Dendritic cells reconstituted with human telomerase gene induce potent cytotoxic T-cell response against different types of tumors

Targeting Telomere Dynamics as an Effective Approach for the Development of Cancer Therapeutics

Telomere is a protective structure located at the end of chromosomes of eukaryotes, involved in maintaining the integrity and stability of the genome. Telomeres play an essential role in cancer progression; accordingly, targeting telomere dynamics emerges as an effective approach for the development of cancer therapeutics. Targeting telomere dynamics may work through multifaceted molecular mechanisms; those include the activation of anti-telomerase immune responses, shortening of telomere lengths, induction of telomere dysfunction and constitution of telomerase-responsive drug release systems. In this review, we summarize a wide variety of telomere dynamics-targeted agents in preclinical studies and clinical trials, and reveal their promising therapeutic potential in cancer therapy. As shown, telomere dynamics-active agents are effective as anti-cancer chemotherapeutics and immunotherapeutics. Notably, these agents may display efficacy against cancer stem cells, reducing cancer stem levels. Furthermore, these agents can be integrated with the capability of tumor-specific drug delivery by the constitution of related nanoparticles, antibody drug conjugates and HSA-based drugs.

Telomerase-based Cancer Therapeutics: A Review on their Clinical Trials

Telomeres are protective chromosomal ends that shield the chromosomes from DNA damage, exonucleolytic degradation, recombination, and end-to-end fusion. Telomerase is a ribonucleoprotein that adds TTAGGG tandem repeats to the telomeric ends. It has been observed that 85 to 90% of human tumors express high levels of telomerase, playing a crucial role in the development of cancers. Interestingly, the telomerase activity is generally absent in normal somatic cells. This selective telomerase expression has driven scientists to develop novel anti-cancer therapeutics with high specificity and potency. Several advancements have been made in this area, which is reflected by the enormous success of the anticancer agent Imetelstat. Since the discovery of Imetelstat, several research groups have contributed to enrich the therapeutic arsenal against cancer. Such contributions include the application of new classes of small molecules, peptides, and hTERT-based immunotherapeutic agents (p540, GV1001, GRNVAC1 or combinations of these such as Vx-001). Many of these therapeutic tools are under different stages of clinical trials and have shown promising outcomes. In this review, we highlight the current status of telomerase-based cancer therapeutics and the outcome of these investigations.

Anti-cancer Immunotherapies Targeting Telomerase

Telomerase is a reverse transcriptase that maintains telomeres length, compensating for the attrition of chromosomal ends that occurs during each replication cycle. Telomerase is expressed in germ cells and stem cells, whereas it is virtually undetectable in adult somatic cells. On the other hand, telomerase is broadly expressed in the majority of human tumors playing a crucial role in the replicative behavior and immortality of cancer cells. Several studies have demonstrated that telomerase-derived peptides are able to bind to HLA (human leukocyte antigen) class I and class II molecules and effectively activate both CD8⁺ and CD4⁺ T cells subsets. Due to its broad and selective expression in cancer cells and its significant immunogenicity, telomerase is considered an ideal universal tumor-associated antigen, and consequently, a very attractive target for anti-cancer immunotherapy. To date, different telomerase targeting immunotherapies have been studied in pre-clinical and clinical settings, these approaches include peptide vaccination and cell-based vaccination. The objective of this review paper is to discuss the role of human telomerase in cancer immunotherapy analyzing recent developments and future perspectives in this field.

Role of Telomeres and Telomeric Proteins in Human Malignancies and Their Therapeutic Potential

Telomeres are the ends of linear chromosomes comprised of repetitive nucleotide sequences in humans. Telomeres preserve chromosomal stability and genomic integrity. Telomere length shortens with every cell division in somatic cells, eventually resulting in replicative senescence once telomere length becomes critically short. Telomere shortening can be overcome by telomerase enzyme activity that is undetectable in somatic cells, while being active in germline cells, stem cells, and immune cells. Telomeres are bound by a shelterin complex that regulates telomere lengthening as well as protects them from being identified as DNA damage sites. Telomeres are transcribed by RNA polymerase II, and generate a long noncoding RNA called telomeric repeat-containing RNA (TERRA), which plays a key role in regulating subtelomeric gene expression. Replicative immortality and genome instability are hallmarks of cancer and to attain them cancer cells exploit telomere maintenance and telomere protection mechanisms. Thus, understanding the role of telomeres and their associated proteins in cancer initiation, progression and treatment is very important. The present review highlights the critical role of various telomeric components with recently established functions in cancer. Further, current strategies to target various telomeric components including human telomerase reverse transcriptase (hTERT) as a therapeutic approach in human malignancies are discussed.

Aspergillus fumigatus Challenged by Human Dendritic Cells: Metabolic and Regulatory Pathway Responses Testify a Tight Battle

Dendritic cells (DCs) are antigen presenting cells which serve as a passage between the innate and the acquired immunity. Aspergillosis is a major lethal condition in immunocompromised patients caused by the adaptable saprophytic fungus Aspergillus fumigatus. The healthy human immune system is capable to ward off A. fumigatus infections however immune-deficient patients are highly vulnerable to invasive aspergillosis. A. fumigatus can persist during infection due to its ability to survive the immune response of human DCs. Therefore, the study of the metabolism specific to the context of infection may allow us to gain insight into the adaptation strategies of both the pathogen and the immune cells. We established a metabolic model of A. fumigatus central metabolism during infection of DCs and calculated the metabolic pathway (elementary modes; EMs). Transcriptome data were used to identify pathways activated when A. fumigatus is challenged with DCs. In particular, amino acid metabolic pathways, alternative carbon metabolic pathways and stress regulating enzymes were found to be active. Metabolic flux modeling identified further active enzymes such as alcohol dehydrogenase, inositol oxygenase and GTP cyclohydrolase participating in different stress responses in A. fumigatus. These were further validated by qRT-PCR from RNA extracted under these different conditions. For DCs, we outlined the activation of metabolic pathways in response to the confrontation with A. fumigatus. We found the fatty acid metabolism plays a crucial role, along with other metabolic changes. The gene expression data and their analysis illuminate additional regulatory pathways activated in the DCs apart from interleukin regulation. In particular, Toll-like receptor signaling, NOD-like receptor signaling and RIG-I-like receptor signaling were active pathways. Moreover, we identified subnetworks and several novel key regulators such as UBC, EGFR, and CUL3 of DCs to be activated in response to A. fumigatus. In conclusion, we analyze the metabolic and regulatory responses of A. fumigatus and DCs when confronted with each other.

