Use of the mannan receptor to selectively target vaccine antigens for processing and antigen presentation through the MHC class I and class II pathways

Development and characterization of a novel conjugated methamphetamine vaccine

BACKGROUND

Methamphetamine (METH) addiction is a major public health concern globally with limited management options. The development of a METH vaccine through hapten design has received significant attention as a promising platform for the potential treatment of METH addiction and overdose, however there is yet to be a successful candidate in human trials.

RESEARCH DESIGN AND METHODS

In this study, we developed a novel conjugated METH vaccine using oxidized mannan (a polymannose) as an immunogenic carrier. A METH hapten was synthesized by using amphetamine and conjugated to mannan with a (Lysine-Glycine-Lysine-Glycine-lysine-Glycine-Lysine-Glycine-Lysine-Glycine) (KG)₅ peptide linker.

RESULTS

The reaction between amphetamine and (KG)₅, oxidation of mannan, and conjugation of amphetamine-(KG)₅ with oxidized mannan were confirmed by color tests, Fourier-transform infrared spectroscopy, gas and liquid chromatography mass spectrometry, thin-layer chromatography, and ultraviolet spectrophotometer. Additionally, the ability of the vaccine to generate antibodies was confirmed in C57BL/6 mice.

CONCLUSIONS

The successful development and characterization of the METH-mannan conjugate vaccine, provides a potential therapeutic intervention to curb METH substance use disorders. Each step of vaccine development was characterized to aid in future research on these vaccines, and the immunogenicity shown in the animal models supports future evaluation of the approach. Future studies of the conjugated METH vaccine should evaluate the efficacy in animal models of acute and chronic METH to pave the way for human studies.

Novel Approaches in the Immunotherapy of Multiple Sclerosis: Cyclization of Myelin Epitope Peptides and Conjugation with Mannan

Multiple Sclerosis (MS) is a serious autoimmune disease. The patient in an advanced state of the disease has restrained mobility and remains handicapped. It is therefore understandable that there is a great need for novel drugs and vaccines for the treatment of MS. Herein we summarise two major approaches applied for the treatment of the disease using peptide molecules alone or conjugated with mannan. The first approach focuses on selective myelin epitope peptide or peptide mimetic therapy alone or conjugated with mannan, and the second on immune-therapy by preventing or controlling disease through the release of appropriate cytokines. In both approaches the use of cyclic peptides offers the advantage of increased stability from proteolytic enzymes. In these approaches, the synthesis of myelin epitope peptides conjugated to mannan is of particular interest as this was found to protect mice against experimental autoimmune encephalomyelitis, an animal model of MS, in prophylactic and therapeutic protocols. Protection was peptide-specific and associated with reduced antigen-specific T cell proliferation. The aim of the studies of these peptide epitope analogs is to understand their molecular basis of interactions with human autoimmune T-cell receptor and a MS-associated human leucocyte antigen (HLA)-DR2b. This knowledge will lead the rational design to new beneficial non-peptide mimetic analogs for the treatment of MS. Some issues of the use of nanotechnology will also be addressed as a future trend to tackle the disease. We highlight novel immunomodulation and vaccine-based research against MS based on myelin epitope peptides and strategies developed in our laboratories.

Mannosylated T/Tn with Freund's adjuvant induces cellular immunity

Inducing cancer-specific cellular immune responses has become an attractive strategy in cancer treatment. In this study, we investigated the role of several adjuvants in eliciting T/Tn-specific cellular immunity and protection against T/Tn expressing tumor challenge. T/Tn (9:1) antigen was purified from blood type “O” erythrocytes donated from healthy Korean volunteers. Immunization was performed using: T/Tn only, T/Tn mixed with Freund’s adjuvant (T/Tn + FA), keyhole limpet hemocyanin (KLH)-conjugated T/Tn mixed with FA (KLH-T/Tn + FA), and oxidized mannan-conjugated T/Tn mixed with FA (ox-M-T/Tn + FA). Mice immunized with ox-M-T/Tn + FA generated T/Tn-specific CD3, helper T (Th) cells, major histocompatibility complex (MHC) II, and MHC I; T/Tn presentation was significantly high and tolerogenic CD11b⁺ was the lowest among the tumor models. To verify Th type, we stained intracellular cytokines (interferon gamma (IFN-γ), granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin (IL)-4, and IL-10) using CD3 co-staining. Th1 (IFN-γ and GM-CSF) cytokines were highly expressed and showed high FasL/Fas ratios, cytotoxic T lymphocyte (CTL) activity, and cytotoxic T lymphocyte precursor (CTLp) activity in mice immunized with ox-M-T/Tn + FA. Lymphocyte infiltration was highest in mice immunized with ox-M-T/Tn + FA. Additionally, we monitored FasL, MHC I, CD301, and T/Tn expression levels using immunohistochemistry (IHC) on macrophage and tumor sites. The expression of all markers was highest in the ox-M-T/Tn + FA group. Furthermore, tumor retardation and survival rate were highest in the ox-M-T/Tn + FA group. These results demonstrate that a vaccine formulation of T/Tn conjugated with ox-M and mixed with FA-induced cellular immunity and sustained a humoral immune response without over-activating the immune system, thus effectively inhibiting tumor growth.

