Re Agreement

Cambridge Antibody Tech Group PLC
21 May 2001

01/CAT/09

FOR IMMEDIATE RELEASE

07.00 BST, 02.00 EST Monday 21 May 2001
For Further Information Contact:

Cambridge Antibody Technology               Square Mile Communications (Europe)

Tel: [phone]                   Tel: [phone]

David Chiswell, CEO                         Kevin Smith

John Aston, Finance Director                Graham Herring

Rowena Gardner, Head of Corporate
Communications
Immunex Corporation                         BMC Communications/The Trout Group
                                            (USA)
Kris Greco (media)
                                            Tel: [phone]
Tel: [phone]
                                            Brad Miles, ext 17 (media)
Mark Leahy (investors)
                                            Brandon Lewis, ext.15 (investors)
Tel: [phone]



CAMBRIDGE ANTIBODY TECHNOLOGY AND IMMUNEX CORPORATION ENTER INTO NEW ALLIANCE
                 FOR HUMAN MONOCLONAL ANTIBODY CO-DEVELOPMENT

               Collaboration will focus on development of novel

                    antibody-based anti-inflammatory drugs


Melbourn, UK and Seattle, WA... Cambridge Antibody Technology (LSE: CAT) and
Immunex Corporation (Nasdaq: IMNX) announce a broad product development
collaboration committed to the joint discovery, development, marketing and
sale of human antibody-based therapeutics for autoimmune and inflammatory
disorders.

Under the terms of the agreement, the two companies will share equal
responsibility for all research and development, and split equally any
potential profits generated by product sales. Immunex will contribute two
undisclosed proprietary targets, scientific and development expertise to the
partnership, while CAT will contribute its proprietary human antibody phage
display technology and high throughput screening capabilities to identify
human antibodies. CAT will have primary responsibility for the discovery and
optimisation of human antibodies specific to the Immunex targets. Immunex will
be primarily responsible for additional pre-clinical evaluation, clinical
trials and product commercialisation.

Dr. David Chiswell, CEO of CAT, said 'We are extremely pleased to be expanding
our relationship with Immunex for the custom design and development of human
antibody drugs. It is a further demonstration of CAT's commitment to share in
the risks and rewards of antibody product development and to build a drug
pipeline serving areas of significant unmet medical need.'

Douglas Williams, PhD, Immunex Executive Vice President and Chief Technology
Officer, said 'This new collaboration with CAT underscores our commitment to
rapidly develop antibody based therapeutics to our validated proprietary
targets. This agreement allows us to work with the skilled scientists and
systems at CAT and to accelerate the development timelines on two important
drug targets.'

In November 2000, Immunex and CAT announced that Immunex received a licence
from CAT to utilise its antibody library for reagent generation and target
validation. Under that agreement, Immunex will also receive up to eight
exclusive product options derived from its in house use of the CAT library and
CAT would potentially receive clinical milestones and royalty payments on
sales.




                                    -ENDS-




Notes to Editors:

Cambridge Antibody Technology (CAT)

CAT is a UK biotechnology company using its proprietary technologies in human
monoclonal antibodies for drug discovery and drug development. Based in
Melbourn, 10 miles south of Cambridge, England, CAT currently employs around
220 people.

CAT is listed on the London Stock Exchange, having raised £41m in its IPO in
March 1997. A secondary offering in March 2000 raised £93m.

CAT has a world-leading platform technology for rapidly isolating fully human
monoclonal antibodies using phage display systems. CAT has an extensive phage
antibody library, currently incorporating around 100 billion distinct
antibodies. This library forms the basis for the company's strategy to develop
a portfolio of clinical development programmes and for discovering new drug
leads using functional genomics. Four human therapeutic antibodies developed
by CAT are at various stages of clinical trials.

CAT has a number of licence and collaborative agreements in place with
pharmaceutical and biotechnology companies including: Eli Lilly, Pfizer, BASF
Pharma (Abbott), Genentech, ICOS, Genetics Institute, Wyeth-Ayerst, Human
Genome Sciences, AstraZeneca, Pharmacia, Oxford GlycoSciences, Genzyme, Zyomyx
and Elan.

Immunex Corporation

Immunex Corporation is a leading biopharmaceutical company dedicated to
improving lives through immune system science innovations.

This press release contains statements about Cambridge Antibody Technology
Group plc (CAT) that are forward looking statements. All statements other than
statements of historical facts included in this press release may be forward
looking statements.

These forward looking statements are based on numerous assumptions regarding
CAT's present and future business strategies and the environment in which CAT
will operate in the future. Certain factors that could cause CAT's actual
results, performance or achievements to differ materially from those in the
forward looking statements include: market conditions, CAT's ability to enter
into and maintain collaborative arrangements, success of product candidates in
clinical trials, regulatory developments and competition.