MHC Class II-restricted Epitopes Research Articles

Tumor cells fail to present MHC-II restricted epitopes derived from oncogenes to CD4+ T cells.

CD4+ T cells play a critical role in anti-tumor immunity via recognition of peptide antigens presented on MHC class II (MHC-II). Although some solid cancers can be induced to express MHC-II, the extent to which this enables direct recognition by tumor-specific CD4+ T cells is unclear. We isolated and characterized T cell antigen receptors (TCRs) from naturally primed CD4+ T cells specific for two oncoproteins, HPV16 E6 and the activating KRASG12V mutation, from head and neck squamous cell carcinoma (HNSCC) and pancreatic ductal adenocarcinoma (PDAC) patients, respectively, and determined their ability to recognize autologous or human leukocyte antigen (HLA)-matched antigen-expressing tumor cells. We find in both cases that the TCRs are capable of recognizing peptide-loaded target cells expressing the relevant MHC-II or B cell antigen-presenting cells (APC) when the antigens are endogenously expressed and directed to the endosomal pathway but fail to recognize tumor cells expressing the source protein even after induction of surface MHC-II expression by IFN- or transduction with CIITA. These results suggest that priming and functional recognition of both a nuclear (E6) and a membrane-associated (KRAS) oncoprotein is predominantly confined to cross-presenting APC rather than via direct recognition of tumor cells induced to express MHC-II.

Expansion of viral variants associated with immune escape and impaired virion secretion in patients with HBV reactivation after resolved infection

HBV reactivation could be induced under immunosuppressive conditions in patients with resolved infection. This study aimed to clarify the viral factors associated with the pathogenesis of HBV reactivation in association with the immunosuppressive status. Whole HBV genome sequences were determined from the sera of 24 patients with HBV reactivation, including 8 cases under strong immunosuppression mediated by hematopoietic stem cell transplantation (HSCT) and 16 cases without HSCT. Ultra-deep sequencing revealed that the prevalence of genotype B and the ratio of non-synonymous to synonymous evolutionary changes in the surface (S) gene were significantly higher in non-HSCT cases than in patients with HSCT. Those non-synonymous variants included immune escape (6/16 cases) and MHC class II-restricted T-cell epitope variants (6/16 cases). Furthermore, reactivated HBV in 11 of 16 (69%) non-HSCT cases possessed substitutions associated with impaired virion secretion, including E2G, L77R, L98V, T118K, and Q129H in the S region, and M1I/V in the PreS2 region. In conclusion, virologic features of reactivated HBV clones differed depending on the intensity of the immunosuppressive condition. HBV reactivation triggered by immunosuppressive conditions, especially those without HSCT, was characterized by the expansion of variants associated with immune escape, MHC class II-restricted T-cell epitope alterations, and/or impaired virion secretion.

IFN-Gamma-Dependent and Independent Mechanisms of CD4⁺ Memory T Cell-Mediated Protection from Listeria Infection.

While CD8+ memory T cells can promote long-lived protection from secondary exposure to intracellular pathogens, less is known regarding the direct protective mechanisms of CD4+ T cells. We utilized a prime/boost model in which mice are initially exposed to an acutely infecting strain of lymphocytic choriomeningitis virus (LCMV), followed by a heterologous rechallenge with Listeria monocytogenes recombinantly expressing the MHC Class II-restricted LCMV epitope, GP61–80 (Lm-gp61). We found that heterologous Lm-gp61 rechallenge resulted in robust activation of CD4+ memory T cells and that they were required for rapid bacterial clearance. We further assessed the relative roles of TNF and IFNγ in the direct anti-bacterial function of CD4+ memory T cells. We found that disruption of TNF resulted in a complete loss of protection mediated by CD4+ memory T cells, whereas disruption of IFNγ signaling to macrophages results in only a partial loss of protection. The protective effect mediated by CD4+ T cells corresponded to the rapid accumulation of pro-inflammatory macrophages in the spleen and an altered inflammatory environment in vivo. Overall, we conclude that protection mediated by CD4+ memory T cells from heterologous Listeria challenge is most directly dependent on TNF, whereas IFNγ only plays a minor role.

