Messenger RNA (mRNA) can be delivered into tissues and cells by encapsulating it into lipid nanoparticles (LNPs), and then injecting the nanoparticles. A target cell engulfs a LNP, and the cargo of mRNA is released into the cytoplasm where it is translated into protein. Typically a protein is manufactured in cells exposed to a LNP-mRNA therapy for a few days only before the last of the delivered mRNA is broken down and recycled, so the end result might be considered a half-way point between the characteristics of a gene therapy and the characteristics of a small molecule drug: a treatment that produces a protein of interest to cause specific desired outcomes in cell behavior, but that only lasts a little while.
The lipid nanoparticle industry looks today much like the viral vector industry did a decade ago. A great deal of research and early stage development of therapeutics is taking place, a great deal of invention, but much of the intellectual property remains locked down and either impossible or very expensive to use in a commercial product. To date only a small number of specific lipid nanoparticle formulations with a small number of different delivery characteristics have made it into clinical trials or become approved drugs. Many very interesting technology demonstrations in animal studies are taking place, however.
Today's open access paper is an example of one of the areas in which LNP-mRNA therapies may really shine, which is to take the concept of chimeric antigen receptor (CAR) cell therapies, and make them affordable. Delivery of a CAR T cell therapy involves taking a patient's cells, engineering them to express the desired CAR, growing their numbers in culture, and then returning the cells to the patient. The artificial receptor steers the T cells towards desired targets, such as cancer cells, and has proven quite effective in treating a number of different forms of cancer. Sadly it is enormously expensive as a mode of therapy, due to the time and complexity required to manufacture each patient-specific batch. LNP-mRNA that can turn native cells into CAR T cells (or in this case CAR natural killer cells) for a short while will be both much less costly and more controllable.
Reprogrammed NK immune cells target cancer and autoimmune disorders
Over the past decade, the U.S. Food and Drug Administration has approved seven new cancer treatments based on engineered T cells called chimeric antigen receptor (CAR) T cells. Chimeric antigen receptors are proteins that can be embedded into T cells, allowing them to detect a target antigen, such as a cancer protein. When the target is detected, the T cell becomes activated and destroys the target cell. In recent years, scientists have begun using a similar strategy to create CAR natural killer (NK) cells. One potential advantage of CAR NK cells over CAR T cells is that they could be used to kill diseased T cells. Using CAR T cells to treat T cell diseases often doesn't work well because T cells that are engineered to target T cell proteins may end up killing each other, in addition to the diseased T cells. That issue doesn't arise when using NK cells to target T cells.
However, manufacturing large quantities of CAR NK cells poses many of the same difficulties as generating CAR T cells. To simplify the process, researchers wanted to come up with a way to generate CAR NK cells in the patient's own body, without having to remove any cells. To generate these cells, the team designed lipid nanoparticles (LNPs) that can deliver an mRNA payload. These strands of mRNA encode a CAR that can be targeted to specific cell types. For example, they could deliver a CAR that targets CD19, a protein found on B cells, or CD3, a protein found on autoreactive T cells. The particles are coated with antibody fragments that bind to receptors found on the surface of NK cells, to ensure they reach the correct targets.
After these particles were infused into mice, the researchers found that they could successfully reprogram about 80% of the targeted NK cells. The researchers then tested the particles' potential to treat cancer and autoimmune hepatitis, which is caused by autoreactive T cells. In a mouse model of an aggressive form of melanoma, three of the five mice that received LNPs that reprogrammed their NK cells to target the cancer cells went into complete remission. The researchers also saw significant tumor destruction when they used the LNPs to treat T cell lymphoma in a humanized mouse model. In these mice, tumors were eradicated after five injections of the reprogramming LNPs. This result was similar to what the researchers saw when they treated mice with CAR NK cells that were generated using the conventional approach.
Lastly, the researchers demonstrated that their LNPs could generate CAR NK cells that target autoreactive T cells. For this application, they studied mice with autoimmune hepatitis, in which T cells attack hepatocytes in the liver. They found that in the treated mice, the autoreactive T cells were destroyed, and liver damage healed. These effects were seen after just one injection of the LNPs.
Targeted lipid nanoparticles (LNPs) offer a nonviral approach for in vivo cell engineering but efficient programming of natural killer (NK) cells remains underexplored. Here we develop NK cell-targeted LNPs (NtLNPs) using engineered biparatopic NK cell ligands to drive receptor-specific uptake and mRNA delivery. Lead NtLNPs achieve up to ~80% NK cell transfection with minimal off-target effects in mice. Systemic delivery of chimeric antigen receptor (CAR) mRNA using NtLNPs generates CAR NK cells in vivo.
CD19-targeted CAR NKs completely deplete circulating B cells in healthy mice and CD3-targeted CAR NKs eliminate nearly all autoreactive T cells in an autoimmune hepatitis model, highlighting a potential advantage over CAR T therapies for T cell-driven disease. In solid tumors, NtLNPs targeting the inhibitory checkpoint NKG2A enhance antitumor efficacy by relieving Qa-1b-mediated immunosuppression. Lastly, we optimized NtLNPs for in vivo engineering of human CAR NK cells, enabling regression of two humanized hematologic malignancy models and establishing NtLNPs as a modular immunotherapy system.
View the full article at FightAging
