Researchers are working on the use of red blood cells engineered to act as drug manufactories, a way to deliver sustained doses of a therapy to patients while circumventing some of the challenges inherent in other delivery methods:
The new technology draws on recent advances in the ability to genetically modify and grow human red blood cells from stem cells in culture. Using established molecular biology techniques, scientists can engineer progenitor cells taken from human bone marrow and grow blood cells that produce specific therapeutic proteins on their surface or inside the cell. Before they become fully mature, mammalian red blood cells eject their genetic material, so as a therapy they are easier to control and less risky than other stem cell and gene therapies, which can lead to abnormal cell growth and tumors. Human red blood cells circulate for as long as four months, meaning they could potentially form the basis of long-term therapies. The cells can get anywhere in the body through the bloodstream and can protect the therapeutic agent from the immune system.
The first drug will be for phenylketonuria, or PKU, a devastating genetic disorder that renders people with the disease unable to digest the amino acid phenylalanine, which is found in most high-protein foods. Researchers have so far tested the PKU drug in animals and in human blood in the lab, and it aims to begin clinical testing next year. Researchers have identified enzymes that can break down phenylalanine, "but you can't just inject an enzyme into the bloodstream," because the body will clear it quickly, and it could induce an immune reaction that would render future treatments with the same enzyme useless. Engineering red blood cells to produce the desired enzyme "answers both problems."
Animal tests suggest that engineered red blood cells can be a "very potent" therapy for a range of diseases. Not-yet-published work has shown that cells modified to produce an antibody to a specific bacterial toxin render mice resistant to many times the lethal dose of that toxin. It takes only a few weeks to grow cells that produce a new protein of interest, and the potential for new drugs based on red blood cells is "only limited by your imagination."