The invention relates to a humanized antibody derived from mouse monoclonal anti-CD4 antibody B-F5. Said antibody is able to activate CD25+CD4+ regulatory T cells and is useful for preparing immunosuppressive compositions.Cette invention a trait à un anticorps humanisé dérivé dun anticorps B-F5 anti-CD4. Cet anticorps, qui est capable dactiver des lymphocytes T régulateurs de CD25+CD4+, se révèle des plus utile en matière de préparation de compositions immunosuppressives.