Self-amplifying RNA replicons are promising platforms for vaccine generation. Their defects in one or more essential functions for viral replication, particle assembly, or dissemination make them highly safe as vaccines. We previously showed that the deletion of the envelope (E) gene from the Middle East respiratory syndrome coronavirus (MERS-CoV) produces a replication-competent propagation-defective RNA replicon (MERS-CoV-ΔE). Evaluation of this replicon in mice expressing human dipeptidyl peptidase 4, the virus receptor, showed that the single deletion of the E gene generated an attenuated mutant. The combined deletion of the E gene with accessory open reading frames (ORFs) 3, 4a, 4b, and 5 resulted in a highly attenuated propagation-defective RNA replicon (MERS-CoV-Δ[3,4a,4b,5,E]). This RNA replicon induced sterilizing immunity in mice after challenge with a lethal dose of a virulent MERS-CoV, as no histopathological damage or infectious virus was detected in the lungs of challenged mice. The four mutants lacking the E gene were genetically stable, did not recombine with the E gene provided in trans during their passage in cell culture, and showed a propagation-defective phenotype in vivo. In addition, immunization with MERS-CoV-Δ[3,4a,4b,5,E] induced significant levels of neutralizing antibodies, indicating that MERS-CoV RNA replicons are highly safe and promising vaccine candidates.

自扩增 RNA 复制子是有前途的疫苗生产平台。它们在病毒复制、颗粒组装或传播的一项或多项基本功能上存在缺陷，这使得它们作为疫苗具有高度的安全性。我们之前表明，从中东呼吸综合征冠状病毒（MERS-CoV）中删除包膜（E）基因会产生具有复制能力的传播缺陷型RNA复制子（MERS-CoV-ΔE）。在表达人二肽基肽酶 4（病毒受体）的小鼠中对该复制子的评估表明，E 基因的单个缺失产生了减毒突变体。E 基因与附加开放阅读框 (ORF) 3、4a、4b 和 5 的联合删除导致高度减毒的繁殖缺陷型 RNA 复制子 (MERS-CoV-Δ[3,4a,4b,5,E] ）。这种 RNA 复制子在受到致命剂量的有毒 MERS-CoV 攻击后，在小鼠体内诱导了绝育免疫，因为在受攻击小鼠的肺部没有检测到组织病理学损伤或感染性病毒。缺乏E基因的四个突变体遗传稳定，在细胞培养物中传代期间不与反式提供的E基因重组，并且在体内表现出繁殖缺陷表型。此外，用 MERS-CoV-Δ[3,4a,4b,5,E] 进行免疫诱导了显着水平的中和抗体，表明 MERS-CoV RNA 复制子是高度安全且有前途的候选疫苗。