Today, thanks to remarkable advances in antiretroviral drugs, most people with the human immunodeficiency virus (HIV) can expect to live an almost normal lifespan. But that means staying on medications for life. If those are stopped, HIV comes roaring back in just weeks. Finding a permanent cure for HIV infection, where the virus is completely and permanently eliminated from the body, has proven much tougher. So, I’m encouraged by recent work that shows it may be possible to eliminate HIV in a mouse model, and perhaps—with continued progress—someday we will actually cure HIV in humans.
This innovative approach relies on a one-two punch: drugs and genetic editing. First, HIV-infected mice received an experimental, long-acting form of antiretroviral therapy (ART) that suppresses viral replication. This step cleared the active HIV infection. But more was needed because HIV can “hide” by inserting its DNA into its host’s chromosomes—lying dormant until conditions are right for viral replication. To get at this infectious reservoir, researchers infused the mice with a gene-editing system designed to snip out any HIV DNA still lurking in the genomes of their spleen, bone marrow, lymph nodes, and other cells. The result? Researchers detected no signs of HIV in more than one-third of mice that received the combination treatment.
The new study in Nature Communications is the product of a collaboration between the NIH-funded labs of Howard Gendelman, University of Nebraska Medical Center, Omaha, and Kamel Khalili, Temple University, Philadelphia [1]. A virologist by training, Khalili years ago realized that HIV’s ability to integrate into the genomes of its host’s cells meant that the disease couldn’t be thought of only as a typical viral infection. It had a genetic component too, suggesting that an HIV cure might require a genetic answer.
At the time, however, the tools to remove HIV DNA from human cells without harming the human genome weren’t available. That’s changed in recent years with the discovery and subsequent development of a very precise gene-editing tool known as CRISPR/Cas9.
CRISPR/Cas9 editing systems rely on a sequence-specific guide RNA to direct a scissor-like, bacterial enzyme (Cas9) to just the right spot in the genome, where it can be used to cut out, replace, or repair disease-causing mutations. Efforts are underway to apply CRISPR/Cas9 to the treatment of sickle cell disease, muscular dystrophy, and more.
Could CRISPR/Cas9 also remove HIV DNA from infected cells and eliminate the infection for good? Such an approach might be particularly helpful for people on ART who have persistent HIV DNA in the cells of their cerebrospinal fluid. A recent NIH-funded study in Journal of Clinical Investigation found that an association between this HIV reservoir and neurocognitive difficulties [2]
Earlier work by Khalili’s team showed that CRISPR could indeed remove HIV DNA from the genomes of host cells [3]. The problem was that, when delivered on its own, CRISPR couldn’t snip out every last bit of viral DNA from all cells as needed to get rid of HIV completely and permanently. It was crucial to reduce the burden of HIV genomes to the lowest possible level.
Meanwhile, Gendelman’s lab had been working to develop a new and more effective way to deliver ART. Often delivered in combinations, standard ART drugs are effective in suppressing HIV replication. However, people need to take their oral medications daily without fail. Also, most ART triple therapy drugs are water soluble, which means its cocktail of medications are swiftly processed and excreted by the body without reaching many places in the body where HIV hides.
In his quest to make ART work more effectively with fewer doses, Gendelman’s team altered the chemical composition of antiretroviral medicines, generating fat-soluble drug nanocrystals. The nanocrystals were then packaged into nanoparticles and delivered by intramuscular injection. The new drug formulation, known as long-acting slow-effective release (LASER) ART, reaches lymph nodes, spleen, gut, and brain tissues where HIV lurks [4]. Once there, it’s stored and released slowly over time. Still, like conventional ART, LASER ART can never completely cure HIV.
So, Gendelman teamed up with Khalili to ask: What would happen if LASER ART was followed by a round of CRISPR/Cas9? In a series of studies, the researchers tested LASER ART and CRISPR/Cas9, both alone and in combination. A total of 23 HIV-infected mice engineered to have some “humanized” immune features received the experimental combination therapy.
As expected, neither LASER ART nor CRISPR/Cas9 by itself proved sufficient to eradicate HIV in the mice. However, when LASER ART and CRISPR/Cas9 were delivered sequentially, the results were much different. Researchers found no evidence of HIV in the spleens or other tissues of more than one-third of the sequentially treated animals.
It’s important to note that this gene-editing approach to eradicating HIV is being applied to non-reproductive cells (somatic). The NIH does not support the use of gene-editing technologies in human embryos (germline) [5].
Of course, mice, even with humanized immune systems, are not humans. More research is needed to replicate these findings and to figure out how to make this approach to HIV treatment more effective in animal models before we can consider moving into human clinical trials. Still, these findings do provide a new reason for increased hope that an actual cure may ultimately be found for the tens of millions of people in the United States and around the globe now living with HIV.
