Press Release

Cellectis announces the presentation of results demonstrating the correction of an XP mutation in a patient's cell line by homologous gene targeting at the first French-German meeting on DNA repair, damage signaling and carcinogenesis in Toulouse.

Biocitech, France - September the 15^th, 2007 - Cellectis SA, the rational genome engineering company specializing in the production of meganuclease recombination systems and in meganuclease engineering, today announced the presentation of results demonstrating the correction of a XP mutation in patient's cell line by homologous gene targeting at the first French-German meeting on DNA repair, damage signaling and carcinogenesis in Toulouse.

The laboratory of Dr. Alain Sarasin (CNRS-FRE2939), located at the Institut Gustave Roussy (IGR) in Villejuif (France), succeeded in inducing the correction of a mutation in a cell line isolated from a xeroderma pigmentosum (XP) patient. XP is a severe genetic disease showing a very high predisposition to skin cancers caused by severe burns when patients are exposed to UV light. Meganuclease-induced gene correction of inherited monogenic diseases appears today as an alternative to classical gene therapy approaches, often based on viral vector-mediated gene transfer. Recently, Cellectis transferred two meganucleases cleaving sequences on the XPC gene to the laboratory of Dr. Alain Sarasin, in order to assay their therapeutic potential. CNRS and IGR researchers from this team used these meganucleases in gene correction experiments and could identify bona fide gene correction events after treatment of patient's cells.

These data have to be considered as preliminary results as the efficacy and specificity of the meganuclease have both to be further investigated. Nevertheless, molecular characterization gave sufficient proof that the gene correction occurred by an homologous gene targeting process, which is usually considered as an extremely rare process in somatic human cells. Thus, these results are an important milestone toward a therapeutic use of homologous gene targeting for inherited monogenic diseases. Further studies will be conducted, by the same laboratory, the ultimate goal being the autograft (graft of patient's own cells) of corrected cells to XP patients.

Dr. Alain Sarasin, CNRS Research Director, declared: "Relying on a combination of recent advances in genome engineering and cellular therapy, this preliminary successful result provides us real hope for an approach of XP gene correction by exact and specific reversion of the causal mutation. This work was supported by the CNRS, IGR, the Agence Nationale de la Recherche and the Association Française contre les Myopathies".

Dr. André Choulika, Cellectis' CEO, declared: "This is the first milestone of a genome surgery approach that could pave the route for a number of therapeutic applications. I want to acknowledge the exceptional commitment of Alain Sarasin and his team in this work. I would also like to thank the National Agency for Research, which supports such program".

Cellectis will keep investing in proving its Meganuclease Recombination System (MRS) being active and safe over the next few months with the ambition to prepare re-implantation of corrected cells to patients. In parallel, Cellectis will keep building up its therapeutic MRS portfolio addressing unmet medical needs including inborn immunodeficiency, hematological genetic diseases such as sickle cell anemia or hemophilia, viral infections such hepatitis B virus infection and organ or cell transplant.

Over the last decade, meganucleases have emerged as powerful tools for efficient and precise genome engineering. This technology is the world standard in gene targeting and is used to precisely substitute, delete, add or correct genetic sequences at a chosen location in any given genome. Meganuclease Recombination Systems (MRSs) address a wide range of applications spanning the fields of agricultural biotechnology, protein production and genomic research tools. However, meganucleases also provide new hope for novel therapeutic agents for curing monogenic inherited diseases and viral infections. The meganuclease technology as such and some of the principle uses of homologous recombination were discovered at Institut Pasteur in Paris, which then granted Cellectis worldwide exclusive rights in 2000. Since then, Cellectis has expanded the potential of this technology by developing meganucleases with tailored specificities, which are thus able to target selected genes in any given organism.