Telomerase-Targeted Cancer Immunotherapy

Telomerase, an enzyme responsible for the synthesis of telomeres, is activated in many cancer cells and is involved in the maintenance of telomeres. The activity of telomerase allows cancer cells to replicate and proliferate in an uncontrolled manner, to infiltrate tissue, and to metastasize to distant organs. Studies to date have examined the mechanisms involved in the survival of cancer cells as targets for cancer therapeutics. These efforts led to the development of telomerase inhibitors as anticancer drugs, drugs targeting telomere DNA, viral vectors carrying a promoter for human telomerase reverse transcriptase (hTERT) genome, and immunotherapy targeting hTERT. Among these novel therapeutics, this review focuses on immunotherapy targeting hTERT and discusses the current evidence and future perspectives.

Human Papillomavirus E2 Regulates SRSF3 (SRp20) To Promote Capsid Protein Expression in Infected Differentiated Keratinocytes

The human papillomavirus (HPV) life cycle is tightly linked to differentiation of the infected epithelial cell, suggesting a sophisticated interplay between host cell metabolism and virus replication. Previously, we demonstrated in differentiated keratinocytes in vitro and in vivo that HPV type 16 (HPV16) infection caused increased levels of the cellular SR splicing factors (SRSFs) SRSF1 (ASF/SF2), SRSF2 (SC35), and SRSF3 (SRp20). Moreover, the viral E2 transcription and replication factor that is expressed at high levels in differentiating keratinocytes could bind and control activity of the SRSF1 gene promoter. Here, we show that the E2 proteins of HPV16 and HPV31 control the expression of SRSFs 1, 2, and 3 in a differentiation-dependent manner. E2 has the greatest transactivation effect on expression of SRSF3. Small interfering RNA depletion experiments in two different models of the HPV16 life cycle (W12E and NIKS16) and one model of the HPV31 life cycle (CIN612-9E) revealed that only SRSF3 contributed significantly to regulation of late events in the virus life cycle. Increased levels of SRSF3 are required for L1 mRNA and capsid protein expression. Capsid protein expression was regulated specifically by SRSF3 and appeared independent of other SRSFs. Taken together, these data suggest a significant role of the HPV E2 protein in regulating late events in the HPV life cycle through transcriptional regulation of SRSF3 expression.

IMPORTANCE

Human papillomavirus replication is accomplished in concert with differentiation of the infected epithelium. Virus capsid protein expression is confined to the upper epithelial layers so as to avoid immune detection. In this study, we demonstrate that the viral E2 transcription factor activates the promoter of the cellular SRSF3 RNA processing factor. SRSF3 is required for expression of the E4(^)L1 mRNA and so controls expression of the HPV L1 capsid protein. Thus, we reveal a new dimension of virus-host interaction crucial for production of infectious virus. SRSF proteins are known drug targets. Therefore, this study provides an excellent basis for developing strategies to regulate capsid protein production in the infected epithelium and the production of new virions.

Extending the lifespan and efficacies of immune cells used in adoptive transfer for cancer immunotherapies-A review

Cells used in adoptive cell-transfer immunotherapies against cancer include dendritic cells (DCs), natural-killer cells, and CD8⁺ T-cells. These cells may have limited efficacy due to their lifespan, activity, and immunosuppressive effects of tumor cells. Therefore, increasing longevity and activity of these cells may boost their efficacy. Four cytokines that can extend immune effector-cell longevity are IL-2, IL-7, IL-21, and IL-15. This review will discuss current knowledge on effector-cell lifespans and the mechanisms by which IL-2, IL-7, IL-15, and IL-21 can extend effector-cell longevity. We will also discuss how lifespan and efficacy of these cells can be regulated to allow optimal clinical benefits.

Cancer immunotherapy using virally transduced dendritic cells: animal studies and human clinical trials

The immune system uses a process known as 'immunosurveillance' to help prevent the outgrowth of tumors. In cancer immunotherapy, a major goal is for immunity against tumor-associated antigens to be generated or strengthened in patients. To achieve this goal, several approaches have been tested, including the use of highly potent antigen-presenting cells called dendritic cells (DCs), which can activate T cells efficiently. Presentation of peptides derived from tumor antigens on the surface of DCs can stimulate strong antitumor immunity. Using recombinant viral vectors encoding tumor-associated antigens, DCs can be engineered efficiently to express sustained levels of tumor-antigen peptides. This review discusses the effectiveness of virally transduced DCs in treating tumors and generating antigen-specific T-cell responses. It covers mouse and nonhuman primate studies, preclinical in vitro human cell experiments and clinical trials.

Modification of human embryonic stem cell-derived dendritic cells with mRNA for efficient antigen presentation and enhanced potency

AIM

Dendritic cell (DC)-based vaccines are designed to exploit the intrinsic capacity of these highly effective antigen presenting cells to prime and boost antigen-specific T-cell immune responses. Successful development of DC-based vaccines will be dependent on the ability to utilize and harness the full potential of these potent immune stimulatory cells. Recent advances to generate DCs derived from human embryonic stem cells (hESCs) that are suitable for clinical use represent an alternative strategy from conventional approaches of using patient-specific DCs. Although the differentiation of hESC-derived DCs in serum-free defined conditions has been established, the stimulatory potential of these hESC-derived DCs have not been fully evaluated.

