CD28, TNF receptor, and IL-12 are critical for CD4-independent cross-priming of therapeutic antitumor CD8+ T cells

HMGB1 released from intestinal epithelia damaged by cholera toxin adjuvant contributes to activation of mucosal dendritic cells and induction of intestinal cytotoxic T lymphocytes and IgA

Cholera toxin (CT) is a potent mucosal adjuvant and oral administration of ovalbumin (OVA) antigens plus CT induces OVA-specific CD8+ cytotoxic T lymphocytes (CTLs) and IgA production in intestinal mucosa. However, the mechanisms of induction of these immune responses remain unknown. Intestinal OVA-specific CD8+ CTLs were not induced by oral administration of the CT active (CTA) or CT binding (CTB) subunit as an adjuvant and CD11c+ DCs were involved in cross-priming of intestinal CTLs. CD8+CD103+CD11c+CD11b-DCs and DCIR2+CD103+CD11c+CD11b+ DCs were distributed in the intestinal lamina propria and mesenteric lymph nodes, both DC subsets expressed DEC-205, and the expression of co-stimulatory molecules such as CD80 and CD86 was enhanced in both DC subsets after oral administration of intact CT but not the CTA or CTB subunit. Intestinal DCs activated by the oral administration of OVA plus CT cross-presented OVA antigens and DCs that captured OVA antigen through DEC-205, but not DCIR2, could cross-present antigen. We found that oral administration of intact CT, but not the CTA or CTB subunit, enhanced cell death, cytoplasmic expression of high-mobility group box 1 protein (HMGB1) in epithelial cell adhesion molecule (EpCAM)+CD45- intestinal epithelial cells (IECs), and HMGB1 levels in fecal extracts. HMGB1 dose-dependently enhanced the expression of CD80 and CD86 on DCs in vitro, and intravenous or oral administration of glycyrrhizin, an HMGB1 inhibitor, significantly suppressed activation of mucosal DCs and induction of intestinal OVA-specific CTLs and IgA by oral CT administration. These results showed that oral administration of intact CT triggers epithelial cell death in the gut and the release of HMGB1 from damaged IECs, and that the released HMGB1 may mediate activation of mucosal DCs and induction of CTLs and IgA in the intestine.

Tumor-specific CD4+ T cells maintain effector and memory tumor-specific CD8+ T cells

Immunotherapies that augment antitumor T cells have had recent success for treating patients with cancer. Here we examined whether tumor-specific CD4(+) T cells enhance CD8(+) T-cell adoptive immunotherapy in a lymphopenic environment. Our model employed physiological doses of tyrosinase-related protein 1-specific CD4(+) transgenic T cells-CD4(+) T cells and pmel-CD8(+) T cells that when transferred individually were subtherapeutic; however, when transferred together provided significant (p ≤ 0.001) therapeutic efficacy. Therapeutic efficacy correlated with increased numbers of effector and memory CD8(+) T cells with tumor-specific cytokine expression. When combined with CD4(+) T cells, transfer of total (naïve and effector) or effector CD8(+) T cells were highly effective, suggesting CD4(+) T cells can help mediate therapeutic effects by maintaining function of activated CD8(+) T cells. In addition, CD4(+) T cells had a pronounced effect in the early posttransfer period, as their elimination within the first 3 days significantly (p < 0.001) reduced therapeutic efficacy. The CD8(+) T cells recovered from mice treated with both CD8(+) and CD4(+) T cells had decreased expression of PD-1 and PD-1-blockade enhanced the therapeutic efficacy of pmel-CD8 alone, suggesting that CD4(+) T cells help reduce CD8(+) T-cell exhaustion. These data support combining immunotherapies that elicit both tumor-specific CD4(+) and CD8(+) T cells for treatment of patients with cancer.

