Immunization of Macaques with Formalin-Inactivated Respiratory Syncytial Virus (RSV) Induces Interleukin-13-Associated Hypersensitivity to Subsequent RSV Infection

Respiratory syncytial virus (RSV) is a major cause of severe respiratory disease in infants and the elderly. RSV vaccine development has been hampered by results of clinical trials in the 1960s, when formalin-inactivated whole-RSV preparations adjuvated with alum (FI-RSV) were found to predispose infants for enhanced disease following subsequent natural RSV infection. We have reproduced this apparently immunopathological phenomenon in infant cynomolgus macaques and identified immunological and pathological correlates. Vaccination with FI-RSV induced specific virus-neutralizing antibody responses accompanied by strong lymphoproliferative responses. The vaccine-induced RSV-specific T cells predominantly produced the Th2 cytokines interleukin-13 (IL-13) and IL-5. Intratracheal challenge with a macaque-adapted wild-type RSV 3 months after the third vaccination elicited a hypersensitivity response associated with lung eosinophilia. The challenge resulted in a rapid boosting of IL-13-producing T cells in the FI-RSV-vaccinated animals but not in the FI-measles virus-vaccinated control animals. Two out of seven FI-RSV-vaccinated animals died 12 days after RSV challenge with pulmonary hyperinflation. Surprisingly, the lungs of these two animals did not show overt inflammatory lesions. However, upon vaccination the animals had shown the strongest lymphoproliferative responses associated with the most pronounced Th2 phenotype within their group. We hypothesize that an IL-13-associated asthma-like mechanism resulted in airway hyperreactivity in these animals. This nonhuman primate model will be an important tool to assess the safety of nonreplicating candidate RSV vaccines.呼吸道合胞病毒（respiratory syncytial virus, RSV）是引发婴幼儿与老年群体罹患重症呼吸道疾病的主要病原体。呼吸道合胞病毒疫苗的研发曾因20世纪60年代的临床试验结果受阻——当时研究发现，以明矾（alum）为佐剂的福尔马林灭活全病毒呼吸道合胞病毒制剂（FI-RSV）会使婴幼儿在后续自然感染RSV时病情加重。本研究在幼食蟹猕猴体内重现了这一典型免疫病理现象，并明确了其免疫与病理相关标志物。FI-RSV疫苗接种可诱导特异性病毒中和抗体应答，同时伴随强烈的淋巴细胞增殖反应。疫苗诱导的RSV特异性T细胞主要分泌Th2型细胞因子白细胞介素-13（IL-13）与IL-5。在第三次接种后3个月，以猕猴适应性野生型RSV对FI-RSV接种组动物实施气管内攻毒，结果引发了与肺嗜酸性粒细胞增多相关的超敏反应。该攻毒操作可快速扩增FI-RSV接种组动物体内分泌IL-13的T细胞，而接种福尔马林灭活麻疹病毒的对照组动物则未出现该现象。7只FI-RSV接种组动物中有2只在RSV攻毒后12天因肺过度充气死亡。令人意外的是，这两只死亡动物的肺部未出现明显炎性病变。但在接种阶段，这两只动物是组内淋巴细胞增殖反应最强、Th2表型最显著的个体。我们推测，与IL-13相关的哮喘样机制导致了这些动物出现气道高反应性。该非人灵长类动物模型将成为评估非复制型候选RSV疫苗安全性的重要工具。