Porcine circovirus type 2 (PCV2) is the causative agent of PCV-associated disease, which harms the swine industry worldwide. Open reading frame 2 of PCV2 encodes the principal immunogenic capsid (Cap) protein, which induces neutralizing antibodies and protective immunity. Cap has been developed as a subunit vaccine against PCV2 infection, although its use is hindered by low immunogenicity. Here, we hypothesized that the truncated diphtheria toxin DT390 might enhance the immunogenicity of Cap. To verify this hypothesis, we fused Cap with DT390, which was expressed using the unique diphtheria toxin-resistant Pichia pastoris expression system. We assessed the immunogenicity of DT390-Cap using BALB/c mice. DT390-Cap induced significantly higher Cap-specific and neutralizing antibodies than Cap alone with or without the ISA201 adjuvant. DT390-Cap with ISA201 adjuvant induced production of more Cap-specific antibodies and neutralizing antibodies than Ingelvac CircoFLEX (positive control). DT390-Cap induced slightly higher Th2-associated interleukin-4 production than Cap alone but did not affect Th1-associated interferon-γ production. The protection study demonstrated that DT390-Cap induced more effective protective immunity than Cap alone, when challenged with PCV2. The viral loads in the lungs, liver, and thymus in mice immunized using DT390-Cap were significantly lower than in those immunized with the corresponding Cap with or without the ISA201 adjuvant. Taken together, the engineered DT390 effectively enhanced the immunogenicity and protective immunity of Cap in mice. Thus, DT390-Cap is a promising novel vaccine candidate against PCV2 infection.

中文翻译：

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截断白喉毒素 DT390 增强小鼠猪圆环病毒 2 型衣壳抗原的体液免疫原性

猪圆环病毒 2 型 (PCV2) 是 PCV 相关疾病的病原体，它危害全球养猪业。PCV2 的开放阅读框 2 编码主要的免疫原性衣壳 (Cap) 蛋白，可诱导中和抗体和保护性免疫。Cap 已被开发为针对 PCV2 感染的亚单位疫苗，尽管它的使用受到低免疫原性的阻碍。在这里，我们假设截断的白喉毒素 DT390 可能会增强 Cap 的免疫原性。为了验证这一假设，我们将 Cap 与 DT390 融合，DT390 使用独特的白喉毒素抗性毕赤酵母表达表达系统。我们使用 BALB/c 小鼠评估了 DT390-Cap 的免疫原性。与单独使用或不使用 ISA201 佐剂的 Cap 相比，DT390-Cap 诱导显着更高的 Cap 特异性和中和抗体。与 Ingelvac CircoFLEX（阳性对照）相比，带有 ISA201 佐剂的 DT390-Cap 诱导产生更多的 Cap 特异性抗体和中和抗体。DT390-Cap 诱导的 Th2 相关白细胞介素 4 产生略高于 Cap 单独产生，但不影响 Th1 相关干扰素-γ生产。保护研究表明，当受到 PCV2 攻击时，DT390-Cap 比单独使用 Cap 诱导更有效的保护性免疫。使用 DT390-Cap 免疫的小鼠的肺、肝脏和胸腺中的病毒载量显着低于使用相应 Cap 免疫的小鼠（有或没有 ISA201 佐剂）。总之，工程化的 DT390 有效地增强了 Cap 在小鼠体内的免疫原性和保护性免疫。因此，DT390-Cap 是一种很有前途的针对 PCV2 感染的新型候选疫苗。