Antagonism of antiviral and allogeneic activity of a human public CTL clonotype by a single altered peptide ligand: implications for allograft rejection

Alloreactive T lymphocytes are central mediators of graft-versus-host disease and allograft rejection. A public CTL clonotype with specificity for the alloantigens HLA-B*4402 and B*4405 is often expanded to large numbers in healthy HLA-B*0801(+) individuals, driven by cross-reactive stimulation with the common, persistent herpesvirus EBV. Since such alloreactive memory CTL expansions have the potential to influence transplantation outcome, altered peptide ligands (APLs) of the target HLA-B*0801-binding EBV peptide, FLRGRAYGL, were screened as specific antagonists for this immunodominant clonotype. One APL, FLRGRFYGL, exerted powerful antagonism of a prototypic T cell clone expressing this immunodominant TCR when costimulated with target cells presenting HLA-B*0801(FLRGRAYGL). Significantly, this APL also reduced the lysis of allogeneic target cells expressing HLA-B*4402 by up to 99%. The affinities of the agonist and antagonist complexes for the public TCR, measured using solution and solid-phase assays, were 8 and 138 muM, respectively. Surprisingly, the half-life of the agonist and antagonist complexes was similar, yet the association rate for the antagonist complex was significantly slower. These observations were further supported by structural studies that suggested a large conformational hurdle was required to ligate the immunodominant TCR to the HLA-B*0801 antagonist complex. By defining an antagonist APL against an immunodominant alloreactive TCR, these findings raise the prospect of exploiting such peptides to inhibit clinical alloreactivity, particularly against clonal T cell expansions that react with alloantigens.

Naturally processed and HLA-B8-presented HPV16 E7 epitope recognized by T cells from patients with cervical cancer

Several major histocompatibility complex (MHC) alleles have been reported to present peptides derived from the HPV16 E7 oncoprotein to T cells. We describe an overrepresentation of the HLA-B8 allele (28.44%) in cervical cancer patients as compared to the MHC class I allele frequency in a local healthy control population (18.80%) and the identification of an HLA-B8-binding peptide TLHEYMLDL (HPV16 E7(7-15)), which is able to drive HPV16 E7-specific and MHC class I-restricted T-cell responses in peripheral blood lymphocytes from healthy individuals. TLHEYMLDL-specific T cells recognize the naturally processed and presented peptide on HPV16+ cervical cancer cells transfected with the HLA-B8 gene defined by IFN-gamma production. This peptide epitope is also recognized by freshly harvested tumor-infiltrating T cells or T cells from tumor-draining lymph nodes from patients with cervical cancer determined by flow cytometry as well as by tetramer in situ staining. HLA-B8-restricted HPV E7(7-15)-specific T cells reside predominantly in the CD8+ CD45RA+ CCR7+ precursor or in the differentiated CD8+ CD45RA+ CCR7- T-cell population.

High responsiveness of HLA-B57-restricted Gag-specific CD8+ T cells in vitro may contribute to the protective effect of HLA-B57 in HIV-infection

HLA-B57 has been shown to be associated with long-term asymptomatic HIV-1 infection. To investigate the biological mechanism by which the HLA-B57 allele could protect from HIV-1 disease, we studied both the number of CD8(+) T cells as well as CD8(+) T cell responsiveness directed to different HIV-1 Gag peptides presented by HLA-A2, -B8 or -B57. T cells specific for the HLA-B57 peptide KAFSPEVIPMF responded more readily and to a higher extend to antigenic stimulation in vitro than T cells specific for the HLA-A2 peptide SLYNTVATL or the HLA-B8 peptide EIYKRWII. This phenomenon was reproducible with T cells from individuals expressing HLA-B57 in combination with one or both of the other alleles and was persistent during long-term follow-up. Lower reactivity of A2- and B8-restricted T cells was not explained by mutations in the B8- or A2-restricted Gag-peptides. Moreover, no correlation between peptide mutation frequency and IFN-gamma production by the corresponding Gag-specific T cells was observed. In conclusion, functional differences were observed between T cells specific for HIV epitopes derived from the same protein presented by different HLA molecules. B57-restricted KAFSPEVIPMF-specific CD8(+) T cells have relatively high responsiveness, which could contribute to the protective effect of HLA-B57 in HIV infection.

