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 ass essing the safety concerns associated with viral vaccines. Assays for the e nzymatic 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 activi ty in viral vaccines grown in chicken cells. Here, we have assessed the per formances of such a PCR-based RT assay-PERT assay-for the quantitative dete ction of RT activity in vaccines. Sensitivity, linearity and reproducibilit y of the method were studied on purified RT and viral vaccines treated to r elease RT from potentially contaminant retroviruses. The level of RT activi ty detected in chicken cell-derived vaccines was higher for live attenuated vaccines compared to inactivated ones. Contrary to other studies, RT activ ity was found in some mammalian cell-derived vaccines. AZT-TP sensitivity o f RT activities detected in these vaccines and discrimination between retro viral and RT-like activities was further investigated. Feasibility and limi ts of PERT assay as a broad-spectrum retroviruses detection method in vacci nes are discussed.