Lin Leon C W, Croft Sarah N, Croft Nathan P, Wong Yik Chun, Smith Stewart A, Tang Swee-Seong, Purcell Anthony W, Tscharke David C
John Curtin School of Medical Research, The Australian National University, Canberra, ACT, Australia.
Infection and Immunity Program and Department of Biochemistry and Molecular Biology, Biomedicine Discovery Institute, Monash University, Clayton, VIC, Australia.
J Virol. 2021 Apr 26;95(10). doi: 10.1128/JVI.00186-21. Epub 2021 Mar 10.
Vaccinia virus (VACV) was the vaccine used to eradicate smallpox and is being repurposed as a vaccine vector. CD8 T cells are key anti-viral mediators, but require priming to become effector or memory cells. Priming requires an interaction with dendritic cells that are either infected (direct priming), or that have acquired virus proteins but remain uninfected (cross priming). To investigate CD8 T cell priming pathways for VACV, we engineered the virus to express CPXV12 and CPXV203, two inhibitors of antigen presentation encoded by cowpox virus. These intracellular proteins would be expected to block direct but not cross priming. The inhibitors had diverse impacts on the size of anti-VACV CD8 T cell responses across epitopes and by different infection routes in mice, superficially suggesting variable use of direct and cross priming. However, when we then tested a form of antigen that requires direct priming, we found surprisingly that CD8 T cell responses were not diminished by co-expression with CPXV12 and CPXV203. We then directly quantified the impact of CPXV12 and CPXV203 on viral antigen presentation using mass spectrometry, which revealed strong, but incomplete inhibition of antigen presentation by the CPXV proteins. Therefore, direct priming of CD8 T cells by poxviruses is robust enough to withstand highly potent viral inhibitors of antigen presentation. This is a reminder of the limits of viral immune evasion and shows that viral inhibitors of antigen presentation cannot be assumed to dissect cleanly direct and cross priming of anti-viral CD8 T cells.CD8 T cells are key to anti-viral immunity, so it is important to understand how they are activated. Many viruses have proteins that protect infected cells from T cell attack by interfering with the process that allows virus infection to be recognised by CD8 T cells. It is thought that these proteins would also stop infected cells from activating T cells in the first place. However, we show here that this is not the case for two very powerful inhibitory proteins from cowpox virus. This demonstrates the flexibility and robustness of immune processes that turn on the immune responses required to fight infection.
牛痘病毒（VACV）曾是用于根除天花的疫苗，现正被重新用作疫苗载体。CD8 T细胞是关键的抗病毒介质，但需要经过致敏才能成为效应细胞或记忆细胞。致敏需要与树突状细胞相互作用，这些树突状细胞要么被感染（直接致敏），要么获取了病毒蛋白但仍未被感染（交叉致敏）。为了研究VACV的CD8 T细胞致敏途径，我们对该病毒进行改造，使其表达CPXV12和CPXV203，这是两种由牛痘病毒编码的抗原呈递抑制剂。预计这些细胞内蛋白会阻断直接致敏而非交叉致敏。这些抑制剂对小鼠体内跨表位以及通过不同感染途径产生的抗VACV CD8 T细胞反应的大小有不同影响，表面上表明直接致敏和交叉致敏的使用存在差异。然而，当我们随后测试一种需要直接致敏的抗原形式时，令人惊讶地发现，与CPXV12和CPXV203共表达时，CD8 T细胞反应并未减弱。然后，我们使用质谱法直接量化了CPXV12和CPXV203对病毒抗原呈递的影响，结果显示CPXV蛋白对抗原呈递有强烈但不完全的抑制作用。因此，痘病毒对CD8 T细胞的直接致敏足够强大，能够抵御抗原呈递的高效病毒抑制剂。这提醒人们注意病毒免疫逃逸的局限性，并表明不能假定抗原呈递的病毒抑制剂能清晰地区分抗病毒CD8 T细胞的直接致敏和交叉致敏。CD8 T细胞是抗病毒免疫的关键，因此了解它们如何被激活很重要。许多病毒都有蛋白质，通过干扰使病毒感染被CD8 T细胞识别的过程，来保护受感染细胞免受T细胞攻击。人们认为这些蛋白质也会首先阻止受感染细胞激活T细胞。然而，我们在此表明，来自牛痘病毒的两种非常强大的抑制性蛋白并非如此。这证明了开启对抗感染所需免疫反应的免疫过程具有灵活性和稳健性。