Designing a Novel Multi-epitope DNA- Based Vaccine Against Tuberculosis: In Silico Approach

Background: Tuberculosis remains a major global threat. Two billion of the world’s population is latently infected with Mycobacterium tuberculosis and is at the risk of progression to active disease. Bacillus Calmette-Guerin (BCG), as the only licensed vaccine, has prophylaxis strategy, which protects children from disseminated form of tuberculosis. Therefore, postexposure vaccine strategy, which targets individuals with latent tuberculosis infection, is an important strategy to control this disease globally. Objectives: In the present study, we designed a novel postexposure multi-epitope DNA construct based on 3 latency-associated antigens of Rv2029c, Rv2031c, and Rv2627c and microtubule-associated protein light chain 3 (LC3) as a hallmark protein of the autophagy system. Methods: A mouse construct was designed based on predicted MHC class I-and class II-restricted T- cell epitopes that fused together tandemly. MHC class I-and class II-restricted epitopes were linked by AAY and GPGPG motifs, respectively. LC3 directly fused to the MHC class II-restricted epitopes at the C-terminus of the peptide. The varieties of expressed construct features were analyzed by bio- informatics tools. Finally, construct codons were optimized and mRNA structure of optimized construct was analyzed. Results: MHC class I-and class II-predicted epitopes showed a high potential to binding to human HLAs alleles, with global broad-spectrum population coverage. The construct had no allergenicity, and the analysis indicated a desirable antigenicity of the construct. The construct had several posttranslational modifications, no signal peptide, and cytoplasmic localization with high score. Also, mRNA analysis showed low ∆G which demonstrated high stability and efficient translation. Conclusions: The results revealed that the novel multi-epitope DNA construct could be an effective candidate in tuberculosis vaccine development, and it is qualified to investigate its potential to induce CD4 and CD8 T- cell immune response in the experimental animal model.

Thioreductase-Containing Epitopes Inhibit the Development of Type 1 Diabetes in the NOD Mouse Model.

Autoreactive CD4+ T cells recognizing islet-derived antigens play a primary role in type 1 diabetes. Specific suppression of such cells therefore represents a strategic target for the cure of the disease. We have developed a methodology by which CD4+ T cells acquire apoptosis-inducing properties on antigen-presenting cells after cognate recognition of natural sequence epitopes. We describe here that inclusion of a thiol-disulfide oxidoreductase (thioreductase) motif within the flanking residues of a single MHC class II-restricted GAD65 epitope induces GAD65-specific cytolytic CD4+ T cells (cCD4+ T). The latter, obtained either in vitro or by active immunization, acquire an effector memory phenotype and lyse APCs by a Fas–FasL interaction. Furthermore, cCD4+ T cells eliminate by apoptosis activated bystander CD4+ T cells recognizing alternative epitopes processed by the same APC. Active immunization with a GAD65 class II-restricted thioreductase-containing T cell epitope protects mice from diabetes and abrogates insulitis. Passive transfer of in vitro-elicited cCD4+ T cells establishes that such cells are efficient in suppressing autoimmunity. These findings provide strong evidence for a new vaccination strategy to prevent type 1 diabetes.

MHC Class II-Restricted Epitopes Containing an Oxidoreductase Activity Prompt CD4+ T Cells with Apoptosis-Inducing Properties

Abrogating an unwanted immune response toward a specific antigen without compromising the entire immune system is a hoped-for goal in immunotherapy. Instead of manipulating dendritic cells and suppressive regulatory T cells, depleting effector T cells or blocking their co-stimulatory pathways, we describe a method to specifically inhibit the presentation of an antigen eliciting an unwanted immune reaction. Inclusion of an oxidoreductase motif within the flanking residues of MHC class II epitopes polarizes CD4+ T cells to cytolytic cells capable of inducing apoptosis in antigen presenting cells (APCs) displaying cognate peptides through MHC class II molecules. This novel function results from an increased synapse formation between both cells. Moreover, these cells eliminate by apoptosis bystander CD4+ T cells activated at the surface of the APC. We hypothesize that they would thereby block the recruitment of cells of alternative specificity for the same autoantigen or cells specific for another antigen associated with the pathology, providing a system by which response against multiple antigens linked with the same disease can be suppressed. These findings open the way toward a novel form of antigen-specific immunosuppression.

Diverse cellular and organismal functions of the lysosomal thiol reductase GILT.

