Induction of a CD8+ cytotoxic T lymphocyte response by cross-priming requires cognate CD4+ T cell help

Activation-induced CD154 expression abrogates tolerance induced by apoptotic cells

The decision to generate a productive immune response or tolerance often depends on the context in which T cells first see Ag. Using a classical system of tolerance induction, we examined the immunological consequence of Ag encountered in the presence of naive or activated apoptotic cells. Naive apoptotic cells induced tolerance when injected i.v.; however, previously activated apoptotic cells induced immunity. Further analysis revealed a key role for CD154, as tolerance resulted after i.v. injection of either naive or activated apoptotic CD154(-/-) T cells, while coinjection of an agonistic anti-CD40 mAb with naive apoptotic T cells induced robust immunity. Dendritic cells fed activated apoptotic T cells in vitro produced IL-12p40 in a CD154-dependent manner, and the use of IL-12p40(-/-) mice or mAb-mediated neutralization of IL-12 revealed a link between CD154, IL-12, and the ability of activated apoptotic T cells to induce immunity rather than tolerance. Collectively, these results show that CD154 expression on apoptotic T cells can determine the outcome of an immune response to Ag recognized within the context of the apoptotic cells and suggest that the balance between naive and activated apoptotic T cells may dictate whether a productive immune response is encouraged.

Dendritic cells pulsed with GST-EGFR fusion protein: effect in antitumor immunity against head and neck squamous cell carcinoma

BACKGROUND

Overexpression of epidermal growth factor receptor (EGFR) is common in head and neck squamous cell carcinoma (HNSCC). Targeting EGFR is an effective approach to treat EGFR-positive HNSCC. However, the clinical benefits of the present EGFR-targeting agents are still limited in HNSCC patients.

METHODS

Recombinant glutathione-S-transferase (GST)-EGFR fusion protein was produced and purified. Dendritic cells (DCs) of C3H mice were pulsed with fusion protein. Mice were challenged with HNSCC cells before or after vaccination with these DCs, and the cytotoxic T-lymphocyte (CTL) response, interferon-gamma (IFN-gamma) secretion, tumor growth, and survival of mice were assessed.

RESULTS

Significant in vitro and in vivo antitumor activities were observed for mice immunized with DCs pulsed with GST-EGFR fusion protein, compared with the control groups (p < .05).

CONCLUSION

The DCs pulsed with GST-EGFR fusion protein can provide not only preventive but also therapeutic antitumor activities against HNSCC in the animal model.

DC-induced CD8(+) T-cell response is inhibited by MHC class II-dependent DX5(+)CD4(+) Treg

CD4(+) T cells are important for CD8(+) T-cell priming by providing cognate signals for DC maturation. We analyzed the capacity of CD4(+) T cells to influence CD8(+) T-cell responses induced by activated DC. Surprisingly, mice depleted for CD4(+) cells were able to generate stronger antigen-specific CD8(+) T-cell responses after DC vaccination than non-depleted mice. The same observation was made when mice were vaccinated with MHC class II(-/-) DC, indicating the presence of a MHC class II-dependent CD4(+) T-cell population inhibiting CD8(+) T-cell responses. Recently we described the expansion of DX5(+)CD4(+) T cells, a T-cell population displaying immune regulatory properties, upon vaccination with DC. Intriguingly, we now observe an inverse correlation between CD8(+) T-cell induction and expansion of DX5(+)CD4(+) T cells as the latter cells did not expand after vaccination with MHC class II(-/-) DC. In vitro, DX5(+)CD4(+) T cells were able to limit proliferation, modulate cytokine production and induce Foxp3(+) expression in OVA-specific CD8(+) T cells. Together, our data show an inhibitory role of CD4(+) T cells on the induction of CD8(+) T-cell responses by activated DC and indicate the involvement of DX5(+)CD4(+), but not CD4(+)CD25(+), T cells in this process.

Plant-produced potato virus X chimeric particles displaying an influenza virus-derived peptide activate specific CD8+ T cells in mice

Plant viruses can be genetically modified to produce chimeric virus particles (CVPs) carrying heterologous peptides. The efficacy of plant-produced CVPs in inducing antibody responses specific to the displayed peptide has been extensively demonstrated. To determine if plants can be used to produce CVPs able to activate peptide-specific major histocompatibility complex (MHC) class I-restricted CD8+ T cells, potato virus X (PVX) has been engineered to display the H-2D(b)-restricted epitope ASNENMETM of influenza A virus nucleoprotein (NP). Engineering criteria were devised to comply not only with plant virus genetic stability and infectivity but also with antigen processing rules. The immunological properties of different doses of endotoxin-free preparations of CVPs or unmodified PVX have been evaluated by s.c. immunizing C57BL/6J mice and testing at different time intervals splenocyte responses by interferon gamma (IFN-gamma) enzyme-linked immunospot (ELISPOT) assay. These experiments demonstrated that CVPs activate ASNENMTEM-specific CD8+ T cells. Remarkably, the best response was achieved without adjuvant co-delivery. These results represent the proof of concept that well-designed plant virus carriers of epitopes produced in plant can reasonably be used into peptide vaccine formulations aimed to activate cell-mediated immune responses.

Effect of B7.1 costimulation on T-cell based immunity against TAP-negative cancer can be facilitated by TAP1 expression

Tumors deficient in expression of the transporter associated with antigen processing (TAP) usually fail to induce T-cell-mediated immunity and are resistant to T-cell lysis. However, we have found that introduction of the B7.1 gene into TAP-negative (TAP⁻) or TAP1-transfected (TAP1⁺) murine lung carcinoma CMT.64 cells can augment the capacity of the cells to induce a protective immune response against wild-type tumor cells. Differences in the strength of the protective immune responses were observed between TAP⁻ and TAP1⁺ B7.1 expressing CMT.64 cells depending on the doses of γ-irradiated cell immunization. While mice immunized with either high or low dose of B7.1-expressing TAP1⁺ cells rejected TAP⁻ tumors, only high dose immunization with B7.1-expressing TAP⁻ cells resulted in tumor rejection. The induced protective immunity was T-cell dependent as demonstrated by dramatically reduced antitumor immunity in mice depleted of CD8 or CD4 cells. Augmentation of T-cell mediated immune response against TAP⁻ tumor cells was also observed in a virally infected tumor cell system. When mice were immunized with a high dose of γ-irradiated CMT.64 cells infected with vaccinia viruses carrying B7.1 and/or TAP1 genes, we found that the cells co-expressing B7.1 and TAP1, but not those expressing B7.1 alone, induced protective immunity against CMT.64 cells. In addition, inoculation with live tumor cells transfected with several different gene(s) revealed that only B7.1- and TAP1-coexpressing tumor cells significantly decreased tumorigenicity. These results indicate that B7.1-provoked antitumor immunity against TAP⁻ cancer is facilitated by TAP1-expression, and thus both genes should be considered for cancer therapy in the future.

