Phase II trial of Modified Vaccinia Ankara (MVA) virus expressing 5T4 and high dose Interleukin-2 (IL-2) in patients with metastatic renal cell carcinoma

A randomized phase II trial to examine modified vaccinia Ankara-5T4 vaccine in patients with relapsed asymptomatic ovarian cancer (TRIOC)

BACKGROUND

Immunotherapy directed at 5T4 tumor antigen may delay the need for further chemotherapy. An attenuated modified vaccinia Ankara virus containing the gene encoding for 5T4 (MVA-5T4) was studied in asymptomatic relapsed ovarian cancer.

OBJECTIVE

To assess the effectiveness and safety of MVA-5T4 as treatment for asymptomatic relapsed ovarian cancer.

METHODS

TRIOC was a phase II randomized (1:1), placebo-controlled, double-blind multicenter study. The primary aim was to assess the effectiveness and safety of MVA-5T4 as a treatment for asymptomatic patients with relapsed ovarian cancer. Eligible patients had International Federation of Gynecology and Obstetrics (FIGO) stage IC1-III or IVA epithelial ovarian, fallopian tube, or primary peritoneal carcinoma, Eastern Cooperative Oncology Group (ECOG) 0-1, with relapse defined by a rise in CA-125 to twice the upper limit of normal or low-volume disease on CT scan. The primary endpoint was disease progression (including deaths from ovarian cancer) at 25 weeks. Following a brief suspension, the trial restarted as a single-arm study. The revised single-arm design required 45 evaluable patients treated with MVA-5T4 to detect a 25-week progression rate of 50%, assuming an expected 70% rate without MVA-5T4; 85% power with one-sided 5% significance.

RESULTS

A total of 94 eligible patients were recruited, median age was 65 years (range 42-82), median follow-up 34 months (range 2-46). Overall, 59 patients received MVA-5T4 and 35 patients received placebo. The median number of MVA-5T4 injections received was 7 (range 0-9), compared with a median of 6 (range 1-12) for patients receiving placebo. Median progression-free survival was the same in both arms (3.0 months). The 25-week progression rate was similar in both arms: 80.0% for patients treated with MVA-5T4 and 85.7% for those receiving placebo (risk difference -5.7%, 95% CI -21.4% to 10.0%). Median time to clinical intervention was improved with MVA-5T4: 7.6 months (range 6.7-9.5) vs 5.6 (range 4.9-7.6), CONCLUSION: MVA-5T4 vaccination in patients with asymptomatic relapse was well-tolerated but did not improve the progression rate at 25 weeks. The majority of patients who received MVA-5T4 had clinical intervention later than those assigned to placebo.

TRIAL REGISTRATION NUMBER

NCT01556841.

Preclinical and clinical trials of oncolytic vaccinia virus in cancer immunotherapy: a comprehensive review

Oncolytic virotherapy has emerged as a promising treatment for human cancers owing to an ability to elicit curative effects via systemic administration. Tumor cells often create an unfavorable immunosuppressive microenvironment that degrade viral structures and impede viral replication; however, recent studies have established that viruses altered via genetic modifications can serve as effective oncolytic agents to combat hostile tumor environments. Specifically, oncolytic vaccinia virus (OVV) has gained popularity owing to its safety, potential for systemic delivery, and large gene insertion capacity. This review highlights current research on the use of engineered mutated viruses and gene-armed OVVs to reverse the tumor microenvironment and enhance antitumor activity in vitro and in vivo, and provides an overview of ongoing clinical trials and combination therapies. In addition, we discuss the potential benefits and drawbacks of OVV as a cancer therapy, and explore different perspectives in this field.

Antigenic targets in clear cell renal cell carcinoma

Immune checkpoint inhibitors (ICIs) have transformed the management of advanced renal cell carcinoma (RCC), but most patients still do not receive a long-term benefit from these therapies, and many experience off-target, immune-related adverse effects. RCC is also different from many other ICI-responsive tumors, as it has only a modest mutation burden, and total neoantigen load does not correlate with ICI response. In order to improve the efficacy and safety of immunotherapies for RCC, it is therefore critical to identify the antigens that are targeted in effective anti-tumor immunity. In this review, we describe the potential classes of target antigens, and provide examples of previous and ongoing efforts to investigate and target antigens in RCC, with a focus on clear cell histology. Ultimately, we believe that a concerted antigen discovery effort in RCC will enable an improved understanding of response and resistance to current therapies, and lay a foundation for the future development of "precision" antigen-directed immunotherapies.

Armored modified vaccinia Ankara in cancer immunotherapy

Cancer immunotherapy relies on unleashing the patient´s immune system against tumor cells. Cancer vaccines aim to stimulate both the innate and adaptive arms of immunity to achieve durable clinical responses. Some roadblocks for a successful cancer vaccine in the clinic include the tumor antigen of choice, the adjuvants employed to strengthen antitumor-specific immune responses, and the risks associated with enhancing immune-related adverse effects in patients. Modified vaccinia Ankara (MVA) belongs to the family of poxviruses and is a versatile vaccine platform that combines several attributes crucial for cancer therapy. First, MVA is an excellent inducer of innate immune responses leading to type I interferon secretion and induction of T helper cell type 1 (Th1) immune responses. Second, it elicits robust and durable humoral and cellular immunity against vector-encoded heterologous antigens. Third, MVA has enormous genomic flexibility, which allows for the expression of multiple antigenic and costimulatory entities. And fourth, its replication deficit in human cells ensures a excellent safety profile. In this review, we summarize the current understanding of how MVA induces innate and adaptive immune responses. Furthermore, we will give an overview of the tumor-associated antigens and immunomodulatory molecules that have been used to armor MVA and describe their clinical use. Finally, the route of MVA immunization and its impact on therapeutic efficacy depending on the immunomodulatory molecules expressed will be discussed.

Current status of antigen-specific T-cell immunotherapy for advanced renal-cell carcinoma

In renal-cell carcinoma (RCC), tumor-reactive T-cell responses can occur spontaneously or in response to systemic immunotherapy with cytokines and immune checkpoint inhibitors. Cancer vaccines and engineered T-cell therapies are designed to selectively augment tumor antigen-specific CD8⁺ T-cell responses with the goal to elicit tumor regression and avoid toxicities associated with nonspecific immunotherapies. In this review, we provide an overview of the central role of T-cell immunity in the treatment of advanced RCC. Clinical outcomes for antigen-targeted vaccines or other T-cell-engaging therapies for RCC are summarized and evaluated, and emerging new strategies to enhance the effectiveness of antigen-specific therapy for RCC are discussed.

Combination Treatment with an Antibody-Drug Conjugate (A1mcMMAF) Targeting the Oncofetal Glycoprotein 5T4 and Carboplatin Improves Survival in a Xenograft Model of Ovarian Cancer

Background

Recurrence occurs in over 75% of women with epithelial ovarian cancer despite optimal treatment. Selectively killing tumour cells thought to initiate relapse using an antibody–drug conjugate could prolong progression-free survival and offer an improved side-effect profile. A1mcMMAF is an antibody–drug conjugate designed to target cells expressing the tumour-associated antigen 5T4. It has shown to be efficacious in various cell line models and have a greater impact when combined with routine chemotherapeutic regimes.

Objectives

This study aims to explore the potential for the use of a 5T4 antibody–drug conjugate in women with ovarian cancer both as a monotherapy and in combination with platinum-based chemotherapy.

