Homing phenotypes of tumor-specific CD8 T cells are predetermined at the tumor site by crosspresenting APCs

Contribution of CD8 T lymphocytes to the immuno-pathogenesis of multiple sclerosis and its animal models

Multiple sclerosis (MS) is an inflammatory disease of the central nervous system (CNS) characterized by multi-focal demyelination, axonal loss, and immune cell infiltration. Numerous immune mediators are detected within MS lesions, including CD4(+) and CD8(+) T lymphocytes suggesting that they participate in the related pathogenesis. Although CD4(+) T lymphocytes are traditionally considered the main actors in MS immunopathology, multiple lines of evidence suggest that CD8(+) T lymphocytes are also implicated in the pathogenesis. In this review, we outline the recent literature pertaining to the potential roles of CD8(+) T lymphocytes both in MS and its animal models. The CD8(+) T lymphocytes detected in MS lesions demonstrate characteristics of activated and clonally expanded cells supporting the notion that these cells actively contribute to the observed injury. Moreover, several experimental in vivo models mediated by CD8(+) T lymphocytes recapitulate important features of the human disease. Whether the CD8(+) T cells can induce or aggravate tissue destruction in the CNS needs to be fully explored. Strengthening our understanding of the pathogenic potential of CD8(+) T cells in MS should provide promising new avenues for the treatment of this disabling inflammatory disease.

Immunotherapy coming of age: what will it take to make it standard of care for glioblastoma?

With the recent approval by the FDA of an immunotherapy for prostate cancer and another positive immunotherapy trial in melanoma, immunotherapy may finally be coming of age. So what will it take for it to become part of the standard treatment for glioblastoma? To put this question into perspective, we summarize critical background information in neuro-immunology, address immunotherapy clinical trial design, and discuss a number of extrinsic factors that will impact the development of immunotherapy in neuro-oncology.

T-cell immunotherapy for malignant glioma: toward a combined approach

PURPOSE OF REVIEW

Immunotherapies using T lymphocytes are now considered as promising approaches for treating malignant glioma patients. This review discusses how basic understanding of antitumor T-cell responses in the brain are now leading to the rational planning of such novel therapeutic modalities.

RECENT FINDINGS

Clinical trials show that therapeutic vaccination with defined glioma antigens or dendritic cells pulsed with glioma lysates is feasible and generally well tolerated, but clinical efficacy has yet to be demonstrated in randomized trials. Preclinical data have established that effector T cells can be engineered to more efficiently recognize tumor cells via high-affinity T-cell receptors or chimeric antibody-like receptors. Animal studies have demonstrated that glioma immunotherapy is enhanced if immunosuppressive molecules (including transforming growth factor-beta) and glioma infiltrating regulatory T cells are inactivated. Clinical trials are under way assessing transforming growth factor-beta2 antisense oligonucleotides and regulatory T cell depletion. Combination of any of the above approaches with chemotherapy or radiotherapy is strongly supported by animal and clinical observations.

SUMMARY

Future T-cell immunotherapies will combine different strategies to deliver potent T cells to the glioma bed. The synergy of immunotherapies with radiotherapy and chemotherapy requires optimization, but it is now clear that these modalities are partners and not enemies.

Overview of cellular immunotherapy for patients with glioblastoma

High grade gliomas (HGG) including glioblastomas (GBM) are the most common and devastating primary brain tumours. Despite important progresses in GBM treatment that currently includes surgery combined to radio- and chemotherapy, GBM patients' prognosis remains very poor. Immunotherapy is one of the new promising therapeutic approaches that can specifically target tumour cells. Such an approach could also maintain long term antitumour responses without inducing neurologic defects. Since the past 25 years, adoptive and active immunotherapies using lymphokine-activated killer cells, cytotoxic T cells, tumour-infiltrating lymphocytes, autologous tumour cells, and dendritic cells have been tested in phase I/II clinical trials with HGG patients. This paper inventories these cellular immunotherapeutic strategies and discusses their efficacy, limits, and future perspectives for optimizing the treatment to achieve clinical benefits for GBM patients.

Immune infiltration of spontaneous mouse astrocytomas is dominated by immunosuppressive cells from early stages of tumor development

Immune infiltration of advanced human gliomas has been shown, but it is doubtful whether these immune cells affect tumor progression. It could be hypothesized that this infiltrate reflects recently recruited immune cells that are immediately overwhelmed by a high tumor burden. Alternatively, if there is earlier immune detection and infiltration of the tumor, the question arises as to when antitumor competency is lost. To address these issues, we analyzed a transgenic mouse model of spontaneous astrocytoma (GFAP-V(12)HA-ras mice), which allows the study of immune interactions with developing glioma, even at early asymptomatic stages. T cells, including a significant proportion of Tregs, are already present in the brain before symptoms develop, followed later by macrophages, natural killer cells, and dendritic cells. The effector potential of CD8 T-cells is defective, with the absence of granzyme B expression and low expression of IFN-gamma, tumor necrosis factor, and interleukin 2. Overall, our results show an early defective endogenous immune response to gliomas, and local accumulation of immunosuppressive cells at the tumor site. Thus, the antiglioma response is not simply overwhelmed at advanced stages of tumor growth, but is counterbalanced by an inhibitory microenvironment from the outset. Nevertheless, we determined that effector molecule expression (granzyme B, IFN-gamma) by brain-infiltrating CD8 T-cells could be enhanced, despite this unfavorable milieu, by strong immune stimuli. This potential to modulate the strong imbalance in local antiglioma immunity is encouraging for the development and optimization of future glioma immunotherapies.

T cells enhance stem-like properties and conditional malignancy in gliomas

Background

Small populations of highly tumorigenic stem-like cells (cancer stem cells; CSCs) can exist within, and uniquely regenerate cancers including malignant brain tumors (gliomas). Many aspects of glioma CSCs (GSCs), however, have been characterized in non-physiological settings.

Methods

We found gene expression similarity superiorly defined glioma “stemness”, and revealed that GSC similarity increased with lower tumor grade. Using this method, we examined stemness in human grade IV gliomas (GBM) before and after dendritic cell (DC) vaccine therapy. This was followed by gene expression, phenotypic and functional analysis of murine GL26 tumors recovered from nude, wild-type, or DC-vaccinated host brains.

Results

GSC similarity was specifically increased in post-vaccine GBMs, and correlated best to vaccine-altered gene expression and endogenous anti-tumor T cell activity. GL26 analysis confirmed immune alterations, specific acquisition of stem cell markers, specifically enhanced sensitivity to anti-stem drug (cyclopamine), and enhanced tumorigenicity in wild-type hosts, in tumors in proportion to anti-tumor T cell activity. Nevertheless, vaccine-exposed GL26 cells were no more tumorigenic than parental GL26 in T cell-deficient hosts, though they otherwise appeared similar to GSCs enriched by chemotherapy. Finally, vaccine-exposed GBM and GL26 exhibited relatively homogeneous expression of genes expressed in progenitor cells and/or differentiation.

Conclusions

T cell activity represents an inducible physiological process capable of proportionally enriching GSCs in human and mouse gliomas. Stem-like gliomas enriched by strong T cell activity, however, may differ from other GSCs in that their stem-like properties may be disassociated from increased tumor malignancy and heterogeneity under specific host immune conditions.

