Targeting human telomerase reverse transcriptase with recombinant lentivector is highly effective to stimulate antitumor CD8 T-cell immunity in vivo. Blood. 2010;115:3025-3032. [PMID: 20130242 DOI: 10.1182/blood-2009-11-253641]

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.

The regulations of telomerase reverse transcriptase (TERT) in cancer

Abnormal activation of telomerase occurs in most cancer types, which facilitates escaping from cell senescence. As the key component of telomerase, telomerase reverse transcriptase (TERT) is regulated by various regulation pathways. TERT gene changing in its promoter and phosphorylation respectively leads to TERT ectopic expression at the transcription and protein levels. The co-interacting factors play an important role in the regulation of TERT in different cancer types. In this review, we focus on the regulators of TERT and these downstream functions in cancer regulation. Determining the specific regulatory mechanism will help to facilitate the development of a cancer treatment strategy that targets telomerase and cancer cell senescence. As the most important catalytic subunit component of telomerase, TERT is rapidly regulated by transcriptional factors and PTM-related activation. These changes directly influence TERT-related telomere maintenance by regulating telomerase activity in telomerase-positive cancer cells, telomerase assembly with telomere-binding proteins, and recruiting telomerase to the telomere. Besides, there are also non-canonical functions that are influenced by TERT, including the basic biological functions of cancer cells, such as proliferation, apoptosis, cell cycle regulation, initiating cell formation, EMT, and cell invasion. Other downstream effects are the results of the influence of transcriptional factors by TERT. Currently, some small molecular inhibitors of TERT and TERT vaccine are under research as a clinical therapeutic target. Purposeful work is in progress.

Full eradication of pre-clinical human papilloma virus-induced tumors by a lentiviral vaccine

Human papillomavirus (HPV) infections are the cause of all cervical and numerous oropharyngeal and anogenital cancers. The currently available HPV vaccines, which induce neutralizing antibodies, have no therapeutic effect on established tumors. Here, we developed an immuno-oncotherapy against HPV-induced tumors based on a non-integrative lentiviral vector encoding detoxified forms of the Early E6 and E7 oncoproteins of HPV16 and 18 genotypes, namely, "Lenti-HPV-07". A single intramuscular injection of Lenti-HPV-07 into mice bearing established HPV-induced tumors resulted in complete tumor eradication in 100% of the animals and was also effective against lung metastases. This effect correlated with CD8+ T-cell induction and profound remodeling of the tumor microenvironment. In the intra-tumoral infiltrates of vaccinated mice, the presence of large amounts of activated effector, resident memory, and transcription factor T cell factor-1 (TCF-1)+ "stem-like" CD8+ T cells was associated with full tumor eradication. The Lenti-HPV-07-induced immunity was long-lasting and prevented tumor growth after a late re-challenge, mimicking tumor relapse. Lenti-HPV-07 therapy synergizes with an anti-checkpoint inhibitory treatment and therefore shows promise as an immuno-oncotherapy against established HPV-mediated malignancies.

An iPSC-derived exosome-pulsed dendritic cell vaccine boosts antitumor immunity in melanoma

Induced pluripotent stem cells (iPSCs) express a broad spectrum of tumor-associated antigens and exert prophylactic effects on various tumors. However, some problems remain, such as potential tumorigenicity, challenges in transport to the lymph nodes and spleen, and limited antitumor effects. Thus, designing a safe and effective iPSC-based tumor vaccine is necessary. We prepared iPSC-derived exosomes and incubated them with DCs (dendritic cells) for pulsing to explore their antitumor effects in murine melanoma models. The antitumor immune response induced by the DC vaccine pulsed with iPSC exosomes (DC + EXO) was assessed in vitro and in vivo. After DC + EXO vaccination, extracted spleen T cells effectively killed a variety of tumor cells (melanoma, lung cancer, breast cancer, and colorectal cancer) in vitro. In addition, DC + EXO vaccination significantly inhibited melanoma growth and lung metastasis in mouse models. Furthermore, DC + EXO vaccination induced long-term T cell responses and prevented melanoma rechallenge. Finally, biocompatibility studies showed that the DC vaccine did not significantly alter the viability of normal cells and mouse viscera. Hence, our research may provide a prospective strategy of a safe and effective iPSC-based tumor vaccine for clinical use.

