What is the titer for the Lentiviral transduction particles?
Each clone is provided as 200 µl containing approximately 1 x 106 TU/ml (via p24 titering assay).

High-Throughput Lentiviral Particle Production Results

How does Sigma measure viral titer?
We use a p24 titer assay, which is an ELISA against the p24 viral coat protein.

Is a titer of 106 too low?
We have optimized our viral production and this titer gives excellent integration efficiency in cultured cells. You may be more familiar with adenovirus, which titers at a range around 109. Lentivirus, however, has many advantages over adenovirus such as stable integration and ability to transduce primary and non-dividing cells, etc. If there are applications that require you to use higher titer virus, the highly stable VSV-G envelope allows concentration of lentiviral particle via ultracentrifugation.

How do you determine functional viral titer (TU/ml) using the p24 assay?
We determine the TU/ml based upon the p24 assay from ZeptoMetrix. We use the conversion from Didier Trono to determine the relationship between pg/ml p24 and viral titer or MOI:

There are approximately 2000 molecules of p24 per physical particle (PP) of lentivirus:
(2 x 103) x (24 x 103 Da of p24 per PP), 48 x 106/Avogadro = (48 x 106) / (6 x 1023) = 8 x 10-17 g of p24 per PP, approximately 1 PP per 1 x 10-16 g of p24, 1 x 104 PP per pg of p24

A reasonably well packaged, VSV-G pseudotyped lentiviral vector will have an infectivity index in the range of 1 TU per 1000 physical particles (PP) to 1 TU per 100 PP (or less). Thus, the range is approximately 10 to 100 TU/pg of p24. It is through this conversion that TU/ml is obtained. Our current viral packaging protocol has given us highly reproducible titers.

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