Synthesis of Mannosylated Lipopeptides with Receptor Targeting Properties

Present on the surface of antigen presenting cells (APCs), the mannose receptor (MR) has long been recognized as a front-line receptor in pathogen recognition. During the past decade many attempts have been made to target this receptor for applications including vaccine and drug development. In the present study, a library of vaccine constructs comprising fluorescently labeled mannosylated lipid-dendrimers that contained the ovalbumin CD4(+) epitope, OVA(323-339), as the model peptide antigen were synthesized using fluorenylmethyloxycarbonyl (Fmoc) solid phase peptide synthesis (SPPS). The vaccine constructs were designed with an alanine spacer between the O-linked mannose moieties to investigate the impact of distance between the mannose units on receptor-mediated uptake and/or binding in APCs. Uptake studies performed on F4/80(+) and CD11c(+) cells showed significant uptake and/or binding for lipopeptides containing mannose, and also the lipopeptide without mannose when compared to the control peptides (peptide with no lipid and peptide with no mannose and no lipid). Furthermore, mannan inhibition assays demonstrated that uptake of the mannosylated and lipidated peptides was receptor mediated. To address the specificity of receptor uptake, surface plasmon resonance studies were performed using biacore technology and confirmed high affinity of the mannosylated and lipidated vaccine constructs toward the MR. These studies confirm that both mannose and lipid moieties play significant roles in receptor-mediated uptake on APCs, potentially facilitating vaccine development.

Mannosylated Linear and Cyclic Single Amino Acid Mutant Peptides Using a Small 10 Amino Acid Linker Constitute Promising Candidates Against Multiple Sclerosis

Multiple sclerosis (MS) is a serious autoimmune demyelinating disease leading to loss of neurological function. The design and synthesis of various altered peptide ligands of immunodominant epitopes of myelin proteins to alter the autoimmune response, is a promising therapeutic approach for MS. In this study, linear and cyclic peptide analogs based on the myelin basic protein 83–99 (MBP_83–99) immunodominant epitope conjugated to reduced mannan via the (KG)₅ and keyhole limpet hemocyanin (KLH) bridge, respectively, were evaluated for their biological/immunological profiles in SJL/J mice. Of all the peptide analogs tested, linear MBP_83–99(F⁹¹) and linear MBP_83–99(Y⁹¹) conjugated to reduced mannan via a (KG)₅ linker and cyclic MBP_83–99(F⁹¹) conjugated to reduce mannan via KLH linker, yielded the best immunological profile and constitute novel candidates for further immunotherapeutic studies against MS in animal models and in human clinical trials.

Mannosylated mucin-type immunoglobulin fusion proteins enhance antigen-specific antibody and T lymphocyte responses

Targeting antigens to antigen-presenting cells (APC) improve their immunogenicity and capacity to induce Th1 responses and cytotoxic T lymphocytes (CTL). We have generated a mucin-type immunoglobulin fusion protein (PSGL-1/mIgG(2b)), which upon expression in the yeast Pichia pastoris became multivalently substituted with O-linked oligomannose structures and bound the macrophage mannose receptor (MMR) and dendritic cell-specific intercellular adhesion molecule-3 grabbing non-integrin (DC-SIGN) with high affinity in vitro. Here, its effects on the humoral and cellular anti-ovalbumin (OVA) responses in C57BL/6 mice are presented.OVA antibody class and subclass responses were determined by ELISA, the generation of anti-OVA CTLs was assessed in (51)Cr release assays using in vitro-stimulated immune spleen cells from the different groups of mice as effector cells and OVA peptide-fed RMA-S cells as targets, and evaluation of the type of Th cell response was done by IFN-γ, IL-2, IL-4 and IL-5 ELISpot assays.Immunizations with the OVA - mannosylated PSGL-1/mIgG(2b) conjugate, especially when combined with the AbISCO®-100 adjuvant, lead to faster, stronger and broader (with regard to IgG subclass) OVA IgG responses, a stronger OVA-specific CTL response and stronger Th1 and Th2 responses than if OVA was used alone or together with AbISCO®-100. Also non-covalent mixing of mannosylated PSGL-1/mIgG(2b), OVA and AbISCO®-100 lead to relatively stronger humoral and cellular responses. The O-glycan oligomannoses were necessary because PSGL-1/mIgG(2b) with mono- and disialyl core 1 structures did not have this effect.Mannosylated mucin-type fusion proteins can be used as versatile APC-targeting molecules for vaccines and as such enhance both humoral and cellular immune responses.

