With the integration of surveillance for measles and rubella, the ideal cell line will be permissive for robust growth of both viruses and is safe and relatively easy to work with. The Vero/hSLAM cell line has been adopted for use in most laboratories in the GMRLN [1]. These cells were developed by transfecting the Vero cell line with a plasmid that encodes the gene for the human signalling lymphocyte-activation molecule (hSLAM) [2].
Previously, many of the network laboratories had used the B95a cell line and measles virus stocks made in the 1990s were often obtained by culturing measles virus on the B95a cells. While highly sensitive for measles virus, the B95a cell line is persistently infected with Epstein-Barr virus and must be handled as infectious material. After the Vero/hSLAM cell line was demonstrated to have an equivalent sensitivity for measles virus as that of the B95a cell line, the transition to Vero/hSLAM was recommended as the preferred cell line for the GMRLN.
Although hSLAM was identified as a cellular receptor for measles virus, the Vero/hSLAM cell line is also sensitive for rubella viruses. However, as with other cell lines used for rubella virus isolation, the cytopathic effect (CPE) is rarely apparent and the presence of rubella virus must be confirmed by RT-PCR or other viral detection methods. A disadvantage of the Vero/hSLAM cell line is the cost of the culture medium. In order to retain the expression of SLAM, Geneticin® must be added to the culture medium. However, once the cell stocks are prepared in the presence of Geneticin®, SLAM expression will be retained for at least 15 subsequent passages in culture medium prepared without addition of Geneticin®.
Note: Cell stocks of the Vero/hSLAM cell line, developed by Dr.Yusuke Yanagi and colleagues at Kyushu University, Japan, have been provided to the GMRLN laboratories by the National Institute of Infectious Diseases, Tokyo, Japan, and are available in regional cell repositories*. Vero/hSLAM cells can be obtained on request (free of charge) through WHO.
By acceptance of the Vero/hSLAM cell line, the laboratory agrees to the following provisions:
- The cell line Vero/hSLAM is used only for laboratory diagnosis of measles and rubella viral infection by virus isolation and/or investigation of measles or rubella strains for molecular epidemiological purposes
- The cell line is not used for commercial purposes
- The cell line is not distributed to laboratories outside the WHO Laboratory Network without Dr Yanagi's and WHO's permission
- Any publication of work using the Vero/hSLAM cell line acknowledges the original publication (Ono et al. J. Virol. 2001, 75:4399-4401)
*For those countries that are bound by the restrictions outlined by the CITES treaty, the transportation of products derived from endangered species including the African green monkey (Vero cells) are not allowed. Efforts are underway to transfect other types of cell lines that are sensitive for rubella growth (RK13, BHK21, JEG3) with hSLAM that would not be affected by the CITES restrictions.