Multiple costimulatory modalities enhance CTL avidity

PRR adjuvants restrain high stability peptides presentation on APCs

Adjuvants can affect APCs function and boost adaptive immune responses post-vaccination. However, whether they modulate the specificity of immune responses, particularly immunodominant epitope responses, and the mechanisms of regulating antigen processing and presentation remain poorly defined. Here, using overlapping synthetic peptides, we screened the dominant epitopes of Th1 responses in mice post-vaccination with different adjuvants and found that the adjuvants altered the antigen-specific CD4+ T-cell immunodominant epitope hierarchy. MHC-II immunopeptidomes demonstrated that the peptide repertoires presented by APCs were significantly altered by the adjuvants. Unexpectedly, no novel peptide presentation was detected after adjuvant treatment, whereas peptides with high binding stability for MHC-II presented in the control group were missing after adjuvant stimulation, particularly in the MPLA- and CpG-stimulated groups. The low-stability peptide present in the adjuvant groups effectively elicited robust T-cell responses and formed immune memory. Collectively, our results suggest that adjuvants (MPLA and CpG) inhibit high-stability peptide presentation instead of revealing cryptic epitopes, which may alter the specificity of CD4+ T-cell-dominant epitope responses. The capacity of adjuvants to modify peptide-MHC (pMHC) stability and antigen-specific T-cell immunodominant epitope responses has fundamental implications for the selection of suitable adjuvants in the vaccine design process and epitope vaccine development.

Immunotherapy Vaccines for Prostate Cancer Treatment

BACKGROUND

Therapeutic tumor vaccines have emerged as a compelling avenue for treating patients afflicted with advanced prostate cancer (PCa), particularly those experiencing biochemical relapse or ineligible for surgical intervention. This study serves to consolidate recent research findings on therapeutic vaccines targeting prostate tumors while delineating prevalent challenges within vaccine research and development.

METHODS

We searched electronic databases, including PubMed, Web of Science, Embase, and Scopus, up to August 31, 2024, using keywords such as 'vaccine', 'prostate cancer', 'immunotherapy', and others. We reviewed studies on various therapeutic vaccines, including dendritic cell-based, antigen, nucleic acid, and tumor cell vaccines.

RESULTS

Studies consistently showed that therapeutic vaccines, notably DC vaccines, had favorable safety profiles with few adverse effects. These vaccines, with varied antigenic formulations, demonstrated strong clinical outcomes, as indicated by metrics such as PSA response rates (9.5%-58%), extended PSA doubling times (52.9%-89.7%), overall survival durations (17.7-33.8 months), two-year mortality rates (0%-12.5%), biochemical relapse rates (42%-73%), and antigen-specific immune responses (33.3%-71.4% in responsive groups).

CONCLUSION

While clinical data for tumor vaccines have illuminated robust evidence of tumoricidal activity, the processes of their formulation and deployment are riddled with complexities. Combining vaccines with other therapies may enhance outcomes, and future research should focus on early interventions and deciphering the immune system's role in oncogenesis.

Adaptive and Innate Cytotoxic Effectors in Chronic Lymphocytic Leukaemia (CLL) Subjects with Stable Disease

Chronic lymphocytic leukaemia (CLL) is characterised by the expansion of a neoplastic mature B cell clone. CLL clinical outcome is very heterogeneous, with some subjects never requiring therapy and some showing an aggressive disease. Genetic and epigenetic alterations and pro-inflammatory microenvironment influence CLL progression and prognosis. The involvement of immune-mediated mechanisms in CLL control needs to be investigated. We analyse the activation profile of innate and adaptive cytotoxic immune effectors in a cohort of 26 CLL patients with stable disease, as key elements for immune-mediated control of cancer progression. We observed an increase in CD54 expression and interferon (IFN)-γ production by cytotoxic T cells (CTL). CTL ability to recognise tumour-targets depends on human leukocyte antigens (HLA)-class I expression. We observed a decreased expression of HLA-A and HLA-BC on B cells of CLL subjects, associated with a significant reduction in intracellular calnexin that is relevant for HLA surface expression. Natural killer (NK) cells and CTL from CLL subjects show an increased expression of the activating receptor KIR2DS2 and a reduction of 3DL1 and NKG2A inhibiting molecules. Therefore, an activation profile characterises CTL and NK cells of CLL subjects with stable disease. This profile is conceivable with the functional involvement of cytotoxic effectors in CLL control.

Phase I/II study of multipeptide cancer vaccine IMA901 after single-dose cyclophosphamide in Japanese patients with advanced renal cell cancer with long-term follow up

BACKGROUND

IMA901 is the first therapeutic vaccine for renal cell cancer (RCC). It contains multiple tumor-associated peptides (TUMAPs) that are naturally present in human cancers.

METHODS

In a phase I/II study, we treated a total of 10 Japanese patients with advanced RCC who were human leukocyte antigen A (HLA-A)*02 +. Vaccination involved i.d. injection of GM-CSF (75 μg), followed within 15-30 min by i.d. injection of IMA901 (containing 413 μg of each peptide). No treatment with either anticancer agents or immunosuppressants was allowed within 4 weeks before entering the trial. Patients were scheduled to receive 7 vaccinations during the first 5 weeks of treatment (induction period), followed by 10 further vaccinations at 3-week intervals for up to 30 weeks (maintenance period). The primary endpoints were safety and tolerability, while the secondary endpoints were PFS, OS, and immunogenicity.

RESULTS

There were no treatment-related serious adverse events or deaths during the study period. When the response was assessed after 4 months, 10% of patients showed a partial response, 80% had stable disease, and 10% had progressive disease. Among patients in whom the T-cell response was analyzed, five patients showed a vaccine-induced T-cell response against at least one HLA class I-restricted TUMAP and two patients had T-cell responses to multiple TUMAPs. PFS was 5.5 months and OS was 18 months.

CONCLUSIONS

This study demonstrated the safety and tolerability of IMA901 vaccine in Japanese RCC patients, and also showed that vaccination elicited an immune response.

