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The problem lies with the mechanism of drug action: all modern drugs are active only against the actively replicating virus.
The virus does become silenced in some situation. For example, the host cells of immune system can become dormant and shut down almost all replication mechanisms. In such cells virus can stay without showing any activity for very long time. As a result, this virus remains completely insensitive to all drugs. Once the cell wakes up, the virus starts to reproduce as well and easily replenish its population in the body if the drugs were discontinued.
There are also so-called anatomical reservoirs of the virus. HIV can hide at different anatomic locations such as gastrointestinal tract and brain of the patients receiving antiretroviral therapy. These sites have various kind of barriers limiting the ability of antiretroviral drugs to reach the infected cells. Again, when the treatment is stopped the virus from these places could cause re-infection.
Some researchers hypothesize that HIV can infect certain non-immune cells and survive there in dormant stages for many years.
Addressing the problem of latent viral pool
The logical answer to the problem of latent viruses lurking somewhere in the safe heavens around the body is to get them out of their hiding places. Two major strategies are currently being developed by researchers working in this field.
First strategy aims to activate the latent cells of immune system. Activation would also turn on the replication process of the virus .With the virus replicating inside the cell, the cell will ultimately die, and the released viruses could be get rid of using the traditional and highly effective antiretroviral therapy.
There are different agents which could potentially help in activating the latent T cells. One such agent, Interleukin-7 (IL7) is currently undergoing clinical trials. Prostratin is another compound that could do this but at present time only limited data is available for its safety profile and efficiency in humans. It will take several years to get enough data and see if these drugs serve the purpose.
The second strategy relies on turning on the HIV genes within the latent cells infected by virus. Histone deacetylase inhibitors (HDACI) seem to be able to do exactly this. These drugs could turn on the gene expression in the viruses present inside the silent T cells thus making them vulnerable for antiretroviral drugs. Further studies are needed to evaluate the efficiency of these drugs.
With the pace of developments in the HIV research, many scientists now believe that the cure for HIV is only few years away. The infection has already proven itself as a very difficult target to treat. Many drugs previously developed with curative intent have failed to their promises.
But this time the level of confidence among scientists and observers is higher than ever. Let’s hope that they are right.