The present invention relates to a polypeptide comprising or consisting of: - a first sequence consisting of at least 8 contiguous amino acid residues selected from the sequence extending from amino acid residues 55 to 67 of the PD protein L1 and at most 30 contiguous amino acid residues selected from the complete sequence of the PD-L1 protein； and / or a second sequence consisting of at least 8 contiguous amino acid residues selected from the sequence extending from amino acid residues 85 to 101 of the PD-L1 protein and at most 30 residues. contiguous amino acids selected from the complete sequence of the PD-L1 protein； and / or - a third sequence consisting of at least 8 contiguous amino acid residues selected within the sequence extending from amino acid residues 111 to 127 of the PD-L1 protein and at most 30 residues contiguous amino acids selected from the complete sequence of the PD-L1 protein； and / or - a fourth sequence consisting of at least 8 contiguous amino acid residues selected within the sequence extending from amino acid residues 138 to 156 of the PD-L1 protein and at most 30 residues contiguous amino acids selected from the complete sequence of the PD-L1 protein； and / or - a fifth sequence consisting of at least 8 contiguous amino acid residues selected from the sequence extending from amino acid residues 208 to 223 of the PD-L1 protein and at most 30 residues of contiguous amino acids selected from the complete sequence of the PD-L1 protein. La présente invention concerne un polypeptide comprenant, ou constitué de : - 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 au sein de la séquence s'étendant de