About Cellectis

Cellectis SA (www.cellectis.com) is a world-leading company in genome engineering and genome surgery. The company is focused on developing and producing custom meganucleases for in vivo DNA surgery and also provides new tools for rational reverse genetics and targeted recombination. Cellectis' products induce unique, site-directed, double-strand DNA breaks in a living cell and can be used in a wide range of biotechnological and therapeutic applications. To date, Cellectis has entered into more than 45 deals on its genome engineering technologies with major players in the pharma, biotech and agrobiotech industries. Cellectis is listed on the Euronext Alternext market (ticker code: ALCLS). For more information on Cellectis, visit our web site: www.cellectis.com.

About Cellectis' technology

A meganuclease is a (protein) molecule that cuts DNA at a highly precise site on a chromosome. Once DNA is broken, it has to be repaired by the cell's natural endogenous maintenance systems. By providing a specifically engineered DNA molecule (called a repair matrix) which will be used as a template to repair the break, one can channel the repair pathway into an insertion, deletion or correction process. Thus, meganucleases can be used to trigger precise modification of specific genes in a variety of cells and organisms. By combining the meganuclease's capacity to cut DNA and DNA's ability to undergo repair, Cellectis is creating new generations of products for a wide spectrum of applications - including human health, since many genetic diseases result from a single mutation in a specific gene. Meganucleases can specifically target this same gene. In parallel, a DNA repair matrix (prepared by Cellectis and including a non-mutated copy of this gene) will be introduced into the cell. Upon cleavage by the meganuclease, the repair matrix will be used as a template to restore a correct gene. By erasing the mutation, gene correction addresses the very cause of the disease, rather than its consequences.

About xeroderma pigmentosum

Xeroderma pigmentosum (XP) is an autosomal, recessive genetic disease characterized by hypersensitivity to exposure to ultraviolet (UV) rays, a high predisposition for developing skin cancers on sunlight-exposed areas, and in some cases, neurological disorders. XP patient' cells are defective in the nucleotide excision repair (NER) process, one of the cellular maintenance systems that protects our chromosomes from various types of damage. As a consequence, XP cells are less able to eliminate UV-induced DNA lesions. To date, the only treatment available to XP patients is either full protection against exposure to the sun or repeated surgery to remove regularly re-occurring skin cancers. Mutations responsible for XP syndromes can be classified into seven complementation groups, with the XP-C group representing half of the XP patients in Europe and North Africa. XP-C patients remain free of the neurological problems observed in other XP groups. Preliminary studies aimed at tissue therapy of XP patients have shown that in vitro retroviral transduction of XP fibroblasts and primary keratinocytes with the cloned XP genes results in full recovery of their DNA repair capacity. Furthermore, cells from the skin lineage can be manipulated in vitro and then used to reconstruct functional skin. Thus, an alternative route for long-term tissue therapy would consist of ex vivo gene correction of the XP-C locus in keratinocytes before grafting back reconstructed skin.

About Cellectis' collaboration policy

Cellectis' policy is to foster research excellence in order to offer new solutions for genome engineering. While the core activity (i.e. the protein engineering itself) is usually conducted solely by Cellectis, upstream and downstream studies are often performed in collaboration with other major players in the relevant field.

Cellectis' Forward-Looking Statements

This communication expressly or implicitly contains certain forward-looking statements concerning Cellectis SA and its business. Such statements involve certain known and unknown risks, uncertainties and other factors, which could cause the actual results, financial condition, performance or achievements of Cellectis SA to be materially different from any future results, performance or achievements expressed or implied by such forward-looking statements. Cellectis SA is providing this communication as of this date and does not undertake to update any forward-looking statements contained herein as a result of new information, future events or otherwise.

For a discussion of risks and uncertainties which could cause actual results, financial condition, performance or achievements of Cellectis SA to differ from those contained in the forward-looking statements please refer to the Risk Factors ("Facteurs de Risque") section of the prospectus approved by the French Autorité des Marchés Financiers ("AMF") on January 22^nd, 2007 under visa number 07-023, available on the websites of the AMF (http://www.amf-france.org) and Cellectis (http://www.cellectis.com).

Disclaimer

This press release, and the information contained herein, does not constitute an offer to sell or a solicitation of an offer to buy or subscribe for shares in Cellectis in any country.