Cytotoxic T lymphocytes: role in immunosurveillance and in immunotherapy

Experiments in mice and recent human clinical studies have clearly shown the contribution of CD8+ T lymphocyte in the control of tumor development. CD8+ T lymphocytes are a constitutive component of the immune response during the development of cancer. In murine models, the efficiency of various cancer vaccines mainly depends on their ability to induce CD8+ T lymphocytes. Clinical responses in immunotherapy treated cancer patients have been associated with the presence of antitumor specific CD8+ T lymphocytes. In spontaneous regressive melanomas, intratumor antigen specific CD8+ cytotoxic T cells were expanded suggesting their involvement in the tumor shrinkage. Administration of antitumor specific cytotoxic T clones in mice resulted in antitumor responses which directly demonstrated the therapeutic efficiency of these cells. However, in most cases during cancer progression, the presence of antitumor CD8 T lymphocyte is not associated with clinical responses. Intrinsic functional abnormalities of these cells or a defect of CD8+ T cell migration to the tumor may in part explain their failure to inhibit tumor development. On the other hand, tumors also develop immune escape mechanisms (down modulation of tumor antigens, secretion of immunosuppressive factors, expression of anti-apoptotic molecules by the tumors, or pro-apoptotic factors inducing T cell death) to resist to the CD8+ T cell attack. To circumvent these tumor escape mechanisms, efficient cancer vaccines will have to recruit CD8+ T cells associated with other immune effectors.     

Review: cancer immunotherapy by exosome-based vaccines

Exosomes (EXOs) are nanometer-sized membrane vesicles secreted from epithelial and hematopoietic cells. They display a spectrum of molecules involved in immune responses and signal transductions. Previous studies showed that tumor antigen-loaded dendritic cell (DC)- and tumor cell-derived EXOs (Dexo and Texo) induce tumor antigen-specific CD8(+) cytotoxic T-lymphocyte responses and antitumor immunity in experimental animal models and human clinical trials. This review will present the main biologic features of Dexo and Texo as cell-free cancer vaccines with emphasis on their immunostimulatory properties and their potential efficacy in cancer immunotherapy.     

Improving antitumor immune responses by circumventing immunoregulatory cells and mechanisms.

Although numerous immunotherapeutic strategies have been studied in patients with cancer, consistent induction of clinical responses remains a formidable challenge. Cancer vaccines are often successful at generating elevated numbers of tumor-specific T lymphocytes in peripheral blood, however, despite this, tumors usually continue to grow unabated. Recent evidence suggests that endogenous regulatory cells, known to play a major role in the induction of immune tolerance to self and prevention of autoimmunity, as well as suppressive myeloid cells invoked in the tumor-bearing state, may be largely responsible for preventing effective antitumor immune responses. This review will focus on the major regulatory cell subtypes, including CD4(+)CD25(+) T-regulatory cells, type 1 regulatory T cells, natural killer T cells, and immature myeloid cells. Studies in humans and in animal models have shown a role for all of these cells in tumor progression, although the mechanisms by which they act to suppress immunity remain largely undefined. Elucidation of the dominant molecular mechanisms mediating immune suppression in vivo will allow more precise targeting of the relevant regulatory cell populations, as well as the development of novel strategies and clinical reagents that will directly block molecules that induce the suppression of antitumor immunity.     

