Supplemental guidance on testing for replication-competent retrovirus in retroviral vector-based gene therapy products and during follow-up of patients in clinical trials using retroviral vectors

Current strategies employed in the manipulation of gene expression for clinical purposes

Abnormal gene expression level or expression of genes containing deleterious mutations are two of the main determinants which lead to genetic disease. To obtain a therapeutic effect and thus to cure genetic diseases, it is crucial to regulate the host's gene expression and restore it to physiological conditions. With this purpose, several molecular tools have been developed and are currently tested in clinical trials. Genome editing nucleases are a class of molecular tools routinely used in laboratories to rewire host's gene expression. Genome editing nucleases include different categories of enzymes: meganucleses (MNs), zinc finger nucleases (ZFNs), clustered regularly interspaced short palindromic repeats (CRISPR)- CRISPR associated protein (Cas) and transcription activator-like effector nuclease (TALENs). Transposable elements are also a category of molecular tools which includes different members, for example Sleeping Beauty (SB), PiggyBac (PB), Tol2 and TcBuster. Transposons have been used for genetic studies and can serve as gene delivery tools. Molecular tools to rewire host's gene expression also include episomes, which are divided into different categories depending on their molecular structure. Finally, RNA interference is commonly used to regulate gene expression through the administration of small interfering RNA (siRNA), short hairpin RNA (shRNA) and bi-functional shRNA molecules. In this review, we will describe the different molecular tools that can be used to regulate gene expression and discuss their potential for clinical applications. These molecular tools are delivered into the host's cells in the form of DNA, RNA or protein using vectors that can be grouped into physical or biochemical categories. In this review we will also illustrate the different types of payloads that can be used, and we will discuss recent developments in viral and non-viral vector technology.

A Sensitive Liquid Chromatography-Mass Spectrometry Method for Determination of Toosendanin in Rat Plasma and its Application to Pharmacokinetic Study

A simple, rapid and sensitive analytical method was developed for the determination of toosendanin in rat plasma using liquid chromatography tandem mass spectrometry (LC-MS/MS). Andrographolide was selected as the internal standard, and the plasma samples were extracted by liquid-liquid extraction with diethyl ether. Chromatographic separation was performed on a Dikma Spursil C18, 3.5 μm (150 × 2.1 mm i.d) analytical column with 85% methanol:water (v/v) containing 0.025% formic acid (pH = 3.9) as mobile phase. The flow rate was 0.25 mL/min, and the total run time was 3 min. Detection was performed with a triple-quadrupole tandem mass spectrometer using negative ion mode electrospray ionization (ESI) in the multiple reaction monitoring (MRM) mode. The MS/MS ion transitions monitored were m/z 573.1 → 531.1 and 349.0 → 287.0 for toosendanin and andrographolide, respectively. Good linearity was observed over the concentration range of 3.125-500 ng/mL in 100 μL of rat plasma with a correlation coefficient ˃0.9997. Intra- and inter-assay variabilities were ˂8.5% in plasma. The recovery and the matrix effect were in the range 71.8-73.5% and 96.4-103.8%, respectively. The analyte was stable under various conditions (at room temperature, during freeze-thaw settings, in the autosampler, and under deep-freeze conditions). The method was successfully applied to a pharmacokinetic study of toosendanin after its oral administration in rats at a dose of 10 mg/kg.

Sensitive detection of integrated and free transcripts in chimeric antigen receptor T-cell manufactured cell products using droplet digital polymerase chain reaction

BACKGROUND AIMS

Viral vectors are commonly used to introduce chimeric antigen receptor (CAR) constructs into cell therapy products for the treatment of human disease. They are efficient at gene delivery and integrate into the host genome for subsequent replication but also carry risks if replication-competent lentivirus (RCL) remains in the final product. An optimal CAR T-cell product should contain sufficient integrated viral material and no RCL. Current product testing methods include cell-based assays with slow turnaround times and rapid quantitative polymerase chain reaction (PCR)-based assays that suffer from high result variability. The authors describe the development of a droplet digital PCR (ddPCR) method for detection of the vesicular stomatitis virus G glycoprotein envelope sequence, required for viral assembly, and the replication response element to measure integration of the CAR construct.

METHODS

Assay validation included precision, linearity, sensitivity, specificity and reproducibility over a range of low to high concentrations.

RESULTS

The limit of detection was 10 copies/μL, whereas negative samples showed <1.3 copies/μL. Within and between assay imprecision coefficients of variation across the reportable range (10-10 000 copies/μL) were <25%. Accuracy and linearity were verified by comparing known copy numbers with measured copy numbers (R² >0.9985, slope ~0.9). Finally, serial measurements demonstrated very good long-term reproducibility (>95% of replicate results within the originally established ± two standard deviations).

CONCLUSIONS

DDPCR has excellent reproducibility, linearity, specificity and sensitivity for detecting RCL and assuring the safety of patient products in a rapid manner. The technique can also likely be adapted for the rapid detection of other targets during cell product manufacturing, including purity, potency and sterility assays.

Chimeric Antigen Receptor T Cell Therapy Management and Safety: A Practical Tool From a Multidisciplinary Team Perspective

Purpose

The use process for chimeric antigen receptor T (CAR-T) cell drugs is complex and has been associated with a number of potentially severe complications, which requires management by a multidisciplinary team. Pharmacists are a key element in the team and have roles and responsibilities. Our objective was to develop a structured and practical guide that supports hospital pharmacist responsibilities and defines specific activities in a CAR-T cell therapy program, specifically in Europe.

Methods

A literature review was performed, and the recommendations related to pharmacy practice in CAR-T therapy programs were analyzed. A multidisciplinary team was assembled, and meetings were held to address the key tasks in the CAR-T cells’ management process and to create the guide, based on national and international recommendations and in expert’s opinions.

Results

The multidisciplinary team defined the following key tasks and issued recommendations to improve patient safety, treatment efficacy, and quality: patient selection and evaluation, CAR-T cell drug order to manufacturer, apheresis and material shipment, reception of CAR-T cell drug and storing, CAR-T cell drug prescription and pharmacy verification, CAR-T cell drug thawing and dispensing, CAR-T cell drug administration, patient education, pharmacovigilance and monitoring and outcomes’ record and evaluation. In each task the pharmacist’s role and how it can improve patient care are defined. A checklist was created to guarantee the compliance of standard operating procedures approved in the institution to manage CAR-T cell therapy and as a tool to collect required data for outcomes’ record and evaluation.