Polarized dendritic cells as cancer vaccines: directing effector-type T cells to tumors

Ex vivo generation and antigen loading of dendritic cells (DCs) from cancer patients helps to bypass the dysfunction of endogenous DCs. It also allows to control the process of DC maturation and to imprint in maturing DCs several functions essential for induction of effective forms of cancer immunity. Recent reports from several groups including ours demonstrate that distinct conditions of DC generation and maturation can prime DCs for preferential interaction with different (effector versus regulatory) subsets of immune cells. Moreover, differentially-generated DCs have been shown to imprint different effector mechanisms in CD4(+) and CD8(+) T cells (delivery of "signal three") and to induce their different homing properties (delivery of "signal four"). These developments allow for selective induction of tumor-specific T cells with desirable effector functions and tumor-relevant homing properties and to direct the desirable types of immune cells to tumors.

Memory T-cell trafficking: new directions for busy commuters

The immune system is unique in representing a network of interacting cells of enormous complexity and yet being based on single cells travelling around the body. The development of effective and regulated immunity relies upon co-ordinated migration of each cellular component, which is regulated by diverse signals provided by the tissue. Co-ordinated migration is particularly relevant to the recirculation of primed T cells, which, while performing continuous immune surveillance, need to promptly localize to antigenic sites, reside for a time sufficient to carry out their effector function and then efficiently leave the tissue to avoid bystander damage. Recent advances that have helped to clarify a number of key molecular mechanisms underlying the complexity and efficiency of memory T-cell trafficking, including antigen-dependent T-cell trafficking, the regulation of T-cell motility by costimulatory molecules, T-cell migration out of target tissue and fugetaxis, are reviewed in this article.

Dendritic cell vaccines for brain tumors

Over the past decade, dendritic cell-based immunotherapy for central nervous system tumors has progressed from preclinical rodent models and safety assessments to phase I/II clinical trials in over 200 patients, which have produced measurable immunologic responses and some prolonged survival rates. Many questions regarding the methods and molecular mechanisms behind this new treatment option, however, remain unanswered. Results from currently ongoing and future studies will help to elucidate which dendritic cell preparations, treatment protocols, and adjuvant therapeutic regimens will optimize the efficacy of dendritic cell vaccination. As clinical studies continue to report results on dendritic cell-mediated immunotherapy, it will be critical to continue refining treatment methods and developing new ways to augment this promising form of glioma treatment.

yuDetecting the percent of peripheral blood mononuclear cells displaying p-STAT-3 in malignant glioma patients

BACKGROUND

The signal transducer and activator of transcription 3 (STAT-3) is frequently overexpressed in cancer cells, propagates tumorigenesis, and is a key regulator of immune suppression in cancer patients. The presence of phosphorylated STAT-3 (p-STAT-3) in the tumor can induce p-STAT-3 in tumor-associated immune cells that can return to the circulatory system. We hypothesized that the number of peripheral blood mononuclear cells (PBMCs) displaying p-STAT-3 would be increased in glioma patients, which would correlate with the extent of tumor-expressed p-STAT-3, and that higher p-STAT-3 levels in peripheral blood would correlate with a higher fraction of immune-suppressive regulatory T cells (Tregs).

METHODS

We measured the percentage of PBMCs displaying p-STAT-3 in 19 healthy donors and 45 patients with primary brain tumors. The level of p-STAT-3 in tumor tissue was determined by immunohistochemistry. The degree of immune suppression was determined based on the fraction of Tregs in the CD4 compartment.

RESULTS

Healthy donors had 4.8 +/- 3.6% of PBMCs that expressed p-STAT-3, while the mean proportion of PBMCs displaying p-STAT-3 in patients with GBM was 11.8 +/- 13.5% (P = 0.03). We did not observe a correlation by Spearman correlation between the degree of p-STAT-3 levels in the tumor and the percent of PBMCs displaying p-STAT-3. Furthermore, the percent of PBMCs displaying p-STAT-3 in glioma patients was not directly correlated with the fraction of Tregs in the CD4 compartment.

CONCLUSION

We conclude that the percent of PBMCs displaying p-STAT-3 may be increased in malignant glioma patients.

Immunotherapy of diffuse gliomas: biological background, current status and future developments

Despite aggressive multimodal treatment approaches, the prognosis for patients with diffuse gliomas remains disappointing. Glioma cells often extensively infiltrate in the surrounding brain parenchyma, a phenomenon that helps them to escape surgical removal, radiation exposure and chemotherapy. Moreover, conventional therapy is often associated with considerable local and systemic side effects. Therefore, the development of novel therapeutic approaches is essential to improve the outcome of these patients. Immunotherapy offers the opportunity to specifically target residual radio-and chemoresistant tumor cells without damaging healthy neighboring brain tissue. Significant progress has been made in recent years both in understanding the mechanisms of immune regulation in the central nervous system (CNS) as well as tumor-induced and host-mediated immunosuppression elicited by gliomas. In this review, after discussing the special requirements needed for the initiation and control of immune responses in the CNS, we focus on immunological phenomena observed in glioma patients, discuss different immunological approaches to attack glioma-associated target structures and touch on further strategies to improve the efficacy of immunotherapy of gliomas.

Dendritic cell therapy of high-grade gliomas

The prognosis of patients with malignant glioma is poor in spite of multimodal treatment approaches consisting of neurosurgery, radiochemotherapy and maintenance chemotherapy. Among innovative treatment strategies like targeted therapy, antiangiogenesis and gene therapy approaches, immunotherapy emerges as a meaningful and feasible treatment approach for inducing long-term survival in at least a subpopulation of these patients. Setting up immunotherapy for an inherent immunosuppressive tumor located in an immune-privileged environment requires integration of a lot of scientific input and knowledge of both tumor immunology and neuro-oncology. The field of immunotherapy is moving into the direction of active specific immunotherapy using autologous dendritic cells (DCs) as vehicle for immunization. In the translational research program of the authors, the whole cascade from bench to bed to bench of active specific immunotherapy for malignant glioma is covered, including proof of principle experiments to demonstrate immunogenicity of patient-derived mature DCs loaded with autologous tumor lysate, preclinical in vivo experiments in a murine orthotopic glioma model, early phase I/II clinical trials for relapsing patients, a phase II trial for patients with newly diagnosed glioblastoma (GBM) for whom immunotherapy is integrated in the current multimodal treatment, and laboratory analyses of patient samples. The strategies and results of this program are discussed in the light of the internationally available scientific literature in this fast-moving field of basic science and translational clinical research.