The role of sargramostim (rhGM-CSF) as immunotherapy

GM-CSF stimulates the differentiation of hematopoietic progenitors to monocytes and neutrophils, and reduces the risk for febrile neutropenia in cancer patients. GM-CSF also has been shown to induce the differentiation of myeloid dendritic cells (DCs) that promote the development of T-helper type 1 (cellular) immune responses in cognate T cells. This review summarizes some of the immunological effects of GM-CSF relevant to antitumor immunity in cancer patients. GM-CSF has been used to augment the activity of rituximab in patients with follicular lymphoma and to induce autologous antitumor immunity in patients with hormone-refractory prostate cancer. GM-CSF causes upregulation of costimulatory molecule expression on leukemia blasts in vitro, enhancing their ability to present antigen to allogeneic T cells, and, in combination with interferon-alpha, can induce antitumor immune responses in patients whose acute leukemia has relapsed following allogeneic hematopoietic progenitor cell transplant. Tumor cells engineered to secrete GM-CSF are particularly effective as antitumor vaccines, and the addition of GM-CSF to standard vaccines may increase their effectiveness by recruiting DCs to the site of vaccination. However, a significant limitation in the use of GM-CSF as an immunostimulatory agent is that objective antitumor responses are infrequent, and are often not durable. Effective and durable antitumor immunity will likely require novel methods to eliminate counterregulatory immune responses that limit activation and expansion of cytotoxic T cells with antitumor activity.     

Synergizing radiation therapy and immunotherapy for curing incurable cancers. Opportunities and challenges

The combination of radiation therapy and immunotherapy holds particular promise as a strategy for cancer therapeutics. Evidence suggests that immunotherapy is most beneficial alone when employed early in the disease process or in combination with standard therapies (eg, radiation) later in the disease process. Indeed, radiation may act synergistically with immunotherapy to enhance immune responses, inhibit immunosuppression, and/or alter the phenotype of tumor cells, thus rendering them more susceptible to immune-mediated killing. As monotherapies, both immunotherapy and radiation may be insufficient to eliminate tumor masses. However, following immunization with a cancer vaccine, the destruction of even a small percentage of tumor cells by radiation could result in crosspriming and presentation of tumor antigens to the immune system, thereby potentiating antitumor responses. Learning how to exploit radiation-induced changes to tumor-cell antigens, and how to induce effective immune responses to these cumulatively immunogenic stimuli, is an exciting frontier in cancer therapy research. This review examines mechanisms by which many forms of radiation therapy can induce or augment antitumor immune responses as well as preclinical systems demonstrating that immunotherapy can be effectively combined with radiation therapy. Finally, we review current clinical trials where standard-of-care radiation therapy is being combined with immunotherapy.     

Antigen-specific immunotherapy and cancer vaccines

The specific activation of the immune system to control cancer growth in vivo has been a long-standing goal in cancer immunology and medical oncology. The identification of tumor-associated antigens has provided the basis for new concepts in antigen-specific immunotherapy. The first clinical trials on cancer vaccines were designed to evaluate the toxicity and objectively measurable immunologic effects in relation to clinical developments mostly in patients with metastatic disease. MHC class I- and II-restricted peptide epitopes, antigenic proteins, viral constructs, mini-genes and whole tumor cells have been used either alone or combined with different cytokines (i.e., IL-2, IL-12, GM-CSF), adjuvants (incomplete Freund's adjuvant, montanide, QS21) or with dendritic cells to induce specific immune responses in vivo. Standardized assay systems to evaluate the immunologic effects of cancer vaccines have been established. Clinical developments during and after vaccination were followed in relation to vaccine-induced immune responses. Prognostic tumor features, i.e., homogeneity of tumor antigen and MHC class I/II expression and intratumoral cellular infiltrates, have been identified that may help to select patients who are more likely to benefit from antigen-specific cancer vaccines in the future.     

Toll-like receptor 9 (TLR9) agonists in the treatment of cancer

Although still early in clinical development, agonists of Toll-like receptor 9 (TLR9) have demonstrated potential for the treatment of cancer. TLR9 agonists directly induce activation and maturation of plasmacytoid dendritic cells and enhance differentiation of B cells into antibody-secreting plasma cells. Preclinical and early clinical data support the use of TLR9 agonists in patients with solid tumors and hematologic malignancies. In preclinical studies, TLR9 agonists have shown activity not only as monotherapy, but also in combination with multiple other therapies, including vaccines, antibodies, cellular therapies, other immunotherapies, antiangiogenic agents, radiotherapy, cryotherapy and some chemotherapies. Phase I and II clinical trials have indicated that these agents have antitumor activity as single agents and enhance the development of antitumor T-cell responses when used as therapeutic vaccine adjuvants. The activity and safety of these novel anticancer agents are being explored in a wide range of tumor types as part of a variety of therapeutic strategies with the goal of harnessing the immune response to fight cancer.     