Gamma-interferon-inducible lysosomal thiol reductase (GILT) is the only enzyme known to catalyze disulfide bond reduction in the endocytic pathway. GILT facilitates the presentation of a subset of epitopes from disulfide bond-containing antigens. Enhanced presentation of MHC class II-restricted epitopes alters central tolerance and modulates CD4+ T cell-mediated autoimmunity. Improved cross-presentation of viral epitopes results in improved cross-priming of viral-specific CD8+ T cells. GILT regulates the cellular redox state. In GILT-/- cells, there is a shift from the reduced to the oxidized form of glutathione, resulting in mitochondrial autophagy, decreased superoxide dismutase 2, and elevated superoxide levels. GILT expression diminishes cellular activation, including decreased phosphorylated ERK1/2, and decreases cellular proliferation. GILT enhances the activity of bacterial hemolysins, such as listeriolysin O, and increases bacterial replication and infection. GILT expression in cancer cells is associated with improved patient survival. These diverse roles of GILT are discussed.

Targeting antigen-loss variant tumors through CD134 plus CD137 dual costimulation-mediated bystander programming (VAC10P.964)

Abstract Tumor-specific cytotoxic CD8 T cell-based therapies can be efficacious in cancer patients. Nevertheless, disease progression often resumes due to outgrowth of antigen-loss variants (ALVs) that lack expression of the targeted MHC class I-restricted epitopes. Co-administration of agonists to the TNF/TNFR costimulatory family members CD134 (OX40) and CD137 (4-1BB) can program antigen-stimulated CD4 T cells to differentiate into cytotoxic Th1 cells, which can directly target MHC II+ tumors and provide classical helper function that facilitates effector differentiation in CD8 T cells responding to a linked epitope. Interestingly, these specific cytotoxic CD4 Th1 cells also imprint antigen-non-responding T cells with a similar ability to express IFN-γ and cytotoxic molecules. Because these bystander-programmed effector T cells are polyclonal, we currently hypothesized that they contain specificities capable of targeting ALVs. In both lymphoma and melanoma models, dual costimulation therapy was markedly enhanced when specific CD4 T cells were engaged to differentiate into cytotoxic Th1 effectors. This augmentation occurred not only when the tumor expressed the MHC class II-restricted epitope recognized by the specific cytotoxic CD4 Th1 cells, but importantly also with tumors modeling ALVs that lack the targeted epitope. Taken together, dual-costimulated tumor-non-specific CD4 T cells provide an alternate form of help that facilitates targeting of ALVs.

Induction of tumor-reactive T helper responses by a posttranslational modified epitope from tumor protein p53.

Posttranslational modifications regulate the function and stability of proteins, and the immune system is able to recognize some of these modifications. Therefore, the presence of posttranslational modifications increases the diversity of potential immune responses to a determinant antigen. The stimulation of tumor-specific CD4(+) helper T lymphocytes (HTLs) is considered important for the production of anti-tumor antibodies by B cells and for the generation and persistence of CD8(+) cytotoxic T lymphocytes, and in some instances, HTLs can directly reduce tumor cell growth. Identification of MHC class II-restricted peptide epitopes from tumor-associated antigens including those generated from posttranslational protein modifications should enable the improvement of peptide-based cancer immunotherapy. We describe here an MHC class II binding peptide from the tumor protein p53, which possesses an acetylated lysine at position 120 (p53110-124/AcK120) that is effective in eliciting CD4(+) T cell responses specific for the acetylated peptide. Most importantly, the acetylated peptide-reactive CD4 HTLs recognized the corresponding naturally processed posttranslational modified epitope presented by either dendritic cells loaded with tumor cell lysates or directly on tumors expressing p53 and the restricting MHC class II molecules. Treatment of tumor cells with a histone deacetylase inhibitor augmented their recognition by the p53110-124/AcK120-reactive CD4(+) T cells. These findings prove that the epitope p53110-124/AcK120 is immunogenic for anti-tumor responses and is likely to be useful for cancer immunotherapy.

