PEPTIDE SELECTION METHOD

Abstract: There is provided a method for selecting a tolerogenic peptide by selecting a peptide which is capable of binding to an MHC class I or II molecule without further processing. There is also provided a peptide selected by such a method and its use in a pharmaceutical composition and a method to treat and/or prevent a disease.

Description: PEPTIDE SELECTION METHOD The present invention relates to a method for selecting a tolerogenic peptide, a peptide identified by such a method and its use in the treatment and/or prevention of a disease. The present invention also relates to a pharmaceutical composition comprising a plurality of such tolerogenic peptides. BACKGROUND In an adaptive immune response, T lymphocytes are capable of recognising internal epitopes of a protein antigen. Antigen presenting cells (APC) take up protein antigens and degrade them into short peptide fragments. A peptide may bind to a major histocompatability complex (MHC) class I or II molecule inside the cell and be carried to the cell surface. When presented at the cell surface in conjunction with an MHC molecule, the peptide may be recognised by a T cell (via the T cell receptor (TCR)), in which case the peptide is a T cell epitope. T cell epitopes play a central role in the adaptive immune response to any antigen, whether self or foreign. The central role played by T cell epitopes in hypersensitivity diseases (which include allergy, autoimmune diseases and transplant rejection) has been demonstrated through the use of experimental models. It is possible to induce inflammatory or allergic diseases by injection of synthetic peptides (based on the structure of T cell epitopes) in combination with adjuvant. By contrast, it has been shown to be possible to induce immunological tolerance towards particular peptide epitopes by administration of peptide epitopes in soluble form. Administration of soluble peptide antigens has been demonstrated as an effective means of inhibiting disease in experimental autoimmune encephalomyelitis (EAE - a model for multiple sclerosis (MS)) (Metzler and Wraith (1993) Int. Immunol. 5:1159-1165; Liu and Wraith (1995) Int. Immunol. 7:1255-1263; Anderton and Wraith (1998) Eur. J. Immunol. 28:1251-1261); and experimental models of arthritis, diabetes, and uveoretinitis (reviewed in Anderton and Wraith (1998) as above). This has also been demonstrated as a means of treating an ongoing disease in EAE (Anderton and Wraith (1998) as above). The use of tolerogenic peptides to treat or prevent disease has attracted considerable attention. One reason for this is that it has been shown that certain tolerogenic epitopes can down-regulate responses of T cells for distinct antigens within the same tissue. This phenomenon, known as "bystander suppression" means that it should be possible to induce tolerance to more than one epitope (preferably all epitopes) within a given antigen, and to more than one antigen for a given disease, using a particular tolerogenic peptide (Anderton and Wraith (1998) as above). This would obviate the need to identify all of the pathogenic antigens within a particular disease. Peptides are also a favourable option for therapy because of their relatively low cost and the fact that peptide analogues can be produced with altered immunological properties. Peptides may thus be modified to alter their interactions with either MHC or TCR. One possible problem with this approach is that it has been shown that not all peptides which act as T cell epitopes are capable of inducing tolerance. The myelin basic protein (MBP) peptide 89-101 is an immunodominant antigen after immunisation and is also a very effective immunogen both in terms of priming for T cell reactivity and induction of EAE. However, this peptide has been shown to be ineffective at inducing tolerance when administered in solution (Anderton and Wraith (1998), as above). A number of explanations for the observed hierarchy in the ability of T cell epitopes to induce tolerance have been proposed (reviewed in Anderton and Wraith (1998) as above). In particular, it has been proposed that there is a correlation between the affinity of the peptide for the MHC and tolerogenicity (Liu and Wraith (1995) as above), but this does not tally with some of the observations. For example, MBP[89-101], which is not tolerogenic, binds to I-A s with relatively high affinity. It is thus not straightforward to predict which peptides will induce tolerance. If there were a rational explanation why only a proportion of peptide epitopes are capable of inducing tolerance, this would facilitate the selection of tolerogenic peptides useful in treating and preventing hypersensitivity disorders. SUMMARY OF THE INVENTION The present inventors have shown that if a peptide epitope is of an appropriate size to be presented by immature APC without antigen processing, it can induce immunological tolerance. The observation that some T cell epitopes are tolerogenic and others are incapable of inducing tolerance can therefore be explained by the fact that some epitopes require further processing before they are capable of being presented by an MHC molecule. These epitopes which require further processing do not induce tolerance when administered in a soluble form, despite their capacity to induce disease when injected in combination with adjuvant. The epitopes which do not require further processing are capable of inducing tolerance, and have been termed "apitopes" (Antigen Processing Independent epiTOPES) by the inventors. This finding provides a rule-based method for selection of tolerogenic T cell epitopes which obviates the need to examine the tolerogenic capacity of a peptide in vivo. This is particularly advantageous in the development of strategies to treat or prevent diseases for which no animal models are available. Even for diseases which have an animal model, the selection method should make the development of tolerance-inducing compositions simpler and safer, because it provides a mechanism whereby the tolerance induction capacity of a peptide can be tested on human T cells (recognising antigen in conjunction with human MHC molecules) in vitro, prior to their use in vivo. In a first aspect, therefore, the present invention provides a method for selecting a tolerogenic peptide which comprises the step of selecting a peptide which is capable of binding to an MHC class I or class II molecule without further processing. In a preferred embodiment, the peptide is capable of binding to an MHC class II molecule without further processing. A number of methods are known in the art for screening for peptides which are capable of acting as T cell epitopes for a given antigen. Commonly, therefore, the method will be used to select a tolerogenic peptide from a plurality of peptides each comprising a T cell epitope. In order to investigate whether a peptide is capable of binding to an MHC class I or II molecule without further processing, one can study the capacity of the peptide to bind MHC class I or II molecules using an antigen processing independent presentation system (APIPS). In a preferred embodiment, therefore the method comprises the following steps: (i) treating an APIPS with a peptide; and (ii) analysing binding of the peptide to MHC class I or II molecules within the APIPS. In a second aspect, the present invention provides peptide selected by the method of the first aspect of the invention. The peptide may be useful in the treatment and/or prevention of a disease. In particular, the peptide may be useful in the treatment and/or prevention of a disease which is mediated by autoreactive T cells. Hypersensitivity reactions are particularly amenable to treatment/prevention using the peptide of the present invention, for example allergy, autoimmunity and transplant rejection. The present inventors have already identified a number of apitopes for myelin basic protein, which is an autoantigen in multiple sclerosis. In an especially preferred embodiment, therefore, the peptides of the present invention are useful in the treatment and/or prevention of multiple sclerosis. It is known that some peptides are capable of inducing tolerance to other epitopes from the same antigen, and even other epitopes from a distinct antigen (by the phenomenon known as bystander suppression). However, the present inventors predict that in order to adequately suppress all the autoreactive T cells, it would be advantageous for a combination of various apitopes to be administered to the patient to treat/prevent a particular disease. In a third aspect, therefore, the present invention provides a pharmaceutical composition comprising a plurality of peptides according to the second aspect of the invention, each peptide being based on a T cell epitope. In a fourth aspect, the present invention provides a method for treating and/or preventing a disease in a subject which comprises the step of