METHODS

hESC-derived DCs were differentiated in serum-free defined culture conditions. The delivery of antigen into hESC-derived DCs was investigated using mRNA transfection and replication-deficient adenoviral vector transduction. hESC-derived DCs modified with antigen were evaluated for their capacity to stimulate antigen-specific T-cell responses with known HLA matching. Since IL-12 is a key cytokine that drives T-cell function, further enhancement of DC potency was evaluated by transfecting mRNA encoding the IL-12p70 protein into hESC-derived DCs.

RESULTS

The transfection of mRNA into hESC-derived DCs was effective for heterologous protein expression. The efficiency of adenoviral vector transduction into hESC-derived DCs was poor. These mRNA-transfected DCs were capable of stimulating human telomerase reverse transcriptase antigen-specific T cells composed of varying degrees of HLA matching. In addition, we observed the transfection of mRNA encoding IL-12p70 enhanced the T-cell stimulation potency of hESC-derived DCs.

CONCLUSION

These data provide support for the development and modification of hESC-derived DCs with mRNA as a potential strategy for the induction of T-cell-mediated immunity.

Genome-wide transcriptome profile of the human osteosarcoma Sa OS and U-2 OS cell lines

With the use of genome-wide cDNA microarrays, we investigated the transcriptome profile of the human osteosarcoma Sa OS and U-2 OS cell lines. In all, 1,098 chip entries were differentially regulated in the two cell lines; of these, 796 entries corresponded to characterized mRNAs. The identified genes are mostly expressed in epithelial tissues and localize on chromosomes 1, 10, and 20. Furthermore, signaling cascades for cell cycle, glycolysis, and gluconeogenesis, the p53 pathway, cell communication, and focal adhesion were found to be differently regulated in the two cell lines. The transcriptome profiles reported here provide novel information about the considerable molecular differences between these two widely used human osteosarcoma cell lines.

Ex vivo expanded telomerase-specific T cells are effective in an orthotopic mouse model for pancreatic adenocarcinoma

Telomerase activity is over-expressed in nearly all pancreatic carcinomas, but not in chronic pancreatitis. Here, we investigated various protocols for expansion of telomerase-specific T cells for adoptive cell transfer and their use in a syngeneic pancreatic carcinoma mouse model. Telomerase-specific T cells were generated by stimulation of splenocytes from peptide-immunized donor mice with either interleukin (IL)-2, IL-15, artificial antigen-presenting cells, anti-signalling lymphocyte activation molecule (SLAM) microbeads or allogeneic dendritic cells in combination with a limited dilution assay. T cells were tested for antigen specificity in vitro and for anti-tumour activity in syngeneic mice with orthotopically implanted tumours pretreated with cyclophosphamide. The immune cells from recipients were immunophenotyped. During a period of 2 weeks, the expansion approach using IL-2 was very successful in generating a high number of telomerase-specific CD8(+) T cells without losing their function after adoptive cell transfer. Significantly slower tumour growth rate and less metastasis were observed after adoptively transferring telomerase specific CD8(+) T cells, expanded using IL-2. Further investigations showed that anti-tumour efficacy was associated with a significant shift from naive CD8(+) T cells to CD8(+) central memory T cells, as well as recruitment of a high number of dendritic cells. Remarkable amounts of telomerase-specific T cells were detectable in the tumour. Generation of telomerase-specific T cells is feasible, whereat IL-2-based protocols seemed to be most effective and efficient. Antigen-specific T cells showed significant cytotoxic activity in a syngeneic, orthotopic mouse model, whereas central memory T cells but not effector memory T cells appear to be of high importance.

A three-plasmid system for construction of armed oncolytic adenovirus

There is growing interest in the use of oncolytic virus as a tool in cancer gene therapy. However, construction of oncolytic adenovirus (Ad) is not an easy task due to lack of convenient, robust methods. A three-plasmid system was introduced for construction of armed oncolytic Ad. Besides the pShuttle-CMV and pAdEasy-1, a third plasmid (pTE-ME1), harboring the E1 region of Ad5, was generated and included in this system. In pTE-ME1, the promoter of E1A was deleted and replaced with a multiple-cloning site (MCS). A therapeutic gene and tissue-specific promoter (TSP) could be inserted routinely into the MCS of pShuttle-CMV and pTE-ME1, respectively. The modified E1 region could then be excised from pTE-ME1 and integrated into the therapeutic gene-containing pShuttle-CMV to form the final shuttle plasmid. This shuttle plasmid was recombined with pAdEasy-1 in Escherichia coli strain BJ5183 to generate Ad plasmid. Finally, the oncolytic Ad could be rescued in Ad plasmid-transfected packaging cells. The GFP gene and the promoter of telomerase reverse transcriptase (TERTp) were chosen as the transgene and TSP, respectively, to test this system. Two oncolytic Ads, Ad-GFP-TPE and Ad-GFP-D19K, were generated successfully. Their oncolytic and replicating abilities were investigated in TERT-positive tumor cells. The results suggest that the three-plasmid system was practicable and could be used to construct other transcriptionally regulated oncolytic Ads carrying a therapeutic gene.

Induction of anti-tumour immunity by dendritic cells transduced with hTERT recombinant adenovirus in mice

Dendritic cells (DCs) transfected with recombinant, replication-defective adenovirus (Ad) vectors encoding the human telomerase reverse transcriptase (hTERT) are potent inducers of cytotoxic T lymphocytes (CTLs) and anti-tumour immunity. However, previous studies have mostly been in vitro. In this study, we sought to determine whether DCs transfected with hTERT (DC/Ad-hTERT) could elicit a potent anti-tumour immunogenic response in vivo. We found that murine DCs transfected with recombinant adenovirus encoding the hTERT gene (DC/Ad-hTERT) induced hTERT-specific CTLs in vivo effectively, compared with Ad-LacZ-transduced DC (DC/Ad-LacZ) controls. These hTERT-specific CTLs lysed various tumour cell lines in an hTERT-specific and MHC-I molecule-restricted fashion. We also found that DC/Ad-hTERT could increase antigen-specific T-cell proliferation and augment the number of IFN-gamma secreting T-cells in mice. These data suggest that the DC/Ad-hTERT vaccine may induce anti-tumour immunity against tumour cells expressing hTERT in an MHC-I molecule-restricted fashion in vivo through the augmentation of the hTERT-specific CTL response. The DC/Ad-hTERT vaccine may thus be used as an efficient DC-based tumour vaccine in clinical applications.

