Human immunodeficiency virus type 1 (HIV-1), the causative agent of AIDS, is a human-speci virus. Because HIV-1 cannot infect and cause disorders in other animals, it has been an arduous struggle to investigate the dynamics of HIV-1 infection in vivo. In order to understand and elucidate HIV-1 pathogenesis in vivo, we have established a human hematopoietic stem cell-transplanted "humanized" mouse model, which has the potential to maintain human hematopoiesis including human CD4-positive leukocytes under a physiological condition. In HIV-1-infected humanized mice, we reproduced HIV-1 pathogenesis including the gradual decline of peripheral CD4-positive T cells and immune activation.HIV-1 encodes four "accessory" genes, Vif, Vpu, Vpr, and Nef. It is known that these accessory genes are occasionally crucial for viral replication in in vitro cell culture system. However, since there were no adequate animal models for HIV-1 infection, the roles of these HIV-1 accessory genes in viral infection, replication, and pathogenesis in vivo remain unclear. By utilizing humanized mouse model and a series of mutated HIV-1, we have revealed that these viral accessory proteins potently promote viral replication by antagonizing/degrading anti-viral cellular proteins or exploiting a unique subset of human CD4-positive T cells.In this paper, I introduce the findings in HIV-1-infected humanized mouse model particularly focusing on the roles of HIV-1 accessory proteins in viral replication in vivo.

The lacrimal gland has an essential role in maintaining a homeostatic environment for a healthy ocular surface by tear secretion. Dry-eye disease, caused by lacrimal gland dysfunction, is a prevalent eye disease that results in corneal epithelial damage. Regenerative medicine, such as stem cell therapy, is expected to be a promising approach to restore the lacrimal gland function. Recently, a novel strategy has been reported of developing a fully functioning bioengineered organ by engraftment of a bioengineered organ germ generated via 3-dimensional cell manipulation using immature stem cells in vitro. We demonstrated an orthotopic transplantation of the bioengineered lacrimal gland germ into adult mice, in which the extra-orbital lacrimal gland has been removed. This mouse model mimics the corneal epithelial damage caused by lacrimal gland dysfunction. The bioengineered lacrimal gland germ and harderian gland germ both developed in vivo; they achieved physiological functionality, including tear secretion in response to nervous stimulation and ocular surface protection. This study provided novel evidence for the successful replacement of a fully functional lacrimal gland via engraftment of a bioengineered germ.

Under physiological and pathological conditions, complex cellular interplays take place in living animals. However, the conventional microscope using two-dimensional analysis is not sufficient for analyzing cell dynamics and functions in vivo. Thus, we improved the in vivo imaging technique based on multi-photon microscopy, and we then identified single platelet behaviors in the developing thrombus. We utilized XYZT high-speed imaging, which visualized platelet fate in vivo. This novel technique is anticipated to provide new insights into physiological and pathological conditions involving platelets.

Recent genome studies have identified recurrent somatic mutations in various myeloid malignancies, including acute myeloid leukemia, myelodysplastic syndrome and myeloproliferative neoplasm. These mutations frequently occur in epigenetic regulator genes, and functions of the proteins encoded by these genes in hematopoietic cells have been extensively analyzed, as reported recently. It is noteworthy that several epigenetic regulator genes, such as DNMT3A, TET2 and ASXL1, have also been identified in pre-leukemic stem cells. As targeting pre-leukemic stem cells would be a promising therapeutic approach, further investigations of epigenetic abnormalities in hematopoietic cells are anticipated to lead to the development of novel epigenetic therapies. In this review, we discuss recent genetic and functional data regarding epigenetic regulator genes and the future landscape of this new research field.

The functional cells or tissues derived from human induced pluripotent stem cells (iPSCs) make it possible to overcome with the insufficiency of cell sources for regenerative medicine, to investigate the precise mechanism of human organogenesis and disease, and to develop the new drugs. Especially for type 1 diabetes, making mature pancreatic beta cells from human iPSCs might have a good opportunity of regenerative medicine. However, so far in vitro, producing the fully maturated pancreatic beta cells is not achieved. Here we review the previous reports and discuss the possibility and validity of our strategy for making mature pancreatic beta cell with three-dimensional culture of pancreatic organoid derived from human iPSCs.

Persistent inflammation in rheumatoid arthritis (RA) can lead to the profound degradation and defect of articular cartilage. We can treat or induce the regeneration for the partial cartilage defect using the autologous chondrocytes implantation (ACI) or the matrix-assisted ACI. However, these regenerative methods cannot be applicable for the large size defect due to their limitation of the formable size or available cell numbers. The cell sheet technology or the intra-articular injection technique using the mesenchymal stem cells or the induced pluripotent stem cells (iPS cells) could be applied for the large size cartilage defect in RA patients in the future after additional studies.

In Japan, around 13 million adults have been estimated to suffer from chronic kidney disease (CKD), and more than 300 thousand patients with end-stage renal failure are receiving dialysis therapy, causing both medical and medicoeconomic problems. Regenerative medicine strategies using induced pluripotent stem (iPS) cells are among the candidate approaches to solve the problems. The mechanisms of kidney development and cell fate in the development of renal lineage cells have been elucidated using experimental animal models. Based on the knowledge of kidney development, intensive research has already been conducted to generate renal lineage cells from mouse embryonic stem (ES) cells, while few reports have been on studies using human iPS/ES cells. Recently, several research groups, including ours, have established methods to differentiate human iPS/ES cells into the intermediate mesoderm, an embryonic germ layer that gives rise to the kidney, and embryonic renal progenitors. Some reports also described the formation of three-dimensional renal tissues, such as renal tubules and glomeruli. Continued efforts are required to elucidate the mechanisms of kidney development and generate renal cells or tissues from human iPS cells, which could open up the new research avenues towards clinical application and practical use to overcome problems associated with kidney disease, such as human embryology, cell therapy, toxicology, drug discovery, and disease modeling.

The mission of our department is to contribute to diagnostic improvement in medicine in order to promote better outcomes. We have clinical expertise in internal medicine including primary care medicine, hematology, allergy, rheumatology, and nephrology. We also have expertise in clinical laboratory medicine and hospital infection control. Specific areas of academic interest include immune-mediated hematological diseases, allergic diseases, autoimmune diseases, and chronic kidney disease. Immune recovery following hematopoietic stem cell transplantation and the immunopathophysiology of bone marrow failure syndrome have been our main topics of interest, and we have been applying our knowledge of T-cell receptor diversity to these areas in order to explore the mechanisms of immunodeficiency and autoimmunity in hematological disorders. We have found that the peripheral expansion of mature T cells in grafts plays an important role in immune reconstitution after stem cell transplantation in humans, and have also found altered T-cell repertoires in immune-mediated chronic acquired pure red cell aplasia. Thus, quantitative and qualitative analyses of immune receptors could be a promising method for assessing immunocompetence and exploring the pathophysiology of autoimmune diseases. Research and development of novel approaches in this field should be intensively conducted.