administering a peptide according to the second aspect of the invention to the subject. A general strategy for treating and/or preventing a disease in a subject may comprise the following steps: (i) identifying an antigen for the disease (ii) identifying an apitope for the antigen; and (iii) administering the apitope to the subject. BRIEF DESCRIPTION OF THE FIGURES Figure 1 shows a typical example of the kinetic profile to Mycobacterium tuberculosis purified protein derivative (PPD) and MBP in Multiple Sclerosis (MS) patients and healthy individuals. Peripheral blood mononuclear cells (PBMC) isolated from an MS patient (A) and normal individual (B) are tested for their ability to proliferate in the presence of PPD and whole MBP; the kinetic profile of the proliferative response to MBP is compared with that of secondary antigen PPD. Figure 2 is a table which summarises PBMC responses to MBP and its peptides in MS patients. Certain individuals are analysed on three separate time points, with a period of approximately 4 to 7 months between each time point. Figure 3 is a table which summarises PBMC responses to MBP and MBP-peptides in healthy individuals. Between 4 and 7 months elapsed between each time point. Figure 4 shows an example of an MS patient (MS 49) who responds to multiple peptides at 2 different time points, but for whom the recognition profile during the second time point, measured 4 months later, differs significantly. PBMC were cultured in the presence of MBP and a panel of peptides spanning the full length of MBP, and proliferation was measures by 3H-thymidine uptake, The broad T-cell proliferative response observed at the first time point was significantly different to the response measured 7 months later (second time point). Figure 5 shows an example of a patient whose broad epitope response (first time point) regresses (second time point) and reappears over a twelve-month period (third time point). Figure 6 shows a map of the fine specificity of the peptide regions identified in the kinetic response assay which is obtained through the use of TCC generated from MS patients and healthy individuals. Most of the peptides used in screening assays are 15-mer in length, however a few are 10-mer, and 1 peptide is 17-mer. The specificity of each TCC is tested at least twice. Figure 7a is a table showing the characterisation of T cell epitopes within myelin basic protein recognised by T lymphocytes from MS patients. Figure 7b is a table showing that all T cell epitopes are not necessarily presented by fixed APC and therefore not apitopes. Figures 8 and 9 show the presentation of various MBP peptides to T cell clones by live and fixed APC. Fig 8A- 30-44, Fig 8B - 110-124, Fig 9A - 130-144, Fig9B - 156-170. Figure 10 is a table which shows peak Stimulation Index (SI) values to MBP and MBP- peptides in MS patients obtained on three separate time points. Samples for the second time point were collected 4-8 months following the 1 st time point, and samples for the 3 rd time point were obtained 3-5 months following the second time point. Background cpm was measured for each day and varied between 80-700 cpm; a positive response (bold) was defined according to SI>3 and δcpm>1000. (It was not possible to collect samples for all three time points from patients MS 19 and MS 67). Figure 11 is a table which shows peak Stimulation Index (SI) values to MBP and MBP- peptides in healthy individuals. Background cpm was measured for each day and varied between 80-700 cpm; a positive response (bold) was defined according to SI>3 and dcρm>1000. Figure 12 shows the response of T-cells isolated from a DR2:MBP82-100 transgenic mouse to presentation of nested MBP peptides in the region 77-100 by APC. Figure 13 shows the response of T cell clone MS 17: A3 to presentation of nested MBP peptides in the region 125-148 by APC. Figure 14 is an illustration of T cell epitope recognition within the MBP 89-101 sequence. There are three distinct but overlapping T cell epitopes within the sequence: 89-94, 92-98 and 95-101. The potential for cleavage between residues 94 and 95 by the action of asparginyl endoepetidase (AEP) is shown. Figure 15 shows the capacity of MBP peptides 87-96 (A) and 89-101 (B) to act as an apitope for T cells responding to the 89-94 epitope. DETAILED DESCRIPTION OF INVENTION In a first aspect, the present invention relates to a method for selecting a tolerogenic peptide. Tolerance As used herein, the term "tolerogenic" means capable of inducing tolerance. Tolerance is the failure to respond to an antigen. Tolerance to self antigens is an essential feature of the immune system, when this is lost, autoimmune disease can result. The adaptive immune system must maintain the capacity to respond to an enormous variety of infectious agents while avoiding autoimmune attack of the self antigens contained within its own tissues. This is controlled to a large extent by the sensitivity of immature T lymphocytes to apoptotic cell death in the thymus (central tolerance). However, not all self antigens are detected in the thymus, so death of self-reactive thymocytes remains incomplete. There are thus also mechanisms by which tolerance may be acquired by mature self-reactive T lymphocytes in the peripheral tissues (peripheral tolerance). A review of the mechanisms of central and peripheral tolerance is given in Anderton et al (1999) (Immunological Reviews 169:123-137). Tolerance may result from or be characterised by the induction of anergy in at least a portion of CD4+ T cells. In order to activate a T cell, a peptide must associate with a "professional" APC capable of delivering two signals to T cells. The first signal (signal 1) is delivered by the MHC-peptide complex on the cell surface of the APC and is received by the T cell via the TCR. The second signal (signal 2) is delivered by costimulatory molecules on the surface of the APC, such as CD80 and CD86, and received by CD28 on the surface of the T cell. It is thought that when a T cell receives signal 1 in the absence of signal 2, it is not activated and, in fact, becomes anergic. Anergic T cells are refractory to subsequent antigenic challenge, and may be capable of suppressing other immune responses. Anergic T cells are thought to be involved in mediating T cell tolerance. Without wishing to be bound by theory, the present inventors predict that peptides which require processing before they can be presented in conjunction with MHC molecules do not induce tolerance because they have to be handled by mature antigen presenting cells. Mature antigen presenting cells (such as macrophages, B cells and dendritic cells) are capable of antigen processing, but also of delivering both signals 1 and 2 to a T cell, leading to T cell activation. Apitopes, on the other hand, will be able to bind class II MHC on immature APC. Thus they will be presented to T cells without costimulation, leading to T cell anergy and tolerance. Of course, apitopes are also capable of binding to MHC molecules at the cell surface of mature APC. However, the immune system contains a greater abundance of immature than mature APC (it has been suggested that less than 10% of dendritic cells are activated, Summers et al. (2001) Am. J. Pathol. 159: 285-295). The default position to an apitope will therefore be anergy/tolerance, rather than activation. It has been shown that, when tolerance is induced by peptide inhalation, the capacity of antigen-specific CD4+ T cells to proliferate is reduced. Also, the production of IL-2, IFN- γ and IL-4 production by these cells is down-regulated, but production of IL-10 is increased. Neutralisation of IL-10 in mice in a state of peptide-induced tolerance has been shown to restore completely susceptibility to disease. It has been proposed that a population of regulatory cells persist in the tolerant state which produce IL-10 and mediate immune regulation (Burkhart et al (1999) Int. Immunol. 