Methods

Immunohistochemical analysis was used to assess 5T4 expression in tumours from patients with ovarian cancer. Effectiveness of A1mcMMAF therapy as a single agent and in combination with carboplatin was assessed in vitro in the ovarian cancer cell line SKOV3 and confirmed in vivo using a serial bioluminescence assay in a SKOV3 xenograft model of ovarian cancer.

Results

5T4 is confirmed as suitably expressed in epithelial ovarian cancers prior to adjuvant therapy and is an independent predictor of poor survival. A1mcMMAF showed specific activity, both in vitro and in vivo, against SKOV3 ovarian cancer cells. When used in combination with carboplatin, in vivo tumour growth was inhibited resulting in prolonged survival in a SKOV3 xenograft model.

Conclusions

These data support further investigation of A1mcMMAF in combination with platinum-based chemotherapy in ovarian and other cancer treatments.

Electronic supplementary material

The online version of this article (10.1007/s11523-019-00650-8) contains supplementary material, which is available to authorized users.

Vaccinia virus-mediated cancer immunotherapy: cancer vaccines and oncolytics

Cancer vaccines and oncolytic immunotherapy are promising treatment strategies with potential to provide greater clinical benefit to patients with advanced-stage cancer. In particular, recombinant vaccinia viruses (VV) hold great promise as interventional agents. In this article, we first summarize the current understanding of virus biology and viral genes involved in host-virus interactions to further improve the utility of these agents in therapeutic applications. We then discuss recent findings from basic and clinical studies using VV as cancer vaccines and oncolytic immunotherapies. Despite encouraging results gleaned from translational studies in animal models, clinical trials implementing VV vectors alone as cancer vaccines have yielded largely disappointing results. However, the combination of VV vaccines with alternate forms of standard therapies has resulted in superior clinical efficacy. For instance, combination regimens using TG4010 (MVA-MUC1-IL2) with first-line chemotherapy in advanced-stage non-small cell lung cancer or combining PANVAC with docetaxel in the setting of metastatic breast cancer have clearly provided enhanced clinical benefits to patients. Another novel cancer vaccine approach is to stimulate anti-tumor immunity via STING activation in Batf3-dependent dendritic cells (DC) through the use of replication-attenuated VV vectors. Oncolytic VVs have now been engineered for improved safety and superior therapeutic efficacy by arming them with immune-stimulatory genes or pro-apoptotic molecules to facilitate tumor immunogenic cell death, leading to enhanced DC-mediated cross-priming of T cells recognizing tumor antigens, including neoantigens. Encouraging translational and early phase clinical results with Pexa-Vec have matured into an ongoing global phase III trial for patients with hepatocellular carcinoma. Combinatorial approaches, most notably those using immune checkpoint blockade, have produced exciting pre-clinical results and warrant the development of innovative clinical studies. Finally, we discuss major hurdles that remain in the field and offer some perspectives regarding the development of next generation VV vectors for use as cancer therapeutics.

Construction of immune-related risk signature for renal papillary cell carcinoma

The kidney renal papillary cell carcinoma (KIRP) is a relatively rare type of kidney cancer. There has been no investigation to find a robust signature to predict the survival outcome of KIRP patients in the aspect of tumor immunology. In this study, 285 KIRP samples from The Cancer Genome Atlas (TCGA) were randomly divided into training and testing set. A total of 1534 immune‐related genes from The Immunology Database and Analysis Portal (ImmPort) were used as candidates to construct the signature. Using univariate Cox analysis, we evaluated the relationship between overall survival and immune‐related genes expression and found 272 immune‐related genes with predicting prognostic ability. In order to construct an efficient predictive model, the Cox proportional hazards model with an elastic‐net penalty was used and identified 23 groups after 1000 iterations. As a result, 15‐genes model showing more stable than other gene groups was chosen to construct our immune‐related risk signature. In line with our expectations, the signature can independently predict the survival outcome of KIRP patients. Patients with high‐immune risk were found correlated with advanced stage. We also found that the high‐immune risk patients with higher PBRM1 and SETD2 mutations, increasing chromosomal instability, together with the gene set enrichment analysis (GSEA) results showing intensive connection of our signature with immune pathways. In conclusion, our study constructs a robust 15‐gene signature for predicting KIRP patients’ survival outcome on the basis of tumor immune environment and may provide possible relationship between prognosis and immune‐related biological function.

Fighting Cancer with Mathematics and Viruses

After decades of research, oncolytic virotherapy has recently advanced to clinical application, and currently a multitude of novel agents and combination treatments are being evaluated for cancer therapy. Oncolytic agents preferentially replicate in tumor cells, inducing tumor cell lysis and complex antitumor effects, such as innate and adaptive immune responses and the destruction of tumor vasculature. With the availability of different vector platforms and the potential of both genetic engineering and combination regimens to enhance particular aspects of safety and efficacy, the identification of optimal treatments for patient subpopulations or even individual patients becomes a top priority. Mathematical modeling can provide support in this arena by making use of experimental and clinical data to generate hypotheses about the mechanisms underlying complex biology and, ultimately, predict optimal treatment protocols. Increasingly complex models can be applied to account for therapeutically relevant parameters such as components of the immune system. In this review, we describe current developments in oncolytic virotherapy and mathematical modeling to discuss the benefit of integrating different modeling approaches into biological and clinical experimentation. Conclusively, we propose a mutual combination of these research fields to increase the value of the preclinical development and the therapeutic efficacy of the resulting treatments.

Novel immunotherapy in metastatic renal cell carcinoma

Despite the rapid development of therapeutic modalities for metastatic renal cell carcinoma (mRCC) over the past decade to include a number of targeted antiangiogenic therapies and traditional immunotherapy, such as high-dose interleukin-2 and interferon-α, mRCC continues to be associated with poor prognosis. Currently, several novel immunotherapy agents, such as cancer vaccines, adoptive cell therapy, and checkpoint inhibitors, such as programmed cell death-1 (PD-1 present on T cells), one of its ligands (PD-L1 present on antigen-presenting cells and tumor cells), and cytotoxic T-lymphocyte-associated protein-4 pathways, are being studied in mRCC and are showing promise as important steps in the management of this disease. This review summarizes the current landscape of standard and emerging immune therapeutics and other modalities for mRCC.

5T4 oncofoetal antigen: an attractive target for immune intervention in cancer

The natural history of a patient's cancer is often characterised by genetic diversity and sequential sweeps of clonal dominance. It is therefore not surprising that identifying the most appropriate tumour-associated antigen for targeted intervention is challenging. The 5T4 oncofoetal antigen was identified by searching for surface molecules shared between human trophoblast and cancer cells with the rationale that they may function to allow survival of the foetus as a semi-allograft in the mother or a tumour in its host. The 5T4 protein is expressed by many different cancers but rarely in normal adult tissues. 5T4 molecules are 72 kD, heavily N-glycosylated proteins with several leucine-rich repeats which are often associated with protein-protein interactions. 5T4 expression is associated with the directional movement of cells through epithelial mesenchymal transition, potentiation of CXCL12/CXCR4 chemotaxis and inhibition of canonical Wnt/beta-catenin while favouring non-canonical pathway signalling; all processes which help drive the spread of cancer cells. The selective pattern of 5T4 tumour expression, association with a tumour-initiating phenotype plus a mechanistic involvement with cancer spread have underwritten the clinical development of different immunotherapeutic strategies including a vaccine, a tumour-targeted superantigen and an antibody drug conjugate. In addition, a chimeric antigen receptor T cell approach targeting 5T4 expressing tumour cells is in pre-clinical development. A key challenge will include how best to combine each 5T4 targeted immunotherapy with the most appropriate standard of care treatment (or adjunct therapy) to maximise the recovery of immune control and ultimately eliminate the tumour.

