The clinical utility of cytotoxic T lymphocyte antigen 4 abrogation by human antibodies

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.

Dendritic cell-based vaccine in advanced melanoma: update of clinical outcome

Dendritic cells (DCs) are unique specialized antigen-presenting cells capable of priming naive T cells and inducing antigen-specific cytotoxic T lymphocytes. This study presents an update of clinical results from a DC-based phase I-II clinical vaccine trial in stage IV melanoma. From 2003 to 2010, 27 patients with metastatic melanoma were treated with mature DCs pulsed with autologous tumor lysate and keyhole limpet hemocyanin and with subcutaneous low-dose interleukin-2. Delayed-type hypersensitivity (DTH) tests for in-vivo immunomonitoring were performed at baseline and every four vaccinations thereafter. Two complete, two mixed and six partial responses, and five stable diseases were observed (overall response, 37.0%; clinical benefit, 55.5%). All 15 responders showed DTH positivity. A median overall survival of 22.9 months [95% confidence interval (CI): 13.4-61.3] for DTH-positive patients (19) and 4.8 months (95% CI: 3.9-11.9) for DTH-negative patients (8; log rank=7.26; P=0.007) was observed. The overall median overall survival was 16 months (95% CI: 9-33). Our results would seem to highlight a relationship between positive-DTH test and an improved survival.

Improving cancer immunotherapy by targeting tumor-induced immune suppression

The status of a host's immune response influences both the development and progression of a malignancy such that immune responses can have both pro- and anti-tumorigenic effects. Cancer immunotherapy is a form of treatment that aims to improve the ability of a cancer-bearing individual to reject the tumor immunologically. However, antitumor immunity elicited by the host or by immunotherapeutic strategies, can be actively attenuated by mechanisms that limit the strength and/or duration of immune responses, including the presence of immunoregulatory cell types or the production of immunosuppressive factors. As our knowledge of tumor-induced immune suppression increases, it has become obvious that these mechanisms are probably a major barrier to effective therapy. The identification of multiple mechanisms of tumor-induced immune suppression also provides a range of novel targets for new cancer therapies. Given the vital role that a host's immune response is known to play in cancer progression, therapies that target immune suppressive mechanisms have the potential to enhance anticancer immune responses thus leading to better immune surveillance and the limitation of tumor escape. In this review, mechanisms of tumor-associated immune suppression have been divided into four forms that we have designated as (1) regulatory cells; (2) cytokines/chemokines; (3) T cell tolerance/exhaustion and (4) metabolic. We discuss select mechanisms representing each of these forms of immunosuppression that have been shown to aid tumors in evading host immune surveillance and overview therapeutic strategies that have been recently devised to "suppress these suppressors."

Unexpected high response rate to traditional therapy after dendritic cell-based vaccine in advanced melanoma: update of clinical outcome and subgroup analysis

We reviewed the clinical results of a dendritic cell-based phase II clinical vaccine trial in stage IV melanoma and analyzed a patient subgroup treated with standard therapies after stopping vaccination. From 2003 to 2009, 24 metastatic melanoma patients were treated with mature dendritic cells pulsed with autologous tumor lysate and keyhole limpet hemocyanin and low-dose interleukin-2. Overall response (OR) to vaccination was 37.5% with a clinical benefit of 54.1%. All 14 responders showed delayed type hypersensitivity positivity. Median overall survival (OS) was 15 months (95% CI, 8–33). Eleven patients underwent other treatments (3 surgery, 2 biotherapy, 2 radiotherapy, 2 chemotherapy, and 4 biochemotherapy) after stopping vaccination. Of these, 2 patients had a complete response and 5 a partial response, with an OR of 63.6%. Median OS was 34 months (range 16–61). Our results suggest that therapeutic DC vaccination could favor clinical response in patients after more than one line of therapy.