11:1625-1634). The induction of tolerance can therefore be monitored by various techniques including: (a) reduced susceptibility to contract the disease for which the peptide is a target epitope in vivo; (b) the induction of anergy in CD4+ T cells (which can be detected by subsequent challenge with antigen in vitro); (c) changes in the CD4+ T cell population, including (i) reduction in proliferation; (ii) down-regulation in the production of IL-2, IFN-γ and IL-4; and (iii) increase in the production of L - 10. Antigen Processing Independent Epitopes (APITOPES) The method of the present invention comprises the step of selecting a peptide which is capable of binding to an MHC class I or II protein without further processing. Such peptides are known herein as "apitopes" (Antigen Processing Independent epiTOPES). en surface presentation of peptides derived from a given antigen is not random and tends to be dominated by a small number of frequently occurring epitopes. The dominance of a particular peptide will depend on many factors, such as relative affinity for binding the MHC molecule, spatio-temporal point of generation within the APC and resistance to degradation. The epitope hierarchy for an antigen can change with progression of an immune response, which has important implications for self-tolerance and autoimmunity. Immunodominant determinant regions are likely to be good tolerogens. Hence, in a preferred embodiment, the apitope of the present invention is based on a dominant epitope. However, after a primary immune response to the immunodominant peptides, epitope "spreading" may occur to sub-dominant determinants (Lehmann et al (1992) Nature 358:155-157). Presentation of sub-dominant epitopes may be important in triggering autoimmunity. The apitope of the present invention may, therefore be based on a subdominant epitope. For any given antigen, cryptic epitopes may also exist. Cryptic epitopes are those which can stimulate a T cell response when administered as a peptide but which fail to produce such a response when administered as a whole antigen. It may be that during processing of the antigen into peptides in the APC the cryptic epitope is destroyed. The present inventors have shown that peptide 92-98 is a cryptic epitope for MBP (Example 2C). Interestingly there is a putative cleavage site for asparaginyl endopeptidase within this peptide region, which may mean that during natural processing, no peptides containing this region are generated by the APC. A cryptic epitope may act as an apitope in vitro, in that it may be capable of binding to an MHC molecule without further processing, and inducing anergy in a T cell which recognises the cryptic epitope. However, such an apitope would be unlikely to be therapeutically useful because it should be incapable of tolerising T cells which recognise a naturally processed epitope of the antigen. Epitopes for an antigen may be identified by measuring the T cell response to overlapping peptides spanning the entire antigen (see below) when presented by APC. Such studies usually result in "nested sets" of peptides, and the minimal epitope for a particular T cell line/clone can be assessed by measuring the response to truncated peptides. It cannot be assumed that a minimal epitope of an antigen will behave as an apitope. It may well be that amino acids flanking the minimal epitope will be required for optimal binding to the MHC. The apitope should be designed to cover the possibility that there may be subtle differences between the minimal epitopes of different T cell clones. It should be emphasised that it may not be possible to identify an apitope for all epitopes. There is clear evidence that some epitopes bind MHC in a way that is dependent on MHC- loading in endosomes and hence require processing (Viner et al (1995) Proc. Natl. Acad. Sci. 92:2214-2218). This is another reason why one cannot assume that each minimal epitope will inevitably behave as an apitope. Identification of peptides containing T cell epitopes There are a number of methods known in the art to identify the T cell epitopes within a given antigen. Naturally processed epitopes may be identified by mass spectrophotometric analysis of peptides eluted from antigen-loaded APC. These are APC that have either been encouraged to take up antigen, or have been forced to produce the protein intracellularly by transformation with the appropriate gene. Typically APC are incubated with protein either in solution or suitably targeted to the APC cell surface. After incubation at 37°C the cells are lysed in detergent and the class II protein purified by, for example affinity chromatography. Treatment of the purified MHC with a suitable chemical medium (for example, acid conditions) results in the elution of peptides from the MHC. This pool of peptides is separated and the profile compared with peptide from control APC treated in the same way. The peaks unique to the protein expressing/fed cells are analysed (for example by mass spectrometry) and the peptide fragments identified. This procedure usually generates information about the range of peptides (usually found in "nested sets") generated from a particular antigen by antigen processing. Another method for identifying epitopes is to screen a synthetic library of peptides which overlap and span the length of the antigen in an in vitro assay. For example, peptides which are 15 amino acids in length and which overlap by 5 or 10 amino acids may be used. The peptides are tested in an antigen presentation system which comprises antigen presenting cells and T cells. For example, the antigen presentation system may be a murine splenocyte preparation, a preparation of human cells from tonsil or PBMC. Alternatively, the antigen presentation system may comprise a particular T cell line/clone and/or a particular antigen presenting cell type. T cell activation may be measured via T cell proliferation (for example using H- thymidine incorporation) or cytokine production. Activation of THl-type CD4+ T cells can, for example be detected via IFNγ production which may be detected by standard techniques, such as an ELISPOT assay. Overlapping peptide studies usually indicate the area of the antigen in which an epitope is located. The minimal epitope for a particular T cell can then be assessed by measuring the response to truncated peptides. For example if a response is obtained to the peptide comprising residues 1-15 in the overlapping library, sets which are truncated at both ends (i.e. 1-14, 1-13, 1-12 etc. and 2-15, 3-15, 4-15 etc.) can be used to identify the minimal epitope. The identification of immunodominant regions of an antigen using in vitro assays (especially those using T cell lines) is predicted to present a skewed pattern of peptide reactivity by the present inventors. In the study to identify MBP epitopes which is described in the examples, they use a kinetic response assay in which the proliferation of PBMC from MS patients and healthy individuals is measured against an overlapping peptide library. This assay is based on the finding that, although T cells form normal individuals and MS patients respond in a similar fashion to purified protein antigen, they respond in a different way to peptides based on the sequence of MBP. T cells from MS patients respond with greater magnitude and more rapid kinetics to peptide antigens when compared with normal healthy donors. This enables screening for and identification of the epitope to which the particular patient responds at a particular time. In the study decribed herein, this approach has revealed a number of epitope-containing regions that were not identified using standard techniques. Moreover is it shown that T cell recognition exhibits a cyclical pattern, appearing at one time point, regressing, and subsequently reappearing at a later date. The kinetic assay described by the inventors provides a valuable tool because it reveals the epitope to which a patient is responding at a particular time. This information may be used to tailor a therapeutic apitope-administration approach for a particular patient by identifying and administering an apitope for the relevant epitope (if there is one). This information may also enable a general pattern to be drawn up for disease progression, so that the therapeutic composition can be designed to include apitopes to the epitopes which are likely to be present at a given stage during the disease. Antigen Processing Independent Presentation Systems (APIPS) Once an epitope has been identified, the next step is to investigate whether it also behaves as an apitope. An apitope must be presented to T cells without the need for antigen processing. Having identified peptides containing T cell epitopes, apitopes may be identified using a processing free system. Truncated peptides and peptide analogues may be tested for activation using an antigen processing independent presentation system (APIPS). Examples of APIPS include: a) fixed APC (with or without antibodies to CD28); b) Lipid membranes containing Class I or II MHC molecules (with or without antibodies to CD28); and c) purified natural or recombinant MHC in plate-bound form (with or without antibodies to CD28). It is known to use fixed APC to investigate T cell responses, for example in studies to investigate the minimal epitope within a polypeptide, by measuring the response to truncated peptides (Fairchild et al (1996) Int. Immunol. 