Evaluation of prime/boost regimens using recombinant poxvirus/tyrosinase vaccines for the treatment of patients with metastatic melanoma

Differential organ-specific tumor response to first-line immune checkpoint inhibitor therapy in non-small cell lung cancer-a retrospective cohort study

Background

Immune checkpoint inhibitors (ICIs) possess remarkable clinical effectiveness in non-small cell lung cancer (NSCLC). Different immune profiles of tumors may play a key role in the efficacy of treatment with ICIs. This article aimed to determine the differential organ responses to ICI in individuals with metastatic NSCLC.

Methods

This research analyzed data of advanced NSCLC patients receiving first-line treatment with ICIs. Major organs such as the liver, lung, adrenal glands, lymph nodes and brain were assessed using the Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 and RECIST-improved organ-specific response criteria.

Results

A retrospective analysis was conducted on a total of 105 individuals with advanced NSCLC with programmed death ligand-1 (PD-L1) expression ≥50% who received single agent anti-programmed cell death protein 1 (PD-1)/PD-L1 monoclonal antibodies as first-line therapy. Overall, 105 (100%), 17 (16.2%), 15 (14.3%), 13 (12.4%), and 45 (42.8%) individuals showed measurable lung tumors and liver, brain, adrenal, and other lymph node metastases at baseline. The median size of the lung, liver, brain, adrenal gland, and lymph nodes were 3.4, 3.1, 2.8, 1.9, and 1.8 cm, respectively. The results recorded mean response times of 2.1, 3.4, 2.5, 3.1, and 2.3 months, respectively. Organ-specific overall response rates (ORRs) were 67%, 30.6%, 34%, 39%, and 59.1%, respectively, with the liver having the lowest remission rate and lung lesions having the highest remission rate. There were 17 NSCLC patients with liver metastasis at baseline, and 6 had different responses to ICI treatment, with remission in the primary lung site and progressive disease (PD) in the metastatic liver site. At baseline, the mean progression-free survival (PFS) of the 17 patients with liver metastasis and 88 patients without liver metastasis was 4.3 and 7 months, respectively (P=0.02, 95% CI: 0.691 to 3.033).

Conclusions

The liver metastases of NSCLC may be less responsive to ICIs than other organs. The lymph nodes respond most favorably to ICIs. Further strategies may include additional local treatment in case of oligoprogression in these organs in patients with otherwise sustained treatment benefit.

A systematic analysis on the clinical safety and efficacy of onco-virotherapy

Several onco-virotherapy candidates have been developed and clinically evaluated for the treatment of cancer, and several are approved for clinical use. In this systematic review we explored the clinical impact of onco-virotherapy compared to other cancer therapies by analyzing factors such as trial design, patient background, therapy design, delivery strategies, and study outcomes. For this purpose, we retrieved clinical studies from three platforms: ClinicalTrials.gov, PubMed, and EMBASE. We found that most studies were performed in patients with advanced and metastatic tumors, using a broad range of genetically engineered vectors and mainly administered intratumorally. Therapeutic safety was the most frequently assessed outcome, while relatively few studies focused on immunological antitumor responses. Moreover, only 59 out of 896 clinical studies were randomized controlled trials reporting comparative data. This systemic review thus reveals the need of more, and better controlled, clinical studies to increase our understanding on the application of onco-virotherapy either as a single treatment or in combination with other cancer immunotherapies.

Exploiting Tumor Neoantigens to Target Cancer Evolution: Current Challenges and Promising Therapeutic Approaches

Immunotherapeutic manipulation of the antitumor immune response offers an attractive strategy to target genomic instability in cancer. A subset of tumor-specific somatic mutations can be translated into immunogenic and HLA-bound epitopes called neoantigens, which can induce the activation of helper and cytotoxic T lymphocytes. However, cancer immunoediting and immunosuppressive mechanisms often allow tumors to evade immune recognition. Recent evidence also suggests that the tumor neoantigen landscape extends beyond epitopes originating from nonsynonymous single-nucleotide variants in the coding exome. Here we review emerging approaches for identifying, prioritizing, and immunologically targeting personalized neoantigens using polyvalent cancer vaccines and T-cell receptor gene therapy. SIGNIFICANCE: Several major challenges currently impede the clinical efficacy of neoantigen-directed immunotherapy, such as the relative infrequency of immunogenic neoantigens, suboptimal potency and priming of de novo tumor-specific T cells, and tumor cell-intrinsic and -extrinsic mechanisms of immune evasion. A deeper understanding of these biological barriers could help facilitate the development of effective and durable immunotherapy for any type of cancer, including immunologically "cold" tumors that are otherwise therapeutically resistant.