Conclusion

This article provides a consensus set of safety recommendations regarding CAR-T therapy management in clinical practice, easily implementable by other institutions in the European setting. The guide identifies key steps where the involvement of hospital pharmacists would improve the safety and quality of the process and is a support guide to standardize hospital pharmacists’ responsibilities within the multidisciplinary team.

Selecting a Cell Engineering Methodology During Cell Therapy Product Development

When considering the development pathway for a genetically modified cell therapy product, it is critically important that the product is engineered consistent with its intended human use. For scientists looking to develop and commercialize a new technology, the decision to select a genetic modification method depends on several practical considerations. Whichever path is chosen, the developer must understand the key risks and potential mitigations of the cell engineering approach. The developer should also understand the clinical implications: permanent/memory establishment versus transient expression, and clinical manufacturing considerations when dealing with transplantation of genetically engineered cells. This review covers important topics for mapping out a strategy for developers of new cell-based therapeutics. Biological, technological, manufacturing, and clinical considerations are all presented to map out development lanes for the initiation and risk management of new gene-based cell therapeutic products for human use.

Gene Replacement Therapy: A Primer for the Health-system Pharmacist

PURPOSE

Comprehensive review of gene replacement therapy with guidance and expert opinion on handling and administration for pharmacists.

SUMMARY

There are currently ∼2600 gene therapy clinical trials worldwide and 4 Food and Drug Administration (FDA)-approved gene therapy products available in the United States. Gene therapy and its handling are different from other drugs; however, there is a lack of guidance from the National Institutes of Health (NIH), FDA, Centers for Disease Control and Prevention (CDC), World Health Organization (WHO), and professional associations regarding their pharmaceutical application. Although the NIH stratifies the backbone biologicals of viral vectors in gene therapies into risk groups, incomplete information regarding minimization of exposure and reduction of risk exists. In the absence of defined guidance, individual institutions develop their own policies and procedures, which often differ and are often outdated. This review provides expert opinion on the role of pharmacists in institutional preparedness, as well as gene therapy handling and administration. A suggested infrastructural model for gene replacement therapy handling is described, including requisite equipment acquisition and standard operating procedure development. Personnel, patient, and caregiver education and training are discussed.

CONCLUSION

Pharmacists have a key role in the proper handling and general management of gene replacement therapies, identifying risk level, establishing infrastructure, and developing adequate policies and protocols, particularly in the absence of consensus guidelines for the handling and transport of gene replacement therapies.

The National Gene Vector Biorepository: Eleven Years of Providing Resources to the Gene Therapy Community

The National Gene Vector Biorepository (NGVB) program has been highly accessed by gene therapy investigators. The reagent repository has distributed over 1,000 reagents to 397 investigators. The Pharmacology/Toxicology Archive contains over 36,000 specimens from a variety of adeno-associated virus (AAV), adenoviral, and other pharmacology/toxicology studies. NGVB also maintains a searchable database of gene therapy pharmacology/toxicology studies to promote data sharing. NGVB has provided Food and Drug Administration (FDA)-mandated replication-competent virus testing for over 70 clinical trials. From 2008 to 2018, there have been 114 publications acknowledging the NGVB. It is unlikely that any other National Institutes of Health (NIH)-funded program has served as many gene therapy investigators as the NGVB.

Management guidelines for paediatric patients receiving chimeric antigen receptor T cell therapy

In 2017, an autologous chimeric antigen receptor (CAR) T cell therapy indicated for children and young adults with relapsed and/or refractory CD19+ acute lymphoblastic leukaemia became the first gene therapy to be approved in the USA. This innovative form of cellular immunotherapy has been associated with remarkable response rates but is also associated with unique and often severe toxicities, which can lead to rapid cardiorespiratory and/or neurological deterioration. Multidisciplinary medical vigilance and the requisite health-care infrastructure are imperative to ensuring optimal patient outcomes, especially as these therapies transition from research protocols to standard care. Herein, authors representing the Pediatric Acute Lung Injury and Sepsis Investigators (PALISI) Network Hematopoietic Stem Cell Transplantation (HSCT) Subgroup and the MD Anderson Cancer Center CAR T Cell Therapy-Associated Toxicity (CARTOX) Program have collaborated to provide comprehensive consensus guidelines on the care of children receiving CAR T cell therapy.

A Phase I-II Study Using Rexin-G Tumor-Targeted Retrovector Encoding a Dominant-Negative Cyclin G1 Inhibitor for Advanced Pancreatic Cancer

Rexin-G is a replication-incompetent retroviral vector displaying a cryptic SIG-binding peptide for targeting abnormal Signature (SIG) proteins in tumors and encoding a dominant-negative human cyclin G1 construct. Herein we report on the safety and antitumor activity of escalating doses of Rexin-G in gemcitabine-refractory pancreatic adenocarcinoma, with one 10-year survivor. For the safety analysis (n = 20), treatment-related grade 1 adverse events included fatigue (n = 6), chills (n = 2), and headache (n = 1), with no organ damage and no DLT. No patient tested positive for vector-neutralizing antibodies, antibodies to gp70, replication-competent retrovirus (RCR), or vector integration into genomic DNA of peripheral blood lymphocytes (PBLs). For the efficacy analysis (n = 15), one patient achieved a complete response (CR), two patients had a partial response (PR), and 12 had stable disease (SD). Median progression-free survival (PFS) was 2.7, 4.0, and 5.6 months at doses 0–I, II, and III, respectively. Median overall survival (OS) and 1-year OS rate at dose 0–I were 4.3 months and 0%, and at dose II–III they were 9.2 months and 33.3%. To date, one patient is still alive with no evidence of cancer 10 years after the start of Rexin-G treatment. Taken together, these data suggest that Rexin-G, the first targeted gene delivery system, is uniquely safe and exhibits significant antitumor activity, for which the FDA granted fast-track designation.