8:1035-1043). APC may be fixed using, for example formaldehyde (usually paraformaldehyde) or glutaraldehyde. Lipid membranes (which may be planar membranes or liposomes) may be prepared using artificial lipids or may be plasma membrane/microsomal fractions from APC. In use, the APIPS may be applied to the wells of a tissue culture plate. Peptide antigens are then added and binding of the peptide to the MHC portion of the APIPS is detected by addition of selected T cell lines or clones. Activation of the T cell line or clone may be measured by any of the methods known in the art, for example via H-thymidine incorporation or cytokine secretion. Peptides The second aspect of the invention relates to a peptide. The term "peptide" is used in the normal sense to mean a series of residues, typically L- amino acids, connected one to the other typically by peptide bonds between the α-amino and carboxyl groups of adjacent amino acids The term includes modified peptides and synthetic peptide analogues. A peptide of the present invention may be any length that is capable of binding to an MHC class I or II molecule without further processing. Peptides that bind to MHC class I molecules are typically 7 to 13, more usually 8 to 10 amino acids in length. The binding of the peptide is stabilised at its two ends by contacts between atoms in the main chain of the peptide and invariant sites in the peptide-binding groove of all MHC class I molecules. There are invariant sites at both ends of the groove which bind the amino and carboxy termini of the peptide. Variations is peptide length are accυmodated by a kinking in the peptide backbone, often at proline or glycine residues that allow the required flexibility. Peptides which bind to MHC class II molecules are typically between 8 and 20 amino acids in length, more usually between 10 and 17 amino acids in length, and can be much longer. These peptides lie in an extended conformation along the MHC II peptide-binding groove which (unlike the MHC class I peptide-binding groove) is open at both ends. The peptide is held in place mainly by main-chain atom contacts with conserved residues that line the peptide-binding groove. The peptide of the present invention may be made using chemical methods (Peptide Chemistry, A practical Textbook. Mikos Bodansky, Springer- Verlag, Berlin.). For example, peptides can be synthesized by solid phase techniques (Roberge JY et al (1995) Science 269: 202-204), cleaved from the resin, and purified by preparative high performance liquid chromatography (e.g., Creighton (1983) Proteins Structures And Molecular Principles, WH Freeman and Co, New York NY). Automated synthesis may be achieved, for example, using the ABI 43 1 A Peptide Synthesizer (Perkin Elmer) in accordance with the instructions provided by the manufacturer. The peptide may alternatively be made by recombinant means, or by cleavage from a longer polypeptide. For example, the peptide may be obtained by cleavage from the target antigen. The composition of a peptide may be confirmed by amino acid analysis or sequencing (e.g., the Edman degradation procedure). In a preferred embodiment the peptide is derivable from a target antigen. A target antigen is a molecule (for example a protein or glycoprotein) which is processed by APC and recognised by T cells during the course of the disease. The target antigen will, of course, depend on the target disease. Preferably the peptide is derivable from a fragment of the antigen which arises by natural processing of the antigen by an APC. For practical purposes, there are various other characteristics which the peptide should show. For example, the peptide should be soluble at a concentration which permits its use in vivo. Preferably the peptide should be soluble at concentrations of up to 0.5 mg/ml, more preferably the peptide should be soluble at concentrations of up to 1 mg/ml, most preferably the peptide should be soluble at concentrations of up to 5 mg/ml. For intranasal administration the maximum volume of dose which can be taken up using current procedures is approximately 200μl per nostril. If the peptide is soluble at lmg/ml, a double dose to each nostril enables 800μg to be given to the patient. It is unusual to give more that 5mg in any individual dose. It is also important that the peptide is sufficiently stable in vivo to be therapeutically useful. The present inventors have found that in vivo, 30 minutes after administration the total amount of a test peptide drops to about 50%, 4 hours after administration the amount drops to about 30%, but that after 5 days the peptide is still detectable (at about 5%). The half-life of the peptide in vivo should be at least 10 minutes, preferably at least 30 minutes, more preferably at least 4 hours, most preferably at least 24 hours. The present inventors have found that following intranasal administration, the amount of peptide in the draining lymph node peaks at about 4 hrs following administration, however peptide is still detectable (at levels of about 5% maximum) after 5 days. Preferably the peptide is sufficiently stable to be present at a therapeutically active concentration in the draining lymph node for long enough to exert a therapeutic effect. The peptide should also demonstrate good bioavailability in vivo. The peptide should maintain a conformation in vivo which enables it to bind to an MHC molecule at the cell surface without due hindrance. Target diseases In one embodiment, the peptide of the second aspect of the invention is for use in the treatment and/or prevention of a disease. An apitope for MHC class II is likely to be particularly useful in diseases which are mediated by CD4+ T cell responses. For example, diseases which are established or maintained by an inappropriate or excessive CD4+T cell response. Such a peptide is likely to be particularly useful in. the treatment of hypersensitivity disorders. Hypersensitivity reactions include: (i) allergies, resulting from inappropriate responses to innocuous foreign substances; (ii) autoimmune diseases, resulting from responses to self tissue antigens; and (iii) graft rejection, resulting from responses to a transplant. Examples of allergies include, but are not limited to: hay fever, extrinsic asthma, insect bite and sting allergies, food and drug allergies, allergic rhinitis, bronchial asthma chronic bronchitis, anaphylactic syndrome, urticaria, angioedema, atopic dermatitis, allergic contact dermatitis, erythema nodosum, erythema multiforme, Stevens- Johnson Syndrome, rhinoconjunctivitis, conjunctivitis, cutaneous necrotizing venulitis, inflammatory lung disease and bullous skin diseases. Examples of the autoimmune diseases include, but are not limited to: rheumatoid arthritis (RA), myasthenia gravis (MG), multiple sclerosis (MS), systemic lupus erythematosus (SLE), autoimmune thyroiditis (Hashimoto's thyroiditis), Graves' disease, inflammatory bowel disease, autoimmune uveoretinitis, polymyositis and certain types of diabetes, systemic vasculitis, polymyositis-dermatomyositis, systemic sclerosis (scleroderma), Sjogren's Syndrome, ankylosing spondylitis and related spondyloarthropathies, rheumatic fever, hypersensitivity pneumonitis, allergic bronchopulmonary aspergillosis, inorganic dust pneumoconioses, sarcoidosis, autoimmune hemolytic anemia, immunological platelet disorders, cryopathies such as cryofibrinogenemia and autoimmune polyendocrinopathies. A variety of tissues are commonly transplanted in clinical medicine, including kidney, liver, heart lung, skin, cornea and bone marrow. All grafts except corneal and some bone marrow grafts usually require long-term immunosuppression at present. In one embodiment of this aspect of the invention, the peptide is for use in the treatment and/or prevention of diabetes. In this embodiment, the peptide may be derivable from the target antigen IA2. In a further embodiment of this aspect of the invention, the peptide is for use in the treatment and/or prevention of multiple sclerosis (MS). Multiple sclerosis (MS) is a chronic inflammatory disease characterised by multiple demyelinating lesions disseminated throughout the CNS white matter and occurring at various sites and times (McFarlin and McFarland, 1982 New England J. Medicine 307:1183-1188 and 1246- 1251). MS is thought to be mediated by autoreactive T cells. In this embodiment the peptide may be derivable from one of autoantigens . in particular myelin basic protein (MBP) or proteolipid protein (PLP). MBP is possibly more appropriate than PLP, because PLP is highly hydrophobic and peptides derived from it tend to clump together. MBP is immunogenic and MBP-specific T lymphocytes have encephalitogenic activity in animals (Segal et al., 1994 J. Neuroimmunol. 