImager SF; Molecular Dynamics, Sunnyvale, CA).
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cDNAs were reamplified using a single TCR BV segment primer and
an unlabeled 3CB1 primer. The amplified product was used as a substrate
for DNA sequencing using the 3CB1 or BJ-R (reverse primer specific for
the BJ region) primer, following purification over PCR Prep DNA
purification columns (Promega, Madison, WI). Direct sequencing of the
PCR products was conducted with fluorescent dideoxy terminators and
analyzed on a model 373A Automated Sequenator (Applied Biosystems,
Foster City, CA). Nucleotide sequences were further confirmed using
specific BJ reverse primers (Table II
).
Criteria for clonal dominance by CDR3 length analysis
Restriction in CDR3 length within a particular BV segment is visualized as a "dominant band" and based on its intensity with respect to the rest of the bands within the TCR BV-specific PCR product. The radioactive gels were scanned using a PhosphorImager, and specific criteria were used to define a band as "dominant" were that >50% of the counts within a V segment/family were contained this band. The clonality of the band was established by direct sequencing of the PCR products with the 3CB1 primer. Pilot studies demonstrated that when the counts within the dominant band were 50% or greater of the entire BV family, a single readable sequence was obtained using the 3CB1 primer. Sequencing with a specific BJ-R primer (selected on the basis of the first 3CB1 primed sequence) yielded a clearly readable sequence in an additional 35% of cases. Thus, in all, 82% of the cases in which the 50% criteria for dominance were met, direct sequencing of the PCR product yielded a single dominant sequence (17).
| Results |
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The multiplex PCR assay was used to assess the clonality of 26
TCR-BV families in the separated CD4+ and CD8+
T lymphocytes of five patients with HAM/TSP, four HTLV-I ACs, and one
patient with ATL. Fig. 2
shows a typical
autoradiogram of the PCR products analyzed by electrophoresis on a 6%
polyacrylamide gel from a patient with HAM/TSP. In this individual,
dominant bands of a single CDR3 length were observed in both the
CD4+ and CD8+ T lymphocyte populations in a
large number of different BV families. Table III
summarizes the TCR BV families shown
to be clonally expanded in both the CD4+ and
CD8+ T lymphocyte populations in all 10 individuals
studied. The results demonstrated that clonal expansion of both
CD4+ and CD8+ T lymphocytes occurs in both
asymptomatic carriers and patients with HAM/TSP. Moreover, while the
total number of expanded clones in the CD8+ T lymphocyte
population was much greater (310 clones) than that of the
CD4+ T lymphocytes (13 clones), no appreciable
differences were observed between asymptomatic carriers and patients
with HAM/TSP. Similarly we were unable to observe differences in
specific V-ß expansion in patients with HAM/TSP compared with
asymptomatic carriers. Even after stratification of HLA phenotype there
was no evidence of expansion involving a unique T cell repertoire.
Within the CD4 T cell populations, we observed clonal expansion in four
of five patients with HAM/TSP involving a total of 18 different clones.
In the asymptomatic carriers, clonal expansion was observed in two of
four individuals and this involved 7 different clones (Table III
). In
one patient with ATL, we observed one specific band in the CD4
population, Vß 7. In contrast, clonal expansion was not observed in
any of the CD4+ T cell populations in three control
HTLV-II-infected individuals. In addition we have shown in previous
studies using the same PCR assay that clonal expansion within
CD4+ T cell population of uninfected individuals occurs
rarely, if at all (17). In the CD8 population, the T cell populations
which did not exhibit clonal expansion were seven Vßs (3, 7, 10, 15, 17, 22, 23) in HAM/TSP and three Vßs (6, 7, 18) in HTLV-I carriers.
Table III
shows that overall Vß utilization was extremely diverse,
and no restricted or consistent pattern was obvious in either the
asymptomatic carriers or HAM/TSP patients.
