EXHIBIT 23.1 CONSENT OF INDEPENDENT CHARTERED ACCOUNTANTS As independent chartered accountants, we hereby consent to the incorporation by reference in this Registration Statement of our report dated 1 May 1998 included in Peptide Therapeutics Group plc's Registration Statement on Form F-4 and to all references to our Firm included in this Registration Statement. /s/ ARTHUR ANDERSEN Cambridge, England 11 May 1999