Business Wire - June 16,2003

In January, as a precautionary measure, FDA placed a "clinical hold" on all active gene therapy trials using retroviral vectors to insert genes into blood stem cells. FDA initiated the action after learning that two children who received a retrovirus in a French gene therapy study for X-linked Severe Combined Immunodeficiency (SCID), commonly known as "bubble baby syndrome" were diagnosed with leukemia.

This action allows Enzo to proceed with its clinical trials. The Company is in the process of reactivating the clinical sites and following the appropriate protocols to proceed with this multi-site Phase I/II trial.

"An increasing number of patients who have been infected for many years are becoming resistant to the antiretroviral drugs used in the highly active antiretroviral cocktail (HAART) that became available in 1996," said Marcus A. Conant, M.D., Professor, University of California Medical Center, San Francisco, the principal investigator of the Phase I study. "I am delighted that FDA has lifted its clinical hold on our gene therapy trial so that we can move forward with this extremely promising therapy in the hopes of developing an entirely new strategy for managing patients with AIDS who are resistant to current therapies."

"We are obviously pleased with FDA's decision," said Dean L. Engelhardt, Executive Vice President of Enzo. "The clinical hold was placed on Enzo's trial as the result of the appearance of leukemia linked to the use of gene therapy in a study of X-SCIDs children conducted in France. Enzo's StealthVector(R) HGTV43 and the trial conducted with this vector were analyzed in the course of this period of clinical hold. At the time our vector was developed, we incorporated two critical safety features into its design. By the incorporation of these features the possibility of inadvertently turning on deleterious genes in the host was minimized."

Enzo's StealthVector(R) HGTV43 medicine consist of three antisense genes designed to interfere with the growth of HIV-1. The vector is used to transfer these genes into blood stem cells, the cells that serve as progenitor cells for all blood cells, including CD4+ immune cells, the cells predominantly infected by HIV-1. The Phase I study demonstrated that the anti-HIV-1 genes could be successfully put into stem cells and that these engineered stem cells were able to survive and to produce CD4+ cell progeny containing functioning antisense genes.

"The ability of the antisense genes to function was monitored by RT/PCR amplification of the expressed RNA and characterization of the amplicon using restriction enzyme digestion and gel analysis," said Dr. Engelhardt at the time the results were announced. "We now need to go ahead with strategies that will increase the proportion of CD4+ cells that have anti-HIV-1 antisense RNA-producing genes."

About Enzo

Enzo Biochem is engaged in the research, development and manufacture of innovative health care products based on molecular biology and genetic engineering techniques, and in providing diagnostic services to the medical community. The Company's proprietary labeling and detection products for gene sequencing and genetic analysis, with approximately 200 patents worldwide, are sold to the life sciences market throughout the world. The Company's therapeutic division is conducting clinical trials of its proprietary gene medicine for HIV-1 infection and clinical trials of its proprietary immune regulation medicines for hepatitis B and hepatitis C infection and for Crohn's Disease. The Company also holds a patent covering a method and materials for correcting point mutations or small insertions or deletions of genetic material that would allow for editing and correcting certain abnormalities in genes. For more information visit our website www.enzo.com.

Except for historical information, the matters discussed in this news release may be considered "forward-looking" statements within the meaning of Section 27A of the Securities Act of 1933, as amended and Section 21E of the Securities Exchange Act of 1934, as amended. Such statements include declarations regarding the intent, belief or current expectations of the Company and its management. Investors are cautioned that any such forward-looking statements are not guarantees of future performance and involve a number of risks and uncertainties that could materially affect actual results. The Company disclaims any obligations to update any forward-looking statement as a result of developments occurring after the date of this press release.

CONTACT: Enzo Biochem

Steve Anreder, 212/532-3232

SOURCE: Enzo Biochem

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