Thiol oxidation and reduction in MHC-restricted antigen processing and presentation

Multifunctional magnetic nanoparticles elicit anti-tumor immunity in a mouse melanoma model

Immunotherapy has emerged as a promising strategy to eradicate cancer cells. Particularly, the development of cancer vaccines to induce a potent and sustained antigen-specific T cell response has become a center of attention. Herein, we describe a novel immunotherapy based on magnetic nanoparticles (MNP) covalently modified with the OVA254-267 antigen and a CpG oligonucleotide via disulfide bonds. The MNP-CpG-COVA significantly enhances dendritic cell activation and CD8+ T cell antitumoral response against B16-OVA melanoma cells in vitro. Notably, the immune response induced by the covalently modified MNP is more potent and sustained over time than that triggered by the free components, highlighting the advantage of nanoformulations in immunotherapies. What is more, the nanoparticles are stable in the blood after in vivo administration and induce potent levels of systemic tumor-specific effector CD8 + T cells. Overall, our findings highlight the potential of covalently functionalized MNP to induce robust immune responses against mouse melanoma.

Synergistic immunomodulatory effect in macrophages mediated by magnetic nanoparticles modified with miRNAs

In this work, we describe the synthesis of magnetic nanoparticles composed of a maghemite core (MNP) and three different coatings (dextran, D-MNP; carboxymethyldextran, CMD-MNP; and dimercaptosuccinic acid, DMSA-MNP). Their interactions with red blood cells, plasma proteins, and macrophages were also assessed. CMD-MNP was selected for its good biosafety profile and for promoting a pro-inflammatory response in macrophages, which was associated with the nature of the coating. Thus, we proposed a smart miRNA delivery system using CMD-MNP as a carrier for cancer immunotherapy applications. Particularly, we prove that CMD-MNP-miRNA155 and CMD-MNP-miRNA125b nanoparticles can display a pro-inflammatory response in human macrophages by increasing the expression of CD80 and the levels of TNF-α and IL-6. Hence, our proposed miRNA-delivery nanosystem can be exploited as a new immunotherapeutic tool based on magnetic nanoparticles.

Maturation-associated gene expression profiles along normal human bone marrow monopoiesis

Human monopoiesis is a tightly coordinated process which starts in the bone marrow (BM) haematopoietic stem cell (HSC) compartment and leads to the production of circulating blood mature monocytes. Although mature monocytes/macrophages have been extensively studied in both normal or inflammatory conditions, monopoiesis has only been assessed in vitro and in vivo animal models, due to low frequency of the monocytic precursors in the normal human BM. Here we investigated the transcriptional profile along normal human BM monopoiesis. Five distinct maturation-associated stages of monocytic precursors were identified and isolated from (fresh) normal human BM through fluorescence-activated cell sorting, and the gene expression profile (GEP) of each monocytic precursor subset was analysed by DNA-oligonucleotide microarrays. Overall, >6000 genes (18% of the genes investigated) were expressed in ≥1 stage of BM monopoiesis at stable or variable amounts, showing early decrease in cell proliferation with increased levels of expression of genes linked with cell differentiation. The here-defined GEP of normal human BM monopoiesis might contribute to better understand monocytic differentiation and the identification of novel monocytic candidate markers, while also providing a frame of reference for the study of monocytic maturation in both neoplastic and non-neoplastic disease conditions involving monocytic precursor cells.

Identification of interferon-γ-inducible-lysosomal thiol reductase (GILT) gene from Mefugu (Takifugu obscures) and its immune response to LPS challenge

Interferon-γ-inducible-lysosomal thiol reductase (GILT) plays a key role in the processing and presentation of MHC class II-restricted antigen (Ag) by catalyzing disulfide bond reduction. In this study, a Mefugu cDNA (ToGILT) encodes a deduced protein of 242 amino acids with a putative molecular weight of 28.6 kDa. It contains typical features of GILT proteins including the signature sequence CQHGX2ECX2NX4C, CXXC motif and other five cysteines. Genomic analysis revealed that ToGILT gene exhibited a similar exon-intron organization to human and mouse GILT. Phylogenetic analysis showed that ToGILT derived from a common ancestor with other vertebrate GILT proteins. The ToGILT mRNA was expressed in a tissue-specific manner and obviously up-regulated in spleen and kidney after LPS induction. These results suggest that ToGILT may be involved in the immune response to bacteria challenge in Takifugu obscurus.

Direct identification of an HPV-16 tumor antigen from cervical cancer biopsy specimens

Persistent infection with high-risk human papilloma viruses (HPV) is the worldwide cause of many cancers, including cervical, anal, vulval, vaginal, penile, and oropharyngeal. Since T cells naturally eliminate the majority of chronic HPV infections by recognizing epitopes displayed on virally altered epithelium, we exploited Poisson detection mass spectrometry (MS³) to identify those epitopes and inform future T cell-based vaccine design. Nine cervical cancer biopsies from HPV-16 positive HLA-A^*02 patients were obtained, histopathology determined, and E7 oncogene PCR-amplified from tumor DNA and sequenced. Conservation of E7 oncogene coding segments was found in all tumors. MS³ analysis of HLA-A^*02 immunoprecipitates detected E7_11–19 peptide (YMLDLQPET) in seven of the nine tumor biopsies. The remaining two samples were E7_11–19 negative and lacked the HLA-A^*02 binding GILT thioreductase peptide despite possessing binding-competent HLA-A^*02 alleles. Thus, the conserved E7_11–19 peptide is a dominant HLA-A^*02 binding tumor antigen in HPV-16 transformed cervical squamous and adenocarcinomas. Findings that a minority of HLA-A^*02:01 tumors lack expression of both E7_11–19 and a peptide from a thioreductase important in processing of cysteine-rich proteins like E7 underscore the value of physical detection, define a potential additional tumor escape mechanism and have implications for therapeutic cancer vaccine development.

Alternative activation of macrophages by IL-4 enhances the proteolytic capacity of their phagosomes through synergistic mechanisms

Alternatively activated macrophages, generated in a T-helper 2 environment, have demonstrated roles in wound repair and tissue remodeling in addition to being charged with immune tasks. Because the hydrolytic chemistries of the phagosomal lumen are central to many of these functions, we investigated their modification after alternative activation with IL-4 and IL-13. Most significantly, we found striking up-regulation of the proteolytic levels within the phagosome of IL-4-activated macrophages. Two synergistic mechanisms were determined to underlie this up-regulation. First, IL-4-activated macrophages displayed increased expression of cathepsin S and L, providing greater proteolytic machinery to the phagosome despite unchanged rates of lysosomal contribution. Secondly, decreased phagosomal NADPH oxidase (NOX2) activity, at least partially resulting from decreased expression of the NOX2 subunit gp91(phox), resulted in a more reductive lumenal microenvironment, which in turn, enhanced activities of local cysteine cathepsins. Decreased NOX2 activity additionally increased the phagosome's ability to reduce disulfides, further enhancing the efficiency of the macrophage to degrade proteins containing disulfide bonds. Together, these changes initiated by IL-4 act synergistically to rapidly and dramatically enhance the macrophage's ability to degrade phagocytosed protein, which, we reason, better equips this cell for its roles in wound repair and tissue remodeling.

Pheophorbide a-Mediated Photodynamic Therapy Triggers HLA Class I-Restricted Antigen Presentation in Human Hepatocellular Carcinoma

The immunomodulatory effects of photodynamic therapy (PDT) have been reported in several photosensitizers. Pheophorbide a (Pa), a chlorophyll derivative, shows antitumor effects on a number of human cancers in a PDT approach (Pa-PDT); however, the potential effect of Pa-PDT on the anticancer immunity has never been studied. In the present work, the underlying action mechanism of Pa-PDT was systemically investigated with a human hepatoma cell line HepG2. We found that Pa-PDT significantly inhibited the growth of HepG2 cells with a half maximal inhibitory concentration/endoplasmic reticulum of 0.35 microM at 24 hours by the induction of apoptosis, as shown by externalization of phosphatidylserine, release of mitochondrial cytochrome c, and activation of the caspases cascade in the treated cells. Interestingly, using two-dimensional polyacrylamide gel electrophoresis analysis, a 57-kDa disulfide-isomerase-like ER resident protein (ERp57) that belongs to the HLA class I-restricted antigen-processing machinery was found to be mediated during the Pa-PDT treatment. This activation of antigen presentation was confirmed by Western blot analysis and immunostaining. Furthermore, a cross-presentation of antigen with HLA class I proteins and 70-kDa heat shock protein was found in Pa-PDT-treated cells, as shown by the confocal microscopic observation and immunoprecipitation assay. Nevertheless, the immunogenicity of HepG2 cells was increased by Pa-PDT treatment that triggered phagocytic capture by human macrophages. Our findings provide the first evidence that Pa-PDT can trigger both apoptosis and cancer immunity in the tumor host.

LAMP-2-deficient human B cells exhibit altered MHC class II presentation of exogenous antigens

Major histocompatibility complex (MHC) class II molecules present antigenic peptides derived from engulfed exogenous proteins to CD4(+) T cells. Exogenous antigens are processed in mature endosomes and lysosomes where acidic proteases reside and peptide-binding to class II alleles is favoured. Hence, maintenance of the microenvironment within these organelles is probably central to efficient MHC class II-mediated antigen presentation. Lysosome-associated membrane proteins such as LAMP-2 reside in mature endosomes and lysosomes, yet their role in exogenous antigen presentation pathways remains untested. In this study, human B cells lacking LAMP-2 were examined for changes in MHC class II-restricted antigen presentation. MHC class II presentation of exogenous antigen and peptides to CD4(+) T cells was impaired in the LAMP-2-deficient B cells. Peptide-binding to MHC class II on LAMP-2-deficient B cells was reduced at physiological pH compared with wild-type cells. However, peptide-binding and class II-restricted antigen presentation were restored by incubation of LAMP-2-negative B cells at acidic pH, suggesting that efficient loading of exogenous epitopes by MHC class II molecules is dependent upon LAMP-2 expression in B cells. Interestingly, class II presentation of an epitope derived from an endogenous transmembrane protein was detected using LAMP-2-deficient B cells. Consequently, LAMP-2 may control the repertoire of peptides displayed by MHC class II molecules on B cells and influence the balance between endogenous and exogenous antigen presentation.

Disulfide bond engineering to trap peptides in the MHC class I binding groove

Immunodominant peptides in CD8 T cell responses to pathogens and tumors are not always tight binders to MHC class I molecules. Furthermore, antigenic peptides that bind weakly to the MHC can be problematic when designing vaccines to elicit CD8 T cells in vivo or for the production of MHC multimers for enumerating pathogen-specific T cells in vitro. Thus, to enhance peptide binding to MHC class I, we have engineered a disulfide bond to trap antigenic peptides into the binding groove of murine MHC class I molecules expressed as single-chain trimers or SCTs. These SCTs with disulfide traps, termed dtSCTs, oxidized properly in the endoplasmic reticulum, transited to the cell surface, and were recognized by T cells. Introducing a disulfide trap created remarkably tenacious MHC/peptide complexes because the peptide moiety of the dtSCT was not displaced by high-affinity competitor peptides, even when relatively weak binding peptides were incorporated into the dtSCT. This technology promises to be useful for DNA vaccination to elicit CD8 T cells, in vivo study of CD8 T cell development, and construction of multivalent MHC/peptide reagents for the enumeration and tracking of T cells-particularly when the antigenic peptide has relatively weak affinity for the MHC.

Efficient presentation of myelin oligodendrocyte glycoprotein peptides but not protein by astrocytes from HLA-DR2 and HLA-DR4 transgenic mice

The role of astrocytes in the pathogenesis of multiple sclerosis (MS) is not well understood. Astrocytes may modulate the activity of pathogenic T cells by presenting myelin antigens in combination with pro- or anti-inflammatory signals. Astrocytes have been shown to present myelin basic protein (MBP) and proteolipid protein (PLP) to T cells, but it has remained unresolved whether astrocytes present myelin oligodendrocyte glycoprotein (MOG), which has been implicated as an important autoantigen in MS. Here, we asked whether astrocytes presented MOG to T cells. To closer model presentation of human MOG by astrocytes in MS patients, we generated astrocytes from transgenic mice expressing the MS-associated MHC class II alleles HLA-DR2 (DRB1*1501) and HLA-DR4 (DRB1*0401). The results show that IFN-gamma-activated HLA-DR2 and HLA-DR4 expressing astrocytes efficiently presented immunodominant and subdominant MOG peptides to T cells. The hierarchy of the presented MOG epitopes was comparable to that of professional APCs, including dendritic cells and microglia. Importantly, astrocytes were poor at processing and presenting native MOG protein. Furthermore, astrocytes induced a mixed Th1/Th2 cytokine response in MOG-specific T cells, whereas dendritic cells induced a predominantly Th1 cell response. Collectively, the results suggest that astrocytes may modulate anti-MOG T cell responses in the CNS.

Cutting edge: induction of the antigen-processing enzyme IFN-gamma-inducible lysosomal thiol reductase in melanoma cells Is STAT1-dependent but CIITA-independent

Presentation and CD4(+) T cell responses to Ag in the context of MHC class II molecules require processing of native proteins into short peptide fragments. Within this pathway, IFN-gamma-inducible lysosomal thiol reductase (GILT) functions to catalyze thiol bond reduction, thus unfolding native protein Ag and facilitating further processing via cellular proteases. In contrast with professional APCs such as B cells, class II-positive human melanomas expressed relatively little to no GILT protein or mRNA. Tumor cell GILT expression was partially restored with IFN-gamma treatment but unlike other genes required for class II Ag presentation, GILT was not regulated by CIITA. Rather, studies revealed STAT1 plays a direct role in IFN-gamma-inducible GILT expression. These results define a molecular mechanism for the uncoupled regulation of MHC class II genes and the processing enzyme GILT in human melanomas.

Endoplasmic reticulum chaperone-specific monoclonal antibodies for flow cytometry and immunohistochemical staining

Endoplasmic reticulum (ER) chaperones of the antigen processing machinery play a crucial role in HLA class I antigen complex assembly and antigen presentation. The characterization of the expression of these chaperones in normal tissues and malignant lesions has been hampered by the lack or limited availability of ER chaperone-specific monoclonal antibodies (mAb) that are suitable for immunohistochemical staining. To overcome this limitation, we have generated human calnexin, ERp57, calreticulin and tapasin-specific mAb-secreting hybridomas from BALB/c mice immunized with peptides and recombinant proteins. The mAb TO-5, TO-2, TO-11 and TO-3 were shown to be specific for calnexin, ERp57, calreticulin and tapasin, respectively, as they react specifically with the corresponding immunizing peptides in ELISA and with the corresponding proteins when tested with human lymphoid cell lysates in Western blotting. Furthermore, the reactivity of the four mAb with the corresponding intracellular antigens yielded intracellular staining when the mAb were tested with formalin-fixed, microwave-treated and saponin-permeabilized cells in indirect immunofluorescence and with formalin-fixed, paraffin-embedded tissue sections in the immunoperoxidase reaction. These results suggest that the ER chaperone-specific mAb we have developed are useful probes for characterizing the expression of ER chaperones of the antigen processing machinery in normal and pathological cells. This information will contribute to defining the effects of abnormalities in their expression on HLA class I antigen expression and function and on the interactions of target cells with the host's immune system.

Human T-cells recognise N-terminally Fmoc-modified peptide

We aimed to generate T-cell clones specific for human pre-proinsulin. An HLA DQ8, CD4+ T-cell clone that recognised a 10mer (C65-A9) peptide from pre-proinsulin was isolated. Further analysis revealed that the clone responded neither to recombinant proinsulin nor to re-synthesised C65-A9 peptide. Analysis of the original peptide revealed minor contamination (<0.5%) with an N-terminal Fmoc adduct. This peptide was synthesised and shown to stimulate the clone. Thus, Fmoc-modified peptides, which are common contaminants in synthetic peptides, can stimulate human CD4+ T-cells. This finding has important implications for the use of synthetic peptides in screening and epitope mapping studies and their use as vaccines in humans.

Major histocompatibility complex class I-restricted antigen processing and presentation

Major histocompatibility complex (MHC) class I molecules present antigenic peptides to CD8-expressing cytotoxic T lymphocytes (CTLs). This antigen recognition system is critically important for immune surveillance against viruses and tumors. Most class I-binding peptides are generated in the cytosol, as side products from the degradation of misfolded proteins by proteasomes. A subset of the resulting peptides are translocated across the endoplasmic reticulum (ER) membrane by a dedicated peptide transporter, and these peptides are then loaded onto peptide-receptive class I molecules in the ER. The stable assembly of class I molecules with peptides is controlled by a variety of accessory proteins, including chaperones with general housekeeping functions and factors with dedicated roles in class I assembly. Peptide-filled class I molecules are then delivered to the cell surface for recognition by CTLs. This highly regulated process permits the host to rapidly counter invading pathogens with strong and sustained CTL responses and, at the same time, avoid misguided attacks. Here, how the class I antigen processing machinery accomplishes this daunting task is reviewed.

HLA-B27 misfolding is associated with aberrant intermolecular disulfide bond formation (dimerization) in the endoplasmic reticulum

The class I protein HLA-B27 confers susceptibility to inflammatory arthritis in humans and when overexpressed in rodents for reasons that remain unclear. We demonstrated previously that HLA-B27 heavy chains (HC) undergo endoplasmic reticulum (ER)-associated degradation. We report here that HLA-B27 HC also forms two types of aberrant disulfide-linked complexes (dimers) during the folding and assembly process that can be distinguished by conformation-sensitive antibodies W6/32 and HC10. HC10-reactive dimers form immediately after HC synthesis in the ER and constitute at least 25% of the HC pool, whereas W6/32-reactive dimers appear several hours later and represent less than 10% of the folded HC. HC10-reactive dimers accumulate in the absence of tapasin or beta(2)-microglobulin, whereas W6/32-reactive dimers are not detected. Efficient formation of W6/32-reactive dimers appears to depend on the transporter associated with antigen processing, tapasin, and beta(2)-microglobulin. The unpaired Cys(67) and residues at the base of the B pocket that dramatically impair HLA-B27 HC folding are critical for the formation of HC10-reactive ER dimers. Although certain other alleles also form dimers late in the assembly pathway, ER dimerization of HLA-B27 may be unique. These results demonstrate that residues comprising the HLA-B27 B pocket result in aberrant HC folding and disulfide bond formation, and thus confer unusual properties on this molecule that are unrelated to peptide selection per se, yet may be important in disease pathogenesis.

Major histocompatibility class I folding, assembly, and degradation: a paradigm for two-stage quality control in the endoplasmic reticulum

Protein folding in living cells is a complex process involving many interdependent factors. The primary site for folding of nascent proteins destined for secretion is the endoplasmic reticulum (ER). Several disease states, including cystic fibrosis, are brought about because of irregularities in protein folding. Under normal cellular conditions, "quality control" mechanisms ensure that only correctly folded proteins are exported from the ER, with incorrectly folded or incompletely assembled proteins being degraded. Quality control mechanisms can be divided into two broad processes: (1) Primary quality control involves general mechanisms that are not specific for individual proteins; these monitor the fidelity of nascent protein folding in the ER and mediate the destruction of incompletely folded proteins. (2) Partially folded or assembled proteins may be subject to secondary quality control mechanisms that are protein- or protein-family-specific. Here we use the folding and assembly of major histocompatibility complex (MHC) class I as an example to illustrate the processes of quality control in the ER. MHC class I, a trimeric complex assembled in the ER of virally infected or malignant cells, presents antigenic peptide to cytotoxic T lymphocytes; this mediates cell killing and thereby prevents the spread of infection or malignancy. The folding and assembly of MHC class I is subjected to both primary and secondary quality control mechanisms that lead either to correct folding, assembly, and secretion or to degradation via a proteasome-associated mechanism.

Reverse immunogenetic and polyepitopic approaches for the induction of cell-mediated immunity against bovine viral pathogens

The control of several infectious diseases of animals by vaccination is perhaps the most outstanding accomplishment of veterinary medicine in the last century. Even the eradication of some pathogens is in sight, at least in some parts of the world. However, infectious diseases continue to cost millions of dollars to the livestock industry. One of the reasons for the failure to control certain pathogens is the limited emphasis placed on cell-mediated immunity (CMI) in the design of vaccines against these pathogens. Traditionally, vaccine-induced immunity has been studied in relation to antibody-mediated protection. More recent studies, however, have focused on understanding CMI and developing means of inducing CMI. This review focuses on recent advances made in the study of CMI in general and of cytotoxic T lymphocytes in particular. Parallels from studies in human and mouse immunology are drawn in order to point out implications to bovine immunology, specifically for immunity against bovine herpesvirus 1.