As we previously observed that the autoadjuvant property is controlled by a determinant located within the core- and cysteine-rich regions of the protein, we synthesized a Tat peptide (pTat) overlapping these two regions and investigated whether it can provide immunogenic properties to two peptides originating from diphtheria toxin (pDT) and from toxin alpha (pT). These two peptides that both contain a helper T-cell epitope but are nonetheless non-immunogenic in BALB/c mice were chemically synthesized in a free form or covalently associated with pTat. Then, to assess the ability to raise a humoral immune response, six groups of BALB/c mice were injected twice at two weeks interval with pTatpT, pTatpDT, pT, pDT, pT + pTat and pT + pTat, respectively.