Interleukin-2: Old and New Approaches to Enhance Immune-Therapeutic Efficacy

Interleukin-2 (IL-2) is a very well-known cytokine that has been studied for the past 35 years. It plays a major role in the growth and proliferation of many immune cells such NK and T cells. It is an important immunotherapy cytokine for the treatment of various diseases including cancer. Systemic delivery of IL-2 has shown clinical benefit in renal cell carcinoma and melanoma patients. However, its use has been limited by the numerous toxicities encountered with the systemic delivery. Intravenous IL-2 causes the well-known "capillary leak syndrome," or the leakage of fluid from the circulatory system to the interstitial space resulting in hypotension (low blood pressure), edema, and dyspnea that can lead to circulatory shock and eventually cardiopulmonary collapse and multiple organ failure. Due to the toxicities associated with systemic IL-2, an aerosolized delivery approach has been developed, which enables localized delivery and a higher local immune cell activation. Since proteins are absorbed via pulmonary lymphatics, after aerosol deposition in the lung, aerosol delivery provides a means to more specifically target IL-2 to the local immune system in the lungs with less systemic effects. Its benefits have extended to diseases other than cancer. Delivery of IL-2 via aerosol or as nebulized IL-2 liposomes has been previously shown to have less toxicity and higher efficacy against sarcoma lung metastases. Dogs with cancer provided a highly relevant means to determine biodistribution of aerosolized IL-2 and IL-2 liposomes. However, efficacy of single-agent IL-2 is limited. As in general, for most immune-therapies, its effect is more beneficial in the face of minimal residual disease. To overcome this limitation, combination therapies using aerosol IL-2 with adoptive transfer of T cells or NK cells have emerged.Using a human osteosarcoma (OS) mouse model, we have demonstrated the efficacy of single-agent aerosol IL-2 and combination therapy aerosol IL-2 and NK cells or aerosol IL-2 and interleukin 11 receptor alpha-directed chimeric antigen receptor-T cells (IL-11 receptor α CAR-T cells) against OS pulmonary metastases. Combination therapy resulted in a better therapeutic effect. A Phase-I trial of aerosol IL-2 was done in Europe and proved to be safe. Others and our preclinical studies provided the basis for the development of a Phase-I aerosol IL-2 trial in our institution to include younger patients with lung metastases. OS, our disease of interest, has a peak incidence in the adolescent and young adult years. Our goal is to complete this trial in the next 2 years.In this chapter, we summarize the different effects of IL-2 and cover the advantages of the aerosol delivery route for diseases of the lung with an emphasis on some of our most recent work using combination therapy aerosol IL-2 and NK cells for the treatment of OS lung metastases.

TroVax in colorectal cancer

Currently, the backbone of therapy for metastatic disease is cytotoxic chemotherapy, along with the recent addition of targeted therapy based on molecular markers with KRAS testing. Despite the improvement in survival for metastatic colon cancer, newer agents are still needed. The clinical activity of TroVax in metastatic colon cancer has been studied in a small number of clinical trials. There is evidence that supports the vaccine's ability to induce humoral and cellular responses, as demonstrated by positive 5T4 and MVA-specific antibody titers and cellular proliferation assays. Future strategies should focus on investigating the immunomodulatory effects of chemotherapy in conjunction with TroVax, understanding the optimal dosing and schedule of the combination, and examining potential predictive biomarkers to determine which patients may benefit from immunotherapy from those who do not.

Enhancing poxvirus vectors vaccine immunogenicity

Attenuated recombinant poxvirus vectors expressing heterologous antigens from pathogens are currently at various stages in clinical trials with the aim to establish their efficacy. This is because these vectors have shown excellent safety profiles, significant immunogenicity against foreign expressed antigens and are able to induce protective immune responses. In view of the limited efficacy triggered by some poxvirus strains used in clinical trials (i.e, ALVAC in the RV144 phase III clinical trial for HIV), and of the restrictive replication capacity of the highly attenuated vectors like MVA and NYVAC, there is a consensus that further improvements of these vectors should be pursuit. In this review we considered several strategies that are currently being implemented, as well as new approaches, to improve the immunogenicity of the poxvirus vectors. This includes heterologous prime/boost protocols, use of co-stimulatory molecules, deletion of viral immunomodulatory genes still present in the poxvirus genome, enhancing virus promoter strength, enhancing vector replication capacity, optimizing expression of foreign heterologous sequences, and the combined use of adjuvants. An optimized poxvirus vector triggering long-lasting immunity with a high protective efficacy against a selective disease should be sought.

Recent advances in the use of therapeutic cancer vaccines in genitourinary malignancies

INTRODUCTION

Despite a recent increase in US FDA-approved treatments, genitourinary malignancies remain a source of significant morbidity and mortality. One focus of research is the use of therapeutic cancer vaccines in these diseases, and a significant body of clinical trial experience now exists for refining vaccine strategies to enhance antitumor efficacy and develop immune-based combination regimens.

AREAS COVERED

In recent years, clinical data from multiple trials in genitourinary malignancies have enhanced our understanding of the potential for immunotherapy in these cancers. There are also emerging clinical strategies that combine cancer vaccines with chemotherapy, radiation, androgen-deprivation therapy and immune checkpoint inhibitors. This review is based on a search of relevant literature for data presented over the past 5 years from clinical trials of cancer vaccines in prostate, bladder and renal carcinomas.

EXPERT OPINION

In the coming years, clinical trials informed by decades of preclinical data and emerging clinical data will help to define the role of immunotherapy in genitourinary malignancies. Combination strategies that capitalize on the immune properties of standard treatments will bring greater clinical benefits, and immune-based combinations will likely be moved to the neoadjuvant setting, where they may have optimal clinical impact.

Immunoglobulin-like transcript 2 (ILT2) is a biomarker of therapeutic response to oncolytic immunotherapy with vaccinia viruses

Background

Oncolytic viruses represent a novel form of cancer immunotherapy. Vaccinia viruses encoding human T cell co-stimulatory molecules have demonstrated clinical activity in phase I clinical trials in patients with advanced melanoma. However, predictive biomarkers of therapeutic response have not yet been identified.

Methods

A customized microarray was performed to identify changes in peripheral blood mononuclear cell (PBMC) gene expression upon exposure to recombinant oncolytic vaccinia viruses. Up-regulated and down-regulated genes were identified and selected for further analysis using PBMC samples from normal donors and oncolytic virus-treated patients before and after viral injection. Quantitative PCR and flow cytometry of defined T cell subsets was performed to evaluate expression patterns and clinical correlations.

Results

The microarray identified 301 genes that were up-regulated and 960 genes that were down-regulated in T cells after exposure to oncolytic vaccinia virus. The B7.1 gene was highly up-regulated and the immunoglobulin-like transcript 2 (ILT2) gene was highly down-regulated by vaccinia-B7.1, which was consistent with the known inverse regulation of these two genes. We observed an inverse association between ILT2 expression in the tumor microenvironment and clinical response and further identified ILT2 as a marker of regulatory CD4+ and suppressor CD8+ T cell responses and whose down-regulation was predictive of therapeutic responses in patients treated with oncolytic virus immunotherapy.