Heterologous Prime Boost Vaccination Induces Protective Melanoma-Specific CD8+ T Cell Responses

Cancer vaccination aims at inducing an adaptive immune response against tumor-derived antigens. In this study, we utilize recombinant human adenovirus serotype 5 (rAd5) and recombinant lymphocytic choriomeningitis virus (rLCMV)-based vectors expressing the melanocyte differentiation antigen gp100. In contrast to single or homologous vaccination, a heterologous prime boost vaccination starting with a rAd5-gp100 prime immunization followed by a rLCMV-gp100 boost injection induces a high magnitude of polyfunctional gp100-specific CD8⁺ T cells. Our data indicate that an optimal T cell induction is dependent on the order and interval of the vaccinations. A prophylactic prime boost vaccination with rAd5- and rLCMV-gp100 protects mice from a B16.F10 melanoma challenge. In the therapeutic setting, combination of the vaccination with low-dose cyclophosphamide showed a synergistic effect and significantly delayed tumor growth. Our findings suggest that heterologous viral vector prime boost immunizations can mediate tumor control in a mouse melanoma model.

Differential Organ-Specific Tumor Response to Immune Checkpoint Inhibitors in Hepatocellular Carcinoma

BACKGROUND AND AIMS

Immune checkpoint inhibitors (ICIs) exhibit significant clinical activity in patients with advanced hepatocellular carcinoma (HCC). This study explored whether tumor response to ICIs in HCC varies among different organs.

METHODS

We reviewed the data of patients with advanced HCC who had received ICIs. Patients with measurable diseases were enrolled. Organ-specific response criteria, adapted from RECIST 1.1 and immune-related RECIST, were used to evaluate the objective response to ICIs in tumors located in the liver, lung, lymph node, and other intra-abdominal sites.

RESULTS

Of the 75 enrolled patients with advanced HCC, 51 and 11 patients had chronic hepatitis B virus and chronic hepatitis C virus infection, respectively. Regarding ICI treatment, 58, 1, and 16 patients had undergone anti-PD-1/anti-PD-L1 monoclonal antibody (mAb) alone, anti-CTLA4 mAb alone, and anti-PD-1 mAb plus anti-CTLA4 mAb, respectively; 20 and 55 patients had received ICIs as first-line or ≥second-line therapy. The overall objective response rate (ORR) was 28.0%. In total, 58, 34, 19, and 18 patients had measurable hepatic tumors and lung, lymph node, and other intra-abdominal metastases, and the corresponding organ-specific ORRs were 22.4, 41.2, 26.3, and 38.9%, respectively. Of the 39 patients who had both hepatic and extrahepatic tumors, 12 had disease control in extrahepatic tumors while progressive disease (PD) in hepatic tumors, whereas only 4 exhibited disease control in hepatic tumors while PD in extrahepatic tumors (p = 0.046, McNemar test). Of the 16 patients with only evaluable tumors in the liver and lungs at baseline, 8 had disease control in the lungs while PD in the liver, and none experienced disease control in the liver while PD in the lungs (p = 0.005).

CONCLUSIONS

The hepatic tumors of HCC may be less responsive to ICIs than extrahepatic lesions. Lung metastases responded most favorably to ICIs. The mechanisms underlying this differential response to ICIs warrant further investigation.