Active CD4+ helper T cells directly stimulate CD8+ cytotoxic T lymphocyte responses in wild-type and MHC II gene knockout C57BL/6 mice and transgenic RIP-mOVA mice expressing islet beta-cell ovalbumin antigen leading to diabetes

CD4+ helper T (Th) cells play crucial role in priming, expansion and survival of CD8+ cytotoxic T lymphocytes (CTLs). However, how CD4+ Th cell's help is delivered to CD8+ T cells in vivo is still unclear. We previously demonstrated that CD4+ Th cells can acquire ovalbumin (OVA) peptide/major histocompatibility complex (pMHC I) and costimulatory CD80 by OVA-pulsed DC (DC(OVA)) stimulation, and then stimulate OVA-specific CD8+ CTL responses in C57BL/6 mice. In this study, we further investigated CD4+ Th cell's effect on stimulation of CD8 CTL responses in major histocompatibility complex (MHC II) gene knockout (KO) mice and transgenic rat insulin promoter (RIP)-mOVA mice with moderate expression of self OVA by using CD4+ Th cells or Th cells with various gene deficiency. We demonstrated that the in vitro DC(OVA)-activated CD4+ Th cells (3 x 10(6) cells/mouse) can directly stimulate OVA-specific CD8+ T-cell responses in wild-type C57BL/6 mice and MHC II gene KO mice lacking CD4+ T cells. A large amount of CD4+ Th cells (12 x 10(6) cells/mouse) can even overcome OVA-specific immune tolerance in transgenic RIP-mOVA mice, leading to CD8+ CTL-mediated mouse pancreatic islet destruction and diabetes. The stimulatory effect of CD4+ Th cells is mediated by its IL-2 secretion and CD40L and CD80 costimulations, and is specifically delivered to OVA-specific CD8+ T cells in vivo via its acquired pMHC I complexes. Therefore, the above elucidated principles for CD4+ Th cells will have substantial implications in autoimmunity and antitumor immunity, and regulatory T-cell-dependent immune suppression.

Enhancing immune responses by targeting antigen to DC

mAb that recognise various cell surface receptors have been used to deliver antigen to DC and thereby elicit immune responses. The encouraging data obtained in mouse models suggests that this immunisation strategy is efficient and could lead to clinical trials. We discuss a number of issues pertinent to this vaccination approach. These include which molecules are the best targets for delivering antigen to DC, which DC subtypes should be targeted, the types of immune responses to be generated and whether additional adjuvants are required. Finally, we discuss some progress towards targeting antigen to human DC.

Th-1 polarization is regulated by dendritic-cell comparison of MHC class I and class II antigens

In the control of T-helper type I (Th-1) polarization, dendritic cells (DCs) must interpret a complex array of stimuli, many of which are poorly understood. Here we demonstrate that Th-1 polarization is heavily influenced by DC-autonomous phenomena triggered by the loading of DCs with antigenically matched major histocompatibility complex (MHC) class I and class II determinants, that is, class I and II peptide epitopes exhibiting significant amino acid sequence overlap (such as would be physiologically present during infectious processes requiring Th-1 immunity for clearance). Data were derived from 13 independent antigenic models including whole-cell systems, single-protein systems, and 3 different pairs of overlapping class I and II binding epitopes. Once loaded with matched class I and II antigens, these "Th-1 DCs" exhibited differential cytokine secretion and surface marker expression, a distinct transcriptional signature, and acquired the ability to enhance generation of CD8(+) T lymphocytes. Mechanistically, tRNA-synthetases were implicated as components of a putative sensor complex involved in the comparison of class I and II epitopes. These data provide rigorous conceptual explanations for the process of Th-1 polarization and the antigenic specificity of cognate T-cell help, enhance the understanding of Th-1 responses, and should contribute to the formulation of more effective vaccination strategies.

NK-cell-mediated killing of target cells triggers robust antigen-specific T-cell-mediated and humoral responses

Previous work showed that administration of antigen-expressing apoptotic cells in vivo results in antigen-specific CD8+ T-cell responses independent of Toll-like receptor signaling. We report here that natural killer (NK) cells can serve a function directly upstream of this pathway and initiate robust adaptive immune responses via killing of antigen-expressing target cells. This pathway is highly sensitive, in that administration of as few as 10(4) target cells induced detectable antigen-specific CD8+ T-cell responses. Importantly, NK cell-mediated cytotoxicity of target cells could also induce robust antigen-specific CD4+ T-cell responses, which were critical for subsequent CD8+ T-cell priming and IgG responses. Unlike adaptive immune responses induced by gamma-irradiated cells, the NK-cell pathway required myeloid differentiating factor 88 (MyD88) and Toll/interleukin-1 receptor domain-containing adapter-inducing interferon-beta (Trif) signaling. NK cells have previously been shown to detect and kill pathogen-infected host cells, as well as neoplastic cells and tissue allografts. The present data provide further evidence that they also discharge a strong tie with their relatives in the adaptive immune system. We think that the recognition and killing of target cells by NK cells represents an important pathway for the generation of robust CD8+ T and humoral responses that may be exploited for vaccine development.

Dendritic cell preparation for immunotherapeutic interventions

Much effort has been made over the last decade to use dendritic cells (DCs) in vaccines to induce specific antitumor immune responses. However, the great hope provided by in vitro and in vivo preclinical investigations was not translated to the clinic in terms of clinical efficacy. Thus, one of the challenges resides in optimizing DC-based therapy to give maximum clinical efficacy while using manufacturing processes that enable quality control and scale-up of consistent products. In this article, we review DC biology and the DC-based clinical trials performed to date and focus on the DC maturation status compatible with the goals of cancer immunotherapy. We also highlight the different approaches used in these clinical studies, such as the DC types or subtypes used and their preparation. Finally, we discuss the immunological and clinical outcomes in treated patients, with emphasis on the strategies that could be used to improve DC-based vaccination.

Influenza virus and poly(I:C) inhibit MHC class I-restricted presentation of cell-associated antigens derived from infected dead cells captured by human dendritic cells

During viral infection, dendritic cells (DCs) capture infected cells and present viral Ags to CD8(+) T cells. However, activated DCs might potentially present cell-associated Ags derived from captured dead cells. In this study, we find that human DCs that captured dead cells containing the TLR3 agonist poly(I:C) produced cytokines and underwent maturation, but failed to elicit autologous CD8(+) T cell responses against Ags of dead cells. Accordingly, DCs that captured dead cells containing poly(I:C), or influenza virus, are unable to activate CD8(+) T cell clones specific to cell-associated Ags of captured dead cells. CD4(+) T cells are expanded with DCs that have captured poly(I:C)-containing dead cells, indicating the inhibition is specific for MHC class I-restricted cross-presentation. Furthermore, these DCs can expand naive allogeneic CD8(+) T cells. Finally, soluble or targeted Ag is presented when coloaded onto DCs that have captured poly(I:C)-containing dead cells, indicating the inhibition is specific for dead cell cargo that is accompanied by viral or poly(I:C) stimulus. Thus, DCs have a mechanism that prevents MHC class I-restricted cross-presentation of cell-associated Ag when they have captured dead infected cells.

