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Scientists 'delete' HIV from human cells

by Staff reporter
24 Jul 2014 at 09:54hrs | Views
Once HIV conquers a human cell, it stays there forever but scientists have for the first time ever "deleted" HIV from human cells, marking a major breakthrough in fight against AIDS.

The virus inserts its deadly genome permanently into the victims' DNA, forcing patients to be on drugs for life.

But now, for the first time, researchers have found a way to eliminate latent HIV-1 virus from human cells - and this could be a cure for other latent infections.

A team of Temple University School of Medicine researchers has designed a way to snip out the integrated HIV-1 genes for good.

"This is one important step on the path toward a permanent cure for AIDS," said Kamel Khalili, professor and chair of the department of Neuroscience at Temple.

Khalili led the work which marks the first successful attempt to eliminate latent HIV-1 virus from human cells.

"It's an exciting discovery, but it's not yet ready to go into the clinic. It's a proof of concept that we're moving in the right direction," added Khalili.

When deployed, a combination of a DNA-snipping enzyme called a nuclease and a targeting strand of RNA called a guide RNA (gRNA) hunt down the viral genome and excise the HIV-1 DNA.

From there, the cell's gene repair machinery takes over, soldering the loose ends of the genome back together - resulting in virus-free cells.

"Since HIV-1 is never cleared by the immune system, removal of the virus is required in order to cure the disease," said Khalili, whose research focuses on the neuropathogenesis of viral infections. The same technique could theoretically be used against a variety of viruses, he said.

The research shows that these molecular tools also hold promise as a therapeutic vaccine; cells armed with the nuclease-RNA combination proved impervious to HIV infection.

Worldwide, more than 33 million people have HIV.

Although highly active antiretroviral therapy (HAART) has controlled HIV-1 for infected people in the developed world over the last 15 years, the virus can rage again with any interruption in treatment.

Even when HIV-1 replication is well controlled with HAART, the lingering HIV-1 presence has health consequences.

"The low level replication of HIV-1 makes patients more likely to suffer from diseases usually associated with aging," Khalili said. These include cardiomyopathy — a weakening of the heart muscle — bone disease, kidney disease, and neurocognitive disorders. "These problems are often exacerbated by the toxic drugs that must be taken to control the virus," Khalili added.

Researchers based the two-part HIV-1 editor on a system that evolved as a bacterial defense mechanism to protect against infection, Khalili said.

Dr Khalili's lab engineered a 20-nucleotide strand of gRNA to target the HIV-1 DNA and paired it with Cas9. The gRNA targets the control region of the gene called the long terminal repeat (LTR). LTRs are present on both ends of the HIV-1 genome. By targeting both LTRs, the Cas9 nuclease can snip out the 9,709-nucleotides that comprise the HIV-1 genome.

To avoid any risk of the gRNA accidentally binding with any part of the patient's genome, the researchers selected nucleotide sequences that do not appear in any coding sequences of human DNA, thereby avoiding off-target effects and subsequent cellular DNA damage.

The editing process was successful in several cell types that can harbor HIV-1, including microglia and macrophages, as well as in T-lymphocytes.

"T-cells and monocytic cells are the main cell types infected by HIV-1, so they are the most important targets for this technology," Khalili said.

The HIV-1 eradication approach faces several significant challenges before the technique is ready for patients, Khalili said.

The researchers must devise a method to deliver the therapeutic agent to every single infected cell. Finally, because HIV-1 is prone to mutations, treatment may need to be individualized for each patient's unique viral sequences.

"We are working on a number of strategies so we can take the construct into preclinical studies," Khalili said. "We want to eradicate every single copy of HIV-1 from the patient. That will cure AIDS. I think this technology is the way we can do it".

Additionally, Danish researchers have used an anti-cancer medicine to to activate HIV hidden in the cells of patients taking anti-HIV drugs, exposing the virus to the immune system and making it susceptible to attack.

The results revealed on Tuesday constitute one of the major scientific discoveries hailed at the Aids 2014 conference in Melbourne, as much of the language shifts away from finding a cure to focusing on big steps in HIV treatment and prevention.

HIV hides in a state of hibernation in CD4 cells, an essential part of the immune system. Yet CD4 cells are unable to fight HIV themselves – that role lies with the immune system's killer T-cells.