DNp73-induced degradation of tyrosinase links depigmentation with EMT-driven melanoma progression

Melanoma is an aggressive cancer with poor prognosis, requiring personalized management of advanced stages and establishment of molecular markers. Melanomas derive from melanocytes, which specifically express tyrosinase, the rate-limiting enzyme of melanin-synthesis. We demonstrate that melanomas with high levels of DNp73, a cancer-specific variant of the p53 family member p73 and driver of melanoma progression show, in contrast to their less-aggressive low-DNp73 counterparts, hypopigmentation in vivo. Mechanistically, reduced melanin-synthesis is mediated by a DNp73-activated IGF1R/PI3K/AKT axis leading to tyrosinase ER-arrest and proteasomal degradation. Tyrosinase loss triggers reactivation of the EMT signaling cascade, a mesenchymal-like cell phenotype and increased invasiveness. DNp73-induced depigmentation, Slug increase and changes in cell motility are recapitulated in neural crest-derived melanophores of Xenopus embryos, underscoring a previously unnoticed physiological role of tyrosinase as EMT inhibitor. This data provides a mechanism of hypopigmentation accompanying cancer progression, which can be exploited in precision diagnosis of patients with melanoma-associated hypopigmentation (MAH), currently seen as a favorable prognostic factor. The DNp73/IGF1R/Slug signature in colorless lesions might aid to clinically discriminate between patients with MAH-associated metastatic disease and those, where MAH is indeed a sign of regression.

Novel Treatments in Development for Melanoma

The past several years can be considered a renaissance era in the treatment of metastatic melanoma. Following a 30-year stretch in which oncologists barely put a dent in a very grim overall survival (OS) rate for these patients, things have rapidly changed course with the recent approval of three new melanoma drugs by the FDA. Both oncogene-targeted therapy and immune checkpoint blockade approaches have shown remarkable efficacy in a subset of melanoma patients and have clearly been game-changers in terms of clinical impact. However, most patients still succumb to their disease, and thus, there remains an urgent need to improve upon current therapies. Fortunately, innovations in molecular medicine have led to many silent gains that have greatly increased our understanding of the nature of cancer biology as well as the complex interactions between tumors and the immune system. They have also allowed for the first time a detailed understanding of an individual patient's cancer at the genomic and proteomic level. This information is now starting to be employed at all stages of cancer treatment, including diagnosis, choice of drug therapy, treatment monitoring, and analysis of resistance mechanisms upon recurrence. This new era of personalized medicine will foreseeably lead to paradigm shifts in immunotherapeutic treatment approaches such as individualized cancer vaccines and adoptive transfer of genetically modified T cells. Advances in xenograft technology will also allow for the testing of drug combinations using in vivo models, a truly necessary development as the number of new drugs needing to be tested is predicted to skyrocket in the coming years. This chapter will provide an overview of recent technological developments in cancer research, and how they are expected to impact future diagnosis, monitoring, and development of novel treatments for metastatic melanoma.

Safety and immunologic correlates of Melanoma GVAX, a GM-CSF secreting allogeneic melanoma cell vaccine administered in the adjuvant setting

Background

Limited adjuvant treatment options exist for patients with high-risk surgically resected melanoma. This first-in-human study investigated the safety, tolerability and immunologic correlates of Melanoma GVAX, a lethally irradiated granulocyte–macrophage colony stimulating factor (GM-CSF)-secreting allogeneic whole-cell melanoma vaccine, administered in the adjuvant setting.

Methods

Patients with stage IIB-IV melanoma were enrolled following complete surgical resection. Melanoma GVAX was administered intradermally once every 28 days for four cycles, at 5E7 cells/cycle (n = 3), 2E8 cells/cycle (n = 9), or 2E8 cells/cycle preceded by cyclophosphamide 200 mg/m² to deplete T regulatory cells (Tregs; n = 8). Blood was collected before each vaccination and at 4 and 6 months after treatment initiation for immunologic studies. Vaccine injection site biopsies and additional blood samples were obtained 2 days after the 1st and 4th vaccines.

Results

Among 20 treated patients, 18 completed 4 vaccinations. Minimal treatment-related toxicity was observed. One patient developed vitiligo and patches of white hair during the treatment and follow-up period. Vaccine site biopsies demonstrated complex inflammatory infiltrates, including significant increases in eosinophils and PD-1+ lymphocytes from cycle 1 to cycle 4 (P < 0.05). Serum GM-CSF concentrations increased significantly in a dose-dependent manner 48 h after vaccination (P = 0.0086), accompanied by increased numbers of activated circulating monocytes (P < 0.0001) and decreased percentages of myeloid-derived suppressor cells among monocytes (CD14+ , CD11b+ , HLA-DR low or negative; P = 0.002). Cyclophosphamide did not affect numbers of circulating Tregs. No significant changes in anti-melanoma immunity were observed in peripheral T cells by interferon-gamma ELIPSOT, or immunoglobulins by serum Western blotting.