Generation of effective antitumor vaccines using photodynamic therapy

Preclinical studies have shown that photodynamic therapy (PDT) of tumors augments the host antitumor immune response. However, the role of the PDT effect on tumor cells as opposed to the host tissues has not been determined. To test the contribution of the direct effects of PDT on tumor cells to the enhanced antitumor response by the host, we examined the immunogenicity of PDT-generated murine tumor cell lysates in a preclinical vaccine model. We found that the PDT-generated tumor cell lysates were potent vaccines and that PDT-generated vaccines are more effective than other modes of creating whole tumor vaccines, i.e., UV or ionizing irradiation, and unlike other traditional vaccines, PDT vaccines do not require coadministration of an adjuvant to be effective. PDT vaccines are tumor specific and appear to induce a cytotoxic T-cell response. We have demonstrated that although both UV and PDT-generated tumor cell lysates are able to induce phenotypic DC maturation, only PDT-generated lysates are able to activate DCs to express IL-12, which is critical to the development of a cellular immune response. Our results show that PDT effects on tumor cells alone are sufficient to generate an antitumor immune response, indicating that the direct tumor effects of PDT play an important role in enhancing that host antitumor immune response. These studies also suggest that in addition to the role of PDT as a therapeutic modality, PDT-generated vaccines may have clinical potential as an adjuvant therapy.     

Therapeutic cancer vaccines

Therapeutic cancer vaccines target the cellular arm of the immune system to initiate a cytotoxic T-lymphocyte response against tumor-associated antigens. Immunotherapy offers one of the few therapeutic options that reproducibly leads to a subset of patients with long-term remissions (seemingly cures) of widely metastatic disease. Therapeutic cancer vaccines tested in clinical trials have included inactivated tumor cells administered in immunological adjuvants or after genetic modification to increase their immunogenicity. Other forms are heat shock protein vaccines and anti-ganglioside antibodies. Tumor-associated antigenic peptides have been fully characterized for some cancers. Finally, strategies to directly expand antitumor T lymphocytes and adoptively transfer them to patients with cancer have been developed and shown to induce objective tumor regressions.     

Whole cell vaccines--past progress and future strategies

Cancer vaccines have shown success in curing tumors in preclinical models. Accumulating evidence also supports their ability to induce immune responses in patients. In many cases, these responses correlate with improved clinical outcomes. However, cancer vaccines have not yet demonstrated their true potential in clinical trials. This is likely due to the difficulty in mounting a significant anti-tumor response in patients with advanced disease because of pre-existing tolerance mechanisms that are actively turning off immune recognition in cancer patients. This review will examine the recent progress being made in the design and implementation of whole cell cancer vaccines, one vaccine approach that simultaneously targets multiple tumor antigens to activate the immune response. These vaccines have been shown to induce antigen-specific T-cell responses. Preclinical studies evaluating these vaccines given in sequence with other agents and cancer treatment modalities support the use of immunomodulating doses of chemotherapy and radiation, as well as immune-modulating pathway-targeted monoclonal antibodies, to enhance the efficacy of cancer vaccines. Based on emerging preclinical data, clinical trials are currently exploring the use of combinatorial immune-based therapies for the treatment of cancer.     