Generation Of Anti-Tumor CD4+ T Helper Cells Using Genetically-Engineered Dendritic Cells Expressing Leukemia-Associated Antigens

Adoptive transfer of antigen-specific T cells is a potentially curative strategy for patients with solid tumors and leukemia. Most clinical trials of adoptive T cell therapy have used cytotoxic CD8+ T cells recognizing MHC class I-restricted tumor antigens. Despite overwhelming evidence suggesting the fundamental influence of CD4+ T cells on the immune system, clinical experience with tumor-specific CD4+ Th cells is almost non-existent. Unlike most other tissues, bone marrow-derived cells constitutively express MHC class II and CD4+ T cells play crucial role in mediating the curative GVL effect after allogeneic SCT and donor lymphocyte infusion (DLI). Furthermore, experimental evidences suggest that MHC class II-restricted antigenic targets recognized by CD4+ T cells exist in both solid cancers and in hematological malignancies. Therefore adoptive immunotherapy using CD4+ T cells in the setting of leukemia might be especially relevant.The goal of this study is to establish a simplified non-individualized protocol of generating LAA-reactive CD4+ T cells from patients and normal donors for adoptive immunotherapy directed against common leukemia-associated antigens (LAA) expressed in acute myeloid leukemias (AML) and myelodysplastic syndrome (MDS). We isolated naïve and memory CD4+ T cells from 3 normal donors and stimulated with twice at weekly interval with autologous monocytes pulsed with libraries of overlapping 15-amino acid length peptides (pepmixes) derived from WT-1, MAGE A3 and A4, PRAME and SSX2 antigens. At the end of the experiment CD4+ T cells were evaluated for reactivity against each LAA by analyzing their ability to specifically release cytokines (IL-2, TNF-α, and IFNγ) using flow cytometry. LAA-specific cells were found in either naïve or memory-derived CD4+ T cells upon stimulation with relevant pepmixes in all donors tested. However specific cytokine production could not be demonstrated when the same T cells were exposed to LAA-transduced autologous targets (LCL and T cells), raising the possibility that the majority of pepmix-reactive cells recognized epitopes that were not naturally processed. Therefore, as an alternative strategy to induce LAA-specific cells capable of targeting only therapeutically-relevant epitopes, we used autologous dendritic cells (DCs) transduced with a lentiviral vector encoding MAGE A3 antigen. Autologous CD4+ T cells were stimulated with MAGE A3 or mock-transduced DCs at an interval of 7-10 days and tested for their antigen-specific cytokine secretion. At the end of the culture we observed that Th cells expanded in presence of MAGE A3-expressing DCs and contained a significant number of cells possessing specific reactive against MAGE A3 pepmix (Figure), but not to unrelated antigenic targets, suggesting induction of LAA-reactivity against naturally-processed MAGE A3 epitopes. [Display omitted] In summary, we demonstrate the feasibility of generating specific anti-tumor CD4+ T cells using autologous DCs engineered to express a full-length tumor antigen. This approach allows for selective expansion of polyclonal Th cells recognizing only naturally processed MHC class II-restricted epitopes. Therefore, this strategy circumvents the limitation inherent to usage of overlapping peptide libraries that might induce the expansion of high-avidity T cells specific to epitopes that are irrelevant to in vivo recognition of tumor targets. Furthermore, this approach does not rely on a particular pre-defined MHC class II restriction element, thus it is applicable to majority of donors or patients irrespective of their MHC haplotype. Disclosures:No relevant conflicts of interest to declare.

Sculpting MHC class II–restricted self and non‐self peptidome by the class I Ag‐processing machinery and its impact on Th‐cell responses

It is generally assumed that the MHC class I antigen (Ag)-processing (CAP) machinery - which supplies peptides for presentation by class I molecules - plays no role in class II-restricted presentation of cytoplasmic Ags. In striking contrast to this assumption, we previously reported that proteasome inhibition, TAP deficiency or ERAAP deficiency led to dramatically altered T helper (Th)-cell responses to allograft (HY) and microbial (Listeria monocytogenes) Ags. Herein, we tested whether altered Ag processing and presentation, altered CD4(+) T-cell repertoire, or both underlay the above finding. We found that TAP deficiency and ERAAP deficiency dramatically altered the quality of class II-associated self peptides suggesting that the CAP machinery impacts class II-restricted Ag processing and presentation. Consistent with altered self peptidomes, the CD4(+) T-cell receptor repertoire of mice deficient in the CAP machinery substantially differed from that of WT animals resulting in altered CD4(+) T-cell Ag recognition patterns. These data suggest that TAP and ERAAP sculpt the class II-restricted peptidome, impacting the CD4(+) T-cell repertoire, and ultimately altering Th-cell responses. Together with our previous findings, these data suggest multiple CAP machinery components sequester or degrade MHC class II-restricted epitopes that would otherwise be capable of eliciting functional Th-cell responses.