Conclusion

Melanoma GVAX was safe and tolerable in the adjuvant setting. Pharmacodynamic testing revealed complex vaccine site immune infiltrates and an immune-reactive profile in circulating monocytic cell subsets. These findings support the optimization of Melanoma GVAX with additional monocyte and dendritic cell activators, and the potential development of combinatorial treatment regimens with synergistic agents.

Trial registration: NCT01435499

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-015-0572-3) contains supplementary material, which is available to authorized users.

The evolution of poxvirus vaccines

After Edward Jenner established human vaccination over 200 years ago, attenuated poxviruses became key players to contain the deadliest virus of its own family: Variola virus (VARV), the causative agent of smallpox. Cowpox virus (CPXV) and horsepox virus (HSPV) were extensively used to this end, passaged in cattle and humans until the appearance of vaccinia virus (VACV), which was used in the final campaigns aimed to eradicate the disease, an endeavor that was accomplished by the World Health Organization (WHO) in 1980. Ever since, naturally evolved strains used for vaccination were introduced into research laboratories where VACV and other poxviruses with improved safety profiles were generated. Recombinant DNA technology along with the DNA genome features of this virus family allowed the generation of vaccines against heterologous diseases, and the specific insertion and deletion of poxvirus genes generated an even broader spectrum of modified viruses with new properties that increase their immunogenicity and safety profile as vaccine vectors. In this review, we highlight the evolution of poxvirus vaccines, from first generation to the current status, pointing out how different vaccines have emerged and approaches that are being followed up in the development of more rational vaccines against a wide range of diseases.

Vitiligo-like depigmentation in patients with stage III-IV melanoma receiving immunotherapy and its association with survival: a systematic review and meta-analysis

PURPOSE

Vitiligo-like depigmentation in patients with melanoma may be associated with more favorable clinical outcome. We conducted a systematic review of patients with stage III to IV melanoma treated with immunotherapy to determine the cumulative incidence of vitiligo-like depigmentation and the prognostic value of vitiligo development on survival.

METHODS

We systemically searched and selected all studies on melanoma immunotherapy that reported on autoimmune toxicity and/or vitiligo between 1995 and 2013. Methodologic quality of each study was appraised using adapted criteria for systematic reviews in prognostic studies. Random-effect models were used to calculate summary estimates of the cumulative incidence of vitiligo-like depigmentation across studies. The prognostic value of vitiligo-like depigmentation on survival outcome was assessed using random-effects Cox regression survival analyses.

RESULTS

One hundred thirty-seven studies were identified comprising 139 treatment arms (11 general immune stimulation, 84 vaccine, 28 antibody-based, and 16 adoptive transfer) including a total of 5,737 patients. The overall cumulative incidence of vitiligo was 3.4% (95% CI, 2.5% to 4.5%). In 27 studies reporting individual patient data, vitiligo development was significantly associated with both progression-free-survival (hazard ratio [HR], 0.51; 95% CI, 0.32 to 0.82; P < .005) and overall survival (HR, 0.25; 95% CI, 0.10 to 0.61; P < .003), indicating that these patients have two to four times less risk of disease progression and death, respectively, compared with patients without vitiligo development.

CONCLUSION

Although vitiligo occurs only in a low percentage of patients with melanoma treated with immunotherapy, our findings suggest clear survival benefit in these patients. Awareness of vitiligo induction in patients with melanoma is important as an indicator of robust antimelanoma immunity and associated improved survival.

Mouse model for pre-clinical study of human cancer immunotherapy

This unit describes protocols for developing tumors in mice, including subcutaneous growth, pulmonary metastases of B16 melanoma, and spontaneous melanoma in B-Raf V600E/PTEN deletion transgenic mouse models. Two immunization methods to prevent B16 tumor growth are described using B16.GM-CSF and recombinant vaccinia virus. A therapeutic approach is also included that uses adoptive transfer of tumor antigen-specific T cells. Methods including CTL induction, isolation, testing, and genetic modification of mouse T cells for adoptive transfer by using retrovirus-expressing genes of interest are provided. Additional sections, including growing B16 melanoma, enumerating pulmonary metastases, tumor imaging technique, and use of recombinant viruses for vaccination, are discussed together with safety concerns.

