Telomerase as a universal tumor-associated antigen for cancer immunotherapy

Telomerase related molecular subtype and risk model reveal immune activity and evaluate prognosis and immunotherapy response in prostate cancer

BACKGROUND

Prostate cancer ranks among the six most lethal malignancies worldwide. Telomerase, a reverse transcriptase enzyme, plays a pivotal role in extending cellular telomeres and is intimately associated with cell proliferation and division. However, the interconnection between prostate cancer and telomerase-related genes (TEASEs) remains unclear.

METHODS

Somatic mutations and copy number alterations of TEASEs were comprehensively analyzed. Subsequently, the transcripts of prostate cancer patients in TCGA and GEO databases were integrated to delineate new molecular subtypes. Followed by constructing a risk model containing nine characteristic genes through Lasso regression and Cox prognostic analysis among different subtypes. Various aspects including prognosis, tumor microenvironment (TME), landscape of immunity, tumor mutational burden (TMB), stem cell correlation, and median inhibitory concentration amongst different risk groups were compared. Finally, the expression, prognosis, and malignant biological behavior of ZW10 interactor (ZWINT) in vitro was explored.

RESULTS

TEASEs exhibited a notably high mutation frequency. Three distinct molecular subtypes and two gene subclusters based on TEASEs were delineated, displaying significant associations with prognosis, immune function regulation, and clinical characteristics. Low-risk patients demonstrated superior prognosis and better response to immunotherapy. Conversely, high-risk patients exhibited higher TMB and stronger stem cell correlations. It was also found that the patients' sensitivity to chemotherapy agents was impacted by the risk score. Finally, ZWINT's potential as a novel diagnostic and prognostic biomarker for prostate cancer was validated.

CONCLUSIONS

TEASEs play a pivotal role in modulating immune regulation and immunotherapeutic responses, thereby significantly impacting the diagnosis, prognosis, and treatment strategies for affected patients.

Tumor biomarkers for diagnosis, prognosis and targeted therapy

Tumor biomarkers, the substances which are produced by tumors or the body's responses to tumors during tumorigenesis and progression, have been demonstrated to possess critical and encouraging value in screening and early diagnosis, prognosis prediction, recurrence detection, and therapeutic efficacy monitoring of cancers. Over the past decades, continuous progress has been made in exploring and discovering novel, sensitive, specific, and accurate tumor biomarkers, which has significantly promoted personalized medicine and improved the outcomes of cancer patients, especially advances in molecular biology technologies developed for the detection of tumor biomarkers. Herein, we summarize the discovery and development of tumor biomarkers, including the history of tumor biomarkers, the conventional and innovative technologies used for biomarker discovery and detection, the classification of tumor biomarkers based on tissue origins, and the application of tumor biomarkers in clinical cancer management. In particular, we highlight the recent advancements in biomarker-based anticancer-targeted therapies which are emerging as breakthroughs and promising cancer therapeutic strategies. We also discuss limitations and challenges that need to be addressed and provide insights and perspectives to turn challenges into opportunities in this field. Collectively, the discovery and application of multiple tumor biomarkers emphasized in this review may provide guidance on improved precision medicine, broaden horizons in future research directions, and expedite the clinical classification of cancer patients according to their molecular biomarkers rather than organs of origin.

Phase 1 study of safety, tolerability and immunogenicity of the human telomerase (hTERT)-encoded DNA plasmids INO-1400 and INO-1401 with or without IL-12 DNA plasmid INO-9012 in adult patients with solid tumors

Background

Human telomerase reverse transcriptase (hTERT) is frequently classified as a ‘universal’ tumor associated antigen due to its expression in a vast number of cancers. We evaluated plasmid DNA-encoded hTERT as an immunotherapy across nine cancer types.

Methods

A phase 1 clinical trial was conducted in adult patients with no evidence of disease following definitive surgery and standard therapy, who were at high risk of relapse. Plasmid DNA encoding one of two hTERT variants (INO-1400 or INO-1401) with or without plasmid DNA encoding interleukin 12 (IL-12) (INO-9012) was delivered intramuscularly concurrent with the application of the CELLECTRA constant-current electroporation device 4 times across 12 weeks. Safety assessments and immune monitoring against native (germline, non-mutated, non-plasmid matched) hTERT antigen were performed. The largest cohort of patients enrolled had pancreatic cancer, allowing for additional targeted assessments for this tumor type.

Results

Of the 93 enrolled patients who received at least one dose, 88 had at least one adverse event; the majority were grade 1 or 2, related to injection site. At 18 months, 54.8% (51/93) patients were disease-free, with median disease-free survival (DFS) not reached by end of study. For patients with pancreatic cancer, the median DFS was 9 months, with 41.4% of these patients remaining disease-free at 18 months. hTERT immunotherapy induced a de novo cellular immune response or enhanced pre-existing cellular responses to native hTERT in 96% (88/92) of patients with various cancer types. Treatment with INO-1400/INO-1401±INO-9012 drove hTERT-specific IFN-γ production, generated hTERT-specific CD4+ and CD8+ T cells expressing the activation marker CD38, and induced hTERT-specific activated CD8 +CTLs as defined by cells expressing perforin and granzymes. The addition of plasmid IL-12 adjuvant elicited higher magnitudes of cellular responses including IFN-γ production, activated CD4+ and CD8+ T cells, and activated CD8+CTLs. In a subset analysis of pancreatic cancer patients, the presence of immunotherapy-induced activated CD8+ T cells expressing PD-1, granzymes and perforin correlated with survival.

Conclusions

Plasmid DNA-encoded hTERT/IL-12 DNA immunotherapy was well-tolerated, immune responses were noted across all tumor types, and a specific CD8+ phenotype increased by the immunotherapy was significantly correlated with survival in patients with pancreatic cancer.

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.

The secrets of telomerase: Retrospective analysis and future prospects

Telomerase plays a significant role to maintain and regulate the telomere length, cellular immortality and senescence by the addition of guanine-rich repetitive sequences. Chronic inflammation or oxidative stress-induced infection downregulates TERT gene modifying telomerase activity thus contributing to the early steps of gastric carcinogenesis process. Furthermore, telomere-telomerase system performs fundamental role in the pathogenesis and progression of diabetes mellitus as well as in its vascular intricacy. The cessation of cell proliferation in cultured cells by inhibiting the telomerase activity of transformed cells renders the rationale for culling of telomerase as a target therapy for the treatment of metabolic disorders and various types of cancers. In this article, we have briefly described the role of immune system and malignant cells in the expression of telomerase with critical analysis on the gaps and potential for future studies. The key findings regarding the secrets of the telomerase summarized in this article will help in future treatment modalities for the prevention of various types of cancers and metabolic disorders notably diabetes mellitus.

