Phase Ia study of the indoleamine 2,3-dioxygenase 1 (IDO1) inhibitor navoximod (GDC-0919) in patients with recurrent advanced solid tumors

BACKGROUND

Indoleamine-2,3-dioxygenase 1 (IDO1) catalyzes the oxidation of tryptophan into kynurenine and is partially responsible for acquired immune tolerance associated with cancer. The IDO1 small molecule inhibitor navoximod (GDC-0919, NLG-919) is active as a combination therapy in multiple tumor models.

METHODS

This open-label Phase Ia study assessed safety, pharmacokinetics (PK), pharmacodynamics (PD), and preliminary anti-tumor activity of navoximod in patients with recurrent/advanced solid tumors, administered as 50-800 mg BID on a 21/28 day and at 600 mg on a 28/28 day schedule. Plasma kynurenine and tryptophan were longitudinally evaluated and tumor assessments were performed.

RESULTS

Patients (n = 22) received a median of 3 cycles of navoximod. No maximum tolerated dose was reached. One dose-limiting toxicity of Grade 4 lower gastrointestinal hemorrhage was reported. Adverse events (AEs) regardless of causality in ≥20% of patients included fatigue (59%), cough, decreased appetite, and pruritus (41% each), nausea (36%), and vomiting (27%). Grade ≥ 3 AEs occurred in 14/22 patients (64%), and were related to navoximod in two patients (9%). Navoximod was rapidly absorbed (Tmax ~ 1 h) and exhibited dose-proportional increases in exposure, with a half-life (t1/2 ~ 11 h) supportive of BID dosing. Navoximod transiently decreased plasma kynurenine from baseline levels with kinetics consistent with its half-life. Of efficacy-evaluable patients, 8 (36%) had stable disease and 10 (46%) had progressive disease.

CONCLUSIONS

Navoximod was well-tolerated at doses up to 800 mg BID decreasing plasma kynurenine levels consistent with its half-life. Stable disease responses were observed.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT02048709 .

Assessing the safety and immunogenicity of recombinant vesicular stomatitis virus Ebola vaccine in healthy adults: a randomized clinical trial

BACKGROUND

The 2013-2016 Ebola virus outbreak in West Africa was the most widespread in history. In response, alive attenuated recombinant vesicular stomatitis virus (rVSV) vaccine expressing Zaire Ebolavirus glycoprotein (rVSVΔG-ZEBOV-GP) was evaluated in humans.

METHODS

In a phase 1, randomized, dose-ranging, observer-blind, placebo-controlled trial, healthy adults aged 18-65 years were randomized into 4 groups of 10 to receive one of 3 vaccine doses or placebo. Follow-up visits spanned 180 days postvaccination for safety monitoring, immunogenicity testing and any rVSV virus shedding.

RESULTS

Forty participants were injected with rVSVΔG-ZEBOV-GP vaccine (n = 30) or saline placebo (n = 10). No serious adverse events related to the vaccine or participant withdrawals were reported. Solicited adverse events during the 14-day follow-up period were mild to moderate and self-limited, with the exception of injection-site pain and headache. Viremia following vaccination was transient and no longer detectable after study day 3, with no virus shedding in saliva or urine. All vaccinated participants developed serum immunoglobulin G (IgG), as measured by Ebola virus envelope glycoprotein-based enzyme-linked immunosorbent assay (ELISA). Immunogenicity was comparable across all dose groups, and sustained IgG titers were detectable through to the last visit, at study day 180.

INTERPRETATION

In this phase 1 study, there were no safety concerns after a single dose of rVSVΔG-ZEBOV-GP vaccine. IgG ELISA showed persistent high titers at 180 days postimmunization. There was a period of reactogenicity, but in general, the vaccine was well tolerated. This study provides evidence of the safety and immunogenicity of rVSVΔG-ZEBOV-GP vaccine and importance of its further investigation. Trial registration: Clinical-Trials.gov no., NCT02374385.

A Recombinant Vesicular Stomatitis Virus Ebola Vaccine

BACKGROUND

The worst Ebola virus disease (EVD) outbreak in history has resulted in more than 28,000 cases and 11,000 deaths. We present the final results of two phase 1 trials of an attenuated, replication-competent, recombinant vesicular stomatitis virus (rVSV)-based vaccine candidate designed to prevent EVD.