Conclusions

ILT2 is a new putative biomarker of T cell and clinical response in patients treated with oncolytic vaccinia virus immunotherapy. Further confirmation of ILT2 as a biomarker requires prospective validation in a larger series of clinical trials.

Progress and potential of immune checkpoint blockade for treating advanced renal cell carcinoma

Adaptive immune responses appear to influence the natural history of cancer progression, as well as therapeutic outcomes, in cancer patients. However, accumulating evidence suggests resistance mechanisms exploited by tumors may play a dominant role in limiting the effectiveness of T cell-mediated cancer therapies. Inhibitory coreceptors expressed by T lymphocytes, or so-called immune checkpoints, are now recognized to play critical roles in regulating the termination of adaptive immune responses. An overview of early-phase trial results distinguish blocking antibodies targeting inhibitory coreceptors as a highly promising approach to cancer immunotherapy for patients with advanced clear cell renal cell carcinoma. Prospects for advanced-phase clinical testing and novel therapy combinations with immune checkpoint blocking agents are discussed.

Vaccination of castration-resistant prostate cancer patients with TroVax (MVA-5T4) in combination with docetaxel: a randomized phase II trial

The attenuated vaccinia virus, modified vaccinia Ankara, has been engineered to deliver the tumor antigen 5T4 (TroVax®). Here, we report results from a randomized open-label phase II trial in castration-resistant prostate cancer patients in which TroVax was administered in combination with docetaxel and compared against docetaxel alone. The aim was to recruit 80 patients (40 per arm), but the study was terminated early due to recruitment challenges. Therefore, this paper reports the comparative safety and immunological and clinical efficacy in 25 patients, 12 of whom were treated with TroVax plus docetaxel and 13 with docetaxel alone. 5T4-specific immune responses were monitored throughout the study. Clinical responses were assessed by measuring changes in tumor burden by CT and bone scan and by quantifying PSA concentrations. TroVax was well tolerated in all patients. Of 10 immunologically evaluable patients, 6 mounted 5T4-specific antibody responses. Patients treated with TroVax plus docetaxel showed a greater median progression-free survival of 9.67 months compared with 5.10 months for patients on the docetaxel alone arm (P = 0.097; HR = 0.31; 95% CI 0.08-1.24). Importantly, a pre-treatment biomarker previously demonstrated to predict 5T4 immune response and treatment benefit showed a strong association with 5T4 antibody response and a statistically significant association with progression-free survival in patients treated with TroVax plus docetaxel, but not docetaxel alone.

Identification of Pre- and Post-Treatment Markers, Clinical, and Laboratory Parameters Associated with Outcome in Renal Cancer Patients Treated with MVA-5T4

The recent approvals of immunotherapeutic agents (Sipuleucel-T and Ipilimumab) for the treatment of different solid tumors gave a boost to the growing cancer immunotherapy field, even though few immunotherapy studies have demonstrated convincingly that there is a direct link between the predicted mode of action of an immunological compound and therapeutic benefit. MVA-5T4 (TroVax^®) is a novel vaccine combining the tumor-associated antigen 5T4 to an engineered vector-modified vaccinia Ankara (MVA). MVA helps to express the oncofetal 5T4 antigen and subsequently trigger a tumor-directed immune reaction. The safety and clinical benefit reported in multiple phase I and II clinical trials using MVA-5T4 were encouraging; immune responses were induced in almost all treated patients, and associations between 5T4-specific cellular or humoral responses and clinical benefit were reported in most of the nine phase II trials. In particular, clinical studies conducted in renal cell carcinoma (RCC) patients have demonstrated an association between 5T4-specific (but not MVA) antibody responses and enhanced survival. This review describes the clinical studies using MVA-5T4 conducted in RCC that convincingly demonstrated that an antigen-specific immune response induced by vaccination is associated with enhanced patient survival and is not simply a function of the general “health” of patients. We will also provide our expert opinions on possible future better-designed clinical trials based on relevant biomarkers. In addition, various combinations of MVA-5T4 and different and newer immunomodulator agents with promising clinical benefit will be discussed.

A single immunization with MVA expressing GnGc glycoproteins promotes epitope-specific CD8+-T cell activation and protects immune-competent mice against a lethal RVFV infection

Background

Rift Valley fever virus (RVFV) is a mosquito-borne pathogen causing an important disease in ruminants often transmitted to humans after epizootic outbreaks in African and Arabian countries. To help combat the spread of the disease, prophylactic measures need to be developed and/or improved.

Methodology/Principal Findings

In this work, we evaluated the immunogenicity and protective efficacy of recombinant plasmid DNA and modified vaccinia virus Ankara (rMVA) vectored vaccines against Rift Valley fever in mice. These recombinant vaccines encoded either of two components of the Rift Valley fever virus: the viral glycoproteins (Gn/Gc) or the nucleoprotein (N). Following lethal challenge with live RVFV, mice immunized with a single dose of the rMVA-Gn/Gc vaccine showed no viraemia or clinical manifestation of disease, but mounted RVFV neutralizing antibodies and glycoprotein specific CD8+ T-cell responses. Neither DNA-Gn/Gc alone nor a heterologous prime-boost immunization schedule (DNA-Gn/Gc followed by rMVAGn/Gc) was better than the single rMVA-Gn/Gc immunization schedule with regards to protective efficacy. However, the rMVA-Gn/Gc vaccine failed to protect IFNAR^−/− mice upon lethal RVFV challenge suggesting a role for innate responses in protection against RVFV. Despite induction of high titer antibodies against the RVFV nucleoprotein, the rMVA-N vaccine, whether in homologous or heterologous prime-boost schedules with the corresponding recombinant DNA vaccine, only conferred partial protection to RVFV challenge.

Conclusions/Significance

Given the excellent safety profile of rMVA based vaccines in humans and animals, our data supports further development of rMVA-Gn/Gc as a vaccine strategy that can be used for the prevention of Rift Valley fever in both humans and livestock.

Rift Valley fever (RVF) is an important disease of ruminants that affects most African and Arabian Peninsula countries where domestic livestock is the basis for subsistence in rural areas. The disease is caused by a bunyavirus that can be transmitted by close contact with infected animals or through the bite of infected mosquitoes thus facilitating the spread of the virus. Safer and practical methods to control virus spread are demanded in order to prevent both human and animal disease after disease outbreaks. The efficacy of a recombinant modified poxvirus vector (the vaccinia modified Ankara virus (rMVA)) and/or DNA-based vaccines in a mouse infection model has been investigated. A single immunization with a rMVA encoding the virus envelope glycoproteins provided sufficient immunity to protect mice against a lethal dose of RVFV. The immune mechanisms underlying the protection were also investigated. A number of specific immune CD8+-T cells could be activated in the presence of at least three different glycoprotein epitopes. On the other hand, the protective effect of the vaccine was found only in immune competent mice since in mice lacking IFN-type-I responses the vaccine was not efficient.

Cancer vaccines: identification of biomarkers predictive of clinical efficacy

Personalized medicine is playing an increasingly important role in the treatment of patients living with cancer. This landmark shift has been driven in part by statistics emerging from the "one size fits all" approach to the treatment of cancer patients. Some reports suggest that only a minority of individuals actually benefit from treatment and adverse effects of medications remain a major cause of hospitalization, morbidities and deaths. Although the side-effect profile of most immunotherapy treatment modalities is usually fairly benign, there is no reason to believe that immunotherapy is any different from other oncology therapies in that some patients are likely to receive more benefit than others. Indeed, the fact that generation of the therapeutic modality requires translation through multiple complex biological processes for an immunotherapy product to be effective may mean that such approaches require an even better understanding of the patient being treated. Furthermore, the very low success rate of cancer immunotherapy approaches to deliver benefit to patients demands a more detailed understanding of who will benefit and why. The identification of biomarkers predictive of treatment benefit is one route to improve the success rate of cancer vaccines.

