In a proof-of-principle study, researchers have designed a means of delivering mRNA directly to bone marrow cells to treat disease and, potentially, avoid the need for depletion chemotherapy. A Children's Hospital of Philadelphia-led team developed a lipid nanoparticle to carry mRNA-altering tools and specially targeted those lipid nanoparticles to hematopoietic stem cells by decorating them with antibodies that recognize CD117 found on their surfaces. As they report in Science, the researchers applied this approach to mice to show their system in vivo before then using it to deliver mRNA encoding a Cas9 adenine base editor and guide RNA targeting the β-globin sickle cell mutation in vitro to hematopoietic stem cells obtained from four individuals with the condition. This, they report, led to a nearly 92 percent increase in functional hemoglobin. They additionally used their approach to deliver mRNA encoding PUMA, a protein that promotes cell death, to show that it could be used instead of chemotherapy to prepare bone marrow for the engraftment of new cells. "Targeted delivery of mRNA-encoded therapeutics to specific tissues and cell types will have an immense impact on the way diseases will be treated with nucleic acids in the future," senior author Hamideh Parhiz from Penn says in a statement.