Constant regulation for stable CD8 T-cell functional avidity and its possible implications for cancer immunotherapy

The functional avidity (FA) of cytotoxic CD8 T cells impacts strongly on their functional capabilities and correlates with protection from infection and cancer. FA depends on TCR affinity, downstream signaling strength, and TCR affinity-independent parameters of the immune synapse, such as costimulatory and inhibitory receptors. The functional impact of coreceptors on FA remains to be fully elucidated. Despite its importance, FA is infrequently assessed and incompletely understood. There is currently no consensus as to whether FA can be enhanced by optimized vaccine dose or boosting schedule. Recent findings suggest that FA is remarkably stable in vivo, possibly due to continued signaling modulation of critical receptors in the immune synapse. In this review, we provide an overview of the current knowledge and hypothesize that in vivo, codominant T cells constantly "equalize" their FA for similar function. We present a new model of constant FA regulation, and discuss practical implications for T-cell-based cancer immunotherapy.

Biomechanics of T Cell Dysfunctions in Chronic Diseases

Understanding the mechanisms behind T cell dysfunctions during chronic diseases is critical in developing effective immunotherapies. As demonstrated by several animal models and human studies, T cell dysfunctions are induced during chronic diseases, spanning from infections to cancer. Although factors governing the onset and the extent of the functional impairment of T cells can differ during infections and cancer, most dysfunctional phenotypes share common phenotypic traits in their immune receptor and biophysical landscape. Through the latest developments in biophysical techniques applied to explore cell membrane and receptor-ligand dynamics, we are able to dissect and gain further insights into the driving mechanisms behind T cell dysfunctions. These insights may prove useful in developing immunotherapies aimed at reinvigorating our immune system to fight off infections and malignancies more effectively. The recent success with checkpoint inhibitors in treating cancer opens new avenues to develop more effective, targeted immunotherapies. Here, we highlight the studies focused on the transformation of the biophysical landscape during infections and cancer, and how T cell biomechanics shaped the immunopathology associated with chronic diseases.

Virotherapy, gene transfer and immunostimulatory monoclonal antibodies

Malignant cells are susceptible to viral infection and consequent cell death. Virus-induced cell death is endowed with features that are known to stimulate innate and adaptive immune responses. Thus danger signals emitted by cells succumbing to viral infection as well as viral nucleic acids are detected by specific receptors, and tumor cell antigens can be routed to professional antigen-presenting cells. The anticancer immune response triggered by viral infection is frequently insufficient to eradicate malignancy but may be further amplified. For this purpose, transgenes encoding cytokines as co-stimulatory molecules can be genetically engineered into viral vectors. Alternatively, or in addition, it is possible to use monoclonal antibodies that either block inhibitory receptors of immune effector cells, or act as agonists for co-stimulatory receptors. Combined strategies are based on the ignition of a local immune response at the malignant site plus systemic immune boosting. We have recently reported examples of this approach involving the Vaccinia virus or Semliki Forest virus, interleukin-12 and anti-CD137 monoclonal antibodies.

Cancer Vaccines: Toward the Next Breakthrough in Cancer Immunotherapy

Until now, three types of well-recognized cancer treatments have been developed, i.e., surgery, chemotherapy, and radiotherapy; these either remove or directly attack the cancer cells. These treatments can cure cancer at earlier stages but are frequently ineffective for treating cancer in the advanced or recurrent stages. Basic and clinical research on the tumor microenvironment, which consists of cancerous, stromal, and immune cells, demonstrates the critical role of antitumor immunity in cancer development and progression. Cancer immunotherapies have been proposed as the fourth cancer treatment. In particular, clinical application of immune checkpoint inhibitors, such as anti-CTLA-4 and anti-PD-1/PD-L1 antibodies, in various cancer types represents a major breakthrough in cancer therapy. Nevertheless, accumulating data regarding immune checkpoint inhibitors demonstrate that these are not always effective but are instead only effective in limited cancer populations. Indeed, several issues remain to be solved to improve their clinical efficacy; these include low cancer cell antigenicity and poor infiltration and/or accumulation of immune cells in the cancer microenvironment. Therefore, to accelerate the further development of cancer immunotherapies, more studies are necessary. In this review, we will summarize the current status of cancer immunotherapies, especially cancer vaccines, and discuss the potential problems and solutions for the next breakthrough in cancer immunotherapy.

Immunotherapy in Prostate Cancer

Immunotherapy encompasses a wide range of therapies to engage the immune system to target malignancies. In recent years, immunotherapy has made a major impact on treatment of metastatic cancer and has altered standard of care for many tumor types. However, predicting and understanding responses across tumor types has been challenging. While some metastatic cancers have shown dramatic responses to immunotherapy, such as melanoma, lung cancer, and renal cell carcinoma, prostate cancer has generally failed to show a significant response. However, small series of prostate cancer patients have shown impressive responses to cellular and immunotherapy. This review summarizes the current data for immunotherapy’s use in prostate cancer, as well as how currently available data might help predict patient responses to immunotherapy. Specifically, we will review vaccine-based therapies, immune checkpoint inhibitors, and future directions that are actively being explored.

Engineering Strategies to Enhance TCR-Based Adoptive T Cell Therapy

T cell receptor (TCR)-based adoptive T cell therapies (ACT) hold great promise for the treatment of cancer, as TCRs can cover a broad range of target antigens. Here we summarize basic, translational and clinical results that provide insight into the challenges and opportunities of TCR-based ACT. We review the characteristics of target antigens and conventional αβ-TCRs, and provide a summary of published clinical trials with TCR-transgenic T cell therapies. We discuss how synthetic biology and innovative engineering strategies are poised to provide solutions for overcoming current limitations, that include functional avidity, MHC restriction, and most importantly, the tumor microenvironment. We also highlight the impact of precision genome editing on the next iteration of TCR-transgenic T cell therapies, and the discovery of novel immune engineering targets. We are convinced that some of these innovations will enable the field to move TCR gene therapy to the next level.

