Molecular Diagnostics Services, Inc.
A Contract Research Organization

Retrovirus Detection


At MDS three different assays are available for the detection of retroviruses and the qualification of cell banks and/or viral vaccine products originating from mammalian and avian cell substrates.
Regulatory guidance advises the use of reverse transcriptase activity packaged into extracellular retrovirus particles as a marker for the potential presence of retrovirus contamination. These reverse transcriptase (RT) assays (also described in the literature as Amp-RT, PBRT and PERT) detect the conversion of RNA template to cDNA (due to the presence of RT enzyme when retroviruses are present in the test sample).
Guidelines:

Relevant tests

Infectivity Assays

At MDS, we use murine cell lines or hybrid cell lines containing a murine component which are capable of producing infectious mouse retroviruses such as:

  • Ecotropic retroviruses
  • Xenotropic retroviruses
  • Amphotropic and mink cell focus-forming (MCF) retroviruses

The following two protocols are offered:

  • Direct focus assays (using one detector cell line) enable direct detection of retrovirus particles. The selected cell line will detect the specific type of retrovirus.
  • Extended assays using an initial cell line to amplify the retrovirus (with three and five passages).  These assays are recommended following a direct focus assay.

Remarks:

  • These extensive amplifications allow more sensitive detection of retrovirus particles. Hence, if the quantity of retrovirus in the test article is expected to be low, the extended protocol will be chosen.
  • If the test articles are supernatants, the inoculation of the test article is directly carried out on the detector cell lines. If the test articles are cells, the latter are co-cultured with the detector cell lines.

 

Detector Cell Lines:


Detector Cell Line *

Assay

Retrovirus Susceptibility

Cell  Line Origin

Fg10 S+L-

Direct focus

Murine ecotropic retroviruses (including Mo-MuLv)

Murine

PG4 S+L-

Direct focus

Murine xenotropic/amphotropic/MCF retroviruses

Feline

NIH3T3 Fg10 S+L

Extended assay with 3 passages followed by a focus assay

Murine ecotropic retroviruses (including Mo-MuLv)

Murine

Mus dunni
PG4 S+L-

Extended assay with 3 passages followed by a focus assay

xenotropic/amphotropic/MCF retroviruses
NIH3T3

Murine/ Feline

NIH3T3** Fg10 S+L

Extended assay with 5 passages followed by a focus assay

Murine ecotropic retroviruses (including Mo-MuLv)

Murine

Mus dunni
PG4 S+L-

Extended assay with 5 passages followed by a focus assay

Xenotropic/amphotropic/MCF retroviruses
NIH3T3

Murine/ Feline

*The detector cell lines are modified with sarcoma-positive (S+) and leukemia negative (L-) isotypes in order to obtain foci and show the presence of the retrovirus in the cells during the focus assay.

 

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