References:
[1] Sequential LASER ART and CRISPR Treatments Eliminate HIV-1 in a Subset of Infected Humanized Mice. Dash PK, Kaminski R, Bella R, Su H, Mathews S, Ahooyi TM, Chen C, Mancuso P, Sariyer R, Ferrante P, Donadoni M, Robinson JA, Sillman B, Lin Z, Hilaire JR, Banoub M, Elango M, Gautam N, Mosley RL, Poluektova LY, McMillan J, Bade AN, Gorantla S, Sariyer IK, Burdo TH, Young WB, Amini S, Gordon J, Jacobson JM, Edagwa B, Khalili K, Gendelman HE. Nat Commun. 2019 Jul 2;10(1):2753.
[2] Spudich S et al. Persistent HIV-infected Cells in Cerebrospinal Fluid are Associated with Poorer Neurocognitive Performance. J Clin Invest. 2019. DOI: 10.1172/JCI127413 (2019).
NIH Support: National Institute of Mental Health; National Institute of Neurological Disorders and Stroke; National Institute of Allergy and Infectious Diseases; National Institute on Aging; National Institute on Drug Abuse; Common Fund
Adapted from Ogrodnik et al., 2019, Cell Metabolism.
Obesity—which affects about 4 in 10 U.S. adults—increases the risk for lots of human health problems: diabetes, heart disease, certain cancers, and even anxiety and depression [1]. It’s also been associated with increased accumulation of senescent cells, which are older cells that resist death even as they lose the ability to grow and divide.
Now, NIH-funded researchers have found that when lean mice are fed a high-fat diet that makes them obese, they also have more senescent cells in their brain and show more anxious behaviors [2]. The researchers could reduce this obesity-driven anxiety using so-called senolytic drugs that cleared away the senescent cells. These findings are among the first to provide proof-of-concept that senolytics may offer a new avenue for treating an array of neuropsychiatric disorders, in addition to many other chronic conditions.
As we age, senescent cells accumulate in many parts of the body [3]. But cells can also enter a senescent state at any point in life in response to major stresses, such as DNA damage or chronic infection. Studies suggest that having lots of senescent cells around, especially later in life, is associated with a wide variety of chronic conditions, including osteoporosis, osteoarthritis, vascular disease, and general frailty.
Senescent cells display a “zombie”-like behavior known as a senescence-associated secretory phenotype (SASP). In this death-defying, zombie-like state, the cells ramp up their release of proteins, bioactive lipids, DNA, and other factors that, like a zombie virus, induce nearby healthy cells to join in the dysfunction.
In fact, the team behind this latest study, led by James Kirkland, Mayo Clinic, Rochester, MN, recently showed that transplanting small numbers of senescent cells into young mice is enough to cause them weakness, frailty, and persistent health problems. Those ill effects were alleviated with a senolytic cocktail, including dasatinib (a leukemia drug) and quercetin (a plant compound). This drug cocktail overrode the zombie-like SASP phenotype and forced the senescent cells to undergo programmed cell death and finally die.
Previous research indicates that senescent cells also accumulate in obesity, and not just in adipose tissues. Moreover, recent studies have linked senescent cells in the brain to neurodegenerative conditions, including Alzheimer’s disease, and showed in mice that dasatinib and quercetin helps to alleviate neurodegenerative disease [4,5]. In the latest paper, published in the journal Cell Metabolism, Kirkland and colleagues asked whether senescent cells in the brain also could explain anxiety-like behavior in obesity.
The answer appears to be “yes.” The researchers showed that lean mice, if allowed to feast on a high-fat diet, grew obese and became more anxious about exploring open spaces and elevated mazes.
The researchers also found that the obese mice had an increase in senescent cells in the white matter near the lateral ventricle, a part of the brain that offers a pathway for cerebrospinal fluid. Those senescent cells also contained an excessive amount of fat. Could senolytic drugs clear those cells and make the obesity-related anxiety go away?
To find out, the researchers treated lean and obese mice with a senolytic drug for 10 weeks. The treatment didn’t lead to any changes in body weight. But, as senescent cells were cleared from their brains, the obese mice showed a significant reduction in their anxiety-related behavior. They lost their anxiety without losing the weight!
More preclinical study is needed to understand more precisely how the treatment works. But, it’s worth noting that clinical trials testing a variety of senolytic drugs are already underway for many conditions associated with senescent cells, including chronic kidney disease [6,7], frailty [8], and premature aging associated with bone marrow transplant [9].
As a matter of fact, just after the Cell Metabolism paper came out, Kirkland’s team published encouraging though preliminary, first-in-human results of the previously mentioned senolytic drug dasatinib in 14 people with age-related idiopathic pulmonary fibrosis, a condition in which lung tissue becomes damaged and scarred [10]. Caution is warranted as we learn more about the associated risks and benefits, but it’s safe to say we’ll be hearing a lot more about senolytics in the years ahead.
