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
On Rare Disease Day 2019, I got to join Patricia Weltin, founder of Beyond the Diagnosis, Pawtucket. RI, to unveil this portrait of Amber. She was born with the rare Giant Axonal Neuropathy. This portrait was part of a larger exhibit, sponsored by Beyond the Diagnosis, that features kids and young adults with genetic disorders and other rare diseases. Each portrait was beautiful and inspiring in portraying the reality of these kids. That is, none are defined by their diagnoses. All have a beauty in every sense of the word. The unveiling was held at NIH on February 28. Credit: NIH
For almost four decades, researchers have worked tirelessly to find a cure for the human immunodeficiency virus (HIV), which causes AIDS. There’s still more work to do, but a recent commentary published in JAMA [1] by Anthony Fauci, director of NIH’s National Institute of Allergy and Infectious Diseases, and his colleagues serves as a reminder of just how far we’ve come. Today, thanks to scientific advances, especially the development of effective antiretroviral therapy (ART), most people living with HIV can live full and productive lives. These developments have started to change how our society views HIV infection.
In their commentary, the NIH scientists describe the painstaking research that has now firmly established that people who take ART daily as prescribed, and who achieve and maintain an undetectable viral load (the amount of HIV in the blood), cannot sexually transmit the virus to others. To put it simply: Undetectable = Untransmittable (U=U).
The U=U message was introduced in 2016 by the Prevention Access Campaign, an international health equity initiative that aims to help end the HIV epidemic and HIV-related social stigma. The major breakthrough in combination ART regimens, which successfully reduced viral loads for many HIV patients, came over 20 years ago. But their importance for HIV prevention wasn’t immediately apparent.
There’d been some hints of U=U, but it was the results of the NIH-funded HIV Prevention Trials Network (HPTN) 052, published in The New England Journal of Medicine [2] in 2011, that offered the first rigorous clinical evidence. Among heterosexual couples in the randomized clinical trial, no HIV transmissions to an uninfected partner were observed when ART consistently, durably suppressed the virus in the partner living with HIV.
The data provided convincing evidence that ART not only treats HIV but also prevents the sexual transmission of HIV infection. The public health implications of what’s sometimes referred to as “treatment as prevention” were obvious and exciting. In fact, the discovery made Science’s 2011 list of top 10 Breakthroughs of the Year .
Three subsequent studies, known as PARTNER 1 and 2 and Opposites Attract, confirmed and extended the findings of the HPTN 052 study. All three showed that people with HIV taking ART, who had undetectable HIV levels in their blood, had essentially no risk of passing the virus on to their HIV-negative partners.
Of course, the success of U=U depends on people with HIV having the needed access to health care and taking their medications as prescribed every day of their lives [3]. ART works by preventing the virus from making more copies of itself. It’s important to note that achieving an undetectable viral load with treatment can take time—up to 6 months. Viral load testing should be performed on a regular basis to ensure that the virus remains at undetectable levels. If treatment is stopped, the virus typically rebounds within a matter of weeks. So, strict adherence to ART over the long term is absolutely essential.
Practically speaking, though, ART alone won’t be enough to end the spread of HIV, and other methods of HIV prevention are still needed. In fact, we’re now at a critical juncture in HIV research as work continues on preventive vaccines that could one day bring about a durable end to the pandemic.
But for now, there are more than 35 million people worldwide who are HIV positive [4]. With currently available interventions, experts have predicted that about 50 million people around the world will become HIV positive from 2015 to 2035 [5]. Work is proceeding actively on the vaccine, and also on ways to totally eradicate the virus from infected individuals (a “cure”), but that is proving to be extremely challenging.
Meanwhile, with continued advances, including improved accessibility to testing, adherence to existing medications, and use of pre-exposure prophylaxis (PrEP) in high risk individuals, the goal is to reduce greatly the number of new cases of HIV/AIDS.
Credit: Oka lab, California Institute of Technology, Pasadena
Whether it’s Rockefeller Center, the White House, or somewhere else across the land, ‘tis the season to gather with neighbors for a communal holiday tree-lighting ceremony. But this festive image has more do with those cups of cider in everyone’s hands than admiring the perfect Douglas fir. What looks like lights and branches are actually components of a high-resolution map from a part of the brain that controls thirst.
The map, drawn up from mouse studies, shows that when thirst arises, neurons activate a gene called c-fos (red)—lighting up the tree—indicating it’s time for a drink. In response, other neurons (green) direct additional parts of the brain to compensate by managing internal water levels. In a mouse that’s no longer thirsty, the tree would look almost all green.
This wiring map comes from a part of the brain called the hypothalamus, which is best known for its role in hunger, thirst, and energy balance. Thanks to powerful molecular tools from NIH’s Brain Research through Advancing Innovative Technologies (BRAIN) Initiative, Yuki Oka of the California Institute of Technology, Pasadena, and his team were able to draw detailed maps of the tree-shaped region, called the median preoptic nucleus (MnPO).
Using a technique called optogenetics, Oka’s team, led by Vineet Augustine, could selectively turn on genes in the MnPO [1]. By doing so, they could control a mouse’s thirst and trace the precise control pathways responsible for drinking or not.
This holiday season, as you gather with loved ones, take a moment to savor the beautiful complexity of biology and the gift of human health. Happy holidays to all of you, and peace and joy into the new year!
Credit: Simone Köhler, Michal Wojcik, Ke Xu, and Abby Dernburg, University of California, Berkeley
Meiosis—the formation of egg and sperm cells—is a highly choreographed process that creates genetic diversity in all plants and animals, including humans, to make each of us unique. This kaleidoscopic image shows cells from a worm exchanging DNA during meiosis.
You can see a protein-based polymer tether (green) from what’s called the synaptonemal complex. The complex holds together partner chromosomes (magenta) to facilitate DNA exchange in nuclei (white). Moving from left to right are views of the molecular assembly that progressively zoom in on the DNA, revealing in exquisite detail (far right) the two paired partner chromosomes perfectly aligned. This is not just the familiar DNA double helix. This is a double helix made up of two double helices!