Murine CD8 T-cell functional avidity is stable in vivo but not in vitro: Independence from homologous prime/boost time interval and antigen density

It is known that for achieving high affinity antibody responses, vaccines must be optimized for antigen dose/density, and the prime/boost interval should be at least 4 weeks. Similar knowledge is lacking for generating high avidity T‐cell responses. The functional avidity (FA) of T cells, describing responsiveness to peptide, is associated with the quality of effector function and the protective capacity in vivo. Despite its importance, the FA is rarely determined in T‐cell vaccination studies. We addressed the question whether different time intervals for short‐term homologous vaccinations impact the FA of CD8 T‐cell responses. Four‐week instead of 2‐week intervals between priming and boosting with potent subunit vaccines in C57BL/6 mice did not improve FA. Equally, similar FA was observed after vaccination with virus‐like particles displaying low versus high antigen densities. Interestingly, FA was stable in vivo but not in vitro, depending on the antigen dose and the time interval since T‐cell activation, as observed in murine monoclonal T cells. Our findings suggest dynamic in vivo modulation for equal FA. We conclude that low antigen density vaccines or a minimal 4‐week prime/boost interval are not crucial for the T‐cell's FA, in contrast to antibody responses.

Recent advances in nanotheranostics for triple negative breast cancer treatment

Triple-negative breast cancer (TNBC) is the most complex and aggressive type of breast cancer encountered world widely in women. Absence of hormonal receptors on breast cancer cells necessitates the chemotherapy as the only treatment regime. High propensity to metastasize and relapse in addition to poor prognosis and survival motivated the oncologist, nano-medical scientist to develop novel and efficient nanotherapies to solve such a big TNBC challenge. Recently, the focus for enhanced availability, targeted cellular uptake with minimal toxicity is achieved by nano-carriers. These smart nano-carriers carrying all the necessary arsenals (drugs, tracking probe, and ligand) designed in such a way that specifically targets the TNBC cells at site. Articulating the targeted delivery system with multifunctional molecules for high specificity, tracking, diagnosis, and treatment emerged as theranostic approach. In this review, in addition to classical treatment modalities, recent advances in nanotheranostics for early and effective diagnostic and treatment is discussed. This review highlighted the recently FDA approved immunotherapy and all the ongoing clinical trials for TNBC, in addition to nanoparticle assisted immunotherapy. Futuristic but realistic advancements in artificial intelligence (AI) and machine learning not only improve early diagnosis but also assist clinicians for their workup in TNBC. The novel concept of Nanoparticles induced endothelial leakiness (NanoEL) as a way of tumor invasion is also discussed in addition to classical EPR effect. This review intends to provide basic insight and understanding of the novel nano-therapeutic modalities in TNBC diagnosis and treatment and to sensitize the readers for continue designing the novel nanomedicine. This is the first time that designing nanoparticles with stoichiometric definable number of antibodies per nanoparticle now represents the next level of precision by design in nanomedicine.

State of the art in immunotherapy of neuroblastoma

Neuroblastoma (NB) is a common and deadly malignancy mostly observed in children. Evolution of therapeutic options for NB led to the addition of immunotherapeutic modalities to the previously recruited chemotherapeutic options. Molecular studies of the NB cells resulted in the discovery of many tumor-associated genes and antigens such as MYCN gene and GD2. MYCN gene and GD2 surface antigen are two of the most practical discoveries regarding immunotherapy of neuroblastoma. The GD2 antigen has been targeted in many animal and human studies including Phase III clinical trials. Even though these antigens have changed the face of pediatric neuroblastoma, they do not take as much credit in immunotherapy of adult-onset neuroblastoma. Monoclonal antibodies have been designed to detect this antigen on the surface of NB tumor cells. Despite bettering the outcomes for NB patients, current therapies still fail in many cases. Studies are underway to discover more specific tumor-associated antigens and more effective treatment options. In the current narrative, immunotherapy of NB - from emerging of this therapeutic backbone in NB to the latest discoveries regarding this malignancy - has been reviewed.

Immune reaction by cytoreductive prostatectomy

Prostate cancer (PCa) is the most common non-cutaneous cancer among men and the second leading cause of male cancer deaths in the United States. With no effective cure for advanced disease, the survival rates of castration-resistant disease and metastatic disease remains poor. Treatment via hormonal manipulation, immunotherapy, and chemotherapy remain marginally effective, indicating the need for novel treatment strategies. Cytoreductive prostatectomy (CRP) has grown as a treatment modality for metastatic castration resistant prostate cancer (mCRPC) and an emerging body of literature has demonstrated its survival benefits. In this review, we hope to further explore immunologic changes after CRP and the resultant effects on oncologic outcomes. Conclusively, the data and technical considerations of CRS evolve, CRS may continue to expand treat various type of metastatic cancer. Still, there are little reports about immunological changed after CRP. However, based on technical improvement, CRP and combinational immunotherapy are developing treatments of metastatic disease.

Theranostics Applications of Nanoparticles in Cancer Immunotherapy

With the advancement in the mechanism of immune surveillance and immune evasion in cancer cells, cancer immunotherapy shows promising results for treating cancer with established efficacy and less toxicity. As a result of the off-target effect, the approach for delivering vaccines, adjuvants, or antibodies directly to tumor sites is gaining widespread attention. An effective alternative is to utilize nanoengineered particles, functioning as drug-delivery systems or as antigens themselves. This article reviews the practical implementation of nanotechnology in cancer immunotherapy.

Distinct Graft-Specific TCR Avidity Profiles during Acute Rejection and Tolerance

Mechanisms implicated in robust transplantation tolerance at the cellular level can be broadly categorized into those that inhibit alloreactive T cells intrinsically (clonal deletion and dysfunction) or extrinsically through regulation. Here, we investigated whether additional population-level mechanisms control T cells by examining whether therapeutically induced peripheral transplantation tolerance could influence T cell populations' avidity for alloantigens. Whereas T cells with high avidity preferentially accumulated during acute rejection of allografts, the alloreactive T cells in tolerant recipients retained a low-avidity profile, comparable to naive mice despite evidence of activation. These contrasting avidity profiles upon productive versus tolerogenic stimulation were durable and persisted upon alloantigen re-encounter in the absence of any immunosuppression. Thus, peripheral transplantation tolerance involves control of alloreactive T cells at the population level, in addition to the individual cell level. Controlling expansion or eliminating high-affinity, donor-specific T cells long term may be desirable to achieve robust transplantation tolerance in the clinic.

