An altered peptide ligand inhibits the activities of matrix metalloproteinase-9 and phospholipase C, and inhibits T cell interactions with VCAM-1 induced in vivo by a myasthenogenic T cell epitope

On Peptides and Altered Peptide Ligands: From Origin, Mode of Action and Design to Clinical Application (Immunotherapy)

T lymphocytes equipped with clonotypic T cell antigen receptors (TCR) recognize immunogenic peptides only when presented in the context of their own major histocompatibility complex (MHC) molecules. Peptide loading to MHC molecules occurs in intracellular compartments (ER for class I and MIIC for class II molecules) and relies on the interaction of the respective peptides and peptide binding pockets on MHC molecules. Those peptide residues not engaged in MHC binding point towards the TCR screening for possible peptide MHC complex binding partners. Natural or intentional modification of both MHC binding registers and TCR interacting residues of peptides - leading to the formation of altered peptide ligands (APLs) - might alter the way peptides interact with TCRs and hence influence subsequent T cell activation events, and consequently T cell effector functions. This review article summarizes how APLs were detected and first described, current concepts of how APLs modify T cellular signaling, which biological mechanisms might force the generation of APLs in vivo, and how peptides and APLs might be used for the benefit of patients suffering from allergic or autoimmune diseases.

A shift in the collagen V antigenic epitope leads to T helper phenotype switch and immune response to self-antigen leading to chronic lung allograft rejection

Immune responses to human leucocyte antigen (HLA) and self-antigen collagen V (Col-V) have been proposed in the pathogenesis of chronic rejection (bronchiolitis obliterans syndrome, BOS) following human lung transplantation (LTx). In this study, we defined the role for the shift in immunodominant epitopes of Col-V in inducing T helper phenotype switch leading to immunity to Col-V and BOS. Sera and lavage from BOS(+) LTx recipients with antibodies to Col-V were analysed. Two years prior to BOS, patients developed antibodies to both Col-V,α1(V) and α2(V) chains. However, at clinical diagnosis of BOS, antibodies became restricted to α1(V). Further, lung biopsy from BOS(+) patients bound to antibodies to α1(V), indicating that these epitopes are exposed. Fourteen Col-V peptides [pep1-14, pep1-4 specific to α1(V), pep5-8 to α1,2(V) and pep9-14 to α2(V)] which bind to HLA-DR4 and -DR7, demonstrated that prior to BOS, pep 6, 7, 9, 11 and 14 were immunodominant and induced interleukin (IL)-10. However, at BOS, the response switched to pep1, 4 and 5 and induced interferon (IFN)-γ and IL-17 responses, but not IL-10. The T helper (Th) phenotype switch is accompanied by decreased frequency of regulatory T cells (T(regs) ) in the lavage. LTx recipients with antibodies to α1(V) also demonstrated increased matrix metalloproteinase (MMP) activation with decreased MMP inhibitor, tissue inhibitor of metalloproteinase (TIMP), suggesting that MMP activation may play a role in the exposure of new Col-V antigenic epitopes. We conclude that a shift in immunodominance of self-antigenic determinants of Col-V results in induction of IFN-γ and IL-17 with loss of tolerance leading to autoimmunity to Col-V, which leads to chronic lung allograft rejection.

Antiangiogenic versus cytotoxic activity in analogues of aeroplysinin-1

A series of analogues of the potentially angiogenic inhibitor aeroplysinin-1 1 were synthesized and their in vitro antiangiogenic and cytotoxic activities evaluated. In the case of epoxy ketone 6 and azlactone 36 the relationship sprouting inhibition assay/cytotoxicity in BAE cells was enhanced by one order and two orders of magnitude, respectively, with respect to the reference. These results imply more specific antiangiogenic properties for the synthesized derivatives.

