Production of lentiviral vectors in protein-free media

Preparation and application of chikungunya pseudovirus containing double reporter genes

Chikungunya virus (CHIKV), a highly infectious and rapidly spread viral pathogen, is classified as a pathogenic agent at the biosafety level 3. Operation of live authentic CHIKV needs a specific laboratory with the P3 or above containment, which greatly confines the CHIKV-associated studies. To establish an evaluation system of CHIKV that can be utilized in a BSL2 laboratory, we constructed a pseudovirus (PsV) system of CHIKV containing double reporter genes (ZsGreen1 and luciferase). The fluorescent ZsGreen1 is a convenient and cheap reporter for monitoring the efficiency of transfection and titration of PsV. The enzyme luciferase is a sensitive reporter for the application of PsV to neutralization assay or drug screening. The CHIKV PsV produced in this study, with a titer of up to 3.16 × 10⁶ TU/ml, was confirmed by Western blotting and transmission electronic microscopy (TEM). Finally, we developed a microneutralization assay with the CHIKV PsV produced in this study, which was successfully applied to evaluate neutralizing activities of convalescent sera from CHIKV-infected patients. In summary, we have established a convenient and sensitive double-reporter CHIKV pseudovirus system, which provides a safe and effective platform for screening anti-CHIKV drugs and evaluating vaccines against CHIKV.

Three-dimensional CRISPR screening reveals epigenetic interaction with anti-angiogenic therapy

Angiogenesis underlies development, physiology and pathogenesis of cancer, eye and cardiovascular diseases. Inhibiting aberrant angiogenesis using anti-angiogenic therapy (AAT) has been successful in the clinical treatment of cancer and eye diseases. However, resistance to AAT inevitably occurs and its molecular basis remains poorly understood. Here, we uncover molecular modifiers of the blood endothelial cell (EC) response to a widely used AAT bevacizumab by performing a pooled genetic screen using three-dimensional microcarrier-based cell culture and CRISPR–Cas9. Functional inhibition of the epigenetic reader BET family of proteins BRD2/3/4 shows unexpected mitigating effects on EC survival and/or proliferation upon VEGFA blockade. Moreover, transcriptomic and pathway analyses reveal an interaction between epigenetic regulation and anti-angiogenesis, which may affect chromosomal structure and activity in ECs via the cell cycle regulator CDC25B phosphatase. Collectively, our findings provide insight into epigenetic regulation of the EC response to VEGFA blockade and may facilitate development of quality biomarkers and strategies for overcoming resistance to AAT.

Through three-dimensional CRISPR screening, He et al. report that functional inhibition of BET family of proteins BRD2/3/4 shows mitigating effects on blood endothelial cell (EC) survival and/or proliferation upon VEGFA blockade. An interaction between epigenetic regulation and anti-angiogenesis, which may affect chromosomal structure and activity in ECs through CDC25B phosphatase, is potentially involved with EC resistance to anti-angiogenic therapy.

A novel selection strategy for antibody producing hybridoma cells based on a new transgenic fusion cell line

The use of monoclonal antibodies is ubiquitous in science and biomedicine but the generation and validation process of antibodies is nevertheless complicated and time-consuming. To address these issues we developed a novel selective technology based on an artificial cell surface construct by which secreted antibodies were connected to the corresponding hybridoma cell when they possess the desired antigen-specificity. Further the system enables the selection of desired isotypes and the screening for potential cross-reactivities in the same context. For the design of the construct we combined the transmembrane domain of the EGF-receptor with a hemagglutinin epitope and a biotin acceptor peptide and performed a transposon-mediated transfection of myeloma cell lines. The stably transfected myeloma cell line was used for the generation of hybridoma cells and an antigen- and isotype-specific screening method was established. The system has been validated for globular protein antigens as well as for haptens and enables a fast and early stage selection and validation of monoclonal antibodies in one step.

Efficiency and Specificity of Targeted Integration Mediated by the Adeno-Associated Virus Serotype 2 Rep 78 Protein

The adeno-associated virus serotype 2 (AAV2) Rep 78 protein, a strand-specific endonuclease (nickase) promotes site-specific integration of transgene sequences bearing homology arms corresponding to the AAVS1 safe harbor locus. To investigate the efficiency and specificity of this approach, plasmid-based donor vectors were tested in concert with nuclease encoding vectors, including an engineered version of the AAV2 Rep 78 protein, an AAVS1-specific zinc finger nuclease (ZFN), and the CRISPR-Cas9 components in HEK 293 cells. The Rep 78 and ZFN-based approaches were also compared in HEK 293 cells and in human induced pluripotent stem cells using integrase deficient lentiviral vectors. The targeting efficiencies involving the Rep 78 protein were similar to those involving the AAVS1-specific ZFN, while the targeting specificity for the Rep 78 protein was lower compared to that of the ZFN. It is anticipated that the Rep 78 nickase-based targeting approach may ultimately contribute to the reduction of risks associated with other genome editing approaches involving DNA double-strand breaks.