Screening Clinical Cell Products for Replication Competent Retrovirus: The National Gene Vector Biorepository Experience

Replication-competent retrovirus (RCR) is a safety concern for individuals treated with retroviral gene therapy. RCR detection assays are used to detect RCR in manufactured vector, transduced cell products infused into research subjects, and in the research subjects after treatment. In this study, we reviewed 286 control (n = 4) and transduced cell products (n = 282) screened for RCR in the National Gene Vector Biorepository. The transduced cell samples were submitted from 14 clinical trials. All vector products were previously shown to be negative for RCR prior to use in cell transduction. After transduction, all 282 transduced cell products were negative for RCR. In addition, 241 of the clinical trial participants were also screened for RCR by analyzing peripheral blood at least 1 month after infusion, all of which were also negative for evidence of RCR infection. The majority of vector products used in the clinical trials were generated in the PG13 packaging cell line. The findings suggest that screening of the retroviral vector product generated in PG13 cell line may be sufficient and that further screening of transduced cells does not provide added value.

Reducing Ex Vivo Culture Improves the Antileukemic Activity of Chimeric Antigen Receptor (CAR) T Cells

The success of chimeric antigen receptor (CAR)-mediated immunotherapy in acute lymphoblastic leukemia (ALL) highlights the potential of T-cell therapies with directed cytotoxicity against specific tumor antigens. The efficacy of CAR T-cell therapy depends on the engraftment and persistence of T cells following adoptive transfer. Most protocols for T-cell engineering routinely expand T cells ex vivo for 9 to 14 days. Because the potential for engraftment and persistence is related to the state of T-cell differentiation, we hypothesized that reducing the duration of ex vivo culture would limit differentiation and enhance the efficacy of CAR T-cell therapy. We demonstrated that T cells with a CAR-targeting CD19 (CART19) exhibited less differentiation and enhanced effector function in vitro when harvested from cultures at earlier (day 3 or 5) compared with later (day 9) timepoints. We then compared the therapeutic potential of early versus late harvested CART19 in a murine xenograft model of ALL and showed that the antileukemic activity inversely correlated with ex vivo culture time: day 3 harvested cells showed robust tumor control despite using a 6-fold lower dose of CART19, whereas day 9 cells failed to control leukemia at limited cell doses. We also demonstrated the feasibility of an abbreviated culture in a large-scale current good manufacturing practice-compliant process. Limiting the interval between T-cell isolation and CAR treatment is critical for patients with rapidly progressing disease. Generating CAR T cells in less time also improves potency, which is central to the effectiveness of these therapies. Cancer Immunol Res; 6(9); 1100-9. ©2018 AACR.

Clinical use of lentiviral vectors

Viral vectors provide an efficient means for modification of eukaryotic cells, and their use is now commonplace in academic laboratories and industry for both research and clinical gene therapy applications. Lentiviral vectors, derived from the human immunodeficiency virus, have been extensively investigated and optimized over the past two decades. Third-generation, self-inactivating lentiviral vectors have recently been used in multiple clinical trials to introduce genes into hematopoietic stem cells to correct primary immunodeficiencies and hemoglobinopathies. These vectors have also been used to introduce genes into mature T cells to generate immunity to cancer through the delivery of chimeric antigen receptors (CARs) or cloned T-cell receptors. CAR T-cell therapies engineered using lentiviral vectors have demonstrated noteworthy clinical success in patients with B-cell malignancies leading to regulatory approval of the first genetically engineered cellular therapy using lentiviral vectors. In this review, we discuss several aspects of lentiviral vectors that will be of interest to clinicians, including an overview of lentiviral vector development, the current uses of viral vectors as therapy for primary immunodeficiencies and cancers, large-scale manufacturing of lentiviral vectors, and long-term follow-up of patients treated with gene therapy products.

Retroviral and Lentiviral Safety Analysis of Gene-Modified T Cell Products and Infused HIV and Oncology Patients

Replication-competent retrovirus/lentivirus (RCR/L) and insertional oncogenesis are potential safety risks with integrating viruses in gene-modified cell therapies. As such, the Food and Drug Administration guidances outline RCR/L-monitoring methods throughout the entire gene therapy treatment cycle. We present data for 17 vector lots, 375 manufactured T cell products, and 308 patients post-infusion across both HIV and oncology indications, showing no evidence of RCR/L. Given our data, a Poisson probability model estimates that a single patient, or a group of patients, would need to be followed for at least 52.8 years to observe one positive RCR/L event, highlighting the unlikelihood of RCR/L development. Additionally, we estimate the median time for lentivirus-modified T cell products to fall below the 1% vector sequence threshold in peripheral or whole blood that would trigger vector integration site analysis. These estimated times are 1.4 months in hematologic malignancies, 0.66 month in solid tumors, and 0.92 month in HIV. Based on these considerable safety data in HIV and oncology and recent Biologics License Applications filed for lentiviral-modified T cell products for hematologic malignancies, this may be an opportune time to re-evaluate the current guidelines for T cell gene therapy product testing and long-term patient monitoring.

Detection of Replication Competent Lentivirus Using a qPCR Assay for VSV-G

Lentiviral vectors are a common tool used to introduce new and corrected genes into cell therapy products for treatment of human diseases. Although lentiviral vectors are ideal for delivery and stable integration of genes of interest into the host cell genome, they potentially pose risks to human health, such as integration-mediated transformation and generation of a replication competent lentivirus (RCL) capable of infecting non-target cells. In consideration of the latter risk, all cell-based products modified by lentiviral vectors and intended for patient use must be tested for RCL prior to treatment of the patient. Current Food and Drug Administration (FDA) guidelines recommend use of cell-based assays to this end, which can take up to 6 weeks for results. However, qPCR-based assays are a quick alternative for rapid assessment of RCL in products intended for fresh infusion. We describe here the development and qualification of a qPCR assay based on detection of envelope gene sequences (vesicular stomatitis virus G glycoprotein [VSV-G]) for RCL in accordance with Minimum Information for Publication of Quantitative Real-Time PCR Experiments (MIQE) guidelines. Our results demonstrate the sensitivity, linearity, specificity, and reproducibility of detection of VSV-G sequences, with a low false-positive rate. These procedures are currently being used in our phase 1 clinical investigations.

