The genetic code of life, DNA, is composed of a string of 4 chemical bases called nucleotides. A molecule called RNA polymerase reads this string and transcribes it into instructions, like a chef reading a recipe for a dish. Sometimes, mistakes occur while DNA is being copied. These mistakes are called mutations, and they can turn off important genes and cause diseases. Few successful patient-specific treatments are currently available to treat diseases on a genetic level, but recent innovations in medical technology at Penn Medicine could change that.
An infant patient, designated baby KJ, was born with a potentially fatal liver disease known as carbamoyl phosphate synthetase 1 deficiency or CPS-1 deficiency. The bodies of people with a deficient CPS-1 gene cannot remove the toxic chemical ammonia, which is produced when proteins are digested.
The CPS-1 deficiency disorder emerges when a baby is born with 2 defective copies of the CPS-1 gene, one inherited from each parent. Patients with this condition only have a 50% chance of surviving infancy, and are generally treated with low-protein diets, medications, and, as a last resort, liver transplants – an option not available for baby KJ.
At Penn Medicine, scientists recently used a DNA-editing technology called CRISPR to modify KJ’s genes. CRISPR can alter the DNA code in our cells through a chemical process that changes specific nucleotides at the molecular level, known as base editing. Using molecules that guide the CRISPR protein to the correct location, known as guide RNA, the researchers used a trial-and-error approach to find the right combination to replace the incorrect nucleotide with the correct one, successfully turning the CPS-1 gene back on.
The team delivered the CRISPR treatment using small particles, referred to as Liquid Nanoparticles or LNPs, containing chemical messengers that translate DNA instructions, called mRNA. LNPs can deliver genetic instructions for the treatment safely through a patient’s bloodstream to any organ, in this case, the liver, where they release the CRISPR editor. The mRNA then targets the patient’s liver cells in an attempt to fix their CPS-1 deficiency.
Researchers at Penn Medicine developed this treatment within baby KJ’s first 6 months of life. To begin, they took samples of KJ’s cells to a lab, injected them into lab-grown liver cells, and then into 6 live, healthy mice to test whether the editing technology worked.
The team was concerned about the potential for CRISPR to accidentally change the wrong DNA base, thus altering a different gene than they intended. This issue is known as off-target editing, so they tested for its effects in the injected mice. They reported that the mice experienced no serious adverse events after being injected, suggesting that the treatment was safe and shouldn’t cause off-target effects in KJ either.
Next, the team administered 2 rounds of CRISPR treatment to KJ at 7 and 8 months old. After the first round of treatment, the baby was able to digest protein but still didn’t have a fully functioning liver, so the team administered a second round. In the 7 weeks after the first round, KJ was able to consume more dietary protein and take a second dose of medication without serious side effects.
The team continued to monitor the baby’s health after the second round of treatment by taking blood samples over the next few months. They found the baby’s blood ammonia levels remained stable – a sign that his liver function and metabolism were improving.
The team concluded that the CRISPR gene-editing method effectively improved KJ’s metabolism, but cautioned that it was not a full cure. They stated that future researchers should determine the fraction of the patient’s liver cells that were actually corrected. Like any emerging treatment, long-term follow-up of the patient is also necessary to assess how well it worked. Furthermore, gene therapies don’t always work the same in different patients. Regardless, they suggested that this treatment’s success could pave the way for more customized gene therapy in the future, providing a method of medicine more precise to a patient’s needs and background.
