To develop the new classical swine fever (CSF) vaccine candidate with differentiating infected vaccinated animals (DIVA) characteristics, a chimeric CSF virus (CSFV) was constructed based on an infectious cDNA clone of the CSF vaccine C-strain. The 5’- and 3’-untranslated regions (UTRs) and partial E2 region (residues 690-860) of the C-strain were substituted with the corresponding regions of bovine viral diarrhoea virus (BVDV) to construct the chimeric cDNA clone pC/bUTRs-tE2. The chimeric virus rC/bUTRs-tE2 was generated by several passages of pC/bUTRs-tE2-transfected PK15 cells. Stable growth and genetic properties of rC/bUTRs-tE2 were obtained after 30 serial passages. Compared to parental rC/bUTRs-tE2 (1^st passage), two residue mutations (M834K and M979K) located in E2 in rC/bUTRs-tE2 P30 were observed. Compared to the C-strain, rC/bUTRs-tE2 exhibited unchanged cell tropism and decreased plaque-forming ability. Substituting the C-strain UTRs with the BVDV UTRs resulted in significantly increased viral replication in PK15 cells. Compared to CSFV E^rns-positive and BVDV tE2-negative antibody responses induced by the CSF vaccine C-strain, immunization of rabbits and piglets with rC/bUTRs-tE2 resulted in serological profiles of CSFV E^rns- and BVDV tE2-positive antibodies, which are used to serologically discriminate pigs that are clinically infected and vaccinated. Vaccination of piglets with rC/bUTRs-tE2 conferred complete protection against lethal CSFV challenge. Our results suggest that rC/bUTRs-tE2 is a promising new CSF marker vaccine candidate.

为了开发具有区分受感染接种动物 (DIVA) 特征的新型经典猪瘟 (CSF) 候选疫苗，基于 CSF 疫苗 C 株的感染性 cDNA 克隆构建了嵌合 CSF 病毒 (CSFV)。将C株的5'-和3'-非翻译区（UTRs）和部分E2区（残基690-860）替换为牛病毒性腹泻病毒（BVDV）的相应区域，构建嵌合cDNA克隆pC/ bUTRs-tE2。嵌合病毒 rC/bUTRs-tE2 是由 pC/bUTRs-tE2 转染的 PK15 细胞传代产生的。连续传代 30 代后，rC/bUTRs-tE2 获得了稳定的生长和遗传特性。与亲本 rC/bUTRs-tE2（^第1passage），观察到位于 rC/bUTRs-tE2 P30 中 E2 的两个残基突变（M834K 和 M979K）。与 C 株相比，rC/bUTRs-tE2 表现出不变的细胞趋向性和降低的噬菌斑形成能力。用 BVDV UTR 替代 C 株 UTR 导致 PK15 细胞中的病毒复制显着增加。与由 CSF 疫苗 C 株诱导的 CSFV E ^{rns阳性和 BVDV tE2 阴性抗体反应相比，用 rC/bUTRs-tE2 免疫兔和仔猪导致 CSFV E rns的血清学特征}- 和 BVDV tE2 阳性抗体，用于血清学区分临床感染和接种疫苗的猪。用 rC/bUTRs-tE2 给仔猪接种疫苗可提供针对致死性 CSFV 攻击的完全保护。我们的结果表明 rC/bUTRs-tE2 是一种很有前途的新 CSF 标记疫苗候选物。