The invention relates to peptides of general formula (I), wherein X is absent or X is present and is X 14 or X 14 -X 15 . wherein X 14 and X 15 , independently from one another, represent an amino acid； their functional variants and fragments, and their pharmaceutically acceptable salts, having the capacity to bind to scurfin and inhibit its biological activity, therefore they regulate or block the activity of regulatory T (Treg) lymphocytes. They are applicable in the treatment of infectious and neoplastic diseases. Arg-Asp-Phe-Gln-Ser-Phe-Arg-Lys-Met-Trp-Pro-Phe-Phe-X (I)