Adenoviral vaccination combined with CD40 stimulation and CTLA-4 blockage can lead to complete tumor regression in a murine melanoma model

Therapeutic vaccination with replication deficient adenovirus expressing a viral antigen linked to invariant chain was recently found to markedly delay the growth of B16.F10 melanomas expressing the same antigen; however, complete regression of the tumors was never observed. Here we show that the delay in tumor growth can be converted to complete regression and long-term survival in 30-40% of the mice by a booster vaccination plus combinational treatment with agonistic anti-CD40 monoclonal antibodies (mAb) and anti-CTLA-4 mAb. Regarding the mechanism underlying the improved clinical effect, analysis of the tumor-specific response revealed a significantly prolonged tumor-specific CD8 T cell response in spleens of the mice receiving the combinational treatment compared with mice receiving either treatment individually. Matching this, CD8 T cell depletion completely prevented tumor control. These results indicate that even with a strong tumor vaccine candidate, combinatorial treatment may be required to obtain clinically relevant results.

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.

Assessing oncologic benefit in clinical trials of immunotherapy agents

BACKGROUND

USA Food and Drug Administration approval for cancer therapy requires demonstration of patient benefit as a marker of clinical efficacy. Prolonged survival is the gold standard for demonstration of efficacy, but other end points such as antitumor response, progression-free survival, quality of life, or surrogate end points may be used.

DESIGN

This study was developed based on discussion during a roundtable meeting of experts in the field of immunotherapy.

RESULTS

In most clinical trials involving cytotoxic agents, response end points use RECIST based on the premise that 'effective' therapy causes tumor destruction, target lesion shrinkage, and prevention of new lesions. However, RECIST may not be appropriate in trials of immunotherapy. Like other targeted agents, immunotherapies may mediate cytostatic rather than direct cytotoxic effects, and these may be difficult to quantify with RECIST. Furthermore, significant time may elapse before clinical effects are quantifiable because of complex response pathways. Effective immunotherapy may even mediate transient lesion growth secondary to immune cell infiltration.

CONCLUSIONS

RECIST may not be an optimal indicator of clinical benefit in immunotherapy trials. This article discusses alternative clinical trial designs and end points that may be more relevant for immunotherapy trials and may offer more effective prediction of survival in pivotal phase III studies.

Autoimmune hypophysitis: expanding the differential diagnosis to CTLA-4 blockade

Autoimmune hypophysitis is an increasingly recognized disorder that enters in the differential diagnosis of nonfunctioning pituitary masses. The differential diagnosis of these conditions is challenging because of similar clinical presentations and radiological signs. This review describes the essential features of hypophysitis and the other nonfunctioning pituitary masses. It also emphasizes a recently described feature of hypophysitis: its appearance with unexpectedly high frequency in patients receiving treatments that abrogate the function of cytotoxic T lymphocyte antigen 4.

Therapeutics targeting tumor immune escape: towards the development of new generation anticancer vaccines

Despite the evidence that immune effectors can play a significant role in controlling tumor growth under natural conditions or in response to therapeutic manipulation, it is clear that malignant cells evade immune surveillance in most cases. Considering that anticancer vaccination has reached a plateau of results and currently no vaccination regimen is indicated as a standard anticancer therapy, the dissection of the molecular events underlying tumor immune escape is the necessary condition to make anticancer vaccines a therapeutic weapon effective enough to be implemented in the routine clinical setting. Recent years have witnessed significant advances in our understanding of the molecular mechanisms underlying tumor immune escape. These mechanistic insights are fostering the development of rationally designed therapeutics aimed at reverting the immunosuppressive circuits that undermine an effective antitumor immune response. In this review, the best characterized mechanisms that allow cancer cells to evade immune surveillance are overviewed and the most debated controversies constellating this complex field are highlighted. In addition, the latest therapeutic strategies devised to overcome tumor immune escape are described, with special regard to those entering clinical phase investigation.

New approaches in metastatic melanoma: biological and molecular targeted therapies

Classical metastatic melanoma therapy is disappointing but important progress has been made in the understanding of melanoma biology. Genetic lesions and several intracellular signaling pathways that could serve as targets for novel therapy have been identified and a number of new agents are under evaluation. Promising tumor cell targets were identified in the cell membrane, cytoplasm and nucleus. New therapeutic approaches, besides monoclonal antibodies and vaccination, include an increasing number of small molecules that have been shown to interfere restrictively with intracellular signaling pathways in melanoma and decrease proliferation, survival, migration or invasion. Other agents can interfere with stromal components of melanoma, such as angiogenesis and components of the immune system.