Tissue destruction caused by cytotoxic T lymphocytes induces deletional tolerance

Autoimmune diseases tend to be chronic and progressive, but how these responses are sustained is not clear. One cell type that might contribute to autoimmunity is the cytotoxic T lymphocyte (CTL), which, as a consequence of causing tissue destruction and production of cytokines, could provide a sustained supply of antigen and inflammatory signals for dendritic cells to maintain immune stimulation. Here we examined whether such CTL-mediated tissue damage alone could provide antigen in the right context to recruit immune effectors and sustain autoimmunity. We show that while CTL-mediated tissue damage caused the release of self-antigens that stimulated the proliferation of naive autoreactive CD8(+) T cells, such responses failed to precipitate disease and, instead, led to deletional tolerance. These findings indicate that despite the capacity of CTLs to produce inflammatory cytokines and to cause tissue damage, their responses are not sustaining, but instead favor induction of self-tolerance.

A novel strategy for tumour therapy combining cell apoptosis and active immunity induced by caspy2, a zebrafish caspase

Caspy2, a zebrafish protease, is an active caspase for inducing apoptosis in mammalian cells. To investigate whether caspy2-mediated apoptosis could be used in cancer therapy, its cDNA was amplified and cloned into eukaryotic expression vector pcDNA3.1(+). The recombinant plasmid was mixed with cationic liposome and introduced into various tumour cell lines in vitro. Our data showed that caspy2 induced remarkable apoptosis of cancer cells in vitro. Treatment of mice-bearing CT26 colon carcinoma or MethA fibrosarcoma with intratumoral injection of liposome-caspy2 plasmid complex resulted in substantial killing of neoplastic cells and long-term survivors. Apoptotic cells were widely distributed in caspy2-treated tumour tissue. Infiltration of CD8(+) T lymphocyte was also observed apparently in the tumour tissue after the treatment with caspy2. Tumour-specific major histocompatibility complex (MHC) class I-dependent CD8(+) cytotoxic T lymphocyte activity was found by means of (51)Cr release assay. In MethA model, the mice acquired a long-time protective immunity against the parental tumour cell re-challenge. These results indicated that caspy2 can act as both apoptosis inducer and immune response initiator, which may account for its extraordinary antitumour effect. Furthermore, in vivo depletion of CD8(+) T lymphocytes could completely abrogate the antitumour immune activity, whereas the depletion of CD4(+) cells showed partial abrogation. In this study, we developed a novel anticancer strategy that combines both induction of apoptosis and immune response in mice-bearing tumours with a single caspy2 gene. This approach may provide an important way for treatment of cancer.

Cutting edge: CD4+ T cell-derived IL-2 is essential for help-dependent primary CD8+ T cell responses

CD4(+) T cell help is essential for primary CD8(+) T cell responses to noninflammatory Ags. IL-2 is one of the principal cytokines made by naive CD4(+) T cells, and we show in this study that it is an essential component of help. Adoptively transferred naive CD4(+) TCR-transgenic OT-II cells supported endogenous primary CD8(+) T cell responses, but IL-2-deficient OT-II cells were unable to provide help, although they responded to Ag in vivo and up-regulated CD40 ligand in vitro. Wild -type OT-II cells helped endogenous CD8(+) T cell responses in IL-2-deficient mice, but not in IL-2Ralpha-deficient mice. Thus, CD4(+) T cell-derived IL-2 is essential for CD8(+) T cell responses to noninflammatory, cell-associated Ags. We suggest that it is also a critical component of help for CD8(+) T cell responses to pathogens, because protective memory also requires CD8(+) T cell stimulation by IL-2 during priming.

CD4+ cells are required for chronic eosinophilic lung inflammation but not airway remodeling

The contribution of CD4 T cells and other CD4+ cells to lung inflammation and airway remodeling remains unclear during bouts of chronic exposure to airborne allergen. Previously, murine models have shown that CD4 T cells are required for initiation of acute inflammation and the remodeling process. However, it is unknown whether CD4 T cells or other CD4+ cells continue to be required for remodeling during ongoing allergen challenges after the development of acute eosinophilic lung inflammation. To test this, mice were sensitized and challenged with ovalbumin (OVA). After acute airway inflammation was established, a CD4 depleting antibody was administered for 4 wk during a period of chronic exposure to intranasal OVA, resulting in effective depletion of CD4+ cells from all organs, including the lung, lung-draining lymph nodes, and spleen. In these mice, levels of peribronchial inflammation, bronchoalveolar (BAL) eosinophils, and lung CD11c+, CD8+, and Siglec-F+CD11c- cells were significantly reduced. However, mucus metaplasia, peribronchial subepithelial fibrosis, and smooth muscle mass were not affected. Additionally, depletion of CD4+ cells before the last week of chronic allergen challenges also led to significant reductions in BAL eosinophils, peribronchial inflammation, and lung CD11c+, CD8+, and Siglec-F+CD11c- cells. These results show that CD4 T cells, and other CD4+ cells including subsets of dendritic cells, iNKT cells, and LTi cells, play a role in ongoing eosinophilic lung inflammation during periods of chronic allergen challenge, but are not required for progressive airway remodeling that develops after initial acute inflammation.

Therapeutic efficacy of antitumor dendritic cell vaccinations correlates with persistent Th1 responses, high intratumor CD8+ T cell recruitment and low relative regulatory T cell infiltration

Despite the increasing number of immunotherapeutic strategies for the treatment of cancer, most approaches have failed to correlate the induction of an anti-tumor immune response with therapeutic efficacy. We therefore took advantage of a successful vaccination strategy-combining dendritic cells and irradiated GM-CSF secreting tumor cells-to compare the immune response induced against 9L gliosarcoma tumors in cured rats versus those with progressively growing tumors. At the systemic level, the tumor specific cytotoxic responses were quite heterogeneous in uncured vaccinated rats, and were surprisingly often high in animals with rapidly-growing tumors. IFN-gamma secretion by activated splenic T cells was more discriminative as the CD4+ T cell-mediated production was weak in uncured rats whereas high in cured ones. At the tumor level, regressing tumors were strongly infiltrated by CD8+ T cells, which demonstrated lytic capacities as high as their splenic counterparts. In contrast, progressing tumors were weakly infiltrated by T cells showing impaired cytotoxic activities. Proportionately to the T cell infiltrate, the expression of Foxp3 was increased in progressive tumors suggesting inhibition by regulatory T cells. In conclusion, the main difference between cured and uncured vaccinated animals does not depend directly upon the induction of systemic cytotoxic responses. Rather the persistence of higher CD4+ Th1 responses, a high intratumoral recruitment of functional CD8+ T cells, and a low proportion of regulatory T cells correlate with tumor rejection.