Lentiviral Vectors as a Vaccine Platform against Infectious Diseases

Lentiviral vectors are among the most effective viral vectors for vaccination. In clear contrast to the reference adenoviral vectors, lentiviral vectors have a high potential for transducing dendritic cells in vivo. Within these cells, which are the most efficient at activating naive T cells, lentiviral vectors induce endogenous expression of transgenic antigens that directly access antigen presentation pathways without the need for external antigen capture or cross-presentation. Lentiviral vectors induce strong, robust, and long-lasting humoral, CD8+ T-cell immunity and effective protection against several infectious diseases. There is no pre-existing immunity to lentiviral vectors in the human population and the very low pro-inflammatory properties of these vectors pave the way for their use in mucosal vaccination. In this review, we have mainly summarized the immunological aspects of lentiviral vectors, their recent optimization to induce CD4+ T cells, and our recent data on lentiviral vector-based vaccination in preclinical models, including prophylaxis against flaviviruses, SARS-CoV-2, and Mycobacterium tuberculosis.

Use of lentiviral vectors in vaccination

INTRODUCTION

Lentiviral vectors have emerged as powerful vectors for vaccination, due to their high efficiency to transduce dendritic cells and to induce long-lasting humoral immunity, CD8⁺ T cells, and effective protection in numerous preclinical animal models of infection and oncology.

AREAS COVERED

Here, we reviewed the literature, highlighting the relevance of lentiviral vectors in vaccinology. We recapitulated both their virological and immunological aspects of lentiviral vectors. We compared lentiviral vectors to the gold standard viral vaccine vectors, i.e. adenoviral vectors, and updated the latest results in lentiviral vector-based vaccination in preclinical models.

EXPERT OPINION

Lentiviral vectors are non-replicative, negligibly inflammatory, and not targets of preexisting immunity in human populations. These are major characteristics to consider in vaccine development. The potential of lentiviral vectors to transduce non-dividing cells, including dendritic cells, is determinant in their strong immunogenicity. Notably, lentiviral vectors can be engineered to target antigen expression to specific host cells. The very weak inflammatory properties of these vectors allow their use in mucosal vaccination, with particular interest in infectious diseases that affect the lungs or brain, including COVID-19. Recent results in various preclinical models have reinforced the interest of these vectors in prophylaxis against infectious diseases and in onco-immunotherapy.

MMP-7 derived peptides with MHC class-I binding motifs from canine mammary tumor tissue elicit strong antigen-specific T-cell responses in BALB/c mice

Matrix Metalloproteinases (MMPs)-induced altered proteolysis of extracellular matrix proteins and basement membrane holds the key for tumor progression and metastasis. Matrix metalloproteinases-7 (Matrilysin), the smallest member of the MMP family also performs quite alike; thus serves as a potential candidate for anti-tumor immunotherapy. Conversely, being an endogenous tumor-associated antigen (TAA), targeting MMP-7 for immunization is challenging. But MMP-7-based xenovaccine can surmount the obstacle of poor immunogenicity and immunological tolerance, often encountered in TAA-based conventional vaccine for anti-tumor immunotherapy. This paves the way for investigating the potential of MMP-7-derived major histocompatibility complex (MHC)-binding peptides to elicit precise epitope-specific T-cell responses towards their possible inclusion in anti-tumor vaccine formulations. Perhaps it also ushers the path of achieving multiple epitope-based broad and universal cellular immunity. In current experiment, an immunoinformatics approach has been employed to identify the putative canine matrix matelloproteinases-7 (cMMP-7)-derived peptides with MHC class-I-binding motifs which can elicit potent antigen-specific immune responses in BALB/c mice. Immunization with the cMMP-7 DNA vaccine induced a strong CD8⁺ cytotoxic T lymphocytes (CTLs) and Th1- type response, with high level of gamma interferon (IFN-γ) production in BALB/c mice. The two identified putative MHC-I-binding nonameric peptides (Peptide_32-40 and Peptide_175-183) from cMMP-7 induced significant lymphocyte proliferation along with the production of IFN-γ from CD8⁺ T-cells in mice immunized with cMMP-7 DNA vaccine. The current observation has depicted the immunogenic potential of the two cMMP-7-derived nonapeptides for their possible exploitation in xenovaccine-mediated anti-tumor immunotherapy in mouse model.

