Measles Vaccine S191 Production Strain Genetic Stability

The Shanghai 191 strain of measles virus is widespread used as measles vaccine productive strain.Measles virus Shanghai 191 isolated from the blood of a two-year-old boy was attenuated by Shanghai Institute of Biological Products in 1960s,and has used for almost 40 years in China.After the introduction of mass vaccination,epidemiologic data showed a significant drop in measles-associated morbidity which revealed that the Shanghai 191 vaccine is adequately safe and immunogenic.Clinical investigation data in recent years suggested that the antibody geometric mean titer(GMT)is descending from about 1:100 in 1970s to about 1:30,though antibody positive seroconversion rate is more than 95%.In our study,we want to inspect the genetic stability of the Shanghai 191 measles vaccine through propagating it in primary culture of chicken embryo fibroblasts(CEF)to analysis the correlation between the changes of virus genome and the passage prolongation in vaccine production,and assess the immune protective efficiency of the measles vaccine currently used.We toke the lyophilized Shanghai 191 virus(CEF-25)from Beijing Tiantan Biological Products Co.,LTD[i.e.S191-BJ25]and the Shanghai 191 virus(CEF-24) from Shanghai Institute of Biological Products to propagate in CEF.S191-BJ25 was subcultured to passage 29,and S191-SH24 to passage 33.Chosen the virus of some different passages,we extracted the virus nucleic acid and sequenced the structure gene fragment including gene N,M,F,H.Compared with the sequence of Shanghai191 measles vaccine published in GenBank in1994 and 2008,the change of N,M,F,H gene of Shanghai191 measles virus was explored.At the same time,we assessed the change of H gene of measles virus Shanghai 191 strain during long term culture by comparing it with that of HAM42 and CEF20.The results showed that the genome of Shanghai 191 after propagated in CEF perform a better stability.None of N,M,H gene of the BJ25 system virus changes,only 1 silence substitution in F gene.9 nucleotide changes of the SH24 system virus were observed:1 in the N,1 in the M,3 in the F,4 in the H.Among those substitutions,1 in F gene and 2 in H gene deduce amino acid change.Compared with the sequence of the Shanghai 191 vaccine in 1994,there are 9 of total 18 substitutions in N,M,F,H gene deducing amino acid changes in viral polypeptides of the BJ25 systems virus,and 12 of total 26 substitutions in gene deducing amino acid changes in polypeptides of the SH24 systems virus.The results are consistent with the data of Shanghai 191 vaccine in 2008.These changes showed that the mutants in the development of measles vaccine are conserved.There are 3 of 7 nucleotide differences in H gene deducing amino acid sequences predicted substitutions of the B J25 systems virus compared with that of the HAM42. These changes conserved in vaccine virus subculture and are consistent with the SH24 system virus.Changes at position 506 and 600 of H protein play an important role in virus attenuation,which represent crucial targets for future studies aimed at understanding the molecular basis of attenuation.