Regulatory T cells and innate immune regulation in tumor immunity

Innate and adaptive immunity play important roles in immunosurveillance and tumor destruction. However, increasing evidence suggests that tumor-infiltrating immune cells may have a dual function: inhibiting or promoting tumor growth and progression. Although regulatory T (Treg) cells induce immune tolerance by suppressing host immune responses against self- or nonself-antigens, thus playing critical roles in preventing autoimmune diseases, they might inhibit antitumor immunity and promote tumor growth. Recent studies demonstrate that elevated proportions of Treg cells are present in various types of cancers and suppress antitumor immunity. Furthermore, tumor-specific Treg cells can inhibit immune responses only when they are exposed to antigens presented by tumor cells. Therefore, Treg cells at tumor sites have detrimental effects on immunotherapy directed to cancer. This review will discuss recent progress in innate immunity, Treg cells, and their regulation through Toll-like receptor (TLR) signaling. It was generally thought that TLR-mediated recognition of specific structures of invading pathogens initiate innate and adaptive immune responses through dendritic cells. New evidence suggests that TLR signaling may directly regulate the suppressive function of Treg cells. Linking TLR signaling to the functional control of Treg cells opens intriguing opportunities to manipulate TLR signaling to control both innate and adaptive immunity against cancer.An erratum to this article can be found at     

Dendritic cell vaccine immunotherapy of cancer targeting MUC1 mucin

The use of dendritic cells (DCs) for cancer vaccination is effective in suppressing cancer progression. This is because the DCs play a crucial role in priming tumor-specific immunity efficiently as antigen-presenting cells. In this study, we analyzed the ability of DCs to elicit tumor-specific immunity and clinical effects of DC vaccine immunotherapy targeting MUC1 tumor antigens. DCs from 14 patients with advanced or metastatic breast or lung cancer (9 positive for MUC1 and 5 negative for MUC1) were loaded with MUC1 antigens or tumor lysate and used for therapeutic vaccination. After vaccination, all the MUC1-positive patients acquired antigen-specific immunity whereas only 1 case with MUC1-negative cancer showed the specific immunity. Clinically, marked effects such as reduction in tumor sizes or tumor marker levels or disappearance of malignant pleural effusion were observed in 7 of the 9 MUC1-positive cases. However, MUC1-negative patients did not respond to DC vaccines, with the exception of 1 case with MAGE3-positive lung cancer. Survival of MUC1-positive patients was significantly prolonged in comparison with MUC1-negative patients (mean survival: 16.75 versus 3.80 months, p=0.0101). These data suggest that MUC1 is sufficiently immunogenic to elicit strong anti-tumor immunity as a tumor antigen and that DC vaccines targeting MUC1 are useful for immunotherapy of cancer.     

Melanoma cell necrosis facilitates transfer of specific sets of antigens onto MHC class II molecules of dendritic cells

Vaccine strategies that target dendritic cells (DC) in order to elicit immunity against tumors are the subject of intense research. For the induction and maintenance of anti-tumor immunity, CD4+ helper T cells are often required, which need to see appropriate MHC class II-peptide complexes on DC. So far, it remained widely unclear what type of tumor cells can feed the MHC class II processing pathway of DC with what type of antigens. Here, we report that peptide loading onto MHC class II molecules of myeloid DC is facilitated by melanoma cells undergoing necrotic rather than apoptotic cell death. Importantly, the set of MHC class II-associated peptides induced by necrotic tumor cells differed from those found upon engagement of apoptotic tumor cells. This may be due to the fact that only necrotic cells liberated heat shock proteins, which bind tumor-derived peptides and thereby may promote processing by DC. The potential of DC to activate T cells was kinetically controlled through their antigen receptivity: CD4+ T cells were easily stimulated upon encountering antigen early in DC maturation, whereas antigen capture at later maturation stages favored activation of CD8+ T cells. These findings may aid in designing future vaccination strategies and in identifying novel tumor-specific helper T cell antigens.     

