A chimeric polypeptide that is capable of being secreted in association with exosomes, characterized in that it comprises or consists of the following domains: (i) a peptide or polypeptide of interest; (ii) an infra-membrane targeting domain, enabling said chimeric polypeptide to be anchored to the membrane of an exosome via one or more molecule(s) for anchoring and/or for interactions between said infra-membrane targeting domain and said membrane but without either being inserted into or passing through the lipid bilayer of the membrane of that exosome, the sequence of said infra-membrane targeting domain being the sequence of a fragment of a protein of the Src family and comprising or consisting of the sequence M-G-S-S-K-S-K-P-K-D-P-S-Q-R-R-R or of the sequence M-G-S-S-K-S-K-P-K-D-P-S-Q-R-R-R-K-S-R-G-P-G-G; and (iii) a mutated derivative of the cytoplasmic domain of a membrane protein, said mutated derivative being defined by substitution, deletion and/or insertion of one or more residue(s) in the sequence of said CD domain, said CD domain being the CD domain of SEQ ID NO. 6 which is the CD domain of the transmembrane protein of the bovine leukemia virus, said mutated derivative having conserved the capacity of said CD domain for addressing said chimeric polypeptide to exosomes and/or to one of the cellular compartment(s) involved in exosome formation, said mutated derivative of the CD domain comprising at least one motif YxxL or DYxxL, and a motif PxxP, in which x represents any residue and Y, L, D and P respectively represent a tyrosine, leucine, aspartic acid and proline residue, the sequence of said mutated derivative having at least 80% identity with the sequence of SEQ ID NO. 8 and differing from the sequence of SEQ ID NO. 6 in at least one of the following characteristics (a) - (b): (a) said mutated derivative is deprived of the sequence KCLTSRLLKLLRQ which is contained in the sequence of SEQ ID NO. 6, (b) in said mutated derivative, the cysteine residue of the sequence PCP which is contained in SEQ ID NO. 6 is deleted or is replaced by the alanine residue; it being understood that said domains (i) and (ii) and (iii) are cytosolic or nuclear domains and that said chimeric polypeptide is deprived of a signal peptide for importation into the endoplasmic reticulum, and in which the domains (i) to (iii) are positioned in succession in the following order, from the N-terminal end towards the C-terminal end in the polypeptide: (ii) - (i) - (iii), or (ii) - (iii) - (i). (i) a peptide or polypeptide of interest; (ii) an infra-membrane targeting domain, enabling said chimeric polypeptide to be anchored to the membrane of an exosome via one or more molecule(s) for anchoring and/or for interactions between said infra-membrane targeting domain and said membrane but without either being inserted into or passing through the lipid bilayer of the membrane of that exosome, the sequence of said infra-membrane targeting domain being the sequence of a fragment of a protein of the Src family and comprising or consisting of the sequence M-G-S-S-K-S-K-P-K-D-P-S-Q-R-R-R or of the sequence M-G-S-S-K-S-K-P-K-D-P-S-Q-R-R-R-K-S-R-G-P-G-G; and (iii) a mutated derivative of the cytoplasmic domain of a membrane protein, said mutated derivative being defined by substitution, deletion and/or insertion of one or more residue(s) in the sequence of said CD domain, said CD domain being the CD domain of SEQ ID NO. 6 which is the CD domain of the transmembrane protein of the bovine leukemia virus, said mutated derivative having conserved the capacity of said CD domain for addressing said chimeric polypeptide to exosomes and/or to one of the cellular compartment(s) involved in exosome formation, said mutated derivative of the CD domain comprising at least one motif YxxL or DYxxL, and a motif PxxP, in which x represents any residue and Y, L, D and P respectively represent a tyrosine, leucine, aspartic acid and proline residue, the sequence of said mutated derivative having at least 80% identity with the sequence of SEQ ID NO. 8 and differing from the sequence of SEQ ID NO. 6 in at least one of the following characteristics (a) - (b): (a) said mutated derivative is deprived of the sequence KCLTSRLLKLLRQ which is contained in the sequence of SEQ ID NO. 6, (b) in said mutated derivative, the cysteine residue of the sequence PCP which is contained in SEQ ID NO. 6 is deleted or is replaced by the alanine residue; (a) said mutated derivative is deprived of the sequence KCLTSRLLKLLRQ which is contained in the sequence of SEQ ID NO. 6, (b) in said mutated derivative, the cysteine residue of the sequence PCP which is contained in SEQ ID NO. 6 is deleted or is replaced by the alanine residue;