An integrated genome-wide approach to discover tumor-specific antigens as potential immunologic and clinical targets in cancer

Tumor-specific antigens (TSA) are central elements in the immune control of cancers. To systematically explore the TSA genome, we developed a computational technology called heterogeneous expression profile analysis (HEPA), which can identify genes relatively uniquely expressed in cancer cells in contrast to normal somatic tissues. Rating human genes by their HEPA score enriched for clinically useful TSA genes, nominating candidate targets whose tumor-specific expression was verified by reverse transcription PCR (RT-PCR). Coupled with HEPA, we designed a novel assay termed protein A/G-based reverse serological evaluation (PARSE) for quick detection of serum autoantibodies against an array of putative TSA genes. Remarkably, highly tumor-specific autoantibody responses against seven candidate targets were detected in 4% to 11% of patients, resulting in distinctive autoantibody signatures in lung and stomach cancers. Interrogation of a larger cohort of 149 patients and 123 healthy individuals validated the predictive value of the autoantibody signature for lung cancer. Together, our results establish an integrated technology to uncover a cancer-specific antigen genome offering a reservoir of novel immunologic and clinical targets.

Vaccines for melanoma and renal cell carcinoma

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

IL-13 receptor-directed cancer vaccines and immunotherapy

Many immunotherapy approaches including therapeutic cancer vaccines targeting specific tumor-associated antigens are at various stages of development. Although the significance of overexpression of (IL-13Rα2) in cancer is being actively investigated, we have reported that IL-13Rα2 is a novel tumor-associated antigen. The IL-13Rα2-directed cancer vaccine is one of the most promising approaches to tumor immunotherapy, because of the selective expression of IL-13Rα2 in various solid tumor types but not in normal tissues. In this article, we will summarize its present status and potential strategies to improve IL-13Rα2-directed cancer vaccines for an optimal therapy 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.

Therapeutic cancer vaccines: are we there yet?

Enthusiasm for therapeutic cancer vaccines has been rejuvenated with the recent completion of several large, randomized phase III clinical trials that in some cases have reported an improvement in progression free or overall survival. However, an honest appraisal of their efficacy reveals modest clinical benefit and a frequent requirement for patients with relatively indolent cancers and minimal or no measurable disease. Experience with adoptive cell transfer-based immunotherapies unequivocally establishes that T cells can mediate durable complete responses, even in the setting of advanced metastatic disease. Further, these findings reveal that the successful vaccines of the future must confront: (i) a corrupted tumor microenvironment containing regulatory T cells and aberrantly matured myeloid cells, (ii) a tumor-specific T-cell repertoire that is prone to immunologic exhaustion and senescence, and (iii) highly mutable tumor targets capable of antigen loss and immune evasion. Future progress may come from innovations in the development of selective preparative regimens that eliminate or neutralize suppressive cellular populations, more effective immunologic adjuvants, and further refinement of agents capable of antagonizing immune check-point blockade pathways.

DNA vaccination: using the patient's immune system to overcome cancer

Cancer is one of the most challenging diseases of today. Optimization of standard treatment protocols consisting of the main columns of chemo- and radiotherapy followed or preceded by surgical intervention is often limited by toxic side effects and induction of concomitant malignancies and/or development of resistant mechanisms. This requires the development of therapeutic strategies which are as effective as standard therapies but permit the patients a life without severe negative side effects. Along this line, the development of immunotherapy in general and the innovative concept of DNA vaccination in particular may provide a venue to achieve this goal. Using the patient's own immune system by activation of humoral and cellular immune responses to target the cancer cells has shown first promising results in clinical trials and may allow reduced toxicity standard therapy regimen in the future. The main challenge of this concept is to transfer the plethora of convincing preclinical and early clinical results to an effective treatment of patients.

Interleukin-13 receptor α2 DNA prime boost vaccine induces tumor immunity in murine tumor models

Background

DNA vaccines represent an attractive approach for cancer treatment by inducing active T cell and B cell immune responses to tumor antigens. Previous studies have shown that interleukin-13 receptor α2 chain (IL-13Rα2), a tumor-associated antigen is a promising target for cancer immunotherapy as high levels of IL-13Rα2 are expressed on a variety of human tumors. To enhance the effectiveness of DNA vaccine, we used extracellular domain of IL-13Rα2 (ECDα2) as a protein-boost against murine tumor models.