Absence of Replication-Competent Lentivirus in the Clinic: Analysis of Infused T Cell Products

Exposure to replication-competent lentivirus (RCL) is a theoretical safety concern for individuals treated with lentiviral gene therapy. For certain ex vivo gene therapy applications, including cancer immunotherapy trials, RCL detection assays are used to screen the vector product as well as the vector-transduced cells. In this study, we reviewed T cell products screened for RCL using methodology developed in the National Gene Vector Biorepository. All trials utilized third-generation lentiviral vectors produced by transient transfection. Samples from 26 clinical trials totaling 460 transduced cell products from 375 subjects were evaluated. All cell products were negative for RCL. A total of 296 of the clinical trial participants were screened for RCL at least 1 month after infusion of the cell product. No research subject has shown evidence of RCL infection. These findings provide further evidence attesting to the safety of third-generation lentiviral vectors and that testing T cell products for RCL does not provide added value to screening the lentiviral vector product.

Therapeutic gene editing: delivery and regulatory perspectives

Gene-editing technology is an emerging therapeutic modality for manipulating the eukaryotic genome by using target-sequence-specific engineered nucleases. Because of the exceptional advantages that gene-editing technology offers in facilitating the accurate correction of sequences in a genome, gene editing-based therapy is being aggressively developed as a next-generation therapeutic approach to treat a wide range of diseases. However, strategies for precise engineering and delivery of gene-editing nucleases, including zinc finger nucleases, transcription activator-like effector nuclease, and CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats-associated nuclease Cas9), present major obstacles to the development of gene-editing therapies, as with other gene-targeting therapeutics. Currently, viral and non-viral vectors are being studied for the delivery of these nucleases into cells in the form of DNA, mRNA, or proteins. Clinical trials are already ongoing, and in vivo studies are actively investigating the applicability of CRISPR/Cas9 techniques. However, the concept of correcting the genome poses major concerns from a regulatory perspective, especially in terms of safety. This review addresses current research trends and delivery strategies for gene editing-based therapeutics in non-clinical and clinical settings and considers the associated regulatory issues.

Genetic Engineering and Manufacturing of Hematopoietic Stem Cells

The marketing approval of genetically engineered hematopoietic stem cells (HSCs) as the first-line therapy for the treatment of severe combined immunodeficiency due to adenosine deaminase deficiency (ADA-SCID) is a tribute to the substantial progress that has been made regarding HSC engineering in the past decade. Reproducible manufacturing of high-quality, clinical-grade, genetically engineered HSCs is the foundation for broadening the application of this technology. Herein, the current state-of-the-art manufacturing platforms to genetically engineer HSCs as well as the challenges pertaining to production standardization and product characterization are addressed in the context of primary immunodeficiency diseases (PIDs) and other monogenic disorders.

Quantitative UPLC-MS/MS assay of urinary 2,8-dihydroxyadenine for diagnosis and management of adenine phosphoribosyltransferase deficiency

Adenine phosphoribosyltransferase (APRT) deficiency is a hereditary disorder that leads to excessive urinary excretion of 2,8-dihydroxyadenine (DHA), causing nephrolithiasis and chronic kidney disease. Treatment with allopurinol or febuxostat reduces DHA production and attenuates the renal manifestations. Assessment of DHA crystalluria by urine microscopy is used for therapeutic monitoring, but lacks sensitivity. We report a high-throughput assay based on ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS) for quantification of urinary DHA. The UPLC-MS/MS assay was optimized by a chemometric approach for absolute quantification of DHA, utilizing isotopically labeled DHA as an internal standard. Experimental screening was conducted with D-optimal design and optimization of the DHA response was performed with central composite face design and related to the peak area of DHA using partial least square regression. Acceptable precision and accuracy of the DHA concentration were obtained over a calibration range of 100 to 5000ng/mL on three different days. The intra- and inter-day accuracy and precision coefficients of variation were well within ±15% for quality control samples analyzed in replicates of six at three concentration levels. Absolute quantification of DHA in urine samples from patients with APRT deficiency was achieved wihtin 6.5min. Measurement of DHA in 24h urine samples from three patients with APRT deficiency, diluted 1:15 (v/v) with 10mM ammonium hydroxide (NH4OH), yielded a concentration of 3021, 5860 and 10563ng/mL and 24h excretion of 816, 1327 and 1649mg, respectively. A rapid and robust UPLC-MS/MS assay for absolute quantification of DHA in urine was successfully developed. We believe this method will greatly facilitate diagnosis and management of patients with APRT deficiency.

Progress and challenges in viral vector manufacturing

Promising results in several clinical studies have emphasized the potential of gene therapy to address important medical needs and initiated a surge of investments in drug development and commercialization. This enthusiasm is driven by positive data in clinical trials including gene replacement for Hemophilia B, X-linked Severe Combined Immunodeficiency, Leber's Congenital Amaurosis Type 2 and in cancer immunotherapy trials for hematological malignancies using chimeric antigen receptor T cells. These results build on the recent licensure of the European gene therapy product Glybera for the treatment of lipoprotein lipase deficiency. The progress from clinical development towards product licensure of several programs presents challenges to gene therapy product manufacturing. These include challenges in viral vector-manufacturing capacity, where an estimated 1-2 orders of magnitude increase will likely be needed to support eventual commercial supply requirements for many of the promising disease indications. In addition, the expanding potential commercial product pipeline and the continuously advancing development of recombinant viral vectors for gene therapy require that products are well characterized and consistently manufactured to rigorous tolerances of purity, potency and safety. Finally, there is an increase in regulatory scrutiny that affects manufacturers of investigational drugs for early-phase clinical trials engaged in industry partnerships. Along with the recent increase in biopharmaceutical funding in gene therapy, industry partners are requiring their academic counterparts to meet higher levels of GMP compliance at earlier stages of clinical development. This chapter provides a brief overview of current progress in the field and discusses challenges in vector manufacturing.

Gene therapy for cancer: regulatory considerations for approval

The rapidly changing field of gene therapy promises a number of innovative treatments for cancer patients. Advances in genetic modification of cancer and immune cells and the use of oncolytic viruses and bacteria have led to numerous clinical trials for cancer therapy, with several progressing to late-stage product development. At the time of this writing, no gene therapy product has been approved by the United States Food and Drug Administration (FDA). Some of the key scientific and regulatory issues include understanding of gene transfer vector biology, safety of vectors in vitro and in animal models, optimum gene transfer, long-term persistence or integration in the host, shedding of a virus and ability to maintain transgene expression in vivo for a desired period of time. Because of the biological complexity of these products, the FDA encourages a flexible, data-driven approach for preclinical safety testing programs. The clinical trial design should be based on the unique features of gene therapy products, and should ensure the safety of enrolled subjects. This article focuses on regulatory considerations for gene therapy product development and also discusses guidance documents that have been published by the FDA.

