Recombinant viral vectors: cancer vaccines

Engineered Cancer Nanovaccines: A New Frontier in Cancer Therapy

Vaccinations are essential for preventing and treating disease, especially cancer nanovaccines, which have gained considerable interest recently for their strong anti-tumor immune capabilities. Vaccines can prompt the immune system to generate antibodies and activate various immune cells, leading to a response against tumor tissues and reducing the negative effects and recurrence risks of traditional chemotherapy and surgery. To enhance the flexibility and targeting of vaccines, nanovaccines utilize nanotechnology to encapsulate or carry antigens at the nanoscale level, enabling more controlled and precise drug delivery to enhance immune responses. Cancer nanovaccines function by encapsulating tumor-specific antigens or tumor-associated antigens within nanomaterials. The small size of these nanomaterials allows for precise targeting of T cells, dendritic cells, or cancer cells, thereby eliciting a more potent anti-tumor response. In this paper, we focus on the classification of carriers for cancer nanovaccines, the roles of different target cells, and clinically tested cancer nanovaccines, discussing strategies for effectively inducing cytotoxic T lymphocytes responses and optimizing antigen presentation, while also looking ahead to the translational challenges of moving from animal experiments to clinical trials.

Revolutionizing Cancer Treatment: Unleashing the Power of Viral Vaccines, Monoclonal Antibodies, and Proteolysis-Targeting Chimeras in the New Era of Immunotherapy

In the realm of cancer immunotherapy, a profound evolution has ushered in sophisticated strategies that encompass both traditional cancer vaccines and emerging viral vaccines. This comprehensive Review offers an in-depth exploration of the methodologies, clinical applications, success stories, and future prospects of these approaches. Traditional cancer vaccines have undergone significant advancements utilizing diverse modalities such as proteins, peptides, and dendritic cells. More recent innovations have focused on the physiological mechanisms enabling the human body to recognize and combat precancerous and malignant cells, introducing specific markers like peptide-based anticancer vaccines targeting tumor-associated antigens. Moreover, cancer viral vaccines, leveraging engineered viruses to stimulate immune responses against specific antigens, exhibit substantial promise in inducing robust and enduring immunity. Integration with complementary therapeutic methods, including monoclonal antibodies, adjuvants, and radiation therapy, has not only improved survival rates but also deepened our understanding of viral virulence. Recent strides in vaccine design, encompassing oncolytic viruses, virus-like particles, and viral vectors, mark the frontier of innovation. While these advances hold immense potential, critical challenges must be addressed, such as strategies for immune evasion, potential off-target effects, and the optimization of viral genomes. In the landscape of immunotherapy, noteworthy innovations take the spotlight from the use of immunomodulatory agents for the enhancement of innate and adaptive immune collaboration. The emergence of proteolysis-targeting chimeras (PROTACs) as precision tools for cancer therapy is particularly exciting. With a focus on various cancers, from melanoma to formidable solid tumors, this Review critically assesses types of cancer vaccines, mechanisms, barriers in vaccine therapy, vaccine efficacy, safety profiles, and immune-related adverse events, providing a nuanced perspective on the underlying mechanisms involving cytotoxic T cells, natural killer cells, and dendritic cells. The Review also underscores the transformative potential of cutting-edge technologies such as clinical studies, molecular sequencing, and artificial intelligence in advancing the field of cancer vaccines. These tools not only expedite progress but also emphasize the multidimensional and rapidly evolving nature of this research, affirming its profound significance in the broader context of cancer therapy.

Cowpea Mosaic Virus Outperforms Other Members of the Secoviridae as In Situ Vaccine for Cancer Immunotherapy

In situ vaccination for cancer immunotherapy uses intratumoral administration of small molecules, proteins, nanoparticles, or viruses that activate pathogen recognition receptors (PRRs) to reprogram the tumor microenvironment and prime systemic antitumor immunity. Cowpea mosaic virus (CPMV) is a plant virus that─while noninfectious toward mammals─activates mammalian PRRs. Application of CPMV as in situ vaccine (ISV) results in a potent and durable efficacy in tumor mouse models and canine patients; data indicate that CPMV outperforms small molecule PRR agonists and other nonrelated plant viruses and virus-like particles (VLPs). In this work, we set out to compare the potency of CPMV versus other plant viruses from the Secoviridae. We developed protocols to produce and isolate cowpea severe mosaic virus (CPSMV) and tobacco ring spot virus (TRSV) from plants. CPSMV, like CPMV, is a comovirus with genome and protein homology, while TRSV lacks homology and is from the genus nepovirus. When applied as ISV in a mouse model of dermal melanoma (using B16F10 cells and C57Bl6J mice), CPMV outperformed CPSMV and TRSV─again highlighting the unique potency of CPMV. Mechanistically, the increased potency is related to increased signaling through toll-like receptors (TLRs)─in particular, CPMV signals through TLR2, 4, and 7. Using knockout (KO) mouse models, we demonstrate here that all three plant viruses signal through the adaptor molecule MyD88─with CPSMV and TRSV predominantly activating TLR2 and 4. CPMV induced significantly more interferon β (IFNβ) compared to TRSV and CPSMV; therefore, IFNβ released upon signaling through TLR7 may be a differentiator for the observed potency of CPMV-ISV. Additionally, CPMV induced a different temporal pattern of intratumoral cytokine generation characterized by significantly increased inflammatory cytokines 4 days after the second of 2 weekly treatments, as if CPMV induced a "memory response". This higher, longer-lasting induction of cytokines may be another key differentiator that explains the unique potency of CPMV-ISV.

The Evolution and Future of Targeted Cancer Therapy: From Nanoparticles, Oncolytic Viruses, and Oncolytic Bacteria to the Treatment of Solid Tumors

While many classes of chemotherapeutic agents exist to treat solid tumors, few can generate a lasting response without substantial off-target toxicity despite significant scientific advancements and investments. In this review, the paths of development for nanoparticles, oncolytic viruses, and oncolytic bacteria over the last 20 years of research towards clinical translation and acceptance as novel cancer therapeutics are compared. Novel nanoparticle, oncolytic virus, and oncolytic bacteria therapies all start with a common goal of accomplishing therapeutic drug activity or delivery to a specific site while avoiding off-target effects, with overlapping methodology between all three modalities. Indeed, the degree of overlap is substantial enough that breakthroughs in one therapeutic could have considerable implications on the progression of the other two. Each oncotherapeutic modality has accomplished clinical translation, successfully overcoming the potential pitfalls promising therapeutics face. However, once studies enter clinical trials, the data all but disappears, leaving pre-clinical researchers largely in the dark. Overall, the creativity, flexibility, and innovation of these modalities for solid tumor treatments are greatly encouraging, and usher in a new age of pharmaceutical development.

