retrovirus titering

How to order virus packaging service

Step 1: Please review the following before ordering Allele’s retrovirus packaging service.

Verify that your plasmids for virus production meet the following criteria:

No internal polyA signal or polyA signal immediately downstream of the coding cistron.

Avoid toxic genes, unusual secondary structures, and expression cassettes > 8kb (5’ to 3’ LTR).

If these concerns can not be satisfied in your vector design, please contact our technical specialist ( for further discussion, as Allele’s proprietary packaging technology might be able to help.

Step 2: Select the service:

Allele offers multiple project discounts: a 5% discount for ordering 3-5 packaging services, and a 10% for 6-10 packaging services.

Additional information can be found here.

Step 3: Send us 10 ug of endotoxin-free plasmid (blue ice shipping) for virus packaging.

To facilitate the completion of the custom virus packaging projects, Allele offers a variety of retro/lentivirus plasmids as well as viral plasmid subcloning and endotoxin-free plasmid preparation services. Please contact us ( or 858-587-6645) for further details.

Once your order is placed, we will contact you about plasmid shipment and provide you with a time frame for completing the project.

Note: If the total project price is more than $1000, a non-refundable down payment (30% of the total service price) is registered before the project is initiated.

    New Product of the Week 121310-121910:

pORB-ICAM/mWasabi-sIRES-VSVG for insect and mammalian cell expression of human membrane protein ICAM, validated and ready to ship. Email

    Promotion of the Wee 120610-121310:

5% discount on high quality cell culture dishes manufactured by Phoenix Biomedical, email with code PH121310EC.

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Wednesday, December 15th, 2010 Viruses and cells No Comments

How to titer retrovirus/lentivirus

A number of methods have been developed for determining the lentiviral/retroviral titers such as using ELISA to assess the amount of p24 antigen, enzyme assay to quantify reverse transcriptase activity, and real time RT-PCR to count viral RNA genome. However, these methods do not differentiate non-infectious from infectious virus particles that are present in the virus preparation; therefore, these measurements rely on some correlation factors to derive a titer, which can be inaccurate.

Because an accurate virus titer is critical for most experimental purposes, Allele Biotech’ pre-packaged viruses are measured by the number of genomic integration events to determine the infectious titer. This functional titering is done by first transducing TE671cells (selected for consistent transduction efficiency) followed by measuring the viral genome integrated into the cell genome with QPCR. The number of cellular genome copies is also measured, and the copy number of viruses is divided by that of cells to obtain active virus titer.
How to titer lentivirus retrovirus

A plot of quantitative PCR (Q-PCR) titering of virus preparation is provided above.
TE671 cells (1×105) were transduced with 2×10-3ml of a virus sample to be titered. Cells were harvested and DNA extracted for QPCR. The titer is determined as followed, transduction unit per ml (TU/ml)=N [X1/(X2/2)]/2×10-3ml, where N is the cell number, X1 is the copy number of integrated virus DNA, and X2 is the copy number of GAPDH DNA.