Targeting telomerase for cancer therapy

Telomere maintenance via telomerase reactivation is a nearly universal hallmark of cancer cells which enables replicative immortality. In contrast, telomerase activity is silenced in most adult somatic cells. Thus, telomerase represents an attractive target for highly selective cancer therapeutics. However, development of telomerase inhibitors has been challenging and thus far there are no clinically approved strategies exploiting this cancer target. The discovery of prevalent mutations in the TERT promoter region in many cancers and recent advances in telomerase biology has led to a renewed interest in targeting this enzyme. Here we discuss recent efforts targeting telomerase, including immunotherapies and direct telomerase inhibitors, as well as emerging approaches such as targeting TERT gene expression driven by TERT promoter mutations. We also address some of the challenges to telomerase-directed therapies including potential therapeutic resistance and considerations for future therapeutic applications and translation into the clinical setting. Although much work remains to be done, effective strategies targeting telomerase will have a transformative impact for cancer therapy and the prospect of clinically effective drugs is boosted by recent advances in structural models of human telomerase.

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.

Therapeutic Targets in Telomerase and Telomere Biology of Cancers

Telomeres play an important role to conserve genomic integrity by protecting the ends of chromosomes in normal cells. Since, their progressive shortening during successive cell division which lead to chromosomal instability. Notably, telomere length is perpetuated by telomerase in large majority of cancers, thereby ensure indefinite cell proliferation-a hallmark of cancer-and this unique feature has provided telomerase as the preferred target for drug development in cancer therapeutics. Cancer cells have acquired the potential to have telomere length maintenance by telomerase activation- up-regulation of hTERT gene expression in tumor cells is synchronized by multiple genetic and epigenetic modification mechanisms viz hTERT structural variants, hTERT promoter mutation and epigenetic modifications through hTERT promoter methylation which have been implicated in various cancers initiation and progression. In view of these facts, strategies have been made to target the underlining molecular mechanisms involved in telomerase reactivation as well as of telomere structure with special reference to distortion of sheltrin proteins. This review is focussed on extensive understanding of telomere and telomerase biology. which will provide indispensable informations for enhancing the efficiency of rational anticancer drug design. However, there is also an urgent need for better understanding of cell signalling pathways for alternative lengthening of telomere which is present in telomerase negative cancer for therapeutic targets.

Cyclic Naphthalene Diimide Dimer with a Strengthened Ability to Stabilize Dimeric G-Quadruplex

A new type of dimeric cyclic naphthalene diimide derivatives (cNDI-dimers) carrying varied linker length were designed and synthesized to recognize dimeric G-quadruplex structures. All of the cNDI-dimers exhibited a high preference for recognizing G-quadruplex structures, and significantly enhanced the thermal stability of the dimeric G-quadruplex structure over the cNDI monomer by increasing the melting temperature by more than 23 °C, which indicated the strengthened ability of cNDI dimers for stabilizing dimeric G-quadruplex. cNDI dimers also showed a stronger ability to inhibit telomerase activity and stop telomere DNA elongation than cNDI monomer, which showed an improved anticancer potentiality for further therapeutic application.

Stem cells, immortality, and the evolution of metastatic properties in breast cancer: telomere maintenance mechanisms and metastatic evolution

Breast cancer is the most significant cause of cancer-related death in women around the world. The vast majority of breast cancer-associated mortality stems from metastasis, which remains an incurable disease state. Metastasis results from evolution of clones that possess the insidious properties required for dissemination and colonization of distant organs. These clonal populations are descended from breast cancer stem cells (CSCs), which are also responsible for their prolonged maintenance and continued evolution. Telomeres impose a lifespan on cells that can be extended when they are actively elongated, as occurs in CSCs. Thus, changes in telomere structure serve to promote the survival of CSCs and subsequent metastatic evolution. The selection of telomere maintenance mechanism (TMM) has important consequences not only for CSC survival and evolution, but also for their coordination of various signaling pathways that choreograph the metastatic cascade. Targeting the telomere maintenance machinery may therefore provide a boon to the treatment of metastatic breast cancer. Here we review the two major TMMs and the roles they play in the development of stem and metastatic breast cancer cells. We also highlight current and future approaches to targeting these mechanisms in clinical settings to alleviate metastatic breast cancers.

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.

Is It Possible to Develop Cancer Vaccines to Neoantigens, What Are the Major Challenges, and How Can These Be Overcome? Neoantigens: Nothing New in Spite of the Name

The term "neoantigen," as applied to molecules newly expressed on tumor cells, has a long history. The groundbreaking discovery of a cancer causing virus in chickens by Rous over 100 years ago, followed by discoveries of other tumor-causing viruses in animals, suggested a viral etiology of human cancers. The search for other oncogenic viruses in the 1960s and 1970s resulted in the discoveries of Epstein-Barr virus (EBV), hepatitis B virus (HBV), and human papilloma virus (HPV), and continues until the present time. Contemporaneously, the budding field of immunology was posing the question can the immune system of animals or humans recognize a tumor that develops from one's own tissues and what types of antigens would distinguish the tumor from normal cells. Molecules encoded by oncogenic viruses provided the most logical candidates and evidence was quickly gathered for both humoral and cellular recognition of viral antigens, referred to as neoantigens. Often, however, serologic responses to virus-bearing tumors revealed neoantigens unrelated to viral proteins and expressed on multiple tumor types, foreshadowing later findings of multiple changes in other genes in tumor cells creating nonviral neoantigens.