Optimization of microbubble-based DNA vaccination with low-frequency ultrasound for enhanced cancer immunotherapy

Immunotherapy is an important cancer treatment strategy; nevertheless, the lack of robust immune cell infiltration in the tumor microenvironment remains a factor in limiting patient response rates. In vivo gene delivery protocols can amplify immune responses and sensitize tumors to immunotherapies, yet non-viral transfection methods often sacrifice transduction efficiency for improved safety tolerance. To improve transduction efficiency, we optimized a strategy employing low ultrasound transmission frequency-induced bubble oscillation to introduce plasmids into tumor cells. Differential centrifugation isolated size-specific microbubbles. The diameter of the small microbubble population was 1.27 ± 0.89 μm and that of larger population was 4.23 ± 2.27 μm. Upon in vitro insonation with the larger microbubble population, 29.7% of cancer cells were transfected with DNA plasmids, higher than that with smaller microbubbles (18.9%, P <0.05) or positive control treatments with a commercial transfection reagent (12%, P < 0.01). After 48 h, gene expression increased more than two-fold in tumors treated with large, as compared with small, microbubbles. Furthermore, the immune response, including tumor infiltration of CD8⁺ T cells and F4/80⁺ macrophages, was enhanced. We believe that this safe and efficacious method can improve preclinical procedures and outcomes for DNA vaccines in cancer immunotherapy in the future.

An Overview of Nanocarrier-Based Adjuvants for Vaccine Delivery

The development of vaccines is one of the most significant medical accomplishments which has helped to eradicate a large number of diseases. It has undergone an evolutionary process from live attenuated pathogen vaccine to killed whole organisms or inactivated toxins (toxoids), each of them having its own advantages and disadvantages. The crucial parameters in vaccination are the generation of memory response and protection against infection, while an important aspect is the effective delivery of antigen in an intelligent manner to evoke a robust immune response. In this regard, nanotechnology is greatly contributing to developing efficient vaccine adjuvants and delivery systems. These can protect the encapsulated antigen from the host’s in-vivo environment and releasing it in a sustained manner to induce a long-lasting immunostimulatory effect. In view of this, the present review article summarizes nanoscale-based adjuvants and delivery vehicles such as viral vectors, virus-like particles and virosomes; non-viral vectors namely nanoemulsions, lipid nanocarriers, biodegradable and non-degradable nanoparticles, calcium phosphate nanoparticles, colloidally stable nanoparticles, proteosomes; and pattern recognition receptors covering c-type lectin receptors and toll-like receptors.

Combined vaccination and immunostimulatory antibodies provides durable cure of murine melanoma and induces transcriptional changes associated with positive outcome in human melanoma patients

We have developed a recombinant adenovirus vaccine encoding dopachrome tautomerase (rHuAd5-hDCT) that produces robust DCT-specific immunity, but only provides modest suppression of murine melanoma. In the current study, an agonist antibody against 4-1BB was shown to enhance rHuAd5-hDCT efficacy and evoke tumor regression, but most tumors ultimately relapsed. The vaccine triggered upregulation of the immune inhibitory PD-1 signaling pathway and PD-1 blockade dramatically enhanced the rHuAd5-hDCT + anti-4-1BB strategy, resulting in complete regression of growing tumors in > 70% of recipients. The impact of the combined anti-4-1BB/anti-PD-1 treatment did not manifest as a dramatic enhancement in either the magnitude or functionality of DCT-specific tumor infiltrating lymphocytes relative to either treatment alone. Rather, a synergistic enhancement in intratumoral cytokine expression was observed, suggesting that the benefit of the combined therapy was a local event within the tumor. Global transcriptional analysis revealed immunological changes within the tumor following the curative vaccination, which extended beyond the T cell compartment. We identified an immune signature of 85 genes associated with clearance of murine melanoma that correlated with improved survival outcome in two independent cohorts of human melanoma patients. Our data reinforce the concept that successful vaccination must overcome local hurdles in the tumor microenvironment that are not manifest within the periphery. Further, tumor rejection following vaccination involves more than simply T cells. Finally, the association of our immune signature with positive survival outcome in human melanoma patients suggests that similar vaccination strategies may be promising for melanoma treatment.

A tumor targeting oncolytic adenovirus can improve therapeutic outcomes in chemotherapy resistant metastatic human breast carcinoma

Breast cancer is the most prevalent malignancy in women, which remains untreatable once metastatic. The treatment of advanced breast cancer is restricted due to chemotherapy resistance. We previously investigated anti-cancer potential of a tumor selective oncolytic adenovirus along with cisplatin in three lung cancer cells; A549, H292, and H661, and found it very efficient. To our surprise, this virotherapy showed remarkable cytotoxicity to chemo-resistant cancer cells. Here, we extended our investigation by using two breast cancer cells and their resistant sublines to further validate CRAd’s anti-resistance properties. Results of in vitro and in vivo analyses recapitulated the similar anti-tumor potential of CRAd. Based on the molecular analysis through qPCR and western blotting, we suggest upregulation of coxsackievirus-adenovirus receptor (CAR) as a selective vulnerability of chemotherapy-resistant tumors. CAR knockdown and overexpression experiments established its important involvement in the success of CRAd-induced tumor inhibition. Additionally, through transwell migration assay we demonstrate that CRAd might have anti-metastatic properties. Mechanistic analysis show that CRAd pre-treatment could reverse epithelial to mesenchymal transition in breast cancer cells, which needs further verification. These insights may prove to be a timely opportunity for the application of CRAd in recurrent drug-resistant cancers.

Targeting Neoantigens for Personalised Immunotherapy

This review discusses the rapidly evolving field of immunotherapy research, focusing on the types of cancer antigens that can be recognised by the immune system and potential methods by which neoantigens can be exploited clinically to successfully target and clear tumour cells. Recent studies suggest that the likelihood of successful immunotherapeutic targeting of cancer will be reliant on immune response to neoantigens. This type of cancer-specific antigen arises from somatic variants that result in alteration of the expressed protein sequence. Massively parallel sequencing techniques now allow the rapid identification of these genomic mutations, and algorithms can be used to predict those that will be processed by the proteasome, bind to the transporter complex and encode peptides that bind strongly to individual MHC molecules. The emerging data from assessment of the immunogenicity of neoantigens suggests that only a minority of mutations will form targetable epitopes and therefore the potential for immunotherapeutic targeting will be greater in cancers with a higher frequency of protein-altering somatic variants. It is evident that neoantigens contribute to the success of some immunotherapeutic interventions and that there is significant scope for specific targeting of these antigens to develop new treatment approaches.