Genetic idiotypic and tumor cell-based vaccine strategies for indolent non Hodgkin's lymphoma

B cell malignancies express a clear tumor-specific antigen (B cell immunoglobulin variable regions) known as idiotype (Id). It is now possible to immunize patients against autologous Id generating humoral and cellular immune responses that correlate with clinical and molecular remissions and the possibility of improved disease-free survival. In its present form, however, individual vaccine preparation by generating heterohybridomas is a technical and financial challenge. DNA vaccination provides a unique opportunity to streamline individual vaccine manufacture by circumventing the need for protein purification. DNA fusion vaccines have been developed in which genetic carriers promote adaptive immunity against the attached Id. Such carriers can specifically bind receptors on dendritic cells (DC) for targeted antigen delivery, or supply high levels of T cell help. Ideally, the carrier should be able to activate innate immunity to enhance the antigen-presenting capacity of DC. The correlates of immunity may vary depending upon the genetic carrier used. Translation to patients has begun with preliminary evidence of Id-specific immune responses. An alternative vaccination strategy that allows for the potential to vaccinate against multiple tumor antigens without the need to identify individual antigens is based on tumor cells themselves to be used as vaccine. To this purpose, however, each patient's tumor cells must be genetically modified to increase their immunogenicity. To overcome the technical limitations inherent with a fully autologous approach, strategies have been devised where a universal, genetically modified bystander cells is expected to provide the immunoenhancing cytokines to allow immune recognition of unmodified patients' tumor cells.     

Immune cell functions in pancreatic cancer

Pancreatic cancer kills nearly 29,000 people in the United States annually-as many people as are diagnosed with the disease. Chemotherapeutic treatment is ineffective in halting progression of the disease. Yet, specific immunity to pancreatic tumor cells in subjects with pancreatic cancer has been demonstrated repeatedly during the last 24 years. Attempts to expand and enhance tumor-specific immunity with biotherapy, however, have not met with success. The question remains, "Why can't specific immunity regulate pancreatic cancer growth?" The idea that tumor cells have evolved protective mechanisms against immunity was raised years ago and has recently been revisited by a number of research laboratories. In pancreatic cancer, soluble factors produced by and for the protection of the tumor environment have been detected and are often distributed to the victim's circulatory system where they may effect a more generalized immunosuppression. Yet the nature of these soluble factors remains controversial, since some also serve as tumor antigens that are recognized by the same T cells that may become inactivated by them. Unless the problem of tumor-derived immunosuppressive products is addressed directly through basic and translational research studies, successful biotherapeutic treatment for pancreatic cancer may not be forthcoming.     

Taming cancer by inducing immunity via dendritic cells

Summary: Immunotherapy seeks to mobilize a patient's immune system for therapeutic benefit. It can be passive, i.e. transfer of immune effector cells (T cells) or proteins (antibodies), or active, i.e. vaccination. In cancer, passive immunotherapy can lead to some objective clinical responses, thus demonstrating that the immune system can reject tumors. However, passive immunotherapy is not expected to yield long-lived memory T cells that might control tumor outgrowth. Active immunotherapy with dendritic cell (DC)-based vaccines has the potential to induce both tumor-specific effector and memory T cells. Early clinical trials testing vaccination with ex vivo -generated DCs pulsed with tumor antigens provide a proof-of-principle that therapeutic immunity can be elicited. Yet, there is a need to improve their efficacy. The next generation of DC vaccines is expected to generate large numbers of high-avidity effector CD8⁺ T cells and to overcome regulatory T cells. Therapeutic vaccination protocols will combine improved ex vivo DC vaccines with therapies that offset the suppressive environment established by tumors.     

Interleukin-10-induced T cell unresponsiveness can be reversed by dendritic cell stimulation

The secretion of immunosuppressive factors like interleukin-10 (IL-10), either by tumor cells or by tumor-infiltrating leukocytes, has been recognized as one of the mechanisms involved in tumor immunological escape and a serious obstacle for successful immunotherapy. Therefore, any therapeutic attempts aimed at inducing antitumor immunity in tumor-bearing hosts must overcome this immunosuppressive state. This study aimed to determine whether dendritic cell (DC) immunization, a promising approach to induce antitumor immunity, could break IL-10-induced anergic state in CD4+ T cells, essential cells in generating tumor-specific immunity. We found that the ability of DC to reverse IL-10-induced anergic state in human CD4+ T cells is dependent on the IL-10 concentration that T cells have been exposed to and the degree of DC maturation. The efficacy of mature DC in reversing T cell anergy can be mimicked by higher cell numbers of immature DC. In addition, activated T cells induced by DC stimulation are sensitive to IL-10 treatment. Collectively, our results suggest the use of mature DC and the necessity of antagonizing the action of tumor-derived IL-10 in immunotherapy of cancer with DC immunization.     