METHODS

We conducted two phase 1, placebo-controlled, double-blind, dose-escalation trials of an rVSV-based vaccine candidate expressing the glycoprotein of a Zaire strain of Ebola virus (ZEBOV). A total of 39 adults at each site (78 participants in all) were consecutively enrolled into groups of 13. At each site, volunteers received one of three doses of the rVSV-ZEBOV vaccine (3 million plaque-forming units [PFU], 20 million PFU, or 100 million PFU) or placebo. Volunteers at one of the sites received a second dose at day 28. Safety and immunogenicity were assessed.

RESULTS

The most common adverse events were injection-site pain, fatigue, myalgia, and headache. Transient rVSV viremia was noted in all the vaccine recipients after dose 1. The rates of adverse events and viremia were lower after the second dose than after the first dose. By day 28, all the vaccine recipients had seroconversion as assessed by an enzyme-linked immunosorbent assay (ELISA) against the glycoprotein of the ZEBOV-Kikwit strain. At day 28, geometric mean titers of antibodies against ZEBOV glycoprotein were higher in the groups that received 20 million PFU or 100 million PFU than in the group that received 3 million PFU, as assessed by ELISA and by pseudovirion neutralization assay. A second dose at 28 days after dose 1 significantly increased antibody titers at day 56, but the effect was diminished at 6 months.

CONCLUSIONS

This Ebola vaccine candidate elicited anti-Ebola antibody responses. After vaccination, rVSV viremia occurred frequently but was transient. These results support further evaluation of the vaccine dose of 20 million PFU for preexposure prophylaxis and suggest that a second dose may boost antibody responses. (Funded by the National Institutes of Health and others; rVSV∆G-ZEBOV-GP ClinicalTrials.gov numbers, NCT02269423 and NCT02280408 .).

Combination immunotherapy for high-risk resected and metastatic melanoma patients

BACKGROUND

Patients with advanced melanoma have a poor outcome. We hypothesize that combination immunotherapy can synergistically activate host immunity to generate an effective treatment for patients with high-risk, resected stage 3, recurrent, refractory, or stage 4 melanoma.

METHODS

We conducted a phase 2 clinical trial of HyperAcute Melanoma (HAM) vaccine (NLG-12036, NewLink Genetics) combined with pegylated interferon (Sylatron, Merck). Trial design consisted of a 12-week regimen with the initial 4 weekly treatments consisting of HAM alone (intradermally) followed by 8 additional treatments of HAM plus Sylatron (subcutaneously, 6 μg/kg). Trial endpoint outcomes include clinical response, overall safety, and correlative findings for observed antitumor effect.

RESULTS

Our cohort consisted of 25 patients with a median age of 60. Twenty-one patients completed the trial and 4 stopped because of progressive disease (PD). According to the Response Evaluation Criteria in Solid Tumors, of the 16 stage 4 patients, 2 had a complete response (CR), 1 had stable disease, and 4 had no evidence of disease (NED) after resection. For stage 2/3 patients, 3 of 9 remained NED, and the 1 stage 2C patient had slow PD with a single site resected and is currently NED. The median overall survival time was 29 months, with 60% of the patients surviving for >1 year. Of the 25 patients, 12 (48%) are still alive. All evaluable patients (21/21) seroconverted, developing autoimmune antibodies. Four of 25 patients developed vitiligo, correlating with 2 CR patients and 2 NED patients.

CONCLUSION

Combination immunotherapy with HAM plus Sylatron shows clinical efficacy with tumor regression and concomitant immune activation. Optimization of dosing schedules and therapeutic efficacy should be further explored to enhance the benefit of this promising immunotherapeutic approach.

Trans-complementing adenoviral vectors for oncolytic therapy of malignant melanoma

BACKGROUND

Despite attempts to develop efficient viral-based gene transfer therapies for the treatment of malignant tumors, only limited progress has been made to improve the efficacy of this approach. As an alternative, the use of replicating oncolytic adenoviruses with and without the expression of therapeutic transgenes is an area of active investigation.

METHODS

We used a human melanoma xenograft tumor nude mouse model to test the efficacy of a bivalent vector approach consisting of two trans-complementing replication-incompetent adenoviral vectors that resulted in tumor-restricted oncolysis. We combined an E1-deleted non-replicating adenoviral vector expressing the herpes simplex virus thymidine kinase gene (AV.C2.TK) and Ad5.dl1014, an E4-deleted/E4orf4-only expressing adenovirus, to allow full replication competence when tumor cells were co-infected with both vectors.

