The invention relates to an isolated polypeptide comprising or consisting of an amino acid sequence according to SEQ ID NO 1 (AS 136-154) (EEAEKAKEAAEKALNEAFE) or an amino acid sequence with a sequence identity of least 70 %, preferably of at least 80 %, more preferably of at least 90 % to SEQ ID NO 1, wherein the polypeptide is no longer than 200, preferably no longer than 170 amino acids. The invention relates to a nucleic acid encoding for said polypeptide, a gene therapy vector comprising said nucleic acid and genetically modified cells expressing said polypeptide. Furthermore, the invention relates to the medical use of said polypeptide, said nucleic acid, said gene therapy vector and/or said cell for the treatment of a disease associated with pathogenic long-lived plasma cells.