Tanox Completes Enrollment of TNX-355 Phase 2 Clinical Trial for the Treatment of HIV

March 9, 2005

HOUSTON -- Tanox, Inc. has completed enrollment in its Phase 2 clinical trial of TNX-355 for the treatment of the human immunodeficiency virus (HIV). The study, which has enrolled the target of 80 patients, is being conducted at 30 sites in the United States, Canada and Puerto Rico.

The Phase 2 study is a three-arm, double-blind, placebo-controlled study evaluating the safety and efficacy of TNX-355, as assessed by viral load reduction. The study compares the effects of two different dosages of TNX-355 added to optimized background therapy (OBT) with the effect of OBT plus placebo in treatment-experienced, HIV-1 infected patients who have failed highly active antiretroviral therapy (HAART).

Following encouraging proof-of-concept results in our Phase 1 trials, we were eager to pursue our studies of TNX-355 as an option for treatment-experienced, HIV-1 infected patients for whom currently available therapies are inadequate, said Nancy T. Chang, president and CEO of Tanox. We plan to present interim, 24-week data from the Phase 2 trial in the fourth quarter of this year.

TNX-355 is a humanized, non-immunosuppressive anti-CD4 monoclonal antibody that works by blocking the ability of HIV to enter CD4-positive cells. The CD4 receptor on host cell surfaces is considered a gateway for HIV infection. This monoclonal antibody is a viral entry inhibitor and a first-in-class CD4 antagonist. Results from Phase 1 studies showed that TNX-355 was well tolerated and resulted in a clinically meaningful reduction of viral load in treatment-experienced patients infected with HIV. A Phase 1b trial showed a viral load reduction lasting five to seven weeks with multiple doses.

TNX-355 received Fast Track Status from the U.S. Food and Drug Administration in 2003.

The feedback from physicians involved in the Phase 2 study has been encouraging, said Dr. Stanley Lewis, Tanoxs medical director for TNX-355. Investigators have reported that they are pleased with adherence and intravenous dosing of the drug has not been an obstacle.

The primary endpoint for the Phase 2 trial is a significant reduction in viral load levels between either of the active arms versus the control - OBT - arm at 24 weeks. A significant viral load reduction is defined as > 0.5 log10. Secondary objectives of the study will focus on change in percentage and number of CD4 cell count from baseline; the proportion of patients who achieve a reduction of > 1.0 log10 HIV-1 RNA; the proportion of patients who achieved an undetectable HIV-1 RNA; the extent of emergence of resistance; time to loss of virologic response (TLOVR); and Average Area Under the Curve Minus Baseline (AAUCMB).

Source: Tanox, Inc.