Herlocher M L, Maassab H F, Webster R G
Department of Virology and Molecular Biology, St. Jude Children's Research Hospital, Memphis, TN 38101.
Proc Natl Acad Sci U S A. 1993 Jul 1;90(13):6032-6. doi: 10.1073/pnas.90.13.6032.
The live cold-adapted (ca) A/AA/6/60 influenza vaccine is being commercially developed for worldwide use in children and is being used as a model for other live vaccines. Although it has been proven safe and immunogenic, the molecular basis of cold adaptation has never been determined. To identify sequence changes responsible for cold adaptation, we have compared the sequence of the master ca vaccine strain to its progenitor wild-type virus, wt A/AA/6/60 E2 (wt2). Only 4 nt differences encoding 2 aa differences were found in three gene segments. Computer-predicted RNA folds project different secondary structures between the ca and wt2 molecules based on the two silent differences between them. Genes coding for the acidic polymerase, matrix, and nonstructural proteins are identical between the two viruses. The few differences found in the ca A/AA/6/60 virus after its long stepwise passage at 25 degrees C in primary chicken kidney cells suggest that cold adaptation resulted in greater genetic stability for the highly variable RNA genome.
减毒活（ca）A/AA/6/60流感疫苗正在进行商业化开发，供全球儿童使用，并被用作其他活疫苗的模型。尽管已证明其安全且具有免疫原性，但冷适应的分子基础从未被确定。为了确定负责冷适应的序列变化，我们将主ca疫苗株的序列与其原始野生型病毒wt A/AA/6/60 E2（wt2）进行了比较。在三个基因片段中仅发现了编码2个氨基酸差异的4个核苷酸差异。基于ca和wt2分子之间的两个沉默差异，计算机预测的RNA折叠显示它们之间的二级结构不同。两种病毒之间编码酸性聚合酶、基质和非结构蛋白的基因是相同的。ca A/AA/6/60病毒在原代鸡肾细胞中于25℃长期逐步传代后发现的少数差异表明，冷适应导致高度可变的RNA基因组具有更高的遗传稳定性。
