Zaremba S, Barzaga E, Zhu M, Soares N, Tsang K Y, Schlom J
Laboratory of Tumor Immunology and Biology, Division of Basic Sciences, National Cancer Institute, Bethesda, Maryland 20892-1750, USA.
Cancer Res. 1997 Oct 15;57(20):4570-7.
A vaccination strategy designed to enhance the immunogenicity of self-antigens that are overexpressed in tumor cells is to identify and slightly modify immunodominant epitopes that elicit T-cell responses. The resultant T cells, however, must maintain their ability to recognize the native configuration of the peptide-MHC interaction on the tumor cell target. We used a strategy to enhance the immunogenicity of a human CTL epitope directed against a human self-antigen, which involved the modification of individual amino acid residues predicted to interact with the T-cell receptor; this strategy, moreover, required no prior knowledge of these actual specific interactions. Single amino acid substitutions were introduced to the CAP1 peptide (YLSGANLNL), an immunogenic HLA-A2+-binding peptide derived from human carcinoembryonic antigen (CEA). In this study, four amino acid residues that were predicted to potentially interact with the T-cell receptor of CAP1-specific CTLs were systematically replaced. Analogues were tested for binding to HLA-A2 and for recognition by an established CTL line directed against CAP1. This line was obtained from peripheral blood mononuclear cells from an HLA-A2+ individual vaccinated with a vaccinia-CEA recombinant. An analogue peptide was identified that was capable of sensitizing CAP1-specific CTLs 10(2)-10(3) times more efficiently than the native CAP1 peptide. This enhanced recognition was shown not to be due to better binding to HLA-A2. Therefore, the analogue CAP1-6D (YLSGADLNL, Asn at position 6 replaced by Asp) meets the criteria of a CTL enhancer agonist peptide. Both the CAP1-6D and the native CAP1 peptide were compared for the ability to generate specific CTL lines in vitro from unimmunized apparently healthy HLA-A2+ donors. Whereas CAP1 failed to generate CTLs from normal peripheral blood mononuclear cells, the agonist peptide was able to generate CD8+ CTL lines that recognized both the agonist and the native CAP1 sequence. Most importantly, these CTLs were capable of lysing human tumor cells endogenously expressing CEA. The use of enhancer agonist CTL peptides may thus represent a new efficient direction for immunotherapy protocols.
一种旨在增强在肿瘤细胞中过度表达的自身抗原免疫原性的疫苗接种策略是识别并轻微修饰引发T细胞反应的免疫显性表位。然而，由此产生的T细胞必须保持其识别肿瘤细胞靶标上肽-MHC相互作用天然构象的能力。我们采用了一种策略来增强针对人类自身抗原的人CTL表位的免疫原性，该策略涉及对预测与T细胞受体相互作用的单个氨基酸残基进行修饰；此外，该策略不需要事先了解这些实际的特异性相互作用。将单个氨基酸取代引入到CAP1肽（YLSGANLNL）中，CAP1肽是一种源自人癌胚抗原（CEA）的具有免疫原性的HLA-A2+结合肽。在本研究中，系统地替换了预测可能与CAP1特异性CTL的T细胞受体相互作用的四个氨基酸残基。对类似物进行了与HLA-A2结合的测试以及由针对CAP1的既定CTL系进行识别的测试。该CTL系取自接种牛痘-CEA重组体的HLA-A2+个体的外周血单个核细胞。鉴定出一种类似物肽，其致敏CAP1特异性CTL的效率比天然CAP1肽高10²-10³倍。这种增强的识别作用并非由于与HLA-A2的结合更好。因此，类似物CAP1-6D（YLSGADLNL，第6位的Asn被Asp取代）符合CTL增强激动剂肽的标准。比较了CAP1-6D和天然CAP1肽在体外从未免疫的表面健康的HLA-A2+供体中产生特异性CTL系的能力。虽然CAP1未能从正常外周血单个核细胞中产生CTL，但激动剂肽能够产生识别激动剂和天然CAP1序列的CD8+CTL系。最重要的是，这些CTL能够裂解内源性表达CEA的人肿瘤细胞。因此，使用增强激动剂CTL肽可能代表免疫治疗方案的一个新的有效方向。