A Charged Amino Acid Residue in the Transmembrane/Cytoplasmic Region of Tapasin Influences MHC Class I Assembly and Maturation

Tapasin influences the quantity and quality of MHC/peptide complexes at the cell surface; however, little is understood about the structural features that underlie its effects. Because tapasin, MHC class I, and TAP are transmembrane proteins, the tapasin transmembrane/cytoplasmic region has the potential to affect interactions at the endoplasmic reticulum membrane. In this study, we have assessed the influence of a conserved lysine at position 408, which lies in the tapasin transmembrane/cytoplasmic domain. We found that substitutions at position K408 in tapasin affected the expression of MHC class I molecules at the cell surface, and down-regulated tapasin stabilization of TAP. In addition to affecting TAP interaction with tapasin, the substitution of alanine, but not tryptophan, for the lysine at tapasin position 408 increased the amount of tapasin found in association with the open, peptide-free form of the HLA-B8 H chain. Tapasin K408A was also associated with more folded, beta(2)-microglobulin-assembled HLA-B8 molecules than wild-type tapasin. Consistent with our observation of a large pool of tapasin K408A-associated HLA-B8 molecules, the rate at which HLA-B8 migrated from the endoplasmic reticulum was slower in tapasin K408A-expressing cells than in wild-type tapasin-expressing cells. Thus, the alanine substitution at position 408 in tapasin may interfere with the stable acquisition by MHC class I molecules of peptides that are sufficiently optimal to allow MHC class I release from tapasin.

Tapasin Is a Facilitator, Not an Editor, of Class I MHC Peptide Binding

Tapasin has been proposed to function as a peptide editor to displace lower affinity peptides and/or to favor the binding of high affinity peptides. Consistent with this, cell surface HLA-B8 molecules in tapasin-deficient cells were less stable and the peptide repertoire was substantially altered. However, the binding affinities of peptides expressed in the absence of tapasin were unexpectedly higher, not lower. The peptide repertoire from cells expressing soluble tapasin was similar in both appearance and affinity to that presented in the presence of full-length tapasin, but the HLA-B8 molecules showed altered cell surface stability characteristics. Similarly, the binding affinities of HLA-A*0201-associated peptides from tapasin(+) and tapasin(-) cells were equivalent, although steady state HLA-A*0201 cell surface expression was decreased and the molecules demonstrated reduced cell surface stability on tapasin(-) cells. These data are inconsistent with a role for tapasin as a peptide editor. Instead, we propose that tapasin acts as a peptide facilitator. In this role, it stabilizes the peptide-free conformation of class I MHC molecules in the endoplasmic reticulum and thus increases the number and variety of peptides bound to class I MHC. Full-length tapasin then confers additional stability on class I MHC molecules that are already associated with peptides.

The immunosuppressive effect of Fusarium mycotoxin as a function of HLA antigens

We examined the blastogenic response to phytohaemaglutinin (PHA) in HLA-B8, DR3 positive and negative subjects in the presence or absence of the immunosuppressive Fusarium mycotoxin. HLA-B8, DR3 haplotype was associated with a depression of the response to mitogen in the absence of the mycotoxin, whereas in the presence of deoxynivalenol we could not detect significant differences among individuals either possessing or lacking this haplotype.