RESULTS

A375 tumors showed apoptosis at the ultrastructural level after transduction with the trans-complementing vector system that was not seen with injection of either vector alone. Apoptotic DNA fragments could be co-localized to sites of infection with the adenoviral vectors. A significant survival benefit was achieved for the trans-complementing vector treated animals compared to animals treated with either vector alone. Interestingly, the administration of GCV did not further increase animal survival over treatment with the trans-complementing system of viruses alone, and long-term survival was only seen in the trans-complementing vector treatment group. Intraperitoneal administration of a pseudo-wild-type vector Ad.dl327 resulted in significant hepatotoxicity, while intraperitoneal administration of the trans-complementing vectors resulted in only mild liver abnormalities.

CONCLUSIONS

The trans-complementing vector approach using a combination of E1- and E4-deleted adenoviral vectors showed similar antitumor efficacy as reported for monovalent replicating vector systems, but may offer additional safety by reducing the risk of dissemination of the replication-competent vectors by requiring the presence of both vectors in a cell to achieve replication competence.

In situ generation of pseudotyped retroviral progeny by adenovirus-mediated transduction of tumor cells enhances the killing effect of HSV-tk suicide gene therapyin vitro andin vivo

BACKGROUND

Hybrid adeno-retroviral vector systems utilize the high efficiency of adenovirus transduction to direct the in situ production of retroviral progeny. In this study, we show that a single-step transduction of glioma cells with trans-complementing hybrid adeno-retroviral vectors effectively turns these cells into retrovirus vector-producing cells, which in turn facilitates the transduction of adjacent cells.

METHODS

We have adapted the adeno-retroviral hybrid viral vector system to enhance the ganciclovir (GCV) killing of glioma cells following transfer of the herpes simplex virus thymidine kinase (HSV-tk) gene. To assess the effect of the in situ production of retroviral vectors on the transduction efficiency of glioma cells, 9L cells were transduced with adeno-retroviral hybrid vectors that separately express a retroviral genome (AVC2.GCEGFP or AVC2.GCTK) and retroviral packaging proteins (AxTetGP and AxTetVSVG). The generation of an integrated HSV-tk provirus by trans-complementation of the adeno-retroviral vectors was verified by analysis of the flanking retroviral LTR sequences. Tumors established on nu/nu mice were injected with the viruses followed by intraperitoneal injections of either PBS or GCV. We also estimated the copy numbers of the HSV-tk transgene present in the tumors of the treated mice. To determine the expression pattern of the HSV-tk transcripts within a tumor, in situ hybridization analysis was performed using an RNA probe specific for HSV-tk.

RESULTS

The co-transduction of rat 9L glioma cells with AVC2.GCEGFP together with vectors expressing packaging proteins of retroviruses increased the transduction efficiency. Transduction with AVC2.GCTK together with packaging vectors increased the in vitro sensitivity of cells to the pro-drug GCV by one log compared with control cells that were incapable of generating retrovirus. In vivo, the injection of established subcutaneous 9L tumors on athymic mice with a combination of AVC2.GCTK and packaging vectors followed by GCV treatment resulted in complete tumor regression in 50% of tumors at day 22, while no tumor regression was observed in control animals. Retroviral sequences diagnostic of 3' LTR reduplication in vivo were detected in genomic DNA extracted from the transduced tumors, indicating pro-viral integration of the retroviral genome derived from the adeno-retroviral hybrid vector. Furthermore, the relative copy number of the HSV-tk gene in tumors treated with the adeno-retroviral vectors was up to approximately 250-fold higher than in control tumors. In situ hybridization suggested dispersion of the HSV-tk product across a wider area of the tumor than in control tumors, which indicates the spread of the in situ generated retroviruses.

CONCLUSIONS

Although the efficacy of this system has to be evaluated in orthotopic models, our observations suggest that this hybrid adeno-retroviral vector system could improve the suicide gene therapy of tumors.

Persistence and expression of the adenosine deaminase gene for 12 years and immune reaction to gene transfer components: long-term results of the first clinical gene therapy trial

The first human gene therapy experiment begun in September 1990 used a retroviral vector containing the human adenosine deaminase (ADA) cDNA to transduce mature peripheral blood lymphocytes from patients with ADA deficiency, an inherited disorder of immunity. Two patients who had been treated with intramuscular injections of pegylated bovine ADA (PEG-ADA) for 2 to 4 years were enrolled in this trial and each received a total of approximately 10(11) cells in 11 or 12 infusions over a period of about 2 years. No adverse events were observed. During and after treatment, the patients continued to receive PEG-ADA, although at a reduced dose. Ten years after the last cell infusion, approximately 20% of the first patient's lymphocytes still carry and express the retroviral gene, indicating that the effects of gene transfer can be remarkably long lasting. On the contrary, the persistence of gene-marked cells is very low (< 0.1%), and no expression of the transgene is detectable in lymphocytes from the second patient who developed persisting antibodies to components of the gene transfer system. Data collected from these original patients have provided novel information about the longevity of T lymphocytes in humans and persistence of gene expression in vivo from vectors driven by the Moloney murine leukemia virus long-terminal repeat (LTR) promoter. This long-term follow-up has also provided unique evidence supporting the safety of retroviral-mediated gene transfer and illustrates clear examples of both the potential and the pitfalls of gene therapy in humans.

