Innovation Center of NanoMedicine (Center Director: Prof. Kazunori Kataoka; Location: Tonomachi, Kawasaki, Japan; Abbreviation: iCONM) and Institute of Science Tokyo (Science Tokyo) are pleased to announce that the results of a joint research project have been published online in ACS Nano (Impact Factor: 17.3 in 2025), a journal published by the American Chemical Society.
Journal: ACS Nano (online publication)
http://doi.org/10.1021/acsnano.6c08403
Title: 2-arm-PEG-oligocations transiently shield the liver sinusoids to mitigate off-target hepatic expression of mRNA lipid nanoparticles
Authors: Anjaneyulu Dirisala; Bhaskar Chatterjee; Nguyen Le; Kazuko Toh; Miki Matsui-Masai; Saed Abbasi; Xueying Liu; Theofilus Tockary; Nan Qiao; Junichi Ishikawa; Jumpei Norimatsu; Yuki Mochida; Shigeto Fukushima; Makoto Oba; Kazunori Kataoka; Satoshi Uchida
Corresponding Authors
Prof. Kazunori Kataoka, Center Director of iCONM
Prof. Satoshi Uchida, Professor of Institute of Science Tokyo
Principal Research Scientist of iCONM
With the commercialization of mRNA vaccines against COVID-19, research and development into the application of mRNA in vaccines and pharmaceuticals is accelerating. In particular, it is attracting attention not only in the field of vaccines for preventing infectious diseases but also in the field of cancer immunotherapy. Regarding infectious diseases, vaccine development is underway for pathogens other than the novel coronavirus; for example, a respiratory syncytial virus (RSV) vaccine has been approved in Japan and overseas, and vaccines for various other infectious diseases are advancing to clinical trials. In cancer immunotherapy, cancer vaccines (Term 1)—which involve administering mRNA encoding proteins (Term 2) specific to cancer cells to elicit an immune response that recognizes those proteins and attacks the cancer cells—are attracting attention. In addition, cytokine therapy (Term 3), which involves the direct administration of mRNA encoding molecules called cytokines that activate the immune system against cancer, is also showing promise. Clinical trials for both cancer vaccines and cytokine therapy are being actively conducted worldwide.
In these applications, mRNA is delivered encapsulated within lipid nanoparticles (Term 4). Lipid nanoparticles stabilize the mRNA within the body, protect it from degradative enzymes, and, once inside the target cells, accelerate the process leading to protein production. Furthermore, by inducing an inflammatory response, they enhance the efficacy of vaccines and immunotherapies. They also migrate easily to lymphoid tissues such as the spleen and lymph nodes, a characteristic that is crucial for achieving high efficacy with vaccines.
However, it is known that lipid nanoparticles accumulate most heavily in the liver among all organs. For example, when administered intravenously, they migrate to the liver via the bloodstream. Furthermore, when administered intramuscularly as a vaccine or directly into a tumor during cytokine therapy, they leak into the bloodstream and accumulate in the liver. This causes two main problems. First, unintended protein production from the mRNA in the liver can lead to side effects. Second, when targeting organs critical for vaccination—such as the spleen—the amount of mRNA reaching the target organ is reduced by the amount that accumulates in the liver.
In this study, we developed a method to inhibit the migration of these lipid nanoparticles into the liver. Since the walls of the hepatic sinusoids—the liver’s capillary network—serve as the entry point for lipid nanoparticles into the liver, we conceived the idea of coating these sinusoidal walls with polyethylene glycol (PEG), a biocompatible polymer. We used a proprietary coating agent consisting of positively charged peptides linked to two PEG chains. Since this coating agent adsorbs to the sinusoidal walls for only a few hours before being excreted, there is no concern that liver function will be impaired for an extended period. Furthermore, because it selectively coats the sinusoidal walls, it does not interfere with the delivery of lipid nanoparticles to other organs. In addition, this coating agent is already in clinical trials for the purpose of delivering oligonucleotide therapeutics (Term 5) to cancer sites, and its safety has been demonstrated.
First, we administered lipid nanoparticles intravenously to mice and observed the livers of live mice using a specialized microscope. When the coating agent was not administered, the lipid nanoparticles accumulated in the liver; however, we confirmed that pre-administration of the coating agent suppressed this accumulation in the liver. Next, when we evaluated the efficiency of protein expression from mRNA, we found that using the coating agent reduced protein expression in the liver by several dozen times. Conversely, protein expression in the spleen increased several-fold. This is thought to be because the lipid nanoparticles that were not captured by the liver accumulated in the spleen. These results demonstrate that the coating agent suppresses protein expression in the liver—which is undesirable for vaccines and immunotherapies—while enhancing protein expression in the spleen, which is crucial for vaccines.
