Enzo Biochem Says Data Shows Significant Progress in Human HIV Gene Medicine Trial.

Business Editors & Health Writers

FARMINGDALE, N.Y.--(BUSINESS WIRE)--June 2, 2000

Results Include Long-Term Survival in Humans of Engineered Cells

and Development of CD4+ Cells Containing Anti-HIV-1 Antisense Genes

Company to Propose Phase 2 Trial With AIDS Patients

Enzo Biochem, Inc. (NYSE:ENZ) announced today preliminary results of a Phase 1 clinical trial of its anti HIV-1 antisense gene therapy product, HGTV-43. These results show an unprecedented eight-month survival of the engineered cells in an HIV-infected individual among the group studied and the development of CD4+ cells expressing the HIV-1 antisense RNA within the cell. Such antisense genes have previously been shown to provide resistance to the virus. These results indicate that the engineered stem cells have replicated and differentiated within participants in the trial.

"Our ultimate goal is to achieve for HIV-1 infected individuals a long-term, lifelong immune responsiveness in a disease characterized by progressive loss of this defensive mechanism. Based on the results thus far we believe we have made significant progress towards this goal," said Dean Engelhardt, Ph.D., a Senior Vice President of Enzo.

"Those of us treating severely ill patients desperately need new therapies that approach this disease from a new paradigm, and we are immensely encouraged that with Enzo's treatment we have for the first time successfully modified the progenerator stem cells in HIV infected patients and demonstrated that those cells have been successfully recolonized in these patients," commented Marcus Conant, M.D. of San Francisco, CA, principal clinical investigator for the trial. "It represents a major advance towards creating an immune system in AIDS patients which can resist the destruction of the critical CD4+ cells."

The results will be reported in a paper to be delivered today by Dr. Engelhardt at the annual meeting of the American Society of Gene Therapy, in Denver Colorado. An Enzo spokesperson said that based on the Phase I trial results Enzo is preparing an application for a Phase 2 study involving patients with frank AIDS.

Dr. Engelhardt reported that to date the Company's procedure is being tolerated well by all the patients. "We are fulfilling our Phase I goals, namely achieving safety milestones and the long-term survival and differentiation of the engineered stem cells," he stated.

Dr. Engelhardt reported data on the three initial patients in the study, at three, six and eight months, that demonstrated that the engineered cells have continued in circulation. The survival of the engineered cells for eight months in the first patient, he pointed out, was well in excess of anything thus far achieved by other researchers using blood stem cells from adult human subjects without first ablating the patient, a process in which blood cells are destroyed. Additionally, Dr. Engelhardt reported that the engineered cells containing the HIV antisense were present among the individuals' CD4+ cells at six and eight months.

Enzo's Phase I human clinical trial uses HGTV-43, its proprietary genetic antisense based therapeutic product, developed to protect human immune cells against infection by a broad spectrum of strains of HIV-1 including its mutational variants. Enzo's HGTV-43 medicine incorporates two proprietary technologies. One involves the insertion of a new type of genetic material into blood cells in order to inhibit the growth of HIV-1. This technology, known as genetic antisense, utilizes a "mirror image" of a gene, called an antisense molecule, to block the virus.

The second technology is based on a novel vector designed to deliver the antisense molecule to the cell. This vector is employed to insert new genes into target cells with the objective of integrating the gene into the chromosome of the cell, in a process known as transduction. Enzo stated previously that it has achieved high levels of transduction within 18 hours, thus limiting inconvenience to the patient, and in achieving levels of stable gene transfer to target cells greater than 30%. The cells containing these new genes, when transferred to the patient, replicate and provide the patient with the newly inserted biological function. The Company believes that its proprietary vector system constitutes a technological breakthrough in the development of commercially viable gene medicine.

"We believe that our HGTV-43 medicine has now passed an important milestone with the preliminary data provided by our Phase I trial," said Elazar Rabbani, Ph.D., Chairman and CEO of Enzo. "We will now take our work to the next stage, where our expectations for similar successful results are very high."

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.

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. Prospective 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.