Class II-restricted Responses Research Articles

Proteomics Analysis Reveals That Structural Proteins of the Virion Core and Involved in Gene Expression Are the Main Source for HLA Class II Ligands in Vaccinia Virus-Infected Cells.

Protective cellular and humoral immune responses require previous recognition of viral antigenic peptides complexed with human leukocyte antigen (HLA) class II molecules on the surface of the antigen presenting cells. The HLA class II-restricted immune response is important for the control and the clearance of poxvirus infection including vaccinia virus (VACV), the vaccine used in the worldwide eradication of smallpox. In this study, a mass spectrometry analysis was used to identify VACV ligands bound to HLA-DR and -DP class II molecules present on the surface of VACV-infected cells. Twenty-six naturally processed viral ligands among the tens of thousands of cell peptides bound to HLA class II proteins were identified. These viral ligands arose from 19 parental VACV proteins: A4, A5, A18, A35, A38, B5, B13, D1, D5, D7, D12, D13, E3, E8, H5, I2, I3, J2, and K2. The majority of these VACV proteins yielded one HLA ligand and were generated mainly, but not exclusively, by the classical HLA class II antigen processing pathway. Medium-sized and abundant proteins from the virion core and/or involved in the viral gene expression were the major source of VACV ligands bound to HLA-DR and -DP class II molecules. These findings will help to understand the effectiveness of current poxvirus-based vaccines and will be important in the design of new ones.

Antibody-Independent Function of Human B Cells Contributes to Antifungal T Cell Responses.

Fungal infections (e.g., Candida albicans) can manifest as serious medical illnesses, especially in the elderly and immune-compromised hosts. T cells are important for Candida control. Whether and how B cells are involved in antifungal immunity has been less clear. Although patients with agammaglobulinemia exhibit normal antifungal immunity, increased fungal infections are reported following B cell-depleting therapy, together pointing to Ab-independent roles of B cells in controlling such infections. To test how human B cells may contribute to fungal-associated human T cell responses, we developed a novel Ag-specific human T cell/B cell in vitro coculture system and found that human B cells could induce C. albicans-associated, MHC class II-restricted responses of naive T cells. Activated B cells significantly enhanced C. albicans-mediated Th1 and Th17 T cell responses, which were both strongly induced by CD80/CD86 costimulation. IL-6+GM-CSF+ B cells were the major responding B cell subpopulation to C. albicans and provided efficient costimulatory signals to the T cells. In vivo B cell depletion in humans resulted in reduced C. albicans-associated T responses. Of note, the decreased Th17, but not Th1, responses could be reversed by soluble factors from B cells prior to depletion, in an IL-6-dependent manner. Taken together, our results implicate an Ab-independent cytokine-defined B cell role in human antifungal T cell responses. These findings may be particularly relevant given the prospects of chronic B cell depletion therapy use in lymphoma and autoimmune disease, as patients age and are exposed to serial combination therapies.

Therapeutic Vaccination against A Modified Minimal Survivin Epitope Induces Functional CD4 T Cells That Recognize Survivin‐Expressing Cells

During the last decade, cancer vaccination has received a great deal of attention; however, documentation of the clinical effect remains limited. The introduction of immune checkpoint inhibitors as a novel therapeutic modality 1–4 could by combination increase the ability of a peptide vaccination to induce clinical responses. Survivin is an anti-apoptotic protein, first discovered in 1997. 5 It is overexpressed in a wide array of cancers, including malignant melanoma (MM), 5,6 and expression is correlated with disease progression and a poor prognosis in e.g. colon cancer and neuroblastoma. 7,8 Survivin is an excellent target for cancer vaccines due to its universal expression in cancer; in addition, down-regulation will impair the tumor cell's ability to proliferate and expand. This article is protected by copyright. All rights reserved.