Effects of mannan oligosaccharide on cytokine secretions by porcine alveolar macrophages and serum cytokine concentrations in nursery pigs

This study explored the hypothesis that mannan oligosaccharide (MOS) acts to reduce systemic inflammation in pigs by evaluating cytokine production of alveolar macrophages (AM) and serum cytokine concentrations. A total of 160 pigs were fed diets containing 0.2 or 0.4% MOS for 2 or 4 wk postweaning compared with control diets without MOS. Dietary MOS did not affect the serum concentration of tumor necrosis factor (TNF)-α and tended (P = 0.081) to increase that of IL-10. These cytokine concentrations also changed over time (P < 0.001). After 2-wk feeding of the control or MOS diets, AM were collected and stimulated ex vivo with lipopolysaccharide (LPS) or polyinosinic:polycytidylic acid (PLIC) as infection models. The LPS-stimulated AM from MOS-fed pigs (n = 12) secreted less TNF-α (P < 0.001) and more IL-10 (P = 0.026) than those from control-fed pigs (n = 6). However, dietary MOS had less effect on ex vivo TNF-α and IL-10 production by PLIC-stimulated AM (P = 0.091 and P > 0.10, respectively. Further, effects of MOS were examined in 4 in vitro experiments. In Exp. 1 (n = 4 pigs), MOS and mannan-rich fraction (MRF), when added to AM cultures, were able to increase TNF-α production. This direct effect of MOS was not due to endotoxin contamination as verified in Exp. 2 (n = 6 pigs) using polymyxin B, an inhibitor of LPS activation of toll-like receptor 4. Polymyxin B inhibited production of TNF-α by AM after treatment with LPS (P < 0.001), but not after treatment with MOS in the absence of LPS (P > 0.70). In Exp. 3 (n = 6 pigs), when MOS was directly applied in vitro, the pattern of cytokine production by LPS-activated AM was similar to that observed ex vivo, as MOS suppressed LPS-induced TNF-α (P < 0.001) and enhanced LPS-induced IL-10 (P = 0.028). In Exp. 4 (n = 6 pigs), when MRF replaced MOS, AM-produced TNF-α induced by LPS or PLIC was suppressed by MRF (P = 0.015 or P < 0.001, respectively). These data establish that MOS and MRF suppress LPS-induced TNF-α secretions by AM. Generally, the study suggests that MOS may be a potent immunomodulator because it directly activates AM to secrete TNF-α and alters the cytokine responses of bacterial endotoxin-induced AM in both ex vivo and in vitro systems. In particular, feeding MOS to pigs for 2 wk reduces TNF-α and increases IL-10 concentrations after ex vivo treatment of AM with LPS. These immunomodulatory properties of MOS may have important implications for both host defense and avoidance of harmful overstimulation of the immune system.

Mannosylated liposomes as antigen delivery vehicles for targeting to dendritic cells

The immune stimulating ability of mannosylated liposomes containing FITC-ovalbumin as a model antigen and displaying either a branched tri-mannose or a mono-mannose ligand on the liposome surface was investigated in human monocyte-derived dendritic cells (MoDCs) and murine bone-marrow-derived dendritic cells (BMDCs). Uptake of liposomes, dendritic cell activation and proliferation of CD8+ T cells from OT-I transgenic mice were determined by flow cytometry. Uptake of liposomes displaying the tri-mannose ligand was enhanced in human MoDCs compared with both non-mannosylated liposomes and liposomes displaying mono-mannose ligands. However, this increased uptake did not result in an increase in expression of CD80 or CD86 on the surface of the MoDCs. In contrast, neither tri-mannose- nor mono-mannose-containing liposomes were taken up by murine BMDCs to a greater extent than non-mannose-containing liposomes. The expression of CD86 and CD40 on the surface of BMDCs was not increased after exposure to mannosylated lipo-somes and BMDCs incubated with mannosylated liposomes were not able to stimulate proliferation of CD8+ T cells to any greater extent than BMDCs incubated with non-mannosylated liposomes. These findings suggest that while mannose-containing ligands can enhance the uptake of antigen-containing liposomes by some dendritic cells, important differences in the affinity of carbohydrate-binding receptors for mannose-containing ligands do exist between species. In addition, the increase in uptake of antigen by dendritic cells using mannosylated liposomes does not necessarily result in enhanced dendritic cell activation.