Expression of the Reverse Transcriptase Domain of Telomerase Reverse Transcriptase Induces Lytic Cellular Response in DNA-Immunized Mice and Limits Tumorigenic and Metastatic Potential of Murine Adenocarcinoma 4T1 Cells

Telomerase reverse transcriptase (TERT) is a classic tumor-associated antigen overexpressed in majority of tumors. Several TERT-based cancer vaccines are currently in clinical trials, but immune correlates of their antitumor activity remain largely unknown. Here, we characterized fine specificity and lytic potential of immune response against rat TERT in mice. BALB/c mice were primed with plasmids encoding expression-optimized hemagglutinin-tagged or nontagged TERT or empty vector and boosted with same DNA mixed with plasmid encoding firefly luciferase (Luc DNA). Injections were followed by electroporation. Photon emission from booster sites was assessed by in vivo bioluminescent imaging. Two weeks post boost, mice were sacrificed and assessed for IFN-γ, interleukin-2 (IL-2), and tumor necrosis factor alpha (TNF-α) production by T-cells upon their stimulation with TERT peptides and for anti-TERT antibodies. All TERT DNA-immunized mice developed cellular and antibody response against epitopes at the N-terminus and reverse transcriptase domain (rtTERT) of TERT. Photon emission from mice boosted with TERT/TERT-HA+Luc DNA was 100 times lower than from vector+Luc DNA-boosted controls. Bioluminescence loss correlated with percent of IFN-γ/IL-2/TNF-α producing CD8+ and CD4+ T-cells specific to rtTERT, indicating immune clearance of TERT/Luc-coexpressing cells. We made murine adenocarcinoma 4T1luc2 cells to express rtTERT by lentiviral transduction. Expression of rtTERT significantly reduced the capacity of 4T1luc2 to form tumors and metastasize in mice, while not affecting in vitro growth. Mice which rejected the tumors developed T-cell response against rtTERT and low/no response to the autoepitope of TERT. This advances rtTERT as key component of TERT-based therapeutic vaccines against cancer.

Identification of a novel PD-L1 positive solid tumor transplantable in HLA-A*0201/DRB1*0101 transgenic mice

HLA-A*0201/DRB1*0101 transgenic mice (A2/DR1 mice) have been developed to study the immunogenicity of tumor antigen-derived T cell epitopes. To extend the use and application of this mouse model in the field of antitumor immunotherapy, we described a tumor cell line generated from a naturally occurring tumor in A2/DR1 mouse named SARC-L1. Histological and genes signature analysis supported the sarcoma origin of this cell line. While SARC-L1 tumor cells lack HLA-DRB1*0101 expression, a very low expression of HLA-A*0201 molecules was found on these cells. Furthermore they also weakly but constitutively expressed the programmed death-ligand 1 (PD-L1). Interestingly both HLA-A*0201 and PD-L1 expressions can be increased on SARC-L1 after IFN-γ exposure in vitro. We also obtained two genetically modified cell lines highly expressing either HLA-A*0201 or both HLA-A*0201/ HLA-DRB1*0101 molecules referred as SARC-A2 and SARC-A2DR1 respectively. All the SARC-L1-derived cell lines induced aggressive subcutaneous tumors in A2DR1 mice in vivo. The analysis of SARC-L1 tumor microenvironment revealed a strong infiltration by T cells expressing inhibitory receptors such as PD-1 and TIM-3. Finally, we found that SARC-L1 is sensitive to several drugs commonly used to treat sarcoma and also susceptible to anti-PD-L1 monoclonal antibody therapy in vivo. Collectively, we described a novel syngeneic tumor model A2/DR1 mice that could be used as preclinical tool for the evaluation of antitumor immunotherapies.

Advances in inducing adaptive immunity using cell-based cancer vaccines: Clinical applications in pancreatic cancer

The incidence of pancreatic ductal adenocarcinoma (PDA) is on the rise, and the prognosis is extremely poor because PDA is highly aggressive and notoriously difficult to treat. Although gemcitabine- or 5-fluorouracil-based chemotherapy is typically offered as a standard of care, most patients do not survive longer than 1 year. Therefore, the development of alternative therapeutic approaches for patients with PDA is imperative. As PDA cells express numerous tumor-associated antigens that are suitable vaccine targets, one promising treatment approach is cancer vaccines. During the last few decades, cell-based cancer vaccines have offered encouraging results in preclinical studies. Cell-based cancer vaccines are mainly generated by presenting whole tumor cells or dendritic cells to cells of the immune system. In particular, several clinical trials have explored cell-based cancer vaccines as a promising therapeutic approach for patients with PDA. Moreover, chemotherapy and cancer vaccines can synergize to result in increased efficacies in patients with PDA. In this review, we will discuss both the effect of cell-based cancer vaccines and advances in terms of future strategies of cancer vaccines for the treatment of PDA patients.

