Versatile Viral Vector Strategies for Postscreening Target Validation and RNAi ON-Target Control.

Our approach aims to optimize postscreening target validation strategies using viral vector-driven RNA interference (RNAi) cell models. The RNAiONE validation platform is an array of plasmid-based expression vectors that each drives tandem expression of the gene of interest (GOI) with one small hairpin RNA (shRNA) from a set of computed candidate sequences. The best-performing shRNA (>85% silencing efficiency) is then integrated in an inducible, all-in-one lentiviral vector to transduce pharmacologically relevant cell types that endogenously express the GOI. VariCHECK is used subsequently to combine the inducible knockdown with an equally inducible rescue of the GOI for ON-target phenotype verification. The complete RNAiONE-VariCHECK system relies on three key elements to ensure high predictability: (1) maximized silencing efficiencies by a focused shRNA validation process, (2) homogeneity of the RNAi cell pools by application of sophisticated viral vector technologies, and (3) exploiting the advantages of inducible expression systems. By using a reversible expression system, our strategy adds critical information to hot candidates from RNAi screens and avoids potential side effects that may be caused by other, irreversible genomic manipulation methods such as transcription activator-like effector nucleases (TALEN) or clustered regularly interspaced short palindromic repeats/Cas9 (CRISPR/Cas). This approach will add credibility to top-hit screening candidates and protect researchers from costly misinterpretations early in the preclinical drug development process.

Systematic improvement of lentivirus transduction protocols by antibody fragments fused to VSV-G as envelope glycoprotein.

Lentiviral vectors (LV) are widely used to successfully transduce cells for research and clinical applications. Lentiviral vectors pseudotyped with the vesicular stomatitis virus glycoprotein (VSV-G) can be produced to high titers and mediate high transduction efficiencies in vitro. For clinical applications the need for optimized transduction protocols and the limited activity of retronectin as LV enhancer, results in the application of a high multiplicity of infection (MOI) to achieve effective transduction efficiencies for a number of therapeutically relevant cells, e.g. CD34(+) hematopoietic stem cells, T- and B-cells. Our study describes an optimized LV infection protocol including a non-toxic poloxamer-based adjuvant combined with antibody-retargeted lentiviral particles, improving transduction efficiency at low MOI. Cell specificity of lentiviral vectors was increased by displaying different ratios of scFv-fused VSV-G glycoproteins on the viral envelope. The system was validated with difficult to transduce human CD30(+) lymphoma cells, and EGFR(+) tumor cells. Highly efficient transduction of lymphoma cells was achieved, >50% of cells were transduced when MOI 1 was used. The scFv displaying lentiviral particles gained relative specificity for transduction of target cells. Preferential gene delivery to CD30(+) or EGFR(+) cells was increased 4-fold in mixed cell cultures by presenting scFv antibody fragments binding to respective surface markers. A combination of spinoculation, poloxamer-based chemical adjuvant, and LV displaying scFv fragments increases transduction efficiencies of hard-to-transduce suspension lymphoma cells, and promises new chances for the future development of improved clinical protocols.