急性肝不全は致死率が高く、欧米では肝移植が選択されるが、本邦では圧倒的なドナー不足の問題を抱えており、内科的治療の進歩が喫緊の課題である。申請者は本疾患の病態に寄与する免疫細胞を同定するために、急性肝不全患者の肝臓および血液中の免疫細胞の種類を解析し、樹状細胞の一種である形質細胞様樹状細胞 (plasmacytoid dendritic cell; pDC)が顕著に減少し、本細胞の移植によりマウス急性肝不全の病態を改善することを見出した(JCI 2019)。本申請研究において、pDCを肝炎急性期の傷害肝により効率的に デリバリーさせる分子メカニズムを明らかにし、急性肝不全に対する自己骨髄細胞を用いた臨床応用への橋渡しを行うことを目的とした。
1. 急性肝不全患者臨床サンプルを用いた検討
健常人21例、急性肝炎患者15例を対象としたフローサイトメトリーを用いた解析の結果、急性AIH患者の末梢血中CD123+BDCA-2+ pDCの割合は健常人と比較して有意に減少していた(健常群0.55% vs. 急性AIH 0.11%)。AIHを成因とする急性肝不全症例の肝移植時摘出肝を用いた免疫組織染色の結果、健常コントロール群（消化管癌肝転移症例）で認められる門脈域を中心としたBDCA-2陽性pDCの数はAIH患者において有意に減少しており、末梢血と同様の結果であった。
2. 急性肝障害モデルマウスを用いたpDCの臓器特異的遊走機序
ConA投与後急性肝障害を発症したマウスのSiglec-H+PDCA-1+ pDCの数は末梢血、肝臓いずれにおいても著明に減少し、pDCが特異的に除去されたSiglec-H-DTRマウスにおいて同肝障害の増悪が認められた。一方、治療応用を想定し肝炎誘発後にFlt-3L添加骨髄細胞由来pDCを経静脈的にマウスに投与すると肝障害の軽減が認められた。さらに，小腸ホーミングレセプターとして知られるCCR9を欠損させたpDCを用いると、pDCの肝集積が高まり、肝障害の軽減作用が増強されることが明らかとなった。以上より、pDCを用いた急性肝障害の病態制御が有用である可能性が示唆された。
Acute liver failure has a high case fatality rate, and liver transplantation is selected in Europe and the United States, but in Japan, there is an overwhelming shortage of donors, therefore progress in medical treatment is an urgent issue. In order to identify the immune cells that contribute to the pathophysiology of this disease, we analyzed the types of immune cells in the liver and blood of patients with acute liver failure. We found that the number of plasmacytoid dendritic cells (pDCs) was significantly reduced during the development of acute liver injury in mice, and the transplantation of these cells improved the pathophysiology (JCI 2019). The purpose of this application study was to clarify the molecular mechanism by which pDC is efficiently delivered to the injured liver in the acute stage of hepatitis, and to bridge the clinical application using autologous bone marrow cells for acute liver failure.
1. Examination using clinical samples of patients with acute liver failure
As a result of analysis using flow cytometry in 21 healthy subjects and 15 acute hepatitis patients, the ratio of CD123 + BDCA-2 + pDC in the peripheral blood of acute AIH patients was significantly reduced compared to healthy subjects. (Healthy group 0.55% vs. Acute AIH 0.11%). The proportion of BDCA-2 positive pDC detected in the portal area observed in the healthy control group was significantly reduced in patients with AIH, which was consistent to that of peripheral blood.
2. Organ-specific migration mechanism of pDC using acute liver injury model mice
The number of Siglec-H + PDCA-1 + pDCs in mice that developed acute liver injury after ConA administration was markedly reduced in both peripheral blood and the liver. Note, exacerbation of the liver injury was observed in Siglec-H-DTR mice where pDCs were specifically removed. On the other hand, assuming therapeutic application, intravenous administration of oDCS derived from Flt-3L-added bone marrow cells to mice after induction of hepatitis was found to reduce the liver damage. Furthermore, it was clarified that the use of pDC deficient in CCR9, which is known as a small intestinal homing receptor, increases the hepatic accumulation of and further enhances the hepatoprotective effect. Based on these results, it was suggested that pDCs might be applicable for regulating acute liver injuries.