Strategies to enhance the induction of high magnitude T cell responses through vaccination are urgently needed. Major histocompatibility complex (MHC) class II–associated invariant chain (Ii) plays a critical role in antigen presentation, forming MHC class II peptide complexes for the generation of CD4⁺ T cell responses. Preclinical studies evaluating the fusion of Ii to antigens encoded in vector delivery systems have shown that this strategy may enhance T cell immune responses to the encoded antigen. We now assess this strategy in humans, using chimpanzee adenovirus 3 and modified vaccinia Ankara vectors encoding human Ii fused to the nonstructural (NS) antigens of hepatitis C virus (HCV) in a heterologous prime/boost regimen. Vaccination was well tolerated and enhanced the peak magnitude, breadth, and proliferative capacity of anti-HCV T cell responses compared to non-Ii vaccines in humans. Very high frequencies of HCV-specific T cells were elicited in humans. Polyfunctional HCV-specific CD8⁺ and CD4⁺ responses were induced with up to 30% of CD3⁺CD8⁺ cells targeting single HCV epitopes; these were mostly effector memory cells with a high proportion expressing T cell activation and cytolytic markers. No volunteers developed anti-Ii T cell or antibody responses. Using a mouse model and in vitro experiments, we show that Ii fused to NS increases HCV immune responses through enhanced ubiquitination and proteasomal degradation. This strategy could be used to develop more potent HCV vaccines that may contribute to the HCV elimination targets and paves the way for developing class II Ii vaccines against cancer and other infections.

迫切需要通过疫苗接种来增强诱导高强度 T 细胞反应的策略。主要组织相容性复合物 (MHC) II 类相关不变链 (Ii) 在抗原呈递中起关键作用，形成 MHC II 类肽复合物以产生 CD4 ⁺T 细胞反应。评估 Ii 与载体递送系统中编码的抗原融合的临床前研究表明，这种策略可以增强 T 细胞对编码抗原的免疫反应。我们现在在人类中评估这种策略，使用黑猩猩腺病毒 3 和改良的牛痘安卡拉载体编码人类 Ii，在异源初免/加强方案中融合丙型肝炎病毒 (HCV) 的非结构 (NS) 抗原。与人类非 Ii 疫苗相比，疫苗接种具有良好的耐受性，并增强了抗 HCV T 细胞反应的峰值幅度、广度和增殖能力。在人类中引发了非常高频率的 HCV 特异性 T 细胞。高达 30% 的 CD3 ⁺ CD8可诱导多功能 HCV 特异性 CD8 ⁺和 CD4 ^+反应+靶向单个 HCV 表位的细胞；这些主要是效应记忆细胞，具有高比例表达 T 细胞活化和细胞溶解标记物。没有志愿者产生抗-Ii T 细胞或抗体反应。使用小鼠模型和体外实验，我们表明融合到 NS 的 Ii 通过增强泛素化和蛋白酶体降解来增加 HCV 免疫反应。该策略可用于开发更有效的 HCV 疫苗，这些疫苗可能有助于实现 HCV 消除目标，并为开发针对癌症和其他感染的 II Ii 类疫苗铺平道路。