Cell fusion: from hybridoma to dendritic cell-based vaccine

The deployment of dendritic cell (DC) and tumor cell fusions is increasing in tumor immunotherapy. In animal and human studies, fusion cell vaccines have been shown to possess the elements essential for processing and presenting tumor antigens to host immune cells, for inducing effective immune response and for breaking T-cell tolerance to tumor-associated antigens. Moreover, fusion cell vaccines provide protection against challenge with tumor cells and mediate regression of established tumors. Despite these unique features of fusion cell vaccines and the observation of tumor eradication in animal studies, limited success has occurred in clinical trials. This article reviews the methods used for optimizing the preparation and selection of DC-tumor fusion cells and analyzes factors influencing the success or failure of fusion cell-mediated immunotherapy. In addition, we discuss the challenges facing effective fusion cell vaccine production, including factors in preparation, selection and quality control of fusion cell vaccines, as well as approaches for enhancing anti-tumor immunity.

Sperm membrane lipid liposomes can evoke an effective immune response against encapsulated antigen in BALB/c mice

In an earlier study, we provided strong evidence that liposomes made of sperm membrane lipids (spermatosomes) can deliver entrapped molecules to the cytosol of target cells. Now we have evaluated the immunological behavior of spermatosome-encapsulated soluble antigen ovalbumin (OVA) in BALB/c mice. Spermatosome-mediated antigen delivery can affect both cytosolic and endosomal antigen-processing pathways, simultaneously, leading to the generation of CD4+ T-helper and CD8+ cytotoxic T-cell responses. Isotype studies revealed that immunization with spermatosome-encapsulated OVA elicits mainly IgG2a and IgG1 subclasses of antibodies. A potential vaccine candidate should impart long-lasting protection against infection; to this end, immunization with spermatosome-encapsulated OVA resulted in expression of CD44 and CD62L cell-surface markers on T cells, suggestive of a desirable memory response. We conclude that spermatosome encapsulation is a useful strategy for vaccine production, because it enhances the immunological activity of the encapsulated antigen.

Primary CD8+ T-cell response to soluble ovalbumin is improved by chloroquine treatment in vivo

The efficiency of cross-presentation of exogenous antigens by dendritic cells (DCs) would seem to be related to the level of antigen escape from massive degradation mediated by lysosomal proteases in an acidic environment. Here, we demonstrate that a short course of treatment with chloroquine in mice during primary immunization with soluble antigens improved the cross-priming of naïve CD8(+) T lymphocytes in vivo. More specifically, priming of chloroquine-treated mice with soluble ovalbumin (OVA), OVA associated with alum, or OVA pulsed on DCs was more effective in inducing OVA-specific CD8(+) T lymphocytes than was priming of untreated mice. We conclude that chloroquine treatment improves the cross-presentation capacity of DCs and thus the size of effector and memory CD8(+) T cells during vaccination.

Immunotherapy of hepatocellular carcinoma with a vaccine based on xenogeneic homologous alpha fetoprotein in mice

alpha-Fetoprotein (AFP) is a diagnostic marker for the presence of hepatocellular carcinoma, and a potential target for immunotherapy. Unfortunately, the immunity to AFP is presumably difficult to elicit because of immune tolerance acquired during the development of immune system. In the present study, we used AFP as a model antigen to explore the feasibility of the immunotherapy of AFP-positive liver cancer by the breaking of immune tolerance against AFP in a cross-reaction between the xenogeneic homologues and self molecules. Recombinant rat AFP was prepared as a vaccine, and mouse AFP was prepared as a control. Immunized with rat AFP was effective at protective and therapeutic antitumor immunity in hepatocellular carcinoma model in mice. Both humoral and cellular immune responses may be responsible for the antitumor activity against AFP-positive tumor cells, and no marked side effects were observed in the immunized mice. Thus, our study may provide an effective vaccine strategy for the treatment of AFP-positive hepatocellular carcinoma, and may be of importance to further exploration of the breaking of immune tolerance to self molecules.

Human CD4+ T lymphocytes recognize a vascular endothelial growth factor receptor-2-derived epitope in association with HLA-DR

PURPOSE

Given the multiple escape mechanisms of tumor cells, immunotherapy targeting tumor-dependent stroma may be an effective cancer treatment strategy. Animal models indicate that inducing immunity to tumor endothelia engenders potent antitumor effects without significant pathology. Recently, the first human tumor endothelial antigen vascular endothelial growth factor receptor-2 (VEGFR-2) recognized by HLA class I-restricted CD8(+) T cells has been characterized. In this study, we sought to investigate specific recognition of this molecule by human CD4(+) T cells.

EXPERIMENTAL DESIGN

To identify HLA-DR-restricted antigenic peptides on VEGFR-2 recognized by CD4(+) T cells of healthy donors and cancer patients.

RESULTS

Nine candidate VEGFR-2 peptides with high binding probability to six common HLA-DRB1 alleles were synthesized using the SYFPEITHI algorithm. One 15-mer peptide (EKRFVPDGNRISWDS), mapping to the 167-181 region of VEGFR-2, stimulated CD4(+) T cells in association with several HLA-DR alleles, including DR4 and DR7. Importantly, the epitope could be naturally processed and presented both by HLA-DR-matched antigen-expressing proliferating endothelial cells and by dendritic cells loaded with the native antigen. Furthermore, circulating VEGFR-2-specific CD4(+) T cells were detected in 4 of 10 healthy donors and 12 of 40 cancer patients even after single-round peptide stimulation in short-term culture. Patient's T cells could recognize antigen-expressing proliferating endothelial cells in a HLA-DR-restricted fashion.

CONCLUSION

These findings indicate an important role for the 167-181 region of VEGFR-2 in the stimulation of CD4(+) T cell responses to VEGFR-2 protein, and may be instrumental both for the development and monitoring of upcoming antitumor vessel vaccines against different cancers based on VEGFR-2 immunogens.

Generating functional CD8+ T cell memory response under transient CD4+ T cell deficiency: implications for vaccination of immunocompromised individuals

Studies based on either MHC class II-knockout or CD4+ T cell-depleted murine models have demonstrated a critical role for CD4+ T cells in the generation of CD8+ T cell memory. However, it is difficult to extend these findings to immunocompromised humans where a complete loss of CD4+ T cells is rarely observed. Here, we have developed a model setting, which allows studies on the generation of CD8+ T cell memory responses in a transient CD4+ T cell-deficient setting similar to that seen in immunocompromised patients. Immunisation with an adenoviral vaccine under transient helpless or help-deficient conditions showed varying degrees of impact on the priming of CD8+ T cell responses. Antigen-specific T cells generated under normal CD4+ T cell help and transient help-deficient conditions showed similar effector phenotype and were capable of proliferation upon secondary antigen encounter. Most importantly, in spite of CD4+ T cell deficiency, the long-term CD8+ T cell memory response remained functionally stable and showed comparable cytotoxic effector function as seen in CD8+ T cells generated with normal CD4+ T cell numbers. These findings provide evidence that in spite of partially impaired activation of a primary CD8+ T cell response, a fully functional and stable memory CTL response can be induced under conditions of severe transient CD4+ T cell deficiency.

