Chen Z W, Shen L, Miller M D, Ghim S H, Hughes A L, Letvin N L
Harvard Medical School, New England Regional Primate Research Center, Southborough, MA 01772.
J Immunol. 1992 Dec 15;149(12):4060-6.
Studies to date assessing HIV escape from CTL in vivo have yielded conflicting results. Previous studies have demonstrated that simian immunodeficiency virus of macaques (SIVmac)-infected rhesus monkeys expressing the MHC class I allele Mamu-A01 reproducibly develop a gag-specific CTL response limited to a 9-amino acid epitope of the SIVmac gag protein (residues 182-190 within peptide 11C). To determine whether CTL have a role in selecting for AIDS virus mutants, we examined mutations in SIVmac proviral DNA encoding this gag CTL epitope in PBL of infected rhesus monkeys. Three Mamu-A01+ rhesus monkeys were infected with SIVmac and assessed for gag- and peptide 11C-specific CTL responses. This specific CTL response was maintained in two monkeys, but lost in the third animal 2 yr after infection. The generation of proviral gag mutations was then determined by sequencing 500-bp proviral fragments amplified from fresh PBL obtained from the monkeys more than 2.5 yr after infection. Although numerous point mutations were characterized in 131 polymerase chain reaction-generated clones of SIVmac gag, only four mutations within the gag CTL epitope-coding region of the genome were identified. Comparison of synonymous and nonsynonymous nucleotide substitutions in the regions encoding peptide 11C (p11C) and the flanking gag protein indicated a lack of selective pressure for viral mutations in the CTL epitope coding region. Interestingly, a predominant gag mutant encoding a single amino acid change in p11C was found in a monkey which lost its CTL activity. However, even in this setting there was no evidence for selection of mutations in the CTL epitope coding region when compared with the flanking region. Furthermore, synthetic peptides corresponding to all naturally occurring variants in the gag epitope-coding region were recognized by cloned and bulk cultured effector cells of the infected monkeys with persistent CTL. These results indicate that SIVmac gag- and p11C-specific CTL do not select for mutations in the immunodominant epitope-coding region and that the naturally occurring mutants do not appear to escape CTL recognition.
迄今为止，评估体内HIV从细胞毒性T淋巴细胞（CTL）逃逸的研究得出了相互矛盾的结果。先前的研究表明，感染了猕猴猿免疫缺陷病毒（SIVmac）且表达MHC I类等位基因Mamu - A01的恒河猴，可重复性地产生针对SIVmac gag蛋白一个9个氨基酸表位（肽段11C内的182 - 190位氨基酸）的gag特异性CTL反应。为了确定CTL在选择艾滋病病毒突变体方面是否起作用，我们检测了感染的恒河猴外周血淋巴细胞（PBL）中编码该gag CTL表位的SIVmac前病毒DNA的突变情况。三只Mamu - A01 + 恒河猴感染了SIVmac，并评估其针对gag和肽段11C的特异性CTL反应。这种特异性CTL反应在两只猴子中得以维持，但在第三只动物感染2年后丧失。然后通过对从感染超过2.5年的猴子新鲜PBL中扩增的500 bp前病毒片段进行测序，确定前病毒gag突变的产生情况。虽然在131个通过聚合酶链反应产生的SIVmac gag克隆中鉴定出了许多点突变，但在基因组的gag CTL表位编码区域仅发现了四个突变。对编码肽段11C（p11C）及其侧翼gag蛋白区域的同义核苷酸替换和非同义核苷酸替换的比较表明，CTL表位编码区域的病毒突变缺乏选择压力。有趣的是，在一只丧失CTL活性的猴子中发现了一种主要的gag突变体，其在p11C中编码单个氨基酸变化。然而，即便在这种情况下，与侧翼区域相比，也没有证据表明在CTL表位编码区域选择了突变。此外，来自具有持续CTL的感染猴子的克隆及大量培养效应细胞可识别与gag表位编码区域中所有天然存在变体相对应的合成肽。这些结果表明，SIVmac gag和p11C特异性CTL不会选择免疫显性表位编码区域中的突变，并且天然存在的突变体似乎不会逃避CTL识别。