Disruption of TGF-beta signaling prevents the generation of tumor-sensitized regulatory T cells and facilitates therapeutic antitumor immunity

Regulatory T (Treg) cells represent a major roadblock to the induction of antitumor immunity through vaccine approaches. TGF-beta is a cytokine implicated in the generation and maintenance of Treg cells, as well as in their suppressive function. These experiments examined whether the generation of tumor-sensitized Treg cells was TGF-beta dependent and evaluated whether TGF-beta produced by Treg cells blocked the priming of tumor-specific T cells in vaccinated reconstituted lymphopenic mice. We show that tumor-sensitized Treg cells (CD25(+)/FoxP3(+)) obtained from tumor-bearing mice block the generation of tumor-specific T cells in reconstituted lymphopenic mice. Strikingly, this suppression is absent if tumor-sensitized Treg cells are acquired from tumor-bearing mice expressing the dominant-negative TGFbetaRII in T cells. This loss of suppression was a result of the crucial role of TGF-beta in generating tumor-sensitized Treg cells, and not due to the insensitivity of naive or tumor-primed effector T cells to the direct suppressive influence of TGF-beta. We conclude that blocking TGF-beta in a tumor-bearing host can inhibit the induction of highly suppressive tumor-sensitized Treg cells. These data suggest that an integrative strategy combining "up-front" Treg cell ablation followed by vaccination and TGF-beta blockade may limit generation of new tumor-sensitized Treg cells and improve the generation of therapeutic immune responses in patients with cancer.

Contribution of IRF-3 mediated IFNbeta production to DNA vaccine dependent cellular immune responses

The mechanism(s) by which DNA vaccines activate Ag-specific cellular immune responses is incompletely understood. Current findings indicate that IRF-3 plays an important role in this process. The IRF-3 dependent signaling pathway is triggered by the presence of intracytoplasmic DNA, and culminates in the production of type I IFNs. DNA vaccination of IRF-3 KO mice elicits a strong Ag-specific humoral response, yet CD4 and CD8 T cell responses (including the production of Th1, Th2 and Th 17 cytokines) are severely impaired. Although expression of the immunogenic protein encoded by the DNA vaccine was similar in IRF-3 KO vs wild type mice, antigen presentation was severely impaired in the KO animals. This defect was remedied by the co-delivery of an IFNbeta encoding plasmid. These findings suggest that the IRF-3/IFNbeta pathways are key to the induction of cellular immunity following DNA vaccination.

Tumor necrosis factor alpha protects against lethal West Nile virus infection by promoting trafficking of mononuclear leukocytes into the central nervous system

West Nile virus (WNV) is a neurotropic flavivirus that has emerged globally as a significant cause of viral encephalitis in humans, especially in immunocompromised individuals. Previous studies have shown essential protective roles for antiviral cytokines (e.g., alpha interferon [IFN-alpha] and IFN-gamma) against WNV in mice. However, studies using cell culture offer conflicting answers regarding whether tumor necrosis factor alpha (TNF-alpha) has an anti-WNV function. To test the biological significance of TNF-alpha against WNV in vivo, experiments were performed with TNF receptor-1 (TNF-R1)-deficient and TNF-alpha-depleted C57BL/6 mice. TNF-R1(-/-) mice had enhanced mortality and decreased survival time after WNV infection compared to congenic wild-type mice. Consistent with this, administration of a neutralizing anti-TNF-alpha monoclonal antibody also decreased survival after WNV infection. Relatively small differences in viral burdens in peripheral tissues of TNF-R1(-/-) mice were observed, and this occurrence correlated with a modest antiviral effect of TNF-alpha on primary macrophages but not dendritic cells. In contrast, the viral titers detected in the central nervous systems of TNF-R1(-/-) mice were significantly increased compared to those of wild-type mice, although TNF-alpha did not have a direct antiviral effect in primary neuron cultures. Whereas no defect in priming of adaptive B- and T-cell responses in TNF-R1(-/-) mice was observed, there were significant reductions in accumulations of CD8+ T cells and macrophages in the brain. Our data are most consistent with a model in which interaction of TNF-alpha with TNF-R1 protects against WNV infection by regulating migration of protective inflammatory cells into the brain during acute infection.