Transgene expression of alpha tumor necrosis factor with mutations D142N and A144R under control of human telomerase reverse transcriptase promoter eradicates well-established tumors and induces long-term antitumor immunity

Recombinant adenoviral vectors (AdVTNF-alpha) expressing alpha tumor necrosis factor (TNF-alpha) under control of cytomegalovirus (CMV) promoter have been used in cancer gene therapy. To reduce its cytotoxicity, we constructed a recombinant AdV(TERT)mTNF-alpha expressing a mutant TNF-alpha (mTNF-alpha) with mutations at D142N and A144R under control of human telomerase reverse transcriptase (hTERT) promoter for treatment of well-established ovalbumin (OVA)-expressing murine B16 melanoma (BL6-10(OVA)) (6 mm in diameter). We demonstrated that the mTNF-alpha with mutations at D142N and A144R has less in vitro cytotoxicity, but maintains its functional effect in the stimulation of T-cell proliferation. The in vitro and in vivo transgene expressions under control of hTERT promoter are highly restricted in tumor cells compared with those under the control of the CMV promoter. AdV(TERT)mTNF-alpha gene therapy by intratumoral injection of AdV(TERT)mTNF-alpha vector (2 x 10(9) PFU) expressing the mutant mTNF-alpha under control of hTERT promoter reduces its in vivo toxicity, eradicates well-established BL6-10(OVA) tumors in 4/10 tumor-bearing mice, and induces OVA-specific CD8(+) T-cell-mediated long-term antitumor immunity. Therefore, AdV(TERT)mTNF-alpha gene therapy may be very useful in the immunotherapy of cancer.

A simplified system for generating oncolytic adenovirus vector carrying one or two transgenes

Oncolytic adenoviruses, also called conditionally replicating adenoviruses (CRADs), have been widely applied in cancer gene therapy. However, the construction of CRADs is still time-consuming. In this study, we attempted to establish a simplified method of generating CRADs based on AdEasy system. A novel plasmid pTE-TPE-GM was constructed, containing sequentially positioned promoter of telomerase reverse transcriptase (TERTp), coding sequence of E1A gene, promoter of E1B gene, granulocyte-macrophage colony-stimulating factor (GM-CSF) gene, internal ribosome entry site sequence and coding sequence of E1B55K gene. The CRAD-generating system reported here include three plasmids: pTE-TPE-GM, pShuttle-CMV and AdEasy-1, one Escherichia coli strain BJ5183, and the packaging cell line 293. Using this system, an oncolytic adenovirus carrying B7-1 (CD80) and GM-CSF genes was successfully constructed and designated as Ad-CD80-TPE-GM. The expression of GM-CSF increased more than 9000 times in tumor cell lines infected by Ad-CD80-TPE-GM at a multiplicity of infection (MOI) of 5, compared with the cells infected by replication-defective control virus. Similarly, the expression of CD80 also increased 9-140 times. Ad-CD80-TPE-GM selectively replicates in TERT-positive tumor cells, and the progeny viruses can reach up to 375 infection units (IU) per cell. In vitro study showed that the Ad-CD80-TPE-GM induced an obvious oncolytic effect at MOI of 0.1, and killed about 80% TERT-positive tumor cells within 7 days at an MOI of 1. The antitumor effect of this vector was also investigated in Hep2 xenograft model of nude mice, and the tumor inhibition rate reached 74% at day 30 after the administration with a total dose of 1 x 10(9) IU Ad-CD80-TPE-GM. Intratumoral injection of Ad-CD80-TPE-GM slightly induced neutralizing antibody against the oncolytic adenovirus in nude mice, which might contribute to the virus clearance in vivo. In conclusion, we successfully constructed an oncolytic CRAD carrying GM-CSF and CD80 gene. More importantly, this system can be modified to generate novel transcriptionally regulated CRADs with different tissue-specific promoters or transgenes.

Characterization of primary renal carcinoma cultures

PURPOSE

For a better understanding of the factors contributing to tumor progression in metastatic renal cell carcinoma and to identify possible targets for immunotherapeutic approaches, we characterized several primary cultures from renal cell carcinoma.

MATERIALS AND METHODS

Cell cultures were tested for activity of telomerase, secretion of immunosuppressive cytokines and others. The induction of cytotoxic activity against the autologous tumor was tested in a cytotoxicity assay after coculture of immunological effector cells with antigen-pulsed dendritic cells. The data were tested for influence on survival.

RESULTS

We were able to establish primary cell cultures from 58 patients with renal cell carcinoma and their metastasis. 48/58 were positive for telomerase activity and all secreted IL-6, TGF-beta, VEGF and IL-8. High TGF-beta secretion, the activity of telomerase and the induction of a telomerase-specific immune response against telomerase peptides in telomerase-positive tumors had a significant impact on survival.

CONCLUSION

TGF-beta secretion, activity of telomerase in telomerase-positive tumors and the ability to generate a telomerase-specific immune response might serve as a prognostic marker for RCC. New approaches might focus on attacking the TGF-beta pathway and on induction of telomerase-specific immune cells.

Synergistic activation of extracellular signal-regulated kinase in human dermal fibroblasts by human telomerase reverse transcriptase and transforming growth factor-beta1

BACKGROUND

Human telomerase reverse transcriptase (hTERT) is primarily known for its ability to elongate telomeres for maintaining chromosomal integrity and delaying cellular senescence. Recently, hTERT has emerged as having a role in promoting cellular proliferation that is independent of telomere elongation. How hTERT elicits this novel function is a fundamental question in cell biology. Understanding this question may have therapeutic implications in regenerative medicine for patients with damaged organs or tissues, cardiovascular disorders, stroke, ischemic chronic wounds, and other ischemia-reperfusion injuries. Toward this end, we treated hTERT-transfected human dermal fibroblasts (HDFs) with transforming growth factor (TGF)-beta1 and investigated the activation of extracellular signal-regulated kinase (ERK) 1/2, vital mediators of cell proliferation.