Vaccinia-based vaccines to biothreat and emerging viruses

The past few years have seen a rash of emerging viral diseases, including the Ebola crisis in West Africa, the pandemic spread of chikungunya, and the recent explosion of Zika in South America. Vaccination is the most reliable and cost-effective method of control of infectious diseases, however, there is often a long delay in production and approval in getting new vaccines to market. Vaccinia was the first vaccine developed for the successful eradication of smallpox and has properties that make it attractive as a universal vaccine vector. Vaccinia can cause severe complications, particularly in immune suppressed recipients that would limit its utility, but nonreplicating and attenuated strains have been developed. Modified vaccinia Ankara is nonreplicating in human cells and can be safely given to immune suppressed individuals. Vaccinia has recently been modified for use as an oncolytic treatment for cancer therapy. These new vaccinia vectors are replicating; but have been attenuated and could prove useful as a universal vaccine carrier as many of these are in clinical trials for cancer therapy. This article reviews the development of a universal vaccinia vaccine platform for emerging diseases or biothreat agents, based on nonreplicating or live attenuated vaccinia viruses.

Synergistic Anti-tumour Effects of Quercetin and Oncolytic Adenovirus expressing TRAIL in Human Hepatocellular Carcinoma

The combination of oncolytic adenoviruses and specific chemotherapy agents is fast emerging as a novel therapeutic approach for resistan the patocellular carcinoma (HCC) cells. A detailed analysis of the network between adenovirus and chemotherapeutic agents can help design an effective strategy to combat HCC. We sought to investigate whether a combined treatment of ZD55-TRAIL and quercetin can have an enhanced cell-killing effect on HCC cells. In-vitro experiments showed that quercetin can enhance ZD55-TRAIL mediated growth inhibition and apoptosis in HCC cells. In addition, we showed that quercetin reduced ZD55-TRAIL mediated NF-κB activation and down-regulated its downstream targets, which in turn promoted the pro-apoptotic action of ZD55-TRAIL. Furthermore, in-vivo experiments in mice injected with HuH-7 cells resulted in significantly greater reduction in tumour growth and volume following combined ZD55-TRAIL and quercetin treatment. In conclusion, we demonstrated that quercetin could sensitize human HCC cells to apoptosis via ZD55-TRAIL in-vitro and in-vivo and presented ZD55-TRAIL and quercetin combination as a suitable anti-HCC therapy.

Current Immunotherapeutic Strategies to Enhance Oncolytic Virotherapy

Oncolytic viruses (OV) represent a promising strategy to augment the spectrum of cancer therapeutics. For efficacy, they rely on two general mechanisms: tumor-specific infection/cell-killing, followed by subsequent activation of the host’s adaptive immune response. Numerous OV genera have been utilized in clinical trials, ultimately culminating in the 2015 Food and Drug Administration approval of a genetically engineered herpes virus, Talminogene laherparepvec (T-VEC). It is generally accepted that OV as monotherapy have only modest clinical efficacy. However, due to their ability to elicit specific antitumor immune responses, they are prime candidates to be paired with other immune-modulating strategies in order to optimize therapeutic efficacy. Synergistic strategies to enhance the efficacy of OV include augmenting the host antitumor response through the insertion of therapeutic transgenes such as GM-CSF, utilization of the prime-boost strategy, and combining OV with immune-modulatory drugs such as cyclophosphamide, sunitinib, and immune checkpoint inhibitors. This review provides an overview of these immune-based strategies to improve the clinical efficacy of oncolytic virotherapy.

Capitalizing on Cancer Specific Replication: Oncolytic Viruses as a Versatile Platform for the Enhancement of Cancer Immunotherapy Strategies

The past decade has seen considerable excitement in the use of biological therapies in treating neoplastic disease. In particular, cancer immunotherapy and oncolytic virotherapy have emerged as two frontrunners in this regard with the first FDA approvals for agents in both categories being obtained in the last 5 years. It is becoming increasingly apparent that these two approaches are not mutually exclusive and that much of the therapeutic benefit obtained from the use of oncolytic viruses (OVs) is in fact the result of their immunotherapeutic function. Indeed, OVs have been shown to recruit and activate an antitumor immune response and much of the current work in this field centers around increasing this activity through strategies such as engineering genes for immunomodulators into OV backbones. Because of their broad immunostimulatory functions, OVs can also be rationally combined with a variety of other immunotherapeutic approaches including cancer vaccination strategies, adoptive cell transfer and checkpoint blockade. Therefore, while they are important therapeutics in their own right, the true power of OVs may lie in their ability to enhance the effectiveness of a wide range of immunotherapies.

Evolving lessons on nanomaterial-coated viral vectors for local and systemic gene therapy

Viral vectors are promising gene carriers for cancer therapy. However, virus-mediated gene therapies have demonstrated insufficient therapeutic efficacy in clinical trials due to rapid dissemination to nontarget tissues and to the immunogenicity of viral vectors, resulting in poor retention at the disease locus and induction of adverse inflammatory responses in patients. Further, the limited tropism of viral vectors prevents efficient gene delivery to target tissues. In this regard, modification of the viral surface with nanomaterials is a promising strategy to augment vector accumulation at the target tissue, circumvent the host immune response, and avoid nonspecific interactions with the reticuloendothelial system or serum complement. In the present review, we discuss various chemical modification strategies to enhance the therapeutic efficacy of viral vectors delivered either locally or systemically. We conclude by highlighting the salient features of various nanomaterial-coated viral vectors and their prospects and directions for future research.

Viro-immune therapy: A new strategy for treatment of pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is an almost uniformly lethal disease with less than 5% survival at five years. This is largely due to metastatic disease, which is already present in the majority of patients when diagnosed. Even when the primary cancer can be removed by radical surgery, local recurrence occurs within one year in 50%-80% of cases. Therefore, it is imperative to develop new approaches for the treatment of advanced cancer and the prevention of recurrence after surgery. Tumour-targeted oncolytic viruses (TOVs) have become an attractive therapeutic agent as TOVs can kill cancer cells through multiple mechanisms of action, especially via virus-induced engagement of the immune response specifically against tumour cells. To attack tumour cells effectively, tumour-specific T cells need to overcome negative regulatory signals that suppress their activation or that induce tolerance programmes such as anergy or exhaustion in the tumour microenvironment. In this regard, the recent breakthrough in immunotherapy achieved with immune checkpoint blockade agents, such as anti-cytotoxic T-lymphocyte-associate protein 4, programmed death 1 (PD-1) or PD-L1 antibodies, has demonstrated the possibility of relieving immune suppression in PDAC. Therefore, the combination of oncolytic virotherapy and immune checkpoint blockade agents may synergistically function to enhance the antitumour response, lending the opportunity to be the future for treatment of pancreatic cancer.

Polymeric oncolytic adenovirus for cancer gene therapy

Oncolytic adenovirus (Ad) vectors present a promising modality to treat cancer. Many clinical trials have been done with either naked oncolytic Ad or combination with chemotherapies. However, the systemic injection of oncolytic Ad in clinical applications is restricted due to significant liver toxicity and immunogenicity. To overcome these issues, Ad has been engineered physically or chemically with numerous polymers for shielding the Ad surface, accomplishing extended blood circulation time and reduced immunogenicity as well as hepatotoxicity. In this review, we describe and classify the characteristics of polymer modified oncolytic Ad following each strategy for cancer treatment. Furthermore, this review concludes with the highlights of various polymer-coated Ads and their prospects, and directions for future research.

