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r5 tropic or dual tropism
Oct 27, 2004

Dear Doc, I was wondering how you know whether you have r5 tropic or dual tropism virus?? Do commercial labs test for this??Thanks,LUke

Response from Dr. Sherer

At present, there is no clinical indication for obtaining this information, and no clear clinical decision making to be done with the answer. So at present I would discourage you from seeking this test and this information.

In general, most people (80%) with untreated HIV are CCR5-tropic, i.e. the virus attaches itself to the CD4 cell with via a CCR5 protein. A minority have the alternate CXCR4 tropism or dual tropism, i.e. capacity for cell entry via either pathway. With later disease, i.e. CD4 cells below 200, CCR5-tropism falls to 60%, and CXCR4 tropism becomes more common.

These characteristics are likely to be important when additional agents, i.e. entry inhibitors, are approved for use in HIV therapy. Many new agents under investigation block cell entry by blocking the CCR5 pathway. It remains unclear whether the use of these agents alone will simply induce the virus to become CXCR4 virus, but there are reasons to believe that will happen. As there are also CXCR4 blockers in study, they may provide a therapeutic answer to this problem, or, if used simultaneously with CCR5 inhibitors, they may offer therapeutic synergy and more completely block cell entry. Such synergy has been observed to date in laboratory studies. It will take 2-3 years or more to answer these questions.

Possible resistance?

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