Novel metronomic chemotherapy and cancer vaccine combinatorial strategy for hepatocellular carcinoma in a mouse model

Hepatocellular carcinoma (HCC) is the most frequent primary liver cancer and represents the third and the fifth leading cause of cancer-related death worldwide in men and women, respectively. Hepatitis B virus (HBV) and hepatitis C virus (HCV) chronic infections account for pathogenesis of more than 80 % of primary HCC. HCC prognosis greatly varies according to stage at beginning of treatment, but the overall 5-year survival rate is approximately 5-6 %. Given the limited number of effective therapeutic strategies available, immunotherapies and therapeutic cancer vaccines may help in improving the clinical outcome for HCC patients. However, the few clinical trials conducted to date have shown contrasting results, indicating the need for improvements. In the present study, a novel combinatorial strategy, based on metronomic chemotherapy plus vaccine, is evaluated in a mouse model. The chemotherapy is a multi-drug cocktail including taxanes and alkylating agents, which is administered in a metronomic-like fashion. The vaccine is a multi-peptide cocktail including HCV as well as universal tumor antigen TERT epitopes. The combinatorial strategy designed and evaluated in the present study induces an enhanced specific T cell response, when compared to vaccine alone, which correlates to a reduced Treg frequency. Such results are highly promising and may pave way to relevant improvements in immunotherapeutic strategies for HCC and beyond.

Targeting cryptic epitope with modified antigen coupled to the surface of liposomes induces strong antitumor CD8 T-cell immune responses in vivo

Active cancer immunotherapy, such as cancer vaccine, is based on the fundamental knowledge that tumor-associated antigens (TAAs) are presented on MHC molecules for recognition by specific T cells. However, most TAAs are self-antigens and are also expressed on normal tissues, including the thymus. This fact raises the issue of the tolerance of the TAA-specific T-cell repertoire and consequently the inability to trigger a strong and efficient antitumor immune response. In the present study, we used antigens chemically coupled to the surface of liposomes to target telomerase reverse transcriptase (TERT), a widely expressed self/tumor antigen. Taking advantage of the high homology between mouse and human TERT, we investigated immunogenicity and antitumor efficiency of the liposomal TERT peptides in HLA-A^*0201 transgenic HHD mice. Using the heteroclitical peptide-modifying approach with antigen-coupled liposomes, we identified a novel cryptic epitope with low affinity for HLA^*0201 molecules derived from TERT. The heteroclitical variant derived from this novel low affinity peptide exhibited strong affinity for HLA^*0201 molecules. However, it induced only weak CD8 T-cell immune responses in HHD mice when emulsified in IFA. By contrast, when coupled to the surface of the liposomes, it induced powerful CD8 T-cell immune responses which cross-reacted against the original cryptic epitope. The induced CD8 T cells also recognized endogenously TERT-expressing tumor cells and inhibited their growth in HHD mice. These data suggest that heteroclitical antigen derived from low affinity epitope of tumor antigens coupled to the surface of liposome may have a role as an effective cancer vaccine candidate.

Immunogenicity evaluation of a rationally designed polytope construct encoding HLA-A*0201 restricted epitopes derived from Leishmania major related proteins in HLA-A2/DR1 transgenic mice: steps toward polytope vaccine

Background

There are several reports demonstrating the role of CD8 T cells against Leishmania species. Therefore peptide vaccine might represent an effective approach to control the infection. We developed a rational polytope-DNA construct encoding immunogenic HLA-A2 restricted peptides and validated the processing and presentation of encoded epitopes in a preclinical mouse model humanized for the MHC-class-I and II.

