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The titers of lentivirus depend on the size of your inserts or genes. Titer will decrease as the size of your insert increases.
If you use our Invitrogen Lentiviral expression system:
1) pLenti6.3/V5 or pLenti7.3/V5 and ViraPower Packaging Mix
2) Lipofectamine 3000 transfection reagent for LV production protocol
3) HEK293T (HEK293T/17 ATCC)
If your insert is: 5Kb, expect a crude LV titer: 0.1-9.0 x10^6 TU/ml
Note: Reference titers are based on antibiotic selection or %GFP measurement in HT1080 cell line.