Root Cause Investigation of Unusual Results Experienced during Master Cell Bank (MCB) Testing and Characterization

We experienced two cases of unexpected results during master cell bank (MCB) testing and characterization at two individual testing companies over the last 5 years. Investigation was launched immediately upon receiving notice from the testing companies involved in an attempt to determine the root cause. In the first case, potential viral contamination of the MCB was suspected based on results from the cell-based in vitro viral screening. Our investigation provided compelling evidence indicating that the viral contaminant did not originate from the MCB; rather, it was introduced into the screening system at the testing facility. Details of this investigation will not be discussed here but can be found in an article published in the journal Biologicals (1). In the second case, unusual responses were observed in adult mice (post-weaning mice) within 3-4 h following inoculation of the MCB test article. The inoculated mice exhibited the following clinical signs: extreme tremors, hunched posture, ruffled coats, and difficulty in breathing. Our investigation has demonstrated that a component of the growth medium used for test article preparation was responsible for the unexpected responses. Potential causative factor(s) that may have contributed to the unexpected observations are discussed. Similar occurrences have not been observed in any other MCB tests.