TNF-alpha is critical for antitumor but not antiviral T cell immunity in mice

TNF-alpha antagonists are widely used in the treatment of inflammatory and autoimmune diseases, but their use is associated with reactivation of latent infections. This highlights the importance of TNF-alpha in immunity to certain pathogens and raises concerns that critical aspects of immune function are impaired in its absence. Unfortunately, the role of TNF-alpha in the regulation of T cell responses is clouded by a myriad of contradictory reports. Here, we show a role for TNF-alpha and its receptors, TNFR1 and TNFR2, specifically in antitumor immunity. TNF-alpha-deficient mice exhibited normal antiviral responses associated with strong inflammation. However, TNF-alpha/TNFR1-mediated signals on APCs and TNF-alpha/TNFR2 signals on T cells were critically required for effective priming, proliferation, and recruitment of tumor-specific T cells. Furthermore, in the absence of TNF-alpha signaling, tumor immune surveillance was severely abrogated. Finally, treatment with a CD40 agonist alone or in combination with TLR2 stimuli was able to rescue proliferation of TNF-alpha-deficient T cells. Therefore, TNF-alpha signaling may be required only for immune responses in conditions of limited immunostimulatory capacity, such as tumor surveillance. Importantly, these results suggest that prolonged continuous TNF-alpha blockade in patients may have long-term complications, including potential tumor development or progression.

Mechanism of third signals provided by IL-12 and OX-40R ligation in eliciting therapeutic immunity following dendritic-tumor fusion vaccination

Dendritic-tumor heterokaryons generated by electrofusion are highly immunogenic. In animal studies, a single vaccination was therapeutic for tumors established in the lung, skin, and brain. However, effective therapy required a third signal which could be provided by exogenous IL-12 or the agonistic anti-OX-40R monoclonal antibody (mAb). In this study, we investigated the mechanism and mode of actions of these two seemingly distinct adjuvants. In immunotherapy of the MCA205 sarcoma, administration of the neutralizing anti-IL-12 mAb nearly completely blocked the adjuvant effect of IL-12, but had minimal inhibitory effects on anti-OX-40R mAb. By contrast, in vivo administration of the antagonistic anti-OX-40L mAb inhibited the adjuvant effects of both IL-12 and anti-OX-40R mAb. Thus, a common pathway of endogenous OX-40 interaction is critical for the development of a therapeutic immune response. Analysis of the third signal mechanism revealed that in the absence of an adjuvant, vaccination with fusion hybrids led to IL-10 production without eliciting IFN-gamma secreting cells. The addition of IL-12 to vaccination suppressed IL-10 production and initiated sensitization of specific IFN-gamma secreting cells, resulting in a type 1-like antitumor immunity. These findings underscore the significance of the third signal in the design of dendritic cell-based cancer vaccines.

Intratumoral injection of dendritic cells in combination with local hyperthermia induces systemic antitumor effect in patients with advanced melanoma

Dendritic cells (DC) are potent antigen-presenting cells that can present tumor antigens chaperoned by heat shock proteins (HSPs), while local hyperthermia (LHT) can increase the expression of HSPs. In this study, we determine if intratumoral injection of immature DC after LHT (LHT+IT-DC) induces systemic antitumor immunity in patients with advanced melanoma, and investigate the potential immunological mechanisms involved in the treatments. Patients were randomly assigned to intratumoral administration of autologous immature DC triweekly, with (LHT+IT-DC, arm A, n = 9) or without (IT-DC, arm B, n = 9) LHT. Our results showed that there were no grade 3/4 toxicities. The time to progress (TTP) of arm A was 5 months, significantly longer than that in arm B (2 months, p < 0.05). However, the overall survival time had no statistical difference (13 months vs. 6 months, p > 0.05) between the 2 groups. Our ELISPOT assay showed a significantly increased melanoma-specific IFN-gamma production in arm A, suggesting that LHT+IT-DC was more effective in the induction of cytotoxic T lymphocytes (CTL) than IT-DC alone. Furthermore, we detected an increased HSPs expression 4 hr after the first LHT, an enhanced Th1/Th2 chemokines production 24 hr after the first LHT+IT-DC treatment, a promoted migration of DC to afferent lymph nodes, and a decreased infiltration of regulatory T cells (CD4(+)CD25(+)) and an increased infiltration of active CTL (CD8(+)CD28(+)) 48 hr after the third DC injection in arm A patients. Therefore, LHT+IT-DC can induce effective specific antitumor immunity and facilitate a Th1-polarized immune response in patients with advanced melanoma.

