State Key Lab of Respiratory Disease, The First Affiliated Hospital of Guangzhou Medical College, Guangzhou Medical University, Guangzhou 510120, China.
Virus Res. 2011 Sep;160(1-2):214-20. doi: 10.1016/j.virusres.2011.06.017. Epub 2011 Jun 29.
Human adenovirus serotype 3 (Ad3) and serotype 7 (Ad7) are important pathogens causing respiratory tract diseases such as acute respiratory disease in pediatric and adult patients, but the immunodominant targets of Ad3- and Ad7-specific neutralizing antibodies (NAbs) remain unclear. A chimeric Ad vector, Ad3/H7, was constructed by replacing the Ad3 hexon gene (H3) with the hexon gene (H7) of Ad7. The chimeric viruses were successfully rescued in HEp-2 cells, and the Ad7 hexon was able to encapsidate the Ad3 genome, and functioned as efficiently as the Ad3 hexon. Furthermore, we tested the host neutralization responses against the viruses using BALB/C mice. Up to 97% of the NAbs produced by mice that were infected with these viruses were specific for the hexon protein in vitro. Preimmunization of mice with one of Ad7 and Ad3/H7 significantly prevented subsequent intranasal infection of the other type in vivo. In contrast, preimmunization of mice with one of Ad3 and Ad3/H7 did not remarkably prevent subsequent infection of the other type. We next evaluated the functional significance of hexon and other structural proteins specific NAbs to suppress the immunogenicity of Ad3/H3 and Ad3/H7 vectors expressing EGFP in mice preimmunized with wild type Ad. Preimmunization of mice with Ad7 evidently suppressed EGFP-specific humoral immune responses elicited by Ad3/H7, and did not exert suppressive effects on Ad3/H3. But contrary to the in vitro neutralization results, EGFP-specific humoral immune responses elicited by Ad3/H7 was remarkably inhibited in Ad3-preimmunization mice. The whole genome of the Ad7 strain was sequenced and aligned with Ad3. The major differences between Ad3 and Ad7 were only observed in the fiber and hexon among all structural proteins, and the variation between the hexons only located in four hypervariable regions (HVRs), HVR-1, -2, -5, and -7. These results thus suggest that Ad3- and Ad7-specific NAbs are directed primarily against the hexon proteins both in vitro and in vivo. But high titer Ad3 fiber-specific NAbs may also play an important role in blunting Ad3 immunogenicity in vivo. These studies contribute to a more profound understanding of Ad immunogenicity and have relevance for the design of novel Ad vaccine.
人腺病毒血清型 3（Ad3）和血清型 7（Ad7）是引起儿科和成年患者呼吸道疾病（如急性呼吸道疾病）的重要病原体，但 Ad3 和 Ad7 特异性中和抗体（NAb）的免疫优势靶标仍不清楚。通过用 Ad7 的六邻体基因（H7）替换 Ad3 的六邻体基因（H3），构建了嵌合 Ad 载体 Ad3/H7。嵌合病毒在 HEp-2 细胞中成功拯救，Ad7 的六邻体能够包装 Ad3 基因组，并且与 Ad3 六邻体一样高效。此外，我们使用 BALB/C 小鼠测试了针对这些病毒的宿主中和反应。用这些病毒感染的小鼠产生的 NAb 中，高达 97%的 NAb 针对体外的六邻体蛋白。用 Ad7 和 Ad3/H7 中的一种预先免疫小鼠，可显著防止体内随后感染另一种类型。相比之下，用 Ad3 和 Ad3/H7 中的一种预先免疫小鼠，并不会显著防止随后感染另一种类型。接下来，我们评估了针对六邻体和其他结构蛋白特异性 NAb 的功能意义，以抑制在预先用野生型 Ad 免疫的小鼠中表达 EGFP 的 Ad3/H3 和 Ad3/H7 载体的免疫原性。用 Ad7 预先免疫小鼠可显著抑制由 Ad3/H7 引起的 EGFP 特异性体液免疫反应，而对 Ad3/H3 没有抑制作用。但与体外中和结果相反，在 Ad3 预先免疫的小鼠中，由 Ad3/H7 引起的 EGFP 特异性体液免疫反应明显受到抑制。对 Ad7 株的全基因组进行测序并与 Ad3 进行比对。在所有结构蛋白中，Ad3 和 Ad7 之间的主要差异仅在纤维和六邻体中观察到，而六邻体之间的差异仅存在于四个高变区（HVR），HVR-1、-2、-5 和-7。因此，这些结果表明，Ad3 和 Ad7 特异性 NAb 主要针对体外和体内的六邻体蛋白。但是高滴度的 Ad3 纤维特异性 NAb 也可能在体内抑制 Ad3 免疫原性方面发挥重要作用。这些研究有助于更深入地了解 Ad 的免疫原性，并为新型 Ad 疫苗的设计提供参考。
