The Antiviral Efficacy of HIV-Specific CD8⁺ T-Cells to a Conserved Epitope Is Heavily Dependent on the Infecting HIV-1 Isolate

A major challenge to developing a successful HIV vaccine is the vast diversity of viral sequences, yet it is generally assumed that an epitope conserved between different strains will be recognised by responding T-cells. We examined whether an invariant HLA-B8 restricted Nef90–97 epitope FL8 shared between five high titre viruses and eight recombinant vaccinia viruses expressing Nef from different viral isolates (clades A–H) could activate antiviral activity in FL8-specific cytotoxic T-lymphocytes (CTL). Surprisingly, despite epitope conservation, we found that CTL antiviral efficacy is dependent on the infecting viral isolate. Only 23% of Nef proteins, expressed by HIV-1 isolates or as recombinant vaccinia-Nef, were optimally recognised by CTL. Recognition of the HIV-1 isolates by CTL was independent of clade-grouping but correlated with virus-specific polymorphisms in the epitope flanking region, which altered immunoproteasomal cleavage resulting in enhanced or impaired epitope generation. The finding that the majority of virus isolates failed to present this conserved epitope highlights the importance of viral variance in CTL epitope flanking regions on the efficiency of antigen processing, which has been considerably underestimated previously. This has important implications for future vaccine design strategies since efficient presentation of conserved viral epitopes is necessary to promote enhanced anti-viral immune responses.开发高效HIV疫苗的核心挑战之一是病毒序列的高度多样性，尽管学界普遍认为，不同毒株间的保守表位可被应答性T细胞识别。本研究旨在探究：在5株高滴度病毒与8株表达不同病毒分离株（亚型A至H）Nef蛋白的重组痘苗病毒中，共享的、受人类白细胞抗原B8（HLA-B8）限制性呈递的恒定Nef90–97表位FL8，能否激活FL8特异性细胞毒性T淋巴细胞（CTL）的抗病毒活性。令人意外的是，尽管该表位具备保守性，我们发现CTL的抗病毒效力取决于感染的病毒分离株。仅23%的由HIV-1分离株或重组痘苗-Nef表达的Nef蛋白，可被CTL最优识别。CTL对HIV-1分离株的识别与亚型分组无关，但与表位侧翼区域的病毒特异性多态性密切相关——这类多态性会改变免疫蛋白酶体的切割效率，进而增强或削弱表位的产生。大多数病毒分离株无法呈递这一保守表位的发现，凸显了CTL表位侧翼区域的病毒变异对抗原加工效率的重要性，而这一点此前被学界严重低估。该研究结果对未来疫苗设计策略具有关键启示：若要诱导强效的抗病毒免疫应答，必须实现保守病毒表位的高效呈递。