Efficacy of GM-CSF-producing tumor vaccine after docetaxel chemotherapy in mice bearing established Lewis lung carcinoma

In this report, we evaluated the efficacy of a GM-CSF-producing tumor vaccine given before and after docetaxel in mice bearing established lung tumors. Mice bearing established 3LL tumors were treated with docetaxel and tumor vaccines transduced with either control or GM-CSF adenoviral vectors. Docetaxel (5-20 mg/kg) treatment alone had only a minimal effect on growth of established 3LL tumors in vivo, although docetaxel was cytotoxic to 3LL cells in vitro. When mice bearing established 3LL tumors were pretreated with docetaxel followed by vaccination with irradiated GM-CSF- transduced 3LL tumor cells, significant tumor regression and prolonged survival were observed compared with chemotherapy alone. Delaying docetaxel treatment until after tumor vaccination abrogated the vaccine's anti-tumor effects. Mice that survived treatment were able to resist a lethal rechallenge of 3LL tumor cells. Memory CTL specific for an epitope (MUT-1) derived from 3LL were detected in surviving mice. Docetaxel induced a mild lymphodepletion in mice, both CD4 and CD8 subsets were reduced in LN and spleens. Interestingly, docetaxel also diminished the number of memory CD8+ T cells (CD122+) and possible CD4+ CD25+ Foxp3+ natural Treg cells. Docetaxel treatment did not affect antigen-driven proliferation of naive T cells but significantly promoted survival of activated T cells. Thus, augmentation of vaccine induced antitumor immunity in docetaxel-treated mice primarily due to the enhanced survival of antigen-experienced T cells.

Immunogenicity of Liposomes Containing Lipid Core Peptides and the Adjuvant Quil A

PURPOSE

The purpose of this study was to investigate the immunogenicity of liposomes containing mannosylated lipid core peptide (manLCP) constructs, both in vitro and in vivo, with or without the addition of the immune stimulating adjuvant Quil A.

METHODS

Mouse bone marrow dendritic cells (BMDC) were cultured with liposome formulations for 48 h, and the resulting level of BMDC activation was determined by flow cytometry. BMDC pulsed with liposome formulations were incubated with 5,6-carboxyfluoroscein diacetate succinimidyl ester-labeled T cells for 72 h and the resulting T cell proliferation was determined by flow cytometry. To investigate the immunogenicity of formulations in vivo, groups of C57Bl/6J mice were immunized by subcutaneous injection, and the resulting antigen-specific cytotoxic and protective immune responses toward tumor challenge evaluated.

RESULTS

Despite being unable to demonstrate the activation of BMDC, BMDC pulsed with liposomes containing manLCP constructs were able to stimulate the proliferation of naïve T cells in vitro. However, in vivo only liposomes containing both manLCP and Quil A were able to stimulate a strong antigen-specific cytotoxic immune response. Liposomes containing manLCP and Quil A within the same particle were able to protect against the growth of tumor cells to a similar level as if the antigen was administered in alum with CD4 help.

CONCLUSION

ManLCPs administered in liposomes are able to stimulate strong cytotoxic and protective immune responses if Quil A is also incorporated as an adjuvant.

The role of human glioma-infiltrating microglia/macrophages in mediating antitumor immune responses

Little is known about the immune performance and interactions of CNS microglia/macrophages in glioma patients. We found that microglia/macrophages were the predominant immune cell infiltrating gliomas ( approximately 1% of total cells); others identified were myeloid dendritic cells (DCs), plasmacytoid DCs, and T cells. We isolated and analyzed the immune functions of CD11b/c+CD45+ glioma-infiltrating microglia/macrophages (GIMs) from postoperative tissue specimens of glioma patients. Although GIMs expressed substantial levels of Toll-like receptors (TLRs), they did not appear stimulated to produce pro-inflammatory cytokines (tumor necrosis factor alpha, interleukin 1, or interleukin 6), and in vitro, lipopolysaccharides could bind TLR-4 but could not induce GIM-mediated T-cell proliferation. Despite surface major histocompatibility complex class II expression, they lacked expression of the costimulatory molecules CD86, CD80, and CD40 critical for T-cell activation. Ex vivo, we demonstrate a corresponding lack of effector/activated T cells, as glioma-infiltrating CD8+ T cells were phenotypically CD8+CD25-. By contrast, there was a prominent population of regulatory CD4 T cells (CD4+CD25+FOXP3+) infiltrating the tumor. We conclude that while GIMs may have a few intact innate immune functions, their capacity to be stimulated via TLRs, secrete cytokines, upregulate costimulatory molecules, and in turn activate antitumor effector T cells is not sufficient to initiate immune responses. Furthermore, the presence of regulatory T cells may also contribute to the lack of effective immune activation against malignant human gliomas.

