Manipulation of T cell costimulatory and inhibitory signals for immunotherapy of prostate cancer

Phase I trial of tremelimumab in combination with short-term androgen deprivation in patients with PSA-recurrent prostate cancer

CTLA-4 blockade has demonstrated antitumor efficacy in human clinical trials. The antitumor mechanism is presumably mediated in part by the expansion of tumor-specific T cells. Androgen deprivation, the cornerstone of treatment for patients with metastatic prostate cancer, has been shown to elicit prostate tissue apoptosis and lymphocytic inflammation. We hypothesized that treatment with androgen deprivation, followed by an anti-CTLA-4 antibody, could augment a tumor-specific immune response elicited by androgen deprivation. We report here the results of a phase I trial evaluating a humanized monoclonal antibody targeting CTLA-4, CP-675,206 (tremelimumab), in combination with androgen deprivation using an antiandrogen. Eligible patients were those with PSA-recurrent prostate cancer after primary surgery and/or radiation therapy, not previously treated with androgen deprivation, and without radiographic evidence of metastatic disease. Subjects were treated in two cycles, 3 months apart, in which they received bicalutamide 150 mg daily days 1-28 and tremelimumab on day 29. The primary endpoint of the trial was safety. Secondary endpoints included measures of PSA kinetics and identification of a maximum tolerated dose. Eleven patients were enrolled and completed at least 1 year of follow-up. Dose-limiting toxicities included grade 3 diarrhea and skin rash. No favorable changes in PSA doubling time were observed in a period shortly after completing treatment; however, three patients experienced a prolongation in PSA doubling time detectable several months after completing treatment. The identification of delayed, prolonged favorable changes in serum PSA suggests that future studies could explore this combination in studies evaluating time to disease progression.

Ipilimumab and cancer immunotherapy: a new hope for advanced stage melanoma

Metastatic melanoma remains one of the most lethal and poorly treated forms of human cancer. Its incidence is on the rise, but no therapies offering improved survival rates have been developed over the last 40 years. This has changed with the recent Food and Drug Administration (FDA) approval of the CTLA-4 function blocking antibody Ipilimumab (Yervoy), proven to extend life in patients with previously treated or untreated metastatic melanoma [39,40]. CTLA-4 is a receptor that normally functions to inhibit inappropriate or prolonged activation of T-cells. This review presents the history of initial research into the function of the CTLA-4 receptor, the pre-clinical evidence for CTLA-4 blockade's utility in cancer treatment, and the recent human clinical trials that have proven its efficacy in advanced stage melanoma. Ipilimumab represents one of a growing class of cancer immunotherapies currently under development and highlights both the promise and relative infancy of these agents in the clinical setting.

Combination of targeted therapy and immunotherapy in melanoma

The treatment of human melanoma has progressed markedly in recent years. Building on the observation that immune recognition is a frequent event in melanoma, a series of immunotherapeutic approaches have been evaluated in clinical trials, culminating in the first phase III study improving overall survival of melanoma patients since 20 years. However, the response rates seen upon immunotherapeutic interventions such as anti-CTLA4 treatment are often low. Furthermore, clinical responses can take several weeks to develop, during which time stage IV melanoma patients often deteriorate. Recent advances in our understanding of the genetic lesions in human melanoma now also allow the specific targeting of the signaling pathway alterations in this disease. Such targeted therapies can lead to high response rates, although the duration of these responses is thus far relatively short. We suggest that the combination of immuno and targeted therapy offers potential for synergy for both conceptual and practical reasons. In this review, we will discuss the potential and possible limitations for such combination therapy, and we describe the most promising combinations of targeted therapy and immunotherapy that can be tested in the clinic in the coming years. The concept of induction therapy by small molecule administration and consolidation by immunotherapeutics also has potential for the treatment of other human cancers.

Immunomodulating antibodies and drugs for the treatment of hematological malignancies

The aim of cancer immunotherapy is to induce immune cells to kill tumor and promote immunological memory that protects against tumor recurrence. Most current immunotherapies, such as monoclonal antibodies (mAb), target the tumor cells directly. Advances in our understanding of the immune system such as the role of co-stimulatory and co-inhibitory receptors, and the advent of new immunomodulatory agents provide new opportunities to target the immune system and enhance anti-tumor immune responses. These promising agents include immunomodulating mAbs, Toll-like receptor agonists, IMiDs, and cytokines. In this review, we discuss the current results of immunomodulating agents in the treatment of hematological malignancies and propose applications that include targeting of the innate and adaptive immune systems as well as combinations with tumor-specific mAbs.

Ipilimumab: a novel immunostimulatory monoclonal antibody for the treatment of cancer

Ipilimumab (Yervoy, developed by Medarex and Bristol-Myers Squibb) is a fully human monoclonal IgG1κ antibody against the cytotoxic T-lymphocyte antigen-4 (CTLA-4), an immune-inhibitory molecule expressed in activated T cells and in suppressor T regulatory cells. Interaction of the monoclonal antibody with CTLA-4 blocks inhibitory signals generated through this receptor and enhances T cell activation, leading to increased antitumor responses. Ipilimumab has been approved by FDA in March 2011 as monotherapy (3mg/kg every 3 weeks for 4 doses) for the treatment of advanced (unresectable or metastatic) melanoma both in pre-treated or chemotherapy naïve patients. Four months later, ipilimumab has received a rapid approval by the European Commission, after a positive opinion from the Committee for Medicinal Products for Human Use. However, the indication in the EU is limited to previously-treated patients with advanced melanoma. Ipilimumab is the first agent that has demonstrated to improve overall survival in patients with metastatic melanoma, which has a very poor prognosis, in randomized phase III clinical trials. The patterns of tumour response to ipilimumab differ from those observed with cytotoxic chemotherapeutic agents, since patients may have a delayed yet durable response and obtain long-term survival benefit despite an initial tumour growth. The major draw-back of ipilimumab is the induction of immune-related adverse effects; the latter can be life-threatening, unless promptly managed with immunosuppressive agents (most frequently corticosteroids) according to specific guidelines. Further development of ipilimumab includes its use in the neoadjuvant or adjuvant high-risk melanoma setting and for the treatment of other refractory and advanced solid tumours, either as single agent or in combination with additional immunostimulating agents or molecularly targeted therapies.

Prostate cancer immunotherapy

The interaction between the immune system and prostate cancer has been an area of research interest for several decades. The recent U.S. Food and Drug Administration approval of 2 first-in-class proof-of-concept immunotherapies (sipuleucel-T and ipilimumab) has stimulated broader interest in manipulating immunity to fight cancer. In the context of prostate cancer, the immunotherapy strategies that have garnered the most interest are the therapeutic vaccination strategies, exemplified by sipuleucel-T and PROSTVAC-VF, and immune checkpoint blockade of CTLA-4 and PD-1. Improved understanding of the immune responses generated by these strategies and development of predictive biomarkers for patient selection will guide rational combinations of these treatments and provide building blocks for future immunotherapies.

Ipilimumab: a novel treatment for metastatic melanoma

OBJECTIVE

To review the mechanism of action, pharmacokinetics, efficacy, safety, drug interactions, dosing, and economic considerations of ipilimumab.

DATA SOURCES

A literature search using MEDLINE (1966-November 2010) was performed using the terms ipilimumab, metastatic melanoma, MDX-010, and MDX-101. Additional data were obtained from meeting abstracts, bibliographies, and media releases.

STUDY SELECTION AND DATA EXTRACTION

English-language articles identified from the data sources were reviewed. Selected studies evaluated the pharmacology, pharmacokinetics, efficacy, and safety of ipilimumab for the treatment of metastatic melanoma.