Epitope diversification driven by non-tumor epitope-specific Th1 and Th17 mediates potent antitumor reactivity

MHC class I-restricted peptide-based vaccination therapies have been conducted to treat cancer patients, because CD8+ CTL can efficiently induce apoptosis of tumor cells in an MHC class I-restricted epitope-specific manner. Interestingly, clinical responders are known to demonstrate reactivity to epitopes other than those used for vaccination; however, the mechanism underlying how antitumor T cells with diverse specificity are induced is unclear. In this study, we demonstrated that dendritic cells (DCs) that engulfed apoptotic tumor cells in the presence of non-tumor MHC class II-restricted epitope peptides, OVA323–339, efficiently presented tumor-associated antigens upon effector-dominant CD4+ T cell balance against regulatory T cells (Treg) for the OVA323–339 epitope. Th1 and Th17 induced tumor-associated antigens presentation of DC, while Th2 ameliorated tumor-antigen presentation for CD8+ T cells. Blocking experiments with anti-IL-23p19 antibody and anti-IL-23 receptor indicated that an autocrine mechanism of IL-23 likely mediated the diverted tumor-associated antigens presentation of DC. Tumor-associated antigens presentation of DC induced by OVA323–339 epitope-specific CD4+ T cells resulted in facilitated antitumor immunity in both priming and effector phase in vivo. Notably, this immunotherapy did not require pretreatment to reduce Treg induced by tumor. This strategy may have clinical implications for designing effective antitumor immunotherapies.

Comparison of antibodies and carbohydrates to target vaccines to human dendritic cells via DC-SIGN

Vaccine efficacy is improved upon specific delivery to professional antigen (Ag) presenting cells, such as dendritic cells (DCs). Antigenicity and adjuvanticity of vaccine components can be enhanced by encapsulation within nanoparticle (NP) vaccine carriers that are targeted to the human DC-specific C-type lectin receptor DC-SIGN. Here we used two strategies to target vaccines components to DC-SIGN: 1) carbohydrates as natural receptor ligands and 2) receptor-specific antibodies (Abs). To determine the optimal targeting strategy, we coated NP vaccines harboring MHC class I or II-restricted Ags and the TLR ligands (TLRLs) poly I:C and resiquimod with either the DC-SIGN ligands Lewis-X (Lex), mannosylated lipoarabinomannan (ManLAM), glycosylated HIV protein gp120, or three distinct DC-SIGN Abs. Although, because of their lower MW, surface coating of NP vaccines with carbohydrates resulted in a higher number of surface molecules per NP than coating with Abs, NP vaccines carrying Abs were more effectively bound and internalized by human DCs than carriers harboring Lex, ManLAM or gp120. Furthermore, NP vaccines harboring TLRLs triggered significant induction of DC maturation markers when compared to those without TLRLs, irrespective of the targeting moiety. Ab- and gp120-mediated targeting induced equally high levels of proinflammatory cytokines and increased presentation of the MHC class I-restricted epitope. By contrast, presentation of the MHC class II-restricted epitope was more efficient upon Ab-mediated targeting than when using gp120, Lex or ManLAM. From these findings we conclude that receptor-specific Abs are more effective than carbohydrates for DC-targeted vaccination strategies.

Cutting Edge: Activation of Virus-Specific CD4 T Cells throughout γ-Herpesvirus Latency

CD4 T cells are essential for immune control of γ-herpesvirus latency. We previously identified a murine MHC class II-restricted epitope in γ-herpesvirus-68 gp150 (gp150(67-83)I-A(b)) that elicits CD4 T cells that are maintained throughout long-term infection. However, it is unknown whether naive cells can be recruited into the antiviral CD4 T cell pool during latency. In this study, we generate a mouse transgenic for a gp150-specific TCR and show epitope-specific activation of transgenic CD4 T cells during acute and latent infections. Furthermore, although only dendritic cells can stimulate virus-specific CD8 T cells during latency, we show that both dendritic cells and B cells stimulate transgenic CD4 T cells. These studies demonstrate that naive CD4 T cells specific for a viral glycoprotein can be stimulated throughout infection, even during quiescent latency, suggesting that CD4 T cell memory is maintained in part by the continual recruitment of naive cells.