Methods

We have developed murine models of tumors naturally expressing IL-13Rα2 (MCA304 sarcoma, 4T1 breast carcinoma) and D5 melanoma tumors transfected with human IL-13Rα2 in syngeneic mice and examined the antitumor activity of DNA vaccine expressing IL-13Rα2 gene with or without ECDα2 protein mixed with CpG and IFA adjuvants as a boost vaccine.

Results

Mice receiving IL-13Rα2 DNA vaccine boosted with ECDα2 protein were superior in exhibiting inhibition of tumor growth, compared to mice receiving DNA vaccine alone, in both prophylactic and therapeutic vaccine settings. In addition, prime-boost vaccination significantly prolonged the survival of mice compared to DNA vaccine alone. Furthermore, ECDα2 booster vaccination increased IFN-γ production and CTL activity against tumor expressing IL-13Rα2. The immunohistochemical analysis showed the infiltration of CD4 and CD8 positive T cells and IFN-γ-induced chemokines (CXCL9 and CXCL10) in regressing tumors of immunized mice. Finally, the prime boost strategy was able to reduce immunosuppressive CD4⁺CD25⁺Foxp3⁺ regulatory T cells (Tregs) in the spleen and tumor of vaccinated mice.

Conclusion

These results suggest that immunization with IL-13Rα2 DNA vaccine followed by ECDα2 boost mixed with CpG and IFA adjuvants inhibits tumor growth in T cell dependent manner. Thus our results show an enhancement of efficacy of IL-13Rα2 DNA vaccine with ECDα2 protein boost and offers an exciting approach in the development of new DNA vaccine targeting IL-13Rα2 for cancer immunotherapy.

Lentiviral vectors for immunization: an inflammatory field

Lentiviruses are retroviruses that are able to transduce both dividing and nondividing cells. Dendritic cells are key players in the innate and adaptive immune responses, and are natural targets for lentiviruses. Lentiviral vectors (LVs) have recently reached the clinical gene therapy arena, prompting their use as clinical vaccines. In recent years, LVs have emerged as a robust and practical experimental platform for gene delivery and rational genetic reprogramming of dendritic cells. Here, we present the status quo of the LV system for protective or therapeutic vaccine development. This vector system has been extensively evaluated for ex vivo and in vivo (immuno)gene delivery. Improvements of the LV design in order to further grant a higher biosafety profile for vaccine development are presented.

Novel therapeutics for the treatment of metastatic melanoma

Metastatic malignant melanoma is an incurable disease with a median survival of 8.5 months and a probability of surviving 5 years after the diagnosis of less than 5%. To date, no systemic therapy has meaningfully changed these survival end points. Currently, in the USA the FDA has approved three agents for the treatment of metastatic melanoma: hydroxyurea, dacarbazine and interleukin-2. None of these have demonstrated a meaningfully prolonged survival of patients with metastatic melanoma. Therefore, a number of innovative therapeutic strategies have been pursued to improve outcomes, including immune therapy, tyrosine kinase inhibitors and angiogenesis inhibitors. Herein, we review some of the recent advances in novel therapeutic developments for the treatment of metastatic melanoma.

Vesicular stomatitis virus as a novel cancer vaccine vector to prime antitumor immunity amenable to rapid boosting with adenovirus

Vesicular stomatitis virus (VSV) has proven to be an effective vaccine vector for immunization against viral infection, but its potential to induce an immune response to a self-tumor antigen has not been investigated. We constructed a recombinant VSV expressing human dopachrome tautomerase (hDCT) and evaluated its immunogenicity in a murine melanoma model. Intranasal delivery of VSV-hDCT activated both CD4(+) and CD8(+) DCT-specific T-cell responses. The magnitude of these responses could be significantly increased by booster immunization with recombinant adenovirus (Ad)-hDCT, which led to enhanced efficacy against B16-F10 melanoma in both prophylactic and therapeutic settings. Notably, the interval of VSV/Ad heterologous vaccination could be shortened to as few as 4 days, making it a potential regimen to rapidly expand antigen-specific effector cells. Furthermore, VSV-hDCT could increase DCT-specific T-cell responses primed by Ad-hDCT, suggesting VSV is efficient for both priming and boosting of the immune response against a self-tumor antigen.