51:7-19; Voskuhl et al, 1993 J. Neuroimmunol 42:187-192; Zamvil et al, 1985 Nature 317:355-8). In a preferred embodiment, the peptide is derivable from one of the immunodominant regions of MBP, namely: 1-24, 30-54, 75-99, 90-114, 105-129, 120-144, 135-159 and 150-170. In an especially preferred embodiment the peptide is selected from one of the MBP peptides shown to act as apitopes by the present inventors, which include the following peptides: 30-44, 80-94, 83-99, 81-95, 82-96, 83-97, 84-98, 110-124, 130-144, 131-145, 132-146 and 133-147. Apitopes for MHC class I may be used, for example, to modify anti-viral CD8+ responses in a tolerogenic fashion. Pharmaceutical composition The present inventors predict that, despite "bystander suppression" it may be necessary to target a number of different T cell clones in order to induce tolerance effectively. Hence a plurality of peptides may be administered to an individual in order to prevent or treat a disease. In a third aspect, the present invention relates to a pharmaceutical composition comprising a plurality of apitopes. The pharmaceutical composition may, for example comprise between 2 and 50 apitopes, preferably between 2 and 15 apitopes. The apitopes may be derivable from the same or different target antigen(s). Preferably the apitopes are either all able to bind to MHC class I, or all able to bind MHC class II, without further processing. In a preferred embodiment all the apitopes in the pharmaceutical composition are either able to bind to MHC class I or class II without further processing. The pharmaceutical composition may be in the form of a kit, in which some or each of the apitopes are provided separately for simultaneous, separate or sequential administration. Alternatively (or in addition) if the pharmaceutical composition (or any part thereof) is to be administered in multiple doses, each dose may be packaged separately. The pharmaceutical composition may comprise a therapeutically or prophylactically effective amount of the or each apitope and optionally a pharmaceutically acceptable carrier, diluent or excipient. Also, in the pharmaceutical compositions of the present invention, the or each apitope may be admixed with any suitable binder(s), lubricant(s), suspending agent(s), coating agent(s), or solubilising agent(s). Administration ine peptide should be administered in soluble form in the absence of adjuvant. Preferably the peptide is administered by a mucosal route. Studies have shown that peptide, when given in soluble form intraperitoneally (i.p.), intravenously (i.v.) or intranasally (i.n.) or orally can induce T cell tolerance (Anderton and Wraith (1998) as above; Liu and Wraith (1995) as above; Metzler and Wraith (1999) Immunology 97:257-263). Preferably the peptide is administered intranasally. Studies in mice have demonstrated that the duration of peptide administration required to induce tolerance depends on the precursor frequency of T cells in the recipient (Burkhart et al (1999) as above). In many experimental studies, it has been shown that repeated doses of peptide are required to induce tolerance (Burkhart et al (1999) as above). The exact dose and number of doses of peptide will therefore depend on the individual, however, in a preferred embodiment a plurality of doses is administered. If a plurality of peptides is administered simultaneously, they may be in the form of a "cocktail" which is suitable for administration in single or multiple doses. Alternatively it may be preferably to give multiple doses but vary the relative concentrations of the peptides between doses. In a preferred embodiment a "dose escalation" protocol may be followed, where a plurality of doses is given to the patient in ascending concentrations. Such an approach has been used, for example, for phospholipase A2 peptides in immunotherapeutic applications against bee venom allergy (Mϋller et al (1998) J. Allergy Clin Immunol. 101:747-754 and Akdis et al (1998) J. Clin. Invest. 102:98-106). EXAMPLES The following examples serve to illustrate the present invention, but should not be construed as a limitation thereof. The invention particularly relates to the specific embodiments described in these examples EXAMPLE 1 - Identification of T cell epitopes in MBP Materials and Methods Antigens Human MBP is prepared from brain white matter as described by Deibler et al. (Deibler et al., 1972 Preparative Biochemistry 2:139), and its purity assessed by SDS-PAGE. MBP and Mycobacterium tuberculosis purified protein derivative (PPD) (UK Central Veterinary Laboratory, Surrey) are used in proliferative assays at previously determined optimal concentrations; the optimum concentration for each antigen is 50 μg/ml. A panel of 15- mer overlapping peptides spanning the whole MBP molecule are synthesized using standard F-moc chemistry on an Abimed AMS 422 multiple peptide synthesizer (Abimed, Langenfeld, Germany). Each peptide is displaced by 5 aa and overlapped by 10 aa. We produce 33 peptides that are pooled into groups of 3 and pools are tested at the optimum concentration of 50 μg/ml, such that in vitro each peptide is present at a concentration of 16.6 μg/ml. Patients and control subjects The subjects of this study consist of 12 patients with clinically definite or laboratory supported definite MS (Poser et al., 1983), with an age range of 29-51 years. Eight of the 12 patients are involved in a trial of interferon-β, otherwise all other MS patients have received no corticosteroid treatment for at least 3 months prior to the commencement of the study. The control group consisted of 13 healthy individuals with an age range of 25- 55 years, and none have received immunosuppressive therapy for at least 3 months prior to the blood sample being obtained. Tissue culture medium RPMI-1640 medium supplemented with 20mM HEPES (Sigma, Poole, UK), penicillin (lOOU/ml), streptomycin sulphate (100 mg/ml), and 4 mM L-glutamine (all from Life Technologies, Paisley, Scotland), is used as the tissue culture medium. Medium without serum is used for washing lymphoid cells and TCL. For all culture conditions and assays, medium is supplemented with 10 % heat inactivated autologous plasma. Culture conditions and T cell proliferative assays Citrated peripheral blood (50-100 ml) is collected by venepuncture from each subject after informed written consent had been obtained. Peripheral blood mononuclear cells (PBMC) are isolated from blood by density centrifugation on Histopaque-1077 (Sigma, Poole, UK), and cultured in 1.5 ml volumes in 24-well tissue culture plates (Nunc International, Costar, Corning Inc. New York, USA) at a concentration of lxl 0 6 cells per ml, containing either PPD, MBP or peptides of MBP. The plates are incubated at 37°C in a humidified atmosphere of 5% CO /95% air. Between days 5 and 14 duplicate aliquots of 100 μl are withdrawn from each culture, transferred to a 96-well round bottom microtitre plate and pulsed with 0.4 μCi [ 3 H] -Thymidine (Amersham International, Amersham, UK). After 18 hours cells are harvested onto glass fibre mats (LKB-Wallac, Turku, Finland) using a Mach 111 harvester 96 (Tomtec, Orange, New Jersey, USA). [ 3 H]- Thymidine incorporation is determined using a Microbeta liquid scintillation counter (LKB-Wallac). Test wells containing antigen are considered positive when the δcpm >1000 and the Stimulation Index (SI) >3, where SI = CPM antigen containing culture/CPM culture without antigen. Generation of T cell lines and T cell clones MBP-specific T cell lines (TCL) are generated from 8 MS patients and 2 healthy control donors. PBMC from each subject are separated as described above and plated out at 1x10 cells/ml in 6-well plates in the presence of MBP (50 μg/ml); a portion of PBMC from each subject is regularly frozen and stored for subsequent restimulations. Seven days later the cells are fed with fresh medium containing 2% IL-2 (Lymphocult-HT; Biotest LTD., Birmingham, UK), and on day 12 of culture all cells are restimulated with antigen, IL-2 and irradiated (2500 Rad) autologous PBMC as a source of antigen presenting cells (APC), at a cell ratio of IT cell:5 APC. Cells are expanded in IL-2 every 3-4 days, and on day 14 are restimulated with antigen, IL-2 and PBMC, as described above. On the day of the first restimulation cells are examined for specific proliferation to MBP. Briefly, 2xl0 4 T cells and lxl 0 5 irradiated autologous PBMC are cultured in triplicate, in 96-well round- bottom plates, in the presence of MBP. Cells are cultured for 2 days and pulsed with ( 3 H)- Thymidine at 0.4 μCi/well during the last 18 hours of the culture. Cells are then harvested as described above, and a TCL is considered to be MBP-specific with a δcpm >1000 and a SI>3. Following 3 restimulation expansion cycles TCL are cloned using PHA (Sigma, Poole, Dorset, UK)) in the presence of autologous irradiated PBMC as APC. T cells are plated under limiting dilution conditions at 0.1 cell/well, 0.3 cell/well and 1 cell/well and cultured in Terasaki plates (Nunc International, Costar) with lxl 0 4 irradiated PBMC, 5μg/ml PHA, and 2% IL-2. After 10-12 days, growth-positive wells are expanded onto 96- well round-bottom plates, using lxl 0 5 irradiated PBMC, 5 μg/ml PHA and IL-2. Three days later wells are fed with fresh medium containing IL-2, and on day 7 the clones are expanded onto 48-well plates using 5xl0 5 irradiated PBMC, PHA and IL-2; at this point clones are tested in proliferation assays for specific responses to MBP. MBP-specific clones are expanded a week later onto 24-well plates, using lxl 0 6 irradiated PBMC with PHA or Dynabeads (Dynal, UK) and IL-2. The clones are maintained in 24-well plates