A little over a century ago, chemists first tagged a small methyl group onto a building block of DNA, and generations later that quiet chemical mark has become a way for the body to decide which of its inscriptions to read and which to leave dormant. Now researchers have borrowed that old language to address hepatitis B, a virus that can hide in liver cells for decades. Their experimental therapy, CRMA-1001, does not chase the virus directly but instead teaches the viral DNA to fall silent, and in mice this has produced lasting suppression. Whether that stillness holds in people, for years rat
Gene Therapy Mutes Hepatitis B's Hidden DNA, Offering a Path Toward Functional Cure
Instead of fighting the threat, the cell ignores it.
Mark
Why does it matter that this silences the DNA rather than killing the virus?
Mimi
Because the viral DNA is what current treatments rarely clear. It sits in liver cells for years, and that leftover DNA is how the virus rebounds.
Mark
So the approach goes after the reservoir itself.
Mimi
In a sense, yes, but it doesn't remove it. It adds methyl tags so the genes stay off.
Luke
Worth saying plainly: the results are in mice. Nothing in this reporting shows it works in people.
Mark
What did the mice show?
Mimi
One dose lowered viral DNA, HBsAg and HBeAg. Three doses, a month apart, left as many as 90% of animals with viral DNA below detectable levels at six months.
Luke
And that 90% is the authors' own reported figure, with the claim that the therapy silences the DNA also coming from them. Undetectable isn't gone, either.
Mark
And the mRNA delivery?
Mimi
It makes the effect temporary in the cell. The proteins are made, then degraded, so the machinery doesn't linger.
Luke
The open question is durability. Six months is what was observed; whether the virus reactivates after that is unknown. The phase I/II trial is meant to probe it.
O Pulso
- Hepatitis B can lie dormant in liver cells for decades, and current treatments rarely remove the viral DNA, leaving it free to rebound.
- CRMA-1001 pairs a CRISPR-Cas9 locator with methylation machinery, quietly switching off viral DNA rather than attacking it head-on.
- In mice, three doses left as many as 90% of animals with less detectable viral DNA six months later, a functional cure rather than full elimination.
- Whether silencing endures for years and whether the virus can reawaken are still unanswered, and an ongoing phase I/II human trial is working to find out.
A little over a century ago, chemists first tagged a small methyl group onto a building block of DNA, and generations later that quiet chemical mark has become a way for the body to decide which of its inscriptions to read and which to leave dormant. Now researchers have borrowed that old language to address hepatitis B, a virus that can hide in liver cells for decades. Their experimental therapy, CRMA-1001, does not chase the virus directly but instead teaches the viral DNA to fall silent, and in mice this has produced lasting suppression. Whether that stillness holds in people, for years rather than months, remains the open question that a human trial now seeks to answer.
In 1904, two chemists added a small methyl group to a building block of DNA, never imagining it would one day matter to a virus. Decades later, scientists discovered that this chemical tag helps cells decide which genes to switch on and which to keep quiet, a system that explains how a liver cell and a brain cell can share the same genes yet become entirely different. That quiet system is now being turned against hepatitis B.
The hepatitis B virus often settles into liver cells and waits. Its DNA can stay present but silent for years, hidden from the immune system, and then awaken. Most treatments hold the virus at bay without removing that DNA, which is why relapse is so common. Researchers reporting in Nature Biomedical Engineering have built CRMA-1001, a therapy that uses a CRISPR-Cas9 guide to find a specific stretch of viral DNA and then adds methyl marks that silence it. Delivered through a transient mRNA platform, the instructions fade once their work is done.
In mice, a single dose reduced several viral markers and left new methyl marks on the viral DNA, a sign the design worked as intended. Three doses went further: six months on, as many as 90% of the animals had viral DNA too scarce to detect. This is not a cure in the strict sense, because the DNA remains in the liver, but it may be a functional cure, with the virus so quiet that it causes no visible harm. Whether that silence lasts and whether the virus can ever stir again are questions only a human trial can answer, and that trial is now under way.
In 1904, two chemists, Henry Wheeler and Treat Johnson, made a variant of cytosine in their laboratory, one of the building blocks of DNA. They attached a methyl group (-CH3) to it and called the result 5-methylcytosine. They had a reason: two other building blocks, thymine and uracil, differ from each other only by a methyl group, so they guessed a methylated cytosine might also turn up in nature.
It did. In 1925 Johnson, working with Robert Coghill, found 5-methylcytosine in the DNA of the bacterium that causes tuberculosis. About two decades later Rollin Hotchkiss found it in the DNA of cows, and it was soon seen in nearly all animals. What nobody could explain was why some cytosines carried the tag and others did not.
The answer came in 1975, when Robin Holliday and John Pugh proposed that methylation was a way for the body to use the information stored in DNA. Every cell holds the full set of genes, each carrying instructions for a particular protein, yet cells specialise. A brain cell has no use for the proteins that digest food. Holliday and Pugh suggested that chemical tags like methylation help establish and activate the genes a cell wants and silence the ones it does not. The idea came to be called epigenetics, a term the British biologist Conrad Waddington had coined in 1942. Enzymes that add and remove such tags were found soon afterward. Cells also use other marks, both on DNA and on the proteins around which it is wound like a vine around a stick. Faults in this system can change gene activity and lead to diseases such as cancers.
A paper published in Nature Biomedical Engineering on September 21 now reports using that control against hepatitis B. Rather than attacking the virus, the work silenced its DNA. That matters because current treatments rarely remove the viral DNA, which lets the virus rebound. Silencing that residue could offer a route to a lasting functional cure.
The hepatitis B virus mainly infects liver cells, where its DNA serves as the template for new viral particles. In many people the immune system clears the infection. When it does not, the viral DNA can persist in the liver for years or decades. It can stay silent, present but not producing virus, which hides it from the immune system, and later it can reactivate. Studies have shown that one way the virus stays quiet is through methylated cytosines.
The authors report an experimental therapy, CRMA-1001, which they claim silences the viral DNA by selectively adding methylation marks to the viral genome. They had to meet three challenges: target viral DNA without methylating the host's cytosines, switch the viral DNA off effectively, and avoid unwanted side effects. For the first two, they paired a locator with an effector. The locator uses the CRISPR-Cas9 tool to find and bind a specific sequence within the viral DNA, carrying the effector to the right spot. The effector includes proteins that add methyl groups to nearby cytosines and proteins that help switch genes off. The whole system is delivered on an mRNA platform, similar to the COVID-19 mRNA vaccines, so it is transient: once a cell has read the instructions and made the proteins, it degrades them and production stops.
Mice infected with hepatitis B received either one dose or three doses a month apart, and were tested regularly for six months. After one dose, several viral markers, including viral DNA and the proteins HBsAg and HBeAg, fell significantly, and the viral DNA showed new methyl groups, suggesting the treatment worked as intended. Three doses did better: six months after the first dose, as many as 90% of the animals had less viral DNA than could be detected.
This is not a cure in the traditional sense, since the viral DNA remains in liver cells. It is a functional cure, with the virus so thoroughly suppressed that there are no active signs of disease. The six-month follow-up showed sustained suppression, but it could not settle whether the virus might reactivate afterward. Questions about whether silencing lasts for years, and whether the virus can ever become active again, are among those an ongoing phase I/II clinical trial is examining. If CRMA-1001 reaches the market, it would be a new way to handle a viral infection: the cell ignores the threat instead of fighting it.
Citações Notáveis
The study did not establish whether the virus could become active again after six months, since the viral DNA is still present.— The Hindu's reporting on the study
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