Memory T cells constitute a subset of the human CD8+CD45RA+ pool with distinct phenotypic and migratory characteristics

Using HLA class I-viral epitope tetramers to monitor herpes virus-specific CD8(+) T cell responses in humans, we have shown that a significant fraction of responding cells revert from a CD45RO(+) to a CD45RA(+) state after priming. All tetramer-binding CD45RA(+) cells, regardless of epitope specificity, expressed a phenotype LFA-1(high)CCR7(low) that was stable for at least 10 years in infectious mononucleosis patients and indefinitely in asymptomatic carriers. CD8(+)CD45RA(+)LFA-1(high) cells were not present in cord blood but in adults account for up to 50% of CD8(+)CD45RA(+) cells. These CD45RA(+)LFA-1(high) cells have significantly shorter telomeres than CD45RA(+)LFA-1(low) cells, suggesting that the latter represent a naive population, while the former are memory cells. CD45RA(+) memory cells are a stable population of noncycling cells, but on stimulation they are potent producers of IFN-gamma, while naive CD8(+) cells produce only IL-2. The chemokine receptor profile and migratory potential of CD45RA(+) memory cells is very similar to CD45RO(+) cells but different to naive CD8 cells. In accord with this, CD45RA(+) memory cells were significantly underrepresented in lymph nodes, but account for virtually all CD8(+)CD45RA(+) T cells in peripheral tissues of the same individuals.

Peptide-MHC class I tetrameric complexes display exquisite ligand specificity

The production of synthetic MHC-peptide tetramers has revolutionized cellular immunology by revealing enormous CD8(+) T cell expansions specific for peptides from various pathogens. A feature of these reagents, essential for their staining function, is that they bind T cells with relatively high avidity. This could, theoretically, promote cross-reactivity with irrelevant T cells leading to overestimates of epitope-specific T cell numbers. Therefore, we have investigated the fine specificity of CTL staining with these reagents for comparison with functional data. Using a panel of CTL clones with distinct fine specificity patterns for analogs of an HLA-B8-binding EBV epitope, together with B8 tetramers incorporating these peptides, we show a very good correlation between tetramer staining and peptide activity in cytotoxicity assays. Significant staining only occurred with tetramers that incorporate strong stimulatory agonist peptides and not weak agonists that are unlikely to induce full T cell activation at physiological levels of presentation. In almost every case where a peptide analog had >10-fold less activity than the optimal EBV peptide in cytotoxicity assays, the corresponding tetramer stained with >10-fold less intensity than the EBV epitope tetramer. Furthermore, by examining an EBV-specific clonotypic T cell expansion in EBV-exposed individuals, we show similar fine specificity in tetramer staining of fresh peripheral T cells. Collectively, our data demonstrate the exquisite specificity of class I MHC-peptide tetramers, underlining their accuracy in quantifying only those T cells capable of recognizing the low levels of cell surface peptide presented after endogenous Ag processing.

Vaccination of melanoma patients with an allogeneic, genetically modified interleukin 2-producing melanoma cell line

Thirty-three metastatic melanoma patients were vaccinated according to a phase I-II study with an allogeneic melanoma cell line that was genetically modified by transfection with a plasmid containing the gene encoding human interleukin 2 (IL-2). The cell line expresses the major melanoma-associated antigens and the HLA class I alleles HLA-A1, -A2, -B8, and Cw7. All patients shared one or more HLA class I alleles with this cell line vaccine. Patients were immunized by three vaccinations, each consisting of 60 x 106 irradiated (100 Gy) melanoma cells (secreting 120 ng of IL-2/10(6) cells/24 hr) administered subcutaneously at weekly intervals for 3 consecutive weeks. Side effects of treatment consisted of swelling of locoregional lymph nodes and induration at the site of injection, i.e., a delayed-type hypersensitivity (DTH) reaction. In three patients, vaccination induced inflammatory responses in distant metastases containing necrosis or apoptosis along with T cell infiltration. Apoptosis occurred only in Bcl-2-negative areas, not in Bcl-2-expressing parts of the metastases. Two other patients experienced complete or partial regression of subcutaneous metastases. Seven patients had protracted stabilization (4 to >46 months) of soft tissue metastases, including one patient who developed vitiligo after vaccination. Immune responses to the vaccine could be detected in 67% of the 27 patients measured. Vaccination was shown to induce a variable change in the number of anti-vaccine cytotoxic T lymphocytes (CTLs) in peripheral blood, which did not correlate with response to treatment. However, in two of five patients the frequency of anti-autologous tumor CTLs measured was significantly higher than before vaccination. This study demonstrates the feasibility, safety, and therapeutic potential of vaccination of humans with allogeneic, gene-modified tumor cells, and that frequencies of vaccine-specific CTLs among patient lymphocytes can be determined by using a modified limited dilution analysis (LDA).

