Bringing the Fight to hidden HIV
We’ve got even more news for the HIV cure front. Yesterday we talked about broadly neutralizing antibodies, today we are going to be touching on that yet again,so if you missed it, you can read more about that here. Now, although HIV can now be effectively suppressed using anti-retroviral drugs, it still comes surging back the moment the flow of drugs is stopped. We sadly saw this delayed response in an infant that was thought to be effectively “cured” of HIV. It is unfortunate, but latent reservoirs of HIV-infected cells, invisible to the body’s immune system and unreachable by pharmaceuticals, ensure that the infection will rebound after therapy is terminated. This is a big reason that, even when the viral load drops below detection, you still need constant check ups and continuous anti-retrovirals.
However, another new strategy devised by researchers harnesses the power of broadly neutralizing antibodies against HIV. We touched on this new discovery yesterday and in a collaboration they pushed the finding even further. Researchers took those broadly neutralizing antibodies along with a combination of compounds that induce viral transcription, in order to attack these latent reservoirs of cells in an approach termed funnily enough, “shock and kill.” In tests on mice, 57 percent of animals treated in this way did not have the expected resurgence of virus in their blood after their treatment ended. Sure it is not 100% or even 80%, but imagine if this result could be transferred with even only similar results in humans.
“This is the first time that any combination of agents has been found to prevent viral rebound in any animal model,” says Nussenzweig.
The issue is that the problematic latent reservoirs of HIV-infected cells are established very early in the infections. Possibly even before tests can detect the presence of the virus, and not only is current drug therapies are unable to kill the latent cells, we have had trouble trying to lure those latent reservoirs out of hiding in the body.
“The latent reservoir remains the major barrier to curing HIV-1 infection,” says Nussenzweig, who is the Zanvil A. Cohn and Ralph M. Steinman Professor and a Howard Hughes Medical Institute investigator. “Our finding suggests that antibodies could play a significant role in disrupting the establishment and maintenance of the latent reservoir, which is believed to be a necessary step to curing patients of HIV-1.”
The tem has worked for several years on broadly neutralizing antibodies, a recently discovered subset of antibodies with an unusually high ability to recognize HIV consistently despite the virus’s ability to rapidly mutate. Broadly neutralizing antibodies have shown great promise for treating HIV infection in mouse and monkey models of HIV as we touched on yesterday here in the Labs. However, by themselves they suffered the same problem that plagued other therapies: when you stop administering them, the virus rebounds.
Counterintuitively, the key to success in this instance was combining broadly neutralizing antibodies with viral inducers, compounds that prompt latent viruses to become active by promoting the transcription of their DNA. The idea is to eliminate the invisibility of the latent reservoir while simultaneously attacking the virus. More than half of the mice that received broadly neutralizing antibodies along with a cocktail of three viral inducers had no viral rebound at all, even three-and-a-half months after their last injection. [As I noted before the broadly neutralizing antibodies alone. Researchers found that even when they were used in combination with a single viral inducer, it did not have this effect, nor did combinations of anti-retroviral drugs and viral inducers that have been attempted in the past.]
The team says that one reason broadly neutralizing antibodies may have succeeded where traditional drugs have failed is their ability to directly harness the power of the body’s own immune system using Fc receptors, which occur on a wide variety of immune system attack cells and help them precisely target the infection.
“A big surprise in this study was the important role the Fc part of the antibody played in amplifying the potency of broadly neutralizing antibodies,” says Ravetch, who is Theresa and Eugene M. Lang Professor. “Their effect in neutralizing latent reservoirs of HIV-1 was largely driven by Fc-receptor binding.”
This research is incredible and hopefully will turn into even more fruitful findings as the research continues. As with my other post on the HIV vaccine, I want to stay hopeful. Although the HIV virus is a very tough contender to fight, there will always be hope as long as we continue to search. Because as long as we fight and look for a cure there will always be a chance. So here’s to the scientists that keep the fight going, you guys rock.
Ariel Halper-Stromberg, Ching-Lan Lu, Florian Klein, Joshua A. Horwitz, Stylianos Bournazos, Lilian Nogueira, Thomas R. Eisenreich, Cassie Liu, Anna Gazumyan, Uwe Schaefer, Rebecca C. Furze, Michael S. Seaman, Rab Prinjha, Alexander Tarakhovsky, Jeffrey V. Ravetch, & Michel C. Nussenzweig (2014). Broadly Neutralizing Antibodies and Viral Inducers Decrease Rebound from HIV-1 Latent Reservoirs in Humanized Mice Cell : 10.1016/j.cell.2014.07.043