Protection of Piglets by a Haemophilus parasuis Ghost Vaccine against Homologous Challenge

Commercial bacterins for Glässer's disease are widely used for the prevention of this disease caused by Haemophilus parasuis; however, the protective efficacy varies depending on the strain and serovar. Bacterial ghosts (BGs) are empty bacterial envelopes that, unlike classic bacterins, suffer no denaturing steps during their production. These properties may lead to superior protection. In this study, a BG vaccine generated from the Haemophilus parasuis serovar 5 reference strain Nagasaki was prepared and used to inoculate piglets. The efficacy of the BG vaccine was evaluated by clinical, bacteriological, serological, and postmortem examinations. Inactivated bacterin (IB) and a placebo control (PC) were compared with the BG vaccine in this study. The results showed that the piglets inoculated with the BG vaccine developed higher antibody activity and higher gamma interferon and interleukin 4 levels than those vaccinated with IB or those in the PC group after primary and secondary exposure to the antigens and challenge. CD4(+) T lymphocyte levels were observed to increase following secondary immunization more in the BG-vaccinated group than in the IB (P < 0.05) and PC (P < 0.05) groups. CD8(+) T lymphocyte levels increased dramatically in all three groups after challenge, and the differences between groups were all significant (P < 0.05). There were fewer tissue lesions and lower bacterial loads in the tissue homogenates in the BG group after challenge. The results suggest that higher CD4(+) T lymphocyte levels and both CD4(+) major histocompatibility complex class II-restricted Th1-type and Th2-type immune responses in the BG group are relevant for protection.

Purified CD4 T Lymphocyte Infusion Can Result in Graft-Versus-Leukemia Reactivity without Gvhd by Recognition of Broadly Expressed Minor Histocompatibility Antigens in HLA Class-II

AbstractAbstract 4116Donor lymphocyte infusion (DLI) after allogeneic stem cell transplantation (alloSCT) can mediate curative Graft-versus-Leukemia (GVL) reactivity although frequently at the cost of Graft-versus-Host Disease (GVHD). We previously illustrated that donor CD8 T lymphocytes recognizing HLA class-I restricted minor histocompatibility antigens (MiHAs) that are broadly expressed on tissues of the recipient cause GVL associated with GVHD, whereas T lymphocytes recognizing MiHAs selectively expressed on hematopoietic cells, including the malignant cells, can selectively mediate GVL without GVHD. Since in contrast to HLA class-I, expression of HLA class-II molecules is predominantly restricted to hematopoietic cells, we hypothesized that infused purified donor CD4 T lymphocytes may selectively recognize and eliminate hematopoietic cells from the recipient resulting in GVL without GVHD.We treated a patient with CML in blastic phase in remission after intensive chemotherapy with T cell depleted alloSCT from his HLA-identical sibling donor after myelo-ablative conditioning. After donor engraftment, recipient hematopoiesis reoccurred within 3 months to 90% of CD8 T lymphocytes, 13% of CD4 T lymphocytes and 5% of myelopoiesis. As part of a clinical trial, the patient was treated with 106/kg positively selected purified donor derived CD4 T lymphocytes resulting within 19 weeks in conversion into full donor chimerism in all hematopoietic cell lineages in the total absence of GVHD.To characterize the nature of this hematopoiesis restricted immune response, in vivo activated HLA-DR positive CD4 and CD8 T lymphocytes were clonally isolated by flowcytometric cell sorting at the time of the clinical response, expanded and tested for alloreactivity on patient and donor derived hematopoietic target cells using IFNγ ELISA. From the 204 expanding CD4 T lymphocyte clones 31 clones were alloreactive, whereas none of the 66 expanding CD8 T lymphocyte clones showed alloreactivity.To further identify the fine specificity of this hematopoiesis directed HLA class-II restricted immune response, target molecules of several T lymphocyte clones were molecularly characterized using whole genome association scanning. We first performed blocking studies with HLA class-II restricted monoclonal antibodies and identified HLA-DR to be the restriction molecule. Next, a large panel of third party EBV-LCLs was retrovirally transduced with each of the possible restriction molecules being HLA-DRB1*11:01, HLA-DRB1*15:01, HLA-DRB3*02:02 and HLA-DRB5*01:01. By comparing the recognition pattern of the transduced EBV-LCLs with the 1.1 million single nucleotide polymorphisms in each EBV-LCL, we identified 3 novel MiHAs. Synthesis and analysis of the patient and donor derived allelic peptide variants further confirmed the specificity of the MiHAs as LB-KHNYN-1K in the context of HLA-DRB5*01:01, LB-CTSB-1G in HLA-DRB1*11:01 and LB-ZDHHC13-1K in HLA-DRB1*15:01. Gene expression profiles of KHNYN (located on chromosome 14), CTSB (chromosome 8) and ZDHHC13 (chromosome 11) illustrated that the genes encoding these MiHAs were not only transcribed in hematopoietic cells, but also in other tissues including GVHD target tissues. These results further illustrated that the hematopoietic specificity of the CD4 T lymphocyte response was mainly defined by the restricted expression of the HLA-DR molecules on hematopoietic cells.We conclude that purified CD4 DLI can lead to GVL without GVHD by a selective HLA class-II restricted immune response against patient hematopoiesis. By molecular characterization of 3 novel HLA-DR restricted MiHAs we illustrated that the relative specificity of HLA class-II molecules on hematopoietic cells under non inflammatory conditions was probably responsible for this effect. Since HLA class-II is predominantly expressed on hematopoietic cells only, infusion of donor CD4 T lymphocytes under non inflammatory conditions after HLA identical alloSCT can result in efficient induction of GVL without the toxicity of GVHD. Disclosures:No relevant conflicts of interest to declare.