Arming oncolytic viruses to leverage antitumor immunity

INTRODUCTION

Over the past decade, the cytolytic capabilities of oncolytic viruses (OVs), exploited to selectively eliminate neoplastic cells, have become secondary to their use to elicit a tumor-directed immune response.

AREAS COVERED

Here, based on an NCBI-PubMed literature survey, we review the efforts undertaken to arm OVs in order to improve therapeutic antitumor responses upon administration of these agents. Specifically, we explore the different options to modulate immune suppression in the tumor microenvironment (TME) and to facilitate the generation of effective antitumor responses that have been investigated in conjunction with OVs in recent years.

EXPERT OPINION

Their induction of immunogenic tumor cell death and association with pro-inflammatory signals make OVs attractive immunotherapeutic modalities. The first promising clinical results with immunologically armed OVs warrant their further optimization and development. OVs should be modified to avoid detrimental effects of pre-existent anti-OV immunity as well as for increased tumor targeting and selectivity, so as to ultimately allow for systemic administration while achieving local immune potentiation and tumor elimination in the TME. In particular, a combination of trans-genes encoding bispecific T-cell engagers, immune checkpoint blockers and antigen-presenting cell enhancers will remove suppressive hurdles in the TME and allow for optimal antitumor efficacy of armed OVs.

Dual tumor targeting with pH-sensitive and bioreducible polymer-complexed oncolytic adenovirus

Oncolytic adenoviruses (Ads) have shown great promise in cancer gene therapy but their efficacy has been compromised by potent immunological, biochemical, and specific tumor-targeting limitations. To take full advantage of the innate cancer-specific killing potency of oncolytic Ads but also exploit the subtleties of the tumor microenvironment, we have generated a pH-sensitive and bio-reducible polymer (PPCBA)-coated oncolytic Ad. Ad-PPCBA complexes showed higher cellular uptake at pH 6.0 than pH 7.4 in both high and low coxsackie and adenovirus receptor-(CAR)-expressing cells, thereby demonstrating Ad-PPCBA's ability to target the low pH hypoxic tumor microenvironment and overcome CAR dependence for target cell uptake. Endocytic mechanism studies indicated that Ad-PPCBA internalization is mediated by macropinocytosis instead of the CAR-dependent endocytic pathway that internalizes naked Ad. VEGF-specific shRNA-expressing oncolytic Ad complexed with PPCBA (RdB/shVEGF-PPCBA) elicited much more potent suppression of U87 human brain cancer cell VEGF gene expression in vitro, and human breast cancer MCF7 cell/Matrigel plug vascularization in a mouse model, when cancer cells had been previously infected at pH 6.0 versus pH 7.4. Moreover, intratumorally and intravenously injected RdB/shVEGF-PPCBA nanocomplexes elicited significantly higher therapeutic efficacy than naked virus in U87-tumor mouse xenograft models, reducing IL-6, ALT, and AST serum levels. These data demonstrated PPCBA's biocompatibility and capability to shield the Ad surface to prevent innate immune response against Ad after both intratumoral and systemic administration. Taken together, these results demonstrate that smart, tumor-specific, oncolytic Ad-PPCBA complexes can be exploited to treat both primary and metastatic tumors.

Going viral with cancer immunotherapy

Recent clinical data have emphatically shown the capacity of our immune systems to eradicate even advanced cancers. Although oncolytic viruses (OVs) were originally designed to function as tumour-lysing therapeutics, they have now been clinically shown to initiate systemic antitumour immune responses. Cell signalling pathways that are activated and promote the growth of tumour cells also favour the growth and replication of viruses within the cancer. The ability to engineer OVs that express immune-stimulating 'cargo', the induction of immunogenic tumour cell death by OVs and the selective targeting of OVs to tumour beds suggests that they are the ideal reagents to enhance antitumour immune responses. Coupling of OV therapy with tumour antigen vaccination, immune checkpoint inhibitors and adoptive cell therapy seems to be ready to converge towards a new generation of multimodal therapeutics to improve outcomes for cancer patients.

Modified vaccinia virus ankara (MVA) as production platform for vaccines against influenza and other viral respiratory diseases

Respiratory viruses infections caused by influenza viruses, human parainfluenza virus (hPIV), respiratory syncytial virus (RSV) and coronaviruses are an eminent threat for public health. Currently, there are no licensed vaccines available for hPIV, RSV and coronaviruses, and the available seasonal influenza vaccines have considerable limitations. With regard to pandemic preparedness, it is important that procedures are in place to respond rapidly and produce tailor made vaccines against these respiratory viruses on short notice. Moreover, especially for influenza there is great need for the development of a universal vaccine that induces broad protective immunity against influenza viruses of various subtypes. Modified Vaccinia Virus Ankara (MVA) is a replication-deficient viral vector that holds great promise as a vaccine platform. MVA can encode one or more foreign antigens and thus functions as a multivalent vaccine. The vector can be used at biosafety level 1, has intrinsic adjuvant capacities and induces humoral and cellular immune responses. However, there are some practical and regulatory issues that need to be addressed in order to develop MVA-based vaccines on short notice at the verge of a pandemic. In this review, we discuss promising novel influenza virus vaccine targets and the use of MVA for vaccine development against various respiratory viruses.

Rapid expansion of CD8+ T cells in wild-type and type I interferon receptor-deficient mice correlates with protection after low-dose emergency immunization with modified vaccinia virus Ankara

Immunization with modified vaccinia virus Ankara (MVA) can rapidly protect mice against lethal ectromelia virus (ECTV) infection, serving as an experimental model for severe systemic infections. Importantly, this early protective capacity of MVA vaccination completely depends on virus-specific cytotoxic CD8(+) T cell responses. We used MVA vaccination in the mousepox challenge model using ECTV infection to investigate the previously unknown factors required to elicit rapid protective T cell immunity in normal C57BL/6 mice and in mice lacking the interferon alpha/beta receptor (IFNAR(-/-)). We found a minimal dose of 10(5) PFU of MVA vaccine fully sufficient to allow robust protection against lethal mousepox, as assessed by the absence of disease symptoms and failure to detect ECTV in organs from vaccinated animals. Moreover, MVA immunization at low dosage also protected IFNAR(-/-) mice, indicating efficient activation of cellular immunity even in the absence of type I interferon signaling. When monitoring for virus-specific CD8(+) T cell responses in mice vaccinated with the minimal protective dose of MVA, we found significantly enhanced levels of antigen-specific T cells in animals that were MVA vaccinated and ECTV challenged compared to mice that were only vaccinated. The initial priming of naive CD8(+) T cells by MVA immunization appears to be highly efficient and, even at low doses, mediates a rapid in vivo burst of pathogen-specific T cells upon challenge. Our findings define striking requirements for protective emergency immunization against severe systemic infections with orthopoxviruses.