CD28-mediated costimulation impacts on the differentiation of DC vaccination-induced T cell responses

Costimulatory signals such as the ones elicited by CD28/B7 receptor ligation are essential for efficient T cell activation but their role in anti-tumour immune responses remains controversial. In the present study we compared the efficacy of DC vaccination-induced melanoma specific T cell responses to control the development of subcutaneous tumours and pulmonary metastases in CD28-deficient mice. Lack of CD28-mediated costimulatory signals accelerated tumour development in both model systems and also the load of pulmonary metastases was strongly increased by the end of the observation period. To scrutinize whether lack of CD28 signalling influences priming, homing or effector function of Trp-2(180-188)/K(b)-reactive T cells we investigated the characteristics of circulating and tumour infiltrating T cells. No difference in the frequency of Trp-2(180-188)/K(b)-reactive CD8+ T cells could be demonstrated among the cellular infiltrate of subcutaneous tumours after DC vaccination between both genotypes. However, the number of IFN-gamma-producing Trp-2-reactive cells was substantially lower in CD28-deficient mice and also their cytotoxicity was reduced. This suggests that CD28-mediated costimulatory signals are essential for differentiation of functional tumour-specific CD8+ T-effector cells despite having no impact on the homing of primed CD8+ T cells.

Prolonged Culture of Vaccine-Primed Lymphocytes Results in Decreased Antitumor Killing and Change in Cytokine Secretion

Adoptive transfer of effector T cells has been used successfully to eliminate metastases in animal models. Because antitumor activity depends on the number of effector cells transferred, some human trials have used in vitro-repetitive activation and expansion techniques to increase cell number. We hypothesized that the prolonged culture period might contribute to the lack of human trial success by decreasing the potency of the effector T cells. Lymph nodes draining a progressively growing murine melanoma tumor transduced to secrete granulocyte/macrophage colony-stimulating factor were harvested and activated in vitro with anti-CD3 monoclonal antibody followed by expansion in IL-2 for a total of 5 days in culture. Some lymphocytes were reactivated and further expanded for a total of 9 days in culture. In vivo activity of the effector T cells was measured by the reduction in lung metastases and is shown to be dose dependent. The prolonged culture period resulted in nearly 3-fold more T cells but at least 8-fold less antitumor activity. This was accompanied by decreased secretion of the proinflammatory cytokine, IFN-gamma, and increased secretion of the anti-inflammatory cytokine, IL-10. Thus, although increased cell number is important to maximize the effectiveness of adoptive immunotherapy, some culture conditions may actually be counterproductive in that decreases in cell potency can outweigh the benefits of increased cell numbers. The T-cell cytokine secretion pattern predicts decreased effector cell function and may explain the decreased antitumor effect.

ISCOM based vaccines for cancer immunotherapy

Immunostimulating complex (ISCOM) vaccines are particulate antigen delivery vehicles composed of saponin, cholesterol, phospholipid and immunogen. Here we illustrate that ISCOM-based vaccines represent an attractive modality for the development of anti-cancer vaccines. Using murine models and a model cancer antigen, ISCOM vaccines were shown to induce potent CD8 T cell responses, to mediate protection in three different tumor models, to promote Th1-biased immunity, and to induce CD8 T cell responses in the absence of CD4+ T cell help. The former three activities were also found to be substantially improved when the vaccine antigen was associated with the ISCOM structure. Furthermore, the presence in vivo of pre-existing antibodies against the vaccine antigen did not inhibit CD8 T cell induction by the ISCOM vaccine. Although vaccination was effective against challenge with vaccine-antigen expressing tumors, no activity against neighboring vaccine-antigen negative tumor cells was observed, indicating that determinant spreading or bystander activity does not lead to significant anti-cancer activity.