MIP3 alpha stimulates the migration of Langerhans cells in models of human papillomavirus (HPV)-associated (pre)neoplastic epithelium

Although human papillomavirus (HPV) DNA is detected in the majority of cervical cancers and their precursors (squamous intraepithelial lesions; SIL), the persistence or progression of cervical lesions could be associated with quantitative and functional alterations of dendritic/Langerhans cells (DC/LC). As LC abnormalities have been associated with a decreased expression of macrophage inflammatory protein 3alpha (MIP3alpha) in cervical SIL, we tested the effect of exogenous MIP3alpha on the migration of LC in a (pre)neoplastic epithelium formed in vitro. By using a Boyden chamber assay, we first showed that the migratory capacity of LC generated in vitro is significantly increased in the presence of MIP3alpha compared to control medium. We next demonstrated that MIP3alpha is able to increase the 3D infiltration of LC in organotypic cultures of HPV-transformed keratinocytes. This property to stimulate LC migration was not altered after inclusion of MIP3alpha in a bioadhesive polycarbophil gel. Moreover, the function of DC to exert cytostatic effects and to present alloantigens was not altered in the presence of MIP3alpha.

Suppression of myasthenogenic responses of a T cell line by a dual altered peptide ligand by induction of CD4+CD25+ regulatory cells

Myasthenia gravis is a T cell-dependent, antibody-mediated autoimmune disease. A dual altered peptide ligand (APL) that is composed of the tandemly arranged two single amino acid analogs of two myasthenogenic peptides, p195-212 and p259-271, was demonstrated to down-regulate in vitro and in vivo myasthenia gravis-associated autoreactive responses. The aims of this study were to demonstrate the suppressive properties and to elucidate the mechanism of action of the dual APL on a T cell line specific to the myasthenogenic peptide p195-212. We demonstrate here that incubation of cells of the line with the dual APL resulted in the inhibition of proliferation and secretion of IL-2 and IFN-gamma triggered by p195-212. In contrast, secretion of TGF-beta and IL-10 was upregulated. The dual APL induced the generation of CD4+CD25+ cells that were characterized by the expression of CD45Rb(low), cytotoxic T lymphocyte-associated antigen-4, TGF-beta, CD62L, Foxp3, and neuropilin. In addition, the dual APL-treated cells were capable of inhibiting the proliferation response of the line when the two sets of cells were cocultured. The role of CD4+CD25+ cells was further confirmed by demonstrating that the suppression was abrogated by blocking/neutralization of CD25. Thus, the dual APL acts by inducing the formation of CD4+CD25+ regulatory cells. By using a T cell line, we could show that the immunosuppressive CD4+CD25+ cells were indeed induced by the dual APL and are not part of the naturally occurring regulatory cells.

Inhibition of obliterative airway disease development in murine tracheal allografts by matrix metalloproteinase-9 deficiency

This study was designed to define the roles of matrix metalloproteinase (MMP)-2 and MMP-9 in obliterative airway disease (OAD) in heterotopic murine tracheal allografts, considered a suitable animal model for chronic lung allograft rejection. BALB/c tracheal allografts were transplanted into MMP-2-deficient (-/-) and MMP-9-/- mice. Also, wild-type recipients were treated with doxycycline, a nonspecific MMP inhibitor. After 10, 20 and 30 days, allografts were analyzed for OAD development, intragraft levels of MMP-2 and MMP-9 and the frequency and cytokine/chemokine production profile of alloreactive T cells. Allografts transplanted into wild-type mice developed OAD lesions within 30 days. These allografts revealed significant upregulation of both MMP-2 and MMP-9. Allografts transplanted into MMP-9-/- and doxycycline-treated recipients did not develop OAD. In contrast, allografts transplanted into MMP-2-/- mice developed OAD lesions with normal kinetics. Interestingly, MMP-9-/- recipients showed an enhanced T cell alloreactivity associated with an abnormal profile of cytokine/chemokine production. The enhanced T cell alloreactivity in MMP-9-/- mice was mediated by enhanced dendritic cell stimulatory capacity as well as enhanced T cell responsive capacity. These results suggest that MMP-9 plays an important role in the pathogenesis of OAD and may represent a target for the therapeutic intervention of chronic lung allograft rejection.