Quantification of tolvaptan in rabbit plasma by LC-MS/MS: Application to a pharmacokinetic study

A sensitive, selective and high-throughput liquid chromatography-tandem mass spectrometry (LC-ESI-MS/MS) method was developed and validated for the quantitation of tolvaptan in rabbit plasma. Sample clean-up involved liquid-liquid extraction (LLE) and chromatography was performed on Zorbax SB C18 analytical column (50 mm×2.1 mm, 3.5 µm) using 0.1% formic acid:methanol (20:80, v/v) as the mobile phase. The parent→product ion transitions for the drug (m/z 449.2→252.1) and IS (m/z 456.2→259.2) were monitored on a triple quadrupole mass spectrometer, operating in the multiple reaction monitoring (MRM) and positive ion mode. The method was validated over the concentration range of 0.10-1000.00 ng/mL and successfully applied to a pharmacokinetic study of healthy rabbits.

Development of a replication-competent lentivirus assay for dendritic cell-targeting lentiviral vectors

It is a current regulatory requirement to demonstrate absence of detectable replication-competent lentivirus (RCL) in lentiviral vector products prior to use in clinical trials. Immune Design previously described an HIV-1-based integration-deficient lentiviral vector for use in cancer immunotherapy (VP02). VP02 is enveloped with E1001, a modified Sindbis virus glycoprotein which targets dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) expressed on dendritic cells in vivo. Vector enveloped with E1001 does not transduce T-cell lines used in standard HIV-1-based RCL assays, making current RCL testing formats unsuitable for testing VP02. We therefore developed a novel assay to test for RCL in clinical lots of VP02. This assay, which utilizes a murine leukemia positive control virus and a 293F cell line expressing the E1001 receptor DC-SIGN, meets a series of evaluation criteria defined in collaboration with US regulatory authorities and demonstrates the ability of the assay format to amplify and detect a hypothetical RCL derived from VP02 vector components. This assay was qualified and used to test six independent GMP production lots of VP02, in which no RCL was detected. We propose that the evaluation criteria used to rationally design this novel method should be considered when developing an RCL assay for any lentiviral vector.

Review on porcine endogenous retrovirus detection assays--impact on quality and safety of xenotransplants

Xenotransplantation of porcine organs, tissues, and cells inherits a risk for xenozoonotic infections. Viable tissues and cells intended for transplantation have to be considered as potentially contaminated non-sterile products. The demands on microbial testing, based on the regulatory requirements, are often challenging due to a restricted shelf life or the complexity of the product itself. In Europe, the regulatory framework for xenogeneic cell therapy is based on the advanced therapy medicinal products (ATMP) regulation (2007), the EMA CHMP Guideline on xenogeneic cell-based medicinal products (2009), as well as the WHO and Council of Europe recommendations. In the USA, FDA guidance for industry (2003) regulates the use of xenotransplants. To comply with the regulations, validated test methods need to be established that reveal the microbial status of a transplant within its given shelf life, complemented by strictly defined action alert limits and supported by breeding in specific pathogen-free (SPF) facilities. In this review, we focus on assays for the detection of the porcine endogenous retroviruses PERV-A/-B/-C, which exhibit highly polymorphic proviral loci in pig genomes. PERVs are transmitted vertically and cannot be completely eliminated by breeding or gene knock out technology. PERVs entail a public health concern that will persist even if no evidence of PERV infection of xenotransplant recipients in vivo has been revealed yet. Nevertheless, infectious risks must be minimized by full assessment of pigs as donors by combining different molecular screening assays for sensitive and specific detection as well as a functional analysis of the infectivity of PERV including an adequate monitoring of recipients.

Analysis of partial recombinants in lentiviral vector preparations

The presence of replication-competent lentivirus (RCL) in lentiviral vector preparations is a major safety concern for clinical applications of such vectors. RCL are believed to emerge from rare recombinant vector genomes that are referred to as partial recombinants or Psi-Gag recombinants. To quantitatively determine the fraction of partial recombinants in lentiviral vector preparations and to analyze them at the DNA sequence level, we established a drug selection assay involving a lentiviral packaging construct containing a drug-resistance gene encoding blasticidin (BSD) resistance. Upon transduction of target cells, the BSD resistance gene confers BSD resistance to the transduced cells. The results obtained indicate that there were up to 156 BSD-resistant colonies in a total of 10(6) transducing vector particles. The predicted recombination events were verified by polymerase chain reaction using genomic DNA obtained from BSD-resistant cell clones and by DNA sequence analysis. In an attempt to reduce the emergence of partial recombinants, sequence overlaps between the packaging and the vector constructs were reduced by substituting the Rev response element (RRE) present in the vector construct using a heterologous RRE element derived from simian immunodeficiency virus (SIVmac239). The results obtained showed that a reduction of sequence overlaps resulted in an up to sevenfold reduction of the frequency of BSD-resistant colonies, indicating that the capacity to form partial recombinants was diminished.

Development of an equine-tropic replication-competent lentivirus assay for equine infectious anemia virus-based lentiviral vectors

The release of lentiviral vectors for clinical use requires the testing of vector material, production cells, and, if applicable, ex vivo-transduced cells for the presence of replication-competent lentivirus (RCL). Vectors derived from the nonprimate lentivirus equine infectious anemia virus (EIAV) have been directly administered to patients in several clinical trials, with no toxicity observed to date. Because EIAV does not replicate in human cells, and because putative RCLs derived from vector components within human vector production cells would most likely be human cell-tropic, we previously developed an RCL assay using amphotropic murine leukemia virus (MLV) as a surrogate positive control and human cells as RCL amplification/indicator cells. Here we report an additional RCL assay that tests for the presence of theoretical "equine-tropic" RCLs. This approach provides further assurance of safety by detecting putative RCLs with an equine cell-specific tropism that might not be efficiently amplified by the human cell-based RCL assay. We tested the ability of accessory gene-deficient EIAV mutant viruses to replicate in a highly permissive equine cell line to direct our choice of a suitable EIAV-derived positive control. In addition, we report for the first time the mathematical rationale for use of the Poisson distribution to calculate minimal infectious dose of positive control virus and for use in monitoring assay positive/spike control failures in accumulating data sets. No RCLs have been detected in Good Manufacturing Practice (GMP)-compliant RCL assays to date, further demonstrating that RCL formation is highly unlikely in contemporary minimal lentiviral vector systems.