PSGL-1 function in immunity and steady state homeostasis

The substantial importance of P-selectin glycoprotein ligand 1 (PSGL-1) in leukocyte trafficking has continued to emerge beyond its initial identification as a selectin ligand. PSGL-1 seemed to be a relatively simple molecule with an extracellular mucin domain extended as a flexible rod, teleologically consistent with its primary role in tethering leukocytes to endothelial selectins. The rolling interaction between leukocyte and endothelium mediated by this selectin-PSGL-1 interaction requires branched O-glycan extensions on specific PSGL-1 amino acid residues. In some cells, such as neutrophils, the glycosyltransferases involved in formation of the O-glycans are constitutively expressed, while in other cells, such as T cells, they are expressed only after appropriate activation. Thus, PSGL-1 supports leukocyte recruitment in both innate and adaptive arms of the immune response. A complex array of amino acids within the selectins engage multiple sugar residues of the branched O-glycans on PSGL-1 and provide the molecular interactions responsible for the velcro-like catch bonds that support leukocyte rolling. Such binding of PSGL-1 can also induce signaling events that influence cell phenotype and function. Scrutiny of PSGL-1 has revealed a better understanding of how it performs as a selectin ligand and yielded unexpected insights that extend its scope from supporting leukocyte rolling in inflammatory settings to homeostasis including stem cell homing to the thymus and mature T-cell homing to secondary lymphoid organs. PSGL-1 has been found to bind homeostatic chemokines CCL19 and CCL21 and to support the chemotactic response to these chemokines. Surprisingly, the O-glycan modifications of PSGL-1 that support rolling mediated by selectins in inflammatory conditions interfere with PSGL-1 binding to homeostatic chemokines and thereby limit responsiveness to the chemotactic cues used in steady state T-cell traffic. The multi-level influence of PSGL-1 on cell traffic in both inflammatory and steady state settings is therefore substantially determined by the orchestrated addition of O-glycans. However, central as specific O-glycosylation is to PSGL-1 function, in vivo regulation of PSGL-1 glycosylation in T cells remains poorly understood. It is our purpose herein to review what is known, and not known, of PSGL-1 glycosylation and to update understanding of PSGL-1 functional scope.

Translational Mini-Review Series on Vaccines for HIV: T lymphocyte trafficking and vaccine-elicited mucosal immunity

Many pathogens use mucosal surfaces to enter and propagate within the host, making particularly desirable vaccines that target immune responses specifically to mucosal compartments. The majority of mucosal vaccine design strategies to date have been empirical in nature. However, an emerging body of basic immunological knowledge is providing new insights into the regulation of tissue-specific lymphocyte trafficking and differentiation. These insights afford the opportunity for the rational design of vaccines that focus immune responses at mucosal surfaces. Mucosal cellular immunity may prove critical for protection in the context of HIV infection, and thus there has been considerable interest in developing vaccines that target HIV-specific cellular immune responses to the gastrointestinal and vaginal mucosa. However, the optimal strategies for eliciting mucosal cellular immune responses through vaccination remain to be determined. Here, we review both recent vaccine studies and emerging paradigms from the basic immunological literature that are relevant to the elicitation of potent and protective mucosal cellular immune memory. Increasing the synergy between these avenues of research may afford new opportunities for mucosal vaccine design.

Improved therapeutic efficacy using vaccination with glioma lysate-pulsed dendritic cells combined with IP-10 in murine glioma

The purpose of the present study was to evaluate the therapeutic efficacy of glioma lysate-pulsed DCs in combination with plasmid DNA vector encoding the murine interferon-induced protein of 10kDa (IP-10 or CXCL10) gene. Mouse models of brain glioma (GL261) were treated with combining glioma lysate-pulsed DCs with direct intratumoral injection of a nonviral plasmid DNA vector encoding the murine IP-10 gene. The survival of mice bearing GL261 glioma was observed. Enzyme-linked immuno-spot assay was used to determine the frequency of brain-infiltrating lymphocytes (BILs) capable of responding to GL261. Cytolytic T lymphocyte (CTL) response was measured by cytotoxic assay, vessel density and tumor cell proliferation were observed by immunostaining, and tumor apoptosis was determined by TUNEL staining. The results revealed that the combination therapy groups showed more significantly enhanced anti-tumor activity, attraction of lymphocytes into tumor tissues, apoptosis of tumor cells, and reduced neovascularization, cell proliferation, and developed a strong CTL response in these mice. In summary, the therapy of glioma lysate-pulsed DCs combined with the IP-10 gene has significant synergistic effect against glioma.

The PEPvIII-KLH (CDX-110) vaccine in glioblastoma multiforme patients

Conventional therapies for glioblastoma multiforme (GBM) fail to target tumor cells exclusively, resulting in non-specific toxicity. Immune targeting of tumor-specific mutations may allow for more precise eradication of neoplastic cells. EGFR variant III (EGFRvIII) is a tumor-specific mutation that is widely expressed in GBM and other neoplasms and its expression enhances tumorigenicity. This in-frame deletion mutation splits a codon, resulting in a novel glycine at the fusion junction producing a tumor-specific epitope target for cellular or humoral immunotherapy. We have previously shown that vaccination with a peptide that spans the EGFRvIII fusion junction (PEPvIII-KLH/CDX-110) is an efficacious immunotherapy in syngeneic murine models. In this review, we summarize our results in GBM patients targeting this mutation in multiple, multi-institutional Phase II immunotherapy trials. These trials demonstrated that a selected population of GBM patients who received vaccines targeting EGFRvIII had an unexpectedly long survival time. Further therapeutic strategies and potential pitfalls of using this approach are discussed.

DCVax-Brain and DC vaccines in the treatment of GBM

BACKGROUND

DCVax-Brain (Northwest Biotherapeutics, Inc., Bethesda, MD, USA) is a personalized treatment for brain tumors. Its approach of administering autologous tumor antigen-bearing dendritic cells (DCs) has garnered hope for more effective and less toxic therapy for patients with malignant brain tumors including glioblastoma multiforme (GBM). DCVax-Brain composition and efficacy are not fully disclosed, although sponsors claim it is poised to critically test clinical DC vaccine efficacy in GBM patients.

OBJECTIVE

This review examines the efficacy of DC vaccine therapy in treating GBM patients. REVIEW QUESTION: To determine if the approach of DC vaccination followed by DCVax-Brain shows ample clinical promise in GBM patients.

SEARCH STRATEGY

All published reports of DC vaccination for GBM and press releases regarding DCVax-Brain findings were evaluated. CRITICAL APPRAISAL OF REPORTS AND SUMMARY OF OUTCOMES: Published DC vaccine trials for high-grade glioma patients suggest favorable clinical outcomes not easily ascribed to non-treatment parameters. Evidence of possible selection bias exists in many reports, but efforts to account for this are evident in the most recent publications.

CONCLUSION

DC vaccine trials provide evidence of low toxicity in GBM patients and effective induction of antitumor immunity in the latest publications correlate with clinical improvements. Preliminary reports on DCVax-Brain clinical outcomes seem to follow these trends.

CD8+ T cells and neuronal damage: direct and collateral mechanisms of cytotoxicity and impaired electrical excitability

Cytotoxic CD8(+) T cells are increasingly recognized as key players in various inflammatory and degenerative central nervous system (CNS) disorders. CD8(+) T cells are believed to actively contribute to neural damage in these CNS conditions. Conceptually, one can separate two possible ways that CD8(+) T cells harm neuronal function or integrity: CD8(+) T cells either directly target neurons and their neurites in an antigen- or contact-dependent fashion, or exert their action via "collateral" mechanisms of neuronal damage that might follow destruction of the myelin sheath or glial cells in both the CNS gray and white matter. After introducing clinical examples, in which the putative relevance CD8(+) T cells has been demonstrated, we summarize knowledge on the sequence of initiation and execution of CD8(+) T-cell responses in the CNS. This includes the initial antigen cross-presentation and priming of naive CD8(+) T cells, followed by the invasion, migration, and target-cell recognition of CD8(+) effector T cells in the CNS parenchyma. Moreover, we discuss mechanisms of impaired electrical signaling and cell death of neurons as direct and collateral targets of CD8(+) T cells in the CNS.

