Frank, "undetectable" in most studies means that less than 500 viral particles per milliliter of blood were measured, though Chiron has a bDNA test that measures to a sensitivity of 25 particles per ml. This means that a viral load of 5 particles per ml would escape detection on any current test, even though the subject would still have 5,000 globs of viral RNA in each liter of blood.
Second, viruses concentrate in other parts of the body, they don't all circulate in blood. Cerebrospinal fluid and lymph, for example, also harbor virus. So even blood were virus-free, there might still be infectious virus in other tissue.
Protease inhibitors work by physically binding to HIV protease enzymes. If every single viral particle in the body were physically bound to a PI molecule, the individual would be "cured", but as long as any virus remains viable, the virus will replicate and disease will recur.
In trials of PI's, results were described in terms of logs of reduction. One log reduction meaning only 10% of virus remained, 2 logs 1%, 3 logs 1/10%, and so on. There were some studies in which there was reduction greater than 4 logs, meaning only one particle of each ten thousand survived. Still, because there are billions of viral particles, the disease remains after the almost complete reduction.
In spite of all this, Dr. David Ho has suggested the possibility of a cure through the strategem of differential suppression (by several drugs) over a long period of time. If a drug inhibiting viral protease is combined with a drug inhibiting viral reverse transcriptase, you can get log 6 reductions. Still, "billions" is log 9, a long way from cure. |