DATA SYNTHESIS

The incidence of melanoma in the US is increasing faster than any other type of cancer in men and more than any other type of cancer, except lung cancer, in women. For patients with metastatic melanoma, systemic therapies are limited by low response rates, short durations of response, and a 5-year survival rate <10%. Ipilimumab, a novel CTLA-4 inhibitor, is under investigation for the treatment of metastatic melanoma. Results of a randomized, controlled Phase 3 trial showed a first-ever overall survival benefit for patients with previously treated metastatic melanoma who received ipilimumab compared with the controls. The majority of adverse events reported with ipilimumab administration are considered to be low-grade immune-related events involving the skin and intestine and can be managed medically. Nonetheless, 10-17% of patients have immune-related adverse events of grade 3 or higher severity, with 2-3% of these events resulting in death.

CONCLUSIONS

Ipilimumab is a novel CTLA-4 inhibitor that has been evaluated for the treatment of metastatic melanoma. On March 25, 2011, the Food and Drug Administration approved ipilimumab, making it the first agent indicated for unresectable or metastatic melanoma in more than a decade.

Inhibitors of B7-CD28 costimulation in urologic malignancies

T-cell costimulatory molecules deliver positive or negative signals to govern the ultimate fate of immune responses. These ligands and receptors that negatively costimulate T cells (including cytotoxic T-lymphocyte antigen [CTLA]-4, B7-H1, programmed death [PD]-1, B7-H3 and B7x) have received significant interest recently owing to their proposed ability to form a molecular shield for tumor cells. CTLA-4 represents the most extensively studied receptor in the costimulatory pathway and functions as a potent inhibitor of T-cell-mediated immunity. Clinical trials with anti-CTLA-4 are ongoing, although numerous objective responses have been observed in heavily pretreated patients, albeit with autoimmune side effects. In renal cell carcinoma, B7-H1, PD-1 and B7x have been observed to be expressed on tumor cells or infiltrating lymphocytes and are individually associated with adverse pathologic features and poor clinical outcome. In prostate cancer, B7-H3 and B7x immunostaining intensity correlate with disease spread, clinical cancer recurrence and cancer-specific death. External validation and prospective studies are now needed to confirm these findings, while further development of humanized monoclonal antibodies, similar to the experience with anti-CTLA-4, are underway. Herein, we review the B7-CD28 family as it applies to urologic malignancies.

Targeting NKT cells and PD-L1 pathway results in augmented anti-tumor responses in a melanoma model

Invariant or Type 1 NKT cells (iNKT cells) are a unique population of lymphocytes that share characteristics of T cells and natural killer (NK) cells. Various studies have shown that positive costimulatory pathways such as the CD28 and CD40 pathways can influence the expansion and cytokine production by iNKT cells. However, little is understood about the regulation of iNKT cells by negative costimulatory pathways. Here, we show that in vivo activation with α-GalCer results in increased cytokine production and expansion of iNKT cells in the absence of programmed cell death ligand-1 (PD-L1, B7-H1, and CD274). To study whether PD-L1 deficiency on NKT cells would enhance antigen-specific T-cell responses, we utilized CD8(+) OT-1 OVA transgenic T cells. α-GalCer enhanced the expansion and cytokine production of OT-1 CD8(+) cells after adoptive transfer into wild-type recipients. However, this expansion was significantly enhanced when OT-1 CD8(+) T cells were adoptively transferred into PD-L1(-/-) recipients. To extend these results to a tumor model, we used the B16 melanoma system. PD-L1(-/-) mice given dendritic cells loaded with antigen and α-GalCer had a significant reduction in tumor growth and this was associated with increased trafficking of antigen-presenting cells and CD8(+) T cells to the tumors. These data demonstrate that abrogating PDL1:PD-1 interactions during the activation of iNKT cells amplifies an anti-tumor response when coupled with DC vaccination.

Anti-CTLA-4 antibody therapy: immune monitoring during clinical development of a novel immunotherapy

Cytotoxic T-lymphocyte-associated antigen (CTLA-4), also known as CD152, is a co-inhibitory molecule that functions to regulate T-cell activation. Antibodies that block the interaction of CTLA-4 with its ligands B7.1 and B7.2 can enhance immune responses, including antitumor immunity. Two CTLA-4-blocking antibodies are presently under clinical investigation: ipilimumab and tremelimumab. CTLA-4 blockade has shown promise in treatment of patients with metastatic melanoma, with a recently completed randomized, double-blind phase III trial demonstrating a benefit in overall survival (OS) in the treated population. However, this approach appears to benefit only a subset of patients. Understanding the mechanism(s) of action of CTLA-4 blockade and identifying prognostic immunologic correlates of clinical endpoints to monitor are presently areas of intense investigation. Several immunologic endpoints have been proposed to correlate with clinical activity. This review will focus on the endpoints of immune monitoring described in studies to date and discuss future areas of additional work needed.

Immune checkpoint proteins: a new therapeutic paradigm for cancer--preclinical background: CTLA-4 and PD-1 blockade

Much of the recent excitement in the translational field of tumor immunology and immunotherapy has been generated by the recognition that immune checkpoint proteins can be blocked by human antibodies with profound effects in vitro, in animal tumor systems, and in patients. Promising clinical data have already been generated in melanoma and other tumor types with human antibodies directed against cytotoxic T lymphocyte antigen-4 (CTLA-4) and programmed death-1 (PD-1). The preclinical data that supported the clinical development of these two antibodies will be discussed in detail in this review, showing that many of the therapeutic effects of these two agents were predicted by the animal models, as were the immune-related side effects noted with these drugs. In contrast, much of the early work with anti-CTLA-4 antibodies indicated that it had a potent therapeutic effect only when combined with granulocyte-macrophage colony-stimulating factor (GM-CSF)-transduced tumor vaccines, and that the antibody alone was effective only in the most immunogenic tumor models in mice. Intriguingly, in patients, the drug alone clearly has had important therapeutic effects, but the addition of vaccines has not added to its clinical benefit. Murine experiments also suggested that CTLA-4 abrogation might function via important effects on natural T-regulatory cells that were CD4(+), CD25(+high), and FOXp3(+), but this has not been borne out in experiments using peripheral blood mononuclear cells from patients treated with anti-CTLA-4 antibodies, and unlike in animals, in humans the exact mechanism(s) by which CTLA-4 abrogation induced an anti-tumor effect is still unclear. Abrogation of PD-1 functions via different immune signaling pathways than CTLA-4 and is likely to have a different spectrum of effects than blocking CTLA-4. For PD-1 blockade, murine experiments have suggested that the antibody alone and combined with adoptive cell transfer or vaccine approaches would be therapeutically beneficial, and that clear effects on T-cell proliferation and activation, as well as T-regulatory cell function would be observed in patients. The clinical development of anti-PD-1 antibody so far has shown that it has a potent effect when administered alone, and trials of vaccines with anti-PD-1 are just being initiated to test the idea that the predicted effects of that antibody observed in animal systems also would be seen in patients. These observations support the idea that animal preclinical therapeutic experiments are an important guide to the conduct of trials employing abrogation of immune checkpoint proteins in T cells in patients. Nonetheless, clinical investigators must be flexible and prepared to find that the biology of those systems may be very different in humans compared to mice.

Development of a syngeneic mouse model of epithelial ovarian cancer

BACKGROUND

Most cases of ovarian cancer are epithelial in origin and diagnosed at advanced stage when the cancer is widely disseminated in the peritoneal cavity. The objective of this study was to establish an immunocompetent syngeneic mouse model of disseminated epithelial ovarian cancer (EOC) to facilitate laboratory-based studies of ovarian tumor biology and preclinical therapeutic strategies.

METHODS

Individual lines of TgMISIIR-TAg transgenic mice were phenotypically characterized and backcrossed to inbred C57BL/6 mice. In addition to a previously described line of EOC-prone mice, two lines (TgMISIIR-TAg-Low) were isolated that express the oncogenic transgene, but have little or no susceptibility to tumor development. Independent murine ovarian carcinoma (MOVCAR) cell lines were established from the ascites of tumor-bearing C57BL/6 TgMISIIR-TAg transgenic mice, characterized and tested for engraftment in the following recipient mice: 1) severe immunocompromised immunodeficient (SCID), 2) wild type C57BL/6, 3) oophorectomized tumor-prone C57BL/6 TgMISIIR-TAg transgenic and 4) non-tumor prone C57BL/6 TgMISIIR-TAg-Low transgenic. Lastly, MOVCAR cells transduced with a luciferase reporter were implanted in TgMISIIR-TAg-Low mice and in vivo tumor growth monitored by non-invasive optical imaging.