Autoimmune T cell responses in the central nervous system

Autoreactive T cell responses have a crucial role in central nervous system (CNS) diseases such as multiple sclerosis. Recent data indicate that CNS autoimmunity can be mediated by two distinct lineages of CD4+ T cells that are defined by the production of either interferon-gamma or interleukin-17. The activity of these CD4+ T cell subsets within the CNS influences the pathology and clinical course of disease. New animal models show that myelin-specific CD8+ T cells can also mediate CNS autoimmunity. This Review focuses on recent progress in delineating the pathogenic mechanisms, regulation and interplay between these different T cell subsets in CNS autoimmunity.

Migration, maintenance and recall of memory T cells in peripheral tissues

After the resolution of an immune response, antigen-specific memory T cells persist at many sites in the body. The antigen-specific memory T-cell pool includes memory T cells that preferentially reside in peripheral tissues, such as the skin, gut and lungs, where they provide a first line of defence against secondary pathogen infection. Determining how peripheral memory T cells are regulated is essential for our understanding of host-pathogen interactions and for vaccine development. In this Review, we discuss recent insights into the generation, control and recall of peripheral T-cell memory responses.

Dendritic cell-based therapeutic cancer vaccines: what we have and what we need

Therapeutic cancer vaccines rely on the immune system to eliminate tumor cells. In contrast to chemotherapy or passive (adoptive) immunotherapies with antibodies or ex vivo-expanded T cells, therapeutic vaccines do not have a direct anti-tumor activity, but aim to reset patients' immune systems to achieve this goal. Recent identification of effective ways of enhancing immunogenicity of tumor-associated antigens, including the use of dendritic cells and other potent vectors of cancer vaccines, provide effective tools to induce high numbers of circulating tumor-specific T cells. However, despite indications that some of the new cancer vaccines may be able to delay tumor recurrence or prolong the survival of cancer patients, their ability to induce cancer regression remains low. Recent reports help to identify and prospectively remove the remaining obstacles towards effective therapeutic vaccination of cancer patients. They indicate that the successful induction of tumor-specific T cells by cancer vaccines is not necessarily associated with the induction of functional cytotoxic T lymphocytes, and that current cancer vaccines may promote undesirable expansion of Treg cells. Furthermore, recent studies also identify the tools to counteract such phenomena, in order to assure the desirable induction of Th1-cytotoxic T lymphocytes, NK-mediated type-1 immunity and appropriate homing of effector cells to tumors.

Self-antigen-specific CD8+ T cell precursor frequency determines the quality of the antitumor immune response

A primary goal of cancer immunotherapy is to improve the naturally occurring, but weak, immune response to tumors. Ineffective responses to cancer vaccines may be caused, in part, by low numbers of self-reactive lymphocytes surviving negative selection. Here, we estimated the frequency of CD8⁺ T cells recognizing a self-antigen to be <0.0001% (∼1 in 1 million CD8⁺ T cells), which is so low as to preclude a strong immune response in some mice. Supplementing this repertoire with naive antigen-specific cells increased vaccine-elicited tumor immunity and autoimmunity, but a threshold was reached whereby the transfer of increased numbers of antigen-specific cells impaired functional benefit, most likely because of intraclonal competition in the irradiated host. We show that cells primed at precursor frequencies below this competitive threshold proliferate more, acquire polyfunctionality, and eradicate tumors more effectively. This work demonstrates the functional relevance of CD8⁺ T cell precursor frequency to tumor immunity and autoimmunity. Transferring optimized numbers of naive tumor-specific T cells, followed by in vivo activation, is a new approach that can be applied to human cancer immunotherapy. Further, precursor frequency as an isolated variable can be exploited to augment efficacy of clinical vaccine strategies designed to activate any antigen-specific CD8⁺ T cells.

Multiphoton imaging of cytotoxic T lymphocyte-mediated antitumor immune responses

The actual contribution of T lymphocytes to protection against tumors is still unclear. In vitro imaging experiments show that tumor specific cytotoxic T lymphocytes (CTLs) are competent to kill target cells by conventional cytotoxic pathways. The emergence of multiphoton imaging in the past decade now allows real time in vivo imaging of CTLs. New insights are available on the behavior of antitumor T cells during the priming phase, during their traffic within the tumor tissue, and on their interactions with tumor cells during the effector phase. Recent reports suggest that direct killing of tumor cells by CTLs is a slow process, suggesting that the ratio of effector to target cells is determinant, or that additional cytotoxic contribution by other cell types is required to induce efficient tumor rejection. This review will focus on the publications that have imaged antitumor immune responses dynamically and discuss how this new information contributes to understand the implication of CTLs in tumor rejection.

Immunotherapeutic approaches for glioma

The development of effective immunotherapy strategies for glioma requires adequate understanding of the unique immunological microenvironment in the central nervous system (CNS) and CNS tumors. Although the CNS is often considered to be an immunologically privileged site and poses unique challenges for the delivery of effector cells and molecules, recent advances in technology and discoveries in CNS immunology suggest novel mechanisms that may significantly improve the efficacy of immunotherapy against gliomas. In this review, we first summarize recent advances in the CNS and CNS tumor immunology. We address factors that may promote immune escape of gliomas. We also review advances in passive and active immunotherapy strategies for glioma, with an emphasis on lessons learned from recent early-phase clinical trials. We also discuss novel immunotherapy strategies that have been recently tested in non-CNS tumors and show great potential for application to gliomas. Finally, we discuss how each of these promising strategies can be combined to achieve clinical benefit for patients with gliomas.

Harnessing T-Cell Immunity to Target Brain Tumors

T-cell mediated immunotherapy is a conceptually attractive treatment option to envisage for glioma, since T lymphocytes can actively seek out neoplastic cells in the brain, and they have the potential to safely and specifically eliminate tumor. Some antigenic targets on glioma cells are already defined, and we can be optimistic that more will be discovered from progress in T-cell epitope identification and gene expression profiling of brain tumors. In parallel, advances in immunology (regional immunology, neuroimmunology, tumor immunology) now equip us to build upon the results from current immunotherapy trials in which the safety and feasibility of brain tumor immunotherapy have already been confirmed. We can now look to the next phase of immunotherapy, in which we must harness the most promising basic science advances and existing clinical expertise, and apply these to randomized clinical trials to determine the real clinical impact and applicability of these approaches for treating patients with currently incurable malignant brain tumors.

Cutting edge: instructive role of peripheral tissue cells in the imprinting of T cell homing receptor patterns

Tissue-specific homing of effector and memory T cells to skin and small intestine requires the imprinting of specific combinations of adhesion molecules and chemokine receptors by dendritic cells in the draining lymph nodes. In this study, we demonstrate that CD8(+) T cells activated by Ag-pulsed bone marrow-derived dendritic cells were induced to express the small intestine homing receptors alpha(4)beta(7) integrin and chemokine receptor CCR9 in coculture with small intestinal epithelial cells. In contrast, in coculture with dermal fibroblasts the skin-homing receptor E-selectin ligand was induced. Interestingly, the imprinting of gut homing receptors on anti-CD3/anti-CD28 stimulated T cells was induced by soluble factors produced by small intestinal epithelial cells. Retinoic acid was identified as a crucial factor. These findings show that peripheral tissue cells directly produce homing receptor imprinting factors and suggest that dendritic cells can acquire their imprinting potential already in the peripheral tissue of origin.