Down-regulation of myasthenogenic T cell responses by a dual altered peptide ligand via CD4+CD25+-regulated events leading to apoptosis

The myasthenogenic peptides p195-212 and p259-271 are sequences of the human acetylcholine receptor and were shown to induce myasthenia gravis-associated immune responses in mice. A dual altered peptide ligand (APL) composed of the two APLs of the myasthenogenic peptides inhibited, in vitro and in vivo, those responses. The aims of this study were to elucidate the events that follow the in vivo treatment with the dual APL and to characterize the cell population that is induced by the latter. We demonstrate here that s.c. administration of the dual APL up-regulates CD4+CD25+ regulatory T cells that are characterized by up-regulated expression of cytotoxic T lymphocyte-associated antigen 4, intracellular and membranal TGF-beta, and Foxp3. Administration of the dual APL to mice concomitant with the immunization with either of the myasthenogenic peptides resulted also in the up-regulation of c-Jun-NH2-terminal kinase activity and of Fas signaling pathway molecules as determined by measuring Fas, Fas ligand, and caspase 8. Thus, our results suggest that the suppression of myasthenia gravis-associated T cell responses exerted by the dual APL is mediated by the CD4+CD25+ immunoregulatory T cell function via TGF-beta or cytotoxic T lymphocyte-associated antigen 4, which further stimulate a cascade of events that up-regulates apoptosis.

Therapeutic vaccines in autoimmunity

Similarly to prophylactic vaccines whose purpose is to prevent infectious diseases, therapeutic vaccines against autoimmune diseases are based on their similarity to the putative causes of the disease. We shall describe here two such examples: a copolymer of amino acids related to myelin basic protein, in the case of multiple sclerosis, and a peptide derived from the nicotinic acetylcholine receptor (AChR), in the case of myasthenia gravis (MG). Copolymer 1 (Cop 1, glatiramer acetate, Copaxone) is a synthetic amino acid random copolymer, immunologically cross-reactive with myelin basic protein and suppresses experimental allergic encephalomyelitis in several animal species. Cop 1 slows the progression of disability and reduces relapse rate in exacerbating-remitting multiple sclerosis patients. It was approved by the Food and Drug Administration in 1996, and today is used by tens of thousands of patients. Cop 1 is a potent inducer of T helper 2 (Th2) regulatory cells in mice and humans, and Th2 cells are found both in the brains and spinal cords of Cop 1-treated mice. MG and experimental autoimmune MG are T cell-regulated, antibody-mediated autoimmune diseases. Two peptides, representing sequences of the human AChR alpha-subunit, p195-212 and p259-271, are immunodominant T cell epitopes in MG patients and in two strains of mice. Altered peptide ligand, composed of the tandemly arranged two single amino acid analogs, inhibits in vitro and in vivo MG-associated autoimmune responses. The active suppression is mediated by the CD4(+)CD25(+) immunoregulatory cells and is associated with the down-regulation of Th1-type cytokines and the up-regulation of the secretion of IL-10 and the immunosuppressive cytokine, transforming growth factor beta.

Characterization of a mutant Bacillus subtilis adenylosuccinate lyase equivalent to a mutant enzyme found in human adenylosuccinate lyase deficiency: asparagine 276 plays an important structural role

Adenylosuccinate lyase, an enzyme catalyzing two reactions in purine biosynthesis (the cleavage of either adenylosuccinate or succinylaminoimidazole carboxamide ribotide), has been implicated in a human disease arising from point mutations in the gene encoding the enzyme. Asn(276) of Bacillus subtilis adenylosuccinate lyase, a residue corresponding to the location of a human enzyme mutation, was replaced by Cys, Ser, Ala, Arg, and Glu. The mutant enzymes exhibit decreased V(max) values (2-400-fold lower) for both substrates compared to the wild-type enzyme and some changes in the pH dependence of V(max) but no loss in affinity for adenylosuccinate. Circular dichroism reveals no difference in secondary structure between the wild-type and mutant enzymes. We show here for the first time that wild-type adenylosuccinate lyase exhibits a protein concentration dependence of molecular weight, secondary structure, and specific activity. An equilibrium constant between the dimer and tetramer was measured by light scattering for the wild-type and mutant enzymes. The equilibrium is somewhat shifted toward the tetramer in the mutant enzymes. The major difference between the wild-type and mutant enzymes appears to be in quaternary structure, with many mutant enzymes exhibiting marked thermal instability relative to the wild-type enzyme. We propose that mutations at position 276 result in structurally impaired adenylosuccinate lyases which are assembled into defective tetramers.