Melanoma vaccines

Over the last century, vaccine studies have demonstrated that the human immune system, with appropriate help, can limit or prevent infection against otherwise lethal pathogens. Encouraged by these results, success in animal models and numerous well-documented reports of immune-mediated melanoma regression in humans, investigators developed melanoma vaccines. However, despite considerable laboratory evidence for vaccine-induced immune responses, clinical responses remain poor. Recent studies have elucidated several mechanisms that hinder or prevent the creation of successful vaccines and suggest novel approaches to overcome these barriers. Unraveling the mechanisms of autoimmunity, dendritic cell activation, regulatory T cells and Toll-like receptors will generate novel vaccines that, when used in conjunction with standard adjuvant therapies, may result in improved clinical outcomes. The objective of this review is to provide an overall summary of recent clinical trials with melanoma vaccines and highlight novel vaccine strategies to evaluate in the near future.

Delivery strategies of melanoma vaccines: an overview

For many years, various cancer vaccines have been widely evaluated, however clinical responses remain rare. In this review, we attempt to address the question of which delivery strategies and platforms are feasible to produce clinical response and define the characteristics of the strategy that will induce long-lasting antitumor response. We limit our analysis and discussion to microparticles/nanoparticles, liposomes, heat-shock proteins, viral vectors and different types of adjuvants. This review aims to provide an overview of the specific characteristics, strengths and limitations of these delivery systems, focusing on their impacts on the development of melanoma vaccine. To date, only adoptive T-cell transfer has shown promising clinical outcomes compared to other treatments.

Recombinant fowlpox virus elicits transient cytotoxic T cell responses due to suboptimal innate recognition and recruitment of T cell help

Recombinant fowlpox viruses (FPVs) have been used in a variety of vaccine strategies; however strong data clearly demonstrating the characteristics of the strength and nature of the resultant immune response elicited by these vectors are lacking. By utilising a recombinant variant of FPV which expresses the nominal antigen chicken ovalbumin (OVA), and assessing innate FPV- and OVA-specific adaptive immune responses, we show that recombinant FPV induces a rapid type I interferon (IFN) response, mediated primarily by plasmacytoid dendritic cells (pDCs). These cells are necessary for the development of a strong but transient CD8(+) T cell effector response directed against OVA-expressing target cells. We propose that a combination of suboptimal type I IFN production, poor CD4(+) T cell helper function and inefficient DC licensing likely contribute to this transient response. These findings now provide a sound basis for rational modifications to be made to recombinant FPV, designed to improve subsequent vaccine responses.

Melanoma cancer vaccines and anti-tumor T cell responses

Melanoma is a disease which has been shown to be responsive to immune intervention. This has been suggested by reports of spontaneous responses of metastatic disease with strong immune infiltrates, and supported by recent data correlating clinical response after IFNalpha treatment with development of generalized autoimmunity. Since the identification of melanoma-associated tumor antigens, many groups have performed clinical trials to take advantage of this discovery with melanoma-specific cancer vaccines. These trials, in which multiple antigen delivery strategies have been tested in hundreds of patients, have demonstrated that these vaccines are safe, immunogenic, and yield a low frequency of objective clinical responses. The ability to perform careful immunological monitoring has allowed important insights into the nature of the anti-tumor immunity generated by these vaccinations. While many trials have found that the absolute frequency of T cells specific for a vaccine-encoded antigen are a marker of immunization, it does not correlate with objective clinical response. Induction of broad immunity to multiple tumor antigens, taking advantage of cross-reactive T cells and activation of persistent T cells may be more important. Harnessing additional modes of amplifying immune responses (lymphodepletion, cytokine support, inhibition of negative immune self-regulation) are now being tested and should improve clinical responses from 5% to 10% complete response seen currently.

