Keichiro Mihara

Allogenic chimeric antigen receptor (CAR)-transduced natural killer (NK) cells have garnered attention due to their efficacy, safety, and potential off-the-shelf nature in patients with refractory and relapsed hematological malignancies. However, producing clinical doses of genetically modified NK cells remains challenging. The current methods for ex vivo expansion and genetic modification of primary NK cells depend on irradiated feeder cells, particularly K562 leukemic cells enforced to express stimulatory molecules. However, this method is limited by high costs, difficulties in scaling up, licensing restrictions, and the potential risk of contamination of cancerous cells in the final cell products. Therefore, we aimed to develop a novel system to generate highly activated primary human NK cells using a combination of multiple cytokines and agonistic antibodies that stimulate CD2 and Natural Killer cell p46-related protein. We cultured unsorted peripheral blood mononuclear cells obtained from healthy adults ex vivo and selectively expanded primary NK cells using stimulatory antibodies and a combination of interleukin (IL)-2, IL-12, IL-18, and IL-21. The activated NK cells were successfully transduced using the RD114-pseudotyped retrovirus vector at high efficiency. Anti-CD19-BB-ζ CAR transduced NK cells showed strong cytotoxicity against B-cell tumors. The remarkable ability of this culture system to expand and generate CAR-NK cells will pave the way for allogenic cancer immunotherapy.

Aggressive periodontitis causes rapid destruction of periodontal tissue. It occurs at a young age with familial clustering. We report on the first time on molecular and cellular basis of a Mendelian form of autosomal dominant aggressive periodontitis. Monoallelic mutations in the monocyte to macrophage differentiation-associated 2 (MMD2) gene, encoding MMD2, in two Japanese families with autosomal dominant aggressive periodontitis are identified. Mutations, c.347 C>T (p.A116V) and c.377 G>C (p.R126P) in MMD2, disturbed fMLP-induced activation of Ras/ERK signaling. Additionally, abnormalities in the proteins of Golgi apparatus, a crucial contributor to innate immune signaling pathways, were identified in patients' neutrophils. The knock-in and knockout mice exhibited alveolar bone loss by ligature-induced periodontitis, along with impaired fMLP-induced chemotaxis, as found in the patients with MMD2 mutation. Our studies revealed that monoallelic mutations in MMD2 underlie the impairment of neutrophil chemotaxis, which leads to the development of autosomal dominant aggressive periodontitis.

The clinical application of T cells engineered with chimeric antigen receptors (CARs) for solid tumors is challenging. A major reason for this involves tumor immune evasion mechanisms, including the high expression of immune checkpoint molecules, such as the programmed death 1 (PD‑1) ligands PD‑L1 and PD‑L2. The inducible expression of PD‑L1 in tumors has been observed after CAR‑T‑cell infusion, even in tumors natively not expressing PD‑L1. Furthermore, numerous types of pediatric cancer do not have suitable targets for CAR‑T‑cell therapy. Therefore, the present study aimed to develop novel CAR‑T cells that target PD‑L1 and PD‑L2, and to evaluate their efficacy against pediatric solid tumors. A novel CAR harboring the immunoglobulin V‑set domain of the human PD‑1 receptor as an antigen binding site (PD‑1 CAR‑T) was developed without using a single‑chain variable fragment. PD‑1 CAR‑T cells were successfully manufactured by adding an anti‑PD‑1 antibody, nivolumab, to the ex vivo expansion culture to prevent fratricide during the manufacturing process due to the inducible expression of PD‑L1 in activated human T cells. The expression of PD‑L1 (and PD‑L2 to a lesser extent) was revealed to be highly upregulated in various pediatric solid tumor cells, which displayed no or very low expression initially, on in vitro exposure to interferon‑γ and/or tumor necrosis factor‑α, which are cytokines secreted by tumor‑infiltrating T cells. Furthermore, PD‑1 CAR-T cells exhibited strong cytotoxic activity against pediatric solid tumor cells expressing PD‑L1 and PD‑L2. Conversely, the effect of PD‑1 CAR‑T cells was significantly attenuated against PD‑L1‑positive cells coexpressing CD80, suggesting that the toxicity of PD‑1 CAR‑T cells to normal immune cells, including antigen presenting cells, can be minimized. In conclusion, PD‑1 ligands are promising therapeutic targets for pediatric solid tumors. PD‑1 CAR‑T cells, either alone or in combination with CAR‑T cells with other targets, represent a potential treatment option for solid tumors.

In this study, we developed an oleoyl-siRNA conjugate in which oleic acid was conjugated at the 5'-end of the sense strand of the siRNA. Furthermore, we examined the effects of RNAi in a mouse model of pancreatic cancer with liver metastasis. The mouse model of pancreatic cancer with liver metastasis was developed by implanting Sui67Luc human pancreatic cancer cells into the portal veins of mice. Sui67Luc cells have high expression of tumor-related genes such as β-catenin, vascular endothelial growth factor, and programmed cell death ligand-1. All genes were knocked down using siRNA, among which siRNA targeting β-catenin exhibited the most suitable RNAi effect. Therefore, we investigated the in vitro RNAi effect of oleoyl-siRNA (Ole-siRNA) targeting the β-catenin gene in Sui67Luc cells and found that it was stronger than that of unmodified siRNA. For in vivo experiments, we investigated the biodistribution, antitumor effect, and change in life expectancy of mice upon systemic administration of Ole-siRNA complexed with Invivofectamine 3.0 (IVF). In terms of biodistribution, the Ole-siRNA/IVF complex likely accumulates in the liver of mice. The antitumor effect of Ole-siRNA in a portal vein infusion liver-metastatic Sui67Luc tumor mouse model was evaluated using an in vivo imaging system. Ole-siRNA had a significant antitumor effect compared with nonmodified siRNA. In addition, mice with metastatic liver Sui67Luc tumors treated with Ole-siRNA showed increased survival. These results suggest that Ole-siRNAs are useful novel RNAi molecules for treating pancreatic cancer and liver metastasis.