MATERIALS AND METHODS

Primary HDFs were transfected with either recombinant adenovirus expressing hTERT (Ad-hTERT) or control adenovirus (Ad-NULL) and subsequently treated with TGF-beta1 (2 pg/mL). ERK 1/2 activation was determined by Western blotting using an antibody recognizing only activated ERK 1/2 that is dually phosphorylated at Thr(202) and Tyr(204). TGF-beta1, TGFbeta-RI, TGFbeta-RII, and Col1 A1 mRNA levels were analyzed by real-time PCR.

RESULTS

Ad-hTERT-transfected HDFs showed more than 7-fold up-regulation of phospho-ERK 1/2 over Ad-NULL-transfected HDFs upon TGF-beta1 treatment. The synergistic ERK 1/2 activation in Ad-hTERT-transfected HDFs occurred as early as 10 min and was sustained for at least 30 min after TGF-beta1 treatment. There were no statistically significant differences in TGF-beta1, TGFbeta-RI, TGFbeta-RII, and Col1 A1 mRNA levels between HDFs that were transfected with Ad-hTERT and those that were transfected with Ad-NULL after TGF-beta1 treatment.

CONCLUSIONS

hTERT and extremely low concentrations of TGF-beta1 (2 pg/mL) synergistically activate ERK 1/2 in HDFs by a mechanism that is independent of the autocrine TGF-beta1 loop.

Prospects and challenges of building a cancer vaccine targeting telomerase

Despite their origin from self-tissue, tumor cells can be immunogenic and trigger immune responses that can profoundly influence tumor growth and development. Clinically, it may be possible to amplify or induce anti-tumor immune responses to achieve tumor rejection in patients. Increasing data over the last 8 years suggest that the human telomerase reverse transcriptase hTERT is immunogenic both in vitro and in vivo and may be a suitable target for novel cancer immunotherapy. Peptides derived from hTERT are naturally processed by tumors and presented on MHC molecules and trigger effector functions of specific T lymphocytes. Vaccination of cancer patients against hTERT epitopes induces anti-tumor T cells without clinical toxicity. If second-generation vaccines and other strategies are able to generate optimal cellular immunity against hTERT without toxicity in humans, the possibility of broad-spectrum immunotherapy or even immunoprevention therapy of cancer may be possible.

Dendritic cells for active immunotherapy: optimizing design and manufacture in order to develop commercially and clinically viable products

Dendritic cell (DC) active immunotherapy is potentially efficacious in a broad array of malignant disease settings. However, challenges remain in optimizing DC-based therapy for maximum clinical efficacy within manufacturing processes that permit quality control and scale-up of consistent products. In this review we discuss the critical issues that must be addressed in order to optimize DC-based product design and manufacture, and highlight the DC based platforms currently addressing these issues. Variables in DC-based product design include the type of antigenic payload used, DC maturation steps and activation processes, and functional assays. Issues to consider in development include: (a) minimizing the invasiveness of patient biological material collection; (b) minimizing handling and manipulations of tissue at the clinical site; (c) centralized product manufacturing and standardized processing and capacity for commercial-scale production; (d) rapid product release turnaround time; (e) the ability to manufacture sufficient product from limited starting material; and (f) standardized release criteria for DC phenotype and function. Improvements in the design and manufacture of DC products have resulted in a handful of promising leads currently in clinical development.

Recent developments in the use of adenoviruses and immunotoxins in cancer gene therapy

Despite setbacks in the past and apparent hurdles ahead, gene therapy is advancing toward reality. The past several years have witnessed this new field of biomedicine developing rapidly both in breadth and depth, especially for the treatment of cancer, thanks largely to the better understanding of molecular and genetic basis of oncogenesis and the development of new and improved vectors and technologies for gene delivery and targeting. This article is intended to provide a brief review of recent advances in cancer gene therapy using adenoviruses, both as vectors and as oncolytic agents, and some of the recent progress in the development of immunotoxins for use in cancer gene therapy.

A novel peptide-nucleotide dual vaccine of human telomerase reverse transcriptase induces a potent cytotoxic T-cell response in vivo

Human telomerase reverse transcriptase (hTERT) is highly expressed in over 85% of human cancers, which makes it a broadly applicable molecular target for cancer therapy. Several groups have demonstrated that hTERT can efficiently evoke specific cytotoxic T lymphocytes (CTL) responses for malignant tumors. In the present study, we developed a novel virus-like particulate peptide-nucleotide dual vaccine (PNDV) of hTERT, which was composed of a low-affinity epitope variant with encoding full-length gene in the same virus-size particulate. We verified the formation of PNDV by DNA retarding assay, DNase I protection assay and transmission electron microscopy, and confirmed its immunogenicity and transfection activities in mammalian cells. Furthermore, in vivo immunization of HLA-A2.1 transgenic mice generated efficient IFN-gamma secretion and hTERT-specific CTLs which are known to cause selective cell death of telomerase positive gastrointestinal cancer cells. To our knowledge, this represents the first report on collocating a low-affinity epitope variant with a full-length hTERT gene for anti-cancer vaccine design. This novel strategy for vaccine design not only enables enhanced immunity to a universal tumor antigen, but also has the potential to generate CTLs effective in telomerase-positive tumor cells of diverse tissue origins. Therefore, our findings bear significant implications for immunotherapy of human cancers.