RESULTS

Engraftment of MOVCAR cells by i.p. injection resulted in the development of disseminated peritoneal carcinomatosis in SCID, but not wild type C57BL/6 mice. Oophorectomized tumor-prone TgMISIIR-TAg mice developed peritoneal carcinomas with high frequency, rendering them unsuitable as allograft recipients. Orthotopic or pseudo-orthotopic implantation of MOVCAR cells in TgMISIIR-TAg-Low mice resulted in the development of disseminated peritoneal tumors, frequently accompanied by the production of malignant ascites. Tumors arising in the engrafted mice bore histopathological resemblance to human high-grade serous EOC and exhibited a similar pattern of peritoneal disease spread.

CONCLUSIONS

A syngeneic mouse model of human EOC was created by pseudo-orthotopic and orthotopic implantation of MOVCAR cells in a susceptible inbred transgenic host. This immunocompetent syngeneic mouse model presents a flexible system that can be used to study the consequences of altered gene expression (e.g., by ectopic expression or RNA interference strategies) in an established MOVCAR tumor cell line within the ovarian tumor microenvironment and for the development and analysis of preclinical therapeutic agents including EOC vaccines and immunotherapeutic agents.

The biologic importance of tumor-infiltrating lymphocytes

Detailed pathologic analysis has delineated a close association between intratumoral CD 8(+) cytotoxic T cells and favorable clinical outcomes in diverse cancers. Conversely, the presence at tumor sites of negative immune regulatory elements, such as FoxP 3(+) T cells (Tregs) and PD-1/PD-L1 co-stimulatory molecules, is closely associated with inferior patient survival. Together, these results indicate the importance of the balance between cytotoxic and regulatory pathways in the tumor microenvironment as a critical determinant of prognosis. This immune index also provides a framework for devising therapeutic strategies to enlarge the population of antitumor cytotoxic T cells and attenuate immune regulation. Among these approaches, vaccination with irradiated, autologous tumor cells engineered to secrete granulocyte-macrophage colony-stimulating factor (GM-CSF) followed by antibody blockade of cytotoxic T-lymphocyte associated antigen-4 (CTLA-4) provides clinical benefits for some advanced-course melanoma patients. The extent of tumor necrosis in post-treatment biopsies is linearly related to the natural logarithm of the ratio of CD 8(+) T cells to FoxP 3(+) Tregs. These findings show a concordance between the immune signature of tumor protection in endogenous and therapy-induced responses, strongly supporting Martin Mihm's original insights.

Enhanced tumor eradication by combining CTLA-4 or PD-1 blockade with CpG therapy

Tumor immunotherapy aims to break effector T-cell anergy and to block suppressive cell types and ligands allowing effector cells to exert tumor eradication. Previous reports demonstrate that cytotoxic T lymphocyte antigen-4 (CTLA-4)-blocking antibodies promote T-cell activation and render T effector cells resistant to T regulatory cells (Tregs) whereas programmed death receptor-1 (PD-1)/PD-L1 blockade results in loss of peripheral tolerance. Herein, we explored single or combined antibody blockade of CTLA-4 and PD-1 alone or combined with the toll-like receptor agonists CpG or bacillus Calmette-Guérin for treatment of murine experimental bladder cancer. In therapeutic studies, tumors were rejected by anti-CTLA-4 (aCTLA-4) while anti-PD-1 (aPD-1) suppressed tumor growth. The combination had no additive effect compared with aCTLA-4 alone. However, elevated levels of circulating CD107a expressing CD8 T cells were found in the aCTLA-4 plus aPD-1 group. In addition, levels of antinuclear antibodies correlated inversely with tumor size. Next, we combined CpG or bacillus Calmette-Guérin with aCTLA-4, aPD-1, or aPD-L1 and found that CpG in combination with aCTLA-4 or aPD-1 increased the survival of mice, with aPD-1 plus CpG being superior to either agent alone. CpG plus aCTLA-4 or aPD-1 increased the numbers of circulating tumor-specific CD107a expressing CD8 T cells as well as activated (CD25FoxP3-) CD4 splenocytes. Further, we investigated the numbers of Tregs in the tumor area of treated animals and detected decreased levels after aCTLA-4 or aPD-1 plus CpG therapy. Thus, the combination of CpG with CTLA-4 or PD-1 blockade improved long-term survival and led to increased levels of tumor-reactive T cells and reduced numbers of Tregs at the tumor site.

Immune regulatory antibodies: are they the next advance?

During the past decade, new insights into the mechanisms by which T-cell activation and proliferation are regulated have led to the identification of checkpoint proteins that either up- or down-modulate T-cell reactivity. In the presence of active malignancy, pathophysiologic inhibition of T-cell activity may predominate over stimulation. A number of antibodies have been generated that can block inhibitory checkpoint proteins or promote the activity of activating molecules. In murine models, their use alone or with a vaccine strategy has resulted in regression of poorly immunogenic tumors and cures of established tumors. The prototypical immune regulatory antibodies are those directed against cytotoxic T-lymphocyte antigen-4, a molecule present on activated T cells. In this review, the preclinical rationale and clinical experience with 2 anticytotoxic T-lymphocyte antigen-4 antibodies are extensively discussed, demonstrating that abrogation of an immune inhibitory molecule can result in significant regression of tumors and long-lasting responses. The unique kinetics of antitumor response and the characteristic immune-related side effects of ipilimumab are also discussed. This clinical efficacy of this promising antitumor agent has been evaluated in 2 randomized phase III trials, whose results are eagerly awaited. Programmed death (PD)-1 is another immune inhibitory molecule against which an abrogating human antibody has been prepared. Initial preclinical testing with anti-PD-1 and anti-PD-L1 has shown encouraging results. Stimulatory molecules such as CD40, 41-BB, and OX-40 are also targets for antibody binding and activation, not blockade, and early dose ranging trials with antibodies against all 3 have shown that they can mediate regression of tumors, albeit with their own spectrum of side effects that are different from those that occur with abrogation of immune inhibition.

CTLA-4 blockade: therapeutic potential in cancer treatments

Enhancing or prolonging T-cell activation by monoclonal antibodies (mAbs) blocking negative signaling receptors such as CTLA4 is one approach to overcoming tumor-induced immune tolerance. Ipilimumab and tremelimumab inhibit CTLA4, prolonging antitumor immune responses and leading to durable anti-tumor effects. Treatment with these mAbs has demonstrated clinically important and durable tumor responses and disease control rates in patients with unresectable advanced melanoma. Durable objective responses have been reported across a spectrum of doses and schedules, with relative safety in this patient population. Although the phase III tremelimumab melanoma study was closed for "futility", the 1-year survival rate of >50% for tremelimumab and the median survival of 11.7 months (compared with 10.7 months for chemotherapy) are notable. Results of the phase III studies testing CTLA4-blockade with ipilimumab are eagerly anticipated. The further development of these agents includes testing in the neoadjuvant melanoma setting (ipilimumab) as well the adjuvant high-risk melanoma setting (ipilimumab). Future progress with CTLA-4 blockade therapy will also likely come from the use of combinations of agents that target several critical regulatory pathways of the immune system and modulate the immune response in the host in a synergistic and controlled fashion.

Androgen ablation augments human HLA2.1-restricted T cell responses to PSA self-antigen in transgenic mice

BACKGROUND

In recent years, there has been an increasing interest in targeting human prostate tumor-associated antigens (TAAs) for prostate cancer immunotherapy as an alternative to other therapeutic modalities. However, immunologic tolerance to TAA poses a significant obstacle to effective, TAA-targeted immunotherapy. We sought to investigate whether androgen deprivation would result in circumventing immune tolerance to prostate TAA by impacting CD8 cell responses.