Role of IL-2 secreted by PADRE-specific CD4+ T cells in enhancing E7-specific CD8+ T-cell immune responses

CD4(+) T helper cells are known to play an integral role in the generation of CD8(+) T-cell immune responses. We have previously shown that co-administration of DNA vaccines containing E6 or E7 protein of human papillomavirus 16 (HPV-16) combined with DNA encoding invariant (Ii) chain in which class II-associated Ii peptide (CLIP) region is replaced with the CD4(+) T helper epitope, PADRE (Pan-DR-epitope) (Ii-PADRE DNA) enhanced HPV antigen-specific CD8(+) T-cell immune responses in vaccinated mice. In the current study, we investigated the enhancement of HPV E7-specific CD8(+) T-cell immune responses by PADRE-specific CD4(+) T cells. We showed that intradermal administration of Ii-PADRE DNA at the same location as E7-expressing DNA is necessary to generate strong E7-specific CD8(+) T-cell immune responses. We also showed that PADRE-specific CD4(+) T cells generated by Ii-PADRE DNA vaccination expressed Th1 cytokine profile. Furthermore, our in vitro study demonstrated that PADRE-specific CD4(+) T cells stimulated with PADRE-loaded dendritic cells secrete IL-2 that leads to the proliferation of E7-specific CD8(+) T cells. Thus, our data suggest that activated PADRE-specific CD4(+) T helper cells may be required at the vicinity of E7-specific CD8(+) T cells where they secrete IL-2, which enhances the E7-specific CD8(+) T-cell immune responses generated by DNA vaccination.

CD4 T cells are required for CD8 T cell survival during both primary and memory recall responses

The role of CD4 T cell help in primary and secondary CD8 T cell responses to infectious pathogens remains incompletely defined. The primary CD8 T response to infections was initially thought to be largely independent of CD4 T cells, but it is not clear why some primary, pathogen-specific CD8 T cell responses are CD4 T cell dependent. Furthermore, although the generation of functional memory CD8 T cells is CD4 T cell help dependent, it remains controversial when the "help" is needed. In this study, we demonstrated that CD4 T cell help was not needed for the activation and effector differentiation of CD8 T cells during the primary response to vaccinia virus infection. However, the activated CD8 T cells showed poor survival without CD4 T cell help, leading to a reduction in clonal expansion and a diminished, but stable CD8 memory pool. In addition, we observed that CD4 T cell help provided during both the primary and secondary responses was required for the survival of memory CD8 T cells during recall expansion. Our study indicates that CD4 T cells play a crucial role in multiple stages of CD8 T cell response to vaccinia virus infection and may help to design effective vaccine strategies.

The absence of invariant chain in MHC II cancer vaccines enhances the activation of tumor-reactive type 1 CD4+ T lymphocytes

Activation of tumor-reactive T lymphocytes is a promising approach for the prevention and treatment of patients with metastatic cancers. Strategies that activate CD8(+) T cells are particularly promising because of the cytotoxicity and specificity of CD8(+) T cells for tumor cells. Optimal CD8(+) T cell activity requires the co-activation of CD4(+) T cells, which are critical for immune memory and protection against latent metastatic disease. Therefore, we are developing "MHC II" vaccines that activate tumor-reactive CD4(+) T cells. MHC II vaccines are MHC class I(+) tumor cells that are transduced with costimulatory molecules and MHC II alleles syngeneic to the prospective recipient. Because the vaccine cells do not express the MHC II-associated invariant chain (Ii), we hypothesized that they will present endogenously synthesized tumor peptides that are not presented by professional Ii(+) antigen presenting cells (APC) and will therefore overcome tolerance to activate CD4(+) T cells. We now report that MHC II vaccines prepared from human MCF10 mammary carcinoma cells are more efficient than Ii(+) APC for priming and boosting Type 1 CD4(+) T cells. MHC II vaccines consistently induce greater expansion of CD4(+) T cells which secrete more IFNgamma and they activate an overlapping, but distinct repertoire of CD4(+) T cells as measured by T cell receptor Vbeta usage, compared to Ii(+) APC. Therefore, the absence of Ii facilitates a robust CD4(+) T cell response that includes the presentation of peptides that are presented by traditional APC, as well as peptides that are uniquely presented by the Ii(-) vaccine cells.

Sustained antigen-specific antitumor recall response mediated by gene-modified CD4+ T helper-1 and CD8+ T cells

Given that specific subsets of T helper 1 (Th1) and T helper 2 (Th2) CD4(+) T cells have been shown to play key roles in tumor rejection models, we wanted to assess the contribution of either Th1 or Th2 CD4(+) cell subtypes for redirected T-cell immunotherapy. In this study, we have developed a novel method involving retroviral transduction and in vitro T-cell polarization to generate gene-engineered mouse CD4(+) Th1 and Th2 cells or T helper intermediate (Thi) cells expressing an anti-erbB2-CD28-zeta chimeric receptor. Gene-modified Th1 and Th2 polarized CD4(+) cells were characterized by the preferential secretion of IFN-gamma and interleukin-4, respectively, whereas Thi cells secreted both cytokines following receptor ligation. In adoptive transfer studies using an erbB2(+) lung metastasis model, complete survival of mice was observed when transduced Th1, Th2, or Thi CD4(+) cells were transferred in combination with an equivalent number of transduced CD8(+) T cells. Tumor rejection was consistently associated with transduced T cells at the tumor site and interleukin-2 secretion. However, the surviving mice treated with gene-modified Th1 CD4(+) cells were significantly more resistant to a subsequent challenge with a different erbB2(+) tumor (4T1.2) implanted s.c. This result correlated with both increased expansion of Th1 CD4(+) and CD8(+) T cells in the blood and a greater number of these cells localizing to the tumor site following rechallenge. These data support the use of gene-modified CD4(+) Th1 and CD8(+) T cells for mediating a sustained antitumor response.

Dendritic cells process antigens encapsulated in a biodegradable polymer, poly(D,L-lactide-co-glycolide), via an alternate class I MHC processing pathway

Biodegradable nanospheres generated from a biocompatible polymer, poly(D,L-lactide-co-glycolide) (PLGA), have been studied extensively as implantable reservoirs for sustained-release drug delivery. PLGA-nanospheres have also been studied as vehicles to deliver antigens to phagocytes. The intracellular processing pathway of antigens delivered to phagocytes by PLGA particles was studied in the present study. Ovalbumin (OVA) encapsulated with PLGA (OVA-nanosphere) was efficiently captured, processed and presented on class I major histocompatibility complex (MHC-I) by dendritic cells (DCs). The MHC-I processing of OVA-nanospheres was resistant to lactacystin, a proteosome inhibitor, and brefeldin A, which blocks anterograde transport from the endoplasmic reticulum (ER) through the Golgi apparatus. Chloroquine, which inhibits phagolysosomal enzymes by increasing phagolysosomal pH, inhibited MHC-I processing of OVA-nanospheres. In addition, DCs generated from TAP-/- mice were markedly suppressed in MHC-I processing of OVA-nanospheres. These results demonstrate that DCs process phagocytosed OVA-nanospheres via a vacuolar alternate MHC-I pathway for presentation of OVA peptides to T lymphocytes.