Peripheral tolerance limits CNS accumulation of CD8 T cells specific for an antigen shared by tumor cells and normal astrocytes

T cell mediated immunotherapies are proposed for many cancers including malignant astrocytoma. As such therapies become more potent, but not necessarily more tumor-specific, the risk of collateral autoimmune damage to normal tissue increases. Tumors of the brain present significant challenges in this respect, as autoimmune destruction of brain tissue could have severe consequences. To investigate local immune reactivity toward a tumor-associated antigen in the brain, transgenic mice were generated that express a defined antigen (CW3 170-179) in astroglial cells. The resulting six transgenic mouse lines expressed the transgenic self-antigen in cells of the gastrointestinal tract and CNS compartments, or in the CNS alone. By challenging transgenic mice with tumor cells that express CW3, self/tumor-specific immune responses were visualized within a normal polyclonal T cell repertoire. A large expansion of the endogenous CW3 170-179-specific CD8 T cell population was observed in nontransgenic mice after both subcutaneous and intracerebral implantation of tumor cells. In contrast, CW3 170-179-specific immune responses were not observed in transgenic mice that exhibited extracerebral transgene expression. Importantly, in certain groups of mice in which transgene expression was restricted to the CNS, antigen-specific immune responses occurred when tumor was implanted subcutaneously, but not intracerebrally. This local immune tolerance in the brain was induced via peripheral (extrathymic) rather than central (thymic) tolerance mechanisms. Thus, this study highlights the role of regional immune regulation in the prevention of autoimmunity in the brain, and the potential impact of these mechanisms for brain tumor immunotherapy.

Dissecting T cell lineage relationships by cellular barcoding

T cells, as well as other cell types, are composed of phenotypically and functionally distinct subsets. However, for many of these populations it is unclear whether they develop from common or separate progenitors. To address such issues, we developed a novel approach, termed cellular barcoding, that allows the dissection of lineage relationships. We demonstrate that the labeling of cells with unique identifiers coupled to a microarray-based detection system can be used to analyze family relationships between the progeny of such cells. To exemplify the potential of this technique, we studied migration patterns of families of antigen-specific CD8⁺ T cells in vivo. We demonstrate that progeny of individual T cells rapidly seed independent lymph nodes and that antigen-specific CD8⁺ T cells present at different effector sites are largely derived from a common pool of precursors. These data show how locally primed T cells disperse and provide a technology for kinship analysis with wider utility.

Trafficking of antigen-specific CD8+ T lymphocytes to mucosal surfaces following intramuscular vaccination

A critical goal of vaccine development for a wide variety of pathogens is the induction of potent and durable mucosal immunity. However, it has been assumed that this goal would be difficult to achieve by systemic vaccination due to the anatomic and functional distinctness of the systemic and mucosal immune systems and the resultant compartmentalization of immune responses. In this study, we show that Ag-specific CD8(+) T lymphocytes traffic efficiently to mucosal surfaces following systemic vaccination. Intramuscular immunization with recombinant adenovirus (rAd) vector-based vaccines expressing SIV Gag resulted in potent, durable, and functional CD8(+) T lymphocyte responses at multiple mucosal effector sites in both mice and rhesus monkeys. In adoptive transfer studies in mice, vaccine-elicited systemic CD8(+) T lymphocytes exhibited phenotypic plasticity, up-regulated mucosal homing integrins and chemokine receptors, and trafficked rapidly to mucosal surfaces. Moreover, the migration of systemic CD8(+) T lymphocytes to mucosal compartments accounted for the vast majority of Ag-specific mucosal CD8(+) T lymphocytes induced by systemic vaccination. Thus, i.m. vaccination can overcome immune compartmentalization and generate robust mucosal CD8(+) T lymphocyte memory. These data demonstrate that the systemic and mucosal immune systems are highly coordinated following vaccination.

Combined triggering of dendritic cell receptors results in synergistic activation and potent cytotoxic immunity

Elimination of malignant cells and intracellular infections involves collaboration between CTLs and Th1 inflammation. Dendritic cells drive this response via costimulation and cytokines. We have defined key signals required for the exponential expansion of specific CD8(+) T cells in vivo in mice. Immunization with two or more TLR agonists, anti-CD40, IFN-gamma, and surfactant were sufficient to drive unprecedented levels of CD8 response to peptide or protein Ag and highly polarized Th1 CD4 responses. CD40 signaling was required for CD8 expansion but could be provided by a concomitant CD4 Th response in place of anti-CD40. Triggering of these pathways activated migration and activation of myeloid and plasmacytoid dendritic cells and secretion of IL-12. Cross-presentation can thus be exploited to induce potent cytotoxic responses and long-term memory to peptide/protein Ags. When combined with a tumor-associated peptide from tyrosinase-related protein 2, our combined adjuvant approach effectively halted tumor growth in an in vivo melanoma model and was more effective than anti-CD40 and a single TLR agonist. Antitumor immunity was associated with long-lived effector memory CD8 cells specific for the naturally processed and presented tumor Ag, and tumor protection was partially but not entirely dependent on CD8 T cells. This flexible strategy is more effective than existing adjuvants and provides a technological platform for rapid vaccine development.

Anti-tumor activity and trafficking of self, tumor-specific T cells against tumors located in the brain

It is commonly believed that T cells have difficulty reaching tumors located in the brain due to the presumed "immune privilege" of the central nervous system (CNS). Therefore, we studied the biodistribution and anti-tumor activity of adoptively transferred T cells specific for an endogenous tumor-associated antigen (TAA), gp100, expressed by tumors implanted in the brain. Mice with pre-established intracranial (i.c.) tumors underwent total body irradiation (TBI) to induce transient lymphopenia, followed by the adoptive transfer of gp100(25-33)-specific CD8+ T cells (Pmel-1). Pmel-1 cells were transduced to express the bioluminescent imaging (BLI) gene luciferase. Following adoptive transfer, recipient mice were vaccinated with hgp100(25-33) peptide-pulsed dendritic cells (hgp100(25-33)/DC) and systemic interleukin 2 (IL-2). This treatment regimen resulted in significant reduction in tumor size and extended survival. Imaging of T cell trafficking demonstrated early accumulation of transduced T cells in lymph nodes draining the hgp100(25-33)/DC vaccination sites, the spleen and the cervical lymph nodes draining the CNS tumor. Subsequently, transduced T cells accumulated in the bone marrow and brain tumor. BLI could also detect significant differences in the expansion of gp100-specific CD8+ T cells in the treatment group compared with mice that did not receive either DC vaccination or IL-2. These differences in BLI correlated with the differences seen both in survival and tumor infiltrating lymphocytes (TIL). These studies demonstrate that peripheral tolerance to endogenous TAA can be overcome to treat tumors in the brain and suggest a novel trafficking paradigm for the homing of tumor-specific T cells that target CNS tumors.