Natural CD4+ T-Cell Responses against Indoleamine 2,3-Dioxygenase

BackgroundThe enzyme indoleamine 2,3-dioxygenase (IDO) contributes to immune tolerance in a variety of settings. In cancer IDO is expressed within the tumor itself as well as in antigen-presenting cells in tumor-draining lymph nodes, where it endorses the establishment of peripheral immune tolerance to tumor antigens. Recently, we described cytotoxic CD8+ T-cell reactivity towards IDO-derived peptides.Methods and FindingsIn the present study, we show that CD4+ helper T cells additionally spontaneously recognize IDO. Hence, we scrutinized the vicinity of the previously described HLA-A*0201-restricted IDO-epitope for CD4+ T-cell epitopes. We demonstrated the presence of naturally occurring IDO-specific CD4+ T cells in cancer patients and to a lesser extent in healthy donors by cytokine release ELISPOT. IDO-reactive CD4+ T cells released IFN-γ, TNF-α, as well as IL-17. We confirm HLA class II-restriction by the addition of HLA class II specific blocking antibodies. In addition, we detected a trend between class I- and class II-restricted IDO responses and detected an association between IDO-specific CD4+ T cells and CD8+ CMV-responses. Finally, we could detect IL-10 releasing IDO-reactive CD4+ T cells.ConclusionIDO is spontaneously recognized by HLA class II-restricted, CD4+ T cells in cancer patients and in healthy individuals. IDO-specific T cells may participate in immune-regulatory networks where the activation of pro-inflammatory IDO-specific CD4+ responses may well overcome or delay the immune suppressive actions of the IDO-protein, which are otherwise a consequence of the early expression of IDO in maturing antigen presenting cells. In contrast, IDO-specific regulatory T cells may enhance IDO-mediated immune suppression.

Functional Macroautophagy Induction by Influenza A Virus without a Contribution to Major Histocompatibility Complex Class II-Restricted Presentation

Major histocompatibility complex (MHC) class II-presented peptides can be derived from both exogenous (extracellular) and endogenous (biosynthesized) sources of antigen. Although several endogenous antigen-processing pathways have been reported, little is known about their relative contributions to global CD4(+) T cell responses against complex antigens. Using influenza virus for this purpose, we assessed the role of macroautophagy, a process in which cytosolic proteins are delivered to the lysosome by de novo vesicle formation and membrane fusion. Influenza infection triggered productive macroautophagy, and autophagy-dependent presentation was readily observed with model antigens that naturally traffic to the autophagosome. Furthermore, treatments that enhance or inhibit macroautophagy modulated the level of presentation from these model antigens. However, validated enzyme-linked immunospot (ELISpot) assays of influenza-specific CD4(+) T cells from infected mice using a variety of antigen-presenting cells, including primary dendritic cells, revealed no detectable macroautophagy-dependent component. In contrast, the contribution of proteasome-dependent endogenous antigen processing to the global influenza CD4(+) response was readily appreciated. The contribution of macroautophagy to the MHC class II-restricted response may vary depending upon the pathogen.

