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Journal of Virology, July 2006, p. 6697-6701, Vol. 80, No. 13
0022-538X/06/$08.00+0 doi:10.1128/JVI.02388-05
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
MRC Human Immunology Unit, Weatherall Institute of Molecular Medicine, Oxford, United Kingdom,1 Division of Clinical Virology, Karolinska Institute, Stockholm, Sweden,2 Department of Virology, John Radcliffe Hospital, Oxford, United Kingdom,3 Peter Medawar Building for Pathogen Research, Nuffield Department of Medicine, Oxford University, Oxford, United Kingdom4
Received 14 November 2005/ Accepted 15 March 2006
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A vigorous HLA-A*2402-restricted FYTPLADQF response is seen in B19-seropositive individuals.
We identified seven HLA-A*2402-positive individuals from a cohort of 22 adult patients with acute B19 infections, as evidenced by arthropathy, rash, fever, and B19 immunoglobulin M (IgM) seropositivity. Ethical approval (CO2.113) and informed patient consent were obtained prior to study initiation and venous sampling. A remotely infected healthy individual was also studied. Three individuals have been identified previously (8). The following epitopes, which were described previously (8), were used in gamma interferon (IFN-
)-specific enzyme-linked immunospot (ELISPOT) assays and/or to construct B19-specific tetrameric complexes: HLA-A*2402-restricted FYTPLADQF, HLA-B35 QPTRVDQKM, HLA-B35 FPGINADAL, HLA-A*201 LLHTDFEQV, HLA-A*201 GLCPHCINV, HLA-B8 TAKSRVHPL, and HLA-B40 SESSFFNLI and TEADVQQWL). Figure 1A shows that for donor O22, the HLA-A*2402 FYTPLADQF response was numerically dominant by direct ex vivo peripheral blood mononuclear cell (PBMC) IFN-
ELISPOT assay 1 month after the onset of symptoms. Six of the seven acutely infected individuals showed vigorous responses to peptide FYTPLADQF by IFN-
ELISPOT assay and/or tetramer staining, with responses ranging from 0.3 to 4.9% of CD8+ T cells (Fig. 1B). In three individuals where responses restricted by other HLA alleles were identified, the A24 responses were immunodominant. Surprisingly, as described previously (8), these responses increased over the first year postinfection, despite the resolution of clinical symptoms and the control of viremia. One HLA-A*2402-positive, remotely infected, IgG-positive, IgM-negative adult with no B19 exposure within 10 years responded to FYTPLADQF by both IFN-
ELISPOT assay and tetramer staining (20 spot-forming units/million PBMC and 0.03% of CD8+ T cells, respectively [data not shown]). This response was further confirmed by the generation of peptide-specific T-cell lines (data not shown).
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FIG. 1. Vigorous B19 HLA-A24 FYTPLADQF-specific CD8+ T-cell responses are seen in acute and remote B19 infections. (A) IFN- ELISPOT responses in acutely B19-infected patient O22 1 month after symptom development. PBMC were stimulated with five B19 CD8+ T-cell epitopes (HLA-A2 LLHTDFEQV, HLA-B40 SESSFFNLI, HLA-B40 TEADVQQWL, HLA-A2 GLCPHCINV, and HLA-A24 FYTPLADQF). Data from triplicate estimations are shown, with positive results defined as the negative control value + 2 standard deviations or two times the negative control (solid horizontal line). SFU, spot-forming units. (B) FYT A24 tetramer staining of PBMC from seven acutely infected HLA-A24-positive individuals and one remotely infected HLA-A24-positive individual (RV1). Months indicate times after symptom development. Patients O1 to O3 and RV1 were described previously (8).
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FIG. 2. The B19 HLA-A24 FYTPLADQF tetramer-specific T-cell response in patient O1 predominantly uses TCR gene segment BV5.1. PBMC from patient O1 (2 months after symptom development) were stained with tetramer and BV monoclonal antibodies. Percentages shown are percentages of tetramer-positive PBMC.
