Helper virus contamination

Assay for infectious helper virus contamination of rAAV... 

Cumulative experience from 106 monkey-years and 23 human-years of retroviral gene therapy had revealed no side-effects or malignancies. Recently, however, three monkeys used in clinical trials developed T cell lymphomas which were traced to a helper virus-contaminated retroviral vector preparation (Anderson, 1992a). Contamination of defective viral vector stocks by infectious viruses produced in helper cells was a serious problem with the early version of the helper cells. New helper cell lines which greatly reduce the probability of virus production have been developed (Miller, 1990). Eurther, it is also imperative to test the lots of vector virus preparations used in therapy for the presence of other infectious viruses. The probability... 

The biggest concern for the hybrid viral systems is the helper virus contamination. Even a marginal level of adenoviral or adenoviral protein contamination could be detrimental for patients. To establish a completely virus-fiee system, essential adenoviral genes (including VA RNA E2A, E4) have also been cloned into the adenoviral helper plasmids (9-11,181,187). In combination with the novel irons helper plasmids mentioned above, the yield of rAAV following transient transfection... 

A number of investigators had reported in earlier studies that 5 -DI particles of VSV, in which one-half or more of the 3 end of the genome is deleted, were fully capable of inhibiting cellular protein synthesis (Baxt and Bablanian, 1976 >). It seems likely that this apparent effect of DI particles on protein synthesis inhibition is due to difficult-to-detect contamination with the helper B virions (standard infection virus). Schnitzlein et al. (1983) detected little or no inhibition of BHK cell protein synthesis by various types of highly purified 5 -DI particles, even at high multiplicities of infection. These DI particles fully retained capacity to inhibit replication of infectious B particles and, as will be discussed later, the 5 -DI particles did not affect the capacity of infectious B virions to inhibit cellular protein synthesis (Schnitzlein et al., 1983). It seems safe to conclude that 5 -DI particles of VSV contain no structural components or biological activity that will inhibit cellular protein synthesis. 

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