Contribution of autophagy to MHC-II mediated presentation of viral antigens (130.9)

Abstract Conventionally, major histocompatibility complex (MHC) class II molecules present peptides derived from exogenous sources of antigen. However, it is now accepted that endogenous antigen can also be processed for MHC class II peptide presentation. Several pathways of endogenous presentation have been reported, including macroautophagy. Here we used siRNA mediated knockdown to determine whether autophagy plays a role in the MHC class II-restricted immune responses to two different viral infections. Reduction of Atg7, a key ubiquitin- like enzyme catalyzing autophagosome expansion, did not significantly alter global MHC class II mediated presentation of epitopes derived from influenza or vaccinia viral infections. As a positive control, the autophagy protein LC3 was fused to the influenza specific MHC class II restricted epitope “Site-1”. In this context, presentation of the epitope was reduced by both chemical and siRNA mediated inhibition of autophagy. Taken together the results indicate that although individual epitopes can be presented on MHC class II via autophagy, the contribution of this pathway to the total MHC class II restricted response to viral infection may be limited.

Patients with B cell chronic lymphocytic leukaemia have an expanded population of CD4+ perforin expressing T cells enriched for human cytomegalovirus specificity and an effector‐memory phenotype

We have previously shown an expansion of cytotoxic antigen-experienced CD4(+)T cells (CTLs) that express perforin (PF) in the peripheral blood of patients with B cell chronic lymphocytic leukaemia (B-CLL). Increased frequencies of CD4(+)CTLs have since been attributed to chronic viral infections, particularly, human cytomegalovirus (HCMV). The present study examined the involvement of CD4(+)CTLs in responses to HCMV in B-CLL, and characterized their differentiation. We studied 36 HCMV seropositive (SP) and seronegative B-CLL patients and 20 healthy age-matched individuals. The HCMV reactivity of CD4(+)PF(+) and CD4(+)PF(-) cells was determined by interferon-gamma expression, and expression of CD45RA and CCR7 was assessed by flow cytometry. Fluorescence in-situ hybridization was used to measure relative telomere lengths. CD4(+)PF(+)T cell expansion in B-CLL patients and controls was strongly associated with HCMV seropositivity. CD4(+)PF(+) compared to CD4(+)PF(-) cells from SP B-CLL patients elicited major histocompatibility complex (MHC) class II-restricted responses to HCMV. CD4(+)PF(+)T cells from patients and controls were enriched with highly differentiated T-effector/memory (CCR7(-)) and revertant (CCR7(-)CD45RA(+)) phenotype. CD4(+)PF(+)T cells from B-CLL patients had shorter telomeres than CD4(+)PF(-)T cells, indicating an extensive replicative history. We conclude that persistent exposure to HCMV antigens in SP B-CLL patients leads to an expansion of the circulating MHC class II-restricted CD4(+)PF(+)T cell population with effector/memory phenotype.

Overlapping synthetic peptides encoding TPD52 as breast cancer vaccine in mice: Prolonged survival

Peptide-based vaccines, one of several anti-tumor immunization strategies currently under investigation, can elicit both MHC Class I-restricted (CD8 +) and Class II-restricted (CD4 +) responses. However, the need to identify specific T-cell epitopes in the context of MHC alleles has hampered the application of this approach. We have tested overlapping synthetic peptides (OSP) representing a tumor antigen as a novel approach that bypasses the need for epitope mapping, since OSP contain all possible epitopes for both CD8 + and CD4 + T cells. Here we report that vaccination of inbred and outbred mice with OSP representing tumor protein D52 (TPD52-OSP), a potential tumor antigen target for immunotherapy against breast, prostate, and ovarian cancer, was safe and induced specific CD8 + and CD4 + T-cell responses, as demonstrated by development of specific cytotoxic T cell (CTL) activity, proliferative responses, interferon (IFN)-γ production and CD107a/b expression in all mice tested. In addition, TPD52-OSP-vaccinated BALB/c mice were challenged with TS/A breast carcinoma cells expressing endogenous TPD52; significant survival benefits were noted in vaccine recipients compared to unvaccinated controls ( p < 0.001). Our proof-of-concept data demonstrate the safety and efficacy of peptide library-based cancer vaccines that obviates the need to identify epitopes or MHC backgrounds of the vaccinees. We show that an OSP vaccination approach can assist in the disruption of self-tolerance and conclude that our approach may hold promise for immunoprevention of early-stage cancers in a general population.