Protection against H1N1 influenza challenge by a DNA vaccine expressing H3/H1 subtype hemagglutinin combined with MHC class II-restricted epitopes

BackgroundMultiple subtypes of avian influenza viruses have crossed the species barrier to infect humans and have the potential to cause a pandemic. Therefore, new influenza vaccines to prevent the co-existence of multiple subtypes within a host and cross-species transmission of influenza are urgently needed.MethodsHere we report a multi-epitope DNA vaccine targeted towards multiple subtypes of the influenza virus. The protective hemagglutinin (HA) antigens from H5/H7/H9 subtypes were screened for MHC II class-restricted epitopes overlapping with predicted B cell epitopes. We then constructed a DNA plasmid vaccine, pV-H3-EHA-H1, based on HA antigens from human influenza H3/H1 subtypes combined with the H5/H7/H9 subtype Th/B epitope box.ResultsEpitope-specific IFN-γ ELISpot responses were significantly higher in the multi-epitope DNA group than in other vaccine and control groups (P < 0.05). The multi-epitope group significantly enhanced Th2 cell responses as determined by cytokine assays. The survival rate of mice given the multi-epitope vaccine was the highest among the vaccine groups, but it was not significantly different compared to those given single antigen expressing pV-H1HA1 vaccine and dual antigen expressing pV-H3-H1 vaccine (P > 0.05). No measurable virus titers were detected in the lungs of the multi-epitope immunized group. The unique multi-epitope DNA vaccine enhanced virus-specific antibody and cellular immunity as well as conferred complete protection against lethal challenge with A/New Caledonia/20/99 (H1N1) influenza strain in mice.ConclusionsThis approach may be a promising strategy for developing a universal influenza vaccine to prevent multiple subtypes of influenza virus and to induce long-term protective immune against cross-species transmission.

Cellular Requirements for Diabetes Induction in DO11.10xRIPmOVA Mice

Type 1 diabetes (T1D) results from the immune-mediated destruction of the insulin-producing β-islet cells in the pancreas. The genetic and environmental mechanisms promoting the development of this disease remain poorly understood. We have explored the cellular requirements for T1D development in DO11.10xRIPmOVA (DORmO) mice, which carry a TCR transgene specific for an MHC class II-restricted epitope from OVA and express membrane-bound OVA in the pancreas under the control of the rat insulin promoter. We found that DORmO.RAG2(-/-) mice do not develop insulitis and are completely protected from diabetes, demonstrating that endogenous lymphocyte receptor rearrangement is required for disease development. Diabetes in DORmO mice is preceded by the development of OVA-specific autoantibodies and is delayed in B cell-deficient DORmO.JhD(-/-) mice, demonstrating that B cells contribute to disease progression. In addition, transfer of CD8(+) T cells from diabetic animals into DORmO.RAG2(-/-) mice promoted insulitis by OVA-specific CD4(+) T cells. Finally, although diabetes develops in DORmO mice in the presence of a significant population of Foxp3(+) OVA-specific regulatory T cells, boosting regulatory T cell numbers by injecting IL-2 immune complexes dampens autoantibody production and prevents development of insulitis and overt diabetes. These results help define the events leading to diabetes in DORmO mice and provide new insights into the cellular interactions required for disease development in an Ag-specific model of T1D.

Long Peptide Vaccination Can Lead to Lethality through CD4+ T Cell-Mediated Cytokine Storm

The optimization of anticancer therapeutic vaccines can lead to better efficacy but also to stronger adverse effects. In a mouse model of antitumor vaccination using a long peptide (LP), which included MHC class I- and II-restricted male (H-Y) epitopes, we observed unexpected mortality. Mice with an increased frequency of anti-H-Y CD4 T cells were primed with LP+CpG and boosted 10 d later. Within hours of boost, they displayed shock-like signs with high mortality. Serum cytokine levels were high. TNF-alpha secreted by the CD4 T cells was identified as the key effector molecule. Priming with a short peptide (SP), which included the MHC class II-restricted epitope, was a more efficient primer than LP, but did not lead to mortality when used as boost. The high mortality induced by LP compared with SP was probably related to its specific ability to be presented by B cells. Finally, targeting the LP sequence to dendritic cells allowed tumor protection without side effects. Our data: 1) confirm that the immune system can be very dangerous; 2) caution against the use of systemic activation of high-frequency Ag-specific T cells as induced by high doses of LP; and 3) underline the benefit of targeting Ag to dendritic cells.