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FIG. 3. B19 HLA-A24 FYTPLADQF-specific T-cell responses show striking BV5.1 TCR usage and efficient cytolysis. (A) BV5.1 usage of HLA-A24 FYTPLADQF tetramer-positive T cells from six acute and one remote responder. (B) Longitudinal BV5.1 monoclonal antibody staining of PBMC from acutely infected patient O1. (C) Chromium release cytolysis (using HLA-A24-positive or -negative B-cell targets) of HLA-A24 FYTPLADQF-specific CD8+ T-cell clone O22 clone 1. The peptide concentration for the left panel was 106 M, and the E:T ratio in the right panel was 1:1.
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HLA-A*2402 FYTPLADQF-specific T-cell clones and clonal lines from unrelated individuals use BV5.1 and BJ2.1, with a conserved CDR3 length and amino acid usage. T-cell lines were derived by stimulation with FYTPLADQF for 10 days ex vivo (8); CTL clones were derived from patients O9 and O22 by limiting dilution, and long-term CTL lines were derived from patient O9 and remotely infected donor OR4 by repeated ex vivo stimulation with peptide-pulsed irradiated autologous B cells (2). CTL clones were CD8+ FYT/HLA-A*2402 tetramer positive, and BV5.1 antibody positive (data not shown). CTL clones killed at low effector/target (E:T) ratios and at nM peptide concentrations, as shown for O22 clone 4 in Fig. 3C. RNA was extracted from either cell-sorted or magnetic bead-enriched cell populations (to exclude feeder cell contamination) using an RNeasy mini kit (QIAGEN, United Kingdom). Reverse transcription was carried out using the Moloney murine leukemia virus reverse transcriptase (Stratagene, Amsterdam, The Netherlands) and oligo(dT)(12-18) primers (Life Technologies, Heidelberg, Germany) according to the manufacturer's instructions. PCR was carried out using Pfu polymerase (Stratagene, Amsterdam, The Netherlands) and BV5.1 (5'ATACTTCAGTGAGACACAGAGAAAC3') and Cß (5'TTCTGATGGCTCAAACAC3') primers. PCR products were gel purified, and DNAs were extracted using a QIAGEN gel extraction kit before either bulk sequencing or subcloning into Topo (Invitrogen) and clone sequencing. All sequences were confirmed by reverse sequencing.
Tables 1 and 2 display the nucleotide and predicted amino acid sequences of the TCR BV CDR3 region sequences of HLA-A*2402-restricted FYTPLADQF-specific T-cell lines and clones. For the O9 lines, both a pool and 30 molecular clone sequences were obtained. Even though molecular cloning showed the line to be polyclonal, the CDR3 length was absolutely conserved even at this stage, and 29/30 clones used the BJ2.1 segment. Seven clones from individual O22 were sister clones with the same nucleotide sequence. The RV1 line amino acid sequence was identical to that obtained from the O22 clones, despite differences at the nucleotide level. This both excludes PCR contamination and suggests antigen-driven selection. All sequences from all three individuals had CDR3 regions of the same length (nine amino acids), and all but one used JB2.1. This region is critical in the recognition of bound peptide in several TCR/major histocompatibility complexes (reviewed in reference 5).
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TABLE 1. TCR beta chain CDR3 region nucleotide sequences of FYT A24 CD8+ cell lines and clones from individuals O9, O22, and RV1
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TABLE 2. Predicted TCR beta chain CDR3 region amino acid sequences of FYT A24 CD8+ cell lines and clones from individuals O9, O22, and RV1
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In summary, seven of eight HLA-A*2402-positive individuals made vigorous responses to the HLA-A*2402-restricted epitope FYTPLADQF that were dominated by a conserved BV5.1 TCR. A highly focused T-cell response may aid in the rapid identification and elimination of even low levels of virus. This has important implications for vaccine development, particularly because HLA-A*2402 is not only the commonest East Asian HLA type but is likely part of a cross-presenting "supertype" that also includes A*2301 and A*3001 (3).
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