Press Release

Cellectis announces the delivery of two meganucleases targeting the p53 gene in the framework of the NETSENSOR European program.

Biocitech, France - July the 26^th, 2007 - Cellectis SA, the rational genome engineering company specializing in the production of meganuclease recombination systems and in meganuclease engineering, today announced the delivery of two meganucleases targeting the p53 gene to its partners in the NETSENSOR collaborative research project (part of the European Union's 6^th Framework program).

NETSENSOR is a research consortium in the field of synthetic biology. Its purpose is to develop a system that detects a particular type of malfunction in the cell: alteration of the p53 protein function, observed in practically all cancers. The system developed by NETSENSOR not only detects the malfunction, but also reacts either by killing the cell or repairing it with a meganuclease.

The approach pursued by NETSENSOR is to build synthetic gene networks able to respond to alterations in cells. By carefully linking chosen genes and regulatory sequences, scientists are able to design and construct "gene networks" that can sense specific conditions or signals in the cell and respond either to detect them or counter their effects. Within NETSENSOR, a multi-disciplinary team is working to develop one such network that will sense errors in p53 signaling - a pathway altered in almost all cancers - and respond either by killing the cell or by actually repairing detected mutations. The technology could have a wide range of applications - from diagnostics to gene therapy. NETSENSOR brings together teams from Cellectis and several prestigious research institutes: the European Molecular Biology Laboratory (Heidelberg), Centro de Regulación Genómica (Barcelona), Centro Nacional de Investigaciones Oncológicas (Madrid), and Medizinische Hochschule Hannover (Hannover).

The protein p53 was chosen as one of the program's primary targets because it is a major tumor suppressor. This protein is directly altered in ~50% of all cancers, while the other 50% carry alterations in genes or mechanisms that directly regulate p53. p53 acts as a checkpoint protein and also controls apoptosis (programmed cell death). Thus, it can prevent the proliferation of damaged cells by blocking their development or triggering apoptosis.

Meganucleases cleaving sequences from the p53 gene have been generated on Cellectis' high throughput screening platform. Meganuclease design relies on Cellectis' proprietary database of meganuclease variants, and on the know how accumulated over several years of meganuclease engineering, which enables the production of meganucleases with tailored specificity for most genes identified to date: indeed, targetable sequences (i. e. sequences that could be cleaved by an engineered meganuclease with a good chance of success) are found once every one thousand base pairs on average (the human genome bears 3 billion base pairs).

These meganucleases will be first used in the repair process triggered by the gene regulatory network designed by NETSENSOR. Further characterization will be required to investigate the therapeutic potential of these meganucleases.

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 Cellectis' collaboration policy

Cellectis' policy is to foster research excellence in order to offer new solutions for genome engineering. To date, the major outcome of this effort has been the production of custom meganucleases that cleave genes of interest; this capability vastly expands the range of potential applications and is a prerequisite for therapeutic use. While the core activity (i.e. the protein engineering itself) is usually conducted solely by Cellectis, upstream studies are often performed in collaboration with major players in the 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.