β‐glucan restores tumor‐educated dendritic cell maturation to enhance antitumor immune responses

Tumors can induce the generation and accumulation of immunosuppressive cells such as myeloid‐derived suppressor cells (MDSCs) in a tumor microenvironment, contributing to tumor escape from immunological attack. Although dendritic cell‐based cancer vaccines can initiate antitumor immune responses, tumor‐educated dendritic cells (TEDCs) involved in the tolerance induction have attracted much attention recently. In this study, we investigated the effect of β‐glucan on TEDCs and found that β‐glucan treatment could promote the maturation and migration of TEDCs and that the suppressive function of TEDCs was significantly decreased. Treatment with β‐glucan drastically decreased the levels of regulatory T (Treg) cells but increased the infiltration of macrophages, granulocytes and DCs in tumor masses, thus elicited Th1 differentiation and cytotoxic T‐lymphocyte responses and led to a delay in tumor progression. These findings reveal that β‐glucan can inhibit the regulatory function of TEDCs, therefore revealing a novel function for β‐glucan in immunotherapy and suggesting its potential clinical benefit. β‐Glucan directly abrogated tumor‐educated dendritic cells‐associated immune suppression, promoted Th1 differentiation and cytotoxic T‐lymphocyte priming and improved antitumor responses.     

2015 Guidance on cancer immunotherapy development in early‐phase clinical studies

The development of cancer immunotherapies is progressing rapidly with a variety of technological approaches. They consist of “cancer vaccines”, which are based on the idea of vaccination, “effector cell therapy”, classified as passive immunotherapy, and “inhibition of immunosuppression”, which intends to break immunological tolerance to autoantigens or immunosuppressive environments characterizing antitumor immune responses. Recent reports showing clinical evidence of efficacy of immune checkpoint inhibitors and adoptive immunotherapies with tumor‐infiltrating lymphocytes and tumor‐specific receptor gene‐modified T cells indicate the beginning of a new era for cancer immunotherapy. This guidance summarizes ideas that will be helpful to those who plan to develop cancer immunotherapy. The aims of this guidance are to discuss and offer important points in early phase clinical studies of innovative cancer immunotherapy, with future progress in this field, and to contribute to the effective development of cancer immunotherapy aligned with the scope of regulatory science. This guidance covers cancer vaccines, effector cell therapy, and inhibition of immunosuppression, including immune checkpoint inhibitors.     

Advances in dendritic cell-based vaccine of cancer

Dendritic cells (DCs) are potent antigen presenting cells that exist in virtually every tissue, and from which they capture antigens and migrate to secondary lymphoid organs where they activate na?ve T cells. Although DCs are normally present in extremely small numbers in the circulation, recent advances in DC biology have allowed the development of methods to generate large numbers of these cells in vitro. Because of their immunoregulatory capacity, vaccination with tumor antigen-presenting DCs has been proposed as a treatment modality for cancer. In animal models, vaccination with DCs pulsed with tumor peptides, lysates, or RNA or loaded with apoptotic/necrotic tumor cells could induce significant antitumor CTL responses and antitumor immunity. However, the results from early clinical trails pointed to a need for additional improvement of DC-based vaccines before they could be considered as practical alternatives to the existing cancer treatment strategies. In this regard, subsequent studies have shown that DCs that express transgenes encoding tumor antigens are more potent primers of antitumor immunity both in vitro and in vivo than DCs simply pulsed with tumor peptides. Furthermore, DCs that have been engineered to express certain cytokines or chemokines can display a substantially improved maturation status, capacity to migrate to secondary lymphoid organs in vivo, and abilities to stimulate tumor-specific T cell responses and induce tumor immunity in vivo. In this review we also discuss a number of factors that are important considerations in designing DC vaccine strategies, including (i) the type and concentrations of tumor peptides used for pulsing DCs; (ii) the timing and intervals for DC vaccination/boostable data on DC vaccination portends bright prospects for this approach to tumor immune therapy, either alone or in conjunction with other therapies.     

