CTLA4 blockade induces frequent tumor infiltration by activated lymphocytes regardless of clinical responses in humans

Enhancement of T cell recruitment and infiltration into tumours

Studies have documented that cancer patients with tumours which are highly infiltrated with cytotoxic T lymphocytes show enhanced survival rates. The ultimate goal of cancer immunotherapy is to elicit high-avidity tumour-specific T cells to migrate and kill malignant tumours. Novel antibody therapies such as ipilumimab (a cytotoxic T lymphocyte antigen-4 blocking antibody) show enhanced T cell infiltration into the tumour tissue and increased survival. More conventional therapies such as chemotherapy or anti-angiogenic therapy and recent therapies with oncolytic viruses have been shown to alter the tumour microenvironment and thereby lead to enhanced T cell infiltration. Understanding the mechanisms involved in the migration of high-avidity tumour-specific T cells into tumours will support and provide solutions for the optimization of therapeutic options in cancer immunotherapy.

Tumor infiltrating lymphocytes (TIL) and prognosis in oral cavity squamous carcinoma: a preliminary study

OBJECTIVES

Tumor infiltrating lymphocytes (TILs) in the microenvironment reflect may tumor biology and predict outcome. We previously demonstrated that infiltrates of CD4, CD8, and FoxP3 positive lymphocytes were associated with HPV-status and survival in oropharyngeal cancers. To determine if TILs were of prognostic importance in oral cancer, TIL levels were evaluated retrospectively in 52 oral cancer patients treated with surgery and correlations with outcome determined.

METHODS

Complete TIL and clinical data were available for 39 patients. Levels of CD4, CD8, FoxP3 (Treg), CD68 and NK cells were assessed by immunohistochemistry in tumor cores on a tissue microarray. Associations with clinical variables, tobacco and alcohol use and histologic features were assessed using Spearman correlation coefficient and the non-parametric Kruskal-Wallis testing. Time-to-event outcomes were determined using univariate and multivariate Cox models. Median follow up was 60 months.

RESULTS

The ratio of CD4/CD8 (p=.01) and CD8 infiltrates (p=.05) were associated with tumor recurrence but not overall survival. Lower CD4 infiltrates were associated with alcohol use (p=.005) and poor tumor differentiation (p=.02). Interestingly, higher levels of CD68+ macrophages were found associated with positive nodes (p=.06) and poorer overall survival (p=.07). Overall and DSS survival were significantly shorter for patients with positive nodes, extracapsular spread, or perineural invasion.

CONCLUSION

Infiltrating immune cell levels in oral cavity cancer appear influenced by health behaviors and tumor characteristics. In contrast to oropharynx cancer, infiltrates of CD68 positive tumor associated macrophages may contribute to metastatic behavior and outcome in advanced oral cavity carcinoma.

Activated lymphocyte recruitment into the tumor microenvironment following preoperative sipuleucel-T for localized prostate cancer

Background

Sipuleucel-T is a US Food and Drug Administration–approved immunotherapy for asymptomatic or minimally symptomatic metastatic castration-resistant prostate cancer (mCRPC). Its mechanism of action is not fully understood. This prospective trial evaluated the direct immune effects of systemically administered sipuleucel-T on prostatic cancer tissue in the preoperative setting.

Methods

Patients with untreated localized prostate cancer were treated on an open-label Phase II study of sipuleucel-T prior to planned radical prostatectomy (RP). Immune infiltrates in RP specimens (posttreatment) and in paired pretreatment biopsies were evaluated by immunohistochemistry (IHC). Correlations between circulating immune response and IHC were assessed using Spearman rank order.

Results

Of the 42 enrolled patients, 37 were evaluable. Adverse events were primarily transient, mild-to-moderate and infusion related. Patients developed T cell proliferation and interferon-γ responses detectable in the blood following treatment. Furthermore, a greater-than-three-fold increase in infiltrating CD3⁺, CD4⁺ FOXP3^-, and CD8⁺ T cells was observed in the RP tissues compared with the pretreatment biopsy (binomial proportions: all P < .001). This level of T cell infiltration was observed at the tumor interface, and was not seen in a control group consisting of 12 concurrent patients who did not receive any neoadjuvant treatment prior to RP. The majority of infiltrating T cells were PD-1⁺ and Ki-67⁺, consistent with activated T cells. Importantly, the magnitude of the circulating immune response did not directly correlate with T cell infiltration within the prostate based upon Spearman’s rank order correlation.