TCR usage by homocysteine-specific human CTL

We have recently demonstrated that homocysteine can modify HLA class I Ags and induce homocysteine-specific CTL (Hom-CTL) responses in humans. Here, we have investigated TCR usage by Hom-CTL from five patients with ankylosing spondylitis or reactive arthritis. TCR of HLA-A68-restricted Hom-CTL from two unrelated donors share the same TCR Valpha, Vbeta, and Jbeta gene segments (AV4, BV23, and BJ2S1, respectively) with similar third complementarity determining regions (CDR3) of the beta-chains. Interestingly, the Va and Vbeta gene segments employed by an HLA-B27-restricted Hom-CTL clone are also closely related to AV4 and BV23, indicating strong selection pressure for AV4, BV23, and related gene products in the homocysteine-specific TCR. An arginine or lysine residue frequently appeared at position alpha93 in the CDR3 of the TCR alpha-chains from Hom-CTL restricted by HLA-A68 or -B8. This may suggest a potential salt bridge between the carboxyl group of homocysteine and specific TCR. TCR usage by HLA-B27-restricted Hom-CTL from unrelated individuals appears to be less conserved, although two T cell clones from one individual rearranged the same V gene segments with identical lengths of CDR3. Implications of these data for the molecular mechanisms for homocysteine modification of HLA Ags are also discussed.

Soluble tapasin restores MHC class I expression and function in the tapasin-negative cell line .220

Tapasin forms a bridge between TAP (transporters associated with antigen processing) and MHC class I molecules and plays a critical role in class I assembly. In its absence, TAP and class I do not associate, and class I cell surface expression is reduced. We now identify two independent functions for tapasin. Tapasin increases TAP levels and allows more peptide to be translocated to the endoplasmic reticulum. Furthermore, when expressed in the tapasin-negative .220 cell line, recombinant soluble tapasin retains its association with class I and restores class I cell surface expression and function, even though it no longer binds TAP or increases TAP levels. This finding suggests that the association of tapasin with class I is sufficient to facilitate loading and assembly of class I molecules.

A broad cytotoxic T lymphocyte response to influenza type B virus presented by multiple HLA molecules

The HLA restriction and epitope specificity of cytotoxic T lymphocytes (CTL) involved in recovery from influenza type B infection have not been extensively characterized. Here lymphocytes obtained from a healthy individual contained virus-specific CTL restricted by class I HLA molecules, HLA-A1, A2, B7 and B8, and the class II HLA molecules, HLA-DR1 and DR3. Four conserved viral epitopes were predicted from allele-specific motifs for peptides interacting with HLA-B8 and HLA-DR1. Bulk CTL recognized three 9mer HLA-B8-restricted peptides from nucleoprotein, residues 30-38, 263-271 and 413-421, and a 13mer HLA-DR1-restricted peptide from hemagglutinin, residues 308-320. The epitopes presented by HLA-A1, HLA-B7 and HLA-DR3 remain undefined. Peptide-specific CTL lines recognized influenza type B virus-infected cells indicating the peptides are representative of naturally processed epitopes. A hemagglutinin peptide-specific CD4 CTL clone expressed approximately 200 molecules of perforin mRNA/cell, suggestive of a functional perforin pathway for target cell lysis. The results indicate a broad CTL response composed of both CD8 CTL and CD4 CTL recognizing viral epitopes presented by multiple HLA molecules.