Cancer vaccines: translation from mice to human clinical trials

Therapeutic cancer vaccines have been a long-sought approach to harness the exquisite specificity of the immune system to treat cancer, but until recently have not had much success as single agents in clinical trials. However, new understanding of the immunoregulatory mechanisms exploited by cancers has allowed the development of approaches to potentiate the effect of vaccines by removing the brakes while the vaccines step on the accelerator. Thus, vaccines that had induced a strong T cell response but no clinical therapeutic effect may now reach their full potential. Here, we review a number of promising approaches to cancer vaccines developed initially in mouse models and their translation into clinical trials, along with combinations of vaccines with other therapies that might allow cancer vaccines to finally achieve clinical efficacy against many types of cancer.

Combining immunotherapies for the treatment of prostate cancer

Sipuleucel-T, a therapeutic dendritic-cell vaccine, was Food and Drug Administration-approved for prostate cancer in 2010. No new immunotherapies for prostate cancer have been approved since. However, novel agents and combination approaches offer great promise for improving outcomes for prostate cancer patients. Here we review the latest developments in immunotherapy for prostate cancer. Sipuleucel-T has demonstrated a survival advantage of 4.1 months in metastatic castration-resistant prostate cancer. PSA-TRICOM (PROSTVAC), a prostate-specific antigen-targeted vaccine platform, showed evidence of clinical and immunologic efficacy in early-phase clinical trials, and results from a phase III trial in advanced disease are pending. While immune checkpoint inhibitors appear to have modest activity as monotherapy, preclinical and clinical data suggest that they may synergize with vaccines, poly [ADP-ribose] polymerase inhibitors, and other agents. Several clinical studies that combine these therapies are underway. Combining prostate cancer vaccines with immune checkpoint inhibitors has great potential for improving clinical outcomes in prostate cancer. Such combination approaches may create and then recruit tumor-specific T cells to tumor while also increasing their effector function. Other emerging agents may also enhance immune-mediated tumor destruction.

Enhanced immunotherapy by combining a vaccine with a novel murine GITR ligand fusion protein

Immunotherapy was significantly enhanced in a murine tumor model by combining a vaccine with a fusion protein designed to target the glucocorticoid-induced tumor necrosis factor (TNF) receptor related gene (GITR) on the surface of T cells. The recombinant poxvirus-based vaccine platform included Modified Vaccinia virus Ankara (rMVA) and fowlpox (rF) vectors as the driver immunogens both engineered to express the human carcinoembryonic antigen (CEA) and three murine costimulatory molecules B7.1, ICAM-1, LFA-3 (designated TRICOM). In previous studies, mice expressing human CEA as a transgene (CEA.Tg mice) vaccinated with rMVA/rF-CEA-TRICOM overcame CEA immune tolerance by inducing anti-CEA‒specific immunity and regression of CEA-expressing tumors. The murine GITR ligand fusion protein (mGITRL-FP) consisted of a mouse IgG2a Fc region, a yeast-derived coiled GCN4 pII and the extracellular GITR-binding domain of murine GITR ligand. The design maximized valency and the potential to agonize the GITR receptor. Combined treatment of the vaccine and mGITRL-FP mediated a more robust tumor regression, leading to sustained improvement in overall survival. The enhanced immunotherapeutic effect was linked to the generation of a strong CD8⁺ T cell antitumor immune response. A treatment schedule with mGITRL-FP administered prior to the priming rMVA-CEA-TRICOM vaccination was of paramount importance. The mechanism of action for the enhanced antitumor effects resided in the depletion of immune cells, particularly FoxP3⁺ regulatory T cells, that express high GITR levels following activation. The results provide evidence that targeting GITR with mGITRL-FP in concert with a cancer vaccine represents a potential novel approach to more effective immunotherapy.

[Immunotherapy: Activation of a system not a pathway]

Immunotherapy is on the roll. After revolutionary effects in melanoma, immunotherapy is invading other locations. If current treatments, chemotherapies or targeted therapies block one pathway, immunotherapy should be understood as the activation of a whole system. Indeed, oncogenesis process is defined as an escape of the immune system and the stimulation of this system can block the carcinogenic process. The aim of the present review is to describe the place of immunotherapy in the treatment of solid cancers.

Therapeutic Cancer Vaccines

Cancer is one of the major leading death causes of diseases. Prevention and treatment of cancer is an important way to decrease the incidence of tumorigenesis and prolong patients' lives. Subversive achievements on cancer immunotherapy have recently been paid much attention after many failures in basic and clinical researches. Based on deep analysis of genomics and proteomics of tumor antigens, a variety of cancer vaccines targeting tumor antigens have been tested in preclinical and human clinical trials. Many therapeutic cancer vaccines alone or combination with other conventional treatments for cancer obtained spectacular efficacy, indicating the tremendously potential application in clinic. With the illustration of underlying mechanisms of cancer immune regulation, valid, controllable, and persistent cancer vaccines will play important roles in cancer treatment, survival extension and relapse and cancer prevention. This chapter mainly summarizes the recent progresses and developments on cancer vaccine research and clinical application, thus exploring the existing obstacles in cancer vaccine research and promoting the efficacy of cancer vaccine.

Poxvirus-based active immunotherapy synergizes with CTLA-4 blockade to increase survival in a murine tumor model by improving the magnitude and quality of cytotoxic T cells

The dramatic clinical benefit of immune checkpoint blockade for a fraction of cancer patients suggests the potential for further clinical benefit in a broader cancer patient population by combining immune checkpoint inhibitors with active immunotherapies. The anti-tumor efficacy of MVA-BN-HER2 poxvirus-based active immunotherapy alone or in combination with CTLA-4 checkpoint blockade was investigated in a therapeutic CT26-HER-2 lung metastasis mouse model. MVA-BN-HER2 immunotherapy significantly improved the median overall survival compared to untreated controls or CTLA-4 blockade alone (p < 0.001). Robust synergistic efficacy was achieved with the combination therapy (p < 0.01). Improved survival following MVA-BN-HER2 administration was accompanied by increased tumor infiltration by HER-2-specific cytotoxic T lymphocytes (CTL). These tumor-specific CTL had characteristics similar to antiviral CTL, including strong expression of activation markers and co-expression of IFNγ and TNFα. Combination with CTLA-4 blockade significantly increased the magnitude of HER-2-specific T cell responses, with a higher proportion co-expressing TNFα and/or IL-2 with IFNγ. Furthermore, in mice treated with MVA-BN-HER2 (alone or in combination with CTLA-4 blockade), the inducible T cell co-stimulator (ICOS) protein was expressed predominantly on CD4 and CD8 effector T cells but not on regulatory T cells (T(reg)). In contrast, mice left untreated or treated solely with CTLA-4 blockade harbored elevated ICOS(+) Treg, a phenotype associated with highly suppressive activity. In conclusion, poxvirus-based active immunotherapy induced robust tumor infiltration by highly efficient effector T cells. Combination with CTLA-4 immune checkpoint blockade amplified this response resulting in synergistically improved efficacy. These hypothesis-generating data may help elucidate evidence of enhanced clinical benefit from combining CTLA-4 blockade with poxvirus-based active immunotherapy.