Plasmodium vivax promiscuous T-helper epitopes defined and evaluated as linear peptide chimera immunogens

Clinical trials of malaria vaccines have confirmed that parasite-derived T-cell epitopes are required to elicit consistent and long-lasting immune responses. We report here the identification and functional characterization of six T-cell epitopes that are present in the merozoite surface protein-1 of Plasmodium vivax (PvMSP-1) and bind promiscuously to four different HLA-DRB1* alleles. Each of these peptides induced lymphoproliferative responses in cells from individuals with previous P. vivax infections. Furthermore, linear-peptide chimeras containing the promiscuous PvMSP-1 T-cell epitopes, synthesized in tandem with the Plasmodium falciparum immunodominant circumsporozoite protein (CSP) B-cell epitope, induced high specific antibody titers, cytokine production, long-lasting immune responses, and immunoglobulin G isotype class switching in BALB/c mice. A linear-peptide chimera containing an allele-restricted P. falciparum T-cell epitope with the CSP B-cell epitope was not effective. Two out of the six promiscuous T-cell epitopes exhibiting the highest anti-peptide response also contain B-cell epitopes. Antisera generated against these B-cell epitopes recognize P. vivax merozoites in immunofluorescence assays. Importantly, the anti-peptide antibodies generated to the CSP B-cell epitope inhibited the invasion of P. falciparum sporozoites into human hepatocytes. These data and the simplicity of design of the chimeric constructs highlight the potential of multimeric, multistage, and multispecies linear-peptide chimeras containing parasite promiscuous T-cell epitopes for malaria vaccine development.

Three subunits contribute amino acids to the active site of tetrameric adenylosuccinate lyase: Lys268 and Glu275 are required

Tetrameric adenylosuccinate lyase (ASL) of Bacillus subtilis catalyzes the cleavage of adenylosuccinate to form AMP and fumarate. We previously reported that two distinct subunits contribute residues to each active site, including the His68 and His89 from one and His141 from a second subunit [Brosius, J. L., and Colman, R. F. (2000) Biochemistry 39, 13336-13343]. Glu(275) is 2.8 A from His141 in the ASL crystal structure, and Lys268 is also in the active site region; Glu275 and Lys268 come from a third, distinct subunit. Using site-directed mutagenesis, we have replaced Lys268 by Arg, Gln, Glu, and Ala, with specific activities of the purified mutant enzymes being 0.055, 0.00069, 0.00028, and 0.0, respectively, compared to 1.56 units/mg for wild-type (WT) enzyme. Glu275 was substituted by Gln, Asp, Ala, and Arg; none of these homogeneous mutant enzymes has detectable activity. Circular dichroism and light scattering reveal that neither the secondary structure nor the oligomeric state of the Lys268 mutant enzymes has been perturbed. Native gel electrophoresis and circular dichroism indicate that the Glu275 mutant enzymes are tetramers, but their conformation is altered slightly. For K268R, the K(m)s for all substrates are similar to WT enzyme. Binding studies using [2-3H]-adenylosuccinate reveal that none of the Glu275 mutant enzymes, nor inactive K268A, can bind substrate. We propose that Lys268 participates in binding substrate and that Glu275 is essential for catalysis because of its interaction with His141. Incubation of H89Q with K268Q or E275Q leads to restoration of up to 16% WT activity, while incubation of H141Q with K268Q or E275Q results in 6% WT activity. These complementation studies provide the first functional evidence that a third subunit contributes residues to each intersubunit active site of ASL. Thus, adenylosuccinate lyase has four active sites per enzyme tetramer, each of which is formed from regions of three subunits.

Gelatinase B: a tuner and amplifier of immune functions

Gelatinase B (matrix metalloproteinase-9) is a secreted multidomain enzyme that is important for the remodeling of the extracellular matrix and the migration of normal and tumor cells. It cleaves denatured collagens (gelatins) and type IV collagen, which is present in basement membranes. In the immune system, this cleavage helps lymphocytes and other leukocytes to enter and leave the blood and lymph circulations. Gelatinase B also cleaves myelin basic protein and type II gelatins, and this clipping leads to remnant epitopes that generate autoimmunity, the so-called REGA model of autoimmunity. Recently, gelatinase B has been found to process cytokines and chemokines, resulting in skewed immune functions. Therefore, gelatinase B, often considered as a pure effector molecule, acts as a switch and catalyst in both innate and specific immunity, and constitutes a prototypic example of the regulation of immune functions by proteolysis.