using a 7-10 day restimulation/expansion cycle, essentially as described above. The ability of T cell clones (TCC) to recognise the panel of MBP peptides is tested by proliferation assays, as described above. Results MBP-peptide recognition amongst MS patients and healthy individuals The present inventors use a kinetic response assay in which PBMC from MS patients and healthy subjects are tested for their ability to respond to a panel of overlapping 15-mer synthetic peptides spanning the full length of human MBP. The proliferative response of PBMC from each culture is examined at 5 time points over a period of 2 weeks, and the kinetic profile of the response to MBP and peptides is compared with the response to PPD, the latter representing a secondary response/memory antigen. No significant difference is found in the PBMC response to MBP and/or peptides between patients on Interferon-β and those on no treatment (data not shown). The response to MBP in both MS patients and healthy controls peaked later than the response to PPD, thereby following the kinetic characteristics of the response to a non-recall antigen. Figure 1 shows a typical example of the kinetic profile to PPD and MBP in MS patients and healthy individuals. As shown in Figure 2, the two peptides most commonly recognised by MS patients are 90- 114 and 75-99 (6/12 patients each), followed by regions 30-54, 135-159 and 150-170 (5/12 patients), and 1-24 and 105-129 (4/12 patients). Three patients respond to aa 15-39 and 120-144. Two patients recognise 45-69, and none of the MS patients respond to region 60-84. According to Figure 10, where all the patients are HLA-DR2 positive, the two peptides most commonly recognised by MS patients are 90-114 and 75-99 (6/11 patients each), followed by regions 120-144, 135-159 and 150-170 (5/11 patients), and 1-24, 15-39, 30-54 and 105-129 (4/11 patients). Three patients respond to aa 45-69, and again none of the MS patients respond to region 60-84. By contrast, healthy individuals recognise significantly fewer peptides, with only 2 control subjects responding to more than 2 peptides (C and J; Figure 3). Control individuals C and J are the only two who recognise aa 60-84, a region not seen by this group of patients. Interestingly both these individuals express the DRBl* 0701 allele. Regions 45-69 and 105-129 are not recognised by any of the healthy donors, whereas 75-99 and 150-170 are recognised by 4 healthy individuals; 135-159 is recognised by three healthy individuals; 1- 24, 30-54, 60-84 and 120-144 is recognised by two healthy individuals; and 15-39 and 90- 114 are recognised by one individual. Overall, 8/13 healthy individuals do not respond to any of the overlapping peptides, whereas only 1/12 MS patients (MS 19) consistently fail to recognise the MBP peptides. Notably this patient is unique in not responding to MBP protein. Figure 11 also shows the response of healthy individuals to MBP peptides. In this study, only 1 control subject responds to more than 2 peptides (Nil). Ni l is also the only individual who recognises aa 60-84, a region not seen by this group of patients. Regions 15-39, 45-69 and 105-129 are not recognised by any of the healthy donors, wheres 120- 144 and 135-159 are recognised by two healthy individuals; and 1-24, 30-54, 60-84, 75- 99, 90-114 and 150-170 are recognised by one individual. Overall, 9/12 healthy individuals do not respond to any of the overlapping peptides. Overall, the day on which the response to MBP and/or peptides peaked did not differ significantly between healthy individuals and patients, and the kinetics in both groups resembled those of a primary antigenic response. In addition, the magnitude of the response to MBP and peptides did not differ between patients and healthy individuals. MBP-peptide recognition changes over time Having established that patients with MS respond to a broad spectrum of MBP peptides, the present inventors decided to examine whether PBMC recognition in the same individuals is focused and stable over the course of approximately 4-12 months. As shown in Figures 2, 10 and 3 neither the MS patients nor the healthy individuals exhibited the same peptide recognition pattern. Figure 4 represents an example of an MS patient (MS 49) who responds to multiple peptides at 2 different time points, but the recognition profile during the second time point, measured 4 months later, differs significantly. That is, in the second kinetic assay the PBMC response to aa 15-39, 30-54 and 150-170 persists, however the response to 75-99 and 105-129 regresses and shifts to regions 90-114 and 135-159. Figure 5 (MS 60) illustrates an example of a patient whose broad epitope response regressed to a focused response over the period of 4 months. The healthy individuals who are tested the second time round fail to respond to any of the peptides (Figure 3). Overall the results demonstrate that patients with MS do not exhibit set patterns of recognition. Within each patient the PBMC response to several peptides can persist, regress, and shift to new regions of MBP, as seen in patient MS 49. Cycling of peptide recognition When the PBMC response to peptides is analysed at 3 or more different time points over a period of 12 months, it becomes clear that in certain patients epitope recognition appears to fluctuate rather than shift irreversibly to new peptide regions. For example, as shown in Figures 2 and 10, patient MS 60 exhibits a cycling pattern of recognition to aa 120-144 and 135-159; that is, residues 120-144 and 135-159 are amongst many recognised at the first time point tested, the response to these 2 regions regresses by the second time point and then reappears at the third time point measured 4 months later. The kinetic profile of patient MS 41 demonstrates, similarly, that recognition of aa 135-159 fluctuates over several time points (see Figures 2 and 10). Amongst the healthy control group (Figure 3), one individual (M) exhibits a fluctuating response to regions 75-99 and 135-159, a second individual (F) recognises 75-99 at two of the three time points analysed, whilst a third subject (D) shows a cyclical response to residue 15-39. Fine mapping the response to MBP TCC are generated from 8 MS patients and 2 healthy individuals, and used to clarify the fine specificity of the peptide regions identified in the kinetic response assay. The specificity of each TCC is tested by its proliferative response to the panel of 15-mer peptides. Clone SD:A7 recognised region 1-24, and within this region this TCC responded to aa 5-19. Region 30-54 is recognised by 4 clones (MS49:D3, MS49:C8, MS49:A8, MS49:B6) and the epitope within this region is 30-44. One clone (MS39:D7) from an MS patient recognises peptide 60-74, and interestingly one healthy individual responds to this region (60-84) in our kinetic response assay. Five clones (MS43:A7, MS41.B6, MS41:A2, MS41:C6, N5:8) recognise aa 83-99 which is contained in region 75-99. One patient produced TCC specific for aa 110-124 (MS60:A2, MS60:B3), contained within the 105- 129 pool, and another TCC from the same patient is specific to 130-144 (MS60:E1), lυuiiu within the 120-144 region. Five individuals produce clones which recognise epitopes within the region 135-159: MS60:F7, MS60.D1, MS59:F1 and N5:19 recognises aa 140-154; MS57:A1 is specific to 140-149, and TCC MS17:A3 responds to sequence 130-144. This panel of clones clearly demonstrates the presence of at least 2 T cell epitopes within the 135-159 region of MBP. Lastly, region 150-170 is recognised by 2 clones specific to aa 156-169. The specificity of all TCC is summarised in Figure 6. EXAMPLE 2 - Identification of apitopes in MBP Materials and methods Antigen-presentation assay using an APIPS Presentation of the peptides to T cell clones is measured by proliferation. APC are fixed in 0.5% paraformaldehyde and plated at 1 x 10 5 cells per well of a 96-well tissue culture plate. T cells clones are plated at 2 x 10 4 cells per well in the presence of varying concentrations of peptide. After incubation for 48 h at 37°C, proliferation is measured by [ 3 H] thymidine incorporation over 16-20h. Results are compared with the ability of T cells to respond to the epitope presented by live APC. Presentation of peptides to T cells isolated from DR2:MBP82-100 transgenic mouse was essentially as described above except APC were plated at 5 x 10 5 cells per well, T cells were plated at 1 x 10 5 cells per well, and incubation was allowed to proceed for 72h prior to the addition of [ 3 H]-thymidine. Results In this experiment, peptides which have been identified as epitopes in the previous example are examined for their capacity to be presented using an APIPS. The results are shown in Figure 7b. Of the five epitopes examined so far, four were found to be apitopes (30-44, 80-94, 110-124 and 130-144) and one was found to act as an epitope but not an apitope (156-170). example 2A - Investigation of MBP peptides 