Cancer vaccines in combination with multimodality therapy

Low-dose cyclophosphamide administered as daily or single dose enhances the antitumor effects of a therapeutic HPV vaccine

Although therapeutic HPV vaccines are able to elicit systemic HPV-specific immunity, clinical responses have not always correlated with levels of vaccine-induced CD8(+) T cells in human clinical trials. This observed discrepancy may be attributable to an immunosuppressive tumor microenvironment in which the CD8(+) T cells are recruited. Regulatory T cells (Tregs) are cells that can dampen cytotoxic CD8(+) T-cell function. Cyclophosphamide (CTX) is a systemic chemotherapeutic agent, which can eradicate immune cells, including inhibitory Tregs. The optimal dose and schedule of CTX administration in combination with immunotherapy to eliminate the Treg population without adversely affecting vaccine-induced T-cell responses is unknown. Therefore, we investigated various dosing and administration schedules of CTX in combination with a therapeutic HPV vaccine in a preclinical tumor model. HPV tumor-bearing mice received either a single preconditioning dose or a daily dose of CTX in combination with the pNGVL4a-CRT/E7(detox) DNA vaccine. Both single and daily dosing of CTX in combination with vaccine had a synergistic antitumor effect as compared to monotherapy alone. The potent antitumor responses were attributed to the reduction in Treg frequency and increased infiltration of HPV16 E7-specific CD8(+) T cells, which led to higher ratios of CD8(+)/Treg and CD8(+)/CD11b(+)Gr-1(+) myeloid-derived suppressor cells (MDSCs). There was an observed trend toward decreased vaccine-induced CD8(+) T-cell frequency with daily dosing of CTX. We recommend a single, preconditioning dose of CTX prior to vaccination due to its efficacy, ease of administration, and reduced cumulative adverse effect on vaccine-induced T cells.

Targeting EGF receptor variant III: tumor-specific peptide vaccination for malignant gliomas

Glioblastoma multiforme (GBM) is the most common and deadly of the human brain cancers. The EGF receptor is often amplified in GBM and provides a potential therapeutic target. However, targeting the normal receptor is complicated by its nearly ubiquitous and high level of expression in certain tissues. A naturally occurring deletion mutant of the EGF receptor, EGFRvIII, is a constitutively active variant originally identified in a high percentage of brain cancer cases, and more importantly is rarely found in normal tissue. A peptide vaccine, rindopepimut (CDX-110, Celldex Therapeutics), is directed against the novel exon 1-8 junction produced by the EGFRvIII deletion, and it has shown high efficacy in preclinical models. Recent Phase II clinical trials in patients with newly diagnosed GBM have shown EGFRvIII-specific immune responses and significantly increased time to progression and overall survival in those receiving vaccine therapy, as compared with published results for standard of care. Rindopepimut therefore represents a very promising therapy for patients with GBM.

Challenges in immunotherapy presented by the glioblastoma multiforme microenvironment

Glioblastoma multiforme (GBM) is the most common and aggressive primary brain tumor in adults. Despite intensive treatment, the prognosis for patients with GBM remains grim with a median survival of only 14.6 months. Immunotherapy has emerged as a promising approach for treating many cancers and affords the advantages of cellular-level specificity and the potential to generate durable immune surveillance. The complexity of the tumor microenvironment poses a significant challenge to the development of immunotherapy for GBM, as multiple signaling pathways, cytokines, and cell types are intricately coordinated to generate an immunosuppressive milieu. The development of new immunotherapy approaches frequently uncovers new mechanisms of tumor-mediated immunosuppression. In this review, we discuss many of the current approaches to immunotherapy and focus on the challenges presented by the tumor microenvironment.

The epidermal growth factor variant III peptide vaccine for treatment of malignant gliomas

Epidermal growth factor variant III (EGFRvIII) is the most common alteration of the epidermal growth factor (EGF) receptor found in human tumors. It is commonly expressed in glioblastoma multiforme (GBM), where it was initially identified. This constitutively active mutant receptor leads to unregulated growth, survival, invasion, and angiogenesis in cells that express it. EGFRvIII results from an in-frame deletion of exons 2 to 7 resulting in the fusion of exon 1 to exon 8 of the EGF receptor gene creating a novel glycine at the junction in the extracellular amino terminal domain. The juxtaposition of ordinarily distant amino acids in combination with the glycine that forms at the junction leads to a novel tumor-specific epitope that would make an ideal tumor-specific target. A peptide derived from the EGFRvIII junction can be used as a vaccine to prevent or induce the regression of tumors. This peptide vaccine has now proceeded to phase 1 and 2 clinical trials where it has been highly successful and is now undergoing investigation in a larger human clinical trial for patients who have newly diagnosed GBM. In this article, the authors discuss the preclinical data that led to the human trials and the exciting preliminary data from the clinical trials.

