Background. Several animal models for xenogenic (xeno) graft versus host disease (GVHD) have been developed in immunodeficient mice, such as C.B-17-scid and nonobese diabetes (NOD)/severe combined immunodeficiency (SCID), by human peripheral blood mononuclear cell (hPBMC) transplantation. However, these models pose problems because they require sublethal total body irradiation of the mice and a large number of hPBMCs to induce GVHD, and the timing of onset of GVHD is also unstable. The aim of this study is to establish improved murine models of xeno-GVHD using novel immunodeficient NOD/Shi-scid IL2rγ^null (NOG) mice. Methods. In three strains of immunodeficient mice, NOG, BALB/cA-RAG2^null IL2rγ^null, and NOD/SCID mice, GVHD was induced by transplantation of hPBMCs with or without total body irradiation, and the GVHD symptoms in these strains were compared. Results. After intravenous transplantation of hPBMCs, NOG mice showed early onset of GVHD symptoms and a small number of hPBMCs (2.5×10⁶) was sufficient to induce GVHD when compared with BALB/cA-RAG2^null IL2rγ^null and NOD/SCID mice. In addition, total body irradiation was not always necessary in the present model. Conclusions. These results indicate that our model using the NOG mouse is a useful tool to investigate GVHD and to develop effective drugs for GVHD.

Peptide vaccination was developed for the prevention and therapy of acute and chronic infectious diseases and cancer. However, vaccine development is challenging, because the patient immune system requires the appropriate human leukocyte antigen (HLA) recognition with the peptide. Moreover, antigens sometimes induce a low response, even if the peptide is presented by antigen-presenting cells and T cells recognize it. This is because the patient immunity is dampened or restricted by environmental factors. Even if the immune system responds appropriately, newly-developed immune checkpoint inhibitors (ICIs), which are used to increase the immune response against cancer, make the immune environment more complex. The ICIs may activate T cells, although the ratio of responsive patients is not high. However, the vaccine may induce some immune adverse effects in the presence of ICIs. Therefore, a system is needed to predict such risks. Humanized mouse systems possessing human immune cells have been developed to examine human immunity in vivo. One of the systems which uses transplanted human peripheral blood mononuclear cells (PBMCs) may become a new diagnosis strategy. Various humanized mouse systems are being developed and will become good tools for the prediction of antibody response and immune adverse effects.

Primary human hepatocytes (PHHs) have been commonly used as the gold standard in many drug metabolism studies, regardless of having large inter-individual variation. These inter-individual variations in PHHs arise primarily from genetic polymorphisms, as well as from donor health conditions and storage conditions prior to cell processing. To equalize the effects of the latter two factors, PHHs were transplanted to quality-controlled mice providing human hepatocyte proliferation niches, and engrafted livers were generated. Cells that were harvested from engrafted livers, call this as experimental human hepatocytes (EHH; termed HepaSH cells), were stably and reproducibly produced from 1014 chimeric mice produced by using 17 different PHHs. Expression levels of acute phase reactant (APR) genes as indicators of a systemic reaction to the environmental/inflammatory insults of liver donors varied widely among PHHs. In contrast to PHHs, the expression of APR genes in HepaSH cells was found to converge within a narrower range than in donor PHHs. Further, large individual differences in the expression levels of drug metabolism-related genes (28 genes) observed in PHHs were greatly reduced among HepaSH cells produced in a unified in vivo environment, and none deviated from the range of gene expression levels in the PHHs. The HepaSH cells displayed a similar level of drug-metabolizing enzyme activity and gene expression as the average PHHs but retained their characteristics for drug-metabolizing enzyme gene polymorphisms. Furthermore, long-term 2D culture was possible and HBV infection was confirmed. These results suggest that the stably and reproducibly providable HepaSH cells with lesser inter-individual differences in drug-metabolizing properties, may have a potential to substitution for PHH as practical standardized human hepatocytes in drug discovery research.