Methods and Findings

HLA-A*0201 restricted epitopes from LPG-3, LmSTI-1, CPB and CPC along with H-2Kd restricted peptides, were lined-up together as a polytope string in a DNA construct. Polytope string was rationally designed by harnessing advantages of ubiquitin, spacers and HLA-DR restricted Th1 epitope. Endotoxin free pcDNA plasmid expressing the polytope was inoculated into humanized HLA-DRB1*0101/HLA-A*0201 transgenic mice intramuscularly 4 days after Cardiotoxin priming followed by 2 boosters at one week interval. Mice were sacrificed 10 days after the last booster, and splenocytes were subjected to ex-vivo and in-vitro evaluation of specific IFN-γ production and in-vitro cytotoxicity against individual peptides by ELISpot and standard chromium-51(⁵¹Cr) release assay respectively. 4 H-2Kd and 5 HLA-A*0201 restricted peptides were able to induce specific CD8 T cell responses in BALB/C and HLA-A2/DR1 mice respectively. IFN-γ and cytolytic activity together discriminated LPG-3-P1 as dominant, LmSTI-1-P3 and LmSTI-1-P6 as subdominant with both cytolytic activity and IFN-γ production, LmSTI-1-P4 and LPG-3-P5 as subdominant with only IFN-γ production potential.

Conclusions

Here we described a new DNA-polytope construct for Leishmania vaccination encompassing immunogenic HLA-A2 restricted peptides. Immunogenicity evaluation in HLA-transgenic model confirmed CD8 T cell induction with expected affinities and avidities showing almost efficient processing and presentation of the peptides in relevant preclinical model. Further evaluation will determine the efficacy of this polytope construct protecting against infectious challenge of Leishmania. Fortunately HLA transgenic mice are promising preclinical models helping to speed up immunogenicity analysis in a human related mouse model.

T cell-based targeted immunotherapies for patients with multiple myeloma

Despite high-dose chemotherapy followed by autologs stem-cell transplantation as well as novel therapeutic agents, multiple myeloma (MM) remains incurable. Following the general trend towards personalized therapy, targeted immunotherapy as a new approach in the therapy of MM has emerged. Better progression-free survival and overall survival after tandem autologs/allogeneic stem cell transplantation suggest a graft versus myeloma effect strongly supporting the usefulness of immunological therapies for MM patients. How to induce a powerful antimyeloma effect is the key issue in this field. Pivotal is the definition of appropriate tumor antigen targets and effective methods for expansion of T cells with clinical activity. Besides a comprehensive list of tumor antigens for T cell-based approaches, eight promising antigens, CS1, Dickkopf-1, HM1.24, Human telomerase reverse transcriptase, MAGE-A3, New York Esophageal-1, Receptor of hyaluronic acid mediated motility and Wilms' tumor gene 1, are described in detail to provide a background for potential clinical use. Results from both closed and on-going clinical trials are summarized in this review. On the basis of the preclinical and clinical data, we elaborate on three encouraging therapeutic options, vaccine-enhanced donor lymphocyte infusion, chimeric antigen receptors-transfected T cells as well as vaccines with multiple antigen peptides, to pave the way towards clinically significant immune responses against MM.

Induction of antigen-specific immune responses by dendritic cells transduced with a recombinant lentiviral vector encoding MAGE-A3 gene

PURPOSE

Melanoma antigen gene A3 (MAGE-A3) is aberrantly expressed in a number of cancer types. Because of its high specificity, MAGE-A3 has shown to be a promising candidate for cancer immunotherapy. Dendritic cells (DCs) have emerged as the natural agents for antigen delivery. DCs transduced with antigen may increase immune response and maintain immune durability. The aim of this study was to investigate the roles of DCs transduced with lentiviral vectors (LVs) encoding full-length MAGE-A3 gene in cancer immunotherapy .

METHODS

A LV containing full-length MAGE-A3 gene (rLV/MAGE-A3) was constructed. Reverse transcriptase-polymerase chain reaction and direct DNA sequencing were performed to verify the construct. Human DCs derived from umbilical cord blood were then transduced with rLV/MAGE-A3. The potency of rLV/MAGE-A3-transduced DCs was examined by measurement of surface markers and mixed lymphocyte reaction. The MAGE-A3-specific T-cell response induced by DCs was detected using the lactate dehydrogenase release assay.

