ViraPower™ Lentiviral Directional TOPO™ Expression Kit

Possible causes include:

- large volume of viral supernatant used for transduction
- cells sensitive to Polybrene regaent
- too much antibiotic used for selection
- antibiotic used too soon after tranduction
- gene of interest is toxic to cells

Poor expression could result from low transduction efficiency, too low of a MOI, too much antibiotic used for selection, usage of antibiotic too soon after transduction, harveting cells too soon after transduction, having a gene of interest that is toxic to cells, or rerrangement in the LTR regions of the expression construct plasmid DNA.

Here are some possible causes and solutions:
- Promoter silencing; CMV promoter is prone to silencing especially in mouse and rat cells, screen multiple antibiotic resistant clones and select the one with the highest expression levels
- Viral stocks stored incorrectly; aliquot and store at -80 degrees C, do not freeze/thaw more than 3 times

Here are some possible causes and solutions:

- Too little antibotic used for selection
- Selection performed on confluent cells; replate cells
- Viral supernatant not diluted sufficiently; titer lentivus using a wider range of 10-fold serial dilutions

Possible causes include:

- low transfection efficiency; Use a high-quality plasmid prep, 293FT cells under passage 16, ensure removal of Geneticin during transfection, ensure correct DNA:lipid ratio, and that cells are plated at the correct confluency
- transfected cells are not cultured in medium containing sodium pyruvate; this reagent provides an extra energy source for cells
- viral supernatant harvested too early; viral supernatants can generally be collected 48-72 hrs post-transfection
- viral supernatant too dilute; concentrate virus using CsCl purification
- viral supernatant frozen and thawed multiple times; 3 times should be the maximum freeze/thaw
- gene of interest is large; viral titers decrease as size of insert increases, inserts larger than 5.6 kb are not recommended
- rearrangement in the LTR region of the epxression construct plasmid DNA; use Stb3 cells for transformatin of the lentiviral construct
- poor choice of titering cell line; use HT1080 cells or similar cell line
- Polybrene reagent is not included during transduction; transduce lentiviral construct into cells in the presence of Polybrene reagent
- Lipofectamine reagent handled incorrectly; ensure proper storage and mix gently before use
- Use fluorescence micrscopy to check titer with HiPerform FastTiter lentivirus

Find additional tips, troubleshooting help, and resources within our Protein Expression Support Center.