Enhancing DNA vaccine potency by combining a strategy to prolong dendritic cell life and intracellular targeting strategies with a strategy to boost CD4+ T cell

Intradermal administration of DNA vaccines, using a gene gun, represents an effective means of delivering DNA directly into professional antigen-presenting cells (APCs) in the skin and thus allows the application of strategies to modify the properties of APCs to enhance DNA vaccine potency. In the current study, we hypothesized that the potency of human papillomavirus (HPV) type 16 E7 DNA vaccines employing intracellular targeting strategies combined with a strategy to prolong the life of dendritic cells (DCs) could be further enhanced by the addition of a DNA vaccine capable of generating high numbers of pan-HLA-DR reactive epitope (PADRE)-specific CD4(+) T cells. We observed that the addition of PADRE DNA to E7 DNA vaccines employing intracellular targeting strategies with a strategy to prolong the life of DCs led to significant enhancement of E7-specific CD8(+) effector and memory T cells as well as significantly improved therapeutic effects against established E7-expressing tumors in tumor-challenged mice. Our data suggest that the potency of a DNA vaccine combining an intracellular targeting strategy as well as a strategy to prolong the life of DCs can be further enhanced by addition of DNA that is capable of generating high numbers of PADRE-specific CD4(+) T cells.

Expansion of human cytomegalovirus-specific T lymphocytes from unfractionated peripheral blood mononuclear cells with artificial antigen-presenting cells

BACKGROUND

The aim of this study was to find a simple and feasible method for ex vivo expansion of human cytomegalovirus (CMV)-specific cytotoxic T cells from unfractionated peripheral blood mononuclear cells (PBMNCs).

STUDY DESIGN AND METHODS

Unfractionated PBMNCs from three HLA-A*0201-CMV-seropositive donors were stimulated with CMVpp65(495-503) peptide-loaded HLA-A*0201-immunoglobulin fusion protein (HLA-A2-Ig) based artificial antigen-presenting cells (aAPCs) on Day 1. Once a week the CMV-specific T cells were harvested and restimulated with fresh aAPCs. T-cell cultures were maintained for 28 days and then analyzed.

RESULTS

With aAPCs and starting with 1x10(7) freshly isolated PBMNCs that were less than 0.1 percent CMV-specific, more than 1x10(7) T cells with a CMV-specific frequency greater than 93 percent in all donors tested were generated. Expanded CD8+ cytotoxic T lymphocytes were functionally active and showed antigen-specific secretion of interferon-gamma and cytotoxic activity. No alloreactivity against unpulsed HLA-A*0201-positive cells was detected.

CONCLUSION

Herein is reported the successful in vitro expansion of CMV-specific cytotoxic CD8+ T cells from unfractionated PBMNCs of healthy CMV-seropositive blood donors by the use of HLA-A2-Ig-based aAPCs. This study demonstrates that more than 1x10(7) CMV-specific T cells can be generated from approximately 1x10(7) unfractionated PBMNCs within 1 month under highly reproducible conditions.

T cell precursor frequency differentially affects CTL responses under different immune conditions

Generation of effective CTL responses is the goal of many vaccination protocols. However, to what extant T cell precursor frequencies will generate a CD8(+) CTL response has not been elucidated properly. In this study, we employed a model system, in which naive CD4(+) and CD8(+) T cells derived from ovalbumin (OVA)-specific TCR transgenic OT II and OT I mice were used for adoptive transfer into wild-type, Ia(b-/-) gene knockout and transgenic RIP-mOVA mice, and assessed OVA-pulsed DC (DC(OVA))-stimulated CD8(+) CTL responses in these mice. We demonstrated that (i) a critical threshold exists above which T cells precursor frequency cannot enhance the CTL responses in wild-type C57BL/6 mice, (ii) increasing CD8(+) T cell precursors is required to generate CTL responses but with functional memory defect in absence of CD4(+) T cell help, and (iii) increasing CD4(+) and CD8(+) T cell precursors overcomes immune suppression to DC(OVA)-stimulated CD8(+) CTL responses in transgenic RIP-mOVA mice with OVA-specific self immune tolerance. Taken together, these findings may have important implications for optimizing immunotherapy against cancer.

Polysaccharides from Antrodia camphorata mycelia extracts possess immunomodulatory activity and inhibits infection of Schistosoma mansoni

Antrodia camphorata (AC) is a commonly used fungus in folk medicine for the treatment of viral hepatitis and cancer. AC polysaccharides (AC-PS) are reported to possess anti-inflammatory, anti-hepatitis B virus, and anticancer activities. In this study, we tested the in vivo effect of AC-PS on immune function by evaluating cytokine expression; on immunomodulation, by evaluating spleen cells; and on Schistosoma mansoni infection in mice. The induction of high levels of interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) mRNA was detected in BALB/c mice after 2, 4, and 6 weeks of oral AC-PS administration. After 6 weeks of oral AC-PS administration to the BALB/c mice, the number of splenic dendritic cells, macrophages, and the surface expression of CD8 alpha+ and major histocompatibility class II I-A/I-E on dendritic cells increased. The CD4+/CD8+ ratio and number of B cells among splenocytes were also augmented. By using a disease model of parasitic infection, we found that AC-PS treatment inhibited S. mansoni infection in BALB/c mice. AC-PS appears to modulate the immune system of mice and has potential for preventing S. mansoni infection.

Human papillomavirus type 16 and 18 E7-pulsed dendritic cell vaccination of stage IB or IIA cervical cancer patients: a phase I escalating-dose trial

The safety and immunogenicity of the human papillomavirus type 16 (HPV16) or HPV18 (HPV16/18) E7 antigen-pulsed mature dendritic cell (DC) vaccination were evaluated for patients with stage IB or IIA cervical cancer. Escalating doses of autologous DC (5, 10, and 15 x 10(6) cells for injection) were pulsed with recombinant HPV16/18 E7 antigens and keyhole limpet hemocyanin (KLH; an immunological tracer molecule) and delivered in five subcutaneous injections at 21-day intervals to 10 cervical cancer patients with no evidence of disease after they underwent radical surgery. Safety, toxicity, delayed-type hypersensitivity (DTH) reaction, and induction of serological and cellular immunity against HPV16/18 E7 and KLH were monitored. DC vaccination was well tolerated, and no significant toxicities were recorded. All patients developed CD4(+) T-cell and antibody responses to DC vaccination, as detected by enzyme-linked immunosorbent spot (ELISpot) and enzyme-linked immunosorbent assays (ELISA), respectively, and 8 out of 10 patients demonstrated levels of E7-specific CD8(+) T-cell counts, detected by ELISpot during or immediately after immunization, that were increased compared to prevaccination baseline levels. The vaccine dose did not predict the magnitude of the antibody or T-cell response or the time to detection of HPV16/18 E7-specific immunity. DTH responses to intradermal injections of HPV E7 antigen and KLH were detected for all patients after vaccination. We conclude that HPV E7-loaded DC vaccination is safe and immunogenic for stage IB or IIA cervical cancer patients. Phase II E7-pulsed DC-based vaccination trials with cervical cancer patients harboring a limited tumor burden, or who are at significant risk of tumor recurrence, are warranted.