Emerging immunotherapeutic strategies targeting telomerases in genitourinary tumors

Telomerase activity and telomere length are essential for the pathogenesis of several human diseases, including genitourinary tumors. Telomerase constitutes a complex system that includes human telomerase reverse transcriptase (hTERT), human telomerase RNA component (hTR) and telomerase associated protein 1 (TEP1), which are overexpressed in tumor cells compared to normal cells and are involved in the carcinogenesis and progression of renal cell carcinoma (RCC), bladder (BC) and prostate cancer (PCa). In addition, telomerase degraded peptide fragments expressed on the surface of tumor cells lead to their recognition by immune cells. On this scenario, in vitro and in vivo studies have shown effective anti-tumor activity of hTERT-tailored strategies in genitourinary tumors, including active immunotherapy with hTERT-peptide vaccines and passive immunotherapy with hTERT-transduced T cell infusion. This review emphasizes the role of telomerase in the carcinogenesis and progression of genitourinary tumors, thus underlying the potential of emerging telomerase-tailored immunotherapies in these patients.

The Emerging Roles for Telomerase in the Central Nervous System

Telomerase, a specialized ribonucleoprotein enzyme complex, maintains telomere length at the 3′ end of chromosomes, and functions importantly in stem cells, cancer and aging. Telomerase exists in neural stem cells (NSCs) and neural progenitor cells (NPCs), at a high level in the developing and adult brains of humans and rodents. Increasing studies have demonstrated that telomerase in NSCs/NPCs plays important roles in cell proliferation, neuronal differentiation, neuronal survival and neuritogenesis. In addition, recent works have shown that telomerase reverse transcriptase (TERT) can protect newborn neurons from apoptosis and excitotoxicity. However, to date, the link between telomerase and diseases in the central nervous system (CNS) is not well reviewed. Here, we analyze the evidence and summarize the important roles of telomerase in the CNS. Understanding the roles of telomerase in the nervous system is not only important to gain further insight into the process of the neural cell life cycle but would also provide novel therapeutic applications in CNS diseases such as neurodegenerative condition, mood disorders, aging and other ailments.

Cellular therapy with human autologous adipose-derived adult cells of stromal vascular fraction for alopecia areata

BACKGROUND

Most common forms of hair loss (alopecia) are caused by aberrant hair follicle cycling and changes in hair follicle morphology. However, current treatments for alopecia do not specifically target these processes. Adipose-derived stromal vascular cells (ADSVCs) that can be harvested from fat cells are one of the latest breakthroughs in the aesthetic field. The potential use of stem cell-based therapies (SCBT) for the repair and regeneration of various tissues and organs offers a paradigm shift that may provide alternative therapeutic solutions, which can be applied to prevent hair loss. This study aimed to present clinical cases of SCBT for the treatment of alopecia areata by transplantation of ADSVCs in the scalp.

METHODS

Twenty patients (9 women and 11 men) were recruited to our retrospectively registered study. After lipoaspiration, autologous ADSVCs were generated and characterized before the injection of 4-4.7 ×  10⁶ cells into the scalp of the patient. Hair regeneration was assessed by three clinical tests: the pull test, hair quality, and hair density.

RESULTS

All patients experienced hair regeneration, increased hair growth and decreased pull test 3 and 6 months after the treatment with ADSVCs [hair density (85.1 ± 8.7 vs 121.1 ± 12.5 hair/cm², P < 0.0001), hair diameter (60.5 ± 1.8 vs 80.8 ± 2.4μ, P < 0.0001) and pull-test values (4.4 ± 0.3 vs 0.8 ± 0.2, P < 0.0001), untreated versus 6 months post-operative)]. Significant variation was observed between men and women only for hair diameter. No significant differences were observed with age.

CONCLUSIONS

The obtained results prove the efficacy and the safety of the treatment, and satisfaction of the patients confirm the quality of the results.

Simultaneous in vitro generation of CD8 and CD4 T cells specific to three universal tumor associated antigens of WT1, survivin and TERT and adoptive T cell transfer for the treatment of acute myeloid leukemia

Previously, we found that most patients with acute myeloid leukemia (AML) expressed at least one of the leukemic associated antigens (LAAs) WT1, survivin and TERT, and different combinations of the three LAAs predicted negative clinical outcomes. Multi-tumor antigen-specific T cells were generated to overcome antigenic variation and may be sufficient to maximize antitumoral effects. To generate triple antigen-specific (Tri)-T cells that recognize three LAAs, dendritic cells (DCs) were transfected with three tumor antigen-encoding RNAs. These DCs were used to stimulate both CD8 and CD4 T cells and to overcome the limitation of known human leukocyte antigen-restricted epitopes. The sum of the antigen-specific T cell frequencies was higher in the Tri-T cells than in the T cells that recognized a single antigen. Furthermore, the Tri-T cells were more effective against leukemic blasts that expressed all three LAAs compared with blasts that expressed one or two LAAs, suggesting a proportional correlation between IFN-γ secretion and LAA expression. Engrafted leukemic blasts in the bone marrow of mice significantly decreased in the presence of Tri-T cells. This technique represents an effective immunotherapeutic strategy in AML.

Roles of telomeres and telomerase in cancer, and advances in telomerase-targeted therapies

Telomeres maintain genomic integrity in normal cells, and their progressive shortening during successive cell divisions induces chromosomal instability. In the large majority of cancer cells, telomere length is maintained by telomerase. Thus, telomere length and telomerase activity are crucial for cancer initiation and the survival of tumors. Several pathways that regulate telomere length have been identified, and genome-scale studies have helped in mapping genes that are involved in telomere length control. Additionally, genomic screening for recurrent human telomerase gene hTERT promoter mutations and mutations in genes involved in the alternative lengthening of telomeres pathway, such as ATRX and DAXX, has elucidated how these genomic changes contribute to the activation of telomere maintenance mechanisms in cancer cells. Attempts have also been made to develop telomere length- and telomerase-based diagnostic tools and anticancer therapeutics. Recent efforts have revealed key aspects of telomerase assembly, intracellular trafficking and recruitment to telomeres for completing DNA synthesis, which may provide novel targets for the development of anticancer agents. Here, we summarize telomere organization and function and its role in oncogenesis. We also highlight genomic mutations that lead to reactivation of telomerase, and mechanisms of telomerase reconstitution and trafficking that shed light on its function in cancer initiation and tumor development. Additionally, recent advances in the clinical development of telomerase inhibitors, as well as potential novel targets, will be summarized.

