by Chael Needle

LifeGuide [Treatment Horizons]

You’re on HAART and your viral load is below 50 copies/mL, but you have an isolated and temporary spike upward of the amount of virus in your blood. Does this mean that the HIV in your body has become resistant to your antiretroviral therapy? Time to find a new drug or class of drugs? Probably not. Researchers at Johns Hopkins University have concluded that “blips”—small increases in HIV levels—generally do not signal mutations leading to drug resistance. When nearly 1,000 viral clones were sequenced before, during, and after the “blips,” the researchers found no new mutations for two key enzymes blocked by drug therapy: protease and reverse transcriptase. This type of clarity is much-needed: Resistance to a particular drug, once developed, is permanent.

“An isolated viral load measurement that goes above fifty copies/mL, and then goes back down, is probably nothing to worry about,” says senior study author and infectious disease specialist Robert Siliciano, MD, PhD, a professor at The Johns Hopkins University School of Medicine and a Howard Hughes Medical Institute investigator. The criteria the researchers used for initiating concern about possible drug resistance is any viral load that shoots above 200 copies or a measurement of over fifty copies twice in a row.

 Published in the Journal of the American Medical Association, the “blip” study results came out of a larger project analyzing how low-level viremia (the presence of virus in the blood) in patients on HAART is related to the viral reservoirs that persist in all patients on this therapy. The researchers proposed that if a cell type is a significant reservoir then it should contribute to this low-level viremia.

Viral reservoirs are removed from the effects of antiretroviral drugs and a cure isn’t possible unless the virus is eliminated from these hiding places. Everyone on HAART who’s undetectable has virus in their blood, he says. “It’s below fifty copies, but it’s there. And that virus has to be coming from some cell type....The reservoir that is the best defined (which was identified by our lab about ten years ago) is in resting memory CD4 cells. That’s called the latent reservoir,” says Dr. Siliciano. “The ‘blip’ part of the study compared what’s in the reservoir with the free virus in the blood—what does the free virus look like before it goes up above fifty copies, when it goes above fifty, and then when it comes back down?”

Part of the reason why “blips” remained a question was that “nobody knew what the shape of a blip was,” he says. “When you sample infrequently, you may be missing a lot of blips and you may not have a good idea of how many blips there are, how long they last, or how high they go.” To this end, the researchers conducted more intensive sampling than previous studies by other researchers: The team conducted an analysis of multiple blood samples from ten HIV-positive patients, taking samples every two to three days for a period of three months.

Assessing mutation, and possible drug resistance, is challenging because “the limit of detection from the clinical resistance assays is 1,000 copies/mL. Even when patients have blips [that reach] 150 or 300, say, it may be impossible to determine whether resistance is present,” says Dr. Siliciano. “Say your viral load is twenty and you’re measuring it with an assay that has an error of plus or minus about .4 logs, or three-fold. If you measure it over and over again, you could get a measure of sixty and sometimes you could get a measure of six. Even if the viral load remained exactly at twenty, and you measured it repeatedly, you would occasionally get blips from the statistical fluctuation of the assay.” The Johns Hopkins team circumvented this fluctuation because they used an extremely sensitive assay that works even when the viral load is less than fifty copies.

A possible next step, says Dr. Siliciano, would be to look at different populations. Most of the patients looked at in this study had had prior nonexpressive therapy and most had started therapy with a low CD4 count. “So whether the same thing is true—say, for patients with higher CD4 counts—should probably be determined.”

Chael Needle wrote about preventive vaccine trials in the February issue.