A reporter system for replication-competent gammaretroviruses: the inGluc-MLV-DERSE assay

While novel retroviral vectors for use in gene-therapy products are reducing the potential for formation of replication-competent retrovirus (RCR), it remains crucial to screen products for RCR for both research and clinical purposes. For clinical grade gammaretrovirus-based vectors, RCR screening is achieved by an extended S+L− or marker rescue assay, while standard methods for replication-competent lentivirus detection are still in development. In this report, we describe a rapid and sensitive method for replication-competent gammaretrovirus detection. We used this assay to detect three members of the gammaretrovirus family and compared the sensitivity of our assay with well-established methods for retrovirus detection, including the extended S+L− assay. Results presented here demonstrate that this assay should be useful for gene-therapy product testing.

Development and validation of amisulpride in human plasma by HPLC coupled with tandem mass spectrometry and its application to a pharmacokinetic study

In this study, authors developed a simple, sensitive and specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for quantification of Amisulpride in human plasma using Amisulpride-d(5) as an internal standard (IS). Chromatographic separation was performed on Zorbax Bonus-RP C18, 4.6 × 75 mm, 3.5 μm column with an isocratic mobile phase composed of 0.2% formic acid:methanol (35:65 v/v), at a flow-rate of 0.5 mL/min. Amisulpride, Amisulpride-d(5) was detected at m/z 370.1→242.1 and 375.1→242.1. The drug and the IS were extracted by a liquid-liquid extraction method. The method was validated over a linear concentration range of 2.0-2500.0 ng/mL for Amisulpride with a correlation coefficient of (r(2)) ≥ 0.9982. This method demonstrated intra- and inter-day precision within 0.9 to 1.7 and 1.5 to 2.8 % and intra- and inter-day accuracy within 98.3 to 101.5 and 96.0 to 101.0 % for Amisulpride. Amisulpride was found to be stable at 3 freeze-thaw cycles, bench top and auto sampler stability studies. The developed method was successfully applied to a pharmacokinetic study.

Replication-competent lentivirus analysis of clinical grade vector products

Lentiviral vectors are now in clinical trials for a variety of inherited and acquired disorders. A challenge for moving any viral vector into the clinic is the ability to screen the vector product for the presence of replication-competent virus. Assay development for replication-competent lentivirus (RCL) is particularly challenging because recombination of vector packaging plasmids and cellular DNA leading to RCL has not been reported with the current viral vector systems. Therefore, the genomic structure of a RCL remains theoretical. In this report, we describe a highly sensitive RCL assay suitable for screening vector product and have screened large-scale vector supernatant, cells used in vector production, and cells transduced with clinical grade vector. We discuss the limitations and challenges of the current assay, and suggest modifications that may improve the suitability of this assay for screening US Food and Drug Administration (US FDA)-licensed products.

A safety grading scale to support dose escalation and define stopping rules for healthy subject first-entry-into-man studies: some points to consider from the French Club Phase I working group

AIM

To propose a relevant grading scale for clinical adverse events or laboratory results, electrocardiogram (ECG) and vital sign findings supporting both dose escalation and stopping decisions in first-entry-into-man (FIM) studies conducted in young healthy subjects.

METHODS

A three-level scale was used for the proposed grading system. The grading is directly derived from the observed severity of discontinuous variables, as are most of clinical adverse events. A 'combined method' based on normal ranges and spontaneous variation is suggested for grading the findings which are continuous variables mainly numerical in nature. One grade, at the subject level, and one algorithm, at the cohort level, support the proposed decision rules. This work was managed by a Club Phase I working group.

RESULTS

Examples of grade 1, 2 and 3 limits are given for the most frequent clinical adverse events and laboratory tests, ECG and vital sign findings. When available, the proposed NIH and FDA limits are also provided. The safety recommendation is to use the grade 2 at least as an alert for caution and the grade 3 as a maximum for stopping, applying the algorithm at the cohort level.

CONCLUSIONS

This paper proposes a safety grading system based on relevant criteria which might be used by investigators and sponsors to support and rationalize dose escalation decisions in healthy young subject FIM studies. These proposals are designed not to be a guideline but some 'points to consider' helping the dose escalation process. This paper supports the recent reinforcement of the safety requirements for FIM studies by European authorities.

Method development and validation of montelukast in human plasma by HPLC coupled with ESI-MS/MS: application to a bioequivalence study

A simple, sensitive, and specific LC-ESIâMS/MS method for quantification of Montelukast (MO) in human plasma using Montelukast-d(6) (MOD6) as an internal standard (IS) is discussed here. Chromatographic separation was performed on YMC-pack pro C(18), 50 x 4.6 mm, S-3 Îm column with an isocratic mobile phase composed of 10mM ammonium formate (pH 4.0):acetonitrile (20:80 v/v), at a flow-rate of 0.8 mL min(â1). MO and MOD6 were detected with proton adducts at m/z 586.2â568.2 and 592.3â574.2 in multiple reaction monitoring (MRM) positive mode respectively. MO and MOD6 were extracted using acetonitrile as precipitating agent. The method was validated over a linear concentration range of 1.0â800.0 ng mL(â1) with correlation coefficient (r(2)) â 0.9996. The intraday precision and accuracy were within 1.91â7.10 and 98.32â99.17. The inter-day precision and accuracy were within 3.42â4.41% and 98.14â99.27% for MO. Both analytes were found to be stable throughout three freeze-thawing cycles, bench top, and autosampler stability studies. This method was utilized successfully for the analysis of plasma samples following oral administration of MO (5 mg) in 31 healthy Indian male human volunteers under fasting conditions.

