Efforts to isolate genes involved in chromosomal translocations have led to the identification of several candidate oncogenes. One of the most frequent targets of gene mutations in human leukemia is AML1 (acute myeloid leukemia 1; also called runt-related transcription factor 1 : RUNX1), which encodes the DNA-binding subunit of the heterodimering transcriptional factor complex ; core-binding factor (CBF, or polyomavirus enhancer-binding protein 2 : PEBP2). This transcription complex plays an essential role in establishing early definitive hematopoietic development as documented through gene-targeting experiments. Many translocation-associated AML1 fusion gene products have been shown to function in leukemogenesis, at least in part, by dominantly interfering with this AML1's normal function by in vitro and in vivo experiments. Careful clinical studies have revealed that inactivating genomic mutations of this gene also contribute to some type of leukemia. Furthermore, many projects are in progress to define the entire pathway of the AML1/CBFB leukemia as a multistep carcinogenesis, using animal models or clinical mass studies, or both. In this review, a current understanding of the molecular basis for AML1 actions in normal and leukemic hematopoiesis is discussed.

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Advances in molecular biology revealed that most immunohematologic diseases are caused by single gene defects, and the genetic analyses for these diseases have been performed. However, genetic analysis is time-consuming and labor-intensive, and a rapid detection was desirable. We have established the flow cytometric detection of X-linked agammaglobulinemia, Wiskott-Aldrich syndrome/X-linked thrombocytopenia, and X-linked lymphoproliferative syndrome by using specific monoclonal antibodies. In the present study, I described a rapid clinical detection with flow cytometry and genetic analysis of these diseases. The flow cytometric analysis provided a sensitive and specific method for detection of the patients and their carriers ; however, further genetic analysis would be required for the precise diagnosis and the genetic counseling. A rapid clinical diagnosis with flow cytometry would be applicable for the detection of genetic immunohematologic diseases, including atypical cases, and the assay could be available in other genetic diseases.

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The treatment of primary immunodeficiencies (PID) includes curative therapy and supportive therapy. As the curative therapy, stem cell transplantations (SCT), including BMT, PBSCT, and CBSCT, have been performed for severe combined immunodeficiencies (SCID), Wiskott-Aldrich syndrome, X-linked hyper-IgM syndrome, and other primary immunodeficiency diseases. Gene therapy is another curative therapy. X-SCID has recently been successfully treated by transducing common gamma chain into the patients' CD34 positive hematopoietic cells by using retroviral vector. Intravenous immunoglobulin infusion is the effective supportive therapy for patients with hypogammaglobulinemia. Patients with T cell defects are susceptible for P. carinii, Cryptosporidium pavum, fungs, and virus, and prevention by using antimicrobes must be considered. Ex vivo activated T cell infusion is a new immunotherapy, and our preliminary results have revealed promising effects for the management of infections in PID patients. In summary, an early diagnosis with early prevention of infections and early SCT if applicable is recommended as a strategy for the treatment of PID.

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The matching of the major histocompatibility antigens (HLA) was thought to be the most important factor in the prognosis of stem cell transplantation (SCT). The resultant nationwide SCT data, which is accumulated and analyzed, demonstrates that the minor histocompatibility antigens (mHa) is no longer a minor factor, but a major one for GVHD after SCT. In fact, the incompatibilities of mHas are radically lower, approximately half, in relatives than in nonrelatives. The discovery of long-term feto-maternal microchimerism became an essential issue for the development of the concept of immunotolerance against non-inherited maternal antigens (NIMA). Mitochondria DNAs are highly polymorphic, and thus their proteins must be sources of mHas. Mother and child siblings have identical mitochondria and also NIMA tolerance. This is found to be because the donors who are HLA haploidentical mismatch maternal, and NIMA mismatched siblings are more compatible than paternal, viz. NIPA (non-inherited paternal antigens) mismatched siblings, and nonrelatives. Consequently, from the viewpoint of the contemporary histocompatibility concept, it is necessary to consider not only HLA and mHa, but also mitochondria, feto-maternal immunotolerance, and NIMA incompatibility in siblings.

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Allogeneic stem cell transplantation (allo-SCT) is now frequently performed for the treatment of hematological malignancies and aplastic anemia. However, graft-versus-host disease (GVHD) is still the major complication after allo-SCT producing immune deficiency, infection, organ damage, and occasionally a patient's death. The antigen-specific signal mediated by the T cell receptor (TCR) is essential for the activation of T cells; however, additional costimulