Antigen degradation or presentation by MHC class I molecules via classical and non-classical pathways

The HLA Region and Autoimmune Disease: Associations and Mechanisms of Action

The HLA region encodes several molecules that play key roles in the immune system. Strong association between the HLA region and autoimmune disease (AID) has been established for over fifty years. Association of components of the HLA class II encoded HLA-DRB1-DQA1-DQB1 haplotype has been detected with several AIDs, including rheumatoid arthritis, type 1 diabetes and Graves' disease. Molecules encoded by this region play a key role in exogenous antigen presentation to CD4+ Th cells, indicating the importance of this pathway in AID initiation and progression. Although other components of the HLA class I and III regions have also been investigated for association with AID, apart from the association of HLA-B*27 with ankylosing spondylitis, it has been difficult to determine additional susceptibility loci independent of the strong linkage disequilibrium (LD) with the HLA class II genes. Recent advances in the statistical analysis of LD and the recruitment of large AID datasets have allowed investigation of the HLA class I and III regions to be re-visited. Association of the HLA class I region, independent of known HLA class II effects, has now been detected for several AIDs, including strong association of HLA-B with type 1 diabetes and HLA-C with multiple sclerosis and Graves' disease. These results provide further evidence of a possible role for bacterial or viral infection and CD8+ T cells in AID onset. The advances being made in determining the primary associations within the HLA region and AIDs will not only increase our understanding of the mechanisms behind disease pathogenesis but may also aid in the development of novel therapeutic targets in the future.

Contrasting responses to selection in class I and class IIα major histocompatibility-linked markers in salmon

Comparison of levels and patterns of genetic variation in natural populations either across loci or against neutral expectation can yield insight into locus-specific differences in the strength and direction of evolutionary forces. We used both approaches to test the hypotheses on patterns of selection on major histocompatibility (MH)-linked markers. We performed temporal analyses of class I and class IIα MH-linked markers and eight microsatellite loci in two Atlantic salmon populations in Ireland on two temporal scales: over six decades and 9 years in the rivers Burrishoole and Delphi, respectively. We also compared contemporary Burrishoole and Delphi samples with nearby populations for the same loci. On comparing patterns of temporal and spatial differentiation among classes of loci, the class IIα MH-linked marker was consistently identified as an outlier compared with patterns at the other microsatellite loci or neutral expectation. We found higher levels of temporal and spatial heterogeneity in heterozygosity (but not in allelic richness) for the class IIα MH-linked marker compared with microsatellites. Tests on both within- and among-population differentiation are consistent with directional selection acting on the class IIα-linked marker in both temporal and spatial comparisons, but only in temporal comparisons for the class I-linked marker. Our results indicate a complex pattern of selection on MH-linked markers in natural populations of Atlantic salmon. These findings highlight the importance of considering selection on MH-linked markers when using these markers for management and conservation purposes.

Serum antibodies critically affect virus-specific CD4+/CD8+ T cell balance during respiratory syncytial virus infections

Following infection with respiratory syncytial virus (RSV), reinfection in healthy individuals is common and presumably due to ineffective memory T cell responses. In peripheral blood of healthy adults, a higher CD4(+)/CD8(+) memory T cell ratio was observed compared with the ratio of virus-specific effector CD4(+)/CD8(+) T cells that we had found in earlier work during primary RSV infections. In mice, we show that an enhanced ratio of RSV-specific neutralizing to nonneutralizing Abs profoundly enhanced the CD4(+) T cell response during RSV infection. Moreover, FcγRs and complement factor C1q contributed to this Ab-mediated enhancement. Therefore, the increase in CD4(+) memory T cell response likely occurs through enhanced endosomal Ag processing dependent on FcγRs. The resulting shift in memory T cell response was likely amplified by suppressed T cell proliferation caused by RSV infection of APCs, a route important for Ag presentation via MHC class I molecules leading to CD8(+) T cell activation. Decreasing memory CD8(+) T cell numbers could explain the inadequate immunity during repeated RSV infections. Understanding this interplay of Ab-mediated CD4(+) memory T cell response enhancement and infection mediated CD8(+) memory T cell suppression is likely critical for development of effective RSV vaccines.

The role of membrane fusion activity of a whole inactivated influenza virus vaccine in (re)activation of influenza-specific cytotoxic T lymphocytes

Induction of cytotoxic T lymphocyte (CTL) activity against conserved influenza antigens, e.g. nucleoprotein (NP) could be a step towards cross-protective influenza vaccine. The major challenge for non-replicating influenza vaccines aiming for activation of CTLs is targeting of antigen to the MHC class I processing and presentation pathway of professional antigen presenting cells, in particular dendritic cells (DCs). Intrinsic fusogenic properties of the vaccine particle itself can enable direct cytosolic delivery of the antigen by enhancing release of the antigen from the endosome to the cytosol. Alternatively, the vaccine particle would need to possess the capacity to activate DCs thereby triggering cell-intrinsic mechanisms of cross-presentation, processes that do not require fusion. Here, using fusion-active and fusion-inactive whole inactivated virus (WIV) as a vaccine model, we studied the relative contribution of these two pathways on priming and reactivation of influenza NP-specific CTLs in a murine model. We show that activation of bone marrow-derived DCs by WIV, as well as reactivation of NP-specific CTLs in vitro and in vivo were not affected by inactivation of membrane fusion of the WIV particles. However, in vivo priming of naive CTLs was optimal only upon vaccination with fusion-active WIV. Thus, DC-intrinsic mechanisms of cross-presentation are involved in the activation of CTLs upon vaccination with WIV. However, for optimal priming of naive CTLs these mechanisms should be complemented by delivery of antigen to the cytosol mediated by the membrane fusion capacity of the WIV particles.

Peptide length extension skews the minor HA-1 antigen presentation toward activated dendritic cells but reduces its presentation efficiency

Minor histocompatibility Ags (mHags) are important targets of the graft-versus-leukemia effect after HLA-matched allogeneic stem cell transplantation. mHags are HLA-restricted polymorphic peptides expressed on normal and leukemia cells. Vaccination with hematopoiesis-restricted mHag peptides, such as HA-1, may boost the graft-versus-leukemia effect. However, some animal studies indicate that peptides exactly reflecting immunogenic T cell epitopes (short peptides [SPs]) induce tolerance that is potentially due to systemic Ag spreading. Peptide length extension (long peptides [LPs]) may optimize immune responses by restricting and prolonging Ag presentation on dendritic cells (DCs). In this study, we compared the in vitro characteristics and T cell-stimulatory capacities of a human 30-mer HA-1 LP with the 9-mer HA-1 SP. DCs presented the HA-1 LP and SP and expanded HA-1-specific cytotoxic T cell lines. As hypothesized, HA-1 LP presentation, but not SP presentation, was largely restricted to activated DCs and was nearly absent on other hematopoietic cells. However, DCs presented the HA-1 LP 2-3 log levels less efficiently than the SP. Finally, the decay of HA-1 LP and SP presentation on DCs was comparable. We conclude that HA-1 LP and SP differ in their in vitro characteristics and that only comparative clinical studies after allogeneic stem cell transplantation may reveal the optimal HA-1 vaccine.

Expressão do complexo de histocompatilidade principal de classe I (MHC I) no sistema nervoso central: plasticidade sináptica e regeneração

Foi demonstrado recentemente que o complexo de histocompatibilidade principal de classe I (MHC I), expresso no sistema nervoso central (SNC), não funciona somente como molécula com papel imunológico, mas também como parte de um mecanismo envolvido na plasticidade sináptica. A expressão de MHC I interfere na intensidade e seletividade da retração de sinapses em contato com neurônios que sofreram lesão e também influencia a reatividade das células gliais próximas a esses neurônios. A intensidade do rearranjo sináptico e resposta glial após lesão, ligadas à expressão de MHC I no SNC, repercute em diferenças na capacidade regenerativa e recuperação funcional em linhagens de camundongos isogênicos. Dessa forma, os novos aspectos sobre a função do MHC I no SNC direcionam futuras pesquisas no sentido de buscar o envolvimento do MHC I em doenças neurológicas e também o desenvolvimento de novas estratégias terapêuticas.

Superior antitumor response induced by large stress protein chaperoned protein antigen compared with peptide antigen

Our previous studies have demonstrated that the natural chaperone complexes of full-length tumor protein Ags (e.g., gp100) and large stress proteins (e.g., hsp110 and grp170) with exceptional Ag-holding capabilities augment potent tumor protective immunity. In this study, we assess the peptide-interacting property of these large chaperones and, for the first time, compare the immunogenicity of the recombinant chaperone vaccines targeting two forms of Ags (protein versus peptide). Both hsp110 and grp170 readily formed complexes with antigenic peptides under physiologic conditions, and the peptide association could be further stimulated by heat shock. The large chaperones displayed similar but distinct peptide-binding features compared with hsp70 and grp94/gp96. Immunization with hsp110- or grp170-tyrosinase-related protein 2 (TRP2(175-192)) peptide complexes effectively primed CD8(+) T cells reactive with TRP2-derived, MHC class I-restricted epitope. However, the tumor protective effect elicited by the TRP2(175-192) peptide vaccine was much weaker than that achieved by full-length TRP2 protein Ag chaperoned by grp170. Furthermore, immunization with combined chaperone vaccines directed against two melanoma protein Ags (i.e., gp100 and TRP2) significantly improved overall anti-tumor efficacy when compared with either of the single Ag vaccine. Lastly, treatment of tumor-bearing mice with these dual Ag-targeted chaperone complexes resulted in an immune activation involving epitope spreading, which was associated with a strong growth inhibition of the established tumors. Our results suggest that high m.w. chaperones are superior to conventional chaperones as a vaccine platform to deliver large protein Ags, and provide a rationale for translating this recombinant chaperoning-based vaccine to future clinical investigation.

PSMB8 (LMP7) but not PSMB9 (LMP2) gene polymorphisms are associated to pigeon breeder's hypersensitivity pneumonitis

Hypersensitivity Pneumonitis (HP) is a lung inflammatory disorder caused by inhalation of organic particles by a susceptible host. However, only a small proportion of individuals exposed to HP-associated antigens develop the disease, suggesting that additional host/environmental factors may play a role. We have previously found that genetic susceptibility associated to the major histocompatibility complex (MHC) plays an important role in this disease. The low molecular weight proteosome (LMP, currently named PSMB) genes code for subunits of the proteosome, a multimeric enzymatic complex that degrades proteins into peptides in order to be presented in the MHC class I pathway. We hypothesized that polymorphisms in PSMB8 or PSMB9 genes could be involved in the susceptibility to HP. Thus, in this study we analyzed the polymorphic site at amino acid position 60 (Arg/His) of the fourth exon in the PSMB9 gene and the amino acid position 49 (Gln/Lys) in the second exon of PSMB8 gene in 50 Mexican patients with HP and 50 healthy ethnically matched controls. PSMB typing was performed using polymerase chain reaction-restriction fragment length polymorphisms (PCR-RFLP). Our results demonstrated that HP patients had a significant increase of the PSMB8 KQ genotype frequency (OR = 7.25, CI = 2.61-21.3; p = 0.000034). No differences were found in the distribution of PSMB9 alleles/genotypes. However, PSMB9-RH/PSMB8 KQ haplotype was significantly increased in HP patients (OR = 6.77, CI = 1.34-65.31, p < 0.02). These findings suggest that PSMB8 KQ genotype could increase the risk to develop hypersensitivity pneumonitis.

Investigating the genetic association between ERAP1 and ankylosing spondylitis

A strong association between ERAP1 and ankylosing spondylitis (AS) was recently identified by the Wellcome Trust Case Control Consortium and the Australo-Anglo-American Spondylitis Consortium (WTCCC-TASC) study. ERAP1 is highly polymorphic with strong linkage disequilibrium evident across the gene. We therefore conducted a series of experiments to try to identify the primary genetic association(s) with ERAP1. We replicated the original associations in an independent set of 730 patients and 1021 controls, resequenced ERAP1 to define the full extent of coding polymorphisms and tested all variants in additional association studies. The genetic association with ERAP1 was independently confirmed; the strongest association was with rs30187 in the replication set (P = 3.4 × 10⁻³). When the data were combined with the original WTCCC-TASC study the strongest association was with rs27044 (P = 1.1 × 10⁻⁹). We identified 33 sequence polymorphisms in ERAP1, including three novel and eight known non-synonymous polymorphisms. We report several new associations between AS and polymorphisms distributed across ERAP1 from the extended case–control study, the most significant of which was with rs27434 (P = 4.7 × 10⁻⁷). Regression analysis failed to identify a primary association clearly; we therefore used data from HapMap to impute genotypes for an additional 205 non-coding SNPs located within and adjacent to ERAP1. A number of highly significant associations (P < 5 × 10⁻⁹) were identified in regulatory sequences which are good candidates for causing susceptibility to AS, possibly by regulating ERAP1 expression.

Molecular mechanisms of MHC class I-antigen processing: redox considerations

Major histocompatibility complex (MHC) class I molecules present antigenic peptides to the cell surface for screening by CD8(+) T cells. A number of ER-resident chaperones assist the assembly of peptides onto MHC class I molecules, a process that can be divided into several steps. Early folding of the MHC class I heavy chain is followed by its association with beta(2)-microglobulin (beta(2)m). The MHC class I heavy chain-beta(2)m heterodimer is incorporated into the peptide-loading complex, leading to peptide loading, release of the peptide-filled MHC class I molecules from the peptide-loading complex, and exit of the complete MHC class I complex from the ER. Because proper antigen presentation is vital for normal immune responses, the assembly of MHC class I molecules requires tight regulation. Emerging evidence indicates that thiol-based redox regulation plays critical roles in MHC class I-restricted antigen processing and presentation, establishing an unexpected link between redox biology and antigen processing. We review the influences of redox regulation on antigen processing and presentation. Because redox signaling pathways are a rich source of validated drug targets, newly discovered redox biology-mediated mechanisms of antigen processing may facilitate the development of more selective and therapeutic drugs or vaccines against immune diseases.

Immune-related gene expression in response to H11N9 low pathogenic avian influenza virus infection in chicken and Pekin duck peripheral blood mononuclear cells

The duck and chicken are important hosts of avian influenza virus (AIV) with distinctive responses to infection. Frequently, AIV infections in ducks are asymptomatic and long-lasting in contrast to the clinically apparent and transient infections observed in chickens. These differences may be due in part to the host response to AIV infection. Using real-time quantitative PCR, we examined the expression of immune-related genes in response to low pathogenic AIV H11N9 infection in peripheral blood mononuclear cells (PBMC) isolated from the blood of chickens and Pekin ducks. While chicken PBMC expressed IL-1beta and IL-6 at high levels similar to mammalian species, duck PBMC expression levels were minimal or unchanged. Similarly, duck IFN-beta expression was nearly unaffected, whereas chicken expression was highly upregulated. Chicken IFN-gamma was expressed to higher levels than duck IFN-gamma, while IFN-alpha was expressed similarly by both species. IL-2 was elevated early in infection in duck PBMC, but returned to baseline levels by the end of the experiment; in contrast, IL-2 was weakly induced in chicken PBMC at late time points. TLR-7 and MHC class I molecule expressions were conserved between species, whereas duck MHC class II expression was downregulated and chicken expression was unchanged. These results show distinct PBMC expression patterns of pro-inflammatory cytokines and IFNs between species. The differences in pro-inflammatory cytokine and IFN expression reflect the asymptomatic and lasting infection observed in ducks and the tendency towards clinical signs and rapid clearance seen in chickens. These results highlight important differences in the host response to AIV of two species thought to be critical in the genesis and maintenance of epidemic strains of AIV.

[Genetic causes of impaired wound healing. Rare differential diagnosis of the non-healing wound]

Chronic leg ulcers affect about 1% of the German population. The intense search for the underlying cause of impaired wound healing is an essential requirement for successful therapy. The most common causes comprise chronic venous insufficiency (70%), peripheral arterial occlusive disease (10%) and diabetes mellitus. Besides vasculitis, infectious diseases and tumors, genetic diseases may constitute the underlying cause for impaired wound healing. In this review various rare genetic diseases causing chronic wounds like the Klinefelter-Syndrome, immunological diseases including the TAP-deficiency-syndrome and the leukocyte adhesion deficiency-syndromes, red blood cell disorders, thalassemia, thrombotic diseases, progeroid syndromes and inherited connective tissue disorders are presented.

Improved retroviral vector design results in sustained expression after adult gene therapy in mucopolysaccharidosis I mice

BACKGROUND

Mucopolysaccharidosis I (MPS I) is a lysosomal storage disease due to alpha-L-iduronidase (IDUA) deficiency that results in the accumulation of glycosaminoglycans (GAG). Gene therapy can reduce most clinical manifestations, but mice that receive transfer as adults lose expression unless they receive immunosuppression. Increasing liver specificity of transgene expression has reduced immune responses to other genes.

METHODS

A gamma retroviral vector was generated with a liver-specific human alpha1-antitrypsin promoter and the canine IDUA cDNA inverted relative to the retroviral long-terminal repeat. Adult MPS I mice received the vector intravenously at 6 weeks of age and were assessed for expression via serial serum IDUA assays. Functional testing and organ analysis were performed at 8 months.

RESULTS

This vector resulted in high specificity of expression in liver, and serum IDUA activity was stable in 90% of animals. Although the average serum IDUA activity was relatively low at 12.6 +/- 8.1 units/ml in mice with stable expression, a relatively high percentage of enzyme contained the mannose 6-phosphorylation necessary for uptake by other cells. At 6.5 months after transduction, most organs had high IDUA activity and normalized GAG levels. There was complete correction of hearing and vision abnormalities and significant improvements in bone, although the aorta was refractory to treatment.

CONCLUSIONS

Stable expression of IDUA in adult MPS I mice can be achieved without immunosuppression by modifying the vector to reduce expression in the spleen. This approach may be effective in patients with MPS I or other lysosomal storage diseases.

Transpeptidation and reverse proteolysis and their consequences for immunity

Reverse proteolysis and transpeptidation lead to the generation of polypeptide sequences that cannot be inferred directly from genome sequences as they are post-translational phenomena. These phenomena have so far received little attention although the physiological consequences may reach far. The protease-mediated synthesis of several immunodominant MHC class I antigens was recently reported, underscoring its importance to immunity. Reverse proteolytic and transpeptidation mechanisms as well as conditions that favor successful protease-catalyzed synthetic events are discussed here.

Alphavirus replicon particles acting as adjuvants promote CD8+ T cell responses to co-delivered antigen

Alphavirus replicon particles induce strong antibody and CD8+ T cell responses to expressed antigens in numerous experimental systems. We have recently demonstrated that Venezuelan equine encephalitis virus replicon particles (VRP) possess adjuvant activity for systemic and mucosal antibody responses. In this report, we demonstrate that VRP induced an increased and balanced serum IgG subtype response to co-delivered antigen, with simultaneous induction of antigen-specific IgG1 and IgG2a antibodies, and increased both systemic and mucosal antigen-specific CD8+ T cell responses, as measured by an IFN-gamma ELISPOT assay. Additionally, VRP further increased antigen-specific T cell immunity in an additive fashion following co-delivery with the TLR ligand, CpG DNA. VRP infection led to recruitment of CD8+ T cells into the mucosal compartment, possibly utilizing the mucosal homing receptor, as this integrin was upregulated on CD8+ T cells in the draining lymph node of VRP-infected animals, where VRP-infected dendritic cells reside. This newly recognized ability of VRP to mediate increased T cell response towards co-delivered antigen provides the potential to both define the molecular basis of alphavirus-induced immunity, and improve alphavirus-based vaccines.

Comparison of DNA- and mRNA-Transfected Mouse Dendritic Cells as Potential Vaccines against the Human Papillomavirus Type 16 associated Oncoprotein E7

Background

Dendritic cells (DCs) mediate the generation of strong cytotoxic T-lymphocyte (CTL) responses by functioning in antigen presentation and exerting adjuvant properties. We compared several activation markers and parameters of biological activity of DNA- and mRNA-transfected DCs in vitro and in vivo.

Methods

CpG-matured, bone marrow derived C57BL/6 mouse DCs were electroporated either with enhanced green fluorescence protein (EGFP) or human papillomavirus type 16 (HPV16) E7 expression plasmids or in vitro transcribed mRNAs encoding for the codon-optimized E7 or a shuffled version thereof. Activation marker expression and antigen presentation was analysed by fluorescence-activated cell sorting. The migratory behaviour of transfected DCs were investigated by in vitro chemotaxis experiments and cytokine expression by ELISA. CTL-priming capacity of transfected DCs were determined by vaccination of mice.

Results

mRNA transfection produced a two- to fourfold increase of the activation markers CD40, CD80, CD86 and MHC I and MHC II molecules. Predominately antigen-expressing DCs migrated after mRNA transfection. Furthermore, mRNA-transfected DCs were capable of inducing a chemokine gradient. After maturation, electroporation and activation with soluble CD40 ligand and interferon-γ, DCs displayed a T-helper cell type 2 cytokine expression pattern. Nevertheless, E7-transfected DCs were able to prime E7-specific CTL responses in vivo. The highest E7-specific CTL frequencies were found in mice immunized with mRNA-transfected DCs. The in vitro expanded CTLs exerted functional E7-specific cytotoxic activity.

Conclusions

Genetically modified DCs are suitable vehicles for the induction of E7-specific CTL responses in mice and hence could help to eradicate HPV-associated lesions in humans.

Niflumic acid renders dendritic cells tolerogenic and up-regulates inhibitory molecules ILT3 and ILT4

Niflumic acid is a member of non-steroidal anti-inflammatory agents, from which aspirin was recently shown to inhibit maturation of human-monocyte derived dendritic cells (DCs). DCs are crucial regulators of the immune response, capable of inducing immunity as well as tolerance. In our in vitro study we showed a tolerogenic effect of NFA on phenotype and function of LPS-matured monocyte-derived DCs. Different drug concentrations dose-dependently down-regulated the expression of co-stimulatory molecules, particularly CD80 and lowered the expression of dendritic cell marker CD1a. Opposingly, the expressions of two inhibitory surface molecules, associated with tolerogenic DCs, immunoglobulin-like transcripts (ILT)3 and ILT4 were induced in treated DCs. The levels of TNFalpha production by NFA-treated DCs did not change significantly compared to controls, whereas the IL-12p70 and IL-10 production was completely abrogated at higher drug concentrations. However, at lower drug concentrations, the production of IL-12p70 was increased. There were no significant differences in the uptake of FITC labeled dextran by treated DCs compared to untreated cells. In allogeneic cultures with whole CD4+ T cells, dendritic cells differentiated in the presence of NFA appeared poor stimulators of CD4+ T-cell proliferation, even compared to immature DCs (iDCs). These results indicate the immunosuppressive properties of NFA, which may be therapeutically useful in controlling chronic immune and/or inflammatory diseases, by modulating DC characteristics towards tolerogenic DCs.

Hotspot Hunter: a computational system for large-scale screening and selection of candidate immunological hotspots in pathogen proteomes

BACKGROUND

T-cell epitopes that promiscuously bind to multiple alleles of a human leukocyte antigen (HLA) supertype are prime targets for development of vaccines and immunotherapies because they are relevant to a large proportion of the human population. The presence of clusters of promiscuous T-cell epitopes, immunological hotspots, has been observed in several antigens. These clusters may be exploited to facilitate the development of epitope-based vaccines by selecting a small number of hotspots that can elicit all of the required T-cell activation functions. Given the large size of pathogen proteomes, including of variant strains, computational tools are necessary for automated screening and selection of immunological hotspots.

RESULTS

Hotspot Hunter is a web-based computational system for large-scale screening and selection of candidate immunological hotspots in pathogen proteomes through analysis of antigenic diversity. It allows screening and selection of hotspots specific to four common HLA supertypes, namely HLA class I A2, A3, B7 and class II DR. The system uses Artificial Neural Network and Support Vector Machine methods as predictive engines. Soft computing principles were employed to integrate the prediction results produced by both methods for robust prediction performance. Experimental validation of the predictions showed that Hotspot Hunter can successfully identify majority of the real hotspots. Users can predict hotspots from a single protein sequence, or from a set of aligned protein sequences representing pathogen proteome. The latter feature provides a global view of the localizations of the hotspots in the proteome set, enabling analysis of antigenic diversity and shift of hotspots across protein variants. The system also allows the integration of prediction results of the four supertypes for identification of hotspots common across multiple supertypes. The target selection feature of the system shortlists candidate peptide hotspots for the formulation of an epitope-based vaccine that could be effective against multiple variants of the pathogen and applicable to a large proportion of the human population.

CONCLUSION

Hotspot Hunter is publicly accessible at http://antigen.i2r.a-star.edu.sg/hh/. It is a new generation computational tool aiding in epitope-based vaccine design.

Phenotypic studies of natural killer cell subsets in human transporter associated with antigen processing deficiency

Peripheral blood natural killer (NK) cells from patients with transporter associated with antigen processing (TAP) deficiency are hyporesponsive. The mechanism of this defect is unknown, but the phenotype of TAP-deficient NK cells is almost normal. However, we noticed a high percentage of CD56^bright cells among total NK cells from two patients. We further investigated TAP-deficient NK cells in these patients and compared them to NK cells from two other TAP-deficient patients with no clinical symptoms and to individuals with chronic inflammatory diseases other than TAP deficiency (chronic lung diseases or vasculitis). Peripheral blood mononuclear cells isolated from venous blood were stained with fluorochrome-conjugated antibodies and the phenotype of NK cells was analyzed by flow cytometry. In addition, ⁵¹Chromium release assays were performed to assess the cytotoxic activity of NK cells. In the symptomatic patients, CD56^bright NK cells represented 28% and 45%, respectively, of all NK cells (higher than in healthy donors). The patients also displayed a higher percentage of CD56^dimCD16⁻ NK cells than controls. Interestingly, this unusual NK cell subtype distribution was not found in the two asymptomatic TAP-deficient cases, but was instead present in several of the other patients. Over-expression of the inhibitory receptor CD94/NKG2A by TAP-deficient NK cells was confirmed and extended to the inhibitory receptor ILT2 (CD85j). These inhibitory receptors were not involved in regulating the cytotoxicity of TAP-deficient NK cells. We conclude that expansion of the CD56^bright NK cell subtype in peripheral blood is not a hallmark of TAP deficiency, but can be found in other diseases as well. This might reflect a reaction of the immune system to pathologic conditions. It could be interesting to investigate the relative distribution of NK cell subsets in various respiratory and autoimmune diseases.

A transporter associated with antigen-processing independent vacuolar pathway for the MHC class I-mediated presentation of endogenous transmembrane proteins

MHC class I molecules present peptides derived from the ectodomains of endogenous transmembrane proteins; however, the processing of these Ags is incompletely understood. As model transmembrane Ags we investigated the processing of MHC-I-derived fusion proteins containing the N-terminally extended K(b)-restricted OVA epitope SIINFEKL in the extracytoplasmic domain. In TAP-deficient, nonprofessional APCs, the epitope was cleaved out of various sequence contexts and presented to T cells. Ag presentation was inhibited by acidophilic amines and inhibitors of the vacuolar proton pump, indicating processing in endosomes. Endosomal aspartic-type cathepsins, and to some extent also the trans-Golgi network protease furin, were involved in processing. Clathrin-dependent and independent internalization from the cell surface targeted MHC-I fusion proteins to early and late endosomes, where SIINFEKL/K(b) complexes were detected by immunofluorescence microscopy. Targeting of MHC-I fusion proteins to processing compartments was independent of sequence motifs in the cytoplasmic tail. Not only TAP-deficient cells, but also TAP-competent APCs used the vacuolar pathway for processing of MHC-I fusion proteins. Thus, endosomal processing of internalized endogenous transmembrane proteins represents a novel alternate pathway for the generation of MHC-I-binding peptides.

Association of antigen processing machinery and HLA class I defects with clinicopathological outcome in cervical carcinoma

HLA class I loss is a significant mechanism of immune evasion by cervical carcinoma, interfering with the development of immunotherapies and cancer vaccines. We report the systematic investigation of HLA class I and antigen processing machinery component expression and association with clinical outcome. A tissue microarray containing carcinoma lesions from 109 cervical carcinoma patients was stained for HLA class I heavy chains, beta(2)-microglobulin, LMP2, LMP7, LMP10, TAP1, TAP2, ERAP1, tapasin, calreticulin, calnexin and ERp57. A novel staining evaluation method was used to ensure optimal accuracy and reliability of expression data, which were correlated with known clinicopathological parameters. Partial HLA class I loss was significantly associated with decreased 5-years overall survival (61% vs. 83% for normal expression; P<0.05) and was associated with decreased 5-years disease-free survival (DFS) (65% vs. 82% for normal expression; P=0.05). All APM components except LMP10, calnexin and calreticulin were down-regulated in a substantial number of cases and, except ERAP1, correlated significantly with HLA class I down-regulation. LMP7, TAP1 and ERAP1 loss was significantly associated with decreased overall and (except LMP7) DFS (P<0.05 and 0.005, respectively). ERAP1 down-regulation was an independent predictor for worse overall and DFS in multivariate analysis (HR 3.08; P<0.05 and HR 2.84; P<0.05, respectively). HLA class I and APM component down-regulation occur frequently in cervical carcinoma, while peptide repertoire alterations due to ERAP1 loss are a major contributing factor to tumour progression and mortality.

Co-immunisation with DNA encoding RANK/RANKL or 4-1BBL costimulatory molecules does not enhance effector or memory CTL responses afforded by immunisation with a tumour antigen-encoding DNA vaccine

T cell mediated immune responses are induced following interaction of MHC-presented epitope on professional antigen presenting cells such as dendritic cells (DCs) with cognate T cell receptor. Up-regulation of receptor-ligand pairs of costimulatory molecules linking DC to T cell enhances the resulting T cell responses. This 'second signalling' occurs through the B7 molecules CD80/86 expressed by DCs, and importantly through members of the TNF ligand/TNF receptor superfamilies. We have previously shown that co-expression of RANK/RANKL or 41BB-L in addition to tumour antigen in dendritic cells augmented cognate effector and memory tumour antigen-directed cytotoxic T cell responses when the DCs were used to immunise mice. Here, we examined whether co-immunisation with naked plasmid DNAs encoding antigen and these costimulatory molecule(s), would enhance antigen specific T cell responses. We demonstrate that co-immunisation with DNAs encoding tumour antigen and costimulatory molecules failed to enhance antigen-directed CTL responses, or tumour protection, afforded by immunisation with DNA encoding tumour antigen alone.

Genetic variation of antigen processing machinery components and association with cervical carcinoma

The antigen processing machinery (APM) plays an important role in immune recognition of virally infected and transformed cells. Defective expression of several APM components is associated with progression and clinical outcome in cervical carcinoma. Genetic variation in the genes encoding APM components is known to be associated with risk of occurrence of several malignancies. However, only limited evidence exists supporting the role of single nucleotide polymorphisms (SNPs) in APM components in cervical carcinoma. We have therefore investigated the occurrence of APM component SNP genotypes and haplotypes in cervical carcinoma. Thirteen coding SNPs in the LMP2, LMP7, TAP1, TAP2, and ERAP1 genes were genotyped in 127 cervical carcinoma patients and 124 controls. Individual genotype and allele distributions were assessed by single-marker analysis. Effects of various SNP combinations were estimated by haplotype construction and subsequent haplotype interaction analysis. Significant haplotypes were modeled on disease risk. Allele distributions at the LMP7-145, TAP2-651, ERAP1-127, and ERAP1-730 loci differed significantly between cases and controls with the major allele at the LMP7 and TAP2 loci and the minor allele at both ERAP1 loci associated with increased cervical carcinoma risk. A combination of the two haplotypes spanning these loci was associated with a three-fold increased risk (OR = 3.024; P << 0.001); approximately 12% of all cervical carcinoma occurrences were attributable to this combination. Our data indicate that combined genetic variation in the TAP2, LMP7, and ERAP1 genes is associated with increased cervical carcinoma risk.

The varicellovirus-encoded TAP inhibitor UL49.5 regulates the presentation of CTL epitopes by Qa-1b1

Impairment of MHC class I Ag processing is a commonly observed mechanism that allows viruses and tumors to escape immune destruction by CTL. The peptide transporter TAP that is responsible for the delivery of MHC class I-binding peptides into the endoplasmic reticulum is a pivotal target of viral-immune evasion molecules, and expression of this transporter is frequently lost in advanced cancers. We recently described a novel population of CTL that intriguingly exhibits reactivity against such tumor-immune escape variants and that recognizes self-peptides emerging at the cell surface due to defects in the processing machinery. Investigations of this new type of CTL epitopes are hampered by the lack of an efficient inhibitor for peptide transport in mouse cells. In this article, we demonstrate that the varicellovirus protein UL49.5, in contrast to ICP47 and US6, strongly impairs the activity of the mouse transporter and mediates degradation of mouse TAP1 and TAP2. Inhibition of TAP was witnessed by a strong reduction of surface MHC class I display and a decrease in recognition of conventional tumor-specific CTL. Analysis of CTL reactivity through the nonclassical molecule Qa-1(b) revealed that the presentation of the predominant leader peptide was inhibited. Interestingly, expression of UL49.5 in processing competent tumor cells induced the presentation of the new category of peptides. Our data show that the varicellovirus UL49.5 protein is a universal TAP inhibitor that can be exploited for preclinical studies on CTL-based immune intervention.

Multiple residues in the transmembrane helix and connecting peptide of mouse tapasin stabilize the transporter associated with the antigen-processing TAP2 subunit

The type I endoplasmic reticulum (ER) glycoprotein tapasin (Tpn) is essential for loading of major histocompatibility complex class I (MHC-I) molecules with an optimal spectrum of antigenic peptides and for stable expression of the heterodimeric, polytopic TAP peptide transporter. In a detailed mutational analysis, the transmembrane domain (TMD) and ER-luminal connecting peptide (CP) of mouse Tpn were analyzed for their capacity to stabilize the TAP2 subunit. Replacement of the TMD of Tpn by TMDs from calnexin or the Tpn-related protein, respectively, completely abolished TAP2 stabilization after transfection of Tpn-deficient cells, whereas TMDs derived from distantly related Tpn molecules (chicken and fish) were functional. A detailed mutational analysis of the TMD and adjacent residues in the ER-luminal CP of mouse Tpn was performed to elucidate amino acids that control the stabilization of TAP2. Single amino acid substitutions, including a conserved Lys residue in the center of the putative TMD, did not affect TAP2 expression levels. Mutation of this Lys plus four additional residues, predicted to be neighbors in an assumed alpha-helical TMD arrangement, abrogated the TAP2-stabilizing capacity of Tpn. In the presence of a wild-type TMD, also the substitution of a highly conserved Glu residue in the CP of Tpn strongly affected TAP2 stabilization. Defective TAP2 stabilization resulted in impaired cell surface expression of MHC-I molecules. This study thus defines a novel, spatially arranged motif in the TMD of Tpn essential for stable expression of the TAP2 protein and a novel protein interaction mode involving an ER-luminal Glu residue close to the membrane.

Reduced cytokine-mediated up-regulation of HLA-DR in TAP-deficient fibroblasts

Human deficiency in transporter associated with antigen processing (TAP) is characterized by a very low surface expression of human leukocyte antigen (HLA) class I molecules in hematopoietic and non hematopoietic cells. Among the latter, TAP-deficient skin fibroblasts have previously been shown by us to be very sensitive to lysis by activated autologous NK cells, even in the presence of cytokines that up-regulate HLA class I expression, a mechanism sufficient to protect normal fibroblasts from NK cell-mediated killing. Our complementary investigations on two TAP-deficient skin fibroblast cell lines surprisingly revealed that in response to proinflammatory cytokines, up-regulation of HLA-DR molecules at the cell surface is much less marked than in the case of normal skin fibroblasts. In contrast, the surface molecules CD40 and CD54 increase as much as observed on normal cells, suggesting that TAP-deficient fibroblasts are able to efficiently transduce cytokine-mediated stimulating signals. Transfection of an intact TAP gene into one of the TAP-deficient fibroblast cell lines restored a normal HLA class I expression that strongly increased upon IFN-gamma-mediated stimulation, whereas HLA-DR still remained lower than in control cells. These results suggest that, in addition to the defect in the HLA class I antigen presentation pathway, HLA-DR up-regulation is affected in TAP-deficient skin fibroblasts through an unknown mechanism probably independent from TAP.

The Yersinia enterocolitica invasin protein promotes major histocompatibility complex class I- and class II-restricted T-cell responses

Yersinia enterocolitica invasin (Inv) protein confers internalization into and expression of proinflammatory cytokines by host cells. Both events require binding of Inv to beta1 integrins, which initiates signaling cascades including activation of focal adhesion complexes, Rac1, mitogen-activated protein kinase, and NF-kappaB. Here we tested whether Inv might be suitable as a delivery molecule and adjuvant if used as a component of a vaccine. For this purpose, hybrid proteins composed of Inv and ovalbumin (OVA) were prepared, applied as a coating to microparticles, and used for vaccination. Fusion of OVA to Inv did not significantly disturb the ability of Inv to promote host cell binding, internalization, and interleukin-8 (IL-8) secretion when applied as a coating to microparticles. The microparticles were used for vaccination of mice adoptively transferred with OVA-specific T cells from OT-1 or DO11.10 mice. Administration of OVA-Inv-coated microparticles induced OVA-specific T-cell responses. OVA-specific CD4 T cells produced both gamma interferon (IFN-gamma) and IL-4 as determined by enzyme-linked immunosorbent assay. Likewise, pronounced OVA-specific CD8 T-cell responses associated with IFN-gamma production were observed. Together, these results suggest that Inv might be an attractive tool in vaccination as it confers both host cell uptake and adjuvant activity by engagement of beta1 integrins of host cells, which leads to CD4 as well as CD8 T-cell responses.

Structure and dynamics of membrane-associated ICP47, a viral inhibitor of the MHC I antigen-processing machinery

To evade the host's immune response, herpes simplex virus employs the immediate early gene product ICP47 (IE12) to suppress antigen presentation to cytotoxic T-lymphocytes by inhibition of the ATP-binding cassette transporter associated with antigen processing (TAP). ICP47 is a membrane-associated protein adopting an alpha-helical conformation. Its active domain was mapped to residues 3-34 and shown to encode all functional properties of the full-length protein. The active domain of ICP47 was reconstituted into oriented phospholipid bilayers and studied by proton-decoupled 15N and 2H solid-state NMR spectroscopy. In phospholipid bilayers, the protein adopts a helix-loop-helix structure, where the average tilt angle of the helices relative to the membrane surface is approximately 15 degrees (+/- 7 degrees ). The alignment of both structured domains exhibits a mosaic spread of approximately 10 degrees . A flexible dynamic loop encompassing residues 17 and 18 separates the two helices. Refinement of the experimental data indicates that helix 1 inserts more deeply into the membrane. These novel insights into the structure of ICP47 represent an important step toward a molecular understanding of the immune evasion mechanism of herpes simplex virus and are instrumental for the design of new therapeutics.

The first N-terminal transmembrane helix of each subunit of the antigenic peptide transporter TAP is essential for independent tapasin binding

The heterodimeric ABC transporter TAP translocates proteasomal degradation products from the cytosol into the lumen of the endoplasmic reticulum, where these peptides are loaded onto MHC class I molecules by a macromolecular peptide-loading complex (PLC) and subsequently shuttled to the cell surface for inspection by cytotoxic T lymphocytes. Tapasin recruits, as a central adapter protein, other components of the PLC at the unique N-terminal domains of TAP. We found that the N-terminal domains of human TAP1 and TAP2 can independently bind to tapasin, thus providing two separate loading platforms for PLC assembly. Moreover, tapasin binding is dependent on the first N-terminal transmembrane helix of TAP1 and TAP2, demonstrating that these two helices contribute independently to the recruitment of tapasin and associated factors.

Intracellular peptide transporters in human--compartmentalization of the "peptidome"

In the human genome, the five adenosine triphosphate (ATP)-binding cassette (ABC) half transporters ABCB2 (TAP1), ABCB3 (TAP2), ABCB9 (TAP-like), and in part, also ABCB8 and ABCB10 are closely related with regard to their structural and functional properties. Although targeted to different cellular compartments such as the endoplasmic reticulum (ER), lysosomes, and mitochondria, they are involved in intracellular peptide trafficking across membranes. The transporter associated with antigen processing (TAP1 and TAP2) constitute a key machinery in the major histocompatibility complex (MHC) class I-mediated cellular immune defense against infected or malignantly transformed cells. TAP translocates the cellular "peptidome" derived primarily from cytosolic proteasomal degradation into the ER lumen for presentation by MHC class I molecules. The homodimeric ABCB9 (TAP-like) complex located in lysosomal compartments shares structural and functional similarities to TAP; however, its biological role seems to be different from the MHC I antigen processing. ABCB8 and ABCB10 are targeted to the inner mitochondrial membrane. MDL1, the yeast homologue of ABCB10, is involved in the export of peptides derived from proteolysis of inner-membrane proteins into the intermembrane space. As such peptides are presented as minor histocompatibility antigens on the surface of mammalian cells, a physiological role of ABCB10 in the antigen processing can be accounted.

Molecular chaperones and cancer immunotherapy

As one of the most abundant and evolutionally conserved intracellular proteins, heat shock proteins, also known as stress proteins or molecular chaperones, perform critical functions in maintaining cell homeostasis under physiological as well as stress conditions. Certain chaperones in extracellular milieu are also capable of modulating innate and adaptive immunity due to their ability to chaperone polypeptides and to interact with the host's immune system, particularly professional antigen-presenting cells. The immunomodulating properties of chaperones have been exploited for cancer immunotherapy. Clinical trials using chaperone-based vaccines to treat various malignancies are ongoing.

The C terminus of the nucleoprotein of influenza A virus delivers antigens transduced by Tat to the trans-golgi network and promotes an efficient presentation through HLA class I

Cytotoxic T lymphocytes (CTLs) are the most powerful weapon of the immune system to eliminate cells infected by intracellular parasites or tumors. However, very often, escape mechanisms overcome CTL immune surveillance by impairing the classical HLA class I antigen-processing pathway. Here, we describe a strategy for CTL activation based on the ability of Tat to mediate transcellular delivery of viral proteins encompassing HLA class I-restricted epitopes. In this system, the recombinant protein TAT-NpFlu containing the transduction domain of Tat of human immunodeficiency virus type 1 fused to the amino acid region 301 to 498 of the nucleoprotein of influenza A virus is proven to sensitize different human cells to lysis by HLA-B27-restricted, Flu 383-391-specific CTL lines. The fusion protein is processed very effectively, since a comparable biological effect is obtained with an amount of protein between 1 and 2 orders of magnitude lower than that of the synthetic peptide. Interestingly, while part of TAT-NpFlu undergoes fast and productive cleavage, a large amount of it remains intact for up to 24 h. Confocal microscopy shows that TAT-NpFlu accumulates in the trans-Golgi network (TGN), where it starts to be detectable 1 h after transduction. Using TAT-NpFlu mutants and hybrid constructs, we demonstrate that enrichment in the TGN occurs only when the carboxy-terminal region of NpFlu (amino acids 400 to 498) is present. These data disclose an unconventional route for presentation of epitopes restricted for HLA class I molecules.

Membrane topology of the transporter associated with antigen processing (TAP1) within an assembled functional peptide-loading complex

The transporter associated with antigen processing (TAP) translocates antigenic peptides from the cytosol into the endoplasmic reticular lumen for subsequent loading onto major histocompatibility complex (MHC) class I molecules. These peptide-MHC complexes are inspected at the cell surface by cytotoxic T-lymphocytes. Assembly of the functional peptide transport and loading complex depends on intra- and intermolecular packing of transmembrane helices (TMs). Here, we have examined the membrane topology of human TAP1 within an assembled and functional transport complex by cysteine-scanning mutagenesis. The accessibility of single cysteine residues facing the cytosol or endoplasmic reticular lumen was probed by a minimally invasive approach using membrane-impermeable, thiol-specific fluorophores in semipermeabilized "living" cells. TAP1 contains ten transmembrane segments, which place the N and C termini in the cytosol. The transmembrane domain consists of a translocation core of six TMs, a building block conserved among most ATP-binding cassette transporters, and a unique additional N-terminal domain of four TMs, essential for tapasin binding and assembly of the peptide-loading complex. This study provides a first map of the structural organization of the TAP machinery within the macromolecular MHCI peptide-loading complex.

The Intracellular Antigen Transport Machinery TAP in Adaptive Immunity and Virus Escape Mechanisms

The transporter associated with antigen processing (TAP) is a crucial element of the adaptive immune system, which translocates proteasomal degradation products into the endoplasmic reticulum, for transfer of these peptides on major histocompatibility complex (MHC) I molecules within a macromolecular peptide-loading complex. After loading and intracellular transport to the cell surface, these peptide/MHC complexes are monitored by cytotoxic T-lymphocytes. This review summarizes the structural organization and function of the ABC transporter TAP. Furthermore, we discuss human diseases and viral evasion strategies associated with TAP function.

The ER aminopeptidase, ERAP1, trims precursors to lengths of MHC class I peptides by a "molecular ruler" mechanism

Endoplasmic reticulum aminopeptidase 1 (ERAP1) is an IFN-gamma-induced aminopeptidase in the endoplasmic reticulum that trims longer precursors to the antigenic peptides presented on MHC class I molecules. We recently reported that purified ERAP1 trimmed N-extended precursors but spared peptides of 8-9 residues, the length required for binding to MHC class I molecules. Here, we show another remarkable property of ERAP1: that it strongly prefers substrates 9-16 residues long, the lengths of peptides transported efficiently into the ER by the transporter associated with antigen processing (TAP) transporter. This aminopeptidase rapidly degraded a model 13-mer to a 9-mer and then stopped, even though the substrate and the product had identical N- and C-terminal sequences. No other aminopeptidase, including the closely related ER-aminopeptidase ERAP2, showed a similar length preference. Unlike other aminopeptidases, the activity of ERAP1 depended on the C-terminal residue of the substrate. ERAP1, like most MHC class I molecules, prefers peptides with hydrophobic C termini and shows low affinity for peptides with charged C termini. Thus, ERAP1 is specialized to process precursors transported by TAP to peptides that can serve as MHC class I epitopes. Its "molecular ruler" mechanism involves binding the hydrophobic C terminus of the substrate 9-16 residues away from the active site.

The turnover kinetics of major histocompatibility complex peptides of human cancer cells

Peptides presented by the major histocompatibility complex (MHC) are derived from the degradation of cellular proteins. Thus, the repertoire of these peptides (the MHC peptidome) should correlate better with the cellular protein degradation scheme (the degradome) than with the cellular proteome. To test the validity of this statement and to determine whether the majority of MHC peptides are derived from short lived proteins, from defective ribosome products, or from regular long lived cellular proteins we analyzed in parallel the turnover kinetics of both MHC peptides and cellular proteins in the same cancer cells. The analysis was performed by pulse-chase experiments based on stable isotope labeling in tissue culture followed by capillary chromatography and tandem mass spectrometry. Indeed only a limited correlation was observed between the proteome and the MHC peptidome observed in the same cells. Moreover a detailed analysis of the turnover kinetics of the MHC peptides helped to assign their origin to normal, to short lived or long lived proteins, or to the defective ribosome products. Furthermore the analysis of the MHC peptides turnover kinetics helped to direct attention to abnormalities in the degradation schemes of their source proteins. These observations can be extended to search for cancer-related abnormalities in protein degradation, including those that lead to loss of tumor suppressors and cell cycle regulatory proteins.

Message in a bottle: role of the 70-kDa heat shock protein family in anti-tumor immunity

Extracellular heat shock protein 70 (HSP70) is a potent agent for tumor immunotherapy, which can break tolerance to tumor-associated antigens and cause specific tumor cell killing by cytotoxic CD8+ T cells. The pro-immune effects of extracellular HSP70 are, to some extent, extensions of its molecular properties as an intracellular stress protein. The HSP70 are characterized by massive inducibility after stress, preventing cell death by inhibiting aggregation of cell proteins and directly antagonizing multiple cell death pathways. HSP70 family members possess a domain in the C terminus that chaperones unfolded proteins and peptides, and a N-terminal ATPase domain that controls the opening and closing of the peptide binding domain. These properties not only enable intracellular HSP70 to inhibit tumor apoptosis, but also promote formation of stable complexes with cytoplasmic tumor antigens that can then escape intact from dying cells to interact with antigen-processing cells (APC) and stimulate anti-tumor immunity. HSP70 may be released from tumors undergoing therapy at high local extracellular concentrations, and send a danger signal to the host leading to APC activation. Extracellular HSP70 bind to high-affinity receptors on APC, leading to activation of maturation and re-presentation of the peptide antigen cargo of HSP70 by the APC. The ability of HSP70-peptide complexes (HSP70-PC) to break tolerance and cause tumor regression employs these dual properties as signaling ligand and antigen transporter. HSP70-PC thus coordinately activate innate immune responses and deliver antigens for re-presentation by MHC class I and II molecules on the APC cell surface, leading to specific anti-tumor immunity.

Clinical and immunological aspects of HLA class I deficiency

Human leukocyte antigen (HLA) class I deficiency is a rare disease with remarkable clinical and biological heterogeneity. The spectrum of possible manifestations extends from the complete absence of symptoms to life-threatening disease conditions. It is usually diagnosed when HLA class I serological typing is unsuccessful; flow cytometric studies then reveal a severe reduction in the cell surface expression of HLA class I molecules (90-99% reduction compared to normal cells). In most cases to date, this low expression is due to a homozygous inactivating mutation in one of the two subunits of the transporter associated with antigen processing (TAP), critically involved in the peptide loading of HLA class I molecules. Although asymptomatic cases have been described, TAP deficiencies are usually characterized by chronic bacterial infections of the upper and lower airways, evolving to bronchiectasis, and in half of the cases, also skin ulcers with features of a chronic granulomatous inflammation. Despite the defect in HLA class-I-mediated presentation of viral antigens to cytotoxic T cells, the patients do not suffer from severe viral infections, presumably because of other efficient antiviral defence mechanisms such as antibodies, non-HLA-class-I-restricted cytotoxic effector cells and CD8+ T-cell responses to TAP-independent antigens. Treatment is at present exclusively symptomatic, and should particularly focus on the prevention of bronchiectasis, which requires early detection.

alpha v beta3-dependent cross-presentation of matrix metalloproteinase-2 by melanoma cells gives rise to a new tumor antigen

A large array of antigens that are recognized by tumor-specific T cells has been identified and shown to be generated through various processes. We describe a new mechanism underlying T cell recognition of melanoma cells, which involves the generation of a major histocompatibility complex class I–restricted epitope after tumor-mediated uptake and processing of an extracellular protein—a process referred to as cross-presentation—which is believed to be restricted to immune cells. We show that melanoma cells cross-present, in an αvβ3-dependent manner, an antigen derived from secreted matrix metalloproteinase–2 (MMP-2) to human leukocyte antigen A*0201-restricted T cells. Because MMP-2 activity is critical for melanoma progression, the MMP-2 peptide should be cross-presented by most progressing melanomas and represents a unique antigen for vaccine therapy of these tumors.

Endoplasmic reticulum targeting sequence enhances HBV-specific cytotoxic T lymphocytes induced by a CTL epitope-based DNA vaccine

CD8(+) T cells play a critical role in protective immunity against Hepatitis B Virus (HBV). Epitope-based DNA vaccines expressing HBV-dominant CTL epitopes can be used as candidate vaccines capable of inducing cytotoxic T Lymphocytes (CTL) responses. A plasmid DNA encoding a CTL epitope of HBV core antigen, HBc(18-27), was constructed. Intramuscular immunization of C57BL/6 mice with this DNA vaccine resulted in successful induction of HBV-specific CTL responses. In order to promote transportation of the peptide into endoplasmic reticulum (ER) to bind to MHC class I molecules for optimal class I antigen presentation, an ER targeting sequence (ERTS) was fused with the C(18-27) encoding gene. ERTS fusion significantly enhanced specific CD8(+) T cell responses in terms of CTL cytolysis as well as IFN-gamma secretion. This enhancement was correlated with promoted epitope presentation on target cell surface. We report here an enhanced immunogenicity of an epitope-based DNA vaccine using an ER targeting signal sequence, which has significant implications for future design of therapeutic HBV vaccine.

The design and implementation of the immune epitope database and analysis resource

Epitopes are defined as parts of antigens interacting with receptors of the immune system. Knowledge about their intrinsic structure and how they affect the immune response is required to continue development of techniques that detect, monitor, and fight diseases. Their scientific importance is reflected in the vast amount of epitope-related information gathered, ranging from interactions between epitopes and major histocompatibility complex molecules determined by X-ray crystallography to clinical studies analyzing correlates of protection for epitope based vaccines. Our goal is to provide a central resource capable of capturing this information, allowing users to access and connect realms of knowledge that are currently separated and difficult to access. Here, we portray a new initiative, "The Immune Epitope Database and Analysis Resource." We describe how we plan to capture, structure, and store this information, what query interfaces we will make available to the public, and what additional predictive and analytical tools we will provide.

