DETECTION OF REVERSE-TRANSCRIPTASE ACTIVITY IN LIVE ATTENUATED VIRUS-VACCINES

Background: Safety considerations require that biological products for human use are free from any agent that might pose a potential health hazard. One method to detect the presence of retroviral particles is t he reverse transcriptase (RT) assay. This assay is capable of detectin g all infectious retrovirus particles, irrespective of genome or prote in composition. Recently, a family of ultrasensitive RT tests, named p roduct-enhanced reverse transcriptase (PERT) assays, has been designed with a detection limit that is 10(6)-10(7) times lower than that of c onventional RT tests. Objectives: To investigate with the PERT assay w hether RT activity is detectable in live attenuated virus vaccines and to characterize eventual RT activities. Study design: A total of 12 d ifferent monovalent and one trivalent virus vaccines containing live a ttenuated viruses were tested for RT activity with the PERT assay and a conventional RT test. RT activities were investigated with respect t o their susceptibility to RT inhibitors, association with physical par ticles, and their possible origin. Results: One trivalent and five dif ferent monovalent vaccines contained RT activity when tested with the PERT assay, but were negative in a conventional RT assay. All lots tes ted of these vaccines showed RT activity. The activity in all vaccines was sensitive to AZT-triphosphate and ddTTP and at least part of it w as associated with particles. Mg2+-dependent RT activity banded at a d ensity of 1.14 g/ml. All positive vaccines were produced using chicken cells. Conclusions: The data indicate the systematic presence of part ially particle-associated retroviral reverse transcriptase in attenuat ed live virus vaccines that are produced in chicken-derived cells. The identification and further characterization of these particles, as we ll as the elucidation of possible interactions with the human organism are imperative goals despite the fact that these vaccines have been s afely used for many years.