New Research Reaffirms Tropism Independence Of TNX-355; Data For Tanox, Inc.'s Novel HIV Viral Entry Inhibitor Presented At 2006 CROI

DENVER, Feb. 9 /PRNewswire-FirstCall/ -- Tanox, Inc. presented study results on the most-advanced antibody in clinical development for HIV/AIDS treatment, TNX-355, Feb. 8, 2006 at the 13th Conference on Retroviruses and Opportunistic Infections (CROI) in Denver. The oral presentation detailed new data regarding the drug candidate's unique ability to block entry of HIV-1 into CD4-positive cells regardless of the virus' co- receptor tropism.

The study tested virus samples from 78 of the 82 patients in the ongoing Phase 2 clinical trial of TNX-355 for susceptibility to the antibody. Susceptibility to TNX-355 was similar for all viruses and was not dependent upon virus tropism. The results are consistent with previous research conducted with samples from a 17-patient subset from a Phase 1b clinical trial of TNX-355. These studies demonstrate that TNX-355 is equally active in vitro against virus strains that target the CCR5 co-receptor or the CXCR4 co- receptor and dual or mixed tropic viruses. TNX-355 is the most-advanced viral-entry inhibitor in development with this valuable property of tropism independence.

"This novel mechanism could provide a significant advantage for TNX-355, as approximately 40 percent of treatment-experienced patients carry dual, mixed or CXCR4 viruses," said Dr. Stanley Lewis, Tanox medical director.

TNX-355 is a humanized viral-entry inhibitor monoclonal antibody that coats CD4-positive cells -- the primary target of HIV infection. By blocking viral entry into CD4, TNX-355 creates a hurdle for HIV different from entry inhibitors that target viral proteins or chemokine co-receptors.

Tanox is continuing the Phase 2 trial through its planned 48-week duration, and administration of TNX-355 has been extended up to 96 weeks for patients who continue to receive benefit from the drug candidate. Through the study's Week 24 primary endpoint, there were no serious side effects related to TNX-355. The company expects to announce complete Phase 2 results in the first half of 2006 and move TNX-355 into late-stage clinical development later this year.

About TNX-355

TNX-355 is a monoclonal antibody that binds to CD4 receptors on the surface of CD4-positive cells, preventing the entry of HIV particles into lymphocytes. TNX-355 is the most-advanced antibody in development for the treatment of HIV/AIDS. A Phase 2 clinical study demonstrated that TNX-355, plus an optimized background regimen, produces a clinically meaningful reduction in viral load against multiple strains of HIV, without depleting CD4-positive cells. TNX-355 was fast tracked by the Food and Drug Administration in 2003. The fast-track designation is designed to expedite approval of therapies for life-threatening diseases and allows for rolling new drug application (NDA) submissions.

About Tanox, Inc.

Tanox is a biotechnology company specializing in the discovery and development of monoclonal antibodies. The company develops innovative biotherapeutics for the treatment of immune-mediated diseases, inflammation, infectious disease and cancer. Tanox's first-approved drug, Xolair(R) (omalizumab), is the first antibody approved to treat moderate-to-severe confirmed allergic asthma. Xolair was developed in collaboration with Genentech, Inc. and Novartis Pharma AG and is approved for marketing in the United States, Canada and major European countries. Tanox is based in Houston and has a manufacturing facility in San Diego. Additional corporate information is available at http://www.tanox.com .

This news release contains forward-looking statements regarding the potential for TNX-355 as a treatment for HIV-1-infected patients. These statements are based on Tanox's current beliefs and expectations, and are subject to risks and uncertainties that could cause actual results to differ materially. The therapeutic potential of TNX-355 as a treatment for HIV-1- infected patients is subject to the risks inherent in drug development. Success in early stage clinical trials does not ensure that later-stage or larger-scale clinical trials will be successful, and the results achieved in later-stage trials may not be sufficient to meet applicable regulatory standards. Problems or delays may arise during clinical trials or in the course of developing, testing or manufacturing drugs. For more detailed information on the risks and uncertainties associated with Tanox's drug development and other activities, see Tanox's periodic reports filed with the Securities and Exchange Commission.

Editor's note: TNX-355 presentation slides are available on the Tanox Web site at http://www.tanox.com in the Investor Relations section.

Photo: NewsCom: http://www.newscom.com/cgi-bin/prnh/20050207/TNOXLOGOPRN Photo Desk photodesk@prnewswire.comTanox, Inc.

CONTACT: Steve Sievert of Tanox, Inc., +1-713-578-4211, orssievert@tanox.com

Web site: http://www.tanox.com/