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

A Novel Aza-MBP Altered Peptide Ligand for the Treatment of Experimental Autoimmune Encephalomyelitis

Myelin basic protein (MBP) is a major target of T cells in lesions of multiple sclerosis (MS) patients and its animal model, experimental autoimmune encephalomyelitis (EAE). Interactions between the major histocompatibility complex II containing antigenic peptides and the T cell receptor activate CD4+ T cells that perpetuate EAE and MS. Previously reported data has shown that treating with an altered peptide ligand (APL) in which the normal antigenic peptide sequence of MBP has been slightly changed at T cell contact positions is helpful in reducing disease in both rodents and humans. The use of natural peptides, which are susceptible to protease degradation, requires high concentrations that can create hypersensitivity reactions. Our hypothesis is that APL containing aza substitutions, CH(R)-N- > N(R)N, could lead to improved protease resistance, reduced clinical disease scores, and a shift in T cell profile. In this study, several aza-APLs and control peptides were synthesized and screened for the best aza-APL candidate (3aza-APL) based on dissociation half time from major histocompatibility complex (MHC) class II, induction of IL-2 response, and resistance to degradation by proteases. The efficacy was then tested in vivo. Results indicate that 3aza-APL is superior to currently available APLs in terms of protease resistance and disease suppression in EAE mice. The 3aza-APL induced anti-inflammatory immune responses by altering key transcription factors and cytokine genes which regulate T cell subpopulations. These data suggest that the novel 3aza-APL has increased protease resistance property and is effective in reducing clinical and physiological signs of disease in EAE animals.

Chemokines as Cancer Vaccine Adjuvants

We are witnessing a new era of immune-mediated cancer therapies and vaccine development. As the field of cancer vaccines advances into clinical trials, overcoming low immunogenicity is a limiting step in achieving full success of this therapeutic approach. Recent discoveries in the many biological roles of chemokines in tumor immunology allow their exploitation in enhancing recruitment of antigen presenting cells (APCs) and effector cells to appropriate anatomical sites. This knowledge, combined with advances in gene therapy and virology, allows researchers to employ chemokines as potential vaccine adjuvants. This review will focus on recent murine and human studies that use chemokines as therapeutic anti-cancer vaccine adjuvants.

Simultaneous activation of T helper function can augment the potency of dendritic cell-based cancer immunotherapy

PURPOSE

Simultaneous activation of T helper 1 (Th1) cell function has crucial roles in induction of potent cytotoxic T lymphocyte (CTL) responses in cancer immunotherapy. Here, we investigated whether dendritic cell (DC)-based vaccines loaded with both tumor-associated antigen (TAA)-derived MHC class I and pan-MHC class II peptides could elicit more potent CTL responses through simultaneous activation of Th1 function and reduction in CD4(+) regulatory T (Treg) cell proliferation.

METHODS

C57BL/6 mice bearing LLC1, a mouse Lewis lung cancer cell line, were subcutaneously administered DCs loaded with both LLC-derived MHC class I (MUT1&2) and LLC-unrelated pan-MHC class II (PADRE) peptides (DC-MUT1&2-PADRE). In assays using samples from advanced lung cancer patients, peripheral blood mononuclear cells were stimulated with autologous DCs loaded with both MUC1 MHC class I and PADRE peptides (DC-MUC1-PADRE) in vitro. Subsequently, TAA-specific CTL responses and the population of CD4(+) Treg cells were analyzed.

RESULTS

The population of spleen CD4(+) PADRE-specific cells producing interferon-gamma (IFNγ) was significantly increased by DC-MUT1&2-PADRE administration. Vaccinations with DC-MUT1&2-PADRE decreased the population of CD4(+) Treg cells in spleen and augmented CTL responses, effectively leading to suppression of tumor growth. In assays with human samples, CD4(+) Treg cells were induced less frequently, and MUC1-specific cytotoxicity was enhanced by stimulation with DC-MUC1-PADRE compared with that by stimulation with DC-MUC1 alone.

CONCLUSIONS

Simultaneous activation of Th1 function by DCs loaded with both TAA-derived MHC class I and PADRE peptides augments TAA-specific CTL responses while reducing Treg cell proliferation.