A novel approach using transcomplementing adenoviral vectors for gene therapy of adrenocortical cancer

Current therapies for adrenocortical carcinomas do not improve the life expectancy of patients. In this study, we tested whether a gene-transfer therapy based upon a suicide gene/prodrug system would be effective in an animal model of the disease. We employed E4- and E1A/B-depleted, herpes simplex virus-thymidine kinase-expressing adenoviral mutants that transcomplement each other within tumor cells, hereby improving transgene delivery and efficacy by viral replication in situ. Transcomplementation of vectors increased the fraction of transduced of tumor cells. This increase was accompanied by greater tumor volume reduction compared to non-transcomplementing approaches. Survival time improved with non-replicating vectors plus GCV compared to controls. However, transcomplementation/replication of vectors led to a further significant increment in anti-tumor activity and survival time (p < 0.02). In treated animals, we observed a high number of apoptotic nuclei both adjacent to and distant from injection sites and sites of viral oncolysis. Ultrastructural analyses exhibited nuclear inclusion bodies characteristic of virus production in situ, and provided further evidence that this therapy induced apoptotic cell death within tumor cells. We conclude that the efficacy of suicide gene therapy is significantly amplified by viral replication and, in combination with GCV, significantly reduces tumor burden and increases survival time.

The release of inflammatory cytokines from human peripheral blood mononuclear cells in vitro following exposure to adenovirus variants and capsid

Preclinical and clinical studies with adenoviral vectors have clearly illustrated the potential advantages of this gene transfer system. However, many studies have also demonstrated potent immune responses directed at both vector and transduced cells. We examined in vitro responses of human peripheral blood mononuclear cells (PBMC) to virus exposure as a model for this host response. PBMC were isolated from normal donors and incubated with wild-type adenovirus (Ad5), Ad5 variants deleted for segments of E1 and/or E3, and empty viral capsids. Proinflammatory cytokine release was monitored for 96 hr. Induction of TNF-alpha by intact virions was low although stimulation by empty capsid gave a significant and sustained response. Induction of IL-6, GM-CSF, and a panel alpha- and beta-chemokines by intact virions was prominent, often approaching results obtained with 2.5 microg/ml of lipopolysaccharide (LPS). Responses were generally independent of virion genetic composition and were only partially blunted when UV-inactivated virus was used. Dose-response data showed 100-fold increases in virion concentration produced a maximum 3-fold increase in cytokine release, suggesting saturation. Surprisingly, prominent stimulation occurred after addition of empty capsid, which typically provoked responses equivalent to those seen with LPS stimulation. We present arguments that cellular signal transduction mechanisms activated by binding of virions/capsids stimulate transcription of proinflammatory cytokine genes.

AV.TK-mediated killing of subcutaneous tumors in situ results in effective immunization against established secondary intracranial tumor deposits

Gene transfer vectors expressing herpes simplex thymidine kinase (HSVtk), in addition to direct killing of tumor cells, often have an associated local "bystander effect" mediated by metabolic coupling of tumor cells. A systemic antitumor effect mediated by the immune system, termed the distant bystander effect, has also been reported. We have observed the development of cytotoxic T-lymphocyte (CTL) populations and long-lasting antitumor immunity following treatment of subcutaneous tumors with an adenoviral vector expressing HSVtk (AV.TK) and ganciclovir (GCV) in rat glioma model. This vaccination effect seen with AV.TK/GCV treatment of subcutaneous tumor could even abrogate or retard growth of previously established secondary intracranial tumors.

