Titer of Viral Vector
Overview of the Titer of Viral Vector
The most important property of viral vectors is infectivity. Assessing infectivity involves examining viral replication within cells to determine the titer of a specific virus stock. Titer denotes the concentration of infectious viral units per specified volume. This calculation serves as a crucial quality control measure in virus manufacturing, ensuring that viral products fulfill customer specifications. As a prominent provider of viral vectors, Creative Biolabs categorizes viral titers into physical and biological titers.
- Physical titer quantifies the total number of both active and inactive virus particles, typically expressed as the number of virus particles per milliliter (VP/mL) or for AAV, as the number of genomic copies per milliliter (GC/mL). This includes viral particle titer (or capsid titer) and genomic titer. Physical titer can be determined through quantitative PCR to ascertain the genomic copy number of viral particles, or by assessing specific proteins within the viral particles.
- Biological titer involves a series of dilutions of the virus infecting experimental cells, with positivity determined by detecting the expression of the target gene (or transgene). It is calculated based on the number of positive cells or wells, in conjunction with the viral dilution, and is quantified in transduction units (TU). For lentiviral or retroviral vectors, biological titer is denoted as transduction units per milliliter (TU/mL). Adenovirus vector titers are typically expressed as plaque-forming units per milliliter (PFU/mL) or infectious units per milliliter (IFU/mL).
We are dedicated to providing diverse titer testing methods, ensuring reliable and high-quality viral vectors, as shown in Tab.1.
Tab.1 Test methods of the viral vector titer.
| Test Items | Methods | Description |
|---|---|---|
| Physical titer | Quantitative PCR (qPCR) | The most commonly utilized approach for assessing viral genomic titer. It is characterized by its simplicity, convenience in operation, and notable advantages in quantitative accuracy, sensitivity, and stability. |
| Droplet digital PCR (ddPCR) | This is a highly precise technique that eliminates the necessity for standard curves or high amplification efficiency. It employs primers and probes designed to target the ITR elements within viral vectors, with the flexibility to adjust targeting to alternative sequences if needed. | |
| ELISA |
The determination of viral particle titers involves assessing color development through enzyme-catalyzed substrate reactions linked to capsid-specific binding antibodies. Such as p24 ELISA is used for lentiviral titer testing. |
|
| Fluorescence-Activated Cell Sorting (FACS) |
FACS is applied to viral vectors encoding fluorescent proteins. This method is employed to evaluate the virus's ability to induce transgene expression accurately in target cells. |
|
| Biological titer | Viral plaque assay |
The viral plaque assay stands as one of the most widely adopted techniques for determining infection titer. A permissive cell line is exposed to virus dilutions at low MOI, leading to virus replication, cell lysis, and plaque formation. The number of plaques counted determines PFU/mL. |
| Immunoassay | Immunoassay provide a quick, complete system to functionally titer virus infectivity. | |
| TCID50 | The TCID50 method quantifies the infectious virus titer by determining the amount of virus needed to induce cytopathic effects or cause cell death in 50% of host cells. |
SERVICES
Various techniques are utilized for titer detection of different viruses, reflecting differences in virus biological traits, detection sensitivity, sample types, laboratory equipment, and cost considerations. Creative Biolabs is dedicated to providing top-tier titer testing services for a wide range of viral vectors.
- Lentiviral Vectors Titration
- Adenovirus Vector Titration
- Adeno-associated Virus Titration
- Plaque-Forming Titer Assays
- For lentivirus, we often use p24 Elisa and qPCR to measure their physical titer and biological titer.
- For Adenovirus, the biological titer has been measured by PFU and immunoassay.
- For Adeno-associated virus (AAV), the physical titer is determined by extracting viral genomes from lysed viral particles and utilizing qPCR to precisely quantify the copy number of viral genomes.
For more detailed information, please feel free to contact us and get a quote. We will get in touch with you within 24 hours and design an optimal method for your project.