Abeta DNA vaccination for Alzheimer's disease: focus on disease prevention

Pre-clinical and clinical data suggest that the development of a safe and effective anti-amyloid-beta (Abeta) immunotherapy for Alzheimer's disease (AD) will require therapeutic levels of anti-Abeta antibodies, while avoiding proinflammatory adjuvants and autoreactive T cells which may increase the incidence of adverse events in the elderly population targeted to receive immunotherapy. The first active immunization clinical trial with AN1792 in AD patients was halted when a subset of patients developed meningoencephalitis. The first passive immunotherapy trial with bapineuzumab, a humanized monoclonal antibody against the end terminus of Abeta, also encountered some dose dependent adverse events during the Phase II portion of the study, vasogenic edema in 12 cases, which were significantly over represented in ApoE4 carriers. The proposed remedy is to treat future patients with lower doses, particularly in the ApoE4 carriers. Currently there are at least five ongoing anti-Abeta immunotherapy clinical trials. Three of the clinical trials use humanized monoclonal antibodies, which are expensive and require repeated dosing to maintain therapeutic levels of the antibodies in the patient. However in the event of an adverse response to the passive therapy antibody delivery can simply be halted, which may provide a resolution to the problem. Because at this point we cannot readily identify individuals in the preclinical or prodromal stages of AD pathogenesis, passive immunotherapy is reserved for those that already have clinical symptoms. Unfortunately those individuals have by that point accumulated substantial neuropathology in affected regions of the brain. Moreover, if Abeta pathology drives tau pathology as reported in several transgenic animal models, and once established if tau pathology can become self propagating, then early intervention with anti-Abeta immunotherapy may be critical for favorable clinical outcomes. On the other hand, active immunization has several significant advantages, including lower cost and the typical immunization protocol should be much less intrusive to the patient relative to passive therapy, in the advent of Abeta-antibody immune complex-induced adverse events the patients will have to receive immuno-supperssive therapy for an extended period until the anti Abeta antibody levels drop naturally as the effects of the vaccine decays over time. Obviously, improvements in vaccine design are needed to improve both the safety, as well as the efficacy of anti-Abeta immunotherapy. The focus of this review is on the advantages of DNA vaccination for anti-Abeta immunotherapy, and the major hurdles, such as immunosenescence, selection of appropriate molecular adjuvants, universal T cell epitopes, and possibly a polyepitope design based on utilizing existing memory T cells in the general population that were generated in response to childhood or seasonal vaccines, as well as various infections. Ultimately, we believe that the further refinement of our AD DNA epitope vaccines, possibly combined with a prime boost regime will facilitate translation to human clinical trials in either very early AD, or preferably in preclinical stage individuals identified by validated AD biomarkers.

Targeting the neonatal fc receptor for antigen delivery using engineered fc fragments

The development of approaches for Ag delivery to the appropriate subcellular compartments of APCs and the optimization of Ag persistence are both of central relevance for the induction of protective immunity or tolerance. The expression of the neonatal Fc receptor, FcRn, in APCs and its localization to the endosomal system suggest that it might serve as a target for Ag delivery using engineered Fc fragment-epitope fusions. The impact of FcRn binding characteristics of an Fc fragment on in vivo persistence allows this property to also be modulated. We have therefore generated recombinant Fc (mouse IgG1-derived) fusions containing the N-terminal epitope of myelin basic protein that is associated with experimental autoimmune encephalomyelitis in H-2(u) mice. The Fc fragments have distinct binding properties for FcRn that result in differences in intracellular trafficking and in vivo half-lives, allowing the impact of these characteristics on CD4(+) T cell responses to be evaluated. To dissect the relative roles of FcRn and the "classical" FcgammaRs in Ag delivery, analogous aglycosylated Fc-MBP fusions have been generated. We show that engineered Fc fragments with increased affinities for FcRn at pH 6.0-7.4 are more effective in delivering Ag to FcRn-expressing APCs in vitro relative to their lower affinity counterparts. However, higher affinity of the FcRn-Fc interaction at near neutral pH results in decreased in vivo persistence. The trade-off between improved FcRn targeting efficiency and lower half-life becomes apparent during analyses of T cell proliferative responses in mice, particularly when Fc-MBP fusions with both FcRn and FcgammaR binding activity are used.

