Tanox has reported Phase II study results for its lead HIV drug candidate, TNX-355, which has shown a unique ability to inhibit entry of HIV-1 into healthy CD4-positive cells regardless of the virus' co-receptor tropism.

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 the CD4 cell in this manner, TNX-355 creates a new hurdle for HIV, different from entry inhibitors that target viral proteins or chemokine co-receptors. Study results show that TNX-355 is equally active in vitro against virus strains that exhibit tropism for CCR5 as well as CXCR4 -- making TNX-355 the most advanced entry inhibitor in development with this crucial property of tropism independence.

Results of the trial demonstrated that, when compared with an optimized background regimen (OBR) alone, TNX-355 in combination with OBR reduces viral loads in HIV-infected patients, without suppressing their immune systems or causing significant side effects.