Qualitative and quantitative characteristics of rotavirus-specific CD8 T cells vary depending on the route of infection

CD8 T-cell response provides an important defense against rotavirus, which infects a variety of systemic locations in addition to the gut. Here we investigated the distribution, phenotype, and function of rotavirus-specific CD8 T cells in multiple organs after rotavirus infection initiated via the intranasal, oral, or intramuscular route. The highest level of virus-specific CD8 T cells was observed in the Peyer's patches of orally infected mice and in the lungs of intranasally infected animals. Very low levels of virus-specific CD8 T cells were detected in peripheral blood or spleen irrespective of the route of infection. Rotavirus-specific CD8 T cells from Peyer's patches of orally infected mice expressed high levels of CCR9, while CXCR6 and LFA-1 expression was associated with virus-specific CD8 T cells in lungs of intranasally infected mice. Oral infection induced the highest proportion of gamma interferon(-) CD107a/b(+) CD8 T cells in Peyer's patches. When equal numbers of rotavirus-specific CD8 T cells were transferred into Rag-1 knockout mice chronically infected with rotavirus, the donor cells derived from Peyer's patches of orally infected mice were more efficient than those derived from lungs of intranasally infected animals in clearing intestinal infection. These results suggest that different routes of infection induce virus-specific CD8 T cells with distinct homing phenotypes and effector functions as well as variable abilities to clear infection.

Antigen controls IL-7R alpha expression levels on CD8 T cells during full activation or tolerance induction

The high-affinity chain of the IL-7 receptor, IL-7Ralpha (CD127), is expressed by effector CD8 T cells that have the capacity to become memory cells. IL-7Ralpha expression is uniformly high on naive CD8 T cells, and the majority of these cells down-regulate expression upon antigenic challenge. At the peak of expansion, the fraction of effectors expressing high IL-7Ralpha varies depending on the response examined. The signals that a CD8 T cell receives during a response to Ag that lead to altered expression of IL-7Ralpha have not been fully defined. In vitro experiments demonstrated that Ag alone is sufficient to down-regulate IL-7Ralpha on all cells and most of the cells rapidly re-express the receptor upon removal from Ag. Expression was not altered by the B7.1 costimulatory ligand or when IL-12 was present to provide the signal needed for development of effector functions, indicating that TCR engagement is sufficient to regulate IL-7Ralpha expression. Consistent with this, in vivo priming with peptide Ag resulted in IL-7Ralpha expression that inversely correlated with Ag levels, and expression levels were not changed when IL-12 or adjuvant were administered with Ag. A large fraction of the cells present at the peak of expansion had re-expressed IL-7Ralpha, but most of these cells failed to survive; those that did survive expressed high IL-7Ralpha levels. Thus, Ag-dependent signals regulate IL-7Ralpha levels on responding CD8 T cells, and this occurs whether the responding cells become fully activated or are rendered tolerant by administration of peptide Ag alone.

The highway code of T cell trafficking

Coordinated migratory events are required for the development of effective and regulated immunity. Naïve T lymphocytes are programmed to recirculate predominantly in secondary lymphoid tissue by non-specific stimuli. In contrast, primed T cells must identify specific sites of antigen location in non-lymphoid tissue to exert targeted effector responses. Following priming, T cells acquire the ability to establish molecular interactions mediated by tissue-selective integrins and chemokine receptors (homing receptors) that allow their access to specific organs, such as the skin and the gut. Recent studies have shown that an additional level of specificity is provided by the induction of specific T cell migration into the tissue following recognition of antigen displayed by the endothelium. In addition, co-stimulatory signals (such as those induced by CD28 and CTLA-4 molecules) have been shown not only to regulate T cell activation and differentiation, but also to orchestrate the anatomy of the ensuing T cell response.

Homing imprinting and immunomodulation in the gut: role of dendritic cells and retinoids

Lymphocyte migration is at the heart of chronic inflammatory ailments, including inflammatory bowel disease (IBD). Whereas naïve lymphocytes migrate to all secondary lymphoid organs, they are mostly excluded from nonlymphoid peripheral tissues. Upon activation, lymphocytes change their pattern of adhesion receptors and acquire the capacity to migrate to extralymphoid tissues. Antigen-experienced T cells are subdivided into different subsets based on their expression of homing receptors that favor their accumulation in specific tissues, such as the skin and the gut mucosa. B cells and antibody-secreting cells (ASC) also show tissue-tropism, which is somewhat correlated with the class of immunoglobulin that they produce. In fact, IgA-ASC are located in mucosal tissues, where they produce IgA, the main class of antibodies found in secretions. Although IgA-ASC are usually considered as a homogeneous pool of cells, those located in the small bowel have some unique migratory characteristics, suggesting that they are generated under different conditions as compared to IgA-ASC in other mucosal compartments. Foxp3(+) regulatory T cells (T(REG)) can also exhibit tissue-specific migratory potential and recent evidence suggests that T(REG) can be imprinted with gut-specific homing. Moreover, foxp3(+) T(REG) are enriched in the small bowel lamina propria, where they can be generated locally. The present review addresses our current understanding of how tissue-specific homing is acquired and modulated on T cells, B cells, and ASC, with a special emphasis on the intestinal mucosa. Harnessing these mechanisms could offer novel, effective, and more specific therapeutic strategies in IBD.

Preferential migration of regulatory T cells mediated by glioma-secreted chemokines can be blocked with chemotherapy

Despite the immunogenicity of glioblastoma multiforme (GBM), immune-mediated eradication of these tumors remains deficient. Regulatory T cells (Tregs) in the blood and within the tumor microenvironment of GBM patients are known to contribute to their dismal immune responses. Here, we determined which chemokine secreted by gliomas can preferentially induce Treg recruitment and migration. In the malignant human glioma cell lines D-54, U-87, U-251, and LN-229, the chemokines CCL22 and CCL2 were detected by intracellular cytokine analysis. Furthermore, tumor cells from eight patients with GBM had a similar chemokine expression profile. However, only CCL2 was detected by enzyme-linked immunosorbent assay, indicating that CCL2 may be the principal chemokine for Treg migration in GBM patients. Interestingly, the Tregs from GBM patients had significantly higher expression levels of the CCL2 receptor CCR4 than did Tregs from healthy controls. Glioma supernatants and the recombinant human chemokines CCL2 and CCL22 induced Treg migration and were blocked by antibodies to the chemokine receptors. Production of CCL2 by glioma cells could also be mitigated by the chemotherapeutic agents temozolomide and carmustine [3-bis (2-chloroethyl)-1-nitrosourea]. Our results indicate that gliomas augment immunosuppression by selective chemokine-mediated recruitment of Tregs into the tumor microenvironment and that modulating this interaction with chemotherapy could facilitate the development of novel immunotherapeutics to malignant gliomas.

Brain microenvironment promotes the final functional maturation of tumor-specific effector CD8+ T cells

During the priming phase of an antitumor immune response, CD8(+) T cells undergo a program of differentiation driven by professional APCs in secondary lymphoid organs. This leads to clonal expansion and acquisition both of effector functions and a specific adhesion molecule pattern. Whether this program can be reshaped during the effector phase to adapt to the effector site microenvironment is unknown. We investigated this in murine brain tumor models using adoptive transfer of tumor-specific CD8(+) T cells, and in spontaneous immune responses of patients with malignant glioma. Our data show proliferation of Ag-experienced tumor-specific T cells within the brain parenchyma. Moreover, CD8(+) T cells further differentiated in the brain, exhibiting enhanced IFN-gamma and granzyme B expression and induction of alpha(E)(CD103)beta(7) integrin. This unexpected integrin expression identified a subpopulation of CD8(+) T cells conditioned by the brain microenvironment and also had functional consequences: alpha(E)(CD103)beta(7)-expressing CD8(+) T cells had enhanced retention in the brain. These findings were further investigated for CD8(+) T cells infiltrating human malignant glioma; CD8(+) T cells expressed alpha(E)(CD103)beta(7) integrin and granzyme B as in the murine models. Overall, our data indicate that the effector site plays an active role in shaping the effector phase of tumor immunity. The potential for local expansion and functional reprogramming should be considered when optimizing future immunotherapies for regional tumor control.