Murine model for non-invasive imaging to detect and monitor ovarian cancer recurrence

Epithelial ovarian cancer is the most lethal gynecologic malignancy in the United States. Although patients initially respond to the current standard of care consisting of surgical debulking and combination chemotherapy consisting of platinum and taxane compounds, almost 90% of patients recur within a few years. In these patients the development of chemoresistant disease limits the efficacy of currently available chemotherapy agents and therefore contributes to the high mortality. To discover novel therapy options that can target recurrent disease, appropriate animal models that closely mimic the clinical profile of patients with recurrent ovarian cancer are required. The challenge in monitoring intra-peritoneal (i.p.) disease limits the use of i.p. models and thus most xenografts are established subcutaneously. We have developed a sensitive optical imaging platform that allows the detection and anatomical location of i.p. tumor mass. The platform includes the use of optical reporters that extend from the visible light range to near infrared, which in combination with 2-dimensional X-ray co-registration can provide anatomical location of molecular signals. Detection is significantly improved by the use of a rotation system that drives the animal to multiple angular positions for 360 degree imaging, allowing the identification of tumors that are not visible in single orientation. This platform provides a unique model to non-invasively monitor tumor growth and evaluate the efficacy of new therapies for the prevention or treatment of recurrent ovarian cancer.

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.

A fully human inhibitory monoclonal antibody to the Wnt receptor RYK

RYK is an unusual member of the receptor tyrosine kinase (RTK) family that is classified as a putative pseudokinase. RYK regulates fundamental biological processes including cell differentiation, migration and target selection, axon outgrowth and pathfinding by transducing signals across the plasma membrane in response to the high affinity binding of Wnt family ligands to its extracellular Wnt inhibitory factor (WIF) domain. Here we report the generation and initial characterization of a fully human inhibitory monoclonal antibody to the human RYK WIF domain. From a naïve human single chain fragment variable (scFv) phage display library, we identified anti-RYK WIF domain–specific scFvs then screened for those that could compete with Wnt3a for binding. Production of a fully human IgG_1κ from an inhibitory scFv yielded a monoclonal antibody that inhibits Wnt5a-responsive RYK function in a neurite outgrowth assay. This antibody will have immediate applications for modulating RYK function in a range of settings including development and adult homeostasis, with significant potential for therapeutic use in human pathologies.

Phenotypic modifications in ovarian cancer stem cells following Paclitaxel treatment

Epithelial ovarian cancer (EOC) is the most lethal gynecologic malignancy. Despite initial responsiveness, 80% of EOC patients recur and present with chemoresistant and a more aggressive disease. This suggests an underlying biology that results in a modified recurrent disease, which is distinct from the primary tumor. Unfortunately, the management of recurrent EOC is similar to primary disease and does not parallel the molecular changes that may have occurred during the process of rebuilding the tumor. We describe the characterization of unique in vitro and in vivo ovarian cancer models to study the process of recurrence. The in vitro model consists of GFP+/CD44+/MyD88+ EOC stem cells and mCherry+/CD44-/MyD88- EOC cells. The in vivo model consists of mCherry+/CD44+/MyD88+ EOC cells injected intraperitoneally. Animals received four doses of Paclitaxel and response to treatment was monitored by in vivo imaging. Phenotype of primary and recurrent disease was characterized by quantitative polymerase chain reaction (qPCR) and Western blot analysis. Using the in vivo and in vitro models, we confirmed that chemotherapy enriched for CD44+/MyD88+ EOC stem cells. However, we observed that the surviving CD44+/MyD88+ EOC stem cells acquire a more aggressive phenotype characterized by chemoresistance and migratory potential. Our results highlight the mechanisms that may explain the phenotypic heterogeneity of recurrent EOC and emphasize the significant plasticity of ovarian cancer stem cells. The significance of our findings is the possibility of developing new venues to target the surviving CD44+/MyD88+ EOC stem cells as part of maintenance therapy and therefore preventing recurrence and metastasis, which are the main causes of mortality in patients with ovarian cancer.

Specific targeting of human interleukin (IL)-13 receptor α2-positive cells with lentiviral vectors displaying IL-13

The ability to selectively and efficiently target transgene delivery to specific cell types in vitro and in vivo remains one of the formidable challenges in gene therapy. Lentiviral vectors have several advantages that make them attractive as gene delivery vehicles and their tropism can be altered through pseudotyping, allowing transgene delivery to specific populations of cells. The human interleukin-13 receptor α2 (IL-13Rα2) is uniquely overexpressed in many different human tumors, making it an attractive target for cancer therapy. In this study, we examined whether IL-13Rα2-positive tumor cells can be specifically targeted with lentiviral vector pseudotypes containing a truncated fusion (F) protein derived from measles virus (MV) and a tail-truncated and receptor-blind MV hemagglutinin (H) protein bearing IL-13 at the C terminus. The retargeted lentiviral vector efficiently transduced cells that express high levels of IL-13Rα2, but not cells expressing low levels of IL-13Rα2 in vitro. In vivo, it specifically targeted IL-13Rα2-positive glioma cell xenografts in immunodeficient mice in the context of subcutaneous and intracranial glioma models. Similar lentiviral vectors may be developed for targeting other tumors expressing specific cell surface receptors.