HIV persists in a small number of infected cells—the viral reservoir—that are not cleared from the body by antiretroviral therapy. A major goal of HIV cure research is to identify a molecule, or biomarker, that distinguishes these reservoir cells from healthy cells. Having such a biomarker would allow researchers to target these reservoir cells and clear them with precision.
The Research Question
In 2017, a team of researchers in France reported that they had found a potential biomarker of the reservoir in the blood—a protein called CD32. In their attempts to replicate the discovery, several other research teams found that CD32 may be a marker of HIV activity in blood cells rather than a specific marker of the latent reservoir. Scientists in this study ask: Could CD32 be a biomarker of HIV activity in the tissues, too?
Scientists examined gut biopsies from four study participants whose medication had reduced the HIV in their blood to undetectable levels. First, researchers noted that despite having undetectable virus in the blood, about four in every 100,000 cells in the tissue had jump-started activity of the provirus, meaning they had begun the first steps towards producing new viruses. These “actively” infected cells may be the first to re-seed viral infection in the blood if antiretroviral therapy is stopped.
Next, the researchers explored whether CD32—the possible biomarker—was present in the actively infected cells, and to what degree. Using two separate techniques, the researchers found that those with undetectable virus in the blood had 100 times fewer actively infected cells in the tissue than those with detectable virus in the blood (viremia). But by one assay, between 60 and 100 percent of actively infected cells had CD32, compared to only 20 percent in those with viremia.
This study confirms the conclusion of other researchers that CD32 may not be a biomarker of the latent reservoir. However, CD32 may be a biomarker of what might be called the active reservoir—the persistent virus that is probably first to re-seed infection when antiretroviral therapy is stopped. Thinking on the nature of the reservoir is evolving to include not only latent, but also active reservoir, and both are major barriers to a cure. Finding a way to differentiate cells harboring active reservoir from healthy, uninfected cells would be an important advance.
The co-lead scientists of this study, Drs. Timothy Henrich and Peter Hunt, are funded by amfAR and are members of the amfAR Institute for HIV Cure Research.
Dr. Flores is amfAR’s associate director of research.