Roadmap to a Better Therapeutic Tumor Vaccine

Cell-based cancer vaccines are a highly attractive alternative to standard cancer therapies. They theoretically have the capability of inciting a multitargeted therapeutic response that functions by reshaping the host-tumor interaction, tipping the balance in favor of tumor rejection. Due to the polyclonal immune response induced, they are less likely to result in therapeutic escape than most cancer treatments in use today. Their immune-based mechanism of action offers a unique approach to management that should not be limited by traditional modes of drug resistance. Their favorable side-effect profile further identifies them as a potential treatment modality of choice. Despite these positive features, a number of hurdles must be overcome in order for cancer vaccines to take their place in the clinic as part of standard cancer therapy. Vaccine protocols must be optimized both to induce a high-quality antitumor T-cell response and to abrogate established mechanisms of immune tolerance that actively function to shut antitumor T cells down. By applying basic knowledge of the molecular features of T-cell biology and immune tolerance to the design of trials that combine tumor vaccines with targeted immunomodulatory drugs, potent strategies for inducing effective antitumor immunity can be developed. The first of these combinatorial trials have already been reported and offer a tantalizing glimpse of the future of cancer immunotherapy.

EGF receptor variant III as a target antigen for tumor immunotherapy

The EGF receptor (EGFR) is the first tyrosine kinase receptor ever cloned and remains at the forefront of targeted therapies against cancer. Currently, there are four US FDA-approved drugs and several more in Phase III studies that target the EGFR. These drugs, while resulting in some dramatic remissions, have not resulted in strong nor consistent improvements in survival. EGFR variant III (EGFRvIII) is the most common variant of the EGFR and is present in many different cancer types but not in normal tissue. It results from the fusion of exon 1 to exon 8 of the EGFR gene, which results in a novel glycine at the junction. This mutant receptor is constitutively active in these tumors and can lead directly to cancer phenotypes due to its oncogenic properties. EGFRvIII is an attractive target antigen for cancer immunotherapy because it is not expressed in normal tissue and because cells producing EGFRvIII have an enhanced capacity for dysregulated growth, survival, invasion and angiogenesis. In this review, we will discuss preclinical and clinical data from studies using EGFRvIII as the target antigen for immunotherapy, with a focus on the potential for greatly improved survival for patients diagnosed with glioblastoma multiforme.

Necrotic tumor cell death in vivo impairs tumor-specific immune responses

The manner in which cells die is believed to have a major impact on the nature of immune responses to their released Ags. In this study, we present the first direct analysis of tumor-specific immune responses to in vivo occurring tumor cell death through apoptosis or necrosis. Mice bearing thymidine kinase-transfected tumors were treated either with ganciclovir to induce tumor cell apoptosis in vivo or a vascular targeting agent, ZD6126, to induce tumor cell necrosis in vivo. In contrast to tumor apoptosis, induction of necrosis reduced the frequency and impaired the function of tumor-specific CD8(+) T cells. Adoptive transfer of lymphocytes from mice with apoptotic tumors into tumor-challenged mice resulted in a significant tumor protection, which was absent when splenocytes were transferred from mice with necrotic tumors. Anti-CD40 treatment reversed impaired Ag-specific CD8(+) T cell responses in these mice. These observations have not only fundamental importance for the development of immunotherapy protocols but also help to understand the underlying mechanism of in vivo immune responses to tumor cell death.

Antitumor properties of dimethyl-celecoxib, a derivative of celecoxib that does not inhibit cyclooxygenase-2: implications for glioma therapy

✓ Celecoxib (Celebrex) appears to be unique among the class of selective COX-2 inhibitors (coxibs), because this particular compound exerts a second function that is independent of its celebrated ability to inhibit COX-2. This second function is the potential to inhibit cell proliferation and stimulate apoptotic cell death at much lower concentrations than any other coxibs. Intriguingly, these two functions are mediated by different moieties of the celecoxib molecule and can be separated. The author, as well as others, have generated and investigated analogs of celecoxib that retain only one of these two functions. One derivative, 2,5-dimethyl-celecoxib (DMC), which retains the antiproliferative and apoptosis-inducing function, but completely lacks the COX-2 inhibitory activity, is able to mimic faithfully all of the numerous antitumor effects of celecoxib that have been investigated so far, including reduction of neovascularization and inhibition of experimental tumor growth in various in vivo tumor models. In view of the controversy that has recently arisen regarding the life-threatening side effects of this class of coxibs, it may be worthwhile to pursue further the potential benefits of drugs such as DMC for anticancer therapy. Because DMC is not a coxib yet potently maintains celecoxib's antitumor potential, one may be inclined to speculate that this novel compound could potentially be advantageous in the management of COX-2–independent cancers. In this summary, the implications of recent findings with DMC will be presented and discussed.