In vivo immunomodulatory effects of Antrodia camphorata polysaccharides in a T1/T2 doubly transgenic mouse model for inhibiting infection of Schistosoma mansoni

Antrodia camphorata (A. camphorata) is a fungus commonly used for treatment of viral hepatitis and cancer in Chinese folk medicine. Extract of A. camphorate is reported to possess anti-inflammatory, antihepatitis B virus and anticancer activities. In this study, we tested the in vivo effects of polysaccharides derived from A. camphorata (AC-PS) on immune function by detection of cytokine expression and evaluation of the immune phenotype in a T1/T2 doubly transgenic mouse model. The protective effect of AC-PS in mice was tested by infection with Schistosoma mansoni. The induction of large amounts of IFN-gamma, IL-2 and TNF-alpha mRNA were detected after 2 and 4 weeks of oral AC-PS administration in BALB/c and C57BL/6 mice. In transgenic mice, 3 to 6 weeks of oral AC-PS administration increased the proportion of CD4(+) T cells and B cells within the spleen. More specifically, there was an increase of Th1 CD4(+) T cells and Be1 cells among spleen cells as observed by detection the of Type1/Type2 marker molecules. By using a disease model of parasitic infection, we found that AC-PS treatment inhibited infection with S. mansoni in BALB/C and C57BL/6 mice. AC-PS appears to influence the immune system of mice into developing Th1 responses and have potential for preventing infection with S. mansoni.

Immunotherapy of murine colon cancer using receptor tyrosine kinase EphA2-derived peptide-pulsed dendritic cell vaccines

BACKGROUND

Further optimization of dendritic cell (DC)-based vaccines is required clinically against advanced stage cancer. Given the broad range of expression levels observed in the recently defined tumor antigen EphA2 in a diverse types of cancers, especially in advanced stage or metastatic cancers, the authors evaluated the effectiveness of vaccination using DCs pulsed with EphA2-derived peptides (Eph-DCs) in a murine colon cancer model.

METHODS

EphA2 protein expression levels were evaluated in advanced colorectal carcinoma tissues from 10 patients by Western blot analysis. C57BL/6 mice were immunized with Eph-DCs twice weekly. Interferon gamma (IFN-gamma) ELISPOT assays were used for the analysis of CD8-positive T cells that were specific for EphA2-derived peptide. Immunized mice were challenged subcutaneously with EphA2-positive murine colorectal adenocarcinoma (MC38) mouse colon tumors or with EphA2-negative BL6 melanoma tumors. In some experiments, mice were injected with anti-CD8, anti-CD4, or antiasialo GM1 antibody to deplete corresponding lymphocyte subsets.

RESULTS

Among 10 samples of advanced colorectal carcinoma, 6 samples (60%) overexpressed EphA2. IFN-gamma ELISPOT assays revealed that EphA2-derived peptide-specific CD8-positive T cells were generated by immunization with Eph-DCs. Immunization with Eph-DCs inhibited MC38 tumor growth compared with immunization using unpulsed DCs or phosphate-buffered saline. In contrast, Eph-DC vaccination had no effect on BL6 growth. Antibody depletion studies revealed that both CD8-positive T cells and CD4-positive T cells, but not natural killer cells, played critical roles in the efficacy observed for immunizations with Eph-DCs. Eph-DC vaccines resulted in long-term antitumor immunity against a rechallenge with MC38 tumor cells.

CONCLUSIONS

The current results demonstrated that Eph-DC vaccines may represent a promising preventative/therapeutic modality in the cancer setting.

The surprising kinetics of the T cell response to live antigenic cells

Cooperation between CD4(+) and CD8(+) T cells is required for the proper development of primary effector and memory CD8(+) T cells following immunization with noninflammatory immunogens. In this study, we characterized murine CD4(+) and CD8(+) T cell responses to male-specific minor histocompatibility (HY) Ags following injection of live male cells into females of the same strain. Male cells are rejected 10-12 days after transfer, coinciding with the expansion and effector function of CD8(+) CTLs to two H-2D(b)-restricted epitopes. Although anti-HY CD4(+) T cell responses are readily detectable day 5 posttransfer, CD8(+) responses are undetectable until day 10. The early CD4(+) response is not dependent on direct presentation of Ag by donor male cells, but depends on presentation of the male cells by recipient APC. The CD4(+) T cell response is required for the priming of CD8(+) T cell effector responses and rejection of HY-incompatible cells. Unexpectedly, HY-specific CD4(+) T cells are also capable of efficiently lysing target cells in vivo. The delay in the CD8(+) T cell response can be largely abrogated by depleting T cells from the male inoculum, and donor male CD8(+) T cells in particular suppress host anti-HY CD8(+) responses. These data demonstrate dramatic differences in host T cell responses to noninflammatory Ags compared with responses to pathogens. We explain the delayed CD8(+) response by proposing that there is a balance between cross-presentation of Ag by helper cell-licensed dendritic cells, on the one hand, and veto suppression by live male lymphocytes on the other.

Pre-clinical evaluation of a CEA DNA prime/protein boost vaccination strategy against colorectal cancer

In preparation for a clinical trial in patients diagnosed with colorectal cancer, a vaccination strategy targeting the carcinoembryonic antigen (CEA) was evaluated in mice using a GMP-produced plasmid DNA vaccine, CEA66, encoding a truncated form of the tumour-associated antigen, CEA. The GMP-produced CEA DNA vaccine was also evaluated for toxicity. Repeated intradermal administration of the GMP-produced vaccine using a novel needle-free jet injection device (Biojector) induced robust CD4 and CD8 T-cell responses in mice, and did not result in any vaccine-related toxicity. In a heterologous DNA prime/protein boost setting, cellular immune responses were of higher magnitude in animals primed with CEA66 DNA than in animals receiving repeated doses of recombinant CEA protein. These responses were further enhanced if recombinant murine granulocyte-macrophage colony-stimulating factor was given as an adjuvant prior to vaccination. In contrast to repeated administration of recombinant CEA protein as a single modality vaccine, the heterologous CEA66 DNA prime/rCEA boost vaccination strategy resulted in a qualitatively broader immune response, and supports clinical testing of this vaccination regimen in humans.

CD8+ dendritic cells use LFA-1 to capture MHC-peptide complexes from exosomes in vivo

Exosomes are secreted vesicles formed in late endocytic compartments. Mature dendritic cells (DCs) secrete exosomes bearing functional MHC-peptide complexes and high levels of ICAM-1. Such exosomes can activate Ag-specific naive T cells but only after recapture by recipient APCs. In this study, we addressed the molecular mechanisms of interaction between exosomes and recipient DCs. We show that exosomes can be presented by mouse DCs without the need for internalization and processing. Exosomes interact with DCs through a specific saturable receptor. Although the two major ligands of ICAM-1, LFA-1 and Mac-1, are expressed by lymphoid organ DCs, only LFA-1 is required for exosome capture by these cells. Accordingly, we show that CD8(+) DCs express higher levels of LFA-1 than CD8(-) DCs, and that they are the main recipients of exosomes in vivo. We propose a new role for LFA-1 on DCs, as a receptor for exosomes to favor Ag transfer between DCs in vivo.

