The present invention relates to a polypeptide which comprises or consists of - a first sequence consisting of at least 8 contiguous amino acid residues selected from within the sequence extending from amino acid residues 55 to 67 of the PD-L1 protein, and at most 30 contiguous amino acid residues selected from within the complete sequence of the PD-L1 protein； and/or - a second sequence consisting of at least 8 contiguous amino acid residues selected from within the sequence extending from amino acid residues 85 to 101 of the PD-L1 protein, and at most 30 contiguous amino acid residues selected from within the complete sequence of the PD-L1 protein； and/or - a third sequence consisting of at least 8 contiguous amino acid residues selected from within the sequence extending from amino acid residues 111 to 127 of the PD-L1 protein, and at most 30 contiguous amino acid residues selected from within the complete sequence of the PD-L1 protein； and/or - a fourth sequence consisting of at least 8 contiguous amino acid residues selected from within the sequence extending from amino acid residues 138 to 156 of the PD-L1 protein, and at most 30 contiguous amino acid residues selected from within the complete sequence of the PD-L1 protein； and/or - a fifth sequence consisting of at least 8 contiguous amino acid residues selected from within the sequence extending from amino acid residues 208 to 223 of the PD-L1 protein, and at most 30 contiguous amino acid residues selected from within the complete sequence of the PD-L1 protein.La présente invention concerne un polypeptide comprenant, ou constitué - une première séquence constituée d'au moins 8 résidus d'acides aminés contigus choisis au sein de la séquence s'étendant des résidus d'acides aminés 55 à 67 de la protéine PD-L1 et d'au plus 30 résidus d'acides aminés contigus choisis au sein de la séquence complète de la protéine PD-L1； et/ou - une deuxième séquence constituée d'au moins 8 résidus d'acides aminés contigus choisis