Antigen-specific T cell therapies for cancer

Adoptively transferred antigen-specific T cells that recognize tumor antigens through their native receptors have many potential benefits as treatment for virus-associated diseases and malignancies, due to their ability to selectively recognize tumor antigens, expand and persist to provide long-term protection. Infusions of T cells targeting Epstein-Barr virus (EBV) antigens have shown encouraging response rates in patients with post-transplant lymphoproliferative disease as well as EBV-positive lymphomas and nasopharyngeal cancer, although a recent study also showed that human papilloma virus-reactive T cells can induce complete regression of metastatic cervical cancer. This strategy is also being evaluated to target non-viral tumor-associated antigens. Targeting these less immunogenic antigens is more challenging, as tumor antigens are generally weak, and high avidity T cells specific for self-antigens are deleted in the thymus, but tumor responses have been reported. Current research focusses on defining factors that promote in vivo persistence of transferred cells and ameliorate the immunosuppressive microenvironment. To this end, investigators are evaluating the effects of combining adoptive transfer of antigen-specific T cells with other immunotherapy moieties such as checkpoint inhibitors. Genetic modification of infused T cells may also be used to overcome tumor evasion mechanisms, and vaccines may be used to promote in vivo proliferation.

Mannan-modified adenovirus targeting TERT and VEGFR-2: A universal tumour vaccine

Antigen-presenting cells including dendritic cells (DCs) express mannan receptors (MR) on their surface, which can be exploited in cancer therapy by designing immune-stimulatory viruses coated with mannan-modified capsids that then bind to DCs and initiate a potent immune response. Although the combination of anti-angiogenesis and cancer immunotherapy agents has a synergistic antitumor effect, more effective strategies for delivering such combinations are still required. Here we report the design and application of mannan-modified adenovirus that expresses both telomerase reverse transcriptase (TERT) and vascular endothelial growth factor receptor-2 (VEGFR-2). Cytotoxic T lymphocytes that are reactive to TERT and VEGFR-2 are capable of mounting an anti-tumour response in murine breast and colon tumour models and in a lung metastatic model. Compared with mannan-modified TERT adenovirus vaccine or mannan-modified VEGFR-2 adenovirus vaccine alone, the combined vaccine showed remarkably synergistic anti-tumour immunity in these models. Both TERT- and VEGFR-2-specific cytotoxic T lymphocytes (CTL) were identified in an in vitro cytotoxicity assay, and the CTL activity against tumour cells was significantly elevated in the combined vaccine group. Furthermore, CTL-mediated toxicity was blocked by anti-CD8 monoclonal antibodies. Thus, the combined mannan-modified TERT and VEGFR-2 adenovirus confers potent anti-tumour immunity by targeting both tumour cells and intratumoural angiogenesis.

Telomere maintenance mechanisms in cancer: clinical implications

The presence of immortal cell populations with an up-regulated telomere maintenance mechanism (TMM) is an almost universal characteristic of cancers, whereas normal somatic cells are unable to prevent proliferation-associated telomere shortening and have a limited proliferative potential. TMMs and related aspects of telomere structure and function therefore appear to be ideal targets for the development of anticancer therapeutics. Such treatments would be targeted to a specific cancer-related molecular abnormality, and also be broad-spectrum in that they would be expected to be potentially applicable to most cancers. However, the telomere biology of normal and malignant human cells is a relatively young research field with large numbers of unanswered questions, so the optimal design of TMM-targeted therapeutic approaches remains unclear. This review outlines the opportunities and challenges presented by telomeres and TMMs for clinical management of cancer.

Therapeutic targeting of replicative immortality

One of the hallmarks of malignant cell populations is the ability to undergo continuous proliferation. This property allows clonal lineages to acquire sequential aberrations that can fuel increasingly autonomous growth, invasiveness, and therapeutic resistance. Innate cellular mechanisms have evolved to regulate replicative potential as a hedge against malignant progression. When activated in the absence of normal terminal differentiation cues, these mechanisms can result in a state of persistent cytostasis. This state, termed “senescence,” can be triggered by intrinsic cellular processes such as telomere dysfunction and oncogene expression, and by exogenous factors such as DNA damaging agents or oxidative environments. Despite differences in upstream signaling, senescence often involves convergent interdependent activation of tumor suppressors p53 and p16/pRB, but can be induced, albeit with reduced sensitivity, when these suppressors are compromised. Doses of conventional genotoxic drugs required to achieve cancer cell senescence are often much lower than doses required to achieve outright cell death. Additional therapies, such as those targeting cyclin dependent kinases or components of the PI3K signaling pathway, may induce senescence specifically in cancer cells by circumventing defects in tumor suppressor pathways or exploiting cancer cells’ heightened requirements for telomerase. Such treatments sufficient to induce cancer cell senescence could provide increased patient survival with fewer and less severe side effects than conventional cytotoxic regimens. This positive aspect is countered by important caveats regarding senescence reversibility, genomic instability, and paracrine effects that may increase heterogeneity and adaptive resistance of surviving cancer cells. Nevertheless, agents that effectively disrupt replicative immortality will likely be valuable components of new combinatorial approaches to cancer therapy.

Autologous lysate-pulsed dendritic cell vaccination followed by adoptive transfer of vaccine-primed ex vivo co-stimulated T cells in recurrent ovarian cancer

Novel strategies for the therapy of recurrent ovarian cancer are warranted. We report a study of a combinatorial approach encompassing dendritic cell (DC)-based autologous whole tumor vaccination and anti-angiogenesis therapy, followed by the adoptive transfer of autologous vaccine-primed CD3/CD28-co-stimulated lymphocytes. Recurrent ovarian cancer patients for whom tumor lysate was available from prior cytoreductive surgery underwent conditioning with intravenous bevacizumab and oral metronomic cyclophosphamide, sequentially followed by (1) bevacizumab plus vaccination with DCs pulsed with autologous tumor cell lysate supernatants, (2) lymphodepletion and (3) transfer of 5 × 10⁹ autologous vaccine-primed T-cells in combination with the vaccine. Feasibility, safety as well as immunological and clinical efficacy were evaluated. Six subjects received this vaccination. Therapy was feasible, well tolerated, and elicited antitumor immune responses in four subjects, who also experienced clinical benefits. Of these, three patients with residual measurable disease received outpatient lymphodepletion and adoptive T-cell transfer, which was well tolerated and resulted in a durable reduction of circulating regulatory T cells and increased CD8⁺ lymphocyte counts. The vaccine-induced restoration of antitumor immunity was achieved in two subjects, who also demonstrated clinical benefits, including one complete response. Our findings indicate that combinatorial cellular immunotherapy for the treatment of recurrent ovarian cancer is well tolerated and warrants further investigation. Several modifications of this approach can be envisioned to optimize immunological and clinical outcomes.

