CTLA-4: negative regulator of the immune response and a target for cancer therapy

A novel approach for cancer immunotherapy is to augment T-cell-mediated immunity by blocking inhibitory signals that suppress T-cell function. Cytotoxic T-lymphocyte antigen-4 (CTLA-4) is a key negative regulator of T-cell activation. CTLA-4 blockade using anti-CTLA-4 monoclonal antibodies (mAbs) potentiates the T-cell response against tumors, and preliminary data on these agents demonstrate good efficacy and tolerability in the treatment of patients with metastatic melanoma and other cancers. This paper will review data from studies with anti-CTLA-4 mAbs to date, discuss some of the key clinical considerations emerging from early clinical trials with this therapeutic strategy, and provide an overview of ongoing and planned clinical trials for anti-CTLA-4 mAb therapy in metastatic melanoma and other cancers.

[Chemotherapy for prostate cancer]

For many years the benefit of chemotherapy in patients with prostate cancer was thought to be limited to palliation of late-stage disease, and thus this treatment option only became involved in patient care towards the end of the disease process, if at all. However, two landmark phase-III trials with docetaxel-based therapy (TAX 327 and Southwest Oncology Group, SWOG, 9916) have shown a survival benefit for patients with hormone refractory prostate cancer (HRPC) thus prompting a change in patterns of care. With raising interest for chemotherapeutic options and clinical trials for new drugs and new indications (neoadjuvant therapy, adjuvant therapy, increasing PSA levels after local treatment, and hormone sensitive cancer) under way our goal was to review within the context of a multidisciplinary team the available evidence and explore the standard for the medical treatment of prostate cancer outside of clinical trials. We are carefully evaluating the current treatment recommendations based on the available evidence and highlight potential future treatment options but also discuss important clinical topics (treatment until progression versus the advantage of chemo holidays, definition of particular patient subgroups and potential second line options) for which there are no clear cut answers to date. The role and importance of radiotherapy, biphosphonate treatment and the medical management of pain and side effects is also discussed. The multitude of treatment options for patients with advanced prostate cancer clearly asks for a close collaboration between urologists, medical oncologists and radiation therapists.

CTLA4 blockade expands FoxP3+ regulatory and activated effector CD4+ T cells in a dose-dependent fashion

Cytotoxic T lymphocyte-associated antigen 4 (CTLA4) delivers inhibitory signals to activated T cells. CTLA4 is constitutively expressed on regulatory CD4(+) T cells (Tregs), but its role in these cells remains unclear. CTLA4 blockade has been shown to induce antitumor immunity. In this study, we examined the effects of anti-CTLA4 antibody on the endogenous CD4(+) T cells in cancer patients. We show that CTLA4 blockade induces an increase not only in the number of activated effector CD4(+) T cells, but also in the number of CD4(+) FoxP3(+) Tregs. Although the effects were dose-dependent, CD4(+) FoxP3(+) regulatory T cells could be expanded at lower antibody doses. In contrast, expansion of effector T cells was seen only at the highest dose level studied. Moreover, these expanded CD4(+) FoxP3(+) regulatory T cells are induced to proliferate with treatment and possess suppressor function. Our results demonstrate that treatment with anti-CTLA4 antibody does not deplete human CD4(+) FoxP3(+) Tregs in vivo, but rather may mediate its effects through the activation of effector T cells. Our results also suggest that CTLA4 may inhibit Treg proliferation similar to its role on effector T cells. This study is registered at http://www.clinicaltrials.gov/ct2/show/NCT00064129, registry number NCT00064129.

Advances in specific immunotherapy for prostate cancer

OBJECTIVES

The absence of effective therapies for advanced prostate cancer has entailed an intensive search for novel treatments. This review presents an overview of specific immunotherapeutic strategies for prostate cancer.

METHODS

Current literature was reviewed regarding the identification of tumor antigens and the design of T-cell- and antibody-based immunotherapy for prostate cancer. The PubMed database was searched using the key words antibodies, clinical trials, dendritic cells, immunotherapy, prostate cancer, and T cells.

RESULTS

T cells and antibodies are powerful components of the specific antitumor immune response. CD8+ cytotoxic T lymphocytes (CTLs) efficiently destroy tumor cells. CD4+ T cells improve the antigen-presenting capacity of dendritic cells (DCs) and support the stimulation of tumor-reactive CTLs. Monoclonal antibodies exhibit their antitumor effects via antibody-dependent cellular cytotoxicity and complement activation. Consequently, much attention has been given to the identification of tumor antigens that represent attractive targets for specific immunotherapy. Several prostate cancer-related antigens were described and used in clinical trials. Such studies were based on the administration of peptides, proteins, or DNA. Furthermore, men with prostate cancer were vaccinated with peptide-, protein-, or RNA-loaded DCs, which display an extraordinary capacity to induce tumor-reactive T cells. Monoclonal antibodies directed against surface antigens were also used. Clinical trials revealed that immunotherapeutic strategies represent safe and feasible concepts for the induction of immunologic and clinical responses in men with prostate cancer.

CONCLUSIONS

Specific immunotherapy represents a promising treatment modality for prostate cancer. Further improvement of the current approaches is required and may be achieved by combining T-cell- and antibody-based vaccination strategies with radio-, hormone-, chemo-, or antiangiogenic therapy.