METHODS

To this end, we generated a transgenic mouse that expresses the human prostate-specific antigen (PSA) specifically in the prostate, and crossed it to the HLA-A2.1 transgenic mouse to evaluate how androgen deprivation affects human HLA A2.1-resticted T cell responses following immunization of PSA-expressing mice by vaccinia-PSA (PROSTVAC).

RESULTS

Our PSA transgenic mouse showed restricted expression of PSA in the prostate and detectable circulating PSA levels. Additionally, PSA expression was androgen-dependent with reduced PSA expression in the prostate within 1 week of castration, and undetectable PSA by day 42 after castration as evaluated by ELISA. Castration of the PSA/A2.1 hybrid mouse prior to immunization with a PSA-expressing recombinant vaccinia virus resulted in a significant augmentation of PSA-specific cytotoxic lymphocytes.

CONCLUSIONS

This humanized hybrid mouse model provides a well-defined system to gain additional insight into the mechanisms of immune tolerance to PSA and to test novel strategies aiming at circumventing immune tolerance to PSA and other TAA for targeted prostate cancer immunotherapy.

Antigen quality determines the efficiency of antitumor immune responses generated in the absence of regulatory T cells

The observation that depletion or inhibition of regulatory T cells (Tregs) unleashes efficient antitumor effector immune responses that can lead to tumor eradication in mice has opened new perspectives for the development of cancer immunotherapy. The quality and overall efficiency of the effector immune responses induced in the absence of Tregs seem to depend on multiple factors that determine the result of a battle involving effector T cells (Teffs), Tregs and tumor cells. In this study, we investigated the quality of tumor-associated antigens (TAAs) as one such factor. We show that the presence of a strong dominant antigen is required for the induction of effector responses capable of tumor eradication in the absence of Tregs. The sole addition of a dominant antigen on tumor cells does not change tumor growth in unmanipulated mice, but improves tumor eradication rate from a few to almost 100% in the absence of Tregs. This eradication can be shown to result from the recruitment and activation of specific Teffs recognizing this antigen. We also show that the presence of such dominant antigens has the side effect of restricting the breadth of the immune response to other TAAs, which could favor the generation of escape mutant by tumor editing. Taken together, our results highlight the potential, and some requirements for cancer immunotherapy based on Treg depletion. They also show that, ultimately, tumor fate depends on multiple factors that should all be taken into consideration for the design of more efficient immunotherapy.

Targeting cytotoxic T-lymphocyte antigen 4 in immunotherapies for melanoma and other cancers

The immune system can simultaneously protect against tumor growth and sculpt resistant tumor strains. By a variety of mechanisms, anti-cytotoxic T-lymphocyte antigen (CTLA)-4 therapy may shift such opposing forces towards tumor elimination. In recent clinical trials, anti-CTLA-4 therapy induces durable responses that correlate with markers of immune activity, such as antigen-specific CD4+ or CD8+ cytokine release, antitumor antibody formation or cellular phenotype differentiation. However, some patients exhibit atypical responses to anti-CTLA-4 therapy, demonstrating transient/delayed responses or heterogeneity by lesion site. Such atypical responses may offer insight into the mechanism of anti-CTLA-4 therapy. The immunogram – a newly described graphical synthesis of treatment data and immune correlates in individual patients – may help us to confirm, reject or formulate new hypotheses regarding the mechanism of anti-CTLA-4 activity.

Modeling prostate cancer: a perspective on transgenic mouse models

Despite considerable success in treatment of early stage localized prostate cancer (PC), acute inadequacy of late stage PC treatment and its inherent heterogeneity poses a formidable challenge. Clearly, an improved understanding of PC genesis and progression along with the development of new targeted therapies are warranted. Animal models, especially, transgenic immunocompetent mouse models, have proven to be the best ally in this respect. A series of models have been developed by modulation of expression of genes implicated in cancer-genesis and progression; mainly, modulation of expression of oncogenes, steroid hormone receptors, growth factors and their receptors, cell cycle and apoptosis regulators, and tumor suppressor genes have been used. Such models have contributed significantly to our understanding of the molecular and pathological aspects of PC initiation and progression. In particular, the transgenic mouse models based on multiple genetic alterations can more accurately address the inherent complexity of PC, not only in revealing the mechanisms of tumorigenesis and progression but also for clinically relevant evaluation of new therapies. Further, with advances in conditional knockout technologies, otherwise embryonically lethal gene changes can be incorporated leading to the development of new generation transgenics, thus adding significantly to our existing knowledge base. Different models and their relevance to PC research are discussed.

IFN-gamma-mediated upmodulation of MHC class I expression activates tumor-specific immune response in a mouse model of prostate cancer

De novo expression of B7-1 impaired tumorigenicity of TRAMP-C2 mouse prostate adenocarcinoma (TRAMP-C2/B7), but it did not elicit a protective response against TRAMP-C2 parental tumor, unless after in vitro treatment with IFN-gamma. TRAMP-C2 cells secrete TGF-beta and show low MHC-I expression. Treatment with IFN-gamma increased MHC-I expression by induction of some APM components and antagonizing the immunosuppressant activity of TGF-beta. Thus, immunization with TRAMP-C2/B7 conferred protection against TRAMP-C2-derived tumors in function of the IFN-gamma-mediated fine-tuned modulation of either APM expression or TGF-beta signaling. To explore possible clinical translation, we delivered IFN-gamma to TRAMP-C2 tumor site by means of genetically engineered MSCs secreting IFN-gamma.

T regulatory cells, the evolution of targeted immunotherapy

T regulatory cells are able to suppress anti-tumour immunity in pre-clinical models and in patients. This review highlights the important discoveries in Treg immunology critical to the evolution of targeted immunotherapy. We also describe the therapeutic applications that are currently being assessed and their future potential.

Efficacy and safety of ipilimumab monotherapy in patients with pretreated advanced melanoma: a multicenter single-arm phase II study

BACKGROUND

This phase II study evaluated the safety and activity of ipilimumab, a fully human mAb that blocks cytotoxic T-lymphocyte antigen-4, in patients with advanced melanoma.

PATIENTS AND METHODS

Patients with previously treated, unresectable stage III/stage IV melanoma received 10 mg/kg ipilimumab every 3 weeks for four cycles (induction) followed by maintenance therapy every 3 months. The primary end point was best overall response rate (BORR) using modified World Health Organization (WHO) criteria. We also carried out an exploratory analysis of proposed immune-related response criteria (irRC).

RESULTS

BORR was 5.8% with a disease control rate (DCR) of 27% (N = 155). One- and 2-year survival rates (95% confidence interval) were 47.2% (39.5% to 55.1%) and 32.8% (25.4% to 40.5%), respectively, with a median overall survival of 10.2 months (7.6-16.3). Of 43 patients with disease progression by modified WHO criteria, 12 had disease control by irRC (8% of all treated patients), resulting in a total DCR of 35%. Adverse events (AEs) were largely immune related, occurring mainly in the skin and gastrointestinal tract, with 19% grade 3 and 3.2% grade 4. Immune-related AEs were manageable and generally reversible with corticosteroids.

CONCLUSION

Ipilimumab demonstrated clinical activity with encouraging long-term survival in a previously treated advanced melanoma population.