Clinically feasible approaches to potentiating cancer cell-based immunotherapies

The immune system exerts both tumor-destructive and tumor-protective functions. Mature dendritic cells (DCs), classically activated macrophages (M1), granulocytes, B lymphocytes, aβ and ɣδ T lymphocytes, natural killer T (NKT) cells, and natural killer (NK) cells may be implicated in antitumor immunoprotection. Conversely, tolerogenic DCs, alternatively activated macrophages (M2), myeloid-derived suppressor cells (MDSCs), and regulatory T (Tregs) and B cells (Bregs) are capable of suppressing antitumor immune responses. Anti-cancer vaccination is a useful strategy to elicit antitumor immune responses, while overcoming immunosuppressive mechanisms. Whole tumor cells or lysates derived thereof hold more promise as cancer vaccines than individual tumor-associated antigens (TAAs), because vaccinal cells can elicit immune responses to multiple TAAs. Cancer cell-based vaccines can be autologous, allogeneic or xenogeneic. Clinical use of xenogeneic vaccines is advantageous in that they can be most effective in breaking the preexisting immune tolerance to TAAs. To potentiate immunotherapy, vaccinations can be combined with other modalities that target different immune pathways. These modalities include 1) genetic or chemical modification of cell-based vaccines; 2) cross-priming TAAs to T cells by engaging dendritic cells; 3) T-cell adoptive therapy; 4) stimulation of cytotoxic inflammation by non-specific immunomodulators, toll-like receptor (TLR) agonists, cytokines, chemokines or hormones; 5) reduction of immunosuppression and/or stimulation of antitumor effector cells using antibodies, small molecules; and 6) various cytoreductive modalities. The authors envisage that combined immunotherapeutic strategies will allow for substantial improvements in clinical outcomes in the near future.

IMA901: a multi-peptide cancer vaccine for treatment of renal cell cancer

Despite a major improvement in the treatment of advanced kidney cancer by the recent introduction of targeted agents such as multi-kinase inhibitors, long-term benefits are still limited and a significant unmet medical need remains for this disease. Cancer immunotherapy has shown its potential by the induction of long-lasting responses in a small subset of patients, however, the unspecific immune interventions with (high dose) cytokines used so far are associated with significant side effects. Specific cancer immunotherapy may circumvent these problems by attacking tumor cells while sparing normal tissue with the use of multi-peptide vaccination being one of the most promising strategies. We here summarize the clinical and translational data from phase I and II trials investigating IMA901. Significant associations of clinical benefit with detectable T cell responses against the IMA901 peptides and encouraging survival data in treated patients has prompted the start of a randomized, controlled phase III trial in 1st line advanced RCC with survival results expected toward the end of 2015. Potential combination strategies with the recently discovered so-called checkpoint inhibitors are also discussed.

Antigen-specific vaccines for cancer treatment

Vaccines targeting pathogens are generally effective and protective because based on foreign non-self antigens which are extremely potent in eliciting an immune response. On the contrary, efficacy of therapeutic cancer vaccines is still disappointing. One of the major reasons for such poor outcome, among others, is the difficulty of identifying tumor-specific target antigens which should be unique to the tumors or, at least, overexpressed on the tumors as compared to normal cells. Indeed, this is the only option to overcome the peripheral immune tolerance and elicit a non toxic immune response. New and more potent strategies are now available to identify specific tumor-associated antigens for development of cancer vaccine approaches aiming at eliciting targeted anti-tumor cellular responses. In the last years this aspect has been addressed and many therapeutic vaccination strategies based on either whole tumor cells or specific antigens have been and are being currently evaluated in clinical trials. This review summarizes the current state of cancer vaccines, mainly focusing on antigen-specific approaches.

Narrowing the Gap: Preserving Repertoire Diversity Despite Clonal Selection during the CD4 T Cell Response

T cell immunity relies on the generation and maintenance of a diverse repertoire of T cell antigen receptors (TCRs). The strength of signaling emanating from the TCR dictates the fate of T cells during development, as well as during the immune response. Whereas development of new T cells in the thymus increases the available TCR repertoire, clonal selection during the immune response narrows TCR diversity through the outgrowth of clonotypes with the fittest TCR. To ensure maintenance of TCR diversity in the antigen-selected repertoire, specific mechanisms can be envisaged that facilitate the participation of T cell clonotypes with less than best fit TCRs. Here, we summarize the evidence for the existence of such mechanisms that can prevent the loss of diversity. A number of T cell-autonomous or extrinsic factors can reverse clonotypic hierarchies set by TCR affinity for given antigen. Although not yet complete, understanding of these factors and their mechanism of action will be critical in interventional attempts to mold the antigen-selected TCR repertoire.

Exploiting synergy: immune-based combinations in the treatment of prostate cancer

Cancer treatment is being revolutionized by the emergence of immunotherapies such as immune checkpoint inhibitors and therapeutic cancer vaccines. Prostate cancer is amenable to such therapeutic approaches. The improved understanding of the relationship between the immune system and tumors has allowed therapeutic targeting of immune checkpoints and tumor associated antigens to be developed. Furthermore, interventions used in prostate cancer are capable of impacting the immune system. As demonstrated by preclinical data and emerging clinical data, radiation therapy, anti-androgen therapy, and chemotherapy can be used with immunotherapies to obtain synergistic results. Current and future clinical trials will further investigate these principles as immunotherapeutics are combined with each other and standard therapies for optimal clinical utility.

