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UPDATED: Rhabdovirus lurks in cell line used to make Flublok

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According to an article to be published in the Journal of Virology on June 15, 2014, the Sf9 cell line, which was derived from moths and is widely used to manufacture biological products, is contaminated with a virus. According to scientists working at the Laboratory of Retroviruses in Bethesda, Md., S. frugiperda rhabdovirus (Sf-rhabdovirus) is a novel virus that previous methods of cell line examination did not detect.

The Sf9 cell line is used as a cell substrate to produce proteins for use in different biological products, including the Flublok flu vaccine. According to documents filed with FDA by its manufacturer, Protein Sciences Corporation, "Flublok [Influenza Vaccine] is a sterile, clear, colorless solution of recombinant hemagglutinin (HA) proteins from three influenza viruses for intramuscular injection. It contains purified HA proteins produced in a continuous insect cell line (expresSF+®) that is derived from Sf9 cells of the fall armyworm, Spodoptera frugiperda, and grown in serum-free medium composed of chemically-defined lipids, vitamins, amino acids, and mineral salts." In addition, the manufacturer comments, "the expresSF+ cell line used in the production of Flublok is the first insect cell substrate used for development of an influenza virus vaccine." Noted in additional documentation is the fact that "Each 0.5mL dose of Flublok may also contain residual amounts of baculovirus and host cell proteins [...], baculovirus and cellular DNA [...], and Triton X-100 [a detergent]."

Although the research team in Bethesda asserts that "Infectivity studies showed the lack of replication of Sf-rhabdovirus in human cell lines," the presence of a virus in a biological product has been linked in the past to adverse effects. Multiple research studies have linked simian virus 40 (SV40) contamination of polio vaccines in use in the United States through the 1970s to malignant mesothelioma, a type of cancer, as well as brain tumors. Additionally, individuals who received SV40-contaminated polio vaccines continue to circulate this virus, even if they themselves have not developed cancer.

It is unclear how many products are made with the Sf9 cell line. However, FDA documents reveal that "several manufacturers are changing from embryonated eggs to other cell types, e.g., MDCK, Vero, and Baculovirus-Sf9, as a cellular source for vaccine production." Experimental vaccines for H5N1, for example, have been produced using Sf9 cell lines. It is unknown at present whether any biological product made using the Sf9 cell line as a substrate has itself been shown to be contaminated.