Modulation of CTLA-4 and GITR for cancer immunotherapy

The rational manipulation of antigen-specific T cells to reignite a tumor-specific immune response in cancer patients is a challenge for cancer immunotherapy. Targeting coinhibitory and costimulatory T cell receptors with specific antibodies in cancer patients is an emerging approach to T cell manipulation, namely "immune modulation." Cytotoxic T-lymphocyte antigen-4 (CTLA-4) and glucocorticoid-induced tumor necrosis factor family receptor (GITR) are potential targets for immune modulation through anti-CTLA-4 blocking antibodies and anti-GITR agonistic antibodies, respectively. In this review, we first discuss preclinical findings key to the understanding of the mechanisms of action of these immunomodulatory antibodies and the preclinical evidence of antitumor activity which preceded translation into the clinic. We next describe the outcomes and immune related adverse effects associated with anti-CTLA-4 based clinical trials with particular emphasis on specific biomarkers used to elucidate the mechanisms of tumor immunity in patients. The experience with anti-CTLA-4 therapy and the durable clinical benefit observed provide proof of principle to effective antitumor immune modulation and the promise of future clinical immune modulatory antibodies.

Ipilimumab monotherapy in patients with pretreated advanced melanoma: a randomised, double-blind, multicentre, phase 2, dose-ranging study

BACKGROUND

Ipilimumab is a human monoclonal antibody that blocks cytotoxic T-lymphocyte antigen 4 and has shown promising activity in advanced melanoma. We aimed to ascertain the antitumour efficacy of ipilimumab in patients with advanced melanoma.

METHODS

We undertook a randomised, double-blind, phase 2 trial in 66 centres from 12 countries. 217 patients with previously treated stage III (unresectable) or stage IV melanoma were randomly assigned a fixed dose of ipilimumab of either 10 mg/kg (n=73), 3 mg/kg (n=72), or 0.3 mg/kg (n=72) every 3 weeks for four cycles (induction) followed by maintenance therapy every 3 months. Randomisation was done with a permuted block procedure, stratified on the basis of type of previous treatment. The primary endpoint was best overall response rate (the proportion of patients with a complete or partial response, according to modified WHO criteria). Efficacy analyses were done by intention to treat, whereas safety analyses included patients who received at least one dose of ipilimumab. This study is registered with ClinicalTrials.gov, number NCT00289640.

FINDINGS

The best overall response rate was 11.1% (95% CI 4.9-20.7) for 10 mg/kg, 4.2% (0.9-11.7) for 3 mg/kg, and 0% (0.0-4.9) for 0.3 mg/kg (p=0.0015; trend test). Immune-related adverse events of any grade arose in 50 of 71, 46 of 71, and 19 of 72 patients at doses of 10 mg/kg, 3 mg/kg, and 0.3 mg/kg, respectively; the most common grade 3-4 adverse events were gastrointestinal immune-related events (11 in the 10 mg/kg group, two in the 3 mg/kg group, none in the 0.3 mg/kg group) and diarrhoea (ten in the 10 mg/kg group, one in the 3 mg/kg group, none in the 0.3 mg/kg group).

INTERPRETATION

Ipilimumab elicited a dose-dependent effect on efficacy and safety measures in pretreated patients with advanced melanoma, lending support to further studies at a dose of 10 mg/kg.

FUNDING

Bristol-Myers Squibb.

Phase I study of ipilimumab, an anti-CTLA-4 monoclonal antibody, in patients with relapsed and refractory B-cell non-Hodgkin lymphoma

PURPOSE

The growth of non-Hodgkin lymphomas can be influenced by tumor-immune system interactions. Cytotoxic T-lymphocyte antigen 4 (CTLA-4) is a negative regulator of T-cell activation that serves to dampen antitumor immune responses. Blocking anti-CTLA-4 monoclonal antibodies improves host resistance to immunogenic tumors, and the anti-CTLA-4 antibody ipilimumab (MDX-010) has clinical activity against melanoma, prostate, and ovarian cancers.

EXPERIMENTAL DESIGN

We did a phase I trial of ipilimumab in patients with relapsed/refractory B-cell lymphoma to evaluate safety, immunologic activity, and potential clinical efficacy. Treatment consisted of ipilimumab at 3 mg/kg and then monthly at 1 mg/kg x 3 months (dose level 1), with subsequent escalation to 3 mg/kg monthly x 4 months (dose level 2).

RESULTS

Eighteen patients were treated, 12 at the lower dose level and 6 at the higher dose level. Ipilimumab was generally well tolerated, with common adverse events attributed to it, including diarrhea, headache, abdominal pain, anorexia, fatigue, neutropenia, and thrombocytopenia. Two patients had clinical responses; one patient with diffuse large B-cell lymphoma had an ongoing complete response (>31 months), and one with follicular lymphoma had a partial response lasting 19 months. In 5 of 16 cases tested (31%), T-cell proliferation to recall antigens was significantly increased (>2-fold) after ipilimumab therapy.

CONCLUSIONS

Blockade of CTLA-4 signaling with the use of ipilimumab is well tolerated at the doses used and has antitumor activity in patients with B-cell lymphoma. Further evaluation of ipilimumab alone or in combination with other agents in B-cell lymphoma patients is therefore warranted.

Tumor vaccines expressing flt3 ligand synergize with ctla-4 blockade to reject preimplanted tumors

The transformation of a healthy cell into a malignant neoplasm involves numerous genetic mutations and aberrations in gene expression. As few of these changes are shared between individuals or types of cancer, the best source for eliciting broad-spectrum tumor immunity remains each patient's own tumor. Previously, we have shown that combining blockade of the T-cell-negative costimulatory molecule CTL-associated antigen 4 (CTLA-4) and vaccination with irradiated B16 tumor expressing granulocyte macrophage colony-stimulating factor (GM-CSF; Gvax) promotes rejection of established murine melanomas. Here we show that, like GM-CSF, the cytokine Flt3 ligand (Flt3L) expressed in B16 and coupled with CTLA-4 blockade promotes both prophylactic and therapeutic rejection of B16. When administered at the site of growing tumor, Gvax fails to prevent tumor outgrowth in any mice, whereas the B16-Flt3L vaccine (Fl3vax) induces the rejection of 75% of melanomas implanted 3 days before vaccination. Relative to Gvax, Fl3vax promotes greater infiltration of both the vaccine site and the tumor site by CD8+ T cells and "sentinel" and plasmacytoid dendritic cells. Gvax and Fl3vax did not synergize when used in combination in treating B16 melanoma even in the context of CD25+ regulatory T-cell depletion. Further, we show that a combination of Flt3L expression and CTLA-4 blockade can also promote the rejection of established TRAMP prostate adenocarcinomas, proving that the utility of this treatment extends beyond melanoma. Engineering Flt3L to be constitutively secreted and attaching an IgG2a tail yielded a B16 vaccine that, when combined with CTLA-4 blockade, prevented the outgrowth of significantly more 5-day implanted B16-BL6 tumors than did Gvax.

Checkpoint blockade in cancer immunotherapy

The progression of a productive immune response requires that a number of immunological checkpoints be passed. Passage may require the presence of excitatory costimulatory signals or the avoidance of negative or coinhibitory signals, which act to dampen or terminate immune activity. The immunoglobulin superfamily occupies a central importance in this coordination of immune responses, and the CD28/cytotoxic T-lymphocyte antigen-4 (CTLA-4):B7.1/B7.2 receptor/ligand grouping represents the archetypal example of these immune regulators. In part the role of these checkpoints is to guard against the possibility of unwanted and harmful self-directed activities. While this is a necessary function, aiding in the prevention of autoimmunity, it may act as a barrier to successful immunotherapies aimed at targeting malignant self-cells that largely display the same array of surface molecules as the cells from which they derive. Therapies aimed at overcoming these mechanisms of peripheral tolerance, in particular by blocking the inhibitory checkpoints, offer the potential to generate antitumor activity, either as monotherapies or in synergism with other therapies that directly or indirectly enhance presentation of tumor epitopes to the immune system. Such immunological molecular adjuvants are showing promise in early clinical trials. This review focuses on the results of the archetypal example of checkpoint blockade, anti-CTLA-4, in preclinical tumor models and clinical trials, while also highlighting other possible targets for immunological checkpoint blockade.

