ABSTRACT

Viral vectors are a potent vaccine platform for inducing humoral and T-cell immune responses. Among the various viral vectors, replication-competent ones are less commonly used for coronavirus disease 2019 (COVID-19) vaccine development compared with replication-deficient ones. Here, we show the availability of a smallpox vaccine LC16m8Δ (m8Δ) as a replication-competent viral vector for a COVID-19 vaccine. M8Δ is a genetically stable variant of the licensed and highly effective Japanese smallpox vaccine LC16m8. Here, we generated two m8Δ recombinants: one harbouring a gene cassette encoding the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike (S) glycoprotein, named m8Δ-SARS2(P7.5-S)-HA; and one encoding the S protein with a highly polybasic motif at the S1/S2 cleavage site, named m8Δ-SARS2(P7.5-S_HN)-HA. M8Δ-SARS2(P7.5-S)-HA induced S-specific antibodies in mice that persisted for at least six weeks after a homologous boost immunization. All eight analysed serum samples displayed neutralizing activity against an S-pseudotyped virus at a level similar to that of serum samples from patients with COVID-19, and more than half (5/8) also had neutralizing activity against the Delta/B.1.617.2 variant of concern. Importantly, most serum samples also neutralized the infectious SARS-CoV-2 Wuhan and Delta/B.1.617.2 strains. In contrast, immunization with m8Δ-SARS2(P7.5-S_HN)-HA elicited significantly lower antibody titres, and the induced antibodies had less neutralizing activity. Regarding T-cell immunity, both m8Δ recombinants elicited S-specific multifunctional CD8⁺ and CD4⁺ T-cell responses even after just a primary immunization. Thus, m8Δ provides an alternative method for developing a novel COVID-19 vaccine.

摘要

病毒载体是诱导体液和 T 细胞免疫反应的有效疫苗平台。在各种病毒载体中，与复制缺陷型病毒相比，复制型病毒载体较少用于 2019 年冠状病毒病 (COVID-19) 疫苗开发。在这里，我们展示了天花疫苗 LC16m8Δ (m8Δ) 作为 COVID-19 疫苗的复制型病毒载体的可用性。M8Δ 是获得许可的高效日本天花疫苗 LC16m8 的基因稳定变体。在这里，我们生成了两个 m8Δ 重组体：一个含有编码严重急性呼吸综合征冠状病毒 2 (SARS-CoV-2) 刺突 (S) 糖蛋白的基因盒，命名为 m8Δ-SARS2(P7.5-S)-HA；一种编码在 S1/S2 切割位点具有高度多碱基基序的 S 蛋白，命名为 m8Δ-SARS2（P7.5-S _HN）-哈。M8Δ-SARS2(P7.5-S)-HA 在小鼠中诱导的 S 特异性抗体在同源加强免疫后持续至少六周。所有八份分析的血清样本都显示出对 S 假型病毒的中和活性，其水平与 COVID-19 患者的血清样本相似，超过一半 (5/8) 也对 Delta/B.1.617 具有中和活性.2 关注的变体。重要的是，大多数血清样本还中和了传染性 SARS-CoV-2 武汉和 Delta/B.1.617.2 菌株。相比之下，用 m8Δ-SARS2(P7.5-S _HN )-HA 免疫引起的抗体滴度显着降低，而诱导的抗体中和活性较低。关于 T 细胞免疫，m8Δ 重组体均引发 S 特异性多功能 CD8 ⁺和 CD4 ⁺即使在初次免疫后也有 T 细胞反应。因此，m8Δ 为开发新型 COVID-19 疫苗提供了另一种方法。