Virus quantification / TCID50 assay
Virus quantification for samples up to biosafety level S2
Virus quantification is an integral part of the development, manufacturing and quality control of virus products, including advanced therapy medicinal products (ATMPs). Coriolis offers a variety of options to quantify viruses. One option is to determine how many virus particles per volume are inside a sample (i.e. the physical titer). This is done by using particle characterization techniques - you can read more about that here. But such techniques may not tell the entire story, because the infectious or functional titer (i.e. how much virus can infect the target cell) is often more important and meaningful and may not directly correlate to the number of virus particles in a sample.
TCID50 is a common assay type
The number of infectious virus particles is frequently quantified by using the Median Tissue Culture Infectious Dose (TCID50) assay. The assay works by adding a serial dilution of the virus sample to cells in a 96 well plate format. The type of cell is specifically selected to show a cytopathic effect (CPE), i.e. morphological changes upon infection with the virus or cell death. After an incubation period, the cells are inspected for CPE or cell death and each well is classified as infected or not infected. Colorimetric or fluorometric readouts are also possible, which can increase assay sensitivity. The dilution, at which 50% of the wells show a CPE, is used to calculate the TCID50 of the virus sample. This calculation can generally be done by a variety of mathematical approaches, e.g., the Spearman-Karber method or the Reed-Muench method. Virus quantity is expressed as TCID50 / ml.
Other biological assays are available
Depending on the virus, the type of cells and the readout parameter indicating an infection, a variety of other virus quantification assays approaches are possible. For viruses that lyse the infected cell, for example, a plague forming assay is commonly employed for quantification. The virus sample is added (in a suitable dilution) to a monolayer-forming cell culture and incubated over several days. Areas with infected cells will be visible as holes or plaques either by the microscopy, or by colorimetric or fluorometric staining. Virus quantity is expressed as infectious units (IFU) / ml or plague forming units (PFU) / ml.
Coriolis offers following services regarding virus quantification up to biosafety level S2:
- Transfer, implementation and application of existing TCID50 assays
- Transfer, implementation and application of existing plague forming assays
- Development of tailor-made virus quantification assays
We perform virus quantification as a standalone service or as part of a formulation development program for viruses, ATMPs and drug substances up to biosafety level S2.