Evolving gene therapy approaches for osteosarcoma using viral vectors: review

This review begins with an introduction to the malignant bone tumor, osteosarcoma [OS] and then moves to a discussion of the commonly used vectors for gene transfer. We first briefly highlight non-viral vectors including polymeric and liposomal delivery systems but concentrate predominantly on the 5 leading viral vectors used in cancer gene therapy, specifically retroviruses, adeno-associated viruses, herpes viruses and lentiviruses with the most detailed analysis reserved for adenoviruses. The 3 main strategies for gene therapy in osteosarcoma are next summarized. As part of this review, the several prodrug-converting enzymes utilized in OS suicide gene therapy are examined. The text then turns to a discussion of adenovirus-mediated gene transfer and the need for tumor targeting via transductional or transcriptional approaches. Because of practical problems with use of replication-incompetent viruses in achieving complete tumor kill in vivo, virotherapy utilizing replication competent viruses has come to the fore. This topic is, thus, next reviewed which allows for a natural transition to a discussion of armed therapeutic viruses many of which are conditionally replicating adenoviruses carrying transgenes with established anti-tumor efficacy. We recognize that several other issues have arisen which hamper progress in the field of cancer gene therapy. We, therefore, review viral-induced toxicity in the host and vector delivery issues which have been found to potentially influence safety. We end with a brief perspective including commenting on animal models used in examining delivery strategies for osteosarcoma gene therapy. The challenges remaining are touched upon most especially the need to deal with pulmonary metastatic disease from OS.

Direct vaccination with pseudotype baculovirus expressing murine telomerase induces anti-tumor immunity comparable with RNA-electroporated dendritic cells in a murine glioma model

Baculovirus pseudotyped with vesicular stomatitis virus G protein (Bac-VSV-G) was found to efficiently transduce and express transgenes on mammalian cells. In this study, this recombinant virus was used for induction of anti-tumor immunity against murine telomerase reverse transcriptase (mTERT) and was compared with RNA-electroporated dendritic cells (DCs) in a murine glioma model. Splenocytes from the mice vaccinated with Bac-VSV-G expressing mTERT (Bac-VSVG-mTERT) showed significantly increased numbers of mTERT-specific IFN-gamma-secreting T cells using an ELISPOT technique, and also showed increased NK cell activity. In addition, the TERT-specific T cells activated by Bac-VSVG-mTERT and mTERT RNA-electroporated DCs were predominantly CD4+ T cells and CD8+ T cells, respectively. The protective anti-tumor effect of Bac-VSVG-mTERT was similar to that of mTERT RNA-electroporated DCs. These results suggest that the pseudotype baculovirus expressing TERT may be a good candidate for a genetic vaccine for use in the treatment of malignant gliomas.

Telomerase-based immunotherapy of cancer

The progression from the cloning of human telomerase reverse transcriptase (hTERT) in 1997 to the first clinical trials of hTERT as an antitumour immunotherapy target has been swift. hTERT is overexpressed in the vast majority of human cancers yet has limited expression in normal adult tissue. It plays a critical role in oncogenesis and may be expressed by cancer stem cells. However, despite being a self antigen, hTERT is immunogenic both in vitro and in vivo. Several Phase I studies of hTERT immunotherapy have been completed in patients with breast, prostate, lung and other cancers, and clinical and immunological results are encouraging. Immunotherapy induces functional, antitumour T cells in patients in the absence of clinical toxicity. The opportunity for vaccinating individuals as an immunoprevention strategy can also be envisioned for hTERT-based therapies.

Cytotoxic T cell responses to human telomerase reverse transcriptase in patients with hepatocellular carcinoma

Human telomerase reverse transcriptase, hTERT, has been identified as the catalytic enzyme required for telomere elongation. hTERT is expressed in most tumor cells but seldom expressed in most human adult cells. It has been reported that 80% to 90% of hepatocellular carcinomas (HCCs) express hTERT, making the enzyme a potential target in immunotherapy for HCC. In the current study, we identified hTERT-derived, HLA-A*2402-restricted cytotoxic T cell (CTL) epitopes and analyzed hTERT-specific CTL responses in patients with HCC. Peptides containing the epitopes showed high affinity to bind HLA-A*2402 in a major histocompatibility complex binding assay and were able to induce hTERT-specific CTLs in both hTERT cDNA-immunized HLA-A*2402/Kb transgenic mice and patients with HCC. The CTLs were able to kill hepatoma cell lines depending on hTERT expression levels in an HLA-A*2402-restricted manner and induced irrespective of hepatitis viral infection. The number of single hTERT epitope-specific T cells detected by ELISPOT assay was 10 to 100 specific cells per 3 x 10(5) PBMCs, and positive T cell responses were observed in 6.9% to 12.5% of HCC patients. hTERT-specific T cell responses were observed even in the patients with early stages of HCC. The frequency of hTERT/tetramer+ CD8+ T cells in the tumor tissue of patients with HCC was quite high, and they were functional. In conclusion, these results suggest that hTERT is an attractive target for T-cell-based immunotherapy for HCC, and the identified hTERT epitopes may be valuable both for immunotherapy and for analyzing host immune responses to HCC.

Adenoviral Human Telomerase Reverse Transcriptase Dramatically Improves Ischemic Wound Healing Without Detrimental Immune Response in an Aged Rabbit Model

Chronic ischemic wounds are major clinical problems, and are especially prevalent in elderly patients. Management of these wounds costs billions of dollars annually in the United States. Because of the severe impairment in tissue repair, ischemic wounds among the aged are major challenges for physicians. For example, transforming growth factor-beta1 stimulates healing of young patients' ischemic wounds, but it is totally ineffective in treating the ischemic wounds of aged patients. Therefore, our goal is to develop a better therapeutic strategy for elderly patient ischemic wounds. Because human telomerase reverse transcriptase (hTERT) has emerged as having a role in promoting cell proliferation, we hypothesized that hTERT overexpression may improve ischemic wound healing in the elderly. We successfully tested this hypothesis by demonstrating for the first time that gene delivery of hTERT by adenovirus (Ad-hTERT) dramatically improved ischemic wound healing in an aged rabbit model. Importantly, our histological data indicate that no deleterious immune response was induced in the aged rabbits. This finding has broad implications for the field of gene therapy because the foremost obstacle in the use of adenoviral vectors for gene therapy is that they provoke strong innate and adaptive immune responses in the host. Moreover, Ad-hTERT significantly improved survival of primary rabbit dermal fibroblasts that were treated with hypoxia and hydrogen peroxide (oxidative stress). This model is clinically relevant because it simulates the ischemia cycle of an ischemia-reperfusion injury, which can lead to stroke, myocardial infarction, and other tissue injuries. We conclude that Ad-hTERT is an effective and novel approach to treating the ischemic wounds of elderly patients.

