RNA Viruses Section, Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA.
Experimental Primate Virology Section, Comparative Medicine Branch, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Poolesville, Maryland, USA.
J Virol. 2020 Dec 22;95(2). doi: 10.1128/JVI.01512-20.
Live-attenuated pediatric vaccines for intranasal administration are being developed for human respiratory syncytial virus (RSV), an important worldwide pediatric respiratory pathogen that lacks a licensed vaccine or suitable antiviral drug. We evaluated a prime-boost strategy in which primary immunization with RSV was boosted by secondary immunization with RSV or with a chimeric recombinant bovine/human parainfluenza virus type 3 (rB/HPIV3) vector expressing the RSV fusion F protein. The vector-expressed F protein had been engineered (DS-Cav1 mutations) for increased stability in the highly immunogenic prefusion (pre-F) conformation, with or without replacement of its transmembrane and cytoplasmic tail domains with their counterparts from bovine parainfluenza virus type 3 (BPIV3) F protein to direct incorporation into the vector virion for increased immunogenicity. In hamsters that received a primary infection with RSV, a booster infection with RSV ∼6 weeks later was completely restricted for producing infectious virus but induced a significant increase in the serum RSV-plaque-reduction neutralizing antibody titer (RSV-PRNT). Boosting instead with the rB/HPIV3-RSV-pre-F vectors resulted in efficient replication and induced significantly higher RSV-PRNTs than RSV. In African green monkeys that received a primary infection with RSV, a booster infection with RSV ∼2, ∼6, or ∼15 months later was highly restricted, whereas booster infections with the vectors had robust replication. Compared with RSV, boosts with the vectors induced 7- to 15-fold higher titers of RSV-specific serum antibodies with high neutralizing activity, as well as significantly higher titers of RSV-specific mucosal IgA antibodies. These findings support further development of this heterologous prime-boost strategy. Immune responses to RSV in infants can be reduced due to immunological immaturity and immunosuppression by RSV-specific maternal antibodies. In infants and young children, two infections with wild-type RSV typically are needed to achieve the titers of RSV-specific serum antibodies and protection against illness that are observed in adults. Therefore, a boost might substantially improve the performance of live pediatric RSV vaccines presently being developed. Hamsters and African green monkeys received a primary intranasal infection with RSV and were given a boost with RSV or a parainfluenza virus (PIV) vector expressing RSV fusion protein engineered for enhanced immunogenicity. The RSV boost was highly restricted but induced a significant increase in serum RSV-neutralizing antibodies. The PIV vectors replicated efficiently and induced significantly higher antibody responses. The use of an attenuated PIV vector expressing RSV antigen to boost a primary immunization with an attenuated RSV warrants further evaluation.
正在开发用于鼻腔给药的活减毒小儿疫苗，用于治疗人呼吸道合胞病毒（RSV），这是一种重要的全球小儿呼吸道病原体，目前尚无许可疫苗或合适的抗病毒药物。我们评估了一种初次免疫和加强免疫策略，初次免疫用 RSV 进行，加强免疫用 RSV 或表达 RSV 融合 F 蛋白的嵌合重组牛/人副流感病毒 3 型（rB/HPIV3）载体进行。载体表达的 F 蛋白经过工程改造（DS-Cav1 突变），以增加在高度免疫原性的预融合（pre-F）构象中的稳定性，无论是否用牛副流感病毒 3 型（BPIV3）F 蛋白的跨膜和胞质尾部取代其，以直接掺入载体病毒粒子中，从而提高免疫原性。在接受 RSV 初次感染的仓鼠中，约 6 周后用 RSV 进行加强感染完全受到限制，无法产生感染性病毒，但可显著增加血清 RSV 蚀斑减少中和抗体滴度（RSV-PRNT）。相反，用 rB/HPIV3-RSV-pre-F 载体进行加强感染可有效复制，并诱导显著高于 RSV 的 RSV-PRNT。在接受 RSV 初次感染的非洲绿猴中，约 2、6 或 15 个月后用 RSV 进行加强感染受到高度限制，而用载体进行加强感染则具有强大的复制能力。与 RSV 相比，载体加强免疫诱导 RSV 特异性血清抗体滴度提高 7-15 倍，具有高中和活性，以及 RSV 特异性粘膜 IgA 抗体滴度显著提高。这些发现支持进一步开发这种异源初免-加强免疫策略。由于 RSV 特异性母抗体的免疫不成熟和免疫抑制作用，婴儿对 RSV 的免疫反应可能会降低。在婴儿和幼儿中，通常需要两次野生型 RSV 感染才能达到成人观察到的 RSV 特异性血清抗体滴度和对疾病的保护。因此，加强免疫可能会显著提高目前正在开发的活小儿 RSV 疫苗的性能。仓鼠和非洲绿猴接受 RSV 鼻腔初次感染，并接受 RSV 或表达 RSV 融合蛋白的副流感病毒（PIV）载体加强免疫。 RSV 加强免疫受到高度限制，但可显著增加血清 RSV 中和抗体。PIV 载体复制效率高，并诱导明显更高的抗体反应。使用表达 RSV 抗原的减毒 PIV 载体加强减毒 RSV 的初次免疫值得进一步评估。
