Cyclic citrullinated MBP87-99 peptide stimulates T cell responses: Implications in triggering disease

Citrullination of myelin basic protein induces a Th17-cell response in healthy individuals and enhances the presentation of MBP85-99 in patients with multiple sclerosis

The post-translational modification citrullination has been proposed to play a role in the pathogenesis of multiple sclerosis (MS). Myelin basic protein (MBP) is a candidate autoantigen which is citrullinated to a minor extent under physiological conditions and hypercitrullinated in MS. We examined immune cell responses elicited by hypercitrullinated MBP (citMBP) in cultures of mononuclear cells from 18 patients with MS and 42 healthy donors (HDs). The immunodominant peptide of MBP, MBP85-99, containing citrulline in position 99, outcompeted the binding of native MBP85-99 to HLA-DR15, which is strongly linked to MS. Moreover, using the monoclonal antibody MK16 as probe, we observed that B cells and monocytes from HLA-DR15+ patients with MS presented MBP85-99 more efficiently after challenge with citMBP than with native MBP. Both citMBP and native MBP induced proliferation of CD4+ T cells from patients with MS as well as TNF-α production by their B cells and CD4+ T cells, and citrullination of MBP tended to enhance TNF-α secretion by CD4+ T cells from HLA-DR15+ patients. Unlike native MBP, citMBP induced differentiation into Th17 cells in cultures from HDs, while neither form of MBP induced Th17-cell differentiation in cultures from patients with MS. These data suggest a role for citrullination in the breach of tolerance to MBP in healthy individuals and in maintenance of the autoimmune response to MBP in patients with MS.

The Use of Electrochemical Voltammetric Techniques and High-Pressure Liquid Chromatography to Evaluate Conjugation Efficiency of Multiple Sclerosis Peptide-Carrier Conjugates

Recent studies have shown the ability of electrochemical methods to sense and determine, even at very low concentrations, the presence and quantity of molecules or analytes including pharmaceutical samples. Furthermore, analytical methods, such as high-pressure liquid chromatography (HPLC), can also detect the presence and quantity of peptides at very low concentrations, in a simple, fast, and efficient way, which allows the monitoring of conjugation reactions and its completion. Graphite/SiO₂ film electrodes and HPLC methods were previously shown by our group to be efficient to detect drug molecules, such as losartan. We now use these methods to detect the conjugation efficiency of a peptide from the immunogenic region of myelin oligodendrocyte to a carrier, mannan. The HPLC method furthermore confirms the stability of the peptide with time in a simple one pot procedure. Our study provides a general method to monitor, sense and detect the presence of peptides by effectively confirming the conjugation efficiency. Such methods can be used when designing conjugates as potential immunotherapeutics in the treatment of diseases, including multiple sclerosis.

Brain Citrullination Patterns and T Cell Reactivity of Cerebrospinal Fluid-Derived CD4+ T Cells in Multiple Sclerosis

Immune responses to citrullinated peptides have been described in autoimmune diseases like rheumatoid arthritis (RA) and multiple sclerosis (MS). We investigated the post-translational modification (PTM), arginine to citrulline, in brain tissue of MS patients and controls (C) by proteomics and subsequently the cellular immune response of cerebrospinal fluid (CSF)-infiltrating T cells to citrullinated and unmodified peptides of myelin basic protein (MBP). Using specifically adapted tissue extraction- and combined data interpretation protocols we could establish a map of citrullinated proteins by identifying more than 80 proteins with two or more citrullinated peptides in human brain tissue. We report many of them for the first time. For the already described citrullinated proteins MBP, GFAP, and vimentin, we could identify additional citrullinated sites. The number of modified proteins in MS white matter was higher than control tissue. Citrullinated peptides are considered neoepitopes that may trigger autoreactivity. We used newly identified epitopes and previously reported immunodominant myelin peptides in their citrullinated and non-citrullinated form to address the recognition of CSF-infiltrating CD4⁺ T cells from 22 MS patients by measuring proliferation and IFN-γ secretion. We did not detect marked responses to citrullinated peptides, but slightly more strongly to the non-modified version. Based on these data, we conclude that citrullination does not appear to be an important activating factor of a T cell response, but could be the consequence of an immune- or inflammatory response. Our approach allowed us to perform a deep proteome analysis and opens new technical possibilities to analyze complex PTM patterns on minute quantities of rare tissue samples.

On the design principles of peptide-drug conjugates for targeted drug delivery to the malignant tumor site

Cancer is the second leading cause of death affecting nearly one in two people, and the appearance of new cases is projected to rise by >70% by 2030. To effectively combat the menace of cancer, a variety of strategies have been exploited. Among them, the development of peptide–drug conjugates (PDCs) is considered as an inextricable part of this armamentarium and is continuously explored as a viable approach to target malignant tumors. The general architecture of PDCs consists of three building blocks: the tumor-homing peptide, the cytotoxic agent and the biodegradable connecting linker. The aim of the current review is to provide a spherical perspective on the basic principles governing PDCs, as also the methodology to construct them. We aim to offer basic and integral knowledge on the rational design towards the construction of PDCs through analyzing each building block, as also to highlight the overall progress of this rapidly growing field. Therefore, we focus on several intriguing examples from the recent literature, including important PDCs that have progressed to phase III clinical trials. Last, we address possible difficulties that may emerge during the synthesis of PDCs, as also report ways to overcome them.

