Incomplete but Infectious Vaccinia Virions Are Produced in the Absence of Oncolysis in Feline SCCF1 Cells

Vaccinia virus is a large, enveloped virus of the poxvirus family. It has broad tropism and typically virus replication culminates in accumulation and lytic release of intracellular mature virus (IMV), the most abundant form of infectious virus, as well as release by budding of extracellular enveloped virus (EEV). Vaccinia viruses have been modified to replicate selectively in cancer cells and clinically tested as oncolytic agents. During preclinical screening of relevant cancer targets for a recombinant Western Reserve strain deleted for both copies of the thymidine kinase and vaccinia growth factor genes, we noticed that confluent monolayers of SCCF1 cat squamous carcinoma cells were not destroyed even after prolonged infection. Interestingly, although SCCF1 cells were not killed, they continuously secreted virus into the cell culture supernatant. To investigate this finding further, we performed detailed studies by electron microscopy. Both intracellular and secreted virions showed morphological abnormalities on ultrastructural inspection, suggesting compromised maturation and morphogenesis of vaccinia virus in SCCF1 cells. Our data suggest that SCCF1 cells produce a morphologically abnormal virus which is nevertheless infective, providing new information on the virus-host cell interactions and intracellular biology of vaccinia virus.

痘苗病毒（Vaccinia virus）是痘病毒科（poxvirus family）中的大型包膜病毒，具有广谱宿主嗜性。病毒复制通常以细胞内成熟病毒（intracellular mature virus, IMV）的积累与裂解释放为高潮——该颗粒是传染性病毒中丰度最高的形式，同时还可通过出芽途径释放细胞外包膜病毒（extracellular enveloped virus, EEV）。痘苗病毒已被改造以实现在癌细胞内的选择性复制，并作为溶瘤制剂（oncolytic agents）开展临床测试。在针对一株敲除了两份胸腺嘧啶核苷激酶（thymidine kinase）与痘苗生长因子（vaccinia growth factor）基因的重组Western Reserve株开展相关癌症靶点的临床前筛选过程中，我们观察到：即便经过长时间感染，SCCF1猫鳞状癌细胞（SCCF1 cat squamous carcinoma cells）的汇合单层培养物也未被破坏。有趣的是，尽管SCCF1细胞未被杀伤，但它们会持续向细胞培养上清液中分泌病毒。为进一步探究这一现象，我们通过电子显微镜术（electron microscopy）开展了细致研究。超微结构观察显示，细胞内与分泌出的病毒颗粒均存在形态学异常，这表明痘苗病毒在SCCF1细胞内的成熟与形态发生过程受到了损害。本研究数据显示，SCCF1细胞可产生形态异常但仍具有感染性的病毒，这为痘苗病毒的病毒-宿主细胞相互作用及其细胞内生物学特性提供了新的研究视角。