Intratumoral administration of secondary lymphoid chemokine and unmethylated cytosine-phosphorothioate-guanine oligodeoxynucleotide synergistically inhibits tumor growth in vivo

Secondary lymphoid tissue chemokine (SLC), which is expressed in T cell zones of secondary lymphoid organs, including the spleen and lymph nodes, strongly recruits both T lymphocytes and mature dendritic cells. As appropriate interaction of tumor-specific T cells and mature dendritic cells, equipped with tumor antigens, is a prerequisite for effective T cell immunity against established tumors, we mobilized lymphocytes and dendritic cells to tumor sites by intratumoral injection of secondary lymphoid tissue chemokine-Fc (SLC-Fc) fusion protein using the B16F10 murine melanoma model. Activation of dendritic cells, another prerequisite for the effective activation of naïve tumor-specific T cells, was achieved by the addition of immunostimulatory cytosine-phosphorothioate-guanine oligodeoxynucleotide (CpG-ODN) into the tumor site. Intratumoral administration of SLC-Fc or CpG-ODN revealed antitumor effects against B16F10 murine melanoma grown in the subcutaneous space. Co-treatment of SLC-Fc and CpG-ODN displayed synergistic effects in reducing the tumor size. The synergistic antitumor effect in co-treatment group was correlated with the synergistic/additive increase in the infiltration of CD4⁺ T cells and CD11c⁺ dendritic cells in the tumor mass compared to the single treatment groups. These results suggest that the combined use of chemokines and adjuvant molecules may be a possible strategy in clinical tumor immunotherapy.     

A ROLE FOR ANTIBODIES IN TUMOR IMMUNITY

Recent advances have demonstrated the clinical utility of specific monoclonal antibodies that recognize tumor-associated antigens on the surface of the tumor cell in the treatment of breast cancer and B cell lymphoma in humans. In addition to these studies, an experimental tumor model, where antibodies that recognize a viral-encoded tumor-specific antigen play a major role in tumor immunity, will be discussed. Together, these studies implicate antibodies as a means of providing tumor immunity against some cancers. The necessity for designing cancer vaccines that induce antibodies with specificity for antigens on the tumor cell will be discussed. antibodies immunity tumors     

Establishment of tumor-specific immunotherapy model utilizing vaccinia virus-reactive helper T cell activity

It was previously demonstrated that preimmunization of mice with live vaccinia virus (VV) and subsequent immunization with VV-infected (modified), syngeneic tumor cells resulted in enhanced induction of tumor-specific immunity through a cellular collaboration between VV-reactive helper T (VV-Th) cells and tumor-specific effector cell precursors. On the basis of this augmenting system, a tumor-specific immunotherapy model was established in which a growing tumor regressed. C3H/HeN mice were pretreated with cyclophosphamide to eliminate nonspecific suppressor T cell activity and subsequently inoculated (primed) s.c. with live VV, leading to augmented induction of VV-Th cell activities. Four weeks later, the mice were inoculated i.d. with syngeneic X5563 myeloma cells. Six days after the tumor cell inoculation, live VV was injected into the tumor mass three times at 2-day intervals. Seven of ten mice which had received VV priming and subsequent VV injection into the tumor mass exhibited complete tumor regression. On the contrary, mice which had received mere intratumoral VV injection in the absence of VV priming failed to exhibit appreciable tumor regression. Mice whose tumor had completely regressed (regressor mice) by the above VV immunotherapy were shown to have acquired systemic anti-tumor immunity, which was confirmed by a challenge with syngeneic tumor cells after the tumor regression. In vitro analysis of these immune mice revealed that potent tumor-specific cytotoxic T lymphocyte responses were preferentially induced, but with no detectable anti-tumor antibody responses. Such a potent tumor-specific immunity was not observed in mice which had received an intratumoral VV injection in the absence of VV priming. Thus the results clearly indicate that the tumor regression was accompanied by concurrent generation of a potent tumor-specific immunity, suggesting that the cellular collaboration between VV-Th cells and tumor-specific effector cell precursors is also functioning in this VV-immunotherapy protocol, likewise the immunoprophylactic model. Therefore, the present model provides an effective maneuver for tumor-specific immunotherapy and this system will be theoretically applicable to human cancer treatment.     

A role for antibodies in tumor immunity

Recent advances have demonstrated the clinical utility of specific monoclonal antibodies that recognize tumor-associated antigens on the surface of the tumor cell in the treatment of breast cancer and B cell lymphoma in humans. In addition to these studies, an experimental tumor model, where antibodies that recognize a viral-encoded tumor-specific antigen play a major role in tumor immunity, will be discussed. Together, these studies implicate antibodies as a means of providing tumor immunity against some cancers. The necessity for designing cancer vaccines that induce antibodies with specificity for antigens on the tumor cell will be discussed.     

