Quantitative detection of RT activity by PERT assay:: Feasibility and limits to a standardized screening assay for human vaccines

The detection of adventitious retroviruses has always been critical for assessing the safety concerns associated with viral vaccines. Assays for the enzymatic activity of reverse transcriptase (RT) are used as general methods for the detection of both known and unknown retroviruses. Several studies using newly-developed ultrasensitive PCR-based RT assays reported RT activity in viral vaccines grown in chicken cells. Here, we have assessed the performances of such a PCR-based RT assay-PERT assay-for the quantitative detection of RT activity in vaccines. Sensitivity, linearity and reproducibility of the method were studied on purified RT and viral vaccines treated to release RT from potentially contaminant retroviruses. The level of RT activity detected in chicken cell-derived vaccines was higher for live attenuated vaccines compared to inactivated ones. Contrary to other studies, RT activity was found in some mammalian cell-derived vaccines. AZT-TP sensitivity of RT activities detected in these vaccines and discrimination between retroviral and RT-like activities was further investigated. Feasibility and limits of PERT assay as a broad-spectrum retroviruses detection method in vaccines are discussed.