Antigen targeting to dendritic cells combined with transient regulatory T cell inhibition results in long-term tumor regression

Therapeutic vaccinations against cancer are still largely ineffective. Major caveats are inefficient delivery of tumor antigens to dendritic cells (DCs) and excessive immune suppression by Foxp3⁺ regulatory T cells (Tregs), resulting in defective T cell priming and failure to induce tumor regression. To circumvent these problems we evaluated a novel combinatorial therapeutic strategy. We show that tumor antigen targeting to DC-SIGN in humanized hSIGN mice via glycans or specific antibodies induces superior T cell priming. Next, this targeted therapy was combined with transient Foxp3⁺ Treg depletion employing hSIGNxDEREG mice. While Treg depletion alone slightly delayed B16-OVA melanoma growth, only the combination therapy instigated long-term tumor regression in a substantial fraction of mice. This novel strategy resulted in optimal generation of antigen-specific activated CD8⁺ T cells which accumulated in regressing tumors. Notably, Treg depletion also allowed the local appearance of effector T cells specific for endogenous B16 antigens. This indicates that antitumor immune responses can be broadened by therapies aimed at controlling Tregs in tumor environments. Thus, transient inhibition of Treg-mediated immune suppression potentiates DC targeted antigen vaccination and tumor-specific immunity.

Combination of vaccine and immune checkpoint inhibitor is safe with encouraging clinical activity

This commentary provides the authors' perspective on the article "Ipilimumab and a poxviral vaccine targeting prostate-specific antigen in metastatic castration-resistant prostate cancer: a phase 1 dose-escalation trial," which has recently been published in The Lancet Oncology.

Therapeutic vaccines as a promising treatment modality against prostate cancer: rationale and recent advances

Cancer immunotherapy was deemed the medical breakthrough of 2013, in part because it can induce a rapid, durable, self-propagating and adaptable immune response. Specifically in prostate cancer, immunotherapy has emerged as a viable and attractive treatment strategy. To date, therapeutic cancer vaccines and immune checkpoint inhibitors are the two classes of immunotherapy that have demonstrated improvements in overall survival in patients with advanced tumors. The 2010 Food and Drug Administration approval of sipuleucel-T for asymptomatic or minimally symptomatic metastatic prostate cancer set the stage for ongoing phase III trials with the cancer vaccine PSA-TRICOM and the immune checkpoint inhibitor ipilimumab. A class effect of these approved immune-based therapies is a benefit in overall survival without short-term changes in disease progression, apparently due to modulation of tumor growth rate kinetics, in which the activated immune system exerts constant immunologic pressure that slows net tumor growth. A growing body of evidence suggests that the ideal population for clinical trials of cancer vaccines as monotherapy is patients with lower tumor volume and less aggressive disease. Combination strategies include immunotherapy with standard therapies or with other immunotherapies. Here we review emerging data on immunotherapy for patients with prostate cancer.

Peptide Dose and/or Structure in Vaccines as a Determinant of T Cell Responses

While T cells recognise the complex of peptide and major histocompatibility complex (MHC) at the cell surface, changes in the dose and/or structure of the peptide component can have profound effects on T cell activation and function. In addition, the repertoire of T cells capable of responding to any given peptide is variable, but broader than a single clone. Consequently, peptide parameters that affect the interaction between T cells and peptide/MHC have been shown to select particular T cell clones for expansion and this impacts on clearance of disease. T cells with high functional avidity are selected on low doses of peptide, while low avidity T cells are favoured in high peptide concentrations. Altering the structure of the peptide ligand can also influence the selection and function of peptide-specific T cell clones. In this review, we will explore the evidence that the choice of peptide dose or the structure of the peptide are critical parameters in an effective vaccine designed to activate T cells.

PROSTVAC® targeted immunotherapy candidate for prostate cancer

Abstract: 

Targeted immunotherapies represent a valid strategy for the treatment of metastatic castrate-resistant prostate cancer. A randomized, double-blind, Phase II clinical trial of PROSTVAC® demonstrated a statistically significant improvement in overall survival and a large, global, Phase III trial with overall survival as the primary end point is ongoing. PROSTVAC immunotherapy contains the transgenes for prostate-specific antigen and three costimulatory molecules (designated TRICOM). Research suggests that PROSTVAC not only targets prostate-specific antigen, but also other tumor antigens via antigen cascade. PROSTVAC is well tolerated and has been safely combined with other cancer therapies, including hormonal therapy, radiotherapy, another immunotherapy and chemotherapy. Even greater benefits of PROSTVAC may be recognized in earlier-stage disease and low-disease burden settings where immunotherapy can trigger a long-lasting immune response.

A combination trial of vaccine plus ipilimumab in metastatic castration-resistant prostate cancer patients: immune correlates

We recently reported the clinical results of a Phase I trial combining ipilimumab with a vaccine containing transgenes for prostate-specific antigen (PSA) and for a triad of costimulatory molecules (PROSTVAC) in patients with metastatic castration-resistant prostate cancer. Thirty patients were treated with escalating ipilimumab and a fixed dose of vaccine. Of 24 chemotherapy-naïve patients, 58 % had a PSA decline. Combination therapy did not exacerbate the immune-related adverse events associated with ipilimumab. Here, we present updated survival data and an evaluation of 36 immune cell subsets pre- and post-therapy. Peripheral blood mononuclear cells were collected before therapy, at 13 days and at 70 days post-initiation of therapy, and phenotyped by flow cytometry for the subsets of T cells, regulatory T cells, natural killer cells, and myeloid-derived suppressor cells. Associations between overall survival (OS) and immune cell subsets prior to treatment, and the change in a given immune cell subset 70 days post-initiation of therapy, were evaluated. The median OS was 2.63 years (1.77-3.45). There were trends toward associations for longer OS and certain immune cell subsets before immunotherapy: lower PD-1(+)Tim-3(NEG)CD4EM (P = 0.005, adjusted P = 0.010), higher PD-1(NEG)Tim-3(+)CD8 (P = 0.002, adjusted P = 0.004), and a higher number of CTLA-4(NEG) Tregs (P = 0.005, adjusted P = 0.010). We also found that an increase in Tim-3(+) natural killer cells post- versus pre-vaccination associated with longer OS (P = 0.0074, adjusted P = 0.015). These results should be considered as hypothesis generating and should be further evaluated in larger immunotherapy trials.