But because killer T-cells can't detect the HIV hidden within CD4 cells, they are unable to attack and eliminate it from the body. While HIV patients on antiretroviral drug treatment often go on to have undetectable levels of HIV in their system, it is never eliminated.

There is always a reservoir left hiding in cells, undetectable to current screening tools and ready to take hold of the immune system again should patients stop their antiretroviral therapy.

But a research team led by Ole Sogaard at Aarhus University's department of infectious diseases in Denmark has used the anti-cancer drug romidepsin to activate the virus and bring it out of hiding.

In principle, this means that the killer T-cells should be able to detect the virus, because it leaves a trace on the outside of CD4 cells as it is activated and moves towards the bloodstream, Sogaard said.

"Despite very effective antiretroviral treatment, there is still this reservoir left of HIV cells that are infected but not producing the virus," he said.

"Once you activate them, these particles will go to the surface and signal to the immune system that this cell is infected and needs to be cleared from the body. So this is a two-step system where we bring the cells to the surface, and then rely on the immune system to kill them."

In the pilot study, researchers gave six patients three doses of romidepsin over three weeks.

Before each dose, no viral particles were detectable in the patients.

"But after the dose was given we easily measured the virus being released into the plasma in five of these six patients," Sogaard said.

"We also saw the virus go back to undetectable levels after seven days, so it came up, then hid away again, returning back to a non-active state until the next dose of cancer drug was given."

However, the researchers found the immune system did not seem to attack the virus after detecting it. Researchers found no significant reduction in the number of infected cells each time the cancer drug brought the virus out of hiding.

"This suggests when you do this reactivation, you also need to also target and activate the immune system and teach it to recognise these cells and attack," Sogaard said.

"That's what we're doing next in this study. We will teach and prime the immune system to recognise HIV before we give patients the cancer drug, and we hope there will be a better chance the immune system can clear those cells when the HIV is reactivated."

Sogaard emphasised it was unknown how much of the HIV reservoir the immune system would be able to clear even if it could be taught to recognise the virus and attack it. Virus left in just one cell might be enough to allow HIV to thrive again.

"We're still learning about this disease and where it hides, and it is a really, really tricky disease to cure because it hides in so many places in the body, it hides really well and can hide for an indefinite period of time," he said.

The difficulty of an HIV cure became particularly apparent with the now famous case of the Mississippi baby, born to an HIV-positive mother.

The child was placed on a strong course of antiretroviral drugs within 30 hours of birth. She continued the treatment for 18 months and when she stopped taking those drugs, she had no detectable virus in her system. It gave hope other infants treated early might be cured.

But 27 months later, the virus was detected and she was placed on antiretroviral drugs again.

In a similar case, two Boston patients received bone marrow transplants that appeared to rid them completely of HIV. They also relapsed, and are now back on antiretroviral treatment.

These cases have been referred to frequently during the AIDS 2014 conference, sometimes brandished as setbacks. But the cases reveal how far HIV treatment has come.

Achieving more than two years without antiretroviral treatment in an infant is unprecedented, especially since the Mississippi baby had no existing immunity to HIV. It has given researchers a new focus on where to fight HIV, as they now know it takes just a tiny amount of dormant virus for HIV to become active again.

The cases have shown that working out exactly where dormant HIV virus resides in the body, and being able to measure it, will be key to future research.

The development of HIV into lethal Aids was once considered inevitable, and less than 30 years after the epidemic began - not a long period in medical science - people living with HIV are able to lead long and healthy lives.

But that all depends on access to treatment, which has the added benefit of protecting against the transmission of HIV during unprotected sex by up to 96%.

The president of the International Aids Society, Françoise Barré-Sinoussi, won a Nobel prize for her role in discovering HIV and said she would not be drawn into talk about how far away a cure for HIV/Aids may be.

"I remember in 1984 someone said we would have a vaccine within two years, and we are now 30 years later," she said.

"We should move on from this. We will need to collaborate and combine different approaches to HIV - work on cures as well as therapies, prevention and vaccines – and strengthen the relationship between researchers to continue to make progress in tackling HIV."

Source - OI/Guardian