Modified human immunodeficiency virus-based lentiviral vectors display decreased sensitivity to trans-dominant Rev

As a first step toward the development of HIV-based conditionally replicating defective interfering particles expressing trans-dominant Rev (TdRev), we studied whether mutation of the splicing signals and replacement of the RRE by the SRV-1 CTE would render these vectors less sensitive to TdRev. Vectors with mutations in the splicing signals (SD-/RRE+) yielded high titers (5 X 10(6) CFU/ml) and showed higher levels of cytoplasmic unspliced mRNA than the corresponding SD+/RRE+ vectors either in the absence of Rev, in the presence of TdRev, or in the presence of both TdRev and Rev. Proviral copies of SD-/RRE+ vectors were rescued more efficiently than SD+/RRE+ vectors when TdRev was expressed. Vectors with the SRV-1 CTE (SD+/CTE+ and SD-/CTE+) expressed high levels of cytoplasmic unspliced mRNA in the absence of Rev expression. Titers obtained with the SD-/CTE+ vectors (10(6) CFU/ml) were higher than the titers obtained with SD+/CTE+ vectors. We also tested the effect of other structural modifications such as the orientation of the expression cassette and the presence of the central polypurine tract (cPPT/CTS). We show that an expression cassette cloned in the reverse orientation with respect to the LTRs or elimination of the cPPT/CTS element severely affected vector titers. We also demonstrated that these vectors can be efficiently mobilized from their proviral state by HIV trans-complementing functions, and transduced into secondary target cells without suffering any genomic rearrangement.

Adeno-retroviral chimeric viruses as in vivo transducing agents

Several hybrid viral gene transfer systems have been described that exploit the favorable features of the two parent viral species. We have developed a hybrid adeno-retroviral vector system to generate a retroviral vector in situ. The system consists of adenoviruses encoding MoMLV gag.pol (Axtet.gag.pol), the VSV-G viral envelope (Axtet.VSV-G), the retroviral vector LXSN expressing the neomycin phosphotransferase gene (AV-LXSN) and a transcriptional regulator to control expression of gag.pol and envelope (AV-rtTA). In vitro, biologically active retroviral vector preparations were generated following adeno-retroviral transduction of 9L rat glioma cells. In vivo the transcomplementing adeno-retroviruses were co-administered intratumorally into subcutaneous 9L glioma tumors in rats and human A375 melanoma xenografts in nude mice. In the 9L rat model, G418 cell cultures were only obtained when 9L cells were harvested from tumors injected with all four transcomplementing adeno-retroviruses. Molecular analysis of DNA extracted from 9L G418 populations derived both in vitro and in vivo showed appropriate integration of the LXSN proviral sequence. Tumor cells were harvested 1, 3 and 4 weeks after adeno-retrovirus administration to the human A375 xenografts. The percentage of G418 colonies recovered from tumors transduced with all of the transcomplementing adeno-retroviruses increased with time, whereas no increase was observed in tumors transduced with AV-LXSN alone. DNA extracted from G418 A375 cell populations showed the presence of integrated proviral sequences only in animals that received the full complement of adeno-retroviruses. These results demonstrate that adenoviral vectors expressing transcomplementing genes for retroviral proteins and retroviral vector RNAs can be used for in situ transduction of target cells.

Anti-tumor immunity generated by tumor cells engineered to express B7-1 via retroviral or adenoviral gene transfer

We engineered B7-1 retroviral and adenoviral gene transfer systems and studied them in four immunogenic tumor models. M-MSV tumor cells, but not K-Balb, 38.2 and 205 tumor cells, when expressing B7-1 by retroviral transduction were rejected and conferred protection against a tumor challenge. Transient expression of B7-1 after transduction with adenoviruses was less efficient. We observed enhanced cytotoxic T-lymphocyte activity accompanied by increased secretion of IL-6, IFNgamma and GM-CSF. GM-CSF secretion correlated with tumor rejection. Enhanced IFNgamma but unchanged IL-4 secretion suggested a T-helper 1-mediated anti-tumor immune response.

Adenoviral vectors capable of replication improve the efficacy of HSVtk/GCV suicide gene therapy of cancer

A major obstacle to the success of gene therapy strategies that directly target cancer cells is the poor vector distribution within solid tumors. To address this problem, we developed an E1b 55 kDa attenuated, replication-competent adenovirus (Ad.TKRC) which expresses the herpes simplex-1 thymidine kinase (HSVtk) gene to sensitize tumors to ganciclovir (GCV). Efficacy of this combined strategy was tested in nude mice with subcutaneous human A375 melanoma and ME180 cervical carcinomas. Intratumoral injection of a replication-defective adenoviral vector expressing HSVtk (Ad.TK) followed by GCV treatment resulted in doubling of the survival time of mice bearing A375 tumors and 20% long-term survival of mice with ME180 tumors. Treatment of tumors with Ad.TKRC without GCV resulted in a similar antitumor effect, confirming that the replicating vector has an oncolytic effect. When GCV was initiated 3 days after Ad.TKRC injection, survival of mice with each tumor type was greatly prolonged, with 60% of animals with ME180 tumors surviving for over 160 days. These results confirm that both the oncolysis caused by a replicating virus and suicide/prodrug gene therapy with HSVtk/GCV have potent antitumor effects. When combined, these two approaches are complementary resulting in a significantly improved treatment outcome.