Costimulatory and coinhibitory receptors in anti-tumor immunity

SUMMARY

Despite the expression of antigens by tumor cells, spontaneous immune-mediated rejection of cancer seems to be a rare event. T-cell receptor engagement by peptide/major histocompatibility complexes constitutes the main signal for the activation of naive T cells but is not sufficient to initiate a productive generation and maintenance of effector cells. Full activation of T cells requires additional signals driven by costimulatory molecules present on activated antigen-presenting cells but rarely on tumors. Following the discovery of B7-1 (CD80), several other costimulatory molecules have been shown to contribute to T-cell activation and have relevance for improving anti-tumor immunity. Moreover, increasing the understanding of coinhibitory receptors has highlighted key additional pathways that can dominantly inhibit anti-tumor T-cell function. Improving positive costimulation, and interfering with negative regulation, continues to represent an attractive immunotherapeutic approach for the treatment of cancer. This review focuses upon those pathways with the highest potential for clinical application in human cancer patients.

Negative regulators of T-cell activation: potential targets for therapeutic intervention in cancer, autoimmune disease, and persistent infections

The generation of productive adaptive immune responses depends on the antigen-specific activation of T and B cells. The outcome of T-cell receptor engagement is influenced by signals from both positive and negative regulatory molecules that can either activate or inhibit T-cell function. CD28 and cytotoxic T-lymphocyte antigen-4 are the prototypical members of an immunoglobulin domain-containing protein family that play important roles in the control of T-cell responses against infection, cancer, and in autoimmune disease. Although the precise molecular details of their functions are still under active investigation, tumors and chronic pathogens seem to have exploited these pathways to achieve immune evasion. Furthermore, malfunction of the inhibitory arm of the immune response appears responsible for the development of multiple autoimmune pathologies. As a result, the negative regulators of T-cell activation have become attractive targets for therapeutic intervention in cancer, chronic infection, and autoimmune disease. The application of findings from basic research has provided insight into the manipulation of these pathways in the clinic and offers promising strategies for the treatment of disease.

Carbon nanosyringe array as a platform for intracellular delivery

We report a novel platform for intracellular delivery of genetic material and nanoparticles, based on vertically aligned carbon nanosyringe arrays (CNSAs) of controllable height. Using this technology, we have shown that plasmid and quantum dots can be efficiently delivered to the cytoplasm of cancer cells and human mesenchymal stem cells. The CNSA platform holds great promise for a myriad of applications including cell-based therapy, imaging, and tracking in vivo, and in biological studies aimed at understanding cellular function.

Melan-A-specific cytotoxic T cells are associated with tumor regression and autoimmunity following treatment with anti-CTLA-4

PURPOSE

Ipilimumab is a monoclonal antibody that blocks the immune-inhibitory interaction between CTL antigen 4 (CTLA-4) and its ligands on T cells. Clinical trials in cancer patients with ipilimumab have shown promising antitumor activity, particularly in patients with advanced melanoma. Often, tumor regressions in these patients are correlated with immune-related side effects such as dermatitis, enterocolitis, and hypophysitis. Although these reactions are believed to be immune-mediated, the antigenic targets for the cellular or humoral immune response are not known.

EXPERIMENTAL DESIGN

We enrolled patients with advanced melanoma in a phase II study with ipilimumab. One of these patients experienced a complete remission of his tumor. The specificity and functional properties of CD8-positive T cells in his peripheral blood, in regressing tumor tissue, and at the site of an immune-mediated skin rash were investigated.

RESULTS

Regressing tumor tissue was infiltrated with CD8-positive T cells, a high proportion of which were specific for Melan-A. The skin rash was similarly infiltrated with Melan-A-specific CD8-positive T cells, and a dramatic (>30-fold) increase in Melan-A-specific CD8-positive T cells was apparent in peripheral blood. These cells had an effector phenotype and lysed Melan-A-expressing tumor cells.

CONCLUSIONS

Our results show that Melan-A may be a major target for both the autoimmune and antitumor reactions in patients treated with anti-CTLA-4, and describe for the first time the antigen specificity of CD8-positive T cells that mediate tumor rejection in a patient undergoing treatment with an anti-CTLA-4 antibody. These findings may allow a better integration of ipilimumab into other forms of immunotherapy.

The mechanism of anti-CTLA-4 activity and the negative regulation of T-cell activation

The survival rate of patients diagnosed with late-stage melanoma is poor--only 5%-10%. Enlisting the immune system in the fight against cancers such as melanoma could help improve the prognosis of these patients. Data have shown that melanocyte proteins make good targets for immune system-based therapy in this disease. However, self-tolerance, which develops to inhibit autoimmune attack, makes this strategy difficult. Two proteins on the surface of T cells--CD28 and cytotoxic T-lymphocyte antigen 4 (CTLA-4)--play important roles in the regulation of immune activation and tolerance. CD28 provides positive modulatory signals in the early stages of an immune response, while CTLA-4 signaling inhibits T-cell activation, particularly during strong T-cell responses. CTLA-4 blockade using anti-CTLA-4 monoclonal antibody therapy has great appeal because suppression of inhibitory signals results in the generation of an antitumor T-cell response. Both clinical and preclinical data indicate that CTLA-4 blockade results in direct activation of CD4+ and CD8+ effector cells, and anti-CTLA-4 monoclonal antibody therapy has shown promise in a number of cancers, particularly melanoma. Interestingly, the occurrence of adverse events among patients treated with CTLA-4 blockade helps shed light on the mechanism of action of anti-CTLA-4 monoclonal antibodies. Most adverse events involve immune-related toxicity to the skin and gastrointestinal tract. Major gastrointestinal toxicity develops in up to 21% of treated patients, and while an objective response occurs in approximately 36% of melanoma patients who develop enterocolitis with treatment, an objective response is found in only 11% of patients who do not experience this adverse reaction.

Tremelimumab (CP-675,206): a fully human anticytotoxic T lymphocyte-associated antigen 4 monoclonal antibody for treatment of patients with advanced cancers

Tremelimumab, a fully human monoclonal IgG2 antibody targeting cytotoxic T lymphocyte-associated antigen 4 (CTLA4), is being developed by Pfizer for treatment of patients with advanced cancers. Treatment with an anti-CTLA4 mAb prevents normal downregulation of T cells and prolongs T cell activation, thereby enhancing immune function. In Phase I and II studies, tremelimumab was well tolerated with predictable and manageable side effects. Antitumor activity with monotherapy was observed in patients with advanced melanoma and colorectal cancer (objective response rates of approximately 10 and 2%, respectively), and most objective responses were durable (defined as lasting > 180 days). Additional Phase II and III studies in combination with other agents will assess antitumor activity in multiple tumor types as well as attempt to identify patient populations most likely to respond.

Anti-cytotoxic T-lymphocyte antigen-4 antibody: the first in an emerging class of immunomodulatory antibodies for cancer treatment

PURPOSE

To evaluate the emerging role of immunomodulatory antibodies in cancer treatment. Antibodies (ipilimumab and tremelimumab) targeting cytotoxic T-lymphocyte antigen-4 (CTLA-4), an inhibitory molecule on T cells, represent the vanguard of these new drugs.

DESIGN

We performed a systematic review of the clinical studies examining the clinical activity of anti-CTLA-4 antibodies. We also review the potential mechanisms and toxicities associated with these treatments.

RESULTS

Clinical activity with anti-CTLA-4 monoclonal antibodies (mAbs) has paved the way for additional T-cell immunomodulatory monoclonal antibody (mAb) approaches for the treatment of cancer to be investigated. Because anti-CTLA-4 mAbs target the immune system and not the tumor, they may provide significant potential advantages over traditional antitumor mAbs, chemotherapies, and immunotherapies (ie, vaccines and cytokines). Other antibodies, such as CD137 agonists, CD40 agonists, and PD-1 antagonists, are currently in various stages of preclinical and clinical development.

CONCLUSION

Available clinical data suggest that anti-CTLA-4 mAbs are very different from traditional mAbs, chemotherapies, and immunotherapies in terms of patterns of response, duration of response, and adverse event profile. Ongoing clinical studies aim to establish the efficacy and safety of anti-CTLA-4 mAbs as monotherapy or in combination with other drugs for the treatment of metastatic melanoma and a variety of other cancer types.