Antigen-specific tolerance to the fetus in murine pregnancy (89.9)

Abstract Tolerance of the maternal immune system is believed to be important for successful pregnancy as the fetus is semi-allogeneic. We examined maternal T cell tolerance in mice using a system in which a model antigen, ovalbumin (OVA), is expressed exclusively in the fetus. This is achieved by breeding females that lack OVA to male mice that transgenically express membrane-bound OVA under the control of the β-actin promoter. By employing T cell receptor (TCR) transgenic mice specific for a MHC class II-restricted epitope of OVA (OT-II) as mothers, we investigated the fate of fetus-specific CD4+ T cells during gestation. OVA-specific CD4+ T cells displayed an activated phenotype in the spleen and lymph nodes of OVA-bred OT-II mice, consistent with their encounter of fetal antigen in peripheral lymphoid tissues. A small percentage of OVA-specific CD4+ T cells were deleted in the periphery of OVA-bred OT-II mice, with evidence of TCR downregulation in a portion of the remaining T cells. Interestingly, deletion and TCR downregulation were also observed in the thymus of OVA-bred OT-II mice, suggesting that fetal antigen may affect central tolerance. These preliminary data indicate that fetal antigen-specific maternal CD4+ T cells are tolerized during gestation. This project is supported by NIH grants HD045611 and HD049480, and a Lied Endowed Basic Science Pilot grant. A. Perchellet is supported by NIH training grant T32HD007455.

MHC class II presentation of gp100 epitopes in melanoma cells requires the function of conventional endosomes and is influenced by melanosomes.

Many human solid tumors express MHC class II (MHC-II) molecules, and proteins normally localized to melanosomes give rise to MHC-II-restricted epitopes in melanoma. However, the pathways by which this response occurs have not been defined. We analyzed the processing of one such epitope, gp100(44-59), derived from gp100/Pmel17. In melanomas that have down-regulated components of the melanosomal pathway, but constitutively express HLA-DR*0401, the majority of gp100 is sorted to LAMP-1(high)/MHC-II(+) late endosomes. Using mutant gp100 molecules with altered intracellular trafficking, we demonstrate that endosomal localization is necessary for gp100(44-59) presentation. By depletion of the AP-2 adaptor protein using small interfering RNA, we demonstrate that gp100 protein internalized from the plasma membrane to such endosomes is a major source for gp100(44-59) epitope production. The gp100 trapped in early endosomes gives rise to epitopes that are indistinguishable from those produced in late endosomes but their production is less sensitive to inhibition of lysosomal proteases. In melanomas containing melanosomes, gp100 is underrepresented in late endosomes, and accumulates in stage II melanosomes devoid of MHC-II molecules. The gp100(44-59) presentation is dramatically reduced, and processing occurs entirely in early endosomes or stage I melanosomes. This occurrence suggests that melanosomes are inefficient Ag-processing compartments. Thus, melanoma de-differentiation may be accompanied by increased presentation of MHC-II restricted epitopes from gp100 and other melanosome-localized proteins, leading to enhanced immune recognition.

Identification of a novel NY‐ESO‐1 promiscuous helper epitope presented by multiple MHC class II molecules found frequently in the Japanese population

NY-ESO-1 is a cancer-testis antigen that elicits strong cellular and humoral immune responses against NY-ESO-1-expressing tumors. Although CD4(+) T cells play a critical role in inducing antitumor immunity, little is known about MHC class II-restricted helper epitopes of the NY-ESO-1 antigen compared with MHC class I-restricted epitopes. Here, we searched for new NY-ESO-1 helper epitopes presented by MHC class II molecules, especially those found frequently in the Japanese population. We established five NY-ESO-1-specific helper T-cell lines from healthy Japanese donors using NY-ESO-1 recombinant protein and peptide. Using MHC class II-specific antibodies and a panel of Epstein-Barr virus-transformed B-cell lines, it was demonstrated that four out of the five T-cell lines recognized a region within NY-ESO-1(119-143) in the context of HLA-DRB1*0802, DRB1*0901, DRB1*1502 or DRB1*0405/*0410. In addition, using a set of overlapping 15-mer synthetic peptides, we found that NY-ESO-1(122-138) was a promiscuous region that bound to four distinct HLA-DR molecules found in the Japanese population. These findings expand the usefulness of NY-ESO-1 as a tool for tumor vaccine therapy in eliciting NY-ESO-1-specific helper T-cell responses, especially in Japanese cancer patients.