30-44, 110-124, 130-144 and 156-170 In order to investigate whether various MBP peptides are apitopes, their capacity to be presented to T-cells by fixed APC is investigated. Live or pre-pulsed Mgar (HLA- DR2+ve) cells are pre-pulsed with the peptide in serum, or serum alone for 3.5 hours. Excess peptide is then removed from cells and the appropriate T cell clone added. The T cell proliferative response is measured by 3 H-thymidine uptake. As shown in Figures 8 and 9, peptides 30-44 (Fig 8A), 110-124 (Fig 8B), and 130-144 (Fig 9A) can be presented by fixed APC without further processing. These peptides are therefore defined as apitopes. Peptide 156-170, on the other hand, requires further processing for presentation to T cells (Fig 9B). Fixed APC are unable to present this epitope to T cells, so 156-170 is not an apitope. Example 2B - Identification of apitopes within the regions 77-100 and 125-148 of MBP For any given epitope, there may exist one or more apitopes, capable of being presented to APC without further processing. The presence of apitopes within two regions of MBP is investigated by incubating live or p-formaldehyde-fixed Mgar (HLA-DR2+ve) cells are incubated with overlapping peptides in serum from MBP regions 77-100 (Figure 12) and 125-148 (Figure 13) or in serum alone. T cells were added and after 72h (Figure 12) or after 48h (Figure 13) the T cell proliferative response was measured by 3 H-thymidine uptake. For MBP 77-100, the T cells are isolated from a DR2:MBP 82-100 transgenic mouse, whereas for MBP 130-144 the T cell clone MS17:A3 is used. For MBP region 77-100 the following peptides are defined as apitopes: MBP 83-99 ENPVVHFFKNIVTPRTP MBP 80-94 TQDENPVVHFFKNIV MBP 81-95 QDENPVVHFFKNIVT MBP 82-96 DENPVVHFFKNrVTP MJ-Jr S3-97 ENPVVHFFKNTVTPR MBP 84-98 MPVVHFFKNIVTPRT The minimum MBP sequence recognised by T cells from DR2 MBP 82-100 transgenic mouse is region 85-94. For MBP region 125-148 the following peptides are defined as apitopes: MBP 130-144 RASDYKSAHKGFKGV MBP 131-145 ASDYKSAHKGFKGVD MBP 132-146 SDYKSAHKGFKGVDA MBP 133-147 DYKSAHKGFKGVDAQ The minimum MBP sequence recognised by T-cell clone MS17:A3 is region 133-144. Example 2C - Investigation of region 89-101 of MBP The present inventors have previously shown that, in contrast to other myelin T cell epitopes, administration of peptide 89-101 in soluble form does not prevent murine experimental autoimmune encephalomyelitis (EAE) induced with either whole myelin or the 89-101 peptide itself (Anderton and Wraith (1998) Eur. J. Immunol. 28:1251). MBP 89-101 comprises three T cell epitopes In order to investigate T cell reactivity to the 81-111 region of MBP, lymph node cells from mice primed with 81-111 are stimulated with 81-111 in vitro and these cells are tested with a panel of overlapping 10-mer peptides with two residue shifts covering the 81- 111 region (namely: 81-90, 83-92, 85-94, 87-96, 89-98, 91-100, 93-102, 95-104, 97-106, 99-108 and 101-111). The response pattern to peptides covering the 89-101 show stimulatory capacity for 5 adjacent peptides (N terminal 87-96 through to 95-104) reflecting the presence of at least two (and perhaps three) distinct epitopes. in order to investigate this region further, three sub-lines are generated from the original 81-111 -responsive T-cell line and these are retested with a panel of overlapping 10-mer peptides with one residue shift covering the 84-106 region. The results reveal the existence of three distinct but overlapping T cell epitopes within the 89-101 sequence: 89- 94, 92-98 and 95-101 (see Figure 14). MBP peptide 92-98 is a cryptic epitope The three epitope-specific T cell lines (TCL) show interesting differences when tested to reactivity to the 89-101 peptide and whole recombinant MBP. All three TCL respond to the peptide (89-101) but only the 89-94 and 95-101-specific TCL respond to whole MBP. This indicates that antigen processing of intact MBP preferentially generates ligands for T cells recognising 89-94 and 95-101 but not those recognising 92-98. This suggests that the 92-98 epitope is cryptic (i.e. cannot be generated by processing of native antigen). It seems that the MBP 89-101 peptide can partake in three distinct interactions with the MHC molecule resulting in peptide/MHC ligands which are recognised by three separate T cell populations. Processing of MBP however only generates ligands for two of these T cell populations (see Fig 14). Induction of EAE requires T cell recognition of autoantigenic epitopes expressed in the CNS as a result of degradation of intact MBP. Immunisation of mice with peptides comprising only one of the three previously identified T cell epitopes shows that only those containing a naturally processed epitope (89-94 or 95-101) are capable of inducing EAE. This further supports the finding that 92-98 is a cryptic epitope. MBP peptide 92-98 is the dominant epitope for MBP region 89-101 As mentioned above, the region 89-101 contains three distinct but overlapping peptides. Of these, peptide 92-98 appears to be dominant for this region. For example, when T cell clones are generated from mice primed with the 89-101 peptide, all six clones which were generated respond to the 92-98. Using 89-101 analog peptides containing individual alanine substitutions at each position, it has been found that substitution of any of the positions 92-98 leads to a lack of responsiveness, showing that alteration of any residues within the 92-98 core has gross effects on recognition of this epitope. MBP peptide 89-101 fails to tolerize EAE-relevant T cells recognising a naturally processed MBP epitope. To summarise the findings above, the present inventors have found that a) the 89-101 sequence has the potential to generate 3 distinct T cell epitopes; b) only two of these epitopes (89-94 and 95-101) are generated by antigen processing of intact MBP (both in vitro and in vivo); c) only peptides containing the naturally processed epitopes and not those containing a cryptic epitope are effective at inducing EAE; d) the 89-101 peptide fails to protect against EAE in peptide therapy experiments. This information provides a basis for investigating the hypothesis that peptide 89-101 fails to tolerize against EAE through a failure to directly ligate the disease relevant T cells. In order to support the hypothesis, the peptide (89-101) should fail to induce tolerance to the major encephalitogenic epitope (89-94) since it will not bind directly to the MHC restriction element (I-A s ) in the appropriate conformation. In other words, 89-101 will not act as an apitope for T cells responding to 89-94. In order to test this possibility tolerance experiments are performed with the 89-101 and 87-96 peptides (Fig 15 A & B). The 87-96 peptide contains the epitope (89-94) most effective at inducing EAE. Methods Mice received 200 μg of peptide in PBS or PBS alone intraperitoneally on days -8, -6 and -4 prior to 100 μg of peptide in complete Freunds adjuvant on day 0. After 10 days, draining lymph node cells (6 xlO 5 per well) were cultured in X-Vivo 15 medium supplemented with 5 x 10 "5 M 2-mercaptoethanol and 2M L-glutamine with or without antigen for 72 hours. Cultures were pulsed for the final 16 hours with 0.5 μCi n.xnymidine and incorporation measured using a liquid scintillation counter. Results are expressed as means counts per minute for triplicate cultures. Results Priming with 87-96 induced a strong recall response to itself and a weaker response to 89- 101 (Fig 15 A and B □ and o respectively). This is consistent with the need for antigen processing to generate 89-94 from 89-101. The use of 87-96 as a tolerogen prior to priming with 87-96 suppressed recall responses to both 87-96 and 89-101 (Fig 15 A ■ and •). This fits with 89-94 reactive T cells ' , once rendered unresponsive in vivo, failing to respond in vitro to 89-94 whether they are generated from 89-96 or 89-101. Crucially, however, the use of 89-101 as the tolerogen prior to priming with 87-96 failed to inhibit recall responses to either 87-96 or 89-101 (Fig 15 B A ■ and •). These data demonstrate that administration of peptide 89-101 in tolerogenic form fails to tolerize to the naturally processed encephalitogenic epitope based on the 89-94 sequence: the 89-101 peptide fails to behave as an apitope for the 89-94 epitope. Without wishing to be bound by theory, the present inventors believe that the obsevrations can be explained by the position of peptide 89-101 in the MHC peptide binding site. If the peptide preferentially binds so that the region 92-98 is in the peptide-binding pocket, then it will be recognised by MBP92-98-specific T cells. This would explain why, when mice are primed with the MBP89-101 peptide, all the T cell clones generated recognise the MBP92-98 epitope. Equally, when 89-101 is used to tolerise T cells, it will mainly tolerise cells which recognise the MBP92-98 epitope. If MBP92-98 is a cryptic epitope, it is not generated