Human TCR-Binding Affinity is Governed by MHC Class Restriction

T cell recognition is initiated by the binding of TCRs to peptide-MHCs (pMHCs), the interaction being characterized by weak affinity and fast kinetics. Previously, only 16 natural TCR/pMHC interactions have been measured by surface plasmon resonance (SPR). Of these, 5 are murine class I, 5 are murine class II, and 6 are human class I-restricted responses. Therefore, a significant gap exists in our understanding of human TCR/pMHC binding due to the limited SPR data currently available for human class I responses and the absence of SPR data for human class II-restricted responses. We have produced a panel of soluble TCR molecules originating from human T cells that respond to naturally occurring disease epitopes and their cognate pMHCs. In this study, we compare the binding affinity and kinetics of eight class-I-specific TCRs (TCR-Is) to pMHC-I with six class-II-specific TCRs (TCR-IIs) to pMHC-II using SPR. Overall, there is a substantial difference in the TCR-binding equilibrium constants for pMHC-I and pMHC-II, which arises from significantly faster on-rates for TCRs binding to pMHC-I. In contrast, the off-rates for all human TCR/pMHC interactions fall within a narrow window regardless of class restriction, thereby providing experimental support for the notion that binding half-life is the principal kinetic feature controlling T cell activation.

Folding of an MHC class II-restricted tumor antigen controls its antigenicity via MHC-guided processing.

CD4(+) and CD8(+) T cell responses to endogenous retroviral envelope glycoprotein gp90 generate protective immunity to murine colon carcinoma CT26. A panel of I-A(d)-restricted T cell hybridomas recognize gp90 synthesized by CT26 cells but not by other gp90-expressing tumors. Here we report that antigenicity resides in an incompletely folded form of gp90 that is unique to CT26. In contrast to more compact forms of gp90 that are present in other tumors, this open conformer is captured by recycling I-A(d) on antigen-presenting cells and is processed intracellularly. Thus, gp90 acquires immunodominance via MHC-guided processing, and the generation of an MHC class II-restricted response can be controlled by the intracellular folding environment of antigen-expressing cells.

Using Overlapping Synthetic Peptides from Tumor-Associated Protein Antigens for Breast Cancer Vaccine Development. (41.11)

Abstract An effective vaccine will need to elicit both CD4+ T helper and CD8+ cytotoxic T lymphocytes (CTL) responses in order to maintain effective CTL functions. Peptide vaccines tailored to certain genetic backgrounds are capable of eliciting MHC Class I-restricted (CD8+) and Class II-restricted (CD4+) responses. However, the need to identify specific T-cell epitopes in the context of MHC alleles hampers this approach. We have developed a novel strategy that bypasses the need for epitope mapping for an outbred population: vaccination with overlapping synthetic peptides (OSP), to generate strong antigen-specific cell-mediated immunity (CMI) in individual vaccine recipients with different MHC backgrounds. OSP contain all possible epitopes for the CD4+ as well as CD8+ T cells of a genetically diverse population. BALB/c mice were immunized with OSP derived from a tumor protein, which is overexpressed in 60% in breast cancer specimens. The vaccinated animals developed an in vitro activity of tumor specific- CTL, proliferative response, IFN-g production and CD107 expression. Immunized mice also were challenged with TS/A tumor cells (a murine mammary adenocarcinoma cell) to induce micrometastasis. Vaccination with OSP significantly increased the animal life span. The OSP vaccine strategy provides a novel opportunity to induce cellular immune responses against developing tumors in a genetically diverse population.

The immune responses to human and microbial heat shock proteins in periodontal disease with and without coronary heart disease