Therapeutic cancer vaccines: past, present, and future

Therapeutic vaccines represent a viable option for active immunotherapy of cancers that aim to treat late stage disease by using a patient's own immune system. The promising results from clinical trials recently led to the approval of the first therapeutic cancer vaccine by the U.S. Food and Drug Administration. This major breakthrough not only provides a new treatment modality for cancer management but also paves the way for rationally designing and optimizing future vaccines with improved anticancer efficacy. Numerous vaccine strategies are currently being evaluated both preclinically and clinically. This review discusses therapeutic cancer vaccines from diverse platforms or targets as well as the preclinical and clinical studies employing these therapeutic vaccines. We also consider tumor-induced immune suppression that hinders the potency of therapeutic vaccines, and potential strategies to counteract these mechanisms for generating more robust and durable antitumor immune responses.

Therapeutic cancer vaccines

Therapeutic cancer vaccines have the potential of being integrated in the therapy of numerous cancer types and stages. The wide spectrum of vaccine platforms and vaccine targets is reviewed along with the potential for development of vaccines to target cancer cell "stemness," the epithelial-to-mesenchymal transition (EMT) phenotype, and drug-resistant populations. Preclinical and recent clinical studies are now revealing how vaccines can optimally be used with other immune-based therapies such as checkpoint inhibitors, and so-called nonimmune-based therapeutics, radiation, hormonal therapy, and certain small molecule targeted therapies; it is now being revealed that many of these traditional therapies can lyse tumor cells in a manner as to further potentiate the host immune response, alter the phenotype of nonlysed tumor cells to render them more susceptible to T-cell lysis, and/or shift the balance of effector:regulatory cells in a manner to enhance vaccine efficacy. The importance of the tumor microenvironment, the appropriate patient population, and clinical trial endpoints is also discussed in the context of optimizing patient benefit from vaccine-mediated therapy.

Identification and characterization of agonist epitopes of the MUC1-C oncoprotein

The MUC1 tumor-associated antigen is overexpressed in the majority of human carcinomas and several hematologic malignancies. Much attention has been paid to the hypoglycosylated variable number of tandem repeats (VNTR) region of the N-terminus of MUC1 as a vaccine target, and recombinant viral vector vaccines are also being evaluated that express the entire MUC1 transgene. While previous studies have described MUC1 as a tumor-associated tissue differentiation antigen, studies have now determined that the C-terminus of MUC1 (MUC1-C) is an oncoprotein, and its expression is an indication of poor prognosis in numerous tumor types. We report here the identification of nine potential CD8⁺ cytotoxic T lymphocyte epitopes of MUC1, seven in the C-terminus and two in the VNTR region, and have identified enhancer agonist peptides for each of these epitopes. These epitopes span HLA-A2, HLA-A3, and HLA-A24 major histocompatibility complex (MHC) class I alleles, which encompass the majority of the population. The agonist peptides, compared to the native peptides, more efficiently (a) generate T-cell lines from the peripheral blood mononuclear cells of cancer patients, (b) enhance the production of IFN-γ by peptide-activated human T cells, and (c) lyse human tumor cell targets in an MHC-restricted manner. The agonist epitopes described here can be incorporated into various vaccine platforms and for the ex vivo generation of human T cells. These studies provide the rationale for the T-cell-mediated targeting of the oncogenic MUC1-C, which has been shown to be an important factor in both drug resistance and poor prognosis for numerous tumor types.

Immune impact induced by PROSTVAC (PSA-TRICOM), a therapeutic vaccine for prostate cancer

PSA-TRICOM (PROSTVAC) is a novel vector-based vaccine designed to generate a robust immune response against prostate-specific antigen (PSA)-expressing tumor cells. The purpose of this report is to present an overview of both published studies and new data in the evaluation of immune responses to the PSA-TRICOM vaccine platform, currently in phase III testing. Of 104 patients tested for T-cell responses, 57% (59/104) demonstrated a ≥ 2-fold increase in PSA-specific T cells 4 weeks after vaccine (median 5-fold increase) compared with pre-vaccine, and 68% (19/28) of patients tested mounted post-vaccine immune responses to tumor-associated antigens not present in the vaccine (antigen spreading). The PSA-specific immune responses observed 28 days after vaccine (i.e., likely memory cells) are quantitatively similar to the levels of circulating T cells specific for influenza seen in the same patients. Measurements of systemic immune response to PSA may underestimate the true therapeutic immune response (as this does not account for cells that have trafficked to the tumor) and does not include antigen spreading. Furthermore, although the entire PSA gene is the vaccine, only one epitope of PSA is evaluated in the T-cell responses. Because this therapeutic vaccine is directed at generating a cellular/Th1 immune response (T-cell costimulatory molecules and use of a viral vector), it is not surprising that less than 0.6% of patients (2/349) tested have evidence of PSA antibody induction following vaccine. This suggests that post-vaccine PSA kinetics were not affected by PSA antibodies. An ongoing phase III study will evaluate the systemic immune responses and correlation with clinical outcomes.

Immunodomination during peripheral vaccinia virus infection

Immunodominance is a fundamental property of CD8(+) T cell responses to viruses and vaccines. It had been observed that route of administration alters immunodominance after vaccinia virus (VACV) infection, but only a few epitopes were examined and no mechanism was provided. We re-visited this issue, examining a panel of 15 VACV epitopes and four routes, namely intradermal (i.d.), subcutaneous (s.c.), intraperitoneal (i.p.) and intravenous (i.v.) injection. We found that immunodominance is sharpened following peripheral routes of infection (i.d. and s.c.) compared with those that allow systemic virus dissemination (i.p. and i.v.). This increased immunodominance was demonstrated with native epitopes of VACV and with herpes simplex virus glycoprotein B when expressed from VACV. Responses to some subdominant epitopes were altered by as much as fourfold. Tracking of virus, examination of priming sites, and experiments restricting virus spread showed that priming of CD8(+) T cells in the spleen was necessary, but not sufficient to broaden responses. Further, we directly demonstrated that immunodomination occurs more readily when priming is mainly in lymph nodes. Finally, we were able to reduce immunodominance after i.d., but not i.p. infection, using a VACV expressing the costimulators CD80 (B7-1) and CD86 (B7-2), which is notable because VACV-based vaccines incorporating these molecules are in clinical trials. Taken together, our data indicate that resources for CD8(+) T cell priming are limiting in local draining lymph nodes, leading to greater immunodomination. Further, we provide evidence that costimulation can be a limiting factor that contributes to immunodomination. These results shed light on a possible mechanism of immunodomination and highlight the need to consider multiple epitopes across the spectrum of immunogenicities in studies aimed at understanding CD8(+) T cell immunity to viruses.