Considerations for the Use of Cytokine-Secreting Tumor Cell Preparations for Cancer Treatment

Limited efficacy of chemotherapy in most solid tumors has revived interest in immunotherapeutic approaches for cancer. One novel form of immunotherapy is the use of cancer vaccines consisting of tumor cells genetically engineered to secrete cytokines. The rationale for this immunization strategy is based on the existence of tumor-specific antigens, on the importance of the cellular arm of the immune system in mediating an effective antitumor response, and on the role of cytokines in regulating the cellular immune response. Such tumor vaccines showed considerable promise in various animal models and induced potent antitumor immunity in the host, which led to regression of established tumors and, moreover, produced immunological memory protecting animals from a subsequent tumor challenge at a distant site. Translated to the human patient, this implies that genetically modified tumor vaccines may be able to eradicate or reduce existing tumor deposits to subclinical levels as well as provide long-term protection from regrowth of tumor cells. This report will review and discuss the concept and rationale for the use of cytokine-secreting tumor vaccines for the treatment of human malignancies.     

Vaccination with liposome--DNA complexes elicits enhanced antitumor immunity

Cationic liposomes have been shown to potentiate markedly the ability of plasmid DNA to activate innate immune responses. We reasoned therefore that liposome-DNA complexes (LDC) could be used to produce more effective plasmid DNA vaccines for cancer. To test this hypothesis, tumor-bearing mice were vaccinated with conventional plasmid DNA vaccines or with LDC vaccines encoding model tumor antigens and CD8(+) T-cell responses and antitumor activity were assessed. We found that although plasmid DNA vaccines generated large increases in antigen-specific CD8(+) T cells, they failed to elicit significant antitumor immunity. In contrast, LDC vaccines elicited large numbers of antigen-specific CD8(+) T cells and also generated significant antitumor activity against established tumors. The antitumor activity elicited by immunization with LDC vaccines was mediated primarily by CD8(+) T cells. Studies of the interaction of LDC with antigen-presenting cells found that LDC triggered dendritic cell production of interleukin-12 and interferon (IFN)-gamma production by natural killer cells in vivo. Activation by LDC was also accompanied by upregulation of costimulatory molecule expression. These findings suggest that by concurrently activating strong systemic innate immune responses and generating cytotoxic T-lymphocyte responses, LDC may be used to increase the effectiveness of therapeutic plasmid DNA vaccination for cancer.     

The History of the Development of Vaccines for the Treatment of Lymphoma

Exploitation of the immune system is an attractive strategy for developing selective lymphoma therapies. In the past several decades, increased knowledge of tumor immunology has granted investigators the tools to formulate a variety of lymphoma-specific vaccines. Vaccines targeting the tumor-specific immunoglobulin (idiotype) of B-cell lymphomas were the first to be developed, owing to successful active vaccination studies in animal models and clinical studies of passive anti-idiotype monoclonal antibodies. In Initials clinical trials, patient-specific idiotype vaccines have been found to induce anti-idiotype immune responses that correlate with improved disease-free and overall survival and the reduction of the level of detectable residual disease. More recent strategies for improving the potency and practicality of idiotype vaccines are utilization of dendritic cells, recombinant idiotype proteins, and DNA vaccination. Custom-made vaccines utilizing whole autologous tumor cells are also being developed. Given the exciting results of these early lymphoma vaccine studies and the accelerated pace of immunologic research, it is hoped that vaccines will someday expand the armamentarium of effective lymphoma therapies.     

Review: anti-CTLA-4 antibody ipilimumab: case studies of clinical response and immune-related adverse events

The immune system is a powerful natural agent against cancer. Cytotoxic T lymphocyte antigen 4 (CTLA-4), a key negative regulator of T-cell responses, can restrict the antitumor immune response. Ipilimumab (MDX-010) is a fully human, monoclonal antibody that overcomes CTLA-4-mediated T-cell suppression to enhance the immune response against tumors. Preclinical and early clinical studies of patients with advanced melanoma show that ipilimumab promotes antitumor activity as monotherapy and in combination with treatments such as chemotherapy, vaccines, or cytokines. Emerging data on the kinetics of response to ipilimumab and associated adverse events are increasing our understanding about how to manage patients treated with this therapy. For example, short-term tumor progression prior to delayed regression has been observed in ipilimumab-treated patients, and objective responses may be of prolonged duration. In some patients clinical improvement manifests as stable disease, which may also extend for months or years. Immune-related adverse events (IRAEs) have been observed in patients after CTLA-4 blockade and most likely reflect the drug mechanism of action and corresponding effects on the immune system. Early clinical data suggest a correlation between IRAEs and response to ipilimumab treatment. This paper briefly reviews the results from several ongoing and completed ipilimumab clinical trials, provides a synopsis of current trials, and presents several cases that demonstrate the kinetics of antitumor responses and the relationship to IRAEs in patients receiving ipilimumab.     