Role of vaccine therapy for renal cell carcinoma in the era of targeted therapy

Renal cell carcinoma is the most common malignant tumor originating from the kidney. Compared with other solid tumors, it does not respond to traditional management modalities, such as chemotherapy and radiotherapy. However, it is well known that renal cell carcinoma represents one of the most immune-responsive cancers and several immunotherapeutic strategies have been investigated in the management of renal cell carcinoma with variable degrees of success. The development of immunotherapy with α-interferon or high-dose interleukin-2 is the best established treatment, and is associated with durable disease control. Although the lack of defined antigens in renal cell carcinoma has hindered more specific vaccine development, research regarding vaccination therapy has been of special interest for the treatment of renal cell carcinoma for more than 30 years. At present, there are three types of cell-based vaccines in renal cell carcinoma treatment: autologous tumor-cell vaccines, genetically modified tumor vaccines and dendritic cell-based vaccines. A further type is peptide-based vaccination with tumor-associated antigens as possible targets, such as carbonic anhydrase IX, survivin and telomerase that are overexpressed in renal cell carcinoma. In the present article, we review data from completed clinical trials of vaccine therapy, and discuss future trials to assess the current knowledge and future role of vaccine therapy for renal cell carcinoma in the era of recently developed targeted therapy.

CD8+ T-cell clones specific for the 5T4 antigen target renal cell carcinoma tumor-initiating cells in a murine xenograft model

The tumor antigen 5T4 is frequently expressed at high levels on renal cell carcinoma (RCC) and other epithelial carcinomas. Surveys of normal tissues demonstrate abundant 5T4 expression on placental trophoblast cells with limited expression elsewhere. 5T4 is the target for a therapeutic cancer vaccine (MVA-5T4) that elicits 5T4-specific serological, proliferative, and cytotoxic T lymphocyte (CTL) responses. However, the antitumor activity of 5T4-specific CTL has not been extensively characterized. CD8 T cells from HLA-A2 healthy donors (n=4) or RCC patients (n=2) were stimulated in vitro with the HLA-A2-binding nonamer peptides 5T417-25 or 5T497-105 and screened by flow cytometry with specific tetramers (TET). CD8/TET T-cell clones specific for 5T417-25 or 5T497-105 peptide were isolated from 4/6 and 1/4 donors, respectively. A subset of clones specific for 5T417-25 was cytolytic for MVA-5T4-infected HLA-A2 EBV-transformed lymphoblastoid cell line target cells and for constitutively HLA-A2-expressing and 5T4-expressing RCC tumor cell lines (including A498 RCC). In a xenoengraftment assay, the coinoculation of a representative 5T417-25-specific CTL clone with A498 RCC tumors cells into immune-deficient mice completely prevented growth of A498 tumors. Taken together, these data demonstrate high-avidity CD8 CTL able to recognize the naturally processed 5T417-25 epitope on RCC tumor cells including putative tumor-initiating cells are present in peripheral blood of both healthy donors and RCC patients. CD8T-cell immunity targeting 5T417-25 is therefore of substantial interest both as a potential target for further development of vaccination or adoptive cellular immunotherapy and for immune monitoring studies in association with nonspecific immunotherapies.

Analysis of pre-treatment markers predictive of treatment benefit for the therapeutic cancer vaccine MVA-5T4 (TroVax)

Cancer vaccines such as MVA-5T4 (TroVax(®)) must induce an efficacious immune response to deliver therapeutic benefit. The identification of biomarkers that impact on the clinical and/or immunological efficacy of cancer vaccines is required in order to select patients who are most likely to benefit from this treatment modality. Here, we sought to identify a predictor of treatment benefit for renal cancer patients treated with MVA-5T4. Statistical modeling was undertaken using data from a phase III trial in which patients requiring first-line treatment for metastatic renal cell carcinoma were randomized 1:1 to receive MVA-5T4 or placebo alongside sunitinib, IL-2 or IFN-α. Numerous pre-treatment factors associated with inflammatory anemia (e.g., CRP, hemoglobin, hematocrit, IL-6, ferritin, platelets) demonstrated a significant relationship with tumor burden and patient survival. From these prognostic factors, the pre-treatment mean corpuscular hemoglobin concentration (MCHC) was found to be the best predictor of treatment benefit (P < 0.01) for MVA-5T4 treated patients and also correlated positively with tumor shrinkage (P < 0.001). Furthermore, MCHC levels showed a significant positive association with 5T4 antibody response (P = 0.01). The latter result was confirmed using an independent data set comprising phase II trials of MVA-5T4 in patients with colorectal, renal and prostate cancers. Retrospective analyses demonstrated that RCC patients who had very large tumor burdens and low MCHC levels received little or no benefit from treatment with MVA-5T4; however, patients with smaller tumor burdens and normal MCHC levels received substantial benefit from treatment with MVA-5T4.

Anti-inflammatory cytokines: important immunoregulatory factors contributing to chemotherapy-induced gastrointestinal mucositis

“Mucositis” is the clinical term used to describe ulceration and damage of the mucous membranes of the entire gastrointestinal tract (GIT) following cytotoxic cancer chemotherapy and radiation therapy common symptoms include abdominal pain, bloating, diarrhoea, vomiting, and constipation resulting in both a significant clinical and financial burden. Chemotherapeutic drugs cause upregulation of stress response genes including NFκB, that in turn upregulate the production of proinflammatory cytokines such as interleukin-1β (IL-1β), Interleukin-6 (IL-6), and tumour necrosis factor-α (TNF-α). These proinflammatory cytokines are responsible for initiating inflammation in response to tissue injury. Anti-inflammatory cytokines and specific cytokine inhibitors are also released to limit the sustained or excessive inflammatory reactions. In the past decade, intensive research has determined the role of proinflammatory cytokines in development of mucositis. However, a large gap remains in the knowledge of the role of anti-inflammatory cytokines in the setting of chemotherapy-induced mucositis. This critical paper will highlight current literature available relating to what is known regarding the development of mucositis, including the molecular mechanisms involved in inducing inflammation particularly with respect to the role of proinflammatory cytokines, as well as provide a detailed discussion of why it is essential to consider extensive research in the role of anti-inflammatory cytokines in chemotherapy-induced mucositis so that effective targeted treatment strategies can be developed.

Poxviral vectors for cancer immunotherapy

INTRODUCTION

Poxviral vaccines have been given to over 1 billion people in the successful global eradication of smallpox. Recombinant poxviruses have been investigated extensively as a novel immunotherapy for cancer, undergoing several iterations to optimize their immunogenicity and efficacy. The current platform expressing multiple costimulatory molecules plus a tumor-associated antigen such as PSA, that is, PSA-TRICOM (PROSTVAC-V/F), is promising and is currently in a Phase III randomized, placebo-controlled clinical trial in metastatic castration-resistant prostate cancer.

AREAS COVERED

This review discusses the clinical development of poxviral-based cancer vaccines, with a particular focus on the rationale for combining vaccines with other treatment modalities, including radiotherapy, chemotherapy, hormonal therapy, other immune-based therapies and molecularly targeted therapy. We also discuss the importance of appropriate patient selection in clinical trial design.