HER-2/neu-gene engineered dendritic cell vaccine stimulates stronger HER-2/neu-specific immune responses compared to DNA vaccination

HER-2/neu is a candidate for developing breast cancer-targeted immunotherapeutics. Although DNA-based and HER-2/neu transgene-modified dendritic cell (DC)-based vaccines are potent at eliciting HER-2/neu-specific antitumor immunity, there has been no side-by-side study comparing them directly. The present study utilizes an in vivo murine tumor model expressing HER-2/neu antigen to compare the efficacy between adenovirus (AdVneu)-transfected dendritic cells (DC(neu)) and plasmid DNA (pcDNAneu) vaccine. Our data showed that DC(neu) upregulated the expression of immunologically important molecules and inflammatory cytokines and partially converted regulatory T (Tr)-cell suppression through interleukin-6 (IL-6) secretion. Vaccination of DC(neu) induced stronger HER-2/neu-specific humoral and cellular immune responses than DNA vaccination, which downregulated HER-2/neu expression and lysed HER-2/neu-positive tumor cells in vitro, respectively. In two HER-2/neu-expressing tumor models, DC(neu) completely protected mice from tumor cell challenge compared to partial or no protection observed in DNA-immunized mice. In addition, DC(neu) significantly delayed breast cancer development in transgenic mice in comparison to DNA vaccine (P<0.05). Taken together, we have demonstrated that HER-2/neu-gene-modified DC vaccine is more potent than DNA vaccine in both protective and preventive animal tumor models. Therefore, DCs genetically engineered to express tumor antigens such as HER-2/neu represent a new direction in DC vaccine of breast cancer.

Immunogenic HLA-B*0702-Restricted Epitopes Derived from Human Telomerase Reverse Transcriptase That Elicit Antitumor Cytotoxic T-Cell Responses

PURPOSE

The human telomerase reverse transcriptase (hTERT) is considered as a potential target for cancer immunotherapy because it is preferentially expressed in tumor cells. To increase the applicability of hTERT-based immunotherapy, we set out to identify CTL epitopes in hTERT restricted by HLA-B*0702 molecule, a common MHC class I allele.

EXPERIMENTAL DESIGN

HLA-B*0702-restricted peptides from hTERT were selected by using a method of epitope prediction and tested for their immunogenicity in human (in vitro) and HLA-B*0702 transgenic mice (in vivo).

RESULTS

All the six hTERT peptides that were predicted to bind to HLA-B*0702 molecule were found to induce primary human CTL responses in vitro. The peptide-specific CD8+ CTL lines were tested against various hTERT+ tumor cells. Although differences were observed according to the tumor origin, only three CTL lines specific for p277, p342, and p351 peptides exhibited cytotoxicity against tumor cells in a HLA-B*0702-restricted manner. In addition, this cytotoxicity was inhibited by the addition of peptide-loaded cold target cells and indicated that these epitopes are naturally processed and presented on the tumor cells. Further, in vivo studies using humanized HLA-B*0702 transgenic mice showed that all the candidate peptides were able to induce CTL responses after peptide immunization. Furthermore, vaccination with a plasmid DNA encoding full-length hTERT elicited peptide-specific CTL responses, indicating that these epitopes are efficiently processed in vivo.

CONCLUSIONS

Together with previously reported hTERT epitopes, the identification of new CTL epitopes presented by HLA-B*0702 increases the applicability of hTERT-based immunotherapy to treating cancer.

Telomerase-specific T-cells kill pancreatic tumor cells in vitro and in vivo

BACKGROUND

Adoptive cell transfer is described as an innovative and challenging option for the treatment of malignant melanoma. In the current study, the generation and expansion of telomerase-specific T-cells for adoptive cell transfer and their use in a syngeneic pancreatic carcinoma mouse model was investigated.

METHODS

Telomerase-specific T-cells were generated either in vitro by coculture of human lymphocytes with telomerase-peptide-pulsed dendritic cells or in vivo by injection of peptide plus adjuvant into C57BL/6 mice. Spleens were harvested after immunization and lymphocytes were expanded in the presence of feeder cells. T-cells were tested in vitro against human leukocyte antigen (HLA)-matched, telomerase-positive pancreatic carcinoma cells. Tumor-bearing (subcutaneous) mice pretreated with cyclophosphamide were injected intravenously with the expanded cells.

RESULTS

It was possible to generate and expand telomerase-specific T-cells with cytotoxic activity. The protocol did not work as well in the murine setting. However, adoptive cell transfer with murine antigen-specific T-cells delayed disease progression in tumor-bearing mice significantly.

CONCLUSIONS

Generation of antigen-specific T-cells is feasible; the expansion of these cells could be accomplished without loss of function. Antigen-specific T-cells demonstrated significant cytotoxic activity in a syngeneic, subcutaneous mouse model. However, further optimization of the expansion protocol is warranted.

Construction of virus-like particle peptide-nucleic acid vaccine of human telomerase reverse transcriptase and identification of its immunogenicity

AIM: To construct a novel virus-like particle peptide-nucleic acid vaccine (VPNV) of human telomerase reverse transcriptase (hTERT), and to identify its imm-unogenicity and transfection activity.

METHODS: Cationic antigenic peptide K₁₈P₉ was syn-thesized and purified, then human GM-CSF and TERT gene were cloned into eukaryotic expression vector pTCAE. The peptide was combined with the nucleic acid vaccine to make VPNV, which were transfected into eukaryotic cells COS-7. The immunogenicity of hGM-CSF and hTERT were detected by enzyme linked imm-unosorbent assay (ELISA) and Western blotting.

RESULTS: Restriction enzyme digestion and sequen-ce analysis confirmed that hGM-CSF and hTERT were cloned into pTCAE and the nucleic acid vaccine of hTERT gene was constructed successfully. Under ele-ctronic microscopy, nucleic acid was packaged by pep-tide, forming into virus-like particle. Furthermore, the transfection activity of VPNV and the immunogenic-ity of hGM-CSF and hTERT could reach 78.5% as co-mpared with the positive controls.

CONCLUSION: The VPNV is successfully constructed, and its immunogenicity is also identified.

Messenger RNA-based vaccines

RNA is the only molecule known to recapitulate all biochemical functions of life: definition, control and transmission of genetic information, creation of defined three-dimensional structures, enzymatic activities and storage of energy. Because of its versatility and thanks to several recent scientific breakthroughs, RNA became the focus of intense research in molecular medicine at the beginning of the millennium. In particular, mRNA can be seen as a safe and efficient alternative to protein-, recombinant virus- or DNA-based therapies in the field of vaccination. This review summarises the most remarkable advances in this area and presents the advantages and limits of the five different mRNA-based vaccination methods. The paper will present the official, industrial and financial aspects of mRNA-based vaccination that are paving the way for therapeutic and prophylactic drugs with mRNA as the active component.

Identification of a potential human telomerase reverse transcriptase-derived, HLA-A1-restricted cytotoxic T-lymphocyte epitope

The catalytic subunit of human telomerase reverse transcriptase (hTERT) is expressed in the majority of tumor cells of different histological origins as opposed to most normal somatic cells. This implicates hTERT as a widely expressed tumor-associated antigen and an attractive candidate for antigen-specific tumor immunotherapy. T lymphocytes specific for hTERT-derived epitopes have been isolated and shown reactive with hTERT-expressing tumor cells. To further increase the applicability of hTERT as a target antigen for immunotherapy, we set out to identify potential hTERT-derived, HLA-A1-restricted cytotoxic T-lymphocyte (CTL) epitopes. The "reverse immunology" approach, involving computer-assisted epitope prediction, in vitro CTL induction, and tetramer-guided CTL isolation, resulted in specific CTLs against hTERT-derived, HLA-A1-binding peptides. Intermediate- to low-avidity CTLs were induced against the hTERT325-333 peptide and recognized endogenously processed hTERT. Recognition of endogenous hTERT depended on an increase of hTERT expression above normal levels in tumor cells through hTERT transduction, most probably as a result of limited CTL avidity. The altered peptide ligand hTERT699T-707 was designed to increase HLA-A1-binding affinity of the hTERT699-707 peptide and was used to induce CTLs. However, these CTLs poorly cross-recognized native hTERT699-707 and failed to recognize endogenously processed hTERT. In conclusion, our study has identified the hTERT325-333 peptide as a potential hTERT-derived epitope that may prove useful for induction and monitoring of hTERT-specific, HLA-A1-restricted CTL responses.

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Colorectal cancer vaccines: principles, results, and perspectives

In the search for novel therapeutic approaches to treat patients with colorectal carcinoma, anticancer vaccination holds promise. A large body of preclinical and clinical evidence has demonstrated that the immune system can be polarized against malignant cells by means of several active specific immunotherapy strategies. Although no vaccination regimen can be currently recommended outside clinical trials, tumor response and immunologic findings observed in animal models and humans prompt researchers to explore further the antitumor potential of such biotherapy in an effort to reproduce in a larger set of patients the cascade of molecular events that characterizes the successful tumor immune rejection currently observed in a minority of vaccinated subjects. In this work, we summarize the principles and the main results of cancer vaccine strategies so far implemented for the treatment of patients with colorectal carcinoma. We also discuss the most recent preclinical tumor immunology insights that might change the way to design the next generation of cancer vaccines, hopefully improving the effectiveness of such a biotherapeutic approach.

Cancer vaccine development: on the way to break immune tolerance to malignant cells

Exploiting a naturally occurring defense system, the immunotherapeutic approach embodies an ideal nontoxic treatment for cancer. Despite the evidence that immune effectors can play a significant role in controlling tumor growth either in natural conditions or in response to therapeutic manipulation, the cascade of molecular events leading to tumor rejection by the immune system remains to be fully elucidated. Nevertheless, some recent tumor immunology advancements might drastically change the way to design the next generation of cancer vaccines, hopefully improving the effectiveness of this therapeutic approach. In the present work, we will focus on three main areas of particular interest for the development of novel vaccination strategies: (a) cellular or molecular mechanisms of immune tolerance to malignant cells; (b) synergism between innate and adaptive immune response; (c) tumor-immune system interactions within the tumor microenvironment.

Conditionally replicative adenovirus driven by the human telomerase promoter provides broad-spectrum antitumor activity without liver toxicity

The human telomerase reverse transcriptase (hTERT) promoter is known to selectively drive transgene expression in many human cancer cells expressing hTERT, the catalytic component of the telomerase ribonucleoprotein complex. We have created a conditionally replicative adenovirus where the viral E1A gene, which is required for viral replication, is under the control of the hTERT promoter (AdhTERTp-E1A). In vitro studies with AdhTERTp-E1A virus on a variety of normal and tumor cell lines have shown that viral genome replication and productive infection is primarily restricted to telomerase-positive tumor cells. Lytic replication was not observed in normal primary fibroblast and epithelial cell lines tested. In vivo administration of the virus into nude mice bearing human liver or prostate tumor xenografts produced significant tumor reduction and, in some cases, resulted in complete tumor regression. AdhTERTp-E1A virus did not actively express E1A in normal mouse liver, in contrast to a control oncolytic vector in which the CMV promoter (AdCMVp-E1A) was driving the E1A gene. In addition, AdhTERTp-E1A virus produced no apparent toxicity to the liver in systemically injected mice. The hTERT promoter-driven oncolytic virus also produced significantly less toxicity to freshly cultured human hepatocytes. These studies demonstrate that an oncolytic virus driven by the telomerase promoter can be used to effectively kill a wide variety of cancer cell types and has the potential to treat primary and metastatic cancer of diverse origins.