Mouse mammary tumor virus uses mouse but not human transferrin receptor 1 to reach a low pH compartment and infect cells

Mouse mammary tumor virus (MMTV) is a pH-dependent virus that uses mouse transferrin receptor 1 (TfR1) for entry into cells. Previous studies demonstrated that MMTV could induce pH 5-dependent fusion-from-with of mouse cells. Here we show that the MMTV envelope-mediated cell-cell fusion requires both the entry receptor and low pH (pH 5). Although expression of the MMTV envelope and TfR1 was sufficient to mediate low pH-dependent syncytia formation, virus infection required trafficking to a low pH compartment; infection was independent of cathepsin-mediated proteolysis. Human TfR1 did not support virus infection, although envelope-mediated syncytia formation occurred with human cells after pH 5 treatment and this fusion depended on TfR1 expression. However, although the MMTV envelope bound human TfR1, virus was only internalized and trafficked to a low pH compartment in cells expressing mouse TfR1. Thus, while human TfR1 supported cell-cell fusion, because it was not internalized when bound to MMTV, it did not function as an entry receptor. Our data suggest that MMTV uses TfR1 for all steps of entry: cell attachment, induction of the conformational changes in Env required for membrane fusion and internalization to an appropriate acidic compartment.

Reducing AD-like pathology in 3xTg-AD mouse model by DNA epitope vaccine - a novel immunotherapeutic strategy

BACKGROUND

The development of a safe and effective AD vaccine requires a delicate balance between providing an adequate anti-Abeta antibody response sufficient to provide therapeutic benefit, while eliminating an adverse T cell-mediated proinflammatory autoimmune response. To achieve this goal we have designed a prototype chemokine-based DNA epitope vaccine expressing a fusion protein that consists of 3 copies of the self-B cell epitope of Abeta(42) (Abeta(1-11)) , a non-self T helper cell epitope (PADRE), and macrophage-derived chemokine (MDC/CCL22) as a molecular adjuvant to promote a strong anti-inflammatory Th2 phenotype.

METHODS AND FINDINGS

We generated pMDC-3Abeta(1-11)-PADRE construct and immunized 3xTg-AD mouse model starting at age of 3-4 months old. We demonstrated that prophylactic immunizations with the DNA epitope vaccine generated a robust Th2 immune response that induced high titers of anti-Abeta antibody, which in turn inhibited accumulation of Abeta pathology in the brains of older mice. Importantly, vaccination reduced glial activation and prevented the development of behavioral deficits in aged animals without increasing the incidence of microhemorrhages.

CONCLUSIONS

Data from this transitional pre-clinical study suggest that our DNA epitope vaccine could be used as a safe and effective strategy for AD therapy. Future safety and immunology studies in large animals with the goal to achieve effective humoral immunity without adverse effects should help to translate this study to human clinical trials.

Antigen release kinetics in the phagosome are critical to cross-presentation efficiency

Cross-presentation of exogenous Ags in MHC class I molecules by dendritic cells is the underlying basis for many developing immunotherapies and vaccines. In the phagosome-to-cytosol pathway, Ags in phagocytosed particles must become freely soluble before being exported to the cytosol, but the kinetics of this process has yet to be fully appreciated. We demonstrate with a yeast vaccine model that the rate of Ag release in the phagosome directly affects cross-presentation efficiency, with an apparent time limit of approximately 25 min postphagocytosis for Ag release to be productive. Ag expressed on the yeast surface is cross-presented much more efficiently than Ag trapped in the yeast cytosol by the cell wall. The cross-presentation efficiency of yeast surface-displayed Ag can be increased by the insertion of linkers susceptible to cleavage in the early phagosome. Ags indirectly attached to yeast through Ab fragments are less efficiently cross-presented when the Ab dissociation rate is extremely slow.