EXPERT OPINION

Preclinical and early clinical studies employing poxviral-vector vaccines have shown promising results with this novel immunologic approach, both alone and combined with other therapies. The challenges of translating the science of immunotherapy to clinical practice include clinical trial design that includes appropriate patient selection, appropriate end points and identification of meaningful surrogate biomarkers.

Evaluation of MVA-5T4 as a novel immunotherapeutic vaccine in colorectal, renal and prostate cancer

This paper reviews the development of the combination of modified vaccinia Ankara (MVA) to deliver the tumor-associated antigen 5T4 as a novel immunotherapeutic vaccine. The oncofetal antigen 5T4 is highly expressed in 80% of breast, kidney, colorectal, prostate and ovarian carcinomas, making it an ideal antigen for vaccine therapy. To date, more than 3000 doses of MVA-5T4 have been administered to colorectal, renal and prostate cancer patients, with rare occurrences of grade 3 or 4 vaccination-related adverse events being observed. Studies have demonstrated that MVA-5T4 is safe and highly immunogenic, both as monotherapy and in combination with other standard of care therapies. Although an immune response has been observed, antitumor activity has been modest or absent in clinical trials. A Phase III trial resulted in the development of an immune response surrogate that is to be applied to all future MVA-5T4 clinical trials. With minimal side effects and the ability to produce a strong immunogenic response, MVA-5T4 is a viable addition to the cancer therapy arsenal.

Vaccines for melanoma and renal cell carcinoma

The inherent immunogenicity of melanoma and renal cell carcinoma (RCC) has made these tumors a focus of considerable research in vaccine development. Recent data from murine studies of immunosurveillance have highlighted the importance of both innate and adaptive immune responses in shaping a tumor's inherent susceptibility to immune surveillance and immunotherapy. Melanoma has been a useful model for the identification of tumor-associated antigens and a number of putative renal cell antigens have been described more recently. These antigens have been targeted using a variety of vaccine strategies, including protein- and peptide-based vaccines, recombinant antigen-expressing vectors, and whole cell vaccine approaches. While evidence for clinical benefit has been disappointing to date, several current phase III clinical trials are in progress based on promising results from phase II studies. Accumulating data suggest that the tumor microenvironment and mechanisms of immunological escape by established tumors are significant barriers that must be overcome before vaccine therapy can be fully realized. This review will discuss the basis for vaccine development, describe some of the more promising vaccine strategies in development, and mention some of the tumor escape mechanisms that block effective anti-tumor immunity for melanoma and RCC.

A vaccinia virus renaissance: new vaccine and immunotherapeutic uses after smallpox eradication

In 1796, Edward Jenner introduced the concept of vaccination with cowpox virus, an Orthopoxvirus within the family Poxviridae that elicits cross protective immunity against related orthopoxviruses, including smallpox virus (variola virus). Over time, vaccinia virus (VACV) replaced cowpox virus as the smallpox vaccine, and vaccination efforts eventually led to the successful global eradication of smallpox in 1979. VACV has many characteristics that make it an excellent vaccine and that were crucial for the successful eradication of smallpox, including (1) its exceptional thermal stability (a very important but uncommon characteristic in live vaccines), (2) its ability to elicit strong humoral and cell-mediated immune responses, (3) the fact that it is easy to propagate, and (4) that it is not oncogenic, given that VACV replication occurs exclusively within the host cell cytoplasm and there is no evidence that the viral genome integrates into the host genome. Since the eradication of smallpox, VACV has experienced a renaissance of interest as a viral vector for the development of recombinant vaccines, immunotherapies, and oncolytic therapies, as well as the development of next-generation smallpox vaccines. This revival is mainly due to the successful use and extensive characterization of VACV as a vaccine during the smallpox eradication campaign, along with the ability to genetically manipulate its large dsDNA genome while retaining infectivity and immunogenicity, its wide mammalian host range, and its natural tropism for tumor cells that allows its use as an oncolytic vector. This review provides an overview of new uses of VACV that are currently being explored for the development of vaccines, immunotherapeutics, and oncolytic virotherapies.

Vaccines for colorectal cancer and renal cell carcinoma

Vaccines have shown promise for the prevention and treatment of solid tumors. Colorectal cancer and renal cell carcinoma are common malignancies that may be amenable to vaccine strategies. This review summarizes target antigens in colorectal and renal cell carcinoma, discusses some of the vaccine approaches in development, and details the results of pivotal phase III trials evaluating therapeutic vaccines in patients with advanced colorectal and renal cell carcinoma. Finally, some of the challenges with vaccine development for colorectal and renal cell carcinoma are described.

Viral vector-based therapeutic cancer vaccines

Most viruses are naturally immunogenic and can be engineered to express tumor antigen transgenes. Moreover, many types of recombinant viruses have been shown to infect professional antigen-presenting cells, specifically dendritic cells, and express their transgenes. This enhanced presentation of tumor antigens to the immune system has led to an increase in the frequency and avidity of cytotoxic T lymphocytes that target tumor cells expressing the tumor antigen(s) encoded in the vaccine vector. Logistically, recombinant viruses can be produced, administered, and quality controlled more easily compared with other immunotherapy strategies. The intrinsic properties of each virus have distinct advantages and disadvantages, which can determine their applicability in a particular therapeutic setting. The disadvantage of some vectors is the development of host-induced neutralizing antibodies to the vector itself, thus limiting its continued use. The "off-the-shelf" nature of viral vaccine platforms renders them exceptionally suitable for multicenter randomized trials. This review described and discussed the strategies used and results using viral-based vaccines, with emphasis on phases II and III clinical trials. Future directions will involve the evaluation of viral-based vaccines in the adjuvant and neoadjuvant settings, in patients with low burden metastatic disease, and in combination with other forms of therapy including immunotherapy.

TroVax® vaccine therapy for renal cell carcinoma

Renal cell carcinoma (RCC) is the most common primary malignancy affecting the kidney. In the past decade, several well-designed clinical trials have shifted the treatment paradigm for RCC to favor targeted therapies as first-line agents. Recognition of the immunogenic nature of RCC has also resulted in the development of immunotherapy approaches with high-dose IL-2 treatment being the best established and associated with durable disease control. The lack of defined antigens in RCC has hindered more specific vaccine development. TroVax® is a novel vaccine based on a modified vaccinia virus Ankara vector engineered to express the 5T4 tumor-associated antigen, found on over 95% of clear cell and papillary RCC tumors. The safety and efficacy of TroVax has been evaluated in several Phase I/II clinical trials and in a multicenter Phase III trial. This article will discuss the clinical background of RCC, the rationale for TroVax development, results of several TroVax clinical trials and future directions for optimizing TroVax therapy in patients with RCC and other cancers.

Immunotherapy for renal cell carcinoma

Although several cytokines have shown antitumor activity in renal cell carcinoma (RCC), the most consistent results have been reported with interleukin-2 (IL-2) and interferon (IFN). Recent insights into how the immune response to a tumor is regulated hold the promise of allowing patients to obtain a durable response to immunotherapy, perhaps without the significant toxicity associated with conventional approaches. This review describes how improvements in patient selection, combination therapy, and investigational agents might expand and better define the role of immunotherapy in metastatic RCC.

Pre-clinical efficacy and safety of experimental vaccines based on non-replicating vaccinia vectors against yellow fever

BACKGROUND

Currently existing yellow fever (YF) vaccines are based on the live attenuated yellow fever virus 17D strain (YFV-17D). Although, a good safety profile was historically attributed to the 17D vaccine, serious adverse events have been reported, making the development of a safer, more modern vaccine desirable.

