THE REVERSE-TRANSCRIPTASE ACTIVITY IN CELL-FREE MEDIUM OF CHICKEN-EMBRYO FIBROBLAST-CULTURES IS NOT ASSOCIATED WITH A REPLICATION-COMPETENTRETROVIRUS

Background: Reverse transcriptase (RT) activity has previously been re ported in concentrated medium of primary chicken embryo cell cultures using the traditional RT assay. Recently, using the newly-developed an d highly-sensitive product-enhanced reverse transcriptase (PERT) assay , RT activity has been detected in live, attenuated vaccines grown in chicken cell substrates. Furthermore, this activity has been associate d with particles that contain RNA related to an ancient, endogenous av ian retrovirus family designated as EAV-0. Objective: To investigate w hether the RT activity present in vaccines produced in specific pathog en-free chicken cell substrates is associated with an infectious retro virus that can replicate in human cells. Study design: The kinetics of RT activity produced by 10-day-old chicken embyro fibroblast (CEF) cu ltures was determined by analyzing cell-free medium in a PCR-based RT (PBRT) assay. Material containing the peak PERT activity was used as t he inoculum to infect various human cell lines and peripheral blood mo nonuclear cells. Filtered supernatants from control and test cultures were analyzed for the presence of replication-competent retroviruses b y the PERT assay. The cells were monitored for other adventitious agen ts by routine observation for cytopathic effect (CPE) and by transmiss ion electron microscopy (TEM) at culture termination. Results: The PER T activity did not increase above the background level in the human ta rget cells through at least five cell passages, thus indicating the ab sence of a replicating retrovirus. No other adventitious agents were d etected based upon TEM analysis and the absence of CPE. Conclusion: Th e RT activity produced by chicken primary cell cultures is not associa ted with a retrovirus that can replicate in human cells. (C) 1998 Publ ished by Elsevier Science B.V. All rights reserved.