Preferential expression of very late antigen-4 on type 1 CTL cells plays a critical role in trafficking into central nervous system tumors

We have previously shown preferential tumor-homing and therapeutic efficacy of adoptively transferred type 1 CTL (Tc1) when compared with type 2 CTL (Tc2) in mice bearing intracranial ovalbumin-transfected melanoma (M05). Further characterizing the expression of a panel of homing receptors on Tc1 and Tc2 cells, we found that very late antigen (VLA)-4 (a heterodimer of CD49d and CD29), but none of other receptors evaluated, was expressed at significantly higher levels on Tc1 cells than on Tc2 cells. Although CD49d (alpha(4) integrin) can form heterodimers with both beta(1) (CD29) and beta(7) integrins, alpha(4)beta(7) complexes were not expressed by either Tc1 or Tc2 cells, suggesting that CD49d is solely expressed in VLA-4 complexes. VLA-4 expression on Tc2 cells was down-regulated in an interleukin (IL)-4 dose-dependent manner but not by other type 2 cytokines, such as IL-10 and IL-13, suggesting that IL-4 uniquely down-regulates VLA-4 expression on these cells. In accordance with the differential expression of VLA-4 on Tc1 versus Tc2 cells, Tc1 cells alone were competent to adhere to plate-bound VCAM-1-Ig fusion protein. Finally, the efficient trafficking of Tc1 cells into intracranial M05 lesions in vivo was efficiently blocked by administration of monoclonal antibodies against CD49d or VCAM-1 or small interfering RNA-mediated silencing of CD49d on Tc1 cells. Collectively, these data support the critical role of VLA-4 in the effective intracranial tumor homing of adoptive-transferred, antigen-specific Tc1 cells and suggest that more effective vaccine and/or ex vivo T-cell activation regimens may be developed by promoting the generation of VLA-4(+) antitumor Tc1 cells.

Long-Term Commitment to Inflammation-Seeking Homing in CD4+ Effector Cells

Access of T effector cells to sites of inflammation is a prerequisite for an efficient action in immune defense and is mediated by different, partly tissue-specific sets of adhesion molecules. To what extent lymphocytes memorize the site of initial priming and develop organ-specific homing properties is still a matter of debate. Notably, data on the stability of homing receptor expression on T cells in vivo are largely lacking. We approached this question by the adoptive transfer of CD4(+) T cells sorted for the expression of P-selectin ligands, which contribute to migration into inflamed sites in skin and other tissues. We observed long-term expression of P-selectin ligands on roughly one-third of effector cells. On those cells that had lost P-selectin ligands, re-expression upon Ag challenge was observed but only within pLNs, similar to the organ-selective induction upon the primary activation of naive T cells. The frequency of cells stably expressing P-selectin ligands was higher when cells were repeatedly stimulated under permissive conditions in the presence of IL-12, indicating a gradual fixation of this phenotype. In line with that finding, isolated P-selectin ligand positive memory T cells showed the highest frequency of long-term expressing cells. A tissue-specific environment was not required for the long-term maintenance of P-selectin ligand expression on the subfraction of effector cells. These data indicate that the expression of selectin ligands can become clonally imprinted under certain conditions, but also that a major fraction of the cells remains flexible and subject to environmental modulation upon restimulation.

Induction of organ-selective CD4+ regulatory T cell homing

Compelling evidence suggests that Foxp3(+)CD25(+)CD4(+) Treg play a fundamental role in immunoregulation. We have previously demonstrated that Treg have to enter peripheral tissues to suppress ongoing inflammation. However, relatively little is known about how Treg acquire the expression of homing receptors required for tissue- or inflammation-specific migration. Migratory properties of conventional naïve T cells are shaped by the tissue microenvironment and organ-specific dendritic cells during priming. Here, we show that this basic concept also holds true for CD25(+)CD4(+) Treg: Priming of Treg within peripheral LN led to the expression of selectin ligands, which facilitate migration into inflamed skin, whereas activation within mesenteric LN led to induction of the integrin alpha(4)beta(7), which is required for migration into mucosal tissues. Furthermore, we could establish in vitro culture systems containing either dendritic cells from mesenteric and peripheral LN, or retinoic acid and IL-12 as polarizing compounds to induce mucosa- and skin-seeking Treg, respectively. Together, our results demonstrate that Treg, similarly to conventional T cells, can be configured with organ-selective homing properties allowing efficient targeting into distinct tissues.

Cutting Edge: Cross-Presented Intracranial Antigen Primes CD8+ T Cells

The CNS is considered immune privileged due to the blood-brain barrier and the absence of conventional lymphatics. Nonetheless, T cell immune responses specific for CNS Ag have been documented. Where these events are initiated and what cellular mechanisms are involved remain unknown. In this study, we established an experimental mouse model to evaluate the requirements for priming CD8+ T cells following the cross-presentation of intracranial Ag. Surprisingly, we find that even with a damaged blood-brain barrier, Ag presentation occurs in regional lymph nodes and not within the CNS itself. Only once the responding cells have expanded can they traffic to the site of CNS injury. Cross-presentation of intracranial Ag is efficient and the subsequent priming of CD8+ T cells is dependent on CD4+ T cell help and CD40 signaling in host APCs. Our findings have important implications for the initiation of T cell immune responses toward CNS Ags.

Helper roles of NK and CD8+ T cells in the induction of tumor immunity. Polarized dendritic cells as cancer vaccines

The work in our laboratory addresses two interrelated areas of dendritic cell (DC) biology: (1) the role of DCs as mediators of feedback interactions between NK cells, CD8+ and CD4+ T cells; and (2) the possibility to use such feedback and the paradigms derived from anti-viral responses, to promote the induction of therapeutic immunity against cancer. We observed that CD8+ T cells and NK cells, the classical "effector" cells, also play "helper" roles, regulating ability of DCs to induce type-1 immune immunity, critical for fighting tumors and intracellular pathogens. Our work aims to delineate which pathways of NK and CD8+ T cell activation result in their helper activity, and to identify the molecular mechanisms allowing them to induce type-1 polarized DCs (DC1s) with selectively enhanced ability to promote type-1 responses and anti-cancer immunity. The results of these studies allowed us and our colleagues to design phase I/II clinical trials incorporating the paradigms of DC polarization and helper activity of effector cells in cancer immunotherapy.

HPV vaccines: the beginning of the end for cervical cancer

Vaccines prophylactic against infection with human papillomavirus (HPV) are based on alum adjuvanted virus-like particles. Two such vaccines have recently been shown to prevent persistent HPV infection and associated cervical cancer precursor lesions. The genotype-specific neutralising antibody directed at conformational epitopes of the L1 major capsid protein is likely to mediate protection. Vaccines therapeutic for persisting HPV infection can eliminate transplantable tumors in animal models, but are of limited efficacy in mice grafted with skin that expresses HPV antigens or in humans. This paradox has been partially resolved by data clarifying the immunoregulatory role of skin cytokines (e.g. transforming growth factor-beta and interleukin-10) and the consequences of antigen presentation by subsets of skin-associated antigen-presenting cells.

