高效多肽疫苗激活T细胞抗肿瘤的复合物结构研究及分子机制

T cell is very powerful at recognition of peptide antigens and killing of abnormal cells. Nowadays it is under intensive researches to use peptide vaccines to stimulate endogenous T cells to attack tumors. However, one of the major bottle necks is the weak stimulation of T cells. We focus on a set of peptide variants which are more effective in vaccines in a mouse colon tumor model than the wildtype peptide from the tumor antigen. These peptide vaccines will bind to the relevant MHC(Major Histocompatibility Complex) molecule, Ld, and be recognized by tumor specific TCR(T Cell Receptor). The data of the binding kinetic by the TCR indicats that the effective peptides variant could go through two phase recognition by the TCR to enhance the recognition. It was not reported before in the field of tumor peptide vaccine recognition and will greatly widen our knowledge. The complex structures of Ld/peptide also suggest that the conformational change of the peptide might be responsible for the two phase recognition by the TCR. We would like to keep forward to solve several complex structurs of the TCR binding to Ld/peptide to see how TCR recognizes the Ld/peptide vaccine.We also want to combine the study of mutations on the TCR to see how the important residues determine the effective TCR recognition and T cell stimulation. It is our final goal to understand the mechanism and principle of how tumor peptide vaccines can stimulate T cells effectively and to design effective peptide vaccines based on that.

T细胞有着很强的识别多肽抗原和杀伤肿瘤细胞的能力。当前通过多肽疫苗激活人体T细胞去攻击肿瘤细胞正受到广泛研究。然而其中的一个主要瓶颈在于激发的免疫强度不够。我们选取小鼠结肠癌模型中一组比肿瘤抗原母体多肽疫苗疗效高很多的模拟多肽疫苗作为研究对象。这些多肽疫苗先结合在MHC（主要组织相容性复合体）分子Ld上，然后被肿瘤特异性TCR（T细胞受体）识别。我们的初步试验结果提示，高效的模拟多肽疫苗能被TCR两步识别，从而加强了免疫识别和应答。这种多肽疫苗识别中的新现象，突破了原有的认识，大大深化了对多肽疫苗识别的理解。Ld/多肽疫苗结构数据也表明模拟多肽上存在的构象变化可能与此相关。我们将进一步开展多个TCR/多肽疫苗/Ld三元复合物的结构研究，同时也将分析TCR上关键残基突变对多肽疫苗识别的动力学影响和对T细胞激活的影响，提出模拟多肽疫苗优化的相关理论和法则并指导设计新的肿瘤多肽疫苗。

T细胞可以很强的识别抗原多肽并杀伤肿瘤细胞，然而未突变的自身肿瘤相关抗原所激活的免疫强度往往较弱，这通常归因于对自身TAA具有高亲和力的T细胞在胸腺中被删除，因此当前如何特异性操纵T细胞来有效杀伤肿瘤细胞已经成为国际免疫医学的研究热点。在基金资助下，我们已经成功地在小鼠中鉴定出高亲和力突变TAA，该突变TAA显示出与具有对未突变TAA低亲和力的大量异质CD8 T细胞的广泛交叉反应性。虽然用未突变的TAA接种疫苗不能保护小鼠免受TAA表达肿瘤的攻击，但突变的TAA几乎100%有效。对T细胞受体接合前后TAA-MHCI复合物的结构研究表明，TAA突变在TCR结合时促进肽中两个酪氨酸的构象改变，并将它们定位为TCR接触的主要部位。我们结果还表明，在低亲和力TAA中适当的突变可以导致其抗原效力的显著提高。在癌症患者中，相似的肿瘤通常表达相同的自身TAA，进而我们提出，有限数量的突变TAA可广泛用于与检查点阻断剂协同疫苗，以促进肿瘤免疫。这些工作将为模拟多肽疫苗的优化提供理论依据,指导设计新的肿瘤多肽疫苗，两篇文章已发表，另有两篇文章正在投稿中。