Institute of Immunology, Hannover Medical School, Hannover, Germany.
Institute for Virology, University of Veterinary Medicine Hannover, Hannover, Germany.
Front Cell Infect Microbiol. 2023 Oct 3;13:1259822. doi: 10.3389/fcimb.2023.1259822. eCollection 2023.
Modified Vaccinia virus Ankara (MVA) represents a promising vaccine vector for respiratory administration to induce protective lung immunity including tertiary lymphoid structure, the bronchus-associated lymphoid tissue (BALT). However, MVA expressing the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Spike protein (MVA-SARS-2-S) required prime-boost administration to induce high titers of anti-Spike antibodies in serum and bronchoalveolar lavage (BAL). As the addition of adjuvants enables efficient tailoring of the immune responses even to live vaccines, we tested whether Toll-like receptor (TLR)-agonists affect immune responses induced by a single dose of intranasally applied MVA-SARS-2-S.
We intranasally immunized C57BL/6 mice with MVA-SARS-2-S vaccine in the presence of either TLR3 agonist polyinosinic polycytidylic acid [poly(I:C)], TLR4 agonist bacterial lipopolysaccharide (LPS) from , or TLR9 agonist CpG oligodeoxynucleotide (CpG ODN) 1826. At different time-points after immunization, we analyzed induced immune responses using flow cytometry, immunofluorescent microscopy, and ELISA.
TLR agonists had profound effects on MVA-SARS-2-S-induced immune responses. At day 1 post intranasal application, the TLR4 agonist significantly affected MVA-induced activation of dendritic cells (DCs) within the draining bronchial lymph nodes, increasing the ratio of CD11bCD86 to CD103CD86 DCs. Nevertheless, the number of Spike-specific CD8 T cells within the lungs at day 12 after vaccination was increased in mice that received MVA-SARS-2-S co-administered with TLR3 but not TLR4 agonists. TLR9 agonist did neither significantly affect MVA-induced DC activation nor the induction of Spike-specific CD8 T cells but reduced both number and size of bronchus-associated lymphoid tissue. Surprisingly, the addition of all TLR agonists failed to boost the levels of Spike-specific antibodies in serum and bronchoalveolar lavage.
Our study indicates a potential role of TLR-agonists as a tool to modulate immune responses to live vector vaccines. Particularly TLR3 agonists hold a promise to potentiate MVA-induced cellular immune responses. On the other hand, additional research is necessary to identify optimal combinations of agonists that could enhance MVA-induced humoral responses.
改良安卡拉痘苗病毒（MVA）是一种很有前途的呼吸道疫苗载体，可用于诱导保护性肺部免疫，包括三级淋巴结构、支气管相关淋巴组织（BALT）。然而，表达严重急性呼吸综合征冠状病毒 2（SARS-CoV-2）刺突蛋白的 MVA（MVA-SARS-2-S）需要进行初次-加强免疫接种，以在血清和支气管肺泡灌洗液（BAL）中诱导高滴度的抗刺突抗体。由于添加佐剂能够使免疫反应得到有效的定制，甚至可以对活疫苗进行定制，因此我们测试了 Toll 样受体（TLR）激动剂是否会影响单次鼻内应用 MVA-SARS-2-S 诱导的免疫反应。
我们用 MVA-SARS-2-S 疫苗对 C57BL/6 小鼠进行鼻内免疫，同时给予 TLR3 激动剂聚肌苷酸聚胞苷酸[poly（I：C）]、TLR4 激动剂革兰氏阴性菌脂多糖（LPS）或 TLR9 激动剂 CpG 寡脱氧核苷酸（CpG ODN）1826。在免疫后不同时间点，我们使用流式细胞术、免疫荧光显微镜和 ELISA 分析诱导的免疫反应。
TLR 激动剂对 MVA-SARS-2-S 诱导的免疫反应有深远的影响。在鼻内应用后第 1 天，TLR4 激动剂显著影响了引流支气管淋巴结中 MVA 诱导的树突状细胞（DC）的激活，增加了 CD11bCD86 与 CD103CD86 DC 的比值。然而，在接种后第 12 天，接种 MVA-SARS-2-S 并联合使用 TLR3 激动剂的小鼠肺部中 Spike 特异性 CD8 T 细胞的数量增加，而使用 TLR4 激动剂则没有。TLR9 激动剂既没有显著影响 MVA 诱导的 DC 激活，也没有诱导 Spike 特异性 CD8 T 细胞，但减少了支气管相关淋巴组织的数量和大小。令人惊讶的是，添加所有 TLR 激动剂都未能提高血清和支气管肺泡灌洗液中 Spike 特异性抗体的水平。
我们的研究表明 TLR 激动剂作为调节活载体疫苗免疫反应的工具具有潜在的作用。特别是 TLR3 激动剂有望增强 MVA 诱导的细胞免疫反应。另一方面，需要进一步研究以确定能够增强 MVA 诱导的体液反应的最佳激动剂组合。