Comparative prime-boost vaccinations using Semliki Forest virus, adenovirus, and ALVAC vectors demonstrate differences in the generation of a protective central memory CTL response against the P815 tumor

Tumor-specific Ags are potential target molecules in the therapeutic treatment of cancer. One way to elicit potent immune responses against these Ags is to use recombinant viruses, which activate both the innate and the adaptive arms of the immune system. In this study, we have compared Semliki Forest virus (SFV), adenovirus, and ALVAC (poxvirus) vectors for their capacity to induce CD8(+) T cell responses against the P1A tumor Ag and to elicit protection against subsequent challenge injection of P1A-expressing P815 tumor cells in DBA/2 mice. Both homologous and heterologous prime-boost regimens were studied. In most cases, both higher CD8(+) T cell responses and better tumor protections were observed in mice immunized with heterologous prime-boost regimens, suggesting that the combination of different viral vectors is beneficial for the induction of an effective immune response. However, homologous immunization with SFV provided potent tumor protection despite a rather moderate primary CD8(+) T cell response as compared with mice immunized with recombinant adenovirus. SFV-immunized mice showed a rapid and more extensive expansion of P1A-specific CD8(+) T cells in the tumor-draining lymph node after tumor challenge and had a higher frequency of CD62L(+) P1A-specific T cells in the blood, spleen, and lymph nodes as compared with adenoimmunized mice. Our results indicate that not only the magnitude but in particular the quality of the CD8(+) T cell response correlates with tumor protection.

Vaccine therapy for melanoma: current status and future directions

A vaccine is typically defined as any preparation used as a preventive inoculation to confer immunity against a specific disease. Vaccines for infectious diseases are highly effective, acting by inducing antigen-specific immunity that prevents subsequent infection. Unfortunately, the success of vaccines in infectious diseases has not been mirrored in oncology. This failure is the result of several challenges facing cancer vaccines, including the conceptual shift from disease prevention to disease treatment, tumor-induced immunosuppression and other mechanisms of immune escape, the similarity between tumor antigens and self antigens to which the patient is tolerant, unfavorable effector-to-target ratios in patients with established tumors, and financial and regulatory issues. Despite this, cancer remains a promising target for vaccine therapy. Melanoma in particular is known for its inherent immunogenicity on the basis of many anecdotal reports of spontaneous immune-based tumor regression, and thus has been the focus of immunotherapeutic approaches. Rare but significant vaccine-induced clinical regression of melanoma has spurred intensive investigations to augment vaccine efficacy. This review explores the many vaccine strategies that have been clinically tested for the treatment of melanoma and considers future approaches of cancer immunotherapy.

Plasmid DNA and viral vector-based vaccines for the treatment of cancer

Plasmid DNA and viral vector-based cancer vaccines have many inherent features that make them promising cancer vaccine candidates. This review focuses on the use of plasmid DNA and viral vector vaccines to deliver tumour-specific antigens to induce a tumour-specific immune response. Examples of different antigen delivery systems that have been tested in recent clinical trials are summarised and advantages and disadvantages of a number of delivery systems and approaches are discussed. Finally, an outlook on how plasmid DNA and viral vectors might be developed further as cancer vaccines is provided.

Recent Advances and Current Challenges in Tumor Immunology and Immunotherapy

Despite advances in animal studies, where the cure of the majority of mice with pre-established (albeit early-stage) tumors has become almost standard, human clinical trials have been much less successful. Here we describe some of the most recent advances in the specialist field of tumor immunology and immunotherapy, highlighting salient work to identify key problem areas and potential solutions. We make particular note of recent developments in adoptive therapy; whole-cell, DNA, and peptide vaccines; and antibody therapy. We also describe the revival of interest in regulatory T cells and conclude by detailing the need for clinical trial read-out autonomy and methods to predict which patients will respond to a particular treatment.

Immunotherapy of melanoma: a critical review of current concepts and future strategies

Advanced melanoma is a devastating disease with a very poor overall prognosis. There are only two agents that are approved by the FDA for use in patients with metastatic melanoma: dacarbazine and IL-2. Both agents have an overall response rate well below 20%, with only rare long-term responders noted. Metastatic melanoma is known to be one of the most resistant cancers to a plethora of treatment modalities, such as single-agent and combination chemotherapy, chemoimmunotherapy and immunotherapy with a host of immune stimulators. Indeed, researchers worldwide have recognized the lack of effective therapies and have refocused their efforts on developing novel and cutting-edge strategies of treatment. This is based on an improved understanding of the complex interactions that occur within the tumor microenvironment, and the central role that the host immune system plays in the surveillance of cancer. This review summarizes the recent results of novel immunotherapeutic regimens and focuses on cutting-edge modalities of treatment that encompass new lines of thinking in the war against cancer and, in particular, melanoma.