呼吸道合胞病毒单克隆抗体逃逸株体内适合度研究

In vivo fitness of respiratory syncytial virus Palivizumab escape mutants

目的此前研究已在体外筛选获得呼吸道合胞病毒（RSV） Palivizumab（PZ）逃逸株MP4，体外评估发现MP4适合度高于A2母株，本研究在免疫缺陷棉鼠模型中进一步评价MP4体内适合度。方法采用大剂量环磷酰胺腹腔注射法制备免疫抑制鼠模型，将PZ逃逸株MP4和母株A2等量混合，经鼻腔接种免疫缺陷动物模型，于接种后4天和4周分批处死动物，取动物肺脏组织研磨后采用差异噬斑形成法或核苷酸序列图谱分析法检测混合病毒群体中母株A2和逃逸株MP4的相对含量，以代表MP4相对于A2的适合度。将肺内病毒F基因片段RT—PCR扩增产物克隆并转化大肠杆菌，随机挑取部分菌落再行PCR扩增F基因片段及序列测定，观察F基因第828位碱基并计算A2株和MP4相对含量。结果差异噬斑法结果显示接种后4天和4周棉鼠肺内病毒混合群体中均以MP4占优，序列图谱分析发现接种后4周8只棉鼠中7只肺内MP4占优。接种后4周克隆的8只棉鼠F基因片段78％（120／154）为MP4基因信号。结论与体外适合度结果类似，MP4在棉鼠肺内的适合度高于A2母株，提示与MP4基因型相同的逃逸株一旦产生，可能在免疫缺陷个体间传播。

Objective To assess the fitness of the Palivizumab（PZ）-resistant respiratory syncytial virus（RSV） stain MP4 in cotton rat lung in vivo. Methods The mixture was made with equal amounts of A2 and MP4 virus and inoculated to immunosuppressed cotton rats which had been treated with cyclophos- phamide. At day 4 and week 4 post inoculation, animals were sacrificed and lungs were harvested for virus titration by differential plaque assay and nueleotide sequence analysis. The F gene fragments were amplified by RT-PCR and cloned into the plasmid, then transformed E. coll. Certain amount of colonies were picked for same F gene fragment amplification, and PCR products were sequenced for A2 or MP4 signal at nucleo- tide 828. Relative amount of MP4 in the mixed viral population were then calculated. Results MP4 pre- dominated in cotton rat lungs either by differential plaque assay or nucleotide sequence analysis at week 4 post inoculation, although the viral population consisted of more complicated viruses. Among the total 154 analyzed F gene clones, the majority （120） contained MP4 gene signal. Conclusion The mutant MP4 vi- rus is of more fitness than parental A2 virus in cotton rat lungs, similar to that seen in vitro fitness assess- ment. Mutant viruses with similar resistance to PZ and increased fitness are more likely to disseminate in the population, particularly in immunocomprimised individuals.