Conclusions

This study is the first to demonstrate a local immune effect from the administration of sipuleucel-T. Neoadjuvant sipuleucel-T elicits both a systemic antigen-specific T cell response and the recruitment of activated effector T cells into the prostate tumor microenvironment.

Anti-CTLA-4 therapy broadens the melanoma-reactive CD8+ T cell response

Anti-CTLA-4 treatment improves the survival of patients with advanced-stage melanoma. However, although the anti-CTLA-4 antibody ipilimumab is now an approved treatment for patients with metastatic disease, it remains unknown by which mechanism it boosts tumor-specific T cell activity. In particular, it is unclear whether treatment amplifies previously induced T cell responses or whether it induces new tumor-specific T cell reactivities. Using a combination ultraviolet (UV)-induced peptide exchange and peptide-major histocompatibility complex (pMHC) combinatorial coding, we monitored immune reactivity against a panel of 145 melanoma-associated epitopes in a cohort of patients receiving anti-CTLA-4 treatment. Comparison of pre- and posttreatment T cell reactivities in peripheral blood mononuclear cell samples of 40 melanoma patients demonstrated that anti-CTLA-4 treatment induces a significant increase in the number of detectable melanoma-specific CD8 T cell responses (P = 0.0009). In striking contrast, the magnitude of both virus-specific and melanoma-specific T cell responses that were already detected before start of therapy remained unaltered by treatment (P = 0.74). The observation that anti-CTLA-4 treatment induces a significant number of newly detected T cell responses-but only infrequently boosts preexisting immune responses-provides strong evidence for anti-CTLA-4 therapy-enhanced T cell priming as a component of the clinical mode of action.

Opportunistic Autoimmune Disorders Potentiated by Immune-Checkpoint Inhibitors Anti-CTLA-4 and Anti-PD-1

To improve the efficacy of immunotherapy for cancer and autoimmune diseases, recent ongoing and completed clinical trials have focused on specific targets to redirect the immune network toward eradicating a variety of tumors and ameliorating the self-destructive process. In a previous review, both systemic immunomodulators and monoclonal antibodies (mAbs), anti-CTLA-4, and anti-CD52, were discussed regarding therapeutics and autoimmune sequelae, as well as predisposing factors known to exacerbate immune-related adverse events (irAEs). This review will focus on immune-checkpoint inhibitors, and the data from most clinical trials involve blockade with anti-CTLA-4 such as ipilimumab. However, despite the mild to severe irAEs observed with ipilimumab in ~60% of patients, overall survival (OS) averaged ~22-25% at 3-5 years. To boost OS, other mAbs targeting programed death-1 and its ligand are undergoing clinical trials as monotherapy or dual therapy with anti-CTLA-4. Therapeutic combinations may generate different spectrum of opportunistic autoimmune disorders. To simulate clinical scenarios, we have applied regulatory T cell perturbation to murine models combined to examine the balance between thyroid autoimmunity and tumor-specific immunity.

CTLA4 blockade broadens the peripheral T-cell receptor repertoire

PURPOSE

To evaluate the immunomodulatory effects of cytotoxic T-lymphocyte-associated protein 4 (CTLA4) blockade with tremelimumab in peripheral blood mononuclear cells (PBMC).

EXPERIMENTAL DESIGN

We used next-generation sequencing to study the complementarity-determining region 3 (CDR3) from the rearranged T-cell receptor (TCR) variable beta (V-beta) in PBMCs of 21 patients, at baseline and 30 to 60 days after receiving tremelimumab.

RESULTS

After receiving tremelimumab, there was a median of 30% increase in unique productive sequences of TCR V-beta CDR3 in 19 out of 21 patients, and a median decrease of 30% in only 2 out of 21 patients. These changes were significant for richness (P = 0.01) and for Shannon index diversity (P = 0.04). In comparison, serially collected PBMCs from four healthy donors did not show a significant change in TCR V-beta CDR3 diversity over 1 year. There was a significant difference in the total unique productive TCR V-beta CDR3 sequences between patients experiencing toxicity with tremelimumab compared with patients without toxicity (P = 0.05). No relevant differences were noted between clinical responders and nonresponders.