Ipilimumab in prostate cancer

INTRODUCTION

Immune checkpoint inhibitors, such as ipilimumab , are a new class of immunotherapeutic agents that have shown significant efficacy in melanoma. A number of ongoing clinical trials are investigating the role of ipilimumab in prostate cancer, either alone or in combination with immunomodulating agents such as radiation and chemotherapy, and in combination with cancer vaccines.

AREAS COVERED

This article reviews the molecular basis, preclinical and clinical evidence on the safety and efficacy of ipilimumab in prostate cancer. Medical literature search using MEDLINE and online abstracts database of national meetings form the basis of this article.

EXPERT OPINION

A number of preliminary clinical studies suggest the potential therapeutic utility of immune checkpoint inhibitors such as ipilimumab in prostate cancer. Pending the results of large-scale studies, the rationale of combining ipilimumab with standard anticancer therapeutics such as radiation, cytotoxic chemotherapy and other immunotherapeutic agents can be of great value in reducing mortality and morbidity in prostate cancer.

Demystifying immunotherapy in prostate cancer: understanding current and future treatment strategies

Immunotherapy has emerged as a viable therapeutic option for patients with prostate cancer. There are multiple potential strategies that use the immune system, including therapeutic cancer vaccines that are designed to stimulate immune cells to target antigens expressed by cancer cells. Sipuleucel-T is a vaccine currently approved for the treatment of minimally symptomatic metastatic prostate cancer, whereas the vaccine PSA-TRICOM and the immune-checkpoint inhibitor ipilimumab are in phase III testing. Although there are no short-term changes in disease progression or available biomarkers to assess response, these agents appear to improve survival. One hypothesis suggests that this apparent paradox can be explained by the growth-moderating effects of these treatments, which do not cause tumor size to diminish, but rather stall or slow their growth rate over time. For this reason, the use of immunotherapy earlier in the disease process is being investigated. Another approach is to block immune-regulatory mechanisms mediated by the molecules cytotoxic T lymphocyte antigen 4 and programmed cell death protein 1. Additional future strategies will combine immunotherapy with other standard therapies, potentially enhancing the latter's clinical impact and thereby improving both time to progression and overall survival due to the combined effects of both treatments. Prospective trials are currently evaluating these hypotheses and will ultimately serve to optimize immunotherapy in the treatment of prostate cancer.

Functional avidity: a measure to predict the efficacy of effector T cells?

The functional avidity is determined by exposing T-cell populations in vitro to different amounts of cognate antigen. T-cells with high functional avidity respond to low antigen doses. This in vitro measure is thought to correlate well with the in vivo effector capacity of T-cells. We here present the multifaceted factors determining and influencing the functional avidity of T-cells. We outline how changes in the functional avidity can occur over the course of an infection. This process, known as avidity maturation, can occur despite the fact that T-cells express a fixed TCR. Furthermore, examples are provided illustrating the importance of generating T-cell populations that exhibit a high functional avidity when responding to an infection or tumors. Furthermore, we discuss whether criteria based on which we evaluate an effective T-cell response to acute infections can also be applied to chronic infections such as HIV. Finally, we also focus on observations that high-avidity T-cells show higher signs of exhaustion and facilitate the emergence of virus escape variants. The review summarizes our current understanding of how this may occur as well as how T-cells of different functional avidity contribute to antiviral and anti-tumor immunity. Enhancing our knowledge in this field is relevant for tumor immunotherapy and vaccines design.

Therapeutic cancer vaccines: the latest advancement in targeted therapy

Therapeutic cancer vaccines represent an emerging therapeutic modality that may play a more prominent role in cancer treatment in the future. Therapeutic cancer vaccines are designed to generate a targeted, immune-mediated antitumor response. There are 2 main types of therapeutic vaccines: patient-specific (generated either from a patient's own cells or tumor) and patient- nonspecific, where a peptide- or vector-based vaccine induces an immune response in vivo against specific tumor-associated antigens. Studies are currently underway to investigate methods to enhance vaccine strategies, including combinations with standard anticancer therapies or immune-modulating agents. Cancer vaccines are usually well tolerated, with minimal toxicity compared with chemotherapy. This review summarizes selected therapeutic cancer vaccines in late clinical development.

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.

Strategies to use immune modulators in therapeutic vaccines against cancer

Cancers so much resemble self that they prove difficult for the immune system to eliminate, and those that have already escaped natural immunosurveillance have gotten past the natural immune barriers to malignancy. A successful therapeutic cancer vaccine must overcome these escape mechanisms. Our laboratory has focused on a multistep "push-pull" approach in which we combine strategies to overcome each of the mechanisms of escape. If tumor epitopes are insufficiently immunogenic, we increase their immunogenicity by epitope enhancement, improving their binding affinity to major histocompatibility complex (MHC) molecules. If the anti-tumor response is too weak or of the wrong phenotype, we use cytokines, costimulatory molecules, Toll-like receptor ligands, and other molecular adjuvants to increase not only the quantity of the response but also its quality, to push the response in the right direction. Finally, the tumor invokes multiple immunosuppressive mechanisms to defend itself, so we need to overcome those as well, including blocking or depleting regulatory cells or inhibiting regulatory molecules, to pull the response by removing the brakes. Some of these strategies individually have now been translated into human clinical trials in cancer patients. Combinations of these in a push-pull approach are promising for the successful immunotherapy of cancer.

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.