IMPORTANCE

We demonstrate that single-shot low-dose immunizations with vaccinia virus MVA can rapidly induce T cell-mediated protective immunity against lethal orthopoxvirus infections. Our data provide new evidence for an efficient protective capacity of vaccination with replication-deficient MVA. These data are of important practical relevance for public health, as the effectiveness of a safety-tested, next-generation smallpox vaccine based on MVA is still debated. Furthermore, producing sufficient amounts of vaccine is expected to be a major challenge should an outbreak occur. Moreover, prevention of other infections may require rapidly protective immunization; hence, MVA could be an extremely useful vaccine for delivering heterologous T cell antigens, particularly for infectious diseases that fit a scenario of emergency vaccination.

Utilizing adenovirus vectors for gene delivery in cancer

INTRODUCTION

Adenovirus (Ad) is a promising candidate vector for cancer gene therapy because of its unique characteristics, which include efficient infection, high loading capacity and lack of insertional mutagenesis. However, systemic administration of Ad is hampered by the host's immune response, hepatocytoxicity, short half-life of the vector and low accumulation at the target site. For these reasons, clinical applications of Ad are currently restricted.

AREAS COVERED

In this review, we focus on recent developments in Ad nanocomplex systems that improve the transduction and targeting efficacy of Ad vectors in cancer gene therapy. We discuss the development of different Ad delivery systems, including surface modification of Ad, smart Ad/nanohybrid systems and hydrogels for sustained release of Ad.

EXPERT OPINION

The fusion of bioengineering and biopharmaceutical technologies can provide solutions to the obstacles encountered during systemic delivery of Ads. The in vivo transgene expression efficiency of Ad nanocomplex systems is typically high, and animal tumor models demonstrate that systemic administration of these Ad complexes can arrest tumor growth. However, further optimization of these smart Ad nanocomplex systems is needed to increase their effectiveness and safety for clinical application in cancer gene therapy.

Evolution of oncolytic viruses: novel strategies for cancer treatment

Many viruses have documented oncolytic activity, with the first evidence observed clinically over a decade ago. In recent years, there has been a resurgence of interest in the field of oncolytic viruses. Viruses may be innately oncotropic, lacking the ability to cause disease in people or they may require engineering to allow selective tumor targeting and attenuation of pathogenicity. Following infection of a neoplastic cell, several events may occur, including direct viral oncolysis, apoptosis, necrotic cell death and autophagic cellular demise. Of late, a large body of work has recognized the ability of oncolytic viruses (OVs) to activate the innate and adaptive immune system, as well as directly killing tumors. The production of viruses expressing transgenes encoding for cytokines, colony-stimulating factors, costimulatory molecules and tumor-associated antigens has been able to further incite immune responses against target tumors. Multiple OVs are now in the advanced stages of clinical trials, with several individual viruses having completed their respective trials with positive results. This review introduces the multiple mechanisms by which OVs are able to act as an antineoplastic therapy, either on their own or in combination with other more traditional treatment modalities. The full benefit and the place where OVs will be integrated into standard-of-care therapies will be determined with ongoing studies ranging from the laboratory to the patient. With various different viruses now in the clinic this therapeutic option is beginning to prove its worth, and the versatility of these agents means further innovative and novel applications will continue to be developed.

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.

Local administration of TLR ligands rescues the function of tumor-infiltrating CD8 T cells and enhances the antitumor effect of lentivector immunization

Cancer vaccines, to date, have shown limited effect to control the growth of established tumors due largely to effector failure of the antitumor immune responses. Tumor lesion is characterized as chronic indolent inflammation in which the effector function of tumor-infiltrating lymphocytes (TILs) is severely impaired. In this study, we investigated whether the effector function of CD8 TILs could be rescued by converting the chronic inflammation milieu to acute inflammation within tumors. We found that injection of TLR3/9 ligands (polyI:C/CpG) into a tumor during the effector phase of lentivector (lv) immunization effectively rescued the function of lv-activated CD8 TILs and decreased the percentage of T regulatory within the tumor, resulting in a marked improvement in the antitumor efficacy of lv immunization. Mechanistically, rescue of the effector function of CD8 TILs by TLR3/9 ligands is most likely dependent on production, within a tumor, of type-1 IFN that can mature and activate tumor-infiltrating dendritic cells. The effector function of CD8 TILs could not be rescued in mice lacking intact type I IFN signaling. These findings have important implications for tumor immunotherapy, suggesting that type I IFN-mediated activation of tumor-infiltrating dendritic cells within a tumor will most likely restore/enhance the effector function of CD8 TILs and thus improve the antitumor efficacy of current cancer vaccines.

Recombinant MVA vaccines: dispelling the myths

Diseases such as HIV/AIDS, tuberculosis, malaria and cancer are prime targets for prophylactic or therapeutic vaccination, but have proven partially or wholly resistant to traditional approaches to vaccine design. New vaccines based on recombinant viral vectors expressing a foreign antigen are under intense development for these and other indications. One of the most advanced and most promising vectors is the attenuated, non-replicating poxvirus MVA (modified vaccinia virus Ankara), a safer derivative of the uniquely successful smallpox vaccine. Despite the ability of recombinant MVA to induce potent humoral and cellular immune responses against transgenic antigen in humans, especially when used as the latter element of a heterologous prime-boost regimen, doubts are occasionally expressed about the ultimate feasibility of this approach. In this review, five common misconceptions over recombinant MVA are discussed, and evidence is cited to show that recombinant MVA is at least sufficiently genetically stable, manufacturable, safe, and immunogenic (even in the face of prior anti-vector immunity) to warrant reasonable hope over the feasibility of large-scale deployment, should useful levels of protection against target pathogens, or therapeutic benefit for cancer, be demonstrated in efficacy trials.

Photochemical targeting of antigens to the cytosol for stimulation of MHC class-I-restricted T-cell responses

Tumour chemotherapy with drugs is typically associated with severe systemic and local side effects for which reason immunotherapy represents a safer alternative. However, vaccination often fails to generate the required cytotoxic CD8 T-cell responses due to insufficient access of antigens to the cytosol and the MHC class I pathway of antigen presentation. One important issue of tumour research is therefore to develop strategies that allow cytosolic targeting or endosomal escape of tumour antigens. The objective of the current study was to test whether endocytosed antigen could be delivered to MHC class I by means of photochemical internalisation (PCI). Briefly, the antigen and the photosensitiser Amphinex were loaded in vitro onto bone-marrow-derived murine dendritic cells (DCs). After light activation, which is supposed to cause disruption of OVA- and Amphinex-containing endosomes, the DCs were cultured with OVA-specific CD8 T cells or used for immunisation of mice. PCI facilitated CD8 T-cell responses as measured by IFN-γ secretion in vitro and CD8 T-cell proliferation in vivo. In conclusion, the current proof-of-concept study is the first to describe PCI-mediated immunisation and the results revealed the feasibility of this novel technology in autologous vaccination for stimulation of CD8 T-cell responses.