Advances in tumour immunotherapy

The clinical goal of tumour immunotherapy is to provide either active or passive immunity against malignancies by harnessing the immune system to target tumours. Although vaccination is an effective strategy to prevent infectious disease, it is less effective in the therapeutic setting for cancer treatment, which might be related to the low immunogenicity of tumour antigens and the reduced immunocompetence of cancer patients. Recent advances in technology have led to the development of passive immunotherapy approaches that utilize the unique specificity of antibodies and T cell receptors to target selected antigens on tumour cells. These approaches are likely to benefit patients and alter the way that clinicians treat malignant disease. In this article we review recent advances in the immunotherapy of cancer, focusing on new strategies to enhance the efficacy of passive immunotherapy with monoclonal antibodies and antigen-specific T cells.

Partially circumventing peripheral tolerance for oncogene-specific prostate cancer immunotherapy

BACKGROUND

Failure of cancer immunotherapy is essentially due to immunological tolerance to tumor-associated antigens (TAAs), as these antigens are also expressed in healthy tissues.

METHODS

Here, we used transgenic adenocarcinoma of mouse prostate (TRAMP) mice, which develop lethal prostate cancer due to prostate-specific expression of SV40 T antigen (Tag), to evaluate effects of prostatic transformation on oncogene TAA-specific tolerance and to test the possibility of breaking such tolerance using a modified recombinant vaccinia virus.

RESULTS

We showed that Tag expression in TRAMP mice is uniquely extra-thymic, and levels of prostatic Tag expression positively correlate with malignant transformation of the prostate. Yet, young tumor-free TRAMP mice were tolerant to Tag antigen. We therefore attempted overcoming such peripheral oncogene-specific T cell tolerance through immunization with a vaccinia construct encoding Tag immunogenic epitopes. This vaccination modality showed that oncogene-specific tolerance was successfully overcome by effective in vivo priming of Tag-specific cytotoxic T cells (CTLs). However, this was restricted to young TRAMP mice. Tag-specific CTL from "tumor naïve" young TRAMP mice showed significant anti-tumor efficacy in vivo by eliminating established heterotopic prostate tumors and prolonging survival in SCID mice harboring Tag-expressing tumors. In contrast, older TRAMP mice with established prostate tumors exhibited oncogene-specific tolerance as evidenced by failure to generate Tag-specific CTL following Tag-specific immunization.

CONCLUSIONS

Peripheral tolerance can be overcome for effective anti-tumor therapy following oncogene-specific immunization. However, this ability to elicit oncogene-specific CTL is impeded in the tumor-bearing host, in the context of increased oncogene expression associated with tumor progression.

Current immunotherapeutic strategies in colon cancer

Because chemotherapy is standard in the treatment of colorectal cancer, it is important to demonstrate whether immunizations may be given to patients receiving systemic chemotherapy. Although some studies have demonstrated immune responses in patients with metastatic colorectal carcinoma who failed standard chemotherapy, the setting of minimal residual disease may be the preferred setting for cancer vaccines. It may be important to choose antigens that have functions important to the cancer cell. The best adjuvant is not well established and may depend on the type of immune response desired. The immune system is "programmed" to down-regulate immune responses once they have become activated to avoid the development of autoimmune disease.

SPAS-1 (stimulator of prostatic adenocarcinoma-specific T cells)/SH3GLB2: A prostate tumor antigen identified by CTLA-4 blockade

Discovery of immunologically relevant antigens in prostate cancer forms the basis for developing more potent active immunotherapy. We report here a strategy using the transgenic adenocarcinoma of mouse prostate (TRAMP) model, which allows for the functional identification of immunogenic prostate tumor antigens with relevance for human immunotherapy. Using a combination of active tumor vaccination in the presence of CTL-associated antigen 4 (CTLA-4) in vivo blockade, we elicited tumor-specific T cells used to expression clone the first T cell-defined TRAMP tumor antigen, called Spas-1 (stimulator of prostatic adenocarcinoma specific T cells-1). Spas-1 expression was increased in advanced primary TRAMP tumors. We show that the immunodominant SPAS-1 epitope SNC9-H(8) arose from a point mutation in one allele of the gene in TRAMP tumor cells, and that immunization with dendritic cells pulsed with SNC9-H(8) peptide resulted in protection against TRAMP-C2 tumor challenge. In humans, the Spas-1 ortholog SH3GLB2 has been reported to be overexpressed in prostate cancer metastases. Additionally, we identified a nonmutated HLA-A2-binding epitope in the human ortholog SH3GLB2, which primed T cells from healthy HLA-A2(+) individuals in vitro. Importantly, in vitro-primed T cells also recognized naturally processed and presented SH3GLB2. Our findings demonstrate that our in vivo CTLA-4 blockade-based T cell expression cloning can identify immunogenic cancer antigens with potential relevance for human immunotherapy.

TLR ligand suppression or enhancement of Treg cells? A double-edged sword in immunity to tumours

Toll-like receptor (TLR) agonists are potent activators of innate immune responses, activating dendritic cell (DC) maturation and inflammatory cytokine secretion by innate immune cells and as a consequence they promote adaptive immune response when coadministered with foreign antigens. There is also some evidence from mouse models that TLR ligands can help to break tolerance to self-antigens and promote immune responses to tumour antigens. Therefore, they have been exploited as adjuvants for tumour vaccines or as immunotherapeutics against cancer. Clinical evaluation of TLR agonists has resulted in a licensed immunotherapeutic for basal cell carcinoma, but there have also been disappointing results from clinical trials, with one pharmaceutical company recently halting its clinical programme. A major obstacle to the development of any active immunotherapeutic approach to cancer is the immunosuppressive environment of the growing tumour, including the induction of tolerogenic DCs and regulatory T (Treg) cells, which suppress the development of protective effector T-cell responses. This can be compounded by the use of TLR ligands as immunotherapeutics. A problem with TLR agonists that has not been fully appreciated is that they can generate suppressive as well as inflammatory responses in innate immune cells and can promote the induction of regulatory as well as effector T cells. This is part of a normal mechanism for limiting collateral damage during infection or sterile inflammation, but can constrain their ability to induce protective antitumour immunity, especially in the immune suppressed environment of the tumour. Alternatively, manipulating the TLR-activated innate immune responses to selectively blocking immunosuppressive arm, as well as that induced by the tumour, may hold the key to enhancing their efficacy as tumour immunotherapeutics and as adjuvants for cancer vaccines.

The role of the CTLA4 blockade in the treatment of malignant melanoma

Metastatic melanoma remains a disease with few effective treatments. The anti-tumor immune response has long been felt to be important in the prognosis of melanoma, and much work has focused on harnessing the immune system to fight this disease. Tumor-specific vaccines, immunomodulatory cytokines and non-specific immunostimulants (such as Bacille Calmette Guerin/BCG) have all been investigated. A new strategy has been identified involving cytotoxic T-lymphocyte antigen-4 (CTLA4). This molecule is expressed on the surface of activated T-lymphocytes and exerts a suppressive effect on the induction of immune responses after interaction between T-cell receptor (TCR) and human lymphocyte antigen (HLA) molecules on the antigen-presenting cell (APC). Work in animal models demonstrated that antibody-mediated blockade of this target could lead to anti-tumor responses. Two fully human monoclonal antibodies, ipilimumab (MDX-010) and tremelimumab (CP-675, 206; formerly known as ticilimumab), are in clinical development. Both have demonstrated hints of clinical activity in metastatic melanoma. Both also have a toxicity profile consistent with their mechanism of action, involving inactivation of a normal immunosuppressive homeostatic mechanism: development of auto-immune breakthrough events (IBE). These include inflammatory bowel disease (IBD), uveitis, dermatitis, arthritis, and others. Generally, these events have been easily managed by cessation of therapy and intravenous or topical steroid therapy and supportive care in most patients, although colectomy had been required in several severe cases and there have been several deaths. Interestingly, patients who develop IBE seem to have the greatest likelihood of clinical benefit, but it is unclear whether clinical benefit and IBE are dissociable events. Other than IBE, no other pharmacodynamic measure has been able to predict response, although certain autoimmune antibody titers may have promise in this regard. Further research will confirm the clinical benefit of these agents alone and in combination with other agents, further define the safety profile and protocols for toxicity management, and identify pharmacodynamic parameters predicting clinical benefit and toxicity.

