Single intranasal immunization with chimpanzee adenovirus-based vaccine induces sustained and protective immunity against MERS-CoV infection

The recently identified Middle East Respiratory Syndrome Coronavirus (MERS-CoV) causes severe and fatal acute respiratory illness in humans. However, no approved prophylactic and therapeutic interventions are currently available. The MERS-CoV envelope spike protein serves as a crucial target for neutralizing antibodies and vaccine development, as it plays a critical role in mediating viral entry through interactions with the cellular receptor, dipeptidyl peptidase 4 (DPP4). Here, we constructed a recombinant rare serotype of the chimpanzee adenovirus 68 (AdC68) that expresses full-length MERS-CoV S protein (AdC68-S). Single intranasal immunization with AdC68-S induced robust and sustained neutralizing antibody and T cell responses in BALB/c mice. In a human DPP4 knock-in (hDPP4-KI) mouse model, it completely protected against lethal challenge with a mouse-adapted MERS-CoV (MERS-CoV-MA). Passive transfer of immune sera to naïve hDPP4-KI mice also provided survival advantages from lethal MERS-CoV-MA challenge. Analysis of sera absorption and isolated monoclonal antibodies from immunized mice demonstrated that the potent and broad neutralizing activity was largely attributed to antibodies targeting the receptor binding domain (RBD) of the S protein. These results show that AdC68-S can induce protective immune responses in mice and represent a promising candidate for further development against MERS-CoV infection in both dromedaries and humans.

近期发现的中东呼吸综合征冠状病毒（Middle East Respiratory Syndrome Coronavirus, MERS-CoV）可引发人类严重乃至致死性的急性呼吸道疾病。然而，目前尚无获批的预防与治疗干预手段。MERS-CoV包膜刺突蛋白是中和抗体研发与疫苗开发的关键靶点，因其通过与细胞受体二肽基肽酶4（dipeptidyl peptidase 4, DPP4）相互作用介导病毒入侵，在病毒入侵过程中发挥核心作用。本研究构建了一株表达全长MERS-CoV S蛋白的稀有血清型黑猩猩腺病毒68（AdC68）重组体（AdC68-S）。对BALB/c小鼠进行单次鼻内免疫AdC68-S，可诱导产生强效且持久的中和抗体与T细胞免疫应答。在人DPP4敲入（human DPP4 knock-in, hDPP4-KI）小鼠模型中，该免疫策略可完全保护小鼠免受鼠适应性MERS-CoV（MERS-CoV-MA）的致死性攻击。将免疫血清被动转移至未免疫的hDPP4-KI小鼠，同样可使其在致死性MERS-CoV-MA攻击中获得生存保护。血清吸附实验与免疫小鼠分离得到的单克隆抗体分析结果显示，这种强效且广谱的中和活性，主要源自靶向S蛋白受体结合域（receptor binding domain, RBD）的抗体。上述研究结果表明，AdC68-S可在小鼠体内诱导保护性免疫应答，有望成为进一步开发用于单峰驼与人类对抗MERS-CoV感染的候选疫苗。