CONCLUSIONS

CTLA4 blockade with tremelimumab diversifies the peripheral T-cell pool, representing a pharmacodynamic effect of how this class of antibodies modulates the human immune system.

COX-2 inhibition prevents the appearance of cutaneous squamous cell carcinomas accelerated by BRAF inhibitors

Keratoacanthomas (KAs) and cutaneous squamous cell carcinomas (cuSCCs) develop in 15-30% of patients with BRAF(V600E) metastatic melanoma treated with BRAF inhibitors (BRAFi). These lesions resemble mouse skin tumors induced by the two-stage DMBA/TPA skin carcinogenesis protocol; in this protocol BRAFi accelerates tumor induction. Since prior studies demonstrated cyclooxygenase 2 (COX-2) is necessary for DMBA/TPA tumor induction, we hypothesized that COX-2 inhibition might prevent BRAFi-accelerated skin tumors. Celecoxib, a COX-2 inhibitor, significantly delayed tumor acceleration by the BRAFi inhibitor PLX7420 and decreased tumor number by 90%. Tumor gene expression profiling demonstrated that celecoxib partially reversed the PLX4720-induced gene signature. In PDV cuSCC cells, vemurafenib (a clinically approved BRAFi) increased ERK phosphorylation and soft agar colony formation; both responses were greatly decreased by celecoxib. In clinical trials trametinib, a MEK inhibitor (MEKi) increases BRAFi therapy efficacy in BRAF(V600E) melanomas and reduces BRAFi-induced KA and cuSCC frequency. Trametinib also reduced vemurafenib-induced PDV soft agar colonies, but less efficiently than celecoxib. The trametinb/celecoxib combination was more effective than either inhibitor alone. In conclusion, celecoxib suppressed both BRAFi-accelerated skin tumors and soft-agar colonies, warranting its testing as a chemopreventive agent for non-melanoma skin lesions in patients treated with BRAFi alone or in combination with MEKi.

Vemurafenib in melanoma

The incidence of malignant melanoma is increasing annually. Early stages can be cured with surgical intervention but metastatic disease has generally had a dismal prognosis with few effective interventions. A half of all melanomas possess a BRAF mutation, which can be targeted by specific inhibitors. Vemurafenib is an orally active, purposely designed mutant BRAF inhibitor, which has recently been shown to have a survival benefit measured in months in metastatic patients. In this article, the authors discuss the scientific rationale, drug development process and clinical trials that have led to vemurafenib becoming the first BRAF inhibitor approved for the treatment of patients with mutant BRAF metastatic melanoma.

Tremelimumab: a review of development to date in solid tumors

Tremelimumab is an investigational, fully human IgG monoclonal antibody directed against CTLA-4, a coinhibitory receptor that represses effector T-cell activity in cancer. Tremelimumab has produced promising anticancer responses in early clinical trials. However, a phase III trial of tremelimumab monotherapy versus chemotherapy in advanced melanoma was stopped early when no statistically significant difference in overall survival was observed between the two interventions. This article describes tremelimumab's putative mechanism of action, its preclinical pharmacology and clinical results to date across a range of cancer settings as monotherapy, as well as in combination with other therapies. The failure of the Phase III trial in melanoma is examined and factors affecting the possible future clinical development of tremelimumab are also explored.

CTLA-4 blockade and the renaissance of cancer immunotherapy

Cytotoxic T-lymphocyte associated antigen 4 (CTLA-4) plays a key role in restraining the adaptive immune response of T-cells towards a variety of antigens including tumor associated antigens (TAAs). The blockade of this immune checkpoint elicits an effective anticancer immune response in a range of preclinical models, suggesting that naturally occurring (or therapeutically induced) TAA specific lymphocytes need to be "unleashed" in order to properly fight against malignant cells. Therefore, investigators have tested this therapeutic hypothesis also in humans: the favorable results obtained with this strategy in patients with advanced cutaneous melanoma are revolutionizing the management of this highly aggressive disease and are fueling new enthusiasm on cancer immunotherapy in general. Here we summarize the biology of CTLA-4, overview the experimental data supporting the rational for targeting CTLA-4 to treat cancer and review the main clinical findings on this novel anticancer approach. Moreover, we critically discuss the current challenges and potential developments of this promising field of cancer immunotherapy.