Production and crystallization of MHC class I B allele single peptide complexes

Major histocompatibility complex class I B alleles, HLA B8, B53 and B3501 have been cloned, expressed, refolded and crystallized in specific complexes with a number of different 8-mer and 9-mer peptides. For some of these crystallization was initiated by cross-seeding between different B allele complexes. All crystallize in the space group P212121, with similar unit cell dimensions of approximately 52 A X 81 A X 112 A, contain one complex per asymmetric unit and diffract to approximately 2.0 A resolution.

Dependence of peptide binding by MHC class I molecules on their interaction with TAP

Major histocompatibility complex (MHC) class I molecules bind peptides that are delivered from the cytosol into the endoplasmic reticulum by the MHC-encoded transporter associated with antigen processing (TAP). Peptide capture by immature heterodimers of class I heavy chains and beta 2-microglobulin may be facilitated by their physical association with TAP. A genetic defect in a human mutant cell line causes the complete failure of diverse class I heterodimers to associate with TAP. This deficiency impairs the ability of the class I heterodimers to efficiently capture peptides and results from loss of function of an unidentified gene or genes linked to the MHC.

Immunogenic HIV variant peptides that bind to HLA-B8 can fail to stimulate cytotoxic T lymphocyte responses

Cytotoxic T lymphocyte responses in HIV infection can be impaired through variation in the epitope regions of viral proteins such as a gag. We report here an analysis of variant epitope peptides in three gag epitopes presented by HLA B8. Fifteen variant peptides were examined for their binding to HLA-B8; all but one bound at concentrations comparable to known epitopes. All except two of those that bound could be recognized by CTL from an HLA-B8 positive HIV-1-infected patient and were therefore immunogenic. However, in a hemophiliac patient studied in detail, there was a failure to respond to two immunogenic peptide epitopes representing virus present as provirus in the patient's peripheral blood. In one case, the patient's CTL had previously responded to the peptide; in the other case, there was a good response to a peptide of closely related sequence. Thus there was a selective failure of the CTL response to some proviral epitopes. This impaired reaction to new variants could contribute to the loss of immune control of the infection.

Specific cytotoxic T lymphocytes recognize the immediate-early transactivator Zta of Epstein-Barr virus

We identified the immediate-early transactivator Zta of Epstein-Barr virus as a target for specific cytotoxic T lymphocytes (CTL). Cells pulsed with overlapping synthetic peptides representing the entire amino acid sequence of Zta proved to be efficient for the in vitro stimulation of Zta-specific CTL in several donors. With peptide-pulsed target cells, we found that CTL from several donors recognize a peptide comprising 15 amino acids. The immune response against this peptide exerted by CTL lines from different donors was found to be restricted by two different molecules of the major histocompatibility complex: HLA-B8 and HLA-Cw6. The latter molecule could for the first time be identified as a restricting element for a CTL response. The epitope of the HLA-B8-restricted CTL could be mapped to an octameric sequence between amino acid positions 190 and 197 of the Zta protein, whereas the minimal epitope of HLA-Cw6-restricted CTL consists of 11 to 15 residues between positions 187 and 201. Thus, the HLA-B8 and HLA-Cw6 epitopes widely overlap but are not completely identical. In vitro stimulation of blood lymphocytes from a panel of HLA-B8-positive or HLA-Cw6-positive virus carriers, using autologous cells pulsed with the Zta peptides comprising the HLA-B8 or HLA-Cw6 epitope, respectively, revealed in both cases that most of these donors developed a Zta-specific cytotoxic activity. These data, as well as the high spread of the major histocompatibility complex molecules HLA-B8 and HLA-Cw6 in most populations, suggest that an efficient CTL response directed against gene products of the immediate-early group of the lytic cycle exists in vivo in a considerable portion of virus carriers. A CTL response against proteins expressed immediately after the switch into the lytic cycle could eliminate lytically activated cells at an early stage and would thus efficiently prevent the production and release of progeny virions.