In this study, we confirmed through animal experiments that the use of a coating agent can improve the efficacy and safety of three therapeutic areas—infectious disease vaccines, cancer vaccines (Term 1), and cancer cytokine therapy (Term 3)—all of which are currently undergoing active clinical development, as described below.
Infectious prevention vaccines: We examined a vaccine targeting the spike protein of the novel coronavirus as a model. This vaccine is administered intramuscularly; however, if it accumulates in the liver, the spike protein is produced within the liver. This can lead to the liver being attacked by immune cells, potentially causing hepatitis; in fact, cases of hepatitis following vaccination have been reported in humans. Conversely, it has also been suggested that the expression of the spike protein in the liver may induce immune tolerance (Term 6) to it, thereby weakening the vaccine’s efficacy. Through this experiment, we demonstrated that the coating agent can suppress protein expression from mRNA in the liver following intramuscular administration. Furthermore, regarding vaccine efficacy, we showed that the ability to induce antibody production against the spike protein was equivalent regardless of the presence or absence of the coating agent, and that the coating agent enhanced the induction of cellular immunity (Term 7) against the spike protein. In other words, the use of the coating agent improved both the safety and efficacy of the infectious disease mRNA vaccine.
Cancer Therapeutic Vaccines: In clinical trials of cancer therapy vaccines, intravenous administration of lipid nanoparticles targeting the spleen is often performed. In mouse experiments, administering the coating agent prior to the vaccine resulted in an enhanced induction of cellular immunity (Term 7), which is essential for cancer vaccines. This is believed to be due to improved protein expression efficiency in the spleen.
Cancer Cytokine Therapy: In treatments involving the direct administration of cytokine mRNA against cancer, a safety concern arises because lipid nanoparticles migrate to the liver, where cytokines are produced and distributed systemically. Regarding this issue, the study demonstrated that the use of a coating agent can suppress cytokine production in the liver and systemic distribution of cytokines without compromising the efficacy of cancer therapy.
As described above, this study developed a technology to avoid accumulation in the liver—a major practical challenge when using lipid nanoparticles in vaccines and immunotherapies. Furthermore, we demonstrated its utility in infectious disease vaccines, cancer vaccines, and cytokine therapy, areas where clinical development is actively underway. Additionally, the fact that the coating agent used here has a proven track record of safety in clinical trials is a key factor for its practical application.
Term 1: Cancer Vaccine: A method of inducing an immune response that attacks cancer cells by administering a vaccine composed of molecules selectively expressed by cancer cells. It is used primarily for treatment, not for cancer prevention.
Term 2: mRNA encoding protein: mRNA functions as a blueprint for proteins; the amino acid sequence of the protein to be synthesized is determined by the sequence of nucleotides in the mRNA. The process of designing the nucleotide sequence to produce the amino acid sequence of a specific protein with the desired pharmacological effect is referred to as “encoding for that protein.”
Term 3: Cytokine Therapy: A method of inducing an immune response that attacks cancer cells by using substances called cytokines to activate the immune system.
Term 4: Lipid nanoparticles: Small capsules made of lipids that encapsulate mRNA, measuring approximately 100 nanometers (one ten-thousandth of a millimeter). They play various roles, such as protecting mRNA from degradation, delivering it to immune tissues, and activating the immune response. They are also used in commercially available COVID-19 vaccines.
Term 5: Oligonucleotide therapeutics: Short strands of DNA or RNA designed to suppress the expression of a target gene. The coating agent used in this study is already being used in clinical trials with the aim of efficiently delivering nucleic acid therapeutics to cancer cells.
Term 6: Immune tolerance: A mechanism that suppresses the immune response to the body’s own proteins. The liver is also known as an organ that induces immune tolerance, and the immune response to proteins expressed in the liver may be suppressed.
Term 7: Cell-mediated immunity: A mechanism in which immune cells themselves attack cells infected with pathogens or cancer cells.
ACS Nano
Experimental study
Animals
2-arm-PEG-oligocations transiently shield the liver sinusoids to mitigate off-target hepatic expression of mRNA lipid nanoparticles
18-Aug-2026
The authors declare the following competing financial interest(s): D.A, M.M.M., K.K., and S.U. have filed a patent application related to this study, and NANO MRNA Co., Ltd. holds a right to the patent. M.M.M. is an employee of NANO MRNA Co., Ltd.