The human 60 kDa and microbial 65 kDa heat shock proteins (HSP) have been implicated in the pathogenesis of chronic periodontitis (P) and coronary heart disease (CHD). We have studied four male non-smoking cohorts of 81 subjects, matched for age. Group (a) consisted of a healthy group with minimal gingivitis (n = 18), group (b) were patients with P (n = 23), group (c) patients with CHD and minimal gingivitis (n = 20) and group (d) patients with CHD and P (n = 20). T cells separated from peripheral blood were found to be primed to both microbial HSP65 and human HSP60 but significant CD4, human leucocyte antigen (HLA) class II-restricted proliferative responses were found only with the human HSP60 in patients with P (P < 0.001) and CHD without (P < 0.001) or with (P < 0.00001) periodontitis. Dose-dependent inhibition of T cell proliferative responses was carried out to determine the receptors involved in recognition of HSP60 and HSP65. Monoclonal antibodies to CD14 showed inhibition of T cell proliferation stimulated by both HSP60 and HSP65, consistent with the role of CD14 as a receptor for these HSPs in P and CHD. The toll-like receptor 2 (TLR-) and TLR-4 were then studied and these showed that TLR-4 was recognized by microbial HSP65, whereas TLR-2 was recognised by human HSP60 in both P and CHD. However, a dissociation was found in the HSP60 and TLR4 interaction, as TLR4 appeared to have been recognized by HSP60 in P but not in CHD. The results suggest an autoimmune or cross-reactive CD4(+) class II-restricted T cell response to the human HSP60 in P and CHD. Further studies are required to determine if there is a common epitope within HSP60 that stimulates T cell proliferation in P and CHD.

Uneven distribution of MHC class II epitopes within the influenza virus

The identification of T cell epitopes is crucial for the understanding of the host immune response during infection. While much is known about the MHC class I-restricted response following influenza virus infection of C57BL/6 mice, with over 16 CD8 epitopes identified to date, less is known about the MHC class II-restricted response. Currently, only a few I-A b-restricted T helper epitopes have been identified. Therefore, several important questions remain about how many class II epitopes exist in this system and whether these epitopes are evenly distributed within the most abundant viral proteins. In order to address these questions, we analyzed the repertoire of epitopes that drive the CD4 + T cell response to influenza virus infection in C57BL/6 (H-2 b) mice. Using a panel of overlapping peptides from each of the viral proteins we show that approximately 20–30 epitopes drive the CD4 T cell response and that the majority of these peptides are derived from the NP and HA proteins. We were also able to demonstrate that vaccination with one of the newly identified epitopes, HA 211–225/A b, resulted in increased epitope-specific T cell numbers and a significant reduction in viral titers following influenza virus challenge.

A cytosolic pathway for MHC class II–restricted antigen processing that is proteasome and TAP dependent

By convention, presentation of major histocompatibility complex (MHC) class I-restricted epitopes involves processing by cytosolic proteasomes, whereas MHC class II-restricted epitopes are generated by endosomal proteases. Here, we show that two MHC class II-restricted epitopes within influenza virus were generated by a proteasome- and TAP-dependent pathway that was accessed by exogenous virus in dendritic cells (DCs) but not cell types with less permeable endosomes. Both epitopes were presented by recycling MHC class II molecules. Challenging mice with influenza or vaccinia viruses demonstrated that a substantial portion of the MHC class II-restricted response was directed against proteasome-dependent epitopes. By complementing endosomal activities, this pathway broadens the array of MHC class II-restricted epitopes available for CD4(+) T cell activation.

In vitro dendritic cell-induced T cell responses to B cell chronic lymphocytic leukaemia enhanced by IL-15 and dendritic cell-B-CLL electrofusion hybrids.

HLA class II-restricted proliferative and cytotoxic T cell (CTL) responses to B cell chronic lymphocytic leukaemia (B-CLL) can be generated using autologous dendritic cells (DCs) pulsed with tumour cell lysate. In this study a number of different approaches were used to optimize further the in vitro system. First, the effects of a variety of maturation agents were studied. The addition of TNF-alpha, polyriboinosinic polyribocytidylic acid (Poly(I:C)) and LPS to autologous DCs resulted in the emergence of only a small percentage of CD83+ DCs, IFN-alpha having no demonstrable effect. Only the addition of Poly(I:C) to DCs resulted in modestly increased specific cytotoxicity to B-CLL targets, IFN-alpha and LPS having no effect. Secondly, T cells were pretreated with IL-15, prior to culturing with lysate-pulsed autologous DCs. A significant increase in T cell activation (P = 0.038), IFN-gamma secretion (P = 0.030) and specific cytotoxicity to B-CLL targets (P = 0.006) was demonstrated compared to untreated T cells. Thirdly, monocyte derived DCs electrofused with B-CLL B cells were compared with lysate-pulsed DCs. T cells stimulated by fused DCs generated higher levels of specific cytotoxicity to autologous B-CLL B cell targets than those stimulated by lysate pulsed DCs (P = 0.013). Blocking studies demonstrated inhibition of this cytotoxicity by both anti-CD4 (P = 0.062) and anti-CD8 monoclonal antibodies (P = 0.018), suggesting the generation of both HLA class I- and HLA class II-restricted CTL responses. In summary, in vitro B-CLL-specific T cell responses can be enhanced further by preincubating T cells with IL-15 and using autologous fused DC-B-CLL hybrids instead of autologous lysate-pulsed DCs. These preliminary data require confirmation with larger numbers of patients. Such an approach, however, may eventually provide effective immunotherapy for treatment of B-CLL.