The bystander effect in the HSVtk/ganciclovir system and its relationship to gap junctional communication

The bystander effect (BSE) is an interesting and important property of the herpes thymidine kinase/ganciclovir (hTK/GCV) system of gene therapy for cancer. With the BSE, not only are the hTK expressing cells killed upon ganciclovir (GCV) exposure but also neighboring wild-type tumor cells. On testing a large number of tumor cell lines in vitro, a wide range of sensitivity to bystander killing was found. Since transfer of toxic GCV metabolites from hTK-modified to wild-type tumor cells via gap junctions (GJ) seemed to be a likely mechanism of the BSE, we tested GJ function in these various tumors with a dye transfer technique and pharmacological agents known to affect GJ communication. We confirmed that mixtures of tumor cell resistant to the BSE did not show dye transfer from cell to cell while bystander-sensitive tumor cells did. Dieldrin, a drug known to decrease GJ communication, diminished dye transfer and also inhibited the BSE. Forskolin, an upregulator of cAMP did increase GJ, but directly inhibited hTK and therefore its effect on BSE could not be determined. We conclude that these observations further support port the concept that functional GJ play an important role in the BSE and further suggest that pharmacological manipulation of GJ may influence the outcome of cancer therapy with hTK/GCV.

Enhancement of the herpes simplex virus thymidine kinase/ganciclovir bystander effect and its antitumor efficacy in vivo by pharmacologic manipulation of gap junctions

Apigenin, a flavinoid, and lovastatin, an HMG-CoA reductase inhibitor, upregulated gap junction (GJ) function and dye transfer in tumors expressing GJ and were inactive in the GJ-negative tumor line N2a. N2a cells transfected with the connexin 43 gene showed restored cell-to-cell dye transfer, which could then be improved nearly fourfold by addition of apigenin. To test the drugs in HSV thymidine kinase/ganciclovir (HSV-tk/GCV) tumor killing, mixtures of 90% wild-type (WT) with 10% HSV-tk gene-modified MCA38 adenocarcinoma cells were exposed in vitro to GCV +/- apigenin or lovastatin. A significant bystander effect (BSE) was seen following GCV treatment alone, while neither apigenin or lovastatin alone had any effect on the recovery of viable tumor colonies. However, GCV-treated cultures also exposed to apigenin or lovastatin showed an increased BSE and reduced tumor cell recovery. Thirty percent of mice bearing tumors from the same mixture of 90% WT and 10% HSV-tk MCA38 cells treated with GCV alone became tumor free. Tumor-bearing mice given only two or three injections of lovastatin or apigenin during GCV treatment had a doubling of the antitumor response rate, with 60-70% of the mice achieving complete remission. These results support the hypothesis that the transfer of phosphorylated GCV from HSV-tk gene-expressing cells to neighboring WT tumor cells is a major component of the BSE and that pharmacological manipulation of GJ function with lovastatin or apigenin can result in striking improvement in the antitumor response in mice with tumors modified to contain as few as 10% HSV-tk cells.

Adenovirus vectors as transcomplementing templates for the production of replication defective retroviral vectors

We have generated an adenovirus containing a retroviral vector sequence encoding the neomycin phosphotransferase (neo) gene (AV-LXSN). AV-LXSN transduction of retroviral packaging cell lines led to production of LXSN retroviral vector with alternative viral envelopes; exposure of target cells to retroviral containing supernatants confirmed envelope specific tropism. Retroviral titers (G418 cfu/ml) were comparable to those produced by standard techniques. Retrovirus could be detected in supernatants within 24 hours of AV-LXSN transduction and persisted as long as 120 hours. Southern blot analysis of DNA purified from populations of G418 cells showed the presence of a single neo containing restriction fragment of the appropriate size that could only be generated by reverse transcription of LXSN to produce LXSN provirus. This adeno-retroviral chimeric vector system could simplify the generation and testing of different retroviral vectors, particularly where assessment of vectors with alternative envelopes carrying novel targeting ligands is required.