Recognition of tumor glycans by antigen-presenting cells

C-type lectin receptors on antigen-presenting cells are potent antigen-uptake receptors with specificity for glycan structures. Glycosylation changes during malignant transformation create tumor-specific carbohydrate structures that interact with C-type lectins on dendritic cells. Recent findings revealed that tumor glycoproteins, such as carcinoembryonic antigen and MUC-1, indeed interact with the C-type lectins DC-SIGN and macrophage galactose-type lectin on antigen-presenting cells. The consequences for anti-cancer immunity or tolerance induction can be extrapolated from the function of C-type lectins in pathogen recognition and antigen presentation. In addition, in vivo studies in mice recently demonstrated the potency of targeting antigens to C-type lectins on antigen-presenting cells for anti-tumor vaccination strategies.     

Decreased wheel-running activity in hamsters post myocardial infarction

Historically cancer vaccines have yielded suboptimal clinical results. We have developed a novel strategy for eliciting antitumor immunity based upon homology between neoplastic tissue and the developing placenta. Placenta formation shares several key processes with neoplasia, namely: angiogenesis, activation of matrix metalloproteases, and active suppression of immune function. Immune responses against xenoantigens are well known to break self-tolerance. Utilizing xenogeneic placental protein extracts as a vaccine, we have successfully induced anti-tumor immunity against B16 melanoma in C57/BL6 mice, whereas control xenogeneic extracts and B16 tumor extracts where ineffective, or actually promoted tumor growth, respectively. Furthermore, dendritic cells were able to prime tumor immunity when pulsed with the placental xenoantigens. While vaccination-induced tumor regression was abolished in mice depleted of CD4 T cells, both CD4 and CD8 cells were needed to adoptively transfer immunity to naïve mice. Supporting the role of CD8 cells in controlling tumor growth are findings that only freshly isolated CD8 cells from immunized mice were capable of inducing tumor cell caspases-3 activation ex vivo. These data suggest feasibility of using xenogeneic placental preparations as a multivalent vaccine potently targeting not just tumor antigens, but processes that are essential for tumor maintenance of malignant potential.     

Immunogenic anti-cancer chemotherapy as an emerging concept

Tumors can acquire mutations or hijack regulatory pathways of the host immune system to render them resistant to immune attack. Standard first line therapies such as chemotherapy and radiation were not thought to provoke natural immunity to cancer, but recent findings demonstrating that dying tumor cells present and release key signals to stimulate or evade neighboring leukocytes are challenging that view. Killing tumor cells in a manner that provides danger signals and tumor antigens in the right context promotes the engagement of innate and adaptive immunity; however, this response alone will not be effective against established cancer. Coincidently driving the immune response with specific monoclonal antibodies and other immunomodulators that activate and mature dendritic cells and co-stimulate T cells and other lymphocytes is one approach. Additionally releasing immune checkpoints and inhibiting tumor-derived molecules that prevent effective tumor immunity is another. Combined these approaches have enormous potential to improve the current outcomes from conventional cancer therapy.     

Tumor immunity meets autoimmunity: antigen levels and dendritic cell maturation

Nai;ve T cells in the draining lymph node (DLN) do not immediately respond to antigenic tissues or antigenic cancers in the periphery. Rather, the conditions under which nai;ve T cells encounter antigen in the DLN can result in the distinct immunological states of ignorance, tolerance or immunity. Recent work suggests that these immunological states are determined by the level of antigen expressed by peripheral tissues and the maturation stage of the dendritic cell presenting the antigen. When antigens are expressed at levels that are sufficient to be cross-presented by mature dendritic cells in the DLN, nai;ve T cells can respond to self antigens or tumor antigens to induce a state of autoimmunity or tumor immunity, respectively. Exploiting these conditions to target unique tumor antigens will enable us to develop better cancer immunotherapies.     

Activation of human B cells by the agonist CD40 antibody CP-870,893 and augmentation with simultaneous toll-like receptor 9 stimulation

Background  

CD40 activation of antigen presenting cells (APC) such as dendritic cells (DC) and B cells plays an important role in immunological licensing of T cell immunity. Agonist CD40 antibodies have been previously shown in murine models to activate APC and enhance tumor immunity; in humans, CD40-activated DC and B cells induce tumor-specific T cells in vitro. Although clinical translation of these findings for patients with cancer has been previously limited due to the lack of a suitable and available drug, promising clinical results are now emerging from phase I studies of the agonist CD40 monoclonal antibody CP-870,893. The most prominent pharmacodynamic effect of CP-870,893 infusion is peripheral B cell modulation, but direct evidence of CP-870,893-mediated B cell activation and the potential impact on T cell reactivity has not been reported, despite increasing evidence that B cells, like DC, regulate cellular immunity.     

