A non-cutting CRISPR epigenetic editor durably silenced hepatitis B virus in mice and human liver cells. The first patient has now received the therapy
A non-cutting CRISPR epigenetic editor durably silenced hepatitis B virus in mice and human liver cells. The first patient has now received the therapy
nChroma Bio and the San Raffaele Telethon Institute for Gene Therapy in Milan presented CRMA-1001, a therapy that uses CRISPR-Cas9 without DNA-cutting activity to add methylation marks to hepatitis B virus DNA and silence its genes. After three doses, the virus was undetectable in 90% of mice by six months, and testing in human cells from nine donors found no off-target effects.
Chronic hepatitis B affects about 250 million people and causes more than a million deaths each year from cirrhosis and liver cancer. The virus persists in liver cells in two forms: free circular DNA, which virologist Fabien Zoulim of the University of Lyon calls the virus's “genomic archive,” and fragments integrated into the cell's own DNA. Both forms produce HBsAg, a viral protein that suppresses the immune response to the infection. Current drugs suppress viral replication but almost never eliminate the virus: fewer than 10% of patients treated for ten years can stop taking medication without risking a relapse.
DNA-cutting approaches to editing are particularly risky in hepatitis B: a cut near an integrated fragment of viral DNA can generate new integrations or active copies of viral DNA, potentially recreating the problem the treatment is meant to solve. RNA-silencing drugs avoid this risk, but they work only while they remain in the cell, and their effects wear off after treatment stops. On September 21, nChroma Bio presented a third approach: CRMA-1001 combines Cas9 without DNA-cutting activity with a gene-silencing domain and an enzyme that adds methylation marks to DNA. This switches the gene off without breaking the DNA strand or requiring continuous treatment. A guide RNA directs the complex to its target sequence; the researchers screened 121 candidates and selected one targeting a sequence conserved in 94% of strains.
Before testing the construct against hepatitis B, the researchers optimized it using PCSK9, the same gene targeted by rival Scribe Therapeutics' non-cutting editor STX-1150, previously covered by Ukhvat. PCSK9 served as an internal benchmark for potency: each round of protein engineering increased gene silencing by 2–3 times, and the best version maintained its effect in primates for two years. The researchers then adapted it to hepatitis B, where silencing increased by almost another 20 times.
In mice with chronic infection, a single dose reduced HBsAg levels by several hundred times for seven months. In a more severe model with free circular viral DNA, it reduced HBsAg levels by almost 2500 times and viral DNA levels by 200 times. Three monthly doses strengthened the effect, leaving the virus undetectable in the 90% of animals mentioned above. In infected human liver cells, treatment reduced both viral proteins by 98%.
In cynomolgus macaques, a single dose was distributed mainly to the liver and spleen and was undetectable in germ cells. Liver enzyme levels rose temporarily only at the highest dose and returned to normal within a month.
In January, the first participant in a trial being conducted in Hong Kong and New Zealand received CRMA-1001 by intravenous infusion. “This is really impressive,” says John Tavis, a virologist at Saint Louis University, referring to the single injection. “This is exactly the direction we need to take to tackle the hepatitis B pandemic worldwide.” Co-author Angelo Lombardo is a co-founder of nChroma Bio and a researcher at the San Raffaele Telethon Institute for Gene Therapy, which in 2016 became the first institution in Europe to obtain approval for a stem cell gene therapy. Lombardo describes the move into human trials as “a huge step” and “the culmination of many years of work.”