METHODOLOGY/PRINCIPAL FINDINGS

A gene encoding the precursor of the membrane and envelope (prME) protein of the YFV-17D strain was inserted into the non-replicating modified vaccinia virus Ankara and into the D4R-defective vaccinia virus. Candidate vaccines based on the recombinant vaccinia viruses were assessed for immunogenicity and protection in a mouse model and compared to the commercial YFV-17D vaccine. The recombinant live vaccines induced γ-interferon-secreting CD4- and functionally active CD8-T cells, and conferred full protection against lethal challenge already after a single low immunization dose of 10(5) TCID(50). Surprisingly, pre-existing immunity against wild-type vaccinia virus did not negatively influence protection. Unlike the classical 17D vaccine, the vaccinia virus-based vaccines did not cause mortality following intracerebral administration in mice, demonstrating better safety profiles.

CONCLUSIONS/SIGNIFICANCE

The non-replicating recombinant YF candidate live vaccines induced a broad immune response after single dose administration, were effective even in the presence of a pre-existing immunity against vaccinia virus and demonstrated an excellent safety profile in mice.

Therapeutic vaccines in renal cell carcinoma

Metastatic renal cell carcinoma (mRCC) is a lethal disease. The advent of tyrosine kinase inhibitors (TKIs) has changed the disease process, yet the majority of patients will develop treatment-resistant disease. IL-2 based immunotherapy in mRCC is the only US FDA-approved treatment with curative results. Immunotherapeutic vaccine approaches to mRCC have been under investigation for several decades with mixed results. The recent FDA-approval of the first cellular immunotherapy in prostate cancer (Provenge(®)) has reinvigorated the search for similar vaccines approaches in mRCC. This review introduces the concepts and different features required for a successful anticancer vaccine approach.

MVA-5T4-induced immune responses are an early marker of efficacy in renal cancer patients

Few immunotherapy compounds have demonstrated a direct link between the predicted mode of action of the product and benefit to the patient. Since cancer vaccines are thought to have a delayed therapeutic effect, identification of the active moiety may enable the development of an early marker of efficacy. Patients with renal cancer and requiring first-line treatment for metastatic disease were randomized 1:1 to receive MVA-5T4 (TroVax(®)) or placebo alongside Sunitinib, IL-2 or IFN-α in a multicentre phase III trial. Antibody responses were quantified following the 3rd and 4th vaccinations. A surrogate for 5T4 antibody response (the immune response surrogate; IRS) was constructed and then used in a survival analysis to evaluate treatment benefit. Seven hundred and thirty-three patients were randomized, and immune responses were assessed in 590 patients. A high 5T4 antibody response was associated with longer survival within the MVA-5T4-treated group. The IRS was constructed as a linear combination of pre-treatment 5T4 antibody levels, hemoglobin and hematocrit and was shown to be a significant predictor of treatment benefit in the phase III study. Importantly, the IRS was also associated with antibody response and survival in an independent dataset comprising renal, colorectal and prostate cancer patients treated with MVA-5T4 in phase I-II studies. The derivation of the IRS formed part of an exploratory, retrospective analysis; however, if confirmed in future studies, the results have important implications for the development and use of the MVA-5T4 vaccine and potentially for other similar vaccines.

A novel candidate HIV vaccine vector based on the replication deficient Capripoxvirus, Lumpy skin disease virus (LSDV)

BACKGROUND

The Capripoxvirus, Lumpy skin disease virus (LSDV) has a restricted host-range and is being investigated as a novel HIV-1 vaccine vector. LSDV does not complete its replication cycle in non-ruminant hosts.

METHODS

The safety of LSDV was tested at doses of 104 and 106 plaque forming units in two strains of immunocompromised mice, namely RAG mice and CD4 T cell knockout mice. LSDV expressing HIV-1 subtype C Gag, reverse transcriptase (RT), Tat and Nef as a polyprotein (Grttn), (rLSDV-grttn), was constructed. The immunogenicity of rLSDV-grttn was tested in homologous prime-boost regimens as well as heterologous prime-boost regimes in combination with a DNA vaccine (pVRC-grttn) or modified vaccinia Ankara vaccine (rMVA-grttn) both expressing Grttn.

RESULTS

Safety was demonstrated in two strains of immunocompromised mice.In the immunogenicity experiments mice developed high magnitudes of HIV-specific cells producing IFN-gamma and IL-2. A comparison of rLSDV-grttn and rMVA-grttn to boost a DNA vaccine (pVRC-grttn) indicated a DNA prime and rLSDV-grttn boost induced a 2 fold (p < 0.01) lower cumulative frequency of Gag- and RT-specific IFN-γ CD8 and CD4 cells than a boost with rMVA-grttn. However, the HIV-specific cells induced by the DNA vaccine prime rLSDV-grttn boost produced greater than 3 fold (p < 0.01) more IFN- gamma than the HIV-specific cells induced by the DNA vaccine prime rMVA-grttn boost. A boost of HIV-specific CD4 cells producing IL-2 was only achieved with the DNA vaccine prime and rLSDV-grttn boost. Heterologous prime-boost combinations of rLSDV-grttn and rMVA-grttn induced similar cumulative frequencies of IFN- gamma producing Gag- and RT-specific CD8 and CD4 cells. A significant difference (p < 0.01) between the regimens was the higher capacity (2.1 fold) of Gag-and RT-specific CD4 cells to produce IFN-γ with a rMVA-grttn prime - rLSDV-grttn boost. This regimen also induced a 1.5 fold higher (p < 0.05) frequency of Gag- and RT-specific CD4 cells producing IL-2.

CONCLUSIONS

LSDV was demonstrated to be non-pathogenic in immunocompromised mice. The rLSDV-grttn vaccine was immunogenic in mice particularly in prime-boost regimens. The data suggests that this novel vaccine may be useful for enhancing, in particular, HIV-specific CD4 IFN- gamma and IL-2 responses induced by a priming vaccine.

An update on TroVax for the treatment of progressive castration-resistant prostate cancer

Prostate cancer is a common human malignancy with few effective therapeutic options for treating advanced castration-resistant disease. The potential therapeutic effectiveness of immunotherapy and vaccines, in particular, has gained popularity based on the identification of prostate-associated antigens, potent expression vectors for vaccination, and data from recent clinical trials. A modified vaccinia Ankara (MVA) virus expressing 5T4, a tumor-associated glycoprotein, has shown promise in preclinical studies and clinical trials in patients with colorectal and renal cell carcinoma. This review will discuss the rationale for immunotherapy in prostate cancer and describe preclinical and limited clinical data in prostate cancer for the MVA-5T4 (TroVax^®) vaccine.

Use of attenuated paramyxoviruses for cancer therapy

Paramyxoviruses, measles virus (MV), mumps virus (MuV) and Newcastle disease virus (NDV), are well known for causing measles and mumps in humans and Newcastle disease in birds. These viruses have been tamed (attenuated) and successfully used as vaccines to immunize their hosts. Remarkably, pathogenic MuV and vaccine strains of MuV, MV and NDV efficiently infect and kill cancer cells and are consequently being investigated as novel cancer therapies (oncolytic virotherapy). Phase I/II clinical trials have shown promise but treatment efficacy needs to be enhanced. Technologies being developed to increase treatment efficacy include: virotherapy in combination with immunosuppressive drugs (cyclophosphamide); retargeting of viruses to specific tumor types or tumor vasculature; using infected cell carriers to protect and deliver the virus to tumors; and genetic manipulation of the virus to increase viral spread and/or express transgenes during viral replication. Transgenes have enabled noninvasive imaging or tracking of viral gene expression and enhancement of tumor destruction.