Epithelial-dendritic cell interactions in allergic disorders

Airway epithelial cells act through multiple mechanisms to function as an important component of the pulmonary defence strategy that is crucial to the maintenance of immune homeostasis. Dendritic cells are uniquely potent inducers of immune responses and it is increasingly clear that epithelium has the capacity to modulate the functional activity of dendritic cells, and vice versa, through production of a diverse array of mediators. Bidirectional interactions between epithelial cells and dendritic cell networks can thus impact upon the development and progression of immunity/tolerance in respiratory tissues. In this brief review we highlight the most recent advances in understanding how airway epithelial/dendritic cell interactions contribute to allergic disorders.     

Immunological ignorance of solid tumors

Many peripheral solid tumors such as sarcomas and carcinomas express tumor-specific antigens that can serve as targets for immune effector T cells. Nevertheless, the immune surveillance against clinically manifest carcinomas and sarcomas seems relatively inefficient. Naïve cytotoxic T cells are activated exclusively in secondary lymphoid organs including the spleen and lymph nodes. Tumor antigen might be either cross-presented to naïve cytotoxic T cells by professional antigen-presenting cells (pAPC), or presented directly by tumor cells that migrated to secondary lymphoid organs. Direct priming is quite inefficient during early tumor development because metastasis to lymphoid organs is usually limited to advanced stage diseases. Similarly, the process of cross-priming by pAPC seems to depend on relatively large antigen amounts and on maturation stimuli for dendritic cells, and both requirements may be limiting during initial tumorigenesis. Therefore, the immunosurveillance of solid tumors may fail because they are ignored for too long by the immune system. However, these situations may prove promising for the induction of tumor-specific T cell immunity by vaccination, as the T cell repertoire against these antigens has a naïve phenotype and is not yet affected by tolerance mechanisms.     

Toll-like receptor (TLR) expression of immune system cells from metastatic breast cancer patients with circulating tumor cells

The risk posed by breast cancer represents a complex interaction among factors affecting tumor immunity of the host. Toll-like receptors (TLRs) are members of the innate immune system and generally function to attract host immune cells upon activation. However, the good intentions of TLRs are sometimes not transferred to positive long-term effects, due to their involvement in exacerbating inflammatory effects and even contributing to continued inflammation. Chronic inflammatory states are considered to favor an increased predisposition to cancer, with continuous activation of inflammatory cytokines and other hallmarks of inflammation exerting a deleterious effect. Circulating tumor cells (CTCs) are neoplastic cells present in the peripheral blood circulation that have been found to be an indicator of disease progression and long-term survival. In the present study, we examined the expression of TLRs on dendritic cells, which play a major role in eliciting anti-tumor immunity, in metastatic breast cancer patients with CTCs. Flow cytometric data showed significant differences between circulating tumor cell (CTC) positive patients and CTC negative patients in their expression of TLR2 by CD8 positive cytotoxic T cells and TLR2, TLR4, TLR3, and TLR8 by CD11c positive dendritic cells (p < 0.05). Expression of TLR2, TLR4, and TLR8 was increased in CTC positive patients, whereas TLR3 expression was decreased in the dendritic cell population.     

Prospects of combinatorial synthetic peptide vaccine-based immunotherapy against cancer

The insight that the immune system is involved in tumor resistance is gaining momentum and this has led to the development of immunotherapeutic strategies aiming at enhancement of immune-mediated tumor destruction. Although some of these strategies have moderate clinical benefit, most stand-alone therapies fail to significantly affect progressive disease and survival or do so only in a minority of patients. Research on the mechanisms underlying the generation of immune responses against tumors and the immune evasion by tumors has emphasized that various mechanisms simultaneously prevent effective immunity against cancer including inefficient presentation of tumor antigens by dendritic cells and induction of negative immune regulation by regulatory T-cells (Tregs) and myeloid derived suppressor cells (MDSCs). Thus the design of therapies that simultaneously improve effective tumor immunity and counteract immune evasion by tumors seems most desirable for clinical efficacy. As it is unlikely that a single immunotherapeutic strategy addresses all necessary requirements, combinatorial strategies that act synergistically need to be developed. Here we discuss the current knowledge and prospects of treatment with synthetic peptide vaccines that stimulate tumor-specific T-cell responses combined with adjuvants, immune modulating antibodies, cytokines and chemotherapy. We conclude that combinatorial approaches have the best potency to accomplish the most significant tumor destruction but further research is required to optimize such approaches.