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Vaccines in Vain But while AIDS scientists began making inroads in developing drug therapies, designing a vaccine was proving nearly impossible. Despite all that they have learned about HIV, experts are still missing one essential ingredient: to this day, they do not know exactly what cells or immune responses could protect the body from HIV infection. Could an antibody that binds to and neutralizes the virus do the trick? Are T cells, specially formulated to recognize portions of HIV's surface proteins, the solution? Or, as many experts now suspect, is some elusive combination of those factors...
ADARC had plenty of company. Vaccine efforts were progressing elsewhere in the AIDS community, but unevenly. Testing for one candidate, made by Merck, began in 2004 with much fanfare and ended three years later with disappointing results: not only had the vaccine not offered protection against HIV infection, but it actually seemed to increase the risk for some people. Because of the Merck results, the NIH, which had a similar vaccine in the works, put off plans for its own study...
...flew to Houston, where he was given a briefing on a new agent called ibalizumab, an antibody that appeared able to block HIV's entry into healthy cells. In the 200 or so HIV-positive patients tested in the early trial, the compound was effective, but Tanox was worried about resistance. No matter how promising ARV drugs were, HIV inevitably found a way to evade them. So while the agent seemed to reduce the burden of virus in the blood up to 90% in patients with full-blown AIDS, no one knew how long the viral standoff would last...
Looking at the numbers, Ho saw more than just another member of the growing arsenal of ARV cocktails. Each of the ARVs focuses on thwarting just one of several different steps in HIV's infection process. Ibalizumab works at the critical juncture where the virus meets a healthy CD4 cell - a critical component of the immune system - essentially interposing itself between the two and preventing infection. If ibalizumab was so good at tamping down HIV in AIDS patients who were already infected, then maybe it could be tweaked to prevent AIDS in the first place. In other words, maybe...
What the ADARC scientists are struggling to achieve is a thorough understanding of how ibalizumab operates and how they can control those machinations. The CD4 cell is a bit like an immunological sentinel, endowed with the ability to recognize snippets of various pathogens, from common influenza to HIV, and mark them for destruction by other cells. Once attached to a CD4, HIV begins an intricate series of steps to gain entry into the cell. Ibalizumab is able to disrupt this intricate molecular choreography by binding to the CD4 and serving as an immunological snare. With the antibody stuck...