Generation of a conditionally neo(r)-containing retroviral producer cell line: effects of neo(r) on retroviral titer and transgene expression

We have developed a method for generating high-titer retroviral producer cell lines conditionally containing a neomycin resistance gene (neo(r)) based on the Cre/loxP system. For this, a bicistronic retroviral splicing vector carrying the green fluorescence protein (GFP) and a marker gene cassette consisting of internal ribosome entry site (IRES) and neo(r) flanked by loxP sites, was constructed and conveniently used to generate a G418 resistant vector producer cell line. Following titer determination and verification of the biological activity of the retroviral supernatants, the selectable expression cassette which was no longer required was excised from the provirus by transient Cre expression using an adenoviral vector. This strategy led to precise excision of neo(r) and generation of retroviral supernatants containing functional 'neo-less' retroviral particles without detrimental effects on the high vector titers found in the parental neo(r)-containing producer lines. GFP expression was significantly increased after the excision of neo(r), in both the producer lines and retrovirally transduced target cells. Reintroduction of neo(r) did not alter GFP expression, suggesting that the neo(r) gene and/or its gene product per se are not acting as a transcriptional silencer.

Efficient directional cloning of recombinant adenovirus vectors using DNA-protein complex

We describe an efficient cloning system utilizing adenoviral DNA-protein complexes which allows the directional cloning of genes into adenoviral expression vectors in a single step. DNA-protein complexes derived from a recombinant adenovirus (AVC2.null) were isolated by sequential use of CsCl step gradients followed by isopycnic centrifugation in a mixture of CsCl and guanidine HCl. AVC2.null is an adenoviral expression vector containing unique restriction sites between the human CMV-IE promoter and the SV40 intron/polyadenylation site. Transgenes were prepared for cloning into this vector by introduction of compatible restriction sites by PCR. A vector expressing rat granulocyte-macrophage colony-stimulating factor (GM-CSF) was constructed using DNA-protein complex as well as by traditional recombination techniques. The efficacy of our adenoviral cloning system utilizing DNA-protein complex was two logs higher than that seen using homologous recombination. All viruses generated by directional ligation of the insert into the vector DNA-protein complexes contained the desired transgene in the correct orientation. This technique greatly simplifies and accelerates the generation of recombinant adenoviral vectors.

Characterization of the antitumor immune response generated by treatment of murine tumors with recombinant adenoviruses expressing HSVtk, IL-2, IL-6 or B7-1

In a cancer gene therapy model recombinant adenoviruses expressing the herpes simplex virus thymidine kinase (HSVtk) gene were injected into tumors in situ, either alone or in combination with adenoviruses (Avs) engineered to express IL-2, IL-6 or the costimulatory molecule B7-1. HSVtk phosphorylates the prodrug ganciclovir, thus converting it into an antimetabolite which kills not only HSVtk expressing cells, but also by the 'bystander effect', neighboring untransduced tumor cells. The tumors regressed in 80% of mice upon AvTK/ganciclovir treatment: combinations with AvIL-2, AvIL-6, or AvB7-1 did not improve these results. Cured mice were protected from further challenge with wild-type tumor but not from challenges with an unrelated syngeneic tumor cell line. Since cytotoxic T lymphocyte responses in this tumor model were weak, we analyzed cytokine secretion from spleen cells of treated animals. The best correlate of antitumor immunity in this model was enhanced secretion of GM-CSF, while secretion of IL-2, IL-6 and IFN gamma was also frequently increased but not as consistently. The enhanced IFN gamma secretion associated with unchanged IL-4 secretion suggests that AvTK treatment results in a predominantly Th1-mediated antitumor immune response.

Gut epithelial cells as targets for gene therapy of hemophilia

Gut epithelium is an attractive target for gene therapy of hemophilia due to the large number of rapidly dividing cells that should be readily accessible to a wide range of vectors by a noninvasive route of administration. We have performed in vitro tests to determine the suitability of gut epithelial cells for gene transfer, protein synthesis, and secretion of coagulation factors VIII and IX. The results with retroviral vectors indicate that transduced epithelial cells from human, rat, or porcine small or large intestine can synthesize significant amounts of factor VIII or factor IX and that two-thirds or more of the recombinant protein is secreted in a basolateral direction (i.e., away from the lumen and toward underlying capillaries and lymphatics). Furthermore, we have demonstrated that intestinal epithelial cells are susceptible to efficient gene transfer by lipofection and adenovirus vectors. In the case of factor IX, we have produced a high-titer adenovirus vector capable of transducing gut epithelial cells resulting in synthesis of factor IX. The results of our in vitro studies indicate that gene transfer targeting gut epithelium as a new approach to hemophilia gene therapy is rational and merits in vivo studies in hemophilia animal models.

T lymphocyte-directed gene therapy for ADA- SCID: initial trial results after 4 years

In 1990, a clinical trial was started using retroviral-mediated transfer of the adenosine deaminase (ADA) gene into the T cells of two children with severe combined immunodeficiency (ADA- SCID). The number of blood T cells normalized as did many cellular and humoral immune responses. Gene treatment ended after 2 years, but integrated vector and ADA gene expression in T cells persisted. Although many components remain to be perfected, it is concluded here that gene therapy can be a safe and effective addition to treatment for some patients with this severe immunodeficiency disease.