Tumor-associated antigens in breast cancer

The targets for the immune system are antigens present on cancer cells; however, many are not cancer-specific and may also be found on normal tissues. These antigens are often products of mutated cellular genes, aberrantly expressed normal genes, or genes encoding viral proteins. Vaccines constitute an active and specific immunotherapy designed to stimulate the intrinsic antitumor immune response by presenting tumor-associated antigens expressed on normal tissues that are overexpressed on tumor cells.

The antiretroviral agent saquinavir enhances hTERT expression and telomerase activity in human T leukaemia cells in vitro

BACKGROUND

Saquinavir, a protease inhibitor utilized in HIV infection, shows antitumor activity in various experimental models. In previous studies performed in our laboratory the drug was found to induce a substantial increase of telomerase activity in normal peripheral blood mononuclear cells. Aim of the present investigation was to test whether saquinavir was able to increase telomerase activity and the expression of the catalytic subunit of telomerase, hTERT, in human malignant hematopoietic cells.

METHODS

Human Jurkat CD4+ T cell leukaemia cell line was used throughout the present study. The antiproliferative effect of saquinavir was tested by the MTT assay. Telomerase activity was determined according to the telomeric repeat amplification protocol. The expression of hTERT mRNA was semi-quantitative evaluated by RT-PCR amplification and quantitative Real Time PCR. The binding of the transcription factor c-Myc to its specific E-Box DNA binding-site of hTERT promoter was analyzed by Electophoretic Mobility Shift Assay (EMSA). The amount of c-Myc in cytoplasm and nucleus of leukemia cells was determined by Western Blot analysis, and c-Myc down-regulation was obtained by siRNA transfection.

RESULTS

Saquinavir produced a substantial increase of telomerase activity in Jurkat cells in vitro without increasing but rather reducing target cell proliferation rate. Telomerase up-regulation appeared to be the result of enhanced expression of hTERT. Saquinavir-mediated up-regulation of hTERT gene was the result of the increased binding of proteins to the E-Box sequence of the promoter. Moreover, saquinavir amplified the expression of c-Myc especially in the nuclear cell fraction. The direct influence of saquinavir on this transcription factor was also demonstrated by the antagonistic effect of the drug on siRNA induced c-Myc suppression. Since c-Myc is the main responsible for hTERT transcription, these findings suggest that the main mechanism underlying saquinavir-induced telomerase activation is mediated by c-Myc up-regulation.

CONCLUSIONS

Saquinavir augments hTERT expression while inhibiting leukemic cell growth. Experimental evidences show that this effect is mediated by saquinavir-influenced increase of c-Myc levels. This could have relevance in terms of enhanced hTERT-dependent tumor cell immunogenicity and suggests new paharmacological approaches interfering with c-Myc dependent pathways.

Phase I/II randomized trial of dendritic cell vaccination with or without cyclophosphamide for consolidation therapy of advanced ovarian cancer in first or second remission

PURPOSE

In spite of increased rates of complete response to initial chemotherapy, most patients with advanced ovarian cancer relapse and succumb to progressive disease. Immunotherapy may have potential for consolidation therapy.

EXPERIMENTAL DESIGN

This randomized open-label phase I/II trial evaluated responses of patients with advanced ovarian cancer in remission for vaccination with monocyte-derived dendritic cells (DC) loaded with Her2/neu, hTERT, and PADRE peptides, with or without low-dose intravenous cyclophosphamide. All patients also received pneumococcal vaccine and were randomized to cyclophosphamide 2 days prior to first vaccination. Blood samples were analyzed by ELISPOT and flow cytometry.

RESULTS

Of 11 patients, 2 recurred during vaccination. Nine received all 4 doses: 3 patients recurred at 6, 17, and 26 months, respectively, and 6 have no evidence of disease at 36 months. No grade 3/4 vaccine-related toxicities were noted. The 3-year overall survival was 90%. Patients receiving cyclophosphamide showed a non-significant improvement in survival over controls. Patients receiving cyclophosphamide had a transient reduction in neutrophils, but no change in total lymphocytes or regulatory T cells. Modest T-cell responses to Her2/neu and hTERT were seen post-vaccine by IFN-γ ELISPOT. Patients demonstrated below normal responses to the diphtheria conjugate protein CRM197, a component of the pneumococcal vaccine.

CONCLUSIONS

In this setting, peptide-loaded DC vaccination elicits modest immune responses, but survival is promising. Pneumococcal vaccination revealed substantial immune suppression, even in patients in remission. Rational design of consolidative strategies for ovarian cancer will need to overcome tolerance and immunosuppression.

Vaccines targeting cancer stem cells: are they within reach?

Increased appreciation of intraclonal heterogeneity of tumors in the past decade has led to the resurgence of the cancer stem cell hypothesis. This hypothesis also has potential implications for immunologic approaches targeting cancer, and it has been suggested that vaccines targeting cancer stem cells may be essential for durable antitumor immunity. Recent studies have provided novel insights into the nature of antigenic targets expressed on putative cancer stem cells and the capacity of both the innate and the adaptive immune system to target these cells, as well as the associated challenges. While the phenotypic properties of cancer stem cells may be plastic, their stemness and capacity for self-renewal may depend on a limited set of genes. Several of these genes overlap with those regulating stemness in embryonal stem cells and are also emerging as potential oncogenes in some cancers. Immunologic approaches targeting stemness-associated pathways in cancer may provide an important strategy for the prevention of diverse cancers, including those occurring in the context of regenerative therapies.

Molecular biology of lung cancer: clinical implications

Lung cancer is a heterogeneous disease clinically, biologically, histologically, and molecularly. Understanding the molecular causes of this heterogeneity, which might reflect changes occurring in different classes of epithelial cells or different molecular changes occurring in the same target lung epithelial cells, is the focus of current research. Identifying the genes and pathways involved, determining how they relate to the biological behavior of lung cancer, and their utility as diagnostic and therapeutic targets are important basic and translational research issues. This article reviews current information on the key molecular steps in lung cancer pathogenesis, their timing, and clinical implications.