CD40-targeted adenoviral cancer vaccines: the long and winding road to the clinic

The ability of dendritic cells (DCs) to orchestrate innate and adaptive immune responses has been exploited to develop potent anti-cancer immunotherapies. Recent clinical trials exploring the efficacy of ex vivo modified autologous DC-based vaccines have reported some promising results. However, in vitro generation of autologous DCs for clinical administration, their loading with tumor associated antigens (TAAs) and their activation, is laborious and expensive, and, as a result of inter-individual variability in the personalized vaccines, remains poorly standardized. An attractive alternative approach is to load resident DCs in vivo by targeted delivery of TAAs, using viral vectors and activating them simultaneously. To this end, we have constructed genetically-modified adenoviral (Ad) vectors and bispecific adaptor molecules to retarget Ad vectors encoding TAAs to the CD40 receptor on DCs. Pre-clinical human and murine studies conducted so far have clearly demonstrated the suitability of a 'two-component' (i.e. Ad and adaptor molecule) configuration for targeted modification of DCs in vivo for cancer immunotherapy. This review summarizes recent progress in the development of CD40-targeted Ad-based cancer vaccines and highlights pre-clinical issues in the clinical translation of this approach.

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.

Immunoglobulin Fc fragment tagging allows strong activation of endogenous CD4 T cells to reshape the tumor milieu and enhance the antitumor effect of lentivector immunization

A major problem with current cancer vaccines is that the induction of CD8 immune responses is rarely associated with antitumor benefits, mainly owing to multiple immune suppressions in established tumor lesions. In this study, we investigated if and how activation of endogenous CD4 T cells could be achieved to influence the suppressive tumor milieu and antitumor effect. We engineered a lentivector (lv) to express a nominal fusion Ag composed of hepatitis B surface protein and IgG2a Fc fragment (HBS-Fc-lv) to increase the magnitude of CD8 response but, more importantly, to induce effective coactivation of CD4 T cells. We found that, remarkably, immunization with HBS-Fc-lv caused significant regression of established tumors. Immunologic analysis revealed that, compared with HBS-lv without Fc fragment, immunization with HBS-Fc-lv markedly increased the number of functional CD8 and CD4 T cells and the level of Th1/Tc1-like cytokines in the tumor while substantially decreasing the regulatory T cell ratio. The favorable immunologic changes in tumor lesions and the improvement of antitumor effects from HBS-Fc-lv immunization were dependent on the CD4 activation, which was Fc receptor mediated. Adoptive transfer of CD4 T cells from the HBS-Fc-lv-immunized mice could activate endogenous CD8 T cells in an IFN-γ-dependent manner. We conclude that endogenous CD4 T cells can be activated by lv expressing Fc-tagged Ag to provide another layer of help--that is, creating a Th1/Tc1-like proinflammatory milieu within the tumor lesion to boost the effector phase of immune responses in enhancing the antitumor effect.

Clinical Efficacy of TroVax in the Treatment of Progressive Castration-resistant Prostate Cancer

With approximately 240,890 new cases expected in 2011, prostate cancer remains the leading cause of non-melanoma cancer deaths in men. Immunotherapies using viral vector-based delivery systems targeting tumor-specific antigens are being studied. Viral vector-based delivery systems present tumor-targeted antigens (TAAs) to the immune system while breaking self-tolerance. Modified vaccinia ankara has been combined with the oncofetal antigen 5T4 to create TroVax for the treatment of castration-resistant prostate cancer (CRPC). The 5T4 antigen is highly expressed in a large number of carcinomas, including prostate cancer, but is rarely expressed in healthy tissue. TroVax has been demonstrated to be safe and highly immunogenic, both as monotherapy and in combination with other standard of care therapies in colorectal, renal cell, and prostate cancer. With minimal side effects and the ability to produce a strong immunogenic response, TroVax (MVA-5T4) is a viable addition to the treatment of prostate cancer.

Chapter six--Adenovirus-based immunotherapy of cancer: promises to keep

Progress in vector design and an increased knowledge of mechanisms underlying tumor-induced immune suppression have led to a new and promising generation of Adenovirus (Ad)-based immunotherapies, which are discussed in this review. As vaccine vehicles Ad vectors (AdVs) have been clinically evaluated and proven safe, but a major limitation of the commonly used Ad5 serotype is neutralization by preexistent or rapidly induced immune responses. Genetic modifications in the Ad capsid can reduce intrinsic immunogenicity and facilitate escape from antibody-mediated neutralization. Further modification of the Ad hexon and fiber allows for liver and scavenger detargeting and selective targeting of, for example, dendritic cells. These next-generation Ad vaccines with enhanced efficacy are now becoming available for testing as tumor vaccines. In addition, AdVs encoding immune-modulating products may be used to convert the tumor microenvironment from immune-suppressive and proinvasive to proinflammatory, thus facilitating cell-mediated effector functions that can keep tumor growth and invasion in check. Oncolytic AdVs, that selectively replicate in tumor cells and induce an immunogenic form of cell death, can also be armed with immune-activating transgenes to amplify primed antitumor immune responses. These novel immunotherapy strategies, employing highly efficacious AdVs in optimized configurations, show great promise and warrant clinical exploration.

Lentivector prime and vaccinia virus vector boost generate high-quality CD8 memory T cells and prevent autochthonous mouse melanoma

Most cancer vaccines, to date, fail to control established tumors. However, their application in preventing tumors is another question that is understudied. In the current study, we investigated the CD8 memory T cell responses of lentivector (lv) immunization and its potential to prevent melanoma using both transplantable B16 tumor and autochthonous melanoma models. We found that lv-expressing xenogenic human gp100 could induce potent CD8 responses that cross-react with mouse gp100. Importantly, the lv-primed CD8 response consisted of a high number of memory precursors and could be further increased by recombinant vaccinia virus vector (vv) boost, resulting in enhanced CD8 memory response. These long-lasting CD8 memory T cells played a critical role in immune surveillance and could rapidly respond and expand after sensing B16 tumor cells to prevent tumor establishment. Although CD8 response plays a dominant role after lv immunization, both CD4 and CD8 T cells are responsible for the immune prevention. In addition, we surprisingly found that CD4 help was not only critical for generating primary CD8 responses, but also important for secondary CD8 responses of vv boost. CD4 depletion prior to lv prime or prior to vv boost substantially reduced the magnitude of secondary CD8 effector and memory responses, and severely compromised the effect of cancer immune prevention. More importantly, the CD8 memory response from lv-vv prime-boost immunization could effectively prevent autochthonous melanoma in tumor-prone transgenic mice, providing a strong evidence that lv-vv prime-boost strategy is an effective approach for cancer immune prevention.