Ipilimumab, vemurafenib, dabrafenib, and trametinib: synergistic competitors in the clinical management of BRAF mutant malignant melanoma

There have been significant advances in the treatment of malignant melanoma with the U.S. Food and Drug Administration approval of two drugs in 2011, the first drugs approved in 13 years. The developments of immune checkpoint modulation via cytotoxic T-lymphocyte antigen-4 blockade, with ipilimumab, and targeting of BRAF(V600), with vemurafenib or dabrafenib, as well as MEK, with trametinib, have been paradigm changing both for melanoma clinical practice and for oncology therapeutic development. These advancements, however, reveal new clinical questions regarding combinations and optimal sequencing of these agents in patients with BRAF mutant disease. We review the development of these agents, putative biomarkers, and resistance mechanisms relevant to their use, and possibilities for sequencing and combining these agents.

The impact of the myeloid response to radiation therapy

Radiation therapy is showing potential as a partner for immunotherapies in preclinical cancer models and early clinical studies. As has been discussed elsewhere, radiation provides debulking, antigen and adjuvant release, and inflammatory targeting of effector cells to the treatment site, thereby assisting multiple critical checkpoints in antitumor adaptive immunity. Adaptive immunity is terminated by inflammatory resolution, an active process which ensures that inflammatory damage is repaired and tissue function is restored. We discuss how radiation therapy similarly triggers inflammation followed by repair, the consequences to adaptive immune responses in the treatment site, and how the myeloid response to radiation may impact immunotherapies designed to improve control of residual cancer cells.

Sequencing CTLA-4 blockade with cell-based immunotherapy for prostate cancer

Background

The FDA recently approved an anti-CTLA-4 antibody (Iplimumab) for the treatment of metastatic melanoma. This decision was based on Phase III results, which demonstrate that blocking this immune checkpoint provides a survival advantage in patients with advanced disease. As a single agent, ipilimumab is also being clinically evaluated in advanced (metastatic, castrate-resistant) prostate cancer and two randomized, placebo-controlled Phase III studies have recently completed accrual.

Methods

We used a well-described genetically engineered mouse (GEM), autochronous prostate cancer model (Pro-TRAMP) to explore the relative sequencing and dosing of anti-CTLA-4 antibody when combined with a cell-based, GM-CSF-secreting vaccine (GVAX).

Results

Our results show that combined treatment results in a dramatic increase in effector CD8 T cells in the prostate gland, and enhanced tumor-antigen directed lytic function. These effects are maximized when CTLA-4 blockade is applied after, but not before, vaccination. Additional experiments, using models of metastatic disease, show that incorporation of low-dose cyclophosphamide into this combined treatment regimen results in an additional pre-clinical benefit.

Conclusions

Together these studies define a combination regimen using anti-CTLA-4/GVAX immunotherapy and low-dose chemotherapy for potential translation to a clinical trial setting.

Multifunctional T-cell analyses to study response and progression in adoptive cell transfer immunotherapy

Adoptive cell transfer (ACT) of genetically engineered T cells expressing cancer-specific T-cell receptors (TCR) is a promising cancer treatment. Here, we investigate the in vivo functional activity and dynamics of the transferred cells by analyzing samples from 3 representative patients with melanoma enrolled in a clinical trial of ACT with TCR transgenic T cells targeted against the melanosomal antigen MART-1. The analyses included evaluating 19 secreted proteins from individual cells from phenotypically defined T-cell subpopulations, as well as the enumeration of T cells with TCR antigen specificity for 36 melanoma antigens. These analyses revealed the coordinated functional dynamics of the adoptively transferred, as well as endogenous, T cells, and the importance of highly functional T cells in dominating the antitumor immune response. This study highlights the need to develop approaches to maintaining antitumor T-cell functionality with the aim of increasing the long-term efficacy of TCR-engineered ACT immunotherapy.

SIGNIFICANCE

A longitudinal functional study of adoptively transferred TCR–engineered lymphocytes yielded revealing snapshots for understanding the changes of antitumor responses over time in ACT immunotherapy of patients with advanced melanoma.

