PROBLEM TO BE SOLVED: To provide novel peptides having very small molecular size in comparison with antibodies with excellent PD-L1 binding, novel peptides excellent in inhibiting interaction between PD-L1 and PD-1, and cancer treating agents comprising the peptides as effective components.SOLUTION: Disclosed is a peptide comprising all or part of an amino acid sequence selected from AELAALEAELAALEGX1X2X3X4X5GDLRFLLRX6LRVLSX7 (formula 3), AELAALEAELAALEGX8X9X10X11X12GX13LX14X15LLDDLX16X17 LX18X19 (formula 4) where each symbol in the formulae (3) and (4) is as defined in the specification, and an amino acid sequence of the formula (3) or (4) having deletion, substitution or addition of one or several amino acids.SELECTED DRAWING: Figure 1COPYRIGHT: (C)2020,JPO&INPIT【課題】抗体と比較して非常に分子サイズが小さく、ＰＤ－Ｌ１への結合性に優れた新規ペプチド、及びＰＤ－Ｌ１とＰＤ－１との相互作用の阻害効果に優れた新規ペプチドの提供。また、該ペプチドを有効成分とする、がんの治療剤の提供。【解決手段】アミノ酸配列：式（３）：ＡＥＬＡＡＬＥＡＥＬＡＡＬＥＧＸ１Ｘ２Ｘ３Ｘ４Ｘ５ＧＤＬＲＦＬＬＲＸ６ＬＲＶＬＳＸ７、若しくは式（４）：ＡＥＬＡＡＬＥＡＥＬＡＡＬＥＧＸ８Ｘ９Ｘ１０Ｘ１１Ｘ１２ＧＸ１３ＬＸ１４Ｘ１５ＬＬＤＤＬＸ１６Ｘ１７ＬＸ１８Ｘ１９（但し、式（３）及び（４）中の各記号は添付の明細書に記載の通りである。）、又は 式（３）若しくは式（４）のアミノ酸配列において１若しくは数個のアミノ酸が欠失、置換若しくは付加されたアミノ酸配列、の全てもしくは一部を有するペプチド。【選択図】図１