Clinical utilization of chemokines to combat cancer: the double-edged sword

Chemokines are a small group of related chemo-attractant peptides that play an essential role in the homeostatic maintenance of the immune system. They control the recruitment of cells needed for the induction and activation of innate and adaptive immune responses. However, tumors also utilize chemokines to actively progress and evade immunosurveillance. In fact, chemokines are involved directly or indirectly in almost every aspect of tumorigenesis. They mediate survival and metastatic spread of tumors, promote new blood vessel formation (neovascularization) and induce an immunosuppressive microenvironment via recruitment of immunosuppressive cells. As a result, a number of therapeutic strategies have been proposed to target almost every step of the chemokine/chemokine receptor involvement in tumors. Yet, despite occasional success stories, most of them appear to be ineffective or impractical, presumably due to 'nonspecific' harm of cells needed for the elimination of tumor escapees and maintenance of immunological memory. The strategy would only be effective if it also promoted antitumor adaptive immune responses capable of combating a residual disease and tumor relapse.

Successful tumor eradication was achieved by collaboration of augmented cytotoxic activity and anti-angiogenic effects following therapeutic vaccines containing helper-activating analog-loaded dendritic cells and tumor antigen DNA

We reported previously that pigeon cytochrome c-derived peptides (Pan-IA), which bind broad ranges of MHC class II molecules efficiently, activate T helper (Th) function in mice. In an experimental model, Pan-IA DNA vaccines augmented antitumor immunity in tumor antigen-immunized mice. To elicit more potent antitumor immunity and to eradicate tumors in a therapeutic setting, Pan-IA-loaded dendritic cells (DCs) were inoculated in combination with vaccines including ovalbumin (OVA) antigen DNA in tumor-bearing mice. Seventy percent of the immunized mice survived tumor-free for at least 4 months after treatment. In contrast, mice vaccinated with OVA DNA, either with or without naïve DCs, did not eliminate the tumors and died within 5 weeks. Only in mice vaccinated with OVA DNA and Pan-IA-loaded DCs were both cytotoxic and helper responses specific for OVA induced at the spleen and tumor sites as well as at the vaccination sites. Furthermore, accumulation of OVA-specific CD4(+) and CD8(+) T lymphocytes and interferon-gamma-mediated anti-angiogenesis were observed in the tumors of these mice. Thus, the combined vaccination primed both tumor-specific cytotoxicity and helper immunity resulting in augmented tumor lysis ability and anti-angiogenic effects. This is the first report to show that most established tumors were successfully eradicated by collaboration of potent antitumor immunity and anti-angiogenic effects by vaccination with tumor antigens and helper-activating analogs. This novel vaccination strategy is broadly applicable, regardless of identifying helper epitopes in target molecules, and contributes to the development of therapeutic cancer vaccines.

Chemokine receptor targeting efficiently directs antigens to MHC class I pathways and elicits antigen-specific CD8+ T-cell responses

Chemokines are key controllers of cell trafficking and are involved in numerous pathologic and inflammatory conditions. However, the fate of a chemokine ligand, once it is endocytosed with its receptor, remains obscure. Here, using chemokine-tumor antigen fusion constructs, we demonstrate for the first time that chemokines are internalized to early/late endosomal and lysosomal compartments through a clathrin-dependent process and subsequently delivered to the cytosol for proteasomal processing, facilitating efficient cross-presentation to the TAP-1-dependent MHC class I processing pathway. These data not only elucidate the intracellular fate of chemokine ligands upon receptor uptake, but also demonstrate the superior carrier potency of chemokines for delivering self-antigens to both class I and II processing pathways to induce CD8(+) and CD4(+) T-cell responses.

Targeting antigen to CD19 on B cells efficiently activates T cells

CD19 is a B cell-surface molecule that participates as an important regulatory signaling complex for antigen bound at the surface by Ig. Triggering of CD19 through its linkage with CD21 amplifies signals transduced through the Src family kinases and modulates B cell differentiation in response to antigen. This study examines the kinetics of antigen uptake and processing of antigen directly targeted to the CD19 protein on purified B cells. We have demonstrated that the antigen internalized within minutes through CD19 forms a cap at the B cell surface and can be found within lysosomes in the cytoplasm in 90 min. B cells acquiring antigen via CD19 express elevated levels of B7-1 and B7-2 co-stimulatory molecules. Moreover, antigen-anti-CD19 complexes administered intravenously bind B cells in vivo and activate antigen-specific T cells more efficiently than non-specific uptake and in a manner similar to antigen taken up through surface IgM on B cells. This work illustrates an important and previously unrecognized mechanism for targeting proteins to B lymphocytes for antigen presentation and activation of CD4 T cells.