A Japanese case of the fibrillar type of dermatitis herpetiformis

BACKGROUND

Although dermatitis herpetiformis (DH) is a relatively common disease in Caucasian populations, this disease is very rare in Asian populations including the Japanese.

METHODS AND RESULTS

We present a Japanese DH patient, who showed a fibrillar pattern of deposition of IgA, IgG, IgM and C3. The HLA typing revealed no B8/DR3. The survey of the Japanese literature and the comparison to studies on American or European DH revealed several interesting differences: high frequency of the fibrillar pattern, relatively high incidence of deposits of immunoglobulins other than IgA, rarity of gluten-sensitive enteropathy and HLA-B8/DR3 in Japanese DH.

CONCLUSION

The present study suggests that there may be a significant difference in pathophysiology between Caucasian and Japanese DH patients.

Endogenous peptides with distinct amino acid anchor residue motifs bind to HLA-A1 and HLA-B8

Distinct amino acid (aa) residue motifs for peptides binding to HLA-A1 and HLA-B8 were identified by sequence analyses of reversed-phase HPLC fractions containing endogenous peptides derived from these HLA molecules. Fifteen different primary sequences were determined for HLA-A1-associated peptides, 12 of which were nine aa in length. Common features among these peptide sequences were Tyr at the COOH-terminus, a negatively charged aa (usually Glu) at position 3 (P3), and Pro at P4. Twenty-seven different primary sequence assignments were made for HLA-B8-associated peptides, most of which were eight aa in length. Lys, and in a few cases Arg, predominated at P3 and P5; Leu and Pro predominated at P2, and Leu was the preferred COOH-terminal residue. Unlike all other human class I molecules whose peptide-binding properties have been studied, both HLA-A1 and HLA-B8 endogenous peptide sequences have a dominant anchor residue at P3, and these aa are opposite in charge to the aa at position 156 of the peptide-binding site. Synthetic peptides corresponding to endogenous peptide sequences bound to their respective HLA molecules in vitro, indicating that they derive from peptides bound to HLA and not from copurifying contaminants. Eight of the HLA-A1 and HLA-B8 endogenous peptide sequences matched intracellularly expressed proteins found in protein sequence data bases. The HLA-A1 peptide-binding motif was then used to identify potential antigenic peptides from influenza A viral proteins that bound to HLA-A1 in vitro.

Natural peptide ligand motifs of two HLA molecules associated with myasthenia gravis

The peptide motifs of two HLA molecules, B8 and DR3(17), which are associated with autoimmune diseases including myasthenia gravis, were determined from natural peptide pools using Edman degradation. The majority of HLA-B8 ligands are nonamers preferentially terminated by leucine. As a characteristic feature of the HLA-B8 motif, there is a high degree of conservation of positively charged amino acids at position 3 and 5, exclusively lysine at position 3, and lysine or arginine at position 5. Additional evidence for this allele-specific motif is the presence of these features in several viral peptides recognized by HLA-B8 restricted T cells. The DR3(17) motif is characterized by four conserved anchor-like positions ordered in an almost symmetrical arrangement, as has been found for DR1 and DR5 motifs. A first hydrophobic/aromatic anchor three to four residues apart from the N-terminus (at relative position 1) appears to be a common feature of DR ligands. The second anchor is an aspartate at relative position 4, which is likely to be the DR3(17)-specific contact site in the groove. Two additional conserved positions closer to the C-terminus are occupied by charged amino acids at relative position 6 and by hydrophobic/aromatic residues at positions 8, 9, or 10. Eight individual naturally processed DR17 ligands were sequenced and were found to be derived from exogenous proteins and cytoplasmic membrane receptors. These natural peptides conform well to the determined motif. A single exchange of the anchor-like positions in a model peptide abrogated binding to DR17+ cells.(ABSTRACT TRUNCATED AT 250 WORDS)