by natural processing of the whole antigen and T-cells recognising this epitope will probably not exist in vivo. Even if an MBP92-98-specific T cells cell did exist in vivo, it would not be relevant to the disease. Hence, 89-101 fails to prevent EAE induced with whole MBP. EXAMPLE 3 - Peptide therapy for a mouse model of MS The present inventors have previously shown that a single dose of peptide antigen administered systemically either by the intraperitoneal (Liu and Wraith (1995) Int Immunol 8:1255-1263) or intranasal (Metzler and Wraith (1993) 5:1159-1165) route will effectively protect mice from experimental autoimmune encephalomyelitis (EAE) for up to three months (Metzler and Wraith (1999) Immunology 97:257-263). At least 5 doses of peptide were required to induce tolerance in the Tg4-transgenic mouse (Burkhart et al (1999) 11:1625-1634) expressing an EAE-specific T cell receptor (Liu et al (1995) Immunity 3:407-415). Recent work has shown the intranasal (IN) route is safer than the intraperitoneal (IP) route in the Tg4 mouse, even though both approaches are equally safe in the non transgenic mouse. Peptide 83-99 of MBP is tested in the Fug/D6 transgenic mouse which expresses both the appropriate HLA-DR2 class II MHC molecule and a TCR from a human T cell clone specific for this peptide. Mice are treated with peptide following either the standard dose used for treatment of the Tg4 transgenic mouse (Tg4 protocol) or the desensitisation protocol of peptide dose escalation which has been used in treatment of patients suffering from allergy (Desensitisation protocol). Tg4 protocol: Groups of mice are treated by intranasal administration of peptide 83-99 (4mg/ml in phosphate-buffered saline (PBS)) or PBS alone in a total volume of 25 μl. Mice are treated every 1 st and 5 th day of the week for 5 weeks giving a total of 10 doses. At the beginning of week 6 each mouse is injected with peptide 83-99 in Complete Freunds Adjuvant (CFA) and also receives an IP injection of Pertussis Toxin (200ng) on day 1 and 3. The progression of EAE is monitored for at least 30 days. Desensitisation protocol: Groups of mice are treated by intranasal administration of an escalating dose of peptide 83-99 or PBS alone in a total vlume of 25 μl. The dose escalation starts at 0.1 μg and proceed through 1, 3, 6, 12, 50 and then three times 100 μg. Mice are treated every 1 st and 5 th day of the week for 5 weeks giving a total of 10 doses. At the beginning of week 6 each mouse is injected with peptide 83-99 in Complete Freunds Adjuvant (CFA) and also receives an IP injection of Pertussis Toxin (200ng) on day 1 and 3. The progression of EAE is monitored for at least 30 days. EXAMPLE 4 - Nasal administration of an apitope cocktail to MS patients A vaccine is made comprising the MBP peptides 30-44, 83-99, 110-124 and 130-144 (i.e. some of those epitopes of MBP which have been identified as apitopes). The vaccine is given to thirty-five patients in a Phase la/lb trial. The trial is a single crossover trial in which patients remain untreated for three months followed by a single dose of peptide (la). Patients are then monitored for three months following the single dose of vaccine to assess safety. Treatment then consists of twice weekly administration by intranasal deposition. For each patient: clinical activity is analysed monthly by magnetic resonance imaging; immunological acitivity is monitored using a kinetic response assay for proliferation; and cytokine production is monitored using a cell-based ELISA. The trial initially involves treatment of 5 patients suffering from chronic progressive (CP) disease. These patients are selected on the basis of low MRI activity and are treated first with the highest dose of peptides. Treatment is started in the CP patient group because they are most likely to demonstrate any possible harmful effects as evidenced by an increase in MRI activity. Treatment of relapsing remitting patients begins once it is clear that the both single and multiple dose treatment is safe in the CP group. A larger group of 30 relapsing remitting patients are recruited on the basis of their suffering enhancing MRI lesions during a monitoring period of 3 months. These are divided into three groups to be treated with a high, medium or low dose of peptide. Abbreviations: APC = antigen presenting cells; MHC ■= major histocompatability complex; TCR = T cell receptor; EAE = experimental autoimmune encephalomyelitis; APITOPE = antigen processing independent epitope; APIPS ■ *•= antigen processing independent presentation system; aa = amino acid; MS = Multiple Sclerosis; MBP = myelin basic protein; PLP = proteolipid protein; TCL ■ *= T cell line; TCC = T cell clone; PBMC = peripheral blood mononuclear cells; PPD = Mycobacterium tuberculosis purified protein derivative; PHA = phytohemagglutinin Various modifications and variations of the described methods and system of the invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention which are obvious to those skilled in chemistry or biology or related fields are intended to be covered by the present invention. All publications mentioned in the above specification are herein incorporated by reference.

Claims: P9611wo CLAIMS 1. A method for selecting a tolerogenic peptide which comprises the step of selecting a peptide which is capable of binding to an MHC class I or II molecule without further processing. 2. A method according to claim 1, wherein the peptide is capable of binding to an MHC class II molecule without further processing. 3. A method according to claim 1 or 2, wherein the peptide is selected from a plurality of peptides each comprising a T cell epitope. 4. A method according to claim 3, wherein the plurality of peptides is eluted from the MHC class II molecules of an antigen presenting cell. 5. A method according to claim 3 or 4, wherein each peptide in the plurality of peptides is capable of inducing a disease associated with the antigen in a subject when administered to the subject with adjuvant. 6. A method according to claim 1 or 2, wherein the peptide is selected from a nested set of truncated peptides. 7. A method according to any preceding claim, wherein the peptide comprises a T cell epitope and presence of a T cell epitope is determined by: (i) treating: a sample of cells from a subject having the disease, and a sample of cells from a subject not having the disease with the peptide; and (ii) comparing the T cell responses between the cell samples. 8. A method according to any preceding claim which comprises the following steps: (i) treating an antigen processing independent presentation system (APIPS) with a peptide; and (ii) analysing binding of the peptide to MHC class I or II molecules within the APIPS. 9. A method according to claim 8, wherein binding of the peptide to MHC class I or II molecules is analysed by adding T cells and measuring T cell activation. 10. A method according to claim 8, wherein the APIPS comprises: (i) fixed antigen presenting cells (ii) lipid membranes comprising MHC class I or II molecules; or (iii) plate-bound MHC class I or II molecules. 11. A peptide selected by the method according to any preceding claim. 12. A peptide according to claim 11, which is selected from the following myelin basic protein peptides: 30-44, 80-94, 83-99, 81-95, 82-96, 83-97, 84-98, 110-124, 130-144, 131- 145, 132-146 and 133-147. 13. A peptide according to claim 11 or 12, for use in the treatment and/or prevention of a disease. 14. A peptide according to claim 13, wherein the disease is a hypersensitivity disorder. 15. A pharmaceutical composition comprising a plurality of peptides according to any of claims 11 to 14, each peptide comprising a T cell epitope for the disease. 16. A method for treating and/or preventing a disease in a subject in need of same which comprises the step of administering a peptide according to any of claims 11 to 14 to the subject. 17. A method according to claim 16, which comprises the following steps: > (i) identifying an antigen for the disease (ii) identifying an apitope for the antigen; and (iii) administering the apitope to the subject. 18. A method according to claim 16 or 17 wherein the peptide or apitope is administered in multiple doses. 19. A method according to any of claims 16 to 18, wherein the peptide or apitope is administered intranasally.

Inventors: ANDERTON STEPHEN MARK, MAZZA GRAZIELLA, PONSFORD MARY, STREETER HEATHER BARBARA, WRAITH DAVID CAMERON, ANDERTON, STEPHEN, MARK, MAZZA, GRAZIELLA, PONSFORD, MARY, STREETER, HEATHER, BARBARA, WRAITH, DAVID, CAMERON
Applicants: ANDERTON STEPHEN MARK, MAZZA GRAZIELLA, PONSFORD MARY, STREETER HEATHER BARBARA, UNIV BRISTOL, WRAITH DAVID CAMERON, ANDERTON, STEPHEN, MARK, MAZZA, GRAZIELLA, PONSFORD, MARY, STREETER, HEATHER, BARBARA, THE UNIVERSITY OF BRISTOL, WRAITH, DAVID, CAMERON
Application year: 2001
Main classification: C07K7
IPC codes: A61K38, A61K39, A61P37, C07K14, C12Q1, G01N33