Activation-induced cell death limits effector function of CD4 tumor-specific T cells

A number of studies have documented a critical role for tumor-specific CD4(+) cells in the augmentation of immunotherapeutic effector mechanisms. However, in the context of an extensive tumor burden, chronic stimulation of such CD4(+) T cells often leads to the up-regulation of both Fas and Fas ligand, and coexpression of these molecules can potentially result in activation-induced cell death and the subsequent loss of effector activity. To evaluate the importance of T cell persistence in an experimental model of immunotherapy, we used DO11 Th1 cells from wild-type, Fas-deficient, and Fas ligand-deficient mice as effector populations specific for a model tumor Ag consisting of an OVA-derived transmembrane fusion protein. We found that the prolonged survival of Fas-deficient DO11 Th1 cells led to a more sustained tumor-specific response both in vitro and in vivo. Importantly, both Fas- and Fas ligand-deficient Th1 cells delayed tumor growth and cause regression of established tumors more effectively than wild-type Th1 cells, indicating that resistance to activation-induced cell death significantly enhances T cell effector activity.

Fine specificity and cross-clade reactivity of HIV type 1 Gag-specific CD4+ T cells

Despite growing evidence that HIV-1-specific CD4(+) T helper (Th) cells may play a role in the control of viremia, discrete Th cell epitopes remain poorly defined. Furthermore, it is not known whether Th cell responses generated using vaccines based on clade B virus sequences will elicit immune responses that are effective in regions of the world where non-clade B viruses predominate. To address these issues we isolated CD4(+) T cell clones from individuals with vigorous HIV-1-specific Th cell responses and identified the minimum epitopes recognized. The minimum peptide length required for induction of CD4(+) T cell proliferation, IFN-gamma secretion, and cytolytic activity ranged from 9 to 16 amino acids in the five epitopes studied. Cross-clade recognition of the defined epitopes was examined for variant peptides from clades A, B, C, D, and AE. Over half the variant epitopes (17 of 32) exhibited impaired recognition, defined as less than 50% of the IFN-gamma secretion elicited by B clade consensus sequence. There was no evidence for antagonistic activity mediated by the variant peptides, and despite strong responses there was no escape of autologous virus from Th responses in the epitopes we studied. Abrogated recognition of variant CD4(+) T cell epitopes presents a potential obstacle to vaccine development.

DNA vaccines, combining form of antigen and method of delivery to raise a spectrum of IFN-gamma and IL-4-producing CD4+ and CD8+ T cells

DNA-based immunizations have been used to determine the patterns of type 1 and type 2 cytokines that can be induced in vivo for Ag-specific CD4(+) and CD8(+) T cells. IL-4 was used as a signature cytokine for a type 2 T cell response and IFN-gamma as the signature cytokine for a type 1 response. Gene gun deliveries of secreted Ags were used to bias responses toward type 2 and saline injections of cell-associated Ags to bias responses toward type 1. The studies revealed that gene gun bombardments of DNAs expressing secreted Ags strongly biased responses toward type 2, inducing IL-4-producing CD8(+) as well as CD4(+) T cells. Saline injections of DNAs expressing cell-associated Ags strongly biased responses toward type 1, inducing IFN-gamma-producing CD8(+) and CD4(+) cells. A mixed type 1/type 2 response of IFN-gamma-producing CD8(+) T cells and IL-4-producing CD4(+) T cells was found for gene gun deliveries of cell-associated Ags. Saline injections of secreted Ags raised a weakly type 1-biased response characterized by only slightly higher frequencies of IFN-gamma- than IL-4-producing CD4(+) and CD8(+) T cells. Studies in B cell knockout and hen egg lysozyme Ig transgenic mice revealed that B cells were required for the generation of IL-4-producing CD8(+) T cells.