| Human diploid cell strains (HDCSs) are one of the important hostsfor the production of human viral vaccines. Since 1960s, vaccines produced in human diploid cell strains have been licensed all over the world, such as inactivated polio vaccine (IPV) and oral polio vaccine (OPV), rubella vaccine, measles vaccine, varicella-zoster vaccine, mumps vaccine and hepatitis A vaccine. Many years of usage have demonstrated that the vaccines produced in HDCS are safe and effective. WHO thus recommends HDCS as the safesthost for the production of viral vaccines. Currently, WI-38 and MRC-5 are two widely used HDCSs in the world. Althoughmany companies and organizations are trying to develop new HDCS, it is extremely slow in progress due to strict ethical reviews as well as the complexity in genetic background check. In the mean time, HDCSs become precious resources due to their limited lifetime and passages. At present, the supply of WI-38 and MRC-5 gradually declines.MRC-5, the widely used HDCS in our country, is also confronted by challenges of too many passages and the external policy. Therefore, it is urgent to develop new HDCSs.KMB-17 and 2BS are two domestically established HDCSs. Due to institutional reasons, the two HDCSs have been used only in a few organizations. It is difficult for other organizations to get the license to use them. Due to the superiority and scarceness of HDCS resources, we started to develop new HDCS in 2008. It took us 7 years to develop a new qualified HDCS, designated as Walvax-2. This HDCS originates from the lung tissue of an aborted 3-month-old human female embryo. We established primary, master and working cell banks that by tissue culture and passage. These cell banks passed cell classification, microorganism and mycoplasma check, viral particle check, retrovirus check as well as human, bovine and porcine virus check. Tumorigenicity is negative. They passed the validation of CFDA. Walvax-2 is a HDCS of good quality.We assessed the adaption of Walvax-2 to several viruses includingthe CTN-1V strain and PV-2061 strain (Pasteur strain of fixed rabies virus), Oka strain of the varicella zoster virus, and the YN5 strain of hepatitis A virus (HAV). MRC-5 was used as a control. Our results showed that the two rabies virus strains raised in Walvax-2 got higher titers than in MRC-5. In the CTN-1V strain, the virus titer reached 4.84 log FFU/ml at first passage and increased to 8.141ogFFU/ml at the 10th passage. In the PV-2061 strain, the titer for the first passage was 4.44 log FFU/mland reached 8.021ogFFU/ml at the 10th passage. By contrast, in the control MRC-5 strain, the titer of CTN-1V strain and PV-2061 strain was 7.41and 7.111ogFFU/ml at 10th passage, respectively.Thus, the virus adaption titer of Walvax-2 cells was higher than that of MRC-5 cells. The difference is statistically significant (P<0.05). As for the Oka strain,the virus titer was 6.28 log PFU/ml in Walvax-2 cells at the first passage and reached 6.66 log PFU/ml at the 41st passage. By contrast, the virus titer was less than 6.0 log PFU/ml in MRC-5 cells. The difference is statistically significant (P<0.05). For the YN5 strain, the titer was 7.0 log CCID50/ml before passage. It reached 7.32 log CCID50/ml at first passage in Walvax-2 cells. By continuous passaging, the titer rose to 7.65 log CCID50/ml at 311st passage. The virus titersin Walvax-2 were generally higher than those in MRC-5 (between 7.0-7.36 log CCID50/ml).In conclusion, our results showed that Walvax-2, the newly established HDCS, demonstrated good adaption to three viral species. The virus titers for three viruses in Walvax-2 cells were all higher than those in MRC-5 cells and the differences are statistically significant. Results from this study suggest that Walvax-2 cell banks are a promising cell substrate and have the potential for the manufacturing of human vaccines. |
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