Coinhibitory molecules in cancer biology and therapy

The adaptive immune response is controlled by checkpoints represented by coinhibitory molecules, which are crucial for maintaining self-tolerance and minimizing collateral tissue damage under physiological conditions. A growing body of preclinical evidence supports the hypothesis that unleashing this immunological break might be therapeutically beneficial in the fight against cancer, as it would elicit an effective antitumor immune response. Remarkably, recent clinical trials have demonstrated that this novel strategy can be highly effective in the treatment of patients with cancer, as shown by the paradigmatic case of ipilimumab (a monoclonal antibody blocking the coinhibitory molecule cytotoxic T lymphocyte associated antigen-4 [CTLA4]) that is opening a new era in the therapeutic approach to a chemoresistant tumor such as cutaneous melanoma. In this review we summarize the biology of coinhibitory molecules, overview the experimental and clinical attempts to interfere with these immune checkpoints to treat cancer and critically discuss the challenges posed by such a promising antitumor modality.

Focus on the target: the tumor microenvironment, Society for Immunotherapy of Cancer Annual Meeting Workshop, October 24th-25th 2012

The Workshop associated with the 27th Annual Meeting of the Society for Immunotherapy of Cancer (SITC), North Bethesda, MD, October 24-25, 2012 focused on targeting the tumor microenvironment as part of an integrative approach to immune-based cancer therapy.

Safety profile and pharmacokinetic analyses of the anti-CTLA4 antibody tremelimumab administered as a one hour infusion

Background

CTLA4 blocking monoclonal antibodies provide a low frequency but durable tumor responses in patients with metastatic melanoma, which led to the regulatory approval of ipilimumab based on two randomized clinical trials with overall survival advantage. The similarly fully human anti-CTLA4 antibody tremelimumab had been developed in the clinic at a fixed rate infusion, resulting in very prolonged infusion times. A new formulation of tremelimumab allowed testing a shorter infusion time.

Methods

A phase 1 multi-center study to establish the safety and tolerability of administering tremelimumab as a 1-hour infusion to patients with metastatic melanoma. Secondary endpoints included pharmacokinetic and clinical effects of tremelimumab.

Results

No grade 3 or greater infusion-related adverse events or other adverse events preventing the administration of the full tremelimumab dose were noted in 44 treated patients. The overall side effect profile was consistent with prior experiences with anti-CTLA4 antibodies. Objective tumor responses were noted in 11% of evaluable patients with metastatic melanoma, which is also consistent with the prior experience with CTLA4 antagonistic antibodies.

Conclusions

This study did not identify any safety concerns when tremelimumab was administered as a 1-hour infusion. These data support further clinical testing of the 1-hour infusion of tremelimumab. (Clinical trial registration number NCT00585000).

Biomarkers on melanoma patient T cells associated with ipilimumab treatment

Background

Ipilimumab induces long-lasting clinical responses in a minority of patients with metastatic melanoma. To better understand the mechanism(s) of action and to identify novel biomarkers associated with the clinical benefit and toxicity of ipilimumab, baseline characteristics and changes in CD4⁺ and CD8⁺ T cells from melanoma patients receiving ipilimumab were characterized by gene profiling and flow cytometry.

Methods

Microarray analysis of flow-cytometry purified CD4⁺ and CD8⁺ T cells was employed to assess gene profiling changes induced by ipilimumab. Selected molecules were further investigated by flow cytometry on pre, 3-month and 6-month post-treatment specimens.

Results

Ipilimumab up-regulated Ki67 and ICOS on CD4⁺ and CD8⁺ cells at both 3- and 6-month post ipilimumab (p ≤ 0.001), decreased CCR7 and CD25 on CD8⁺ at 3-month post ipilimumab (p ≤ 0.02), and increased Gata3 in CD4⁺ and CD8⁺ cells at 6-month post ipilimumab (p ≤ 0.001). Increased EOMES⁺CD8⁺, GranzymeB⁺EOMES⁺CD8⁺ and decreased Ki67⁺EOMES⁺CD4⁺ T cells at 6 months were significantly associated with relapse (all p ≤ 0.03). Decreased Ki67⁺CD8⁺ T cells were significantly associated with the development of irAE (p = 0.02). At baseline, low Ki67⁺EOMES⁺CD8⁺ T cells were associated with relapse (p ≤ 0.001), and low Ki67⁺EOMES⁺CD4⁺ T cells were associated with irAE (p ≤ 0.008).

Conclusions

Up-regulation of proliferation and activation signals in CD4⁺ and CD8⁺ T cells were pharmacodynamic markers for ipilimumab. Ki67⁺EOMES⁺CD8⁺ and Ki67⁺EOMES⁺CD4⁺T cells at baseline merit further testing as biomarkers associated with outcome and irAEs, respectively.