Adjuvant effect of HER-2/neu-specific adenoviral vector stimulating CD8⁺ T and natural killer cell responses on anti-HER-2/neu antibody therapy for well-established breast tumors in HER-2/neu transgenic mice

Approximately one third of patients with advanced human epidermal growth factor receptor 2 (HER-2)/neu-positive breast cancer respond to trastuzumab monotherapy, a humanized anti-HER-2/neu antibody. However, de novo and acquired antibody resistance is one of the major limitations of trastuzumab therapy warranting the search for other therapeutic strategies. One of the most remarkable features of adenovirus (AdV)-based vaccine is its ability to induce exceptionally high and sustained frequencies of transgene product-specific CD8(+) T-cell responses. In this study, we constructed two recombinant AdVs (AdV(OVA) and AdV(HER-2)) expressing ovalbumin (OVA) and HER-2/neu, and assessed AdV-induced antigen-specific cellular immune responses and preventive/therapeutic antitumor immunity. We demonstrate that AdV(OVA) stimulates efficient OVA-specific CD8(+) cytotoxic T lymphocyte (CTL) and natural killer responses, leading to preventive long-term immunity against OVA-expressing BL6-10ova melanoma in wild-type C56BL/6 mice. We further demonstrate that AdV(HER-2) stimulates HER-2/neu-specific CD8(+) CTL responses, leading to a significant reduction in breast carcinogenesis in transgenic FVBneuN mice (P<0.05), but has little therapeutic effect on pre-existing Tg1-1 tumor even at early stage (15 mm(3)). In contrast, the anti-HER-2/neu antibody therapy is capable of completely inhibiting Tg1-1 tumor growth at early stage, but fails to eradicate well-established Tg1-1 breast tumor (100 mm(3)). Interestingly, a combinatorial immunotherapy of anti-HER-2/neu antibody with AdV(HER-2) vaccine was capable of curing 4 of 10 studied mice bearing well-established Tg1-1 breast tumors and significantly delaying in death of the remaining six tumor-bearing mice (P<0.05). Taken together, our results suggest an adjuvant effect of AdV(HER-2) on anti-HER-2/neu antibody therapy for well-established breast tumor in transgenic FVBneuN mice, and this combinatorial immunotherapy of trastuzumab with AdV(HER-2) vaccine may be used as a new therapeutic strategy for treatment of advanced HER-2/neu-positive breast cancer.

Immunological and clinical effects of vaccines targeting p53-overexpressing malignancies

Approximately 50% of human malignancies carry p53 mutations, which makes it a potential antigenic target for cancer immunotherapy. Adoptive transfer with p53-specific cytotoxic T-lymphocytes (CTL) and CD4⁺ T-helper cells eradicates p53-overexpressing tumors in mice. Furthermore, p53 antibodies and p53-specific CTLs can be detected in cancer patients, indicating that p53 is immunogenic. Based on these results, clinical trials were initiated. In this paper, we review immunological and clinical responses observed in cancer patients vaccinated with p53 targeting vaccines. In most trials, p53-specific vaccine-induced immunological responses were observed. Unfortunately, no clinical responses with significant reduction of tumor-burden have occurred. We will elaborate on possible explanations for this lack of clinical effectiveness. In the second part of this paper, we summarize several immunopotentiating combination strategies suitable for clinical use. In our opinion, future p53-vaccine studies should focus on addition of these immunopotentiating regimens to achieve clinically effective therapeutic vaccination strategies for cancer patients.

Intracellular delivery of a protein antigen with an endosomal-releasing polymer enhances CD8 T-cell production and prophylactic vaccine efficacy

Protein-based vaccines have significant potential as infectious disease and anticancer therapeutics, but clinical impact has been limited in some applications by their inability to generate a coordinated cellular immune response. Here, a pH-responsive carrier incorporating poly(propylacrylic acid) (PPAA) was evaluated to test whether improved cytosolic delivery of a protein antigen could enhance CD8+ cytotoxic lymphocyte generation and prophylactic tumor vaccine responses. PPAA was directly conjugated to the model ovalbumin antigen via reducible disulfide linkages and was also tested in a particulate formulation after condensation with cationic poly(dimethylaminoethyl methacrylate) (PDMAEMA). Intracellular trafficking studies revealed that both PPAA-containing formulations were stably internalized and evaded exocytotic pathways, leading to increased intracellular accumulation and potential access to the cytosolic MHC-1 antigen presentation pathway. In an EG.7-OVA mouse tumor protection model, both PPAA-containing carriers robustly inhibited tumor growth and led to an approximately 3.5-fold increase in the longevity of tumor-free survival relative to controls. Mechanistically, this response was attributed to the 8-fold increase in production of ovalbumin-specific CD8+ T-lymphocytes and an 11-fold increase in production of antiovalbumin IgG. Significantly, this is one of the first demonstrated examples of in vivo immunotherapeutic efficacy using soluble protein-polymer conjugates. These results suggest that carriers enhancing cytosolic delivery of protein antigens could lead to more robust CD8+ T-cell response and demonstrate the potential of pH-responsive PPAA-based carriers for therapeutic vaccine applications.

Blockade of programmed death-1 pathway rescues the effector function of tumor-infiltrating T cells and enhances the antitumor efficacy of lentivector immunization

Despite intensive effort, the antitumor efficacy of tumor vaccines remains limited in treating established tumors regardless of the potent systemic tumor-specific immune response and the increases of tumor infiltration of T effector cells. In the current study, we demonstrated that although lentivector (lv) immunization markedly increased Ag-dependent tumor infiltration of CD8 and CD4 T cells and generated Ag-specific antitumor effect, it simultaneously increased the absolute number of myeloid-derived suppressor cells and regulatory T cells in the tumor lesions. In addition, lv immunization induced expression of programmed death-ligand 1 in the tumor lesions. Furthermore, the tumor-infiltrating CD8 T cells expressed high levels of programmed death-1 and were partially dysfunctional, producing lower amounts of effector cytokines and possessing a reduced cytotoxicity. Together, these immune-suppression mechanisms in the tumor microenvironment pose a major obstacle to effective tumor immunotherapy and may explain the limited antitumor efficacy of lv immunization. The loss of effector function in the tumor microenvironment is reversible, and the effector function of CD8 T cells in the tumor could be partially rescued by blocking programmed death-1 and programmed death-ligand 1 pathway in vitro and in vivo, resulting in enhanced antitumor efficacy of lv immunization. These data suggest that immunization alone may exacerbate immune suppression in the tumor lesions and that methods to improve the tumor microenvironment and to rescue the effector functions of tumor-infiltrating T cells should be incorporated into immunization strategies to achieve enhanced antitumor efficacy.