Viral vectors for gene transfer: current status of gene therapeutics

Gene therapy for the correction of inherited or acquired disease has gained increasing importance in recent years. Successful treatment of children suffering from severe combined immunodeficiency (SCID) was achieved using retrovirus vectors for gene transfer. Encouraging improvements of vision were reported in a genetic eye disorder (LCA) leading to early childhood blindness. Adeno-associated virus (AAV) vectors were used for gene transfer in these trials. This chapter gives an overview of the design and delivery of viral vectors for the transport of a therapeutic gene into a target cell or tissue. The construction and production of retrovirus, lentivirus, and AAV vectors are covered. The focus is on production methods suitable for biopharmaceutical upscaling and for downstream processing. Quality control measures and biological safety considerations for the use of vectors in clinical trials are discussed.

Advanced phase I/II studies of targeted gene delivery in vivo: intravenous Rexin-G for gemcitabine-resistant metastatic pancreatic cancer

Rexin-G, a nonreplicative pathology-targeted retroviral vector bearing a cytocidal cyclin G1 construct, was tested in a phase I/II study for gemcitabine-resistant pancreatic cancer. The patients received escalating doses of Rexin-G intravenously from 1 × 10¹¹ colony-forming units (cfu) 2–3× a week (dose 0–1) to 2 × 10¹¹ cfu 3× a week (dose 2) for 4 weeks. Treatment was continued if there was less than or equal to grade 1 toxicity. No dose-limiting toxicity (DLT) was observed, and no vector DNA integration, replication-competent retrovirus (RCR), or vector-neutralizing antibodies were noted. In nine evaluable patients, 3/3 patients had stable disease (SD) at dose 0–1. At dose 2, 1/6 patients had a partial response (PR) and 5/6 patients had SD. Median progression-free survival (PFS) was 3 months at dose 0–1, and >7.65 months at dose 2. Median overall survival (OS) was 4.3 months at dose 0–1, and 9.2 months at dose 2. One-year survival was 0% at dose 0–1 compared to 28.6% at dose 2, suggesting a dose–response relationship between OS and Rexin-G dosage. Taken together, these data indicate that (i) Rexin-G is safe and well tolerated, and (ii) Rexin-G may help control tumor growth, and may possibly prolong survival in gemcitabine-resistant pancreatic cancer, thus, earning US Food and Drug Administration's (FDA) fast-track designation as second-line treatment for pancreatic cancer.

Phase I/II and phase II studies of targeted gene delivery in vivo: intravenous Rexin-G for chemotherapy-resistant sarcoma and osteosarcoma

Rexin-G, a pathotropic nanoparticle bearing a cytocidal cyclin G1 construct was tested in a phase I/II study for chemotherapy-resistant sarcomas and a phase II study for chemotherapy-resistant osteosarcoma. Twenty sarcoma patients and 22 osteosarcoma patients received escalating doses of Rexin-G intravenously from 8 x 10(11) to 24 x 10(11) colony forming units (cfu)/cycle. Treatment was continued if there was <or= grade 1 toxicity. No dose-limiting toxicity (DLT) was observed, and no vector DNA integration, replication-competent retrovirus (RCR) or vector-neutralizing antibodies were noted. In the phase I/II study, 3/6 patients had stable disease (SD) at the lowest dose; median progression-free survival (PFS) was 1.2 months, and overall survival (OS), 3.3 months. At higher doses, 10/14 patients had SD; median PFS was 3.7 months and median OS, 7.8 months. In this phase I/II study, a dose-response relationship with Rexin-G dosage was observed for progression-free and OS times (P = 0.02 and 0.005, respectively). In the phase II study, 10/17 evaluable patients had SD, median PFS was >or=3 months and median OS, 6.9 months. These studies suggest that Rexin-G is safe, may help control tumor growth, and may possibly improve survival in chemotherapy-resistant sarcoma and osteosarcoma.

Phase 2 gene therapy trial of an anti-HIV ribozyme in autologous CD34+ cells

Gene transfer has potential as a once-only treatment that reduces viral load, preserves the immune system, and avoids lifetime highly active antiretroviral therapy. This study, the first randomized, double-blind, placebo-controlled, phase II cell-delivered gene transfer clinical trial, was conducted in 74 HIV-1 infected adults who received a tat/vpr specific anti-HIV ribozyme (OZ1) or placebo delivered in autologous CD34+ hematopoietic progenitor cells. There were no OZ1-related adverse events. There was no statistical difference in viral load between the OZ1 and placebo group at the primary end-point (average at weeks 47 and 48) but time weighted areas under the curve from weeks 40-48 and 40-100 were significantly lower in the OZ1 group. Throughout the 100 weeks, CD4+ lymphocyte counts were higher in the OZ1 group. This study provides the first indication that cell-delivered gene transfer is safe and biologically active in HIV patients and can be developed as a conventional therapeutic product.

Manufacturing validation of biologically functional T cells targeted to CD19 antigen for autologous adoptive cell therapy

On the basis of promising preclinical data demonstrating the eradication of systemic B-cell malignancies by CD19-targeted T lymphocytes in vivo in severe combined immunodeficient-beige mouse models, we are launching phase I clinical trials in patients with chronic lymphocytic leukemia (CLL) and acute lymphoblastic leukemia. We present here the validation of the bioprocess which we developed for the production and expansion of clinical grade autologous T cells derived from patients with CLL. We demonstrate that T cells genetically modified with a replication-defective gammaretroviral vector derived from the Moloney murine leukemia virus encoding a chimeric antigen receptor (CAR) targeted to CD19 (1928z) can be expanded with Dynabeads CD3/CD28. This bioprocess allows us to generate clinical doses of 1928z+ T cells in approximately 2 to 3 weeks in a large-scale semiclosed culture system using the Wave Bioreactor. These 1928z+ T cells remain biologically functional not only in vitro but also in severe combined immunodeficient-beige mice bearing disseminated tumors. The validation requirements in terms of T-cell expansion, T-cell transduction with the 1928z CAR, biologic activity, quality control testing, and release criteria were met for all 4 validation runs using apheresis products from patients with CLL. Additionally, after expansion of the T cells, the diversity of the skewed Vbeta T-cell receptor repertoire was significantly restored. This validated process will be used in phase I clinical trials in patients with chemorefractory CLL and in patients with relapsed acute lymphoblastic leukemia. It can also be adapted for other clinical trials involving the expansion and transduction of patient or donor T cells using any CAR or T-cell receptor.