RESULTS

rLV/MAGE-A3 was constructed successfully and used to transduce DCs efficiently. DCs transduced with rLV/MAGE-A3 stably expressed MAGE-A3 and yielded high percentage of cells expressing CD80, CD86, and HLA-DR. rLV/MAGE-A3 transduction did not impair DCs viability and maturation at a multiplicity of infection of 30. The rLV/MAGE-A3-transduced DCs induced MAGE-A3-specific T lymphocytes that exhibited a significant lysis activity against MAGE-A3-bearing tumor cell lines (HuH-7 and SGC-7901).

CONCLUSIONS

DC-directed rLV/MAGE-A3 efficiently induced antigen-specific immune responses, indicating the possibility of DC-based MAGE-A3 antigen vaccine as a promising strategy for treatment of MAGE-A3-associated cancer.

Highly optimized DNA vaccine targeting human telomerase reverse transcriptase stimulates potent antitumor immunity

High levels of human telomerase reverse transcriptase (hTERT) are detected in more than 85% of human cancers. Immunologic analysis supports that hTERT is a widely applicable target recognized by T cells and can be potentially studied as a broad cancer immunotherapeutic, or a unique line of defense against tumor recurrence. There remains an urgent need to develop more potent hTERT vaccines. Here, a synthetic highly optimized full-length hTERT DNA vaccine (phTERT) was designed and the induced immunity was examined in mice and non-human primates (NHP). When delivered by electroporation, phTERT elicited strong, broad hTERT-specific CD8 T-cell responses including induction of T cells expressing CD107a, IFN-γ, and TNF-α in mice. The ability of phTERT to overcome tolerance was evaluated in an NHP model, whose TERT is 96% homologous to that of hTERT. Immunized monkeys exhibited robust [average 1,834 spot forming unit (SFU)/10(6) peripheral blood mononuclear cells (PBMC)], diverse (multiple immunodominant epitopes) IFN-γ responses and antigen-specific perforin release (average 332 SFU/10(6) PBMCs), suggesting that phTERT breaks tolerance and induces potent cytotoxic responses in this human-relevant model. Moreover, in an HPV16-associated tumor model, vaccination of phTERT slows tumor growth and improves survival rate in both prophylactic and therapeutic studies. Finally, in vivo cytotoxicity assay confirmed that phTERT-induced CD8 T cells exhibited specific cytotoxic T lymphocyte (CTL) activity, capable of eliminating hTERT-pulsed target cells. These findings support that this synthetic electroporation-delivered DNA phTERT may have a role as a broad therapeutic cancer vaccine candidate.

Diminished Memory T-Cell Expansion Due to Delayed Kinetics of Antigen Expression by Lentivectors

Memory CD8⁺ T lymphocytes play a central role in protective immunity. In attempt to increase the frequencies of memory CD8⁺ T cells, repeated immunizations with viral vectors are regularly explored. Lentivectors have emerged as a powerful vaccine modality with relatively low pre-existing and anti-vector immunity, thus, thought to be ideal for boosting memory T cells. Nevertheless, we found that lentivectors elicited diminished secondary T-cell responses that did not exceed those obtained by priming. This was not due to the presence of anti-vector immunity, as limited secondary responses were also observed following heterologous prime-boost immunizations. By dissecting the mechanisms involved in this process, we demonstrate that lentivectors trigger exceptionally slow kinetics of antigen expression, while optimal activation of lentivector-induced T cells relays on durable expression of the antigen. These qualities hamper secondary responses, since lentivector-encoded antigen is rapidly cleared by primary cytotoxic T cells that limit its presentation by dendritic cells. Indeed, blocking antigen clearance by cytotoxic T cells via FTY720 treatment, fully restored antigen presentation. Taken together, while low antigen expression is expected during secondary immunization with any vaccine vector, our results reveal that the intrinsic delayed expression kinetics of lentiviral-encoded antigen, further dampens secondary CD8⁺ T-cell expansion.

