Licensing Agreement

Stem Cell Sciences plc
03 November 2005


FOR IMMEDIATE RELEASE


            Stem Cell Sciences Grants Lexicon Genetics
                Exclusive License to IRES technology

The Woodlands, Texas and Edinburgh, Scotland, November 3, 2005 - Lexicon
Genetics Incorporated (Nasdaq: LEXG) and Stem Cell Sciences plc (AIM: STEM)
announced today a significant expansion related to Lexicon's rights to SCS's
proprietary Internal Ribosome Entry Site ("IRES") technology for genetically
modified mice. IRES technology is commonly used to enhance the accuracy of gene
expression in genetically altered mice and cultured stem cells.

As part of this expansion, SCS has granted to Lexicon an exclusive license to
the IRES technology, subject to non-exclusive licenses previously granted by 
SCS. The term of this exclusive license extends through the life of the IRES
technology patents and provides Lexicon with the right to grant sub-licenses in
the United States and Europe. Lexicon obtained a non-exclusive research license
to the IRES technology in 2004 and has used the IRES technology in conjunction
with its patented gene targeting technology to effectively translate reporter
genes in genetically altered mice and mouse embryonic stem cells.

In consideration for this exclusive license, Lexicon will provide SCS with an
upfront payment and share with SCS future revenues generated by sublicenses to
the IRES technology. In addition, Lexicon has granted SCS certain non-exclusive
rights under patents controlled by Lexicon covering its proprietary gene
targeting technology for use in stem cell and progenitor cell lines.

"Given the complementary nature of our technologies and Lexicon's success in
licensing its proprietary gene targeting technology to biotechnology and
pharmaceutical companies, we believe Lexicon is the ideal partner to develop the
full commercial value of our IRES patent position with respect to mouse models,"
said Peter Mountford, Ph.D., president and chief executive officer of SCS.
"Importantly, this agreement also enables SCS to expand the range of products it
can offer to pharmaceutical company customers from its stem cell-based drug
discovery platform."

"We have used IRES technology to enhance our ability to detect the expression of
genes within tissues and individual cells, thereby increasing the power of our
in vivo models for gene function discovery," said Brian Zambrowicz, Ph.D.,
executive vice president of research at Lexicon. "As a result of our experience
with the technology, we recognized the value of adding this exclusive license to
our already substantial patent estate in the area of gene knockout technology."

                                   
About Stem Cell Sciences

Stem Cell Sciences has been a leading company in the stem cell research arena
since 1994. It is focused on technologies to grow, differentiate, genetically
modify and purify stem cells and stem cell derived cell products. The SCS group
has its headquarters in Edinburgh, United Kingdom and has operations in
Melbourne, Australia and Kobe, Japan. It is expanding operations in 2006 to
Cambridge, U.K. and the United States. The new U.K. site in Cambridge will focus
on automation of cell-based drug discovery assays for the pharmaceutical
industry. The U.S. expansion will initially be based on licensing opportunities
of key SCS technologies, including Stem Cell Selection and novel Neural Stem
cells reported in August this year. Stem Cell Sciences plc is listed on the
London Stock Exchange Alternative Investment Market under the code STEM.

About Lexicon Genetics

Lexicon Genetics is a biopharmaceutical company focused on the discovery and
development of breakthrough treatments for human disease. Lexicon is
systematically discovering the physiological and behavioral functions of genes
to identify potential points of therapeutic intervention, or drug targets.
Lexicon makes these discoveries using its proprietary gene knockout technology
to model the physiological effects that could be expected from prospective drugs
directed against novel targets. The Company has advanced knockout-validated
targets into drug discovery programs in six therapeutic areas: diabetes and
obesity, cardiovascular disease, psychiatric and neurological disorders, cancer,
immune system disorders and ophthalmic disease. Lexicon is working both
independently and through strategic collaborations and alliances to accelerate
the development and commercialization of its discoveries. Additional information
about Lexicon is available through its corporate website,
www.lexicon-genetics.com.

Lexicon Genetics Safe Harbor Statement

This press release contains "forward-looking statements," including statements
about Lexicon's growth and future operating results, discovery and development
of products, strategic alliances and intellectual property, as well as other
matters that are not historical facts or information. These forward-looking
statements are based on management's current assumptions and expectations and
involve risks, uncertainties and other important factors, specifically including
those relating to Lexicon's ability to successfully conduct preclinical
development of its drug candidates and advance such candidates into clinical
development, achieve its operational objectives, obtain patent protection for
its discoveries and establish strategic alliances, as well as those relating to
manufacturing, the regulatory process, intellectual property rights, and the
therapeutic or commercial value of its drug candidates, that may cause Lexicon's
actual results to be materially different from any future results expressed or
implied by such forward-looking statements. Information identifying such
important factors is contained under "Factors Affecting Forward-Looking
Statements" and "Business - Risk Factors" in Lexicon's annual report on Form
10-K for the year ended December 31, 2004, as filed with the Securities and
Exchange Commission. Lexicon undertakes no obligation to update or revise any
such forward-looking statements, whether as a result of new information, future
events or otherwise.

                                     # # #

Contacts:

Stem Cell Sciences: 
Peter Mountford 
President and Chief Executive Officer
[phone]
[e-mail]

Weber Shandwick / Square Mile:
Yvonne Alexander
European PR
[phone]
[e-mail]

Lexicon Genetics: 
Bobbie Faulkner  
Manager, Investor Relations 
[phone]   
[e-mail]            


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