Cytotoxic T-Lymphocyte–Associated Antigen-4: Fig. 1

Previously, the development of immune-based therapies has primarily focused on vaccines and cytokines, yielding benefit in a small percentage of patients. Recent advances in our understanding of the function of costimulatory molecules have revitalized enthusiasm in the development of immune therapies for cancer. This family of proteins possesses properties involved in both lymphocyte activation and immune-inhibitory functions. The costimulatory molecule with the greatest translation into the clinic thus far is CTL-associated antigen-4 (CTLA-4). CTLA-4 engagement leads to T-cell inhibition by two principle mechanisms. The first involves competitive binding with CD28 for B7 on the antigen-presenting cell. The second is direct intracellular inhibitory signals mediated by the CTLA-4 cytoplasmic tail. Numerous clinical trials testing the blockade of CTLA-4 signaling with fully human monoclonal antibodies have treated a variety of cancers, with the most experience in the treatment of metastatic melanoma. Significant antitumor activity as well as potential autoimmune-related toxicities have been observed. Further clinical investigation with CTLA-4 blockade, planned clinical trials testing manipulation of other costimulatory molecules, and continued improvement in understanding of costimulatory pathways present a new era of immune therapies for cancer patients.

Update on anti-CTLA-4 antibodies in clinical trials

Breaking immune tolerance against tumor self-antigens is presently an area of intense research in the design of cancer therapies. One possible method to enhance immune system activation against tumor antigens is by blocking the inhibitory co-stimulatory signals mediated by cytotoxic T lymphocyte antigen 4, (CTLA-4) expressed on activated T cells. The fully human monoclonal antibodies that are directed against human CTLA-4, ipilimumab (Medarex/Bristol-Myers Squibb) and CP-675,206 (Pfizer/Abgenix, now Amgen), have demonstrated activity against metastatic melanoma, hormone refractory prostate cancer and other malignancies. They have also uncovered unusual immune-related adverse events manifesting as self-limiting inflammatory reactions of the bowel, skin and pituitary. This article reviews preclinical development and data generated from Phase I, II and III studies with regard to the end points reported and immune-related adverse events.

Systemic CTLA-4 blockade ameliorates glioma-induced changes to the CD4+ T cell compartment without affecting regulatory T-cell function

PURPOSE

Patients with malignant glioma suffer global compromise of their cellular immunity, characterized by dramatic reductions in CD4(+) T cell numbers and function. We have previously shown that increased regulatory T cell (T(reg)) fractions in these patients explain T-cell functional deficits. Our murine glioma model recapitulates these findings. Here, we investigate the effects of systemic CTLA-4 blockade in this model.

EXPERIMENTAL DESIGN

A monoclonal antibody (9H10) to CTLA-4 was employed against well-established glioma. Survival and risks for experimental allergic encephalomyelitis were assessed, as were CD4(+) T cell numbers and function in the peripheral blood, spleen, and cervical lymph nodes. The specific capacities for anti-CTLA-4 to modify the functions of regulatory versus CD4(+)CD25(-) responder T cells were evaluated.

RESULTS

CTLA-4 blockade confers long-term survival in 80% of treated mice, without eliciting experimental allergic encephalomyelitis. Changes to the CD4 compartment were reversed, as anti-CTLA-4 reestablishes normal CD4 counts and abrogates increases in CD4(+)CD25(+)Foxp3(+)GITR(+) regulatory T cell fraction observed in tumor-bearing mice. CD4(+) T-cell proliferative capacity is restored and the cervical lymph node antitumor response is enhanced. Treatment benefits are bestowed exclusively on the CD4(+)CD25(-) T cell population and not T(regs), as CD4(+)CD25(-) T cells from treated mice show improved proliferative responses and resistance to T(reg)-mediated suppression, whereas T(regs) from the same mice remain anergic and exhibit no restriction of their suppressive capacity.

CONCLUSIONS

CTLA-4 blockade is a rational means of reversing glioma-induced changes to the CD4 compartment and enhancing antitumor immunity. These benefits were attained through the conferment of resistance to T(reg)-mediated suppression, and not through direct effects on T(regs).

CTLA-4 blockade in murine bone marrow chimeras induces a host-derived antileukemic effect without graft-versus-host disease

We studied the effect of CTLA-4 blockade on graft-versus-leukemia and graft-versus-host responses in a mouse model of minor histocompatibility-mismatched bone marrow transplantation. Early CTLA-4 blockade induced acute graft-versus-host disease. Delayed CTLA-4 blockade resulted in a lethal condition with lymphosplenomegaly, but with stable mixed T-cell chimerism, unchanged alloreactive T-cell frequencies and absent anti-host reactivity in vitro. In contrast, multiorgan lymphoproliferative disease with autoimmune hepatitis and circulating anti-DNA auto-antibodies were documented. Splenic lymphocytes exhibited ex vivo spontaneous proliferation and a marked proliferative response against host-type dendritic cells pulsed with syngeneic (host-type) tissue-peptides. Both phenomena were exclusively mediated by host and not donor T cells, supporting an autoimmune pathogenesis. Selectively host-derived T-cell immune reactivity was equally documented against leukemia-peptide-pulsed dendritic cells, and this was paralleled by a strong in vivo antileukemic effect in anti-CTLA-4-treated and subsequently leukemia-challenged chimeras. In conclusion, delayed CTLA-4 blockade induced a host-derived antileukemic effect, occurring in the context of an autoimmune syndrome and strictly separated from graft-versus-host disease. Both antileukemic and autoimmune responses depended on the allogeneic component, as neither effect was seen after syngeneic bone marrow transplantation. Our findings reveal the potential of using CTLA-4 blockade to establish antileukemic effects after allogeneic hematopoietic stem cell transplantation, provided autoimmunity can be controlled.

A pilot study of CTLA-4 blockade after cancer vaccine failure in patients with advanced malignancy

PURPOSE

Eleven patients with progressive advanced malignancy after administration of a cancer vaccine received a fully human anti-CTLA-4 monoclonal antibody (ipilimumab). The primary end point was to determine drug toxicity. Tumor response, tumor-specific CD8+ T-cell immune responses, and modulation of CD4+ CD25+ FoxP3+ regulatory T-cell (Treg) numbers were secondary end points.

EXPERIMENTAL DESIGN

Three patients with colon cancer, four with non-Hodgkin's lymphoma, and four with prostate cancer were treated. The first dose was given at 3 mg/kg and subsequent doses were administered monthly at 1.5 mg/kg for a total of four cycles.

RESULTS

Tumor regression was observed in two patients with lymphoma; one of which obtained a partial response of 14-month duration. Ipilimumab was well tolerated with predominantly grade 1/2 toxicities. One drug-related grade 3 toxicity was observed. One patient died within 30 days of treatment due to progressive colon cancer. No increase in vaccine-specific T-cell responses was observed after therapy. Tregs as detected by expression of CD4+CD25+CD62L+ declined at early time points but rebounded to levels at or above baseline values at the time of the next infusion.

CONCLUSIONS

Ipilimumab treatment depressed Treg numbers at early time points in the treatment cycle but was not accompanied by an increase in vaccine-specific CD8+ T-cell responses in these patients previously treated with a variety of investigational anticancer vaccines. A partial response was observed in one patient with follicular lymphoma. A phase I/II trial evaluating ipilimumab in patients with follicular lymphoma is currently ongoing.