The HIV-1 HLA-A2-SLYNTVATL is a help-independent CTL epitope

The CTL response to the HLA-A*0201-restricted, HIV-1 p17 Gag(77-85) epitope (SLYNTVATL; SL9) has been extensively studied in patients. Although this reactivity is exceptionally prominent in chronically infected patients and inversely correlated to viral load, SL9-specific CTLs (SL9-CTLs) are rarely detected in acute infection. To explore the cellular basis for this unusual manifestation, SL9-CTLs primed ex vivo from naive circulating CD8(+) T cells of healthy, seronegative donors were generated and characterized. SL9 appeared to differ from other well-studied A*0201-restricted epitopes in several significant respects. In contrast to published reports for influenza and melanoma peptides and the HIV gag IV9 epitope studied here in parallel, SL9-CTLs were primed by immature but not mature autologous dendritic cells. Highly activated SL9-CTLs produce sufficient autocrine mediators to sustain clonal expansion and CTL differentiation for months without CD4(+) T cells or exogenous IL-2. Moreover, SL9-CTLs were sensitive to paracrine IL-2-induced apoptosis. IL-2 independence and sensitivity to paracrine IL-2 were also characteristic of SL9-CTLs immunized by dendritic cells transduced by a nonreplicating lentiviral vector encoding full-length Gag. In vitro-primed SL9-CTLs resembled those derived from patients in degeneracy of recognition and functional avidities for both SL9 and its natural mutations. Together, these data show that SL9 is a highly immunogenic, help-independent HIV epitope. The scarcity of SL9-CTLs in acute infection may result from cytokine-induced apoptosis with the intense activation of the innate immunity. In contrast, SL9-CTLs that constitutively produce autocrine help would predominate during CD4-diminished chronic infection.

Donor APCs are required for maximal GVHD but not for GVL

Graft-versus-host disease (GVHD) is a major source of morbidity in allogenic stem cell transplantation. We previously showed that recipient antigen-presenting cells (APCs) are required for CD8-dependent GVHD in a mouse model across only minor histocompatibility antigens (minor H antigens). However, these studies did not address the function of donor-derived APCs after GVHD is initiated. Here we show that GVHD develops in recipients of donor major histocompatibility complex class I-deficient (MHC I(-)) bone marrow. Thus, after initial priming, CD8 cells caused GVHD without a further requirement for hematopoietic APCs, indicating that host APCs are necessary and sufficient for GHVD. Nonetheless, GVHD was less severe in recipients of MHC I(-) bone marrow. Therefore, once initiated, GVHD is intensified by donor-derived cells, most probably donor APCs cross-priming alloreactive CD8 cells. Nevertheless, donor APCs were not required for CD8-mediated graft-versus-leukemia (GVL) against a mouse model of chronic-phase chronic myelogenous leukemia. These studies identify donor APCs as a new target for treating GVHD, which may preserve GVL.

Mechanism of allorecognition and skin graft rejection in CD28 and CD40 ligand double-deficient mice

BACKGROUND

It has been shown that simultaneous blockade of CD28- and CD40-mediated costimulatory signals significantly prolongs allograft survival. Although these results led to an expectation of the establishment of specific immunotolerant therapy for organ transplantation, it became evident that these treatments rarely resulted in indefinite allograft survival. To uncover the mechanisms underlying these costimulation blockade-resistant allograft rejections, we studied the process of allogenic skin graft rejection in CD28 and CD40 ligand (L) double-deficient (double-knockout [dKO]) mice.

METHODS

Skin grafts from BALB/c or BALB.B mice were transplanted to C57BL/6 background dKO mice. The frequency of CD4+ and CD8+ T cells responding to alloantigens presented by direct or indirect pathways were defined by the use of a cytostaining assay.

RESULTS

BALB/c skin grafts were rapidly rejected by dKO mice. This CD28 and CD40L independent allograft rejection was inhibited by the depletion of CD8+ T cells. In vitro studies indicated that CD8+ T cells from BALB/c skin-grafted dKO mice responded to donor antigen presented only by the direct pathway. Unlike major histocompatibility complex (MHC)-mismatched donors, allogenic skin grafts from MHC-matched donors were accepted by dKO mice.

CONCLUSION

In the absence of CD28 and CD40 costimulatory signals, CD8+ T cells recognize MHC antigens by the direct pathway, resulting in the rejection of skin grafts from MHC-mismatched donors. In contrast, MHC-matched and non-MHC-mismatched donor skin grafts indefinitely survive in dKO mice. These results indicated that donor-host MHC matching may still be critical to costimulation blockade therapy for organ transplantation.