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To determine whether the CDR3 of the TCR in patients with HAM/TSP
may be restricted or conserved, we conducted extensive nucleotide
sequencing of this region. Tables
IVVI
showed a representative analysis of the predicted amino acid sequences
of the CDR3 regions in asymptomatic HTLV-I carriers, patients with
HAM/TSP, and in the one patient with ATL. The average length of the
CDR3 region was not different among patients with HAM/TSP (10.66 in
CD4, 10.48 in CD8), ATL (10 in CD4, 10.25 in CD8), and HTLV-I ACs
(10.29 in CD4, 10.48 in CD8). PG or related sequence (PXG) motifs were
more frequently observed in CD8 T cell populations of patients with
HAM/TSP than in those of HTLV-I carriers. Eight of 29 clones (27.6%)
had this sequence in HAM/TSP compared with 2 of 31 clones (6.5%) in
HTLV-I carriers. However these differences were not of statistical
significance when analyzed by Fishers exact test
(
2 = 3.417, p = 0.06). It was
interesting to note that 4 of 8 clones having a PG or related motif
were from HAM/TSP patients bearing HLA-A2. LXG motifs were more
frequently observed in HTLV-I carriers (6 of 38; 15.8%) than in
HAM/TSP (3 of 35; 8.6%). JB utilization showed some conservation in
that JB2.1 was detected in 50% of patients with HAM/TSP and in 29% of
asymptomatic carriers.
| Discussion |
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and Vß utilization (28),
and sequence analysis of the CDR3 regions showed evidence of an
oligoclonal expansion in responding T cells (12). A more detailed study
on TCR Vß regions based on analysis of cDNA from central nervous
system lesions of HAM/TSP patients suggested that T cells containing
restricted Vß CDR3 motifs become activated upon HTLV-I infection
(29). Recently, Höger et al. (13) clearly demonstrated the
accumulation of T cell clones in patients with HAM/TSP using PCR-based
SSCP methods which allowed the detection of conformational polymorphism
of the CDR3 regions of TCR Vß. This method detected T cell
oligoclonality as labeled bands in a background smear pattern following
SSCP gel electrophoresis. The numbers of reported clones ranged from 65
to 94 and were much higher in patients with HAM/TSP compared with ACs.
However, these studies were limited in that no attempts were made to
differentiate expansion in isolated CD4+ and
CD8+ cell populations.
The CDR3 loops of both
- and ß-chains are thought to carry the
fine specificity of Ag recognition by T cells (30). Because nucleotide
transferases add or remove nucleotides at the various V-D and D-J
junctions during recombination, the CDR3 region of any V-J combination
may vary in length by as many as 68 amino acids (31). A recently
developed multiplex PCR approach that allows for the quantitative
evaluation of the CDR3 length profile of each Vß segment families was
utilized in our study (17, 18, 19, 20, 21, 22). The detection of biased peaks compared
with the expected symmetrical background distribution of the several
bands can be regarded as evidence of clonality within the T cell
repertoire, and Ag-driven clonal T cell expansion can be evaluated more
conveniently as compared with the SSCP method described above. The
major difference between the SSCP method and our procedure is related
to the detection of clonality based on conformation vs the length of
the CDR3 regions. In our studies, we could demonstrate the following.
1) Mono- or polyclonal expansion of CD4+ T cells was
confirmed in two of four ACs and in four of five patients with HAM/TSP.
In the one patient with ATL, a specific clone bearing Vß 7 was
detected in the CD4+ T cell subset. 2) Accumulated
oligoclonality within the CD8+ T cell subset was evident in
all subjects, including ACs (310 clones), HAM/TSP patients (38
clones), and an ATL patient (8 clones). The mean value of the number of
clones was 6.8 clones per individual. No statistically significant
differences in the average number of clones were observed between
individuals with HAM/TSP and ACs. 3) The repertoire of the clonally
expanded T cells was extremely diverse and there was no bias in Vß
gene usage. 4) There was no statistically significant restriction in
the CDR3 motifs of the TCR Vßs. 5) In two patients with HAM/TSP, who
were HLA-A2 positive, PG, or related motifs (PXG) in the Vß CDR3
sequence were detected in four predominant clones.
The clonal expansion within CD4+ T cells observed in our study would seem to be related at least in part to the proliferation of cells as a result of virus infection. HTLV-I has a preferential and often exclusive tropism for CD4+ T lymphocytes and clonal expansion of HTLV-I-infected cells has been predicted by Southern blot hybridization assays (8, 32), and more recently by ligation mediated inverse PCR amplification methods (9, 10, 11). Our study provides the first direct demonstration of in vivo clonal expansion of infected cells within the fractionated CD4+ T cell subset. However, further studies that would require the isolation of individually expanded populations with subsequent molecular analysis to detect the presence of integrated HTLV-I provirus are required to definitely confirm the association of infection with expansion. In our experience, such studies are technically difficult in that the successful isolation of the expanded CD4+ T lymphocyte population requires very large quantities of peripheral blood mononuclear cells as starting material, and this is difficult to obtain from most patients. Moreover, these studies are also restricted by the limited availability of specific Vß Abs that would be required to isolate the expanded population. However, at present we are attempting to overcome these difficulties and carry out such studies. The view that clonal expansion of CD4+ T lymphocyte populations is due to HTLV-I infection is also supported by the observations that expansion is only rarely observed in uninfected normal individuals and was not observed in any of three HTLV-II-infected individuals included in this study. In contrast to HTLV-I, HTLV-II has a preferential tropism for CD8+ T lymphocytes (34), and this would be consistent with the absence of clonal expansion of CD4+T lymphocytes in HTLV-II infection and its presence in HTLV-I infection.