Molecular aspects of drug recognition by specific T cells.

Adverse reactions to drugs are a major problem in pharmacotherapy. About 1/6 of all side-effects are thought to be drug-induced immune-mediated reactions. It is well established that T and B cells recognize a drug if it is bound as hapten to carrier molecules. However, the model does not explain many T cell-mediated reactions with chemically inert compounds. This review will first discuss the hapten-carrier concept of drug-presentation to T cells and the currently used methods to predict an allergenic potential of a drug. It then introduces our new model of drug-uptake- and processing-free HLA class II-restricted T-cell response termed "direct metabolism-independent T-cell stimulation". This led us to an other new concept: the pharmacological interaction of drugs with immunological receptors, namely the MHC and T-cell receptors. Additionally, we focus on certain conditions of non-covalent drug presentation by antigen presenting cells and on the molecular recognition of MHC/peptide/drug complexes by specific T-cell receptors. Finally, we discuss the clinical relevance of drug-specific T cells, namely that T cells seem to exert a certain pathology (e.g. drug-induced exanthema or pustular eruptions) depending on their function. These findings, which are based on the analysis of clinical drug allergy, have major implications for our understanding of T-cell biology and on the concept how to test and predict the allergenic potential of a drug.

Enhancement of MHC class II-restricted responses by receptor-mediated uptake of peptide antigens.

Peptides, either as altered peptide ligands, competitors, or vaccines, offer an outstanding potential for regulating immune responses because of their exquisite specificity. However, a major problem associated with peptide therapies is that they are poorly taken up by APCs. Because of poor bioavailability, high concentrations and repeated treatments are required for peptide therapies in vivo. To circumvent this problem, we tested whether covalently coupling a peptide T cell determinant, OVA(323-339), to transferrin (Tf) enhances APC uptake and presentation as monitored by Th cell activation. Functional analysis of the Tf-peptide conjugates revealed that the conjugates were presented 10,000- and 100-fold more effectively by B cells than intact Ag and free peptide, respectively. Furthermore, we demonstrate that the Tf-peptide conjugates are taken up by B cells through a receptor-mediated process and subsequently delivered to the lysosomal compartment. Using an adoptive transfer assay, we show that that the Tf-peptide complexes are 100-fold more effective in vivo than the free peptide in activating CD4(+) T cells by following an early activation marker, CD69. Our results demonstrate that coupling peptides to Tf enhances peptide presentation, thereby making it possible to take full advantage of peptide-specific therapies in modulating T cell responses.

Immune complex-mediated antigen presentation induces tumor immunity.

Antigen uptake receptors on dendritic cells (DCs) provide efficient entry for the initiation of antigen-specific adaptive immunity. Here we show that targeting of antigen to Fc receptors on DCs accomplishes combined activation of Th1 CD4 and CD8 effector responses in vivo, namely delayed-type hypersensitivity and tumor immunity. Tumor immunity specific for ovalbumin-expressing tumors was provided by immunization with wild-type but not FcgammaRgamma(-/-) DCs loaded with ovalbumin-containing immune complexes. Tumor protection was eliminated when immune complex-loaded DCs lacked beta(2) microglobulin, TAP, or MHC class II, demonstrating that Fc receptor-targeted antigenic uptake led to both MHC class I- and class II-restricted responses, which together are required for effector tumor immunity. Thus the cross-presentation pathway accessed by antigens acquired endocytically through Fc receptors links humoral and cellular immunity. These data suggest that administration of antitumor antibodies may enhance tumor-specific T cell responses in vivo and provide the rationale for Fc receptor targeting in vaccine development.