The innate immune system is activated by stimulation of vaginal epithelial cells with Staphylococcus aureus and toxic shock syndrome toxin 1

Despite knowledge of the effects of toxic shock syndrome (TSS) toxin 1 (TSST-1) on the adaptive immune system, little is known about stimulation of the innate immune system, particularly epithelial cells. This study investigated the interactions of TSS Staphylococcus aureus and TSST-1 with human vaginal epithelial cells (HVECs) and porcine mucosal surfaces. When cocultured with HVECs for 6 h, TSS S. aureus MN8 proliferated, formed aggregates on the HVEC surfaces, and produced exotoxins. Receptor binding studies showed that 35S-TSST-1 bound to 5 x 10(4) receptors per HVEC, with saturation at 15 min. Affymetrix Human GeneChip U133A microarray analysis determined S. aureus MNSM (100 bacteria/HVEC) caused at least twofold up- or down-regulation of 410 HVEC genes by 6 h; these data were also confirmed with S. aureus MN8. TSST-1 (100 microg/ml) caused up- or down-regulation of 2,386 HVEC genes by 6 h. In response to S. aureus, the HVEC genes most up-regulated compared to those in controls were those coding for chemokines or cytokines--MIP-3alpha, 478-fold; GRO-alpha, 26-fold; GRO-beta, 14-fold; and GRO-gamma, 30-fold--suggesting activation of innate immunity. TSST-1 also caused up-regulation of chemokine/cytokine genes. Chemokine/cytokine gene up-regulation was confirmed by enzyme-linked immunosorbent assays measuring the corresponding proteins induced by S. aureus and TSST-1. S. aureus MN8, when incubated with porcine vaginal tissue, increased the flux of 35S-TSST-1 across the mucosal surface. This was accompanied by influx of lymphocytes into the upper layers of the tissue. These data suggest innate immune system activation through epithelial cells, reflected in chemokine/cytokine production and influx of lymphocytes, may cause changes in vaginal mucosa permeability, facilitating TSST-1 penetration.

A role for the protease-sensitive loop region of Shiga-like toxin 1 in the retrotranslocation of its A1 domain from the endoplasmic reticulum lumen

Shiga-like toxin I (Slt-I) is a ribosome-inactivating protein that undergoes retrograde transport to the endoplasmic reticulum to exert its cytotoxic effect on eukaryotic cells. Its catalytically active A(1) domain subsequently migrates from the endoplasmic reticulum (ER) lumen to the cytoplasm. To study this final retrotranslocation event, a suicide assay was developed based on the cytoplasmic expression and ER-targeting of the cytotoxic Slt-I A(1) fragment in Saccharomyces cerevisiae. Expression of the Slt-I A(1) domain (residues 1-251) with and without an ER-targeting sequence was lethal to the host and demonstrated that this domain can efficiently migrate from the ER compartment to the cytosol. Deletion analyses revealed that residues 1-239 represent the minimal A(1) segment displaying full enzymatic activity. This fragment, however, accumulates in the ER lumen when directed to this compartment. The addition of residues 240-251 restores the translocation property of the A(1) chain in yeast. However, single mutations within this region do not significantly alter this function in the context of the 251-residue long A(1) domain or affect the toxicity of the resulting Slt-I variants toward Vero cells in the context of the holotoxin. Since this mechanism of retrotranslocation is common to other protein toxins lacking a peptide motif similar in sequence to residues 240-251, the present results suggest that the ER export mechanism may involve the recognition of a more universal structural element, such as a misfolded or altered peptide domain localized at the C terminus of the A(1) chain (residues 240-251) rather than a unique ER export signal sequence.

Patterns of variability at the major histocompatibility class II alpha locus in Atlantic salmon contrast with those at the class I locus

In order to investigate the mechanisms creating and maintaining variability at the major histocompatibility (MH) class II alpha (DAA) locus we examined patterns of polymorphism in two isolated Atlantic salmon populations which share a common post-glacial origin. As expected from their common origin, but contrary to the observation at the MH class I locus, these populations shared the majority of DAA alleles: out of 17 sequences observed, 11 were common to both populations. Recombination seems to play a more important role in the origin of new alleles at the class II alpha locus than at the class I locus. A greater than expected proportion of sites inferred to be positively selected (potentially peptide binding residues, PBRs) were found to be involved in recombination events, suggesting a mechanism for increasing MH variability through an interaction between recombination and natural selection. Thus it appears that although selection and recombination are important mechanisms for the evolution of both class II alpha and class I loci in the Atlantic salmon, the pattern of variability differs markedly between these classes of MH loci.

A novel approach to identify antigens recognized by CD4 T cells using complement-opsonized bacteria expressing a cDNA library

In patients with hematological malignancies receiving HLA-matched stem cell transplantation, T cells specific for minor histocompatibility antigens play a major role in graft rejection, induction of graft-versus-host disease and beneficial graft-versus-leukemia reactivity. Several human minor histocompatibility antigens recognized by T cells have been identified, but only two are presented by HLA class II molecules. In search of an efficient approach to identify antigenic peptides processed through the HLA class II pathway, we constructed a cDNA library in bacteria that were induced to express proteins. Bacteria were opsonized with complement to enforce receptor-mediated uptake by Epstein-Barr virus immortalized B cells that were subsequently used as antigen-presenting cells. This approach was validated with an HLA class II-restricted antigen encoded by gene DBY. We were able to identify bacteria expressing DBY diluted into a 300-fold excess of bacteria expressing a nonrelevant gene. Screening of a bacterial library using a DBY-specific CD4 T cell clone resulted in the isolation of several DBY cDNAs. We propose this strategy for a rapid identification of HLA class II-restricted antigenic peptides recognized by CD4 T cells.

Recombinant HIV-1 Pr55gag virus-like particles: potent stimulators of innate and acquired immune responses

Several previous reports have clearly demonstrated the strong effectiveness of human immunodeficiency virus (HIV) Gag polyprotein-based virus-like particles (VLP) to stimulate humoral and cellular immune responses in complete absence of additional adjuvants. Yet, the mechanisms underlying the strong immunogenicity of these particulate antigens are still not very clear. However, current reports strongly indicate that these VLP act as "danger signals" to trigger the innate immune system and possess potent adjuvant activity to enhance the immunogenicity of per se only weakly immunogenic peptides and proteins. Here, we review the current understanding of how various particle-associated substances and other impurities may contribute to the observed immune-activating properties of these complex immunogens.

Genetic approaches for the induction of a CD4+ T cell response in cancer immunotherapy

Recently, it has become more and more obvious that not only CD8+ cytotoxic T lymphocytes, but also CD4+ T helper cells are required for the induction of an optimal, long-lasting anti-tumor immune response. CD4+ T helper cells, and in particular IFN-gamma-secreting type 1 T helper cells, have been shown to fulfill a critical function in the mounting of a cancer-specific response. Consequently, targeting antigens into MHC class II molecules would greatly enhance the efficacy of an anti-cancer vaccine. The dissection of the MHC class II presentation pathway has paved the way for rational approaches to achieve this goal: novel systems have been developed to genetically manipulate the MHC class II presentation pathway. First, different genetic approaches have been used for the delivery of known epitopes into the MHC class II processing pathway or directly onto the peptide-binding groove of the MHC molecules. Second, several strategies exist for the targeting of whole tumor antigens, containing both MHC class I and class II restricted epitopes, to the MHC class II processing pathway. We review these data and describe how this knowledge is currently applied in vaccine development.