CD8+ T cell-mediated airway hyperresponsiveness and inflammation is dependent on CD4+IL-4+ T cells

CD4+ T cells, particularly Th2 cells, play a pivotal role in allergic airway inflammation. However, the requirements for interactions between CD4+ and CD8+ T cells in airway allergic inflammation have not been delineated. Sensitized and challenged OT-1 mice in which CD8+ T cells expressing the transgene for the OVA(257-264) peptide (SIINFEKL) failed to develop airway hyperresponsiveness (AHR), airway eosinophilia, Th2 cytokine elevation, or goblet cell metaplasia. OT-1 mice that received naive CD4+IL-4+ T cells but not CD4+IL-4- T cells before sensitization developed all of these responses to the same degree as wild-type mice. Moreover, recipients of CD4+IL-4+ T cells developed significant increases in the number of CD8+IL-13+ T cells in the lung, whereas sensitized OT-1 mice that received primed CD4+ T cells just before challenge failed to develop these responses. Sensitized CD8-deficient mice that received CD8+ T cells from OT-1 mice that received naive CD4+ T cells before sensitization increased AHR and eosinophil numbers in bronchoalveolar lavage fluid when challenged with allergen. In contrast, sensitized CD8-deficient mice receiving CD8+ T cells from OT-1 mice without CD4+ T cells developed reduced AHR and eosinophil numbers in bronchoalveolar lavage fluid when challenged. These data suggest that interactions between CD4+ and CD8+ T cells, in part through IL-4 during the sensitization phase, are essential to the development of CD8+IL-13+ T cell-dependent AHR and airway allergic inflammation.

In vivo splenic CD11c cells downregulate CD4 T-cell response thereby decreasing systemic immunity to gene-modified tumour cell vaccine

One of the factors influencing the efficacy of tumour cell vaccines is the site of immunization. We have shown previously that gene-modified vaccines delivered directly inside the spleen induced antigen cross-presentation by splenic antigen-presenting cells (not B cells). Here, we examined the interaction between splenic CD11c(+) cells and antigen-specific CD4(+) T cells. We used tumour cells expressing ovalbumin (OVA), a situation where CD4(+) T-cell help is required for the generation of a cytotoxic T lymphocyte response. Using in vivo bioluminescence imaging of luciferase-expressing EL4-OVA cells, we could demonstrate that tumour cells were located exclusively inside the spleen following intrasplenic injection. We showed that after intrasplenic immunization with T/SA-OVA cells, splenic class I(+) class II(+) CD11c(+) cells engulfed and presented in vivo the OVA class I-restricted peptide SIINFEKL. However, in vivo previously adoptively transferred 5,6-carboxy-succinimidyl-fluorescein-ester-labelled transgenic CD4(+)KJI-26(+) cells specific for the class II OVA(323-339) peptide underwent abortive proliferation in the spleen. These CD4(+)KJI-26(+) cells were only transiently activated and produced IL-10 and IL-4 and not IFN-gamma. It appears that splenic CD11c(+) cells can downregulate splenic specific CD4(+) T-cell response thereby leading to a decrease in antitumour systemic immunity.

Pathways of helper CD4 T cell allorecognition in generating alloantibody and CD8 T cell alloimmunity

BACKGROUND

The relative contributions of the "direct" and "indirect" pathways of CD4 T cell allorecognition in providing help for generating effective humoral and CD8 T cell alloimmunity remain unclear. Here, the generation of alloantibody and cytotoxic CD8 T cell responses to a vascularized allograft were examined in a murine adoptive-transfer model in which help could only be provided by transferred CD4 T cells recognizing alloantigen exclusively through the direct pathway.

METHODS

Rejection kinetics and the development of alloantibody and cytotoxic CD8 T cell responses to MHC-mismatched H-2d heart grafts were compared when CD4 T cell help was present (wild-type H-2d recipients), or absent (CD4 T cell deficient, MHC class II-/- H-2b recipients [B6CII-/-]), or available only through the direct pathway (B6CII-/- mice reconstituted with wild-type CD4 T cells).

RESULTS

BALB/c allografts were rejected by B6 mice rapidly (median survival time [MST] 7 days) with strong CD8 T cell effector and alloantibody responses, but were rejected by B6CII-/- mice more slowly (MST 23 days), with markedly reduced CD8 T cell responses and no detectable alloantibody. CD4 T cell reconstitution of B6CII-/- recipients accelerated heart graft rejection to near that of wild-type recipients (MST 13 days), with complete restoration of cytotoxic CD8 T cell responses but without detectable IgM or IgG alloantibody.

CONCLUSIONS

Different pathways of helper T cell allorecognition are responsible for generating humoral and CD8 T cell alloimmunity. CD4 T cell help provided exclusively through the direct pathway generates strong cytotoxic CD8 T cell responses that effect rapid heart graft rejection.

In vitro induction of immune responses to shared tumor-associated antigens in rhabdomyosarcoma

PURPOSE

Currently, novel therapies to improve survival of patients with rhabdomyosarcoma (RMS) are being investigated. One of the new approaches involves immunotherapy using tumor-specific T-lymphocytes. An effective prolonged immune-mediated response against tumor cells is dependent upon the response of helper T-lymphocytes (HTLs) to tumor-associated antigens in the presence of histocompatibility lymphocyte antigen surface proteins.

METHODS

Rhabdomyosarcoma tumor lysate-pulsed human dendritic cells were used to stimulate HTL precursors (naive CD4+ T-cells) in vitro. After 3 rounds of antigen stimulation with antigen-presenting cells, the T-cells were tested for reactivity (T-cell proliferation assays) against a large panel of tumor lysate-pulsed autologous antigen-presenting cells.

RESULTS

Using peripheral blood mononuclear cells from normal naive donors, we have been able to generate HTL clones that recognize and proliferate to multiple tumor cell lines. The HTLs were induced using lysate from a single alveolar RMS tumor cell line (RMS13). The clones generated recognized all of the alveolar RMS cell lines (RMS13, Rh18, Rh28, Rh30, and Rh41), prostate cancer cell lines (LNCAP and LAPC4), melanoma cell lines (Mel 624 and G361), and breast cancer cell line (SKBR3). Helper T-lymphocytes recognition was also confirmed by interferon-gamma production. The clones did not recognize colon, lymphoma, ovarian carcinoma, ERMS or Epstein-Barr virus (EBV) transformed B-cells. This recognition was histocompatibility lymphocyte antigen class II restricted and was not an allogeneic response.

CONCLUSION

The results of this work demonstrate that HTLs, exposed to RMS lysate, are able to recognize and respond to a broad range of tumor types suggesting that a common antigen exist among these different tumors. These findings suggest novel treatment strategies for patients with RMS using tumor lysate to induce antitumor immune responses.

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.