Xenogeneic human p53 DNA vaccination by electroporation breaks immune tolerance to control murine tumors expressing mouse p53

The pivotal role of p53 as a tumor suppressor protein is illustrated by the fact that this protein is found mutated in more than 50% of human cancers. In most cases, mutations in p53 greatly increase the otherwise short half-life of this protein in normal tissue and cause it to accumulate in the cytoplasm of tumors. The overexpression of mutated p53 in tumor cells makes p53 a potentially desirable target for the development of cancer immunotherapy. However, p53 protein represents an endogenous tumor-associated antigen (TAA). Immunization against a self-antigen is challenging because an antigen-specific immune response likely generates only low affinity antigen-specific CD8⁺ T-cells. This represents a bottleneck of tumor immunotherapy when targeting endogenous TAAs expressed by tumors. The objective of the current study is to develop a safe cancer immunotherapy using a naked DNA vaccine. The vaccine employs a xenogeneic p53 gene to break immune tolerance resulting in a potent therapeutic antitumor effect against tumors expressing mutated p53. Our study assessed the therapeutic antitumor effect after immunization with DNA encoding human p53 (hp53) or mouse p53 (mp53). Mice immunized with xenogeneic full length hp53 DNA plasmid intramuscularly followed by electroporation were protected against challenge with murine colon cancer MC38 while those immunized with mp53 DNA were not. In a therapeutic model, established MC38 tumors were also well controlled by treatment with hp53 DNA therapy in tumor bearing mice compared to mp53 DNA. Mice vaccinated with hp53 DNA plasmid also exhibited an increase in mp53-specific CD8⁺ T-cell precursors compared to vaccination with mp53 DNA. Antibody depletion experiments also demonstrated that CD8⁺ T-cells play crucial roles in the antitumor effects. This study showed intramuscular vaccination with xenogeneic p53 DNA vaccine followed by electroporation is capable of inducing potent antitumor effects against tumors expressing mutated p53 through CD8⁺ T cells.

Targeting antitumor CD4 helper T cells with universal tumor-reactive helper peptides derived from telomerase for cancer vaccine

Current cancer immunotherapies predominantly rely on CD8(+) T cells to fight against tumors. However accumulative evidence showed that proinflammatory CD4(+) helper T cells are critical determinants of effective antitumor immunity. The utilization of universal tumor-reactive helper peptides from telomerase represents a powerful approach to the fully use of CD4(+) T cell-based immunotherapy.

A nonintegrative lentiviral vector-based vaccine provides long-term sterile protection against malaria

Trials testing the RTS,S candidate malaria vaccine and radiation-attenuated sporozoites (RAS) have shown that protective immunity against malaria can be induced and that an effective vaccine is not out of reach. However, longer-term protection and higher protection rates are required to eradicate malaria from the endemic regions. It implies that there is still a need to explore new vaccine strategies. Lentiviral vectors are very potent at inducing strong immunological memory. However their integrative status challenges their safety profile. Eliminating the integration step obviates the risk of insertional oncogenesis. Providing they confer sterile immunity, nonintegrative lentiviral vectors (NILV) hold promise as mass pediatric vaccine by meeting high safety standards. In this study, we have assessed the protective efficacy of NILV against malaria in a robust pre-clinical model. Mice were immunized with NILV encoding Plasmodium yoelii Circumsporozoite Protein (Py CSP) and challenged with sporozoites one month later. In two independent protective efficacy studies, 50% (37.5-62.5) of the animals were fully protected (p = 0.0072 and p = 0.0008 respectively when compared to naive mice). The remaining mice with detectable parasitized red blood cells exhibited a prolonged patency and reduced parasitemia. Moreover, protection was long-lasting with 42.8% sterile protection six months after the last immunization (p = 0.0042). Post-challenge CD8+ T cells to CSP, in contrast to anti-CSP antibodies, were associated with protection (r = -0.6615 and p = 0.0004 between the frequency of IFN-g secreting specific T cells in spleen and parasitemia). However, while NILV and RAS immunizations elicited comparable immunity to CSP, only RAS conferred 100% of sterile protection. Given that a better protection can be anticipated from a multi-antigen vaccine and an optimized vector design, NILV appear as a promising malaria vaccine.