[Lymphocyte trafficking and immunesurveillance]

The homeostasis of the immune system is maintained by the recirculation of naive lymphocytes through the secondary lymphoid tissues, such as the lymph nodes, Peyer's patches and spleen. Upon antigen encounter in the secondary lymphoid tissues, lymphocytes become activated and undergo a reprogramming of their trafficking properties. Most antigen-experienced lymphocytes traffic through the secondary lymphoid organs, but they can also migrate to extralymphoid tissues, where they exert effector functions. Dendritic cells in the secondary lymphoid tissues are crucial for the reprogramming of trafficking properties of activated T-lymphocytes. The exquisite specificity of such lymphocyte trafficking is determined by tissue-specific guidance signals expressed by the vascular endothelial cells, combined with counter receptors expressed by circulating lymphocytes. The high endothelial venules can selectively recruit naive lymphocytes into the lymph nodes and Peyer's patches by expressing a unique combination of vascular addressins and chemoattractants. The inflamed postcapillary venules in extralymphoid tissues also use a distinct array of endothelial adhesion molecules and tissue selective chemokines to support the recruitment of effector and memory lymphocytes that express appropriate trafficking receptors. Exit of lymphocytes from lymphoid and extralymphoid tissues into circulation is actively regulated by signals through specific receptors for sphingosine-1-phosphate and a certain chemokine(s), respectively. This review summarizes the present understandings of the mechanisms regulating homeostatic recirculation of naive lymphocytes through the secondary lymphoid tissues and tissue-specific trafficking of antigen-experienced lymphocytes.

Initiation of adaptive immune responses by transcutaneous immunization

The development of new, effective, easy-to-use and lower-cost vaccination approaches for the combat against malignant and infectious diseases is a pre-eminent need: cancer is a leading cause of morbidity in the Western World; there are numerous pathogenic diseases for which we still have no protective or therapeutic cure; and the financial limitations of developing countries to fight these diseases. In this mini-review we focus on transcutaneous immunization (TCI), a relatively new route for antigen delivery. TCI protocols appear to be particularly promising by gaining access to skin resident APC, which are highly efficient for the initiation of humoral and/or cellular immune responses. Consisting of an adjuvant as a stimulus in combination with an antigen which defines the target, TCI offers a most attractive immunization strategy to mount highly specific full-blown adaptive immune responses. As a topically applicable cell-free adjuvant/antigen mixture, TCI might be suitable to improve patient compliance, as well as feasible economically for the use in Third World countries. In addition, this non-invasive procedure might increase the safety of vaccinations by eliminating the risk of infections related to the recycling and improper disposal of needles. The dissection of antigen and adjuvant is important because it allows "free" combinations in contrast to classical immunizations which are based on application of the pathogen of interest. The most relevant ways and means to find new, effective pathogenic target antigens are "reverse vaccinology" and the direct peptide-epitope identification from MHC molecules with mass-spectrometry. Due to these efficient approaches the variety of antigenic epitopes for potential protective/therapeutic use is perpetually expanding. The most studied adjuvants in TCI approaches are cholera toxin (CT) and its less toxic relative, the heat-labile enterotoxin (LT). Both CT and LT can serve as antigen as well. In contrast to these large proteins, which can only penetrate "pre-treated" skin barrier, the immune response modifier, TLR7 agonist R-837 (Imiquimod) is a small compound adjuvant that easily passages non-disrupted epidermis. It remains currently elusive which cells of the complex-structured "skin-associated lymphoid tissue" (SALT) respond to the adjuvant and which APC carries the antigen to the draining lymphnodes for subsequent initiation of adaptive immune responses.

The essential role of chemokines in the selective regulation of lymphocyte homing

Knowledge of lymphocyte migration has become a major issue in our understanding of acquired immunity. The selective migration of naïve, effector, memory and regulatory T-cells is a multiple step process regulated by a specific arrangement of cytokines, chemokines and adhesion receptors that guide these cells to specific locations. Recent research has outlined two major pathways of lymphocyte trafficking under homeostatic and inflammatory conditions, one concerning tropism to cutaneous tissue and a second one related to mucosal-associated sites. In this article we will outline our present understanding of the role of cytokines and chemokines as regulators of lymphocyte migration through tissues.

Islet beta-cell-specific T cells can use different homing mechanisms to infiltrate and destroy pancreatic islets

Organ infiltration by T cells depends on the adhesion molecules expressed in these sites and on homing receptors expressed by the T cells. Here, we have studied which form of priming can enable T cells to home to pancreatic islets. To this end, we have used transgenic mice expressing the model autoantigen ovalbumin in pancreatic islets and transgenic ovalbumin-specific CD4 and CD8 T cells. We demonstrate that these T cells were imprinted with homing receptor patterns characteristic for the site of priming, such as alpha4beta7 integrin for mucosal antigen delivery or functionally active alpha4beta1 integrin for islet autoantigens. The adhesion molecules corresponding to these receptors were found to be constitutively expressed in islets, enabling T cells bearing these receptors to infiltrate the islets and to cause diabetes. Disease was prevented only by blockade of the endothelial adhesion molecule, ligand of homing receptors with which the T cells were imprinted. Thus, different priming locations induced different homing mechanisms, allowing T cells to target the islets. This may contribute to the susceptibility of islets to T-cell-mediated attack. Furthermore, it may pertain to the design of adhesion-modulating therapies alone or in combination with external autoantigen administration.

Toll like receptor-3 ligand poly-ICLC promotes the efficacy of peripheral vaccinations with tumor antigen-derived peptide epitopes in murine CNS tumor models

Background

Toll-like receptor (TLR)3 ligands serve as natural inducers of pro-inflammatory cytokines capable of promoting Type-1 adaptive immunity, and TLR3 is abundantly expressed by cells within the central nervous system (CNS). To improve the efficacy of vaccine strategies directed against CNS tumors, we evaluated whether administration of a TLR3 ligand, polyinosinic-polycytidylic (poly-IC) stabilized with poly-lysine and carboxymethylcellulose (poly-ICLC) would enhance the anti-CNS tumor effectiveness of tumor peptide-based vaccinations.

Methods

C57BL/6 mice bearing syngeneic CNS GL261 glioma or M05 melanoma received subcutaneous (s.c.) vaccinations with synthetic peptides encoding CTL epitopes- mEphA2 (671–679), hgp100 (25–33) and mTRP-2 (180–188) for GL261, or ovalbumin (OVA: 257–264) for M05. The mice also received intramuscular (i.m.) injections with poly-ICLC.

Results

The combination of subcutaneous (s.c.) peptide-based vaccination and i.m. poly-ICLC administration promoted systemic induction of antigen (Ag)-specific Type-1 CTLs expressing very late activation antigen (VLA)-4, which confers efficient CNS-tumor homing of vaccine-induced CTLs based on experiments with monoclonal antibody (mAb)-mediated blockade of VLA-4. In addition, the combination treatment allowed expression of IFN-γ by CNS tumor-infiltrating CTLs, and improved the survival of tumor bearing mice in the absence of detectable autoimmunity.

Conclusion

These data suggest that poly-ICLC, which has been previously evaluated in clinical trials, can be effectively combined with tumor Ag-specific vaccine strategies, thereby providing a greater index of therapeutic efficacy.