The present studies also provide the first description of the frequent clonal T cell expansions within fractionated CD8+ cell population (6.8 clones per individual), which suggests there is Ag-driven polyclonal CD8+ cell expansion in HTLV-I-infected individuals. However, further studies will also be required to confirm this and to identify the Ags involved. While clonal expansion of CD8+ cell populations certainly occurs in normal uninfected individuals (17, 18, 19, 20), the number of expanded clones in the HTLV-I-infected group is higher than would be expected. The reason for the discordance in the numbers of clones (per subject) with the previously reported results using the PCR-based SSCP assay (13) (6594 clones reported for HAM/TSP patients) is unknown but may partially result from the differences in the methods employed. Our results also differ from this study in that we could not demonstrate differences in the number of expanded clones between ACs and patients with HAM/TSP. However, direct comparison of the two studies is very difficult, as the latter study also did not differentiate between expansion of the CD4 and CD8 populations. Hara et al. (29) suggested the presence of restriction in CDR3 motifs of infiltrating lymphocytes in the spinal cord lesions of HAM/TSP patients as encephalitis-related motifs (LXG). We found no evidence for this. LXG motifs were only detected in 3 of 35 predominant clones identified in patients with HAM/TSP, but were also detected in ACs. PG or related motifs (PXG) of the TCR Vß CDR3 regions, which previously were reported as structural motifs of the HTLV-I Tax-specific CTL clones restricted by HLA-A2, were detected in eight predominant clones in patients with HAM/TSP (four of these clones were also identified in HLA-A2-bearing patients). However, based on the innate tendency of the terminal deoxytransferase to increase the incorporation of glycine residues (33), the evaluation of CDR3 motifs involving G residues requires careful interpretation.
In HAM/TSP patients, both the high proviral DNA load (35, 36, 37, 38) and the extremely low levels of viral replication in PBLs (38) are accompanied by higher and active humoral immune responses (40 42) and a higher frequency of HTLV-I-specific CD8+ CTLs compared with ACs (25). HLA haplotype analysis has been rewarding in pinpointing the role of cellular immune responses against HTLV-I in the pathogenesis of HAM/TSP (41) and a proliferative potency of the PBLs responding to HTLV-I in HAM/TSP patients has received attention as an in vitro equivalent of the cellular inflammation in the central nervous system of the patients (43, 44, 45, 46). Taken together, the data support the involvement and importance of anti-HTLV-I CTL activities in the pathogenesis of HAM/TSP (23, 24, 25). HTLV-I-specific CD8+ CTLs have been demonstrated directly in lymphocytes in the peripheral blood and CSF of HAM/TSP patients (23, 24, 25, 47) and in the peripheral blood of ACs (26, 27). Although the impairment of some nonspecific cellular immune activities has been reported in patients with HAM/TSP (48, 49, 50), a beneficial effect of immunosuppressive therapies in a majority of the patients is well established (51). The detection of oligoclonal expansions of CD8+ T cells in HTLV-I-infected individuals as demonstrated in the present study may preferentially reflect the presence of the HTLV-I-specific CTL clones in these subjects. In our comparative analysis, there was no significant difference in the TCR Vß CDR3 length profile between HAM/TSP patients and ACs, suggesting that the presence of oligoclonal expansion of CD8+ T cells may be only one of the prerequisites for the development of disease.
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| Footnotes |
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2 Address correspondence and reprint requests to Dr. William W. Hall at his current address, Department of Medical Microbiology, University College Dublin, Belfield, Dublin 4, Ireland. E-mail address: ![]()
3 Abbreviations used in this paper: HTLV, human T cell lymphotropic virus; AC, asymptomatic carrier; ATL, adult T cell leukemia; HAM/TSP, HTLV-I-associated myelopathy/tropical spastic paraparesis; SSCP, single-strand conformation polymorphism; HLA, human leukocyte Ag; CDR, complementarity-determining region. ![]()
Received for publication December 4, 1997. Accepted for publication August 14, 1998.
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