In this study, we showed that a codon optimized version of the spike (S) protein of SARS-CoV-2 can migrate to the cell membrane. However, efficient production of Moloney murine leukemia (MLV) infectious viral particles was only achieved with stable expression of a shorter S version in C-terminal (ΔS) in MLV Gag-pol expressing cells. As compared to transient transfections, this platform generated viruses with a 1000-fold higher titer. ΔS was 15-times more efficiently incorporated into VLPs as compared to S, and that was not due to steric interference between the cytoplasmic tail and the MLV capsid, as similar differences were also observed with extracellular vesicles. The amount of ΔS incorporated into VLPs released from producer cells was high and estimated at 1.25 μg/mL S2 equivalent (S is comprised of S1 and S2). The resulting VLPs could potentially be used alone or as a boost of other immunization strategies for COVID-19.

在这项研究中，我们表明SARS-CoV-2的穗状蛋白（S）的密码子优化版本可以迁移到细胞膜。但是，只有在MLV Gag-pol表达细胞的C端（ΔS）中稳定表达较短的S型，才能实现Moloney鼠白血病（MLV）感染性病毒颗粒的高效生产。与瞬时转染相比，该平台产生的病毒滴度高1000倍。与S相比，ΔS结合到VLP中的效率提高了15倍，这不是由于细胞质尾部和MLV衣壳之间的空间干扰，因为在细胞外囊泡中也观察到了类似的差异。从生产细胞释放的VLP中掺入的ΔS数量很高，估计为1.25μg/ mL S2当量（S由S1和S2组成）。