A phase II study of the cancer vaccine TG4010 alone and in combination with cytokines in patients with metastatic renal clear-cell carcinoma: clinical and immunological findings

MUC1 over-expression in renal clear-cell carcinoma (RCC) is associated with poor prognosis. This phase II study determined the efficacy and tolerability of TG4010, a cancer vaccine based on a modified vaccinia virus expressing MUC1 and interleukin-2, in combination with cytokines, as first-line therapy in metastatic RCC. Thirty-seven patients with progressive, MUC1-positive RCC received TG4010 10(8) pfu/inj weekly for 6 weeks, then every 3 weeks until progression, when TG4010 was continued in combination with interferon-α2a and interleukin-2. Assessments included clinical response (primary endpoint), safety, time to treatment failure (TTF), overall survival (OS), and immune response. No objective clinical responses occurred. Five of the 27 evaluable patients (18%) had stable disease for >6 months with TG4010 alone and six of 20 patients (30%) had stable disease for >6 months with TG4010 plus cytokines. Median TTF was 4.1, 3.6, and 9.3 months for monotherapy, combination therapy, and overall, respectively. Median OS was 19.3 months for all patients and 22.4 months combination therapy recipients. The most frequent TG4010-related adverse events were minor-to-moderate injection-site reactions, fatigue, and flu-like symptoms. Six of 28 patients showed a MUC1 CD4+ T cell proliferative response during therapy. Anti-MUC1 CD8+ T cells were detected before and after therapy in 3 and 4 patients, respectively. MUC1-specific CD8+ T cell responses were associated with longer survival. Therapy with TG4010 plus cytokines appears to be feasible and well tolerated in patients with metastatic RCC. However, these data should be interpreted with caution, as additional prospective studies are necessary to clarify the clinical efficacy of this therapy.

Vaccination of metastatic renal cancer patients with MVA-5T4: a randomized, double-blind, placebo-controlled phase III study

PURPOSE

The TroVax Renal Immunotherapy Survival Trial was a randomized, placebo-controlled phase III study that investigated whether modified vaccinia Ankara encoding the tumor antigen 5T4 (MVA-5T4) prolonged survival of patients receiving first-line standard-of-care (SOC) treatment for metastatic renal cell cancer.

EXPERIMENTAL DESIGN

Patients with metastatic clear cell renal cancer, prior nephrectomy, and good or intermediate prognosis were randomized 1:1 to receive up to 13 immunizations of MVA-5T4/placebo in combination with either sunitinib, interleukin-2 or interferon-α. The primary end point was overall survival. Secondary end points included progression-free survival, overall response rate, and safety.

RESULTS

Seven hundred thirty-three patients were recruited (365 MVA-5T4 and 368 placebo). Treatment arms were well balanced for SOC and prognosis. No significant difference in the incidence of adverse events or serious adverse events was observed. No significant difference in overall survival was evident in the two treatment arms (median 20.1 months MVA-5T4 versus 19.2 months placebo; P = 0.55). The magnitude of the 5T4-specific antibody response induced by vaccination with MVA-5T4 was associated with enhanced patient survival. Furthermore, exploratory analyses suggested a number of pretreatment hematologic factors that could identify patients who derive significant benefit from this vaccine.

CONCLUSION

MVA-5T4 in combination with SOC was well tolerated, but no difference in survival was observed in the overall study population. Exploratory analyses indicate that there may be subsets of patients who could gain significant benefit from MVA-5T4, but such results would need to be confirmed in future randomized clinical studies.

New flow cytometric assays for monitoring cell-mediated cytotoxicity

The exact immunologic responses after vaccination that result in effective antitumor immunity have not yet been fully elucidated and the data from ex vivo T-cell assays have not yet defined adequate surrogate markers for clinical efficacy. A more detailed knowledge of the specific immune responses that correlate with positive clinical outcomes should help to develop better or novel strategies to effectively activate the immune system against tumors. Furthermore, clinically relevant material is often limited and, thus, precludes the ability to perform multiple assays. The two main assays currently used to monitor lymphocyte-mediated cytoxicity in cancer patients are the (51)Cr-release assay and IFN-gamma ELISpot assay. The former has a number of disadvantages, including low sensitivity, poor labeling and high spontaneous release of isotope from some tumor target cells. Additional problems with the (51)Cr-release assay include difficulty in obtaining autologous tumor targets, and biohazard and disposal problems for the isotope. The ELISpot assays do not directly measure cytotoxic activity and are, therefore, a surrogate marker of cyotoxic capacity of effector T cells. Furthermore, they do not assess cytotoxicity mediated by the production of the TNF family of death ligands by the cytotoxic cells. Therefore, assays that allow for the simultaneous measurement of several parameters may be more advantageous for clinical monitoring. In this respect, multifactor flow cytometry-based assays are a valid addition to the currently available immunologic monitoring assays. Use of these assays will enable detection and enumeration of tumor-specific cytotoxic T lymphocytes and their specific effector functions and any correlations with clinical responses. Comprehensive, multifactor analysis of effector cell responses after vaccination may help to detect factors that determine the success or failure of a vaccine and its immunological potency.

Update on vaccine development for renal cell cancer

Renal cell carcinoma (RCC) remains a significant health concern that frequently presents as metastatic disease at the time of initial diagnosis. Current first-line therapeutics for the advanced-stage RCC include antiangiogenic drugs that have yielded high rates of objective clinical response; however, these tend to be transient in nature, with many patients becoming refractory to chronic treatment with these agents. Adjuvant immunotherapies remain viable candidates to sustain disease-free and overall patient survival. In particular, vaccines designed to optimize the activation, maintenance, and recruitment of specific immunity within or into the tumor site continue to evolve. Based on the integration of increasingly refined immunomonitoring systems in both translational models and clinical trials, allowing for the improved understanding of treatment mechanism(s) of action, further refined (combinational) vaccine protocols are currently being developed and evaluated. This review provides a brief history of RCC vaccine development, discusses the successes and limitations in such approaches, and provides a rationale for developing combinational vaccine approaches that may provide improved clinical benefits to patients with RCC.

Tumor immunogenicity and responsiveness to cancer vaccine therapy: the state of the art

Despite enormous effort, promising pre-clinical data in animal studies and over 900 clinical trials in the United States, no cancer vaccine has ever been approved for clinical use. Over the past decade a great deal of progress has been in both laboratory and clinical studies defining the interactions between developing tumors and the immune system. The results of these studies provide a rationale that may help explain the failure of recent therapeutic cancer vaccines in terms of vaccine principles, in selecting which tumors are the most appropriate to target and instruct the design and implementation of state-of-the-art cancer vaccines.

Viruses as vaccine vectors for infectious diseases and cancer

Recent developments in the use of viruses as vaccine vectors have been facilitated by a better understanding of viral biology. Advances occur as we gain greater insight into the interrelationship of viruses and the immune system. Viral-vector vaccines remain the best means to induce cellular immunity and are now showing promise for the induction of strong humoral responses. The potential benefits for global health that are offered by this field reflect the scope and utility of viruses as vaccine vectors for human and veterinary applications, with targets ranging from certain types of cancer to a vast array of infectious diseases.