Antitumor effect of new multiple antigen peptide based on HLA-A0201-restricted CTL epitopes of human telomerase reverse transcriptase (hTERT)

The development of peptide vaccines aimed at enhancing immune responses against tumor cells is becoming a promising area of research. Human telomerase reverse transcriptase (hTERT) is an ideal universal target for novel immunotherapies against cancers. The aim of this work was to verify whether the multiple antigen peptides (MAP) based on HLA-A0201-restricted CTL epitopes of hTERT could trigger a better and more sustained CTL response and kill multiple types of hTERT-positive tumor cells in vitro and ex vivo. Dendritic cells (DC) pulsed with MAP based on HLA-A0201-restricted CTL epitopes of hTERT (hTERT-540, hTERT-865 and hTERT-572Y) were used to evaluate immune responses against various tumors and were compared to the immune responses resulting from the use of corresponding linear epitopes and a recombinant adenovirus-hTERT vector. A 4-h standard (51) Cr-release assay and an ELISPOT assay were used for both in vitro and ex vivo analyses. Results demonstrated that targeting hTERT with an adenovector was the most effective way to stimulate a CD8(+) T cell response. When compared with linear hTERT epitopes, MAP could trigger stronger hTERT-specific CTL responses against tumor cells expressing hTERT and HLA-A0201. In contrast, the activated CTL could neither kill the hTERT-negative tumor cells, such as U2OS cells, nor kill HLA-A0201 negative cells, such as HepG2 cells. We also found that these peptide-specific CTL could not kill autologous lymphocytes and DC with low telomerase activity. Our results indicate that MAP from hTERT can be exploited for cancer immunotherapy.

Immunization delivered by lentiviral vectors for cancer and infectious diseases

The increasing level of understanding of the lentivirus biology has been instrumental in shaping the design strategy of creating therapeutic lentiviral delivery vectors. As a result, lentiviral vectors have become one of the most powerful gene transfer vehicles. They are widely used for therapeutic purposes as well as in studies of basic biology, due to their unique characteristics. Lentiviral vectors have been successfully employed to mediate durable and efficient antigen expression and presentation in dendritic cells both in vitro and in vivo, leading to the activation of cellular immunity and humoral responses. This capability makes the lentiviral vector an ideal choice for immunizations that target a wide range of cancers and infectious diseases. Further advances into optimizing the vector system and understanding the relationship between the immune system and diseases pathogenesis will only augment the potential benefits and utility of lentiviral vaccines for human health.

Telomerase and primary T cells: biology and immortalization for adoptive immunotherapy

Telomeres are specialized repeats, present at the end of chromosomes, whose loss during cell division is followed by growth arrest, a central mechanism of replicative senescence in human cells. Telomere length in stem cells is maintained by telomerase, a specialized reverse transcriptase, whose function is to restore shortening telomeres. Unlike most somatic cell types, human T lymphocytes are capable of briefly reactivating telomerase expression at the time of stimulation. Telomerase expression in T lymphocytes is modulated by a variety of external stimuli and by viral infections. However, telomerase reactivation in stimulated, proliferating human T lymphocytes is limited and cannot prevent the ultimate onset of senescence. Ectopic telomerase expression can rescue human and macaque antigen-specific T cells from senescence. Primary T cells have been engineered with telomerase to have substantially extended replicative lifespans without the loss of primary cell functions or malignant transformation. 'Immortal' antigen-specific T-cell lines and clones overexpressing telomerase are an invaluable source of well-characterized quasi-primary T cells for research of T-cell biology and are potentially useful for immunotherapy of cancer and AIDS.

Immunogenicity of a recombinant lentiviral vector carrying human telomerase tumor antigen in HLA-B*0702 transgenic mice

Over expression of telomerase represents a hallmark of cancer cells and the induction of T cell immunity against this universal tumor antigen have gained promising interest for anticancer immunotherapy. In this study we evaluated a recombinant lentiviral vector expressing the human telomerase reverse transcriptase (lv-hTERT) vaccination in the humanized HLA-B*0702 transgenic (HLA-B7 Tg) mice. A single lv-hTERT vector immunization induces potent and broad HLA-B7-restricted CTL responses against hTERT. Unlike conventional hTERT peptide or DNA immunization, the lv-hTERT vector triggers high and sustained IFN-gamma producing CD8(+) T cell responses in HLA-B7 Tg mice. The avidity and in vivo cytotoxicity of CD8(+) T cells were stronger in lv-hTERT vector-immunized mice than in hTERT peptide or DNA vaccinated groups. The study also showed that the use of prime-boost vaccination drastically improved the magnitude and strength of lentivector-primed CD8(+) T cells. Our data indicated that lentiviral delivery of hTERT is suitable for enhancing cellular immunity against hTERT and offers a promising alternative for telomerase-based cancer vaccine.