Detection Assay for Replication-Competent Adenovirus by Concentration Passage and Real-Time Quantitative Polymerase Chain Reaction (qPCR)

The sensitivity of an assay for replication-competent adenoviruses (RCAs) can often be enhanced by biological amplification of the RCAs with serial passage. Here, we describe an extension of this technique, termed “concentration passage,” in which RCA replicated during the first plating of the vector is collected and concentrated onto one-tenth of the original number of cells. This significantly increases the chances of detecting the RCAs. Combining this approach with the use of quantitative polymerase chain reaction (qPCR) for sensitive detection of the RCA E1 gene, we are able to reach levels of sensitivity of 1 IU of RCAs in 10 11 vector particles. The protocol described here is tailored for HuAd5 vectors using wild-type HuAd5 as the RCA surrogate. However, we have also adapted this technique with similar sensitivity to vectors based on other adenovirus serotypes. If other adenovirus serotypes are assayed, careful consideration should be given to the appropriate RCA surrogate. Strictly speaking, if the vector is propagated in HEK-293 or similar cell lines, the RCA surrogate should be a hybrid virus containing the HuAd5 E1 gene.