Cyclization of PLP139-151 peptide reduces its encephalitogenic potential in experimental autoimmune encephalomyelitis

We report the novel synthesis of cyclic PLP_139-151 (cPLP) and its application in SJL/J mice to study its encephalitogenic effects. Our results indicate that the cPLP analog is minimally encephalitogenic when administered to induce experimental autoimmune encephalomyelitis (low disease burden, minimal inflammatory, demyelinating and axonopathic pathology compared to its linear counterpart). Proliferation assays confirmed the low stimulatory potential of the cPLP compared to linPLP (2.5-fold lower proliferation) as well as inducing lower antibody responses. Molecular modeling showed a completely different TCR recognition profile of cPLP in regard to linPLP, where H¹⁴⁷ replaces W¹⁴⁴ and F¹⁵¹-K¹⁵⁰ replace H¹⁴⁷ as TCR contacts, which may explain the difference on each peptide's response.

Multiple Sclerosis: Immunopathology and Treatment Update

The treatment of multiple sclerosis (MS) has changed over the last 20 years. All immunotherapeutic drugs target relapsing remitting MS (RRMS) and it still remains a medical challenge in MS to develop a treatment for progressive forms. The most common injectable disease-modifying therapies in RRMS include β-interferons 1a or 1b and glatiramer acetate. However, one of the major challenges of injectable disease-modifying therapies has been poor treatment adherence with approximately 50% of patients discontinuing the therapy within the first year. Herein, we go back to the basics to understand the immunopathophysiology of MS to gain insights in the development of new improved drug treatments. We present current disease-modifying therapies (interferons, glatiramer acetate, dimethyl fumarate, teriflunomide, fingolimod, mitoxantrone), humanized monoclonal antibodies (natalizumab, ofatumumb, ocrelizumab, alentuzumab, daclizumab) and emerging immune modulating approaches (stem cells, DNA vaccines, nanoparticles, altered peptide ligands) for the treatment of MS.

Design and Synthesis of Non-Peptide Mimetics Mapping the Immunodominant Myelin Basic Protein (MBP83-96) Epitope to Function as T-Cell Receptor Antagonists

Encephalitogenic T cells are heavily implicated in the pathogenesis of multiple sclerosis (MS), an autoimmune demyelinating disease of the central nervous system. Their stimulation is triggered by the formation of a trimolecular complex between the human leukocyte antigen (HLA), an immunodominant myelin basic protein (MBP) epitope, and the T cell receptor (TCR). We detail herein our studies directed towards the rational design and synthesis of non-peptide mimetic molecules, based on the immunodominant MBP_83-96 epitope that is recognized by the TCR in complex with HLA. We focused our attention on the inhibition of the trimolecular complex formation and consequently the inhibition of proliferation of activated T cells. A structure-based pharmacophore model was generated, in view of the interactions between the TCR and the HLA-MBP_83-96 complex. As a result, new candidate molecules were designed based on lead compounds obtained through the ZINC database. Moreover, semi-empirical and density functional theory methods were applied for the prediction of the binding energy between the proposed non-peptide mimetics and the TCR. We synthesized six molecules that were further evaluated in vitro as TCR antagonists. Analogues 15 and 16 were able to inhibit to some extent the stimulation of T cells by the immunodominant MBP_83-99 peptide from immunized mice. Inhibition was followed to a lesser degree by analogues 17 and 18 and then by analogue 19. These studies show that lead compounds 15 and 16 may be used for immunotherapy against MS.

Cyclic MOG35-55 ameliorates clinical and neuropathological features of experimental autoimmune encephalomyelitis

EAE is induced to susceptible mice using linear peptides of myelin proteins of the central nervous system. Specific peptide motifs within the peptide-binding groove of the MHC peptide-complex determines the affinity of the peptide in each animal and the consequent T-cell receptor recognition and activation of the cell. Altered peptide ligand (APL) vaccination is a novel approach based on an effort to induce T-cell tolerance or alter cytokine profile from pro-inflammatory to anti-inflammatory. In the present study we synthesized the MOG_35-55 peptide and altered its 3-dimensional conformation to make it a cyclic one (c-MOG_35-55). EAE was induced in C57BL/6 mice and pathology was studied on acute and chronic phase of the disease. Our data indicates that c-MOG_35-55 peptide alone induces a mild transient acute phase without chronic axonopathy. Administration of the c-MOG_35-55 peptide at a 1:1 ratio during disease induction significantly ameliorates clinical disease and underlying pathology, such as demyelination and axonopathy in the acute and chronic phases. Binding and structural studies revealed milder interactions between the c-MOG_35-55 and mouse or human MHC class II alleles (H2-IA^b and HLA-DR2). Collectively, we provide data supporting for the first time the concept that the cyclic modification of an established encephalitogenic peptide ameliorates the clinical outcomes and underlying pathological processes of EAE. Such a cyclic modification of linear peptides could provide a novel treatment approach for future, patient-selective, immunomodulative treatments of multiple sclerosis.