Melanoma vaccines and modulation of the immune system in the clinical setting: building from new realities

To endow the immune system with the capacity to fight cancer has always attracted attention, although the clinical results obtained have been until recently disappointing. Cutaneous melanoma is a highly immunogenic tumor; therefore most of the attempts to produce cancer vaccines have been addressed to this disease. New advances in the comprehension of the mechanisms of antigen presentation by dendritic cells, in the immune responses triggered by adjuvants, as well as the understanding of the role of immunosuppressor molecules such as cytotoxic T-lymphocyte antigen-4 (CTLA-4), which led to the recent approval of the anti-CTLA-4 monoclonal antibody ipilimumab, have opened new hopes about the installment of immunotherapy as a new modality to treat cancer.

Targeting costimulatory molecules to improve antitumor immunity

The full activation of T cells necessitates the concomitant activation of two signals, the engagement of T-cell receptor by peptide/major histocompatibility complex II and an additional signal delivered by costimulatory molecules. The best characterized costimulatory molecules belong to B7/CD28 and TNF/TNFR families and play crucial roles in the modulation of immune response and improvement of antitumor immunity. Unfortunately, tumors often generate an immunosuppressive microenvironment, where T-cell response is attenuated by the lack of costimulatory molecules on the surface of cancer cells. Thus, targeting costimulatory pathways represent an attractive therapeutic strategy to enhance the antitumor immunity in several human cancers. Here, latest therapeutic approaches targeting costimulatory molecules will be described.

New challenges in endpoints for drug development in advanced melanoma

During the past 3 decades, the field of clinical research for the treatment of advanced melanoma lacked significant advances. Available drugs had low antitumor activity and no proven benefit in overall survival. Recently, new drugs developed based on an in-depth understanding of the biology of this disease have shown significant benefit, with ipilimumab and vemurafenib having recently shown a positive impact in overall survival in patients with metastatic melanoma leading to approval in this indication by the U.S. Food and Drug Administration. This rapid introduction of new active agents is likely to challenge current notions on how to develop future agents for the treatment of melanoma. The strong evidence of benefit for initial agents that modulate immune regulatory checkpoints or target driver oncogenes has spurred great interest in developing other similarly acting agents. However, this will pose problems in the choice of endpoints for the future definitive clinical trials, and the hurdles for achieving these endpoints will be higher given the similar activity for comparator agents or the availability of competing agents for salvage therapy. This new reality will likely require tailoring registrational clinical trial endpoints to the patient benefits shown in early clinical testing. In this perspective article, we illustrate the challenges in the choice of endpoints for registrational trials in metastatic melanoma and that, with an improved understanding of the agent being developed, the design of the registrational programs can be informed by earlier mechanistic studies to define the assumptions for definitive clinical testing.

Blockade of cytotoxic T-lymphocyte antigen-4 as a new therapeutic approach for advanced melanoma

INTRODUCTION

The incidence of melanoma continues to rise, and prognosis in patients with metastatic melanoma remains poor. The cytotoxic T-lymphocyte antigen-4 (CTLA-4) serves as one of the primary immune check points and downregulates T-cell activation pathways. Enhancing T-cell activation by antibody blockade of CTLA-4 provides a new approach to overcome tumor-induced immune tolerance. Recently, anti-CTLA-4 therapy demonstrated significant clinical benefits in patients with metastatic melanoma, which led to the approval of ipilimumab by the FDA in early 2011.

AREAS COVERED

The fundamental concepts underlying CTLA-4 blockade-potentiated immune activation are presented in this paper, along with the scientific rationale for and the preclinical evidence supporting CTLA-4-targeted cancer immunotherapy. It also provides an update on clinical trials with anti-CTLA-4 inhibitors and discusses the associated autoimmune toxicity.

EXPERT OPINION

Given that overall survival is the only validated end point for anti-CTLA-4 therapy, the clinical implications of the antigen or tumor-specific immunity in patients remain to be clarified. Additional research is necessary to elucidate the prognostic significance of immune-related side effects and significantly optimize the treatment regimens. An improved understanding of the mechanisms of action of CTLA-4 antibodies may also culminate in wide-ranging clinical applications of this new therapy for other tumor types.