Vaccination strategies for the treatment and prevention of cervical cancer

PURPOSE OF REVIEW: Immunotherapy of HPV-induced premalignant anogenital lesions and cervical cancer has made impressive progress. HPV as causative agent is targeted by prophylactic and therapeutic vaccination strategies. Preclinical and clinical studies have shown induction of natural and/or vaccine-induced immune responses. This review will summarize the status of vaccine development and clinical testing published since March 2003. RECENT FINDINGS: For prophylactic vaccines there is first clinical evidence of effectivity (ie, 100% protection from HPV infection and dysplasia by virus-like particle (VLP) vaccine-induced neutralizing antibodies). Also, therapeutic vaccines have entered clinical evaluation. While prophylactic VLP vaccines are immunogenic per se, therapeutic vaccines will need further adjuvants to guide T cell differentiation, expansion, survival, and homing to tumor sites. To enhance clinical outcome of successful T cell induction in patients, the susceptibility of the tumor cells for lysis must be addressed in the future, since tumor immune evasion is a severe problem in cervical cancer. SUMMARY: While successful prophylactic HPV vaccines have entered large clinical trials, therapeutic HPV vaccines, in spite of T cell induction, lack clinical responses due to the problem of tumor immune evasion. Adjuvants for systemic and local immune modulation will be mandatory for effective therapy.     

Immunobiology and immunotherapy of head and neck cancer

The development of head and neck cancer (HNC) is strongly influenced by the host immune system. Immunoselection of tumors resistant to immune attack and the ability of established tumors to disarm or eliminate immune cells favor tumor progression. Recent evidence for local as well as systemic apoptosis of T lymphocytes, the paucity of dendritic cells (DC) at the tumor site, or the presence of signaling defects in T lymphocytes of patients with HNC emphasizes the fact that their antitumor responses are compromised. The clinical and biologic importance of these immune biomarkers is revealed by the finding that they appear to independently predict 5-year survival in patients with oral carcinoma. Whereas the mechanisms responsible for immune dysfunction in HNC are being investigated, new immunotherapeutic strategies, including antitumor vaccines and DC-based interventions, aim at the restoration of tumor-targeted immune responses. These novel biologic therapies, alone or in combination with conventional therapies, might be expected to protect immune cells from dysfunction or death and to enhance their antitumor activity.     

Cancer vaccines for the treatment and prevention of non small-cell lung cancer

Cancer vaccines targeting non small-cell lung cancer (NSCLC) have been studied for decades; clinical trials, for the most part, have focused on the use of autologous and allogeneic whole-tumor cell vaccines. Recent advances in molecular biology and immunology, however, have allowed the identification of many tumor antigens involved in the generation of immunity to NSCLC. Although small-cell lung cancer (SCLC) is commonly thought of as an immunogenic tumor, it is now clear that NSCLC is also capable of eliciting an endogenous immune response in patients with the disease and, in fact, has a natural history that may make NSCLC more amenable to vaccine therapy as an adjuvant treatment strategy. This review will high-light the major components of the immune system that may potentially interact with tumor-associated proteins as well as outline the immunologic similarities and differences between SCLC and NSCLC. Tumor antigens that elicit immune responses in patients with NSCLC will be discussed. Finally, clinical trials of whole-tumor cell vaccines, both autologous and allogeneic, and tumor antigen-specific vaccines will also be discussed.