HLA-B7 β-pleated sheet-derived synthetic peptides are immunodominant T-cell epitopes regulating alloresponses

Abstract

Chronic rejection of transplanted allografts is the major cause of graft loss after clinical solid organ transplantation. Recent data link the indirect presentation of allopeptides to chronic graft loss; thus, identification of immunodominant epitopes on major histocompatibility complex (MHC) antigens could significantly contribute to establishing novel ways for monitoring and managing chronic rejection. Here, we show that synthetic allo-MHC-derived peptides covering the polymorphic region 56 to120 of HLA-B7 modulate alloresponses. In particular, the 2 ␤-pleated sheet-derived peptides covering residues 91 to 105 and 96 to 120, respectively, but not sequences from the ␣1 helix, were presented by autologous peripheral blood lymphocytes to induce T-cell proliferation. In addition, the 2 ␤-pleated sheetderived peptides and the ␣1-derived peptide residues 60 to 75 abrogated lysis of HLA-B7 target cells by anti-HLA-B7 cytotoxic T lymphocytes (CTLs). Although most residues between 91 and 120 are normally not directly accessible to T cells, our results indicate that peptides derived from the lower surface of the peptidebinding groove of HLA-B7 are immunodominant in HLA-B7 alloresponses. To characterize the binding and stability of allopeptides to T cells, the 62-70 peptidederived from the 60-75 allopeptide that blocked cytotoxicity of anti-HLA-B7 CTL-was synthesized and coupled with fluorescein isothiocyanate. The peptide specifically labeled anti-B7 CTL, but not anti-HLA-A2 CTL as measured by flow cytometry. Peptide binding to CTL was specific at 4°C and remained stable for 12 hours, whereas it remained stable for less than 2 hours at 37°C. These studies allow the identification of HLA-B7 T-cell epitopes and reveal for the first time a novel, previously unrecognized application of synthetic HLA-derived allopeptides to visualize alloreactive T cells. IntroductionStructural studies show that T-cell receptor (TCR) contacts bind peptide and large stretches of ␣1 and ␣2 major histocompatibility complex (MHC) helices. 1,2 In general, endogenous peptides derived from allo-MHC are seen by T cells as foreign-eliciting alloresponses. 3 T cells may recognize peptide-induced conformational changes, and they may also recognize surface MHC structures in addition to or independent of bound peptide. 4 Furthermore, allospecific cytotoxic T lymphocytes (CTLs) that are peptidedependent and peptide-specific have been described in the literature. 5 In general, however, when donor and recipient MHCs are structurally similar, the endogenous peptide appears to be the dominant target of alloreactive T cells, 5-7 a phenomenon backed by clinical data in graft-versus-host disease. 8 Synthetic allopeptides have been used in many different models to modulate alloresponses and to study alloreactivity. [9][10][11] In other studies, class I-and class II-derived allopeptides were used to induce tolerance. 12-14 By studying a series of rat-derived synthetic allo-MHC peptides, immunodominant regions of allogeneic MHC molecules that modulate graft surviv...

Soluble HLA‐G Molecules Induce Apoptosis in Natural Killer Cells

“…Interestingly, these isoforms are equally effective in regulating NK cells as we previously reported for T cells that were blocked by alternatively spliced sHLA or those obtained by enzyme cleavage of the transmembrane and cytoplasmic tails 28 . This is also consistent with the observation that alloreactive T cells are effectively regulated by synthetic peptides derived from MHC molecules 38,39 . In addition, similar results have been reported for HLA‐G isoforms, which have been seen to drive U937 myelomonocytic cell production of TGF‐ β 1 39 .…”

Allogeneic core amino acids of an immunodominant allopeptide are important for MHC binding and TCR recognition

“…Similar studies in allotransplantation have been hampered by the fact that, in contrast with autoimmune diseases, the immunodominant peptides responsible for the activation of the alloreactive T cells are determined by the MHC disparities between donors and recipients and thus are specific for each donor-recipient combination [12]. The identification and characterization of immunodominant allopeptides should facilitate the development of antigen-specific therapy after transplantation [13,34]. In the present study, we investigated the effects of allochimeric peptide analogues derived from the immunodominant WF MHC class I peptide P1 (RT1.A u ) on the alloimmune response in LEW (RT1 l ) rats.…”

“…The RT1.A u amino acids 5L, 9L, and 10T were subsequently replaced by the corresponding RT1.A l amino acids: methionine (5M), aspartic acid (9D), and isoleucine (10I). The syngeneic peptide Ac, with a sequence identical to LEW (RT1.A l , residues [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], was used as control peptide. Peptides were synthesized at MWG AG Biotech (München, Germany) and Jerini AG (Berlin, Germany) with a purity of 95% as determined by high-pressure liquid chromatography and mass chromatography.…”

“…An increasing body of evidence indicates in both humans and rodents that the indirect pathway of allorecognition plays a central role in acute and chronic allograft rejection [6 -11]. Moreover, it has been demonstrated that the indirect T-cell response is directed against a single or a few dominant peptides derived from the allogeneic MHC molecule [12][13][14]. Recent studies suggest that the indirect pathway is amenable to antigen-specific immunosuppression [15,16].…”