A Phase 1 study to evaluate the safety and immunogenicity of a recombinant HIV type 1 subtype C-modified vaccinia Ankara virus vaccine candidate in Indian volunteers

A recombinant modified vaccinia Ankara virus vaccine candidate (TBC-M4) expressing HIV-1 subtype C env, gag, tat-rev, and nef-RT genes was tested in a randomized, double-blind, dose escalation Phase I trial in 32 HIV-uninfected healthy volunteers who received three intramuscular injections of TBC-M4 at 0, 1, and 6 months of 5 x 10(7) plaque-forming units (pfu) (low dosage, LD) (n = 12) or 2.5 x 10(8) pfu (high dosage, HD) (n = 12) or placebo (n = 8). Local and systemic reactogenicity was experienced by approximately 67% and 83% of vaccine recipients, respectively. The reactogenicity events were mostly mild in severity. Severe but transient systemic reactogenicity was seen in one volunteer of the HD group. No vaccine-related serious adverse events or events suggesting perimyocarditis were seen. A higher frequency of local reactogenicity events was observed in the HD group. Cumulative HIV-specific IFN-gamma ELISPOT responses were detected in frozen PBMCs from 9/11 (82%), 12/12 (100%), and 1/8 (13%) volunteers after the third injection of the LD, HD, and placebo groups, respectively. Most of the responses were to gag and env proteins (maximum of 430 SFU/10(6) PBMCs) persisting across multiple time points. HIV-specific ELISA antibody responses were detected in 10/11, 12/12, and 0/8 volunteers post-third vaccination, in the LD, HD, and placebo groups, respectively. No neutralizing activity against HIV-1 subtype C isolates was detected. TBC-M4 appears to be generally safe and well-tolerated. The immune response detected was dose dependent, modest in magnitude, and directed mostly to env and gag proteins, suggesting further evaluation of this vaccine in a prime-boost regimen.

An MVA-based vaccine targeting the oncofetal antigen 5T4 in patients undergoing surgical resection of colorectal cancer liver metastases

We investigated the use of a therapeutic vaccine, TroVax in patients undergoing surgical resection of colorectal cancer liver metastases. Systemic immunity generated by vaccination before and after resection of metastases was measured in addition to assessing safety and analyzing the function and phenotype of tumor-associated lymphocytes. Twenty patients were scheduled to receive 2 TroVax vaccinations at 2-week intervals preoperatively and 2 postoperatively; if immune responses were detected, 2 further vaccinations were offered. Blood was taken at trial entry and 2 weeks after each vaccination; tumor biopsies were collected at surgery. 5T4-specific cellular responses were assessed by lymphocyte proliferation and enzyme-linked immunosorbent spot, with antibody responses by enzyme-linked immunosorbent assay. Immunohistochemistry characterized the phenotype of tumor-infiltrating lymphocytes. Seventeen of 19 colorectal cancer patients showed 5T4 expression in the liver metastases or surrounding stroma and 18 mounted a 5T4-specific cellular and/or humoral response. In patients who received at least 4 vaccinations and potentially curative surgery (n=15), those with above median 5T4-specific proliferative responses or T-cell infiltration into the resected tumor showed significantly longer survival compared with those with below median responses. Seven of 8 patients who had preexisting proliferative responses to 5T4 were longer-term survivors; these patients showed significantly higher proliferative responses after vaccination than those who subsequently died. These data suggest that the magnitude of 5T4 proliferative responses and the density of CD3 cells in colorectal cancer liver metastases are associated with longer survival. These observations warrant more studies to identify the precise underlying mechanisms.

Lentivector immunization stimulates potent CD8 T cell responses against melanoma self-antigen tyrosinase-related protein 1 and generates antitumor immunity in mice

Recombinant lentivector immunization has been demonstrated to induce potent CD8 T cell responses in vivo. In this study, we investigated whether lentivector delivering a self/tumor Ag, tyrosinase related protein 1 (TRP1), could stimulate effective antitumor T cell responses. We found that immunization with lentivector expressing mutated TRP1 Ag elicited potent CD8 T cell responses against multiple TRP1 epitopes. Importantly, the activated CD8 T cells effectively recognize wild-type TRP1 epitopes. At peak times, as many as 10% of CD8 T cells were effector cells against TRP1 Ag. These cells killed wild-type TRP1 peptide-pulsed target cells in vivo and produced IFN-gamma after ex vivo stimulation. The CD8 T cell responses were long-lasting (3-4 wk). Immunized mice were protected from B16 tumor cell challenge. In a therapeutic setting, lentivector immunization induced potent CD8 T cell responses in tumor bearing mice. The number of infiltrating T cells and the ratio of CD8/CD4 were dramatically increased in the tumors of immunized mice. The tumor-infiltrating CD8 T cells were functional and produced IFN-gamma. The potent CD8 T cell responses stimulated by lentivector immunization eliminated small 3-day s.c. B16 tumors and strongly inhibited the growth of more established 5-day tumors. These studies demonstrate that genetic immunization with lentivector expressing mutated self/tumor Ag can generate potent CD8 T cell immune responses and antitumor immunity that prevent and inhibit B16 tumor growth, suggesting that lentivector immunization has the potential for tumor immunotherapy and immune prevention.

Vaccination of renal cell cancer patients with modified vaccinia ankara delivering tumor antigen 5T4 (TroVax) administered with interleukin 2: a phase II trial

PURPOSE

The attenuated vaccinia virus modified vaccinia ankara (MVA) has been engineered to deliver the tumor antigen 5T4 (TroVax). TroVax has been evaluated in an open-label phase II trial in metastatic renal cell cancer patients in which the vaccine was administered in combination with interleukin-2 (IL-2). The safety, immunologic, and clinical efficacy of TroVax in combination with IL-2 was determined.

EXPERIMENTAL DESIGN

Twenty-five patients with metastatic renal cell cancer were treated with TroVax plus IL-2. 5T4-specific cellular and humoral responses were monitored throughout the study. Clinical responses were assessed by measuring changes in tumor burden by computed tomography or magnetic resonance imaging scan.

RESULTS

TroVax was well tolerated with no serious adverse event attributed to vaccination. Of 25 intention-to-treat patients, 21 mounted 5T4-specific antibody responses. Two patients showed a complete response for > 24 months and one a partial response for > 12 months. Six patients had disease stabilization from 6 to > 21 months. Median progression-free survival (PFS) and overall survival (OS) were > 3.37 months (range, 1.50- > 24.76) and > 12.87 months (range, 1.90- > 24.76), respectively. A statistically significant relationship was detected between the magnitude of 5T4-specific antibody responses and PFS and OS.

CONCLUSION

TroVax in combination with IL-2 was safe and well tolerated in all patients. The high frequency of 5T4-specific immune responses and good clinical response rate are encouraging and warrant further investigation.