Healing HIV has become even more complicated. Can CRISPR help? | Science

SEATTLE, WASHINGTON-Antiretroviral drugs (ARVs) have turned HIV infection from the death penalty into chronic disease. In most people, drugs regularly buffer HIV levels so low that standard tests do not detect any viruses in blood samples. But inexplicably, in about 10% of those infected, HIV remains easily detectable in the blood, even if they take their daily pills and are not clogged with drug-resistant virus mutants.

A study presented last week at the largest American conference on HIV / AIDS offers a solution to this puzzle: "repliclones", replicating cell populations containing the HIV genome. "This is the most interesting presentation I've seen here," says Dr. George Pavlakis, retrovirologist at the National Cancer Institute in Frederick, Maryland.

These replicas point to what could be a serious gap in a popular HIV treatment strategy. They also draw attention to a radical approach to rooting out the persistent virus: using the CRISPR genome editor to remove HIV genes from infected cells. A monkey study on the approach presented at the same meeting showed signs of success, and a biotech company is now hoping to launch a clinical trial.

People infected with HIV who still have small amounts of virus in their blood despite antiretroviral therapy (ARVs) leave doctors "maddened," says virologist John Mellors of the University of Pittsburgh, Pennsylvania. Assuming that the virus has acquired resistance, they often change the treatment regimen of their patients and order many additional tests. "Each of these creates anxiety and new side effects," says Mellors. In addition, these people can still have a viral load high enough to infect others.

At the Conference on Retroviruses and Opportunistic Infections, virologist Elias Halvas, who works at Mellors' lab, described a careful badysis of viral isolates and blood cells from eight men and one woman suffering from the disease. a mysterious and persistent persistent viremia for 3 years despite ARVs. Halvas and his colleagues noticed something curious. Normally, whenever HIV infects a cell, the virus copies the genome of its RNA into a version of the DNA that integrates into a new location among the chromosomes of the cell. But in each of these patients, all their infected cells had HIV integrated into the same chromosomal region – a different location from one person to the next. The sequence of HIV DNA taken from different cells of the same person was also identical.

Researchers have long known that HIV can reproduce in two ways. In the basic replication cycle, HIV DNA embedded in a chromosome creates new virions that grow from that cell and then infect other cells by acquiring mutations each time. ARVs block several steps in this process.

In the second pathway, HIV is essentially unscathed because it infects an immune cell that clones itself, producing more cells that carry the viral genome. ARVs have no impact on this scenario and viral DNA is found at the same chromosomal location in all progeny cells, without acquiring new mutations. These clones can produce new virions themselves, but ARVs taken by patients derail new infections. The Mellors team has shown that this path alone explains the low but persistent viral loads in these patients.

Daniel Kuritzkes, an HIV / AIDS clinician at Brigham and Women's Hospital in Boston, says new data suggests doctors should not worry about low virus rates in patients who say they adhere treatment and no obvious immune damage. "It is safe to badume that in the absence of increasing viremia, it is not necessary to change [ARVs], "Says Kuritzkes, whose own lab reported a similar finding when examining a single patient.

The discovery, however, casts doubt on the proposed approach to cure an infection: "kicking" cells that harbor HIV DNA in a latent, non-replicative form, in order to extract new copies of the virus and to destroy himself. These replicons spit virions but, for some reason, they do not self-destruct quickly and are not eliminated by immune responses, says Mellors. So something more is needed to kill them. "If we can not eliminate these people with our therapies, then killing and killing will not work," he says.

But another approach could: directly extract persistent HIV DNA from a person's chromosomes with the CRISPR genome editor. "It's a science fiction idea that a day may be possible," says Pavlakis. Currently, he says, the risks are too high that CRISPR's Cas9 enzyme cuts in the wrong place and directing the editor to the appropriate cells is not easy. "CRISPR is not here yet," he says.

At the meeting, neurovirologist Tricia Burdo of Temple University in Philadelphia, Pennsylvania, described a first step: using the editor to extract at least a portion of the simian version of the AIDS virus, SIV, chromosomes of two monkeys. Previous work has shown that CRISPR can excise HIV nested inside mouse cells designed to have an immune system to the human image. In this new study, the researchers infused a harmless, adeno-badociated virus carrying the CRISPR targeted molecular scissor genes into the veins of two SIV-infected monkeys. The monkeys were on ARVs and had low levels of SIV.

Necropsies of the treated animals showed that CRISPR had cut SIV DNA into blood, spleen, lymph node and lung cells, which apparently deactivated the virus. The blood of the CRISPR'd monkeys can not infect white blood cells, unlike the blood of a control animal. The group also discovered the presence of Cas9 in the 14 tissues studied, suggesting that the virus was transmitted as expected. "The data shows much greater effects than before, so it's a step in the right direction," says John Coffin, a retrovirologist in a branch of Tufts University in Boston.

Burdo says that in a future experiment, his team will remove ARVs from the monkey treated by CRISPR to see if the virus is bouncing back. They also plan to transfer millions of blood cells from CRISPR-treated monkeys to uninfected animals, another sensitive way to determine whether even traces of intact SIV remain hidden.

Burdo collaborator, Temple University neurovirologist Kamel Khalili, hopes to develop a human version of this CRISPR gene therapy. Khalili announced that its company, Excision BioTherapeutics, based in Philadelphia, was seeking permission to launch clinical trials on CRISPR excision of HIV in humans by the end of the year. l & # 39; year.

Some remain skeptical CRISPR could ever hit all HIV-infected cells. Douglas Richman, a virologist at the University of California at San Diego, notes that even a person with undetectable viral load can have as many as 100 million cells containing HIV DNA. "The problem with all healing interventions is that they impact a few cells," says Richman. "It still leaves a huge amount of virus. And when you eliminate something dangerous, you must have them all. "