Retrovirus mediated gene transfer as therapy for adenosine deaminase (ADA) deficiency

ADA deficiency manifests as a severe combined immunodeficiency with profound T-lymphocytopenia. Affected individuals have variable defects of both T- and B-lymphocyte function and greatly increased morbidity and mortality caused by frequent viral and bacterial infection. In 1990 a clinical protocol for the treatment of this disease using retrovirus mediated transfer of the ADA gene into peripheral lymphocytes was begun and in 1993 an amendment permitting gene transfer to CD34+ stem cells isolated from peripheral blood or from umbilical cord blood was approved. Five patients have been treated on this protocol and have been analyzed for the persistence of cells containing the transferred gene and for immunologic reconstitution.

Strategies for gene therapy

The use of retroviral-mediated gene transfer to introduce a DNA label into T cells (TIL) being used in the immunotherapy of patients with malignant melanoma finally opened the door to the clinical application of gene therapy for a wide variety of inherited and acquired diseases. The gene therapy trial for ADA deficiency SCID has demonstrated that long term stable expression of exogenous genes can be achieved in human T lymphocytes using retroviral vectors for ex vivo treatment and that significant immune reconstitution can be achieved in these patients following periodic infusions with ADA gene-corrected autologous T cells. Newer clinical applications include the insertion of genes into CD34 enriched stem cell populations, the testing of autologous tumor vaccines employing cytokine gene-modified tumor cells and the direct transfer of the herpes thymidine kinase gene into brain tumors in situ in order to render those tumors sensitive to treatment with the ordinarily non-cytotoxic drug ganciclovir.

Analysis of repetitive sequence elements containing tRNA-like sequences

Several repetitive sequence elements from diverse species share extensive sequence homology with tRNA molecules. Analysis of the tRNA-like sequences within these elements suggest that they have originated from authentic tRNA sequences. Elements containing tRNA-like sequences can be divided into three distinct groups whose members share extensive sequence homology, have similar sequence organization and have unique species distribution. We suggest that these three groups represent independent examples of retroposon families that have originated from tRNAs.

A universal model for the secondary structure of 5.8S ribosomal RNA molecules, their contact sites with 28S ribosomal RNAs, and their prokaryotic equivalent

The phylogenetic approach (ref. 1) has been utilized in construction of a universal 5.8S rRNA secondary structure model, in which about 65% of the residues exist in paired structures. Conserved nucleotides primarily occupy unpaired regions. Multiple compensating base changes are demonstrated to be present in each of the five postulated helices, thereby forming a major basis for their proof. The results of chemical and enzymatic probing of 5.8S rRNAs (ref. 13, 32) are fully consistent with, and support, our model. This model differs in several ways from recently proposed 5.8S rRNA models (ref. 3, 4), which are discussed. Each of the helices in our model has been extended to the corresponding bacterial, chloroplast and mitochondrial sequences, which are demonstrated to be positionally conserved by alignment with their eukaryotic counterparts. This extension is also made for the base paired 5.8S/28S contact points, and their prokaryotic and organelle counterparts. The demonstrated identity of secondary structure in these diverse molecules strongly suggests that they perform equivalent functions in prokaryotic and eukaryotic ribosomes.

Adenovirus type 2 fiber mRNA synthesis: no evidence for a cytoplasmic processing pathway

Adenovirus type 2 fiber mRNA exists in several forms in the cytoplasm which differ in the presence or absence of extra 5'-leader segments (L. T. Chow and T. R. Broker, Cell 15:497-510, 1978). We have investigated the possibility that forms possessing extra leader segments serve as precursors to the mature form in the cytoplasm. Pulse-labeled fiber mRNA became considerably shorter (150 to 250 bases) during a chase; however, most of the pulse-labeled species failed to hybridize to DNA fragments known to encode extra leader segments. Moreover, the entire decrease in size appeared to be due to extensive shortening of the polyadenylic acid tail. Mature-sized fiber mRNA was synthesized normally in cells infected with the nondefective adenovirus type 2-simian virus 40 hybrid virus Ad2+ND5, in which the region encoding the extra leader segments is deleted. These results indicate that the additional 5'-leader segments present in wild-type adenovirus type 2 fiber mRNA are not required for the production of mature fiber mRNA and that species that possess them are not cytoplasmic precursors to the mature form.