Repeat administration of proteins to the eye with a single intraocular injection of an adenovirus vector

Delivery of therapeutic proteins, such as antiangiogenic proteins, to the eye is a demonstrated method for the control of age-related macular degeneration (AMD). However, one of the key limitations is the requirement for frequent and repeated intraocular injections. In this article, we demonstrate that repeated protein production in the eye can be stimulated from the cytomegalovirus (CMV) promoter without repeat intraocular injections using a small molecule, all-trans retinoic acid (ATRA). ATRA by systemic delivery can stimulate protein production multiple times in the eye. Administration of ATRA resulted in stimulation of gene expression to relevant levels that block abnormal blood vessel growth in an experimental animal model for AMD. These data support the principles of this technological discovery to therapeutic applications for chronic ocular diseases.

Downstream processing of oncoretroviral and lentiviral gene therapy vectors

Retroviral vectors from both oncoretroviral and lentiviral origins have a great potential as gene delivery vehicles. A number of research groups have devoted considerable effort to the development of large-scale production strategies for retroviral vectors. However, the manufacturing of clinical-grade vectors for gene therapy, especially for in vivo applications, additionally requires scaleable purification strategies to remove the contaminants present in the harvested supernatants while preserving the functionality of the vectors. In this article, we review recent advances made in the field of downstream processing of retroviral vectors. The methods currently described in the literature for clarification, concentration and purification of retroviral vectors will be presented, with special emphasis on novel chromatography methods that open up the possibility to selectively and efficiently purify retroviruses on a large-scale. Problems associated with stability and quantification of retroviral particles will be outlined and future challenges will be discussed.

Lentiviral vectors

We review the use of lentiviral vectors in current human gene therapy applications that involve genetic modification of nondividing tissues with integrated transgenes. Safety issues, including insertional mutagenesis and replication-competent retroviruses, are discussed. Innate cellular defenses against retroviruses and their implications for human gene therapy with different lentiviral vectors are also addressed.

A replication competent lentivirus (RCL) assay for equine infectious anaemia virus (EIAV)-based lentiviral vectors

Lentiviral vectors are being developed to satisfy a wide range of currently unmet medical needs. Vectors destined for clinical evaluation have been rendered multiply defective by deletion of all viral coding sequences and nonessential cis-acting sequences from the transfer genome. The viral envelope and accessory proteins are excluded from the production system. The vectors are produced from separate expression plasmids that are designed to minimize the potential for homologous recombination. These features ensure that the regeneration of the starting virus is impossible. It is a regulatory requirement to confirm the absence of any replication competent virus, so we describe here the development and validation of a replication competent lentivirus (RCL) assay for equine infectious anaemia virus (EIAV)-based vectors. The assay is based on the guidelines developed for testing retroviral vectors, and uses the F-PERT (fluorescent-product enhanced reverse transcriptase) assay to test for the presence of a transmissible reverse transcriptase. We have empirically modelled the replication kinetics of an EIAV-like entity in human cells and devised an amplification protocol by comparison with a replication competent MLV. The RCL assay has been validated at the 20 litre manufacturing scale, during which no RCL was detected. The assay is theoretically applicable to any lentiviral vector and pseudotype combination.

An improved method for detection of replication-competent retrovirus in retrovirus vector products

Contamination by replication-competent retrovirus (RCR) is one of the most important safety issues of retrovirus vector products for gene therapy clinical research. To improve the sensitivity of RCR detection and to shorten the assay period, we have developed a novel RCR detection method (infectivity RT-PCR method) based on real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR) in combination with virus infection and a novel virus concentration method using polyethyleneimine (PEI)-conjugated magnetic beads. In this method, permissive cells were infected with RCR samples, and amplified RCR in the culture supernatants was adsorbed by PEI-beads. Then RCR RNA extracted from PEI-beads was quantified by real-time RT-PCR. We demonstrated that 1 infectious unit (iu) of RCR spiked in 10(6) cfu/ml of vector products could be detected within 3 days, and the sensitivity for viral detection was increased 3- to 10-fold compared with the direct S+L- assay. By this method, the presence of retroviral vector interfered with RCR detection only slightly. In conclusion, infectivity RT-PCR conducted in conjunction with virus concentration using PEI-beads can detect RCR more sensitively and rapidly than the conventional infectivity assay.

Detection of replication-competent adenoviruses spiked into recombinant adenovirus vector products by infectivity PCR

The presence of replication-competent adenovirus (RCA) in clinical lots of adenovirus vectors raises a variety of safety concerns. To detect RCA in adenovirus vector products, the cell culture/cytopathic effect (CPE) method has generally been preferred. However, it is difficult to evaluate the amount of RCA clearly and quantitatively by this method. In addition, the cell culture/CPE method requires large-scale cell culturing and a substantial amount of time. For the purpose of establishing a method to detect RCA more sensitively and rapidly, we developed the infectivity PCR, a hybrid method that combines the infectivity assay and quantitative PCR. This method allows RCA to be quantified by real-time quantitative PCR using primers and a probe designed for E1 DNA. By infectivity PCR, 1 pfu of RCA spiked into 10(9) particles of adenovirus vectors could be detected. In contrast, CPE was observed in the cells infected with 10(4) pfu of RCA spiked into 10(9) particles of adenovirus vectors. The glass-beads method was suitable for extracting DNA rapidly from the RCA-infected cells. These results showed that infectivity PCR combined with the glass-beads-based DNA extraction method was useful for the detection of RCA in adenovirus vector products.

Replication of enhancer-deficient amphotropic murine leukemia virus in human cells

Amphotropic murine leukemia virus (MLV) replicates in cells from various mammalian species, including humans, and is a potential contaminant in MLV vector preparations for human gene transfer studies. The generation of replication-competent virus is considered less likely with vectors that delete the viral transcription elements. This conclusion is based on data obtained in rodents, where MLV replication depends on the expression of viral genes under the control of 75-bp enhancer elements in the long terminal repeat. We demonstrate here that in some human cells replication of amphotropic MLV is possible in the absence of these enhancer elements. Replication of the enhancer-deficient virus MLV-(MOA)Delta E is observed in selected human sarcoma and B lymphoma lines and proceeds at a lower rate than that of the intact virus. No insertion of a foreign promoter or enhancer into the long terminal repeat was detected. Our data suggest the presence of a secondary enhancer element within the MLV provirus that can in selected human cells mediate virus transcription and replication in the absence of the 75-bp U3 enhancers.