Mannosylation of mutated MBP83-99 peptides diverts immune responses from Th1 to Th2

Multiple sclerosis (MS) is an autoimmune demyelinating disease mediated primarily by CD4+ T cells. The design of peptide mutants of disease-associated myelin epitopes to alter immune responses offers a promising avenue for the treatment of MS. We designed and synthesized a number of peptide analogs by mutating the principal TCR contact residue based on MBP83-99 epitope and these peptides were conjugated to reduced mannan. Immune responses were diverted from Th1 to Th2 in SJL/J mice and generated antibodies which did not cross-react with native MBP protein. Peptide [Y91]MBP83-99 gave the best cytokine and antibody profile and constitutes a promising candidate peptide for immunotherapy of MS. Structural alignment of existing crystal structures revealed the peptide binding motif of I-As. Molecular modeling was used to identify H-bonding and van der Waals interactions between peptides and MHC (I-A(s)).

Mannan derivatives induce phenotypic and functional maturation of mouse dendritic cells

Mannan, a polysaccharide isolated from yeast binds to C-type lectins of the mannose receptor family, expressed by antigen-presenting cells (APCs) including dendritic cells (DCs) and macrophages. As these receptors mediate endocytosis, they have been targeted with ligands to deliver antigens into APCs to initiate immune responses. Immunization with tumour antigen MUC1 conjugated to oxidized mannan (OM) or reduced mannan (RM) induced differential immune responses in mice, and only mice immunized with OM-MUC1 elicited strong MUC1-specific cytotoxic T lymphocyte responses and protected mice from a MUC1 tumour challenge. In this study, the adjuvant effect of mannan and its derivatives including OM and RM, in comparison to lipopolysaccharide, on DCs were investigated. Mannan, OM and RM were capable of stimulating mouse bone marrow-derived DC in vitro, eliciting enhanced allogeneic T-cell proliferation and enhancing OTI/OTII peptide-specific T-cell responses. Injection of mice with mannan, OM and RM induced a mature phenotype of lymph node and splenic DCs. Analysis by reverse transcription-polymerase chain reaction indicated that Manna, OM and RM also stimulated up-regulation of inflammatory cytokines including interleukin-1beta and tumour necrosis factor-alpha, and differential T helper 1 (Th1)/Th2 cytokines. Subsequent experiments demonstrated that activation of DCs was Toll-like receptor-4-dependent. The data presented here, together with evidence reported previously on OM and RM in induction of immune responses in vivo, suggest that OM and RM exert a dual capacity to target antigen to APCs as well as mature DCs.

Synthesis and study of the electrophoretic behavior of mannan conjugates with cyclic peptide analogue of myelin basic protein using lysine-glycine linker

New approaches for the treatment of multiple sclerosis involve the design and synthesis of peptide or nonpeptide analogues of myelin sheath, which could alter the immune response of patients. For this purpose, the cyclo(75-82) myelin basic protein (MBP)(74-85) analogue was conjugated to mannan (a polymannose) via (Lys-Gly)(5) linker. Monitoring of synthesis of the (Lys-Gly)(5)-containing cyclic analogue of MBP, mannan oxidation, and the conjugation reaction of this analogue to oxidized mannan was performed with capillary electrophoresis (CE) in operating buffers of different pH values. The (Lys-Gly)(5)cyclo(75-82)MBP(74-85) was efficiently synthesized by solid-phase synthesis and purified to a high degree, as confirmed by CE analysis in a low-pH (3.0) phosphate buffer and normal polarity. Oxidation of mannan was monitored using a high-pH (9.3) borate buffer, and the generation of heterogeneous products and even UV-absorbing peaks was shown by CE. CE analysis in a pH 5.1 phosphate buffer offers high resolution of oxidized mannan and the conjugation product and can be used for screening of the reaction products. Mannan-peptide conjugates of varying degrees of substitution and unreacted mannan were observed. The developed CE analysis presents distinct advantages over sodium dodecyl sulfate-polyacrylamide gel electrophoresis such as high versatility, high separation efficiency, short analysis time, low cost, and low solvent consumption.