Targeting telomerase-expressing cancer cells

The role of telomeres and telomerase as a target for cancer therapeutics is an area of continuing interest. This review is intended to provide an update on the field, pointing to areas in which our knowledge remains deficient and exploring the details of the most promising areas being advanced into clinical trials. Topics that will be covered include the role of dysfunctional telomeres in cellular aging and how replicative senescence provides an initial barrier to the emergence of immortalized cells, a hallmark of cancer. As an important translational theme, this review will consider possibilities for selectively targeting telomeres and telomerase to enhance cancer therapy. The role of telomerase as an immunotherapy, as a gene therapy approach using telomerase promoter driven oncolytic viruses and as a small oligonucleotide targeted therapy (Imetelstat) will be discussed.

Is telomerase a viable target in cancer?

The ideal cancer treatment would specifically target cancer cells yet have minimal or no adverse effects on normal somatic cells. Telomerase, the ribonucleoprotein reverse transcriptase that maintains the ends of human chromosome, is an attractive cancer therapeutic target for exactly this reason [1]. Telomerase is expressed in more than 85% of cancer cells, making it a nearly universal cancer marker, while the majority of normal somatic cells are telomerase negative. Telomerase activity confers limitless replicative potential to cancer cells, a hallmark of cancer which must be attained for the continued growth that characterizes almost all advanced neoplasms [2]. In this review we will summarize the role of telomeres and telomerase in cancer cells, and how properties of telomerase are being exploited to create targeted cancer therapies including telomerase inhibitors, telomerase-targeted immunotherapies and telomerase-driven virotherapies. A frank and balanced assessment of the current state of telomerase inhibitors with caveats and potential limitations will be included.

Multidrug-resistance proteins are weak tumor associated antigens for colorectal carcinoma

BACKGROUND

Multidrug resistance (MDR) is a clinically, highly relevant phenomenon. Under chemotherapy many tumors show an increasing resistance towards the applied substance(s) and to a certain extent also towards other agents. An important molecular cause of this phenomenon is an increased expression of transporter proteins. The functional relationship between high expression levels and chemotherapy resistance makes these MDR and MRP (MDR related protein) proteins to interesting therapeutic targets. We here wanted to systematically analyze, whether these proteins are tumor specific antigens which could be targeted immunologically.

RESULTS

Using the reverse immunology approach, 30 HLA-A2.1 restricted MDR and MRP derived peptides (MDP) were selected. Stimulated T cell lines grew well and mainly contained activated CD8+ cells. Peptide specificity and HLA-A2.1 restriction were proven in IFN-γ-ELISpot analyses and in cytotoxicity tests against MDP loaded target cells for a total of twelve peptides derived from MDR-1, MDR-3, MRP-1, MRP-2, MRP-3 and MRP-5. Of note, two of these epitopes are shared between MDR-1 and MDR-3 as well as MRP-2 and MRP-3. However, comparably weak cytotoxic activities were additionally observed against HLA-A2.1+ tumor cells even after upregulation of MDR protein expression by in vitro chemotherapy.

CONCLUSIONS

Taken together, these data demonstrate that human T cells can be sensitised towards MDPs and hence, there is no absolute immunological tolerance. However, our data also hint towards rather low endogenous tumor cell processing and presentation of MDPs in the context of HLA-A2.1 molecules. Consequently, we conclude that MDR and MRP proteins must be considered as weak tumor specific antigens-at least for colorectal carcinoma. Their direct contribution to therapy-failure implies however, that it is worth to further pursue this approach.

Vaccination with autologous dendritic cells pulsed with multiple tumor antigens for treatment of patients with malignant melanoma: results from a phase I/II trial

BACKGROUND AND AIM

Dendritic cells are regarded as the most effective antigen presenting cells and coordinators of the immune response and therefore suitable as vaccine basis. Here we present results from a clinical study in which patients with malignant melanoma (MM) with verified progressive disease received vaccination with autologous monocyte-derived mature dendritic cells (DC) pulsed with p53, survivin and telomerase-derived peptides (HLA-A2+ patients) or with autologous/allogeneic tumor lysate (HLA-A2(−) patients) in combination with low-dose interleukin (IL)-2 and interferon (IFN)-alpha2b.

RESULTS

Of 46 patients who initiated treatment, 10 stopped treatment within 1-4 weeks because of rapid disease progression and deterioration. After 8 weeks, 36 patients were evaluable: no patient had an objective response, 11 patients had stable disease (SD); six had continued SD after 4 months, and three patients had prolonged SD for more than 6 months. The mean overall survival time was 9 months, with a significantly longer survival (18.4 months) of patients who attained SD compared with patients with progressive disease (PD) (5 months). Induction of antigen-specific T-cell responses was analyzed by multidimensional encoding of T cells using HLA-A2 major histocompatibility complex (MHC) multimers. Immune responses against five high-affinity vaccine peptides were detectable in the peripheral blood of six out of 10 analyzed HLA-A2+ patients. There was no observed correlation between the induction of immune responses and disease stabilization. A significant lower blood level of regulatory T cells (CD25(high) CD4 T cells) was demonstrable after six vaccinations in patients with SD compared with PD.

CONCLUSIONS

Vaccination was feasible and safe. Treatment-associated SD was observed in 24% of the patients. SD correlated with prolonged survival suggesting a clinical benefit. Differences in the level of regulatory T cells among SD and PD patients could indicate a significant role of these immune suppressive cells.

Regulatory T cells: overcoming suppression of T-cell immunity

Regulatory T cells inhibit cellular immunity and represent an obstacle for the development of cancer immunotherapy. The understanding of Treg cellular biology has exponentially increased during the last 10 years, driven primarily by elegant in vivo studies of mouse models systems and in vitro studies of human cells. Numerous clinical strategies are under active investigation to achieve Treg depletion or inhibition in patients with cancer, including low-dose cyclophosphamide and interleukin-2 or anti-interleukin-2R immunotoxins. To date, only modest results have been reported in patients. Our preliminary data suggest that the antihuman CD25 monoclonal daclizumab may be useful as an alternative approach for in vivo Treg depletion, but the mechanism of action of this effect remains to be elucidated. Certain immune modulatory agents may indirectly affect Tregs in patients with cancer but not necessarily in the desired direction for the therapeutic setting. More sophisticated techniques that have become available for Treg analysis in patients will assist in this important translational effort.

Spontaneous and therapy-induced immunity to pluripotency genes in humans: clinical implications, opportunities and challenges

Recent studies have suggested that the core pathways regulating pluripotency in embryonal stem cells bear considerable overlap with oncogenesis. Here, we discuss recent insights into the capacity of the human immune system to target some of the key pluripotency-associated genes. Immunity to these genes is also induced in humans in the context of chemotherapy-induced cell death in patients with germ cell tumors. Immunologic targeting of pathways associated with stemness has implications for both immune regulation of tumor growth as well as emerging regenerative therapies with embryonal stem cells.

Targeting telomerase in hematologic malignancy

Over the past two decades, it has become increasingly apparent that telomerase-mediated telomere maintenance plays a crucial role in hematopoiesis. Supporting evidence is underscored by recent findings of mutations in genes involved in telomerase-mediated telomere maintenance that contribute to the pathogenesis of bone marrow failure syndromes. More recently described telomere-independent functions of telomerase are also likely to contribute to both normal hematopoiesis and hematologic diseases. The high levels of telomerase detected in aggressive leukemias have fueled fervent investigation into diverse approaches to targeting telomerase in hematologic malignancies. Successful preclinical investigations that employed genetic strategies, oligonucleotides, small-molecule inhibitors and immunotherapy have resulted in a rapid translation to clinical trials. Further investigation of telomere-independent functions of telomerase and detailed preclinical studies of telomerase inhibition in both normal and malignant hematopoiesis will be invaluable for refining treatments to effectively and safely exploit telomerase as a therapeutic target in hematologic malignancies.

The effects of telomerase inhibition on prostate tumor-initiating cells

Prostate cancer is the most common malignancy in men, and patients with metastatic disease have poor outcome even with the most advanced therapeutic approaches. Most cancer therapies target the bulk tumor cells, but may leave intact a small population of tumor-initiating cells (TICs), which are believed to be responsible for the subsequent relapse and metastasis. Using specific surface markers (CD44, integrin alpha(2)beta(1) and CD133), Hoechst 33342 dye exclusion, and holoclone formation, we isolated TICs from a panel of prostate cancer cell lines (DU145, C4-2 and LNCaP). We have found that prostate TICs have significant telomerase activity which is inhibited by imetelstat sodium (GRN163L), a new telomerase antagonist that is currently in Phase I/II clinical trials for several hematological and solid tumor malignancies. Prostate TICs telomeres were of similar average length to the telomeres of the main population of cells and significant telomere shortening was detected in prostate TICs as a result of imetelstat treatment. These findings suggest that telomerase inhibition therapy may be able to efficiently target the prostate TICs in addition to the bulk tumor cells, providing new opportunities for combination therapies.

Topoisomerase II alpha as a universal tumor antigen: antitumor immunity in murine tumor models and H-2K(b)-restricted T cell epitope

Topoisomerase II alpha (Top2alpha) is an attractive candidate to be used as a tumor antigen for cancer immunotherapy, because it is abundantly expressed in various tumors and serves as a target for a number of chemotherapeutic agents. In this study, we demonstrated the immunogenicity of Top2alpha, using dendritic cells (DC) electroporated with RNA encoding the Top2alpha C-terminus (Top2alphaCRNA/DC). Top2alphaCRNA/DC were able to demonstrate in vitro stimulation of T cells from mice that were previously vaccinated with Top2alpha-expressing tumor lysate-pulsed DC. Vaccination with Top2alphaCRNA/DC induced Top2alpha-specific T cell responses in vivo as well as antitumor effects in various murine tumor models including MC-38, B16F10, and GL26. DC pulsed with p1327 (DSDEDFSGL), defined as an epitope presented by H-2K(b), also induced Top2alpha-specific immune responses and antitumor effects. Based on these data, Top2alpha is suggested to be a universal target for cancer immunotherapy.

Immunity to stemness genes in human cancer

A growing body of data points to not only intraclonal heterogeneity and hierarchy of growth potential, but also plasticity of cellular differentiation within human tumors. Recent studies have also identified surprising overlap between pathways that regulate pluripotency in embryonal stem (ES) cells and oncogenesis. While there is a long history of targeting embryonal tissues toward cancer vaccines, recent identification of crucial stemness pathways in ES cells as well as putative cancer stem cells (CSCs) provides novel opportunities for antigen-specific targeted therapy. Here we discuss recent insights into the capacity of the immune system to target these pathways. Immunologic targeting of pathways associated with stemness has implications for both immune regulation of tumor growth as well as regenerative therapies with embryonal stem cells.

Antigen-specific Tregs control T cell responses against a limited repertoire of tumor antigens in patients with colorectal carcinoma

Spontaneous antitumor T cell responses in cancer patients are strongly controlled by Tregs, and increased numbers of tumor-infiltrating Tregs correlate with reduced survival. However, the tumor antigens recognized by Tregs in cancer patients and the impact of these cells on tumor-specific T cell responses have not been systematically characterized. Here we used a broad panel of long synthetic peptides of defined tumor antigens and normal tissue antigens to exploit a newly developed method to identify and compare ex vivo the antigen specificities of Tregs with those of effector/memory T cells in peripheral blood of colorectal cancer patients and healthy subjects. Tregs in tumor patients were highly specific for a distinct set of only a few tumor antigens, suggesting that Tregs exert T cell suppression in an antigen-selective manner. Tumor-specific effector T cells were detectable in the majority of colorectal cancer patients but not in healthy individuals. We detected differences in the repertoires of antigens recognized by Tregs and effector/memory T cells in the majority of colorectal cancer patients. In addition, only effector/memory T cell responses against antigens recognized by Tregs strongly increased after Treg depletion. The selection of antigens according to preexisting T cell responses may improve the efficacy of future immunotherapies for cancer and autoimmune disease.

Clinical use of anti-CD25 antibody daclizumab to enhance immune responses to tumor antigen vaccination by targeting regulatory T cells

CD4(+) regulatory T cells frustrate productive tumor immune surveillance and represent an obstacle for cancer immunotherapy. In mice, anti-CD25 antibody is an effective method of depleting CD25(+) FOXP3(+) T regulatory cells (Tregs) in vivo and enhancing cancer immunity. Here, we propose the use of the anti-CD25 monoclonal antibody daclizumab for the depletion of Tregs in cancer patients. In early results from an ongoing clinical trial, a single intravenous infusion of daclizumab in patients with metastatic breast cancer is associated with a marked and prolonged elimination of CD25(+) FOXP3(+) Tregs in peripheral blood. When a cancer antigen peptide vaccine is administered during the daclizumab-induced Treg nadir, effective generation of cytotoxic T lymphocytes has been observed, including those specific for neo-antigens, such as cytomegalovirus peptide used as an immunological control. If confirmed in additional patients, these observations suggest that daclizumab may be an effective and available therapeutic agent for Treg modulation in patients with cancer.

Unconventional cytokine profiles and development of T cell memory in long-term survivors after cancer vaccination

Cancer vaccine trials frequently report on immunological responses, without any clinical benefit. This paradox may reflect the challenge of discriminating between effective and pointless immune responses and sparse knowledge on their long-term development. Here, we have analyzed T cell responses in long-term survivors after peptide vaccination. There were three main study aims: (1) to characterize the immune response in patients with a possible clinical benefit. (2) To analyze the long-term development of responses and effects of booster vaccination. (3) To investigate whether the Th1/Th2-delineation applies to cancer vaccine responses. T cell clones were generated from all nine patients studied. We find that surviving patients harbor durable tumor-specific responses against vaccine antigens from telomerase, RAS or TGFbeta receptor II. Analyses of consecutive samples suggest that booster vaccination is required to induce robust T cell memory. The responses exhibit several features of possible clinical advantage, including combined T-helper and cytotoxic functionality, recognition of naturally processed antigens and diverse HLA-restriction and fine-specificity. CD4(-)CD8(-) T cell clones display unconventional cytotoxicity and specifically kill tumor cells expressing mutated TGFbeta receptor II. Cytokine profiling on the long-term survivors demonstrates high IFN gamma/IL10-ratios, favoring immunity over tolerance, and secretion of multiple chemokines likely to mobilize the innate and adaptive immune system. Interestingly, these pro-inflammatory cytokine profiles do not follow a Th1/Th2-delineation. Most IFN gamma(high)/IL4(low)/IL10(low) cultures include high concentrations of hallmark Th2-cytokines IL-5 and IL-13. This does not reflect a mixture of Th1- and Th2-clones, but applies to 19/20 T cell clones confirmed to be monoclonal through TCR clonotype mapping. The present study identifies several factors that may promote clinical efficacy and suggests that cytokine profiling should not rely on the Th1/Th2-paradigm, but assess the overall inflammatory milieu and the balance between key cytokines.

Telomere and telomerase as targets for cancer therapy

Telomere maintenance and telomerase reactivation is essential for the transformation of most human cancer cells. Telomere shortening to the threshold length, mutations of the telomere-associated proteins, and/or telomerase RNA lead to telomeric dysfunction and therefore genomic instability. Telomerase up-regulation in 85% of human cancer cells has become a hallmark of cancers, hence a promising target for anticancer therapy. In this review, we discuss the mechanism of cancer due to telomere dysfunction and the resulting biological effects, the control of telomerase activity, and the new developments in cancer therapies targeting telomere and telomerase.

Telomerase structure paves the way for new cancer therapies

Inappropriate activation of a single enzyme, telomerase, is associated with the uncontrollable proliferation of cells observed in as many as 90% of all of human cancers. Since the mid-1990s, when telomerase activity was detected in human tumors, scientists have eyed the enzyme as an ideal target for developing broadly effective anticancer drugs. One of the missing links in the effort to identify such therapies has been the high-resolution structure of the enzyme, a powerful tool used for the identification and development of clinical drugs. A recent structure of the catalytic subunit of teleomerase from the Skordalakes laboratory, a major advancement in the field of telomeres, has opened the door to the development of new, broadly effective cancer drugs, as well as anti-aging therapies. Here we present a brief description of telomerase biology, current efforts to identify telomerase function modulators and the potential importance of the telomerase structure in future drug development.

Telomerase as a universal tumor antigen for cancer vaccines

T-cell immunotherapy relies on the fundamental concept that tumor antigens exist and are presented in the context of MHC molecules for recognition by specific T cells capable of cytolysis. However, heterogeneous expression of most characterized tumor antigens limits the broad applicability of cancer vaccines that target such antigens. Telomerase, on the other hand, represents a prototype of a universal tumor antigen due to both its expression by the vast majority of tumors and its inherent functional involvement in oncogenic transformation. Given these attractive features, the identification of epitopes within human telomerase reverse transcriptase (hTERT), the catalytic subunit of telomerase, has led to the investigation of this tumor antigen as a broadly applicable immunological target. Basic immunological analyses have revealed that hTERT is immunogenic, and initial clinical trials of multiple vaccine formulations have demonstrated that hTERT-specific immune responses can be safely induced in patients and impact on clinical outcomes. Second-generation vaccines are now addressing strategies to enhance cellular immunity against hTERT without toxicity. Findings obtained from these trials will inform the possibility of broad-spectrum cancer immunotherapy or even immunoprevention.

Human tankyrases are aberrantly expressed in colon tumors and contain multiple epitopes that induce humoral and cellular immune responses in cancer patients

PURPOSE

Tankyrases 1 and 2 are telomere-associated poly(ADP-ribose) polymerases (PARP) that can positively regulate telomere elongation and interact with multiple cellular proteins. Recent reports implicated tankyrases as tumor antigens and potential targets of anticancer treatment. We examined expression of tankyrases in colon tumors and immune response to these enzymes in patients with different types of cancer.

METHODS

mRNA and protein expression was evaluated by quantitative real-time RT-PCR and Western blotting, respectively. Humoral immune response to recombinant tankyrases was investigated by modified enzyme-linked immunoassays. Cellular immune response was analysed by ELISPOT and (51)Cr release assays.

RESULTS

We found that both mRNA and protein levels of tankyrase 2 (TNKL) are upregulated in colon tumors. In contrast, protein level of tankyrase 1 (TNKS) is downregulated, while mRNA level shows variable changes. More than a quarter of colon cancer patients develop humoral immune response to at least one of the two tankyrases. In this study we mapped common and unique B-cell epitopes located in different domains of the two proteins. Additionally, we present evidence for T-cell responses both to epitopes that are unique for TNKL and to those shared between TNKL and TNKS.

CONCLUSION

Our study favors a biomarker usage of antibody response to tankyrases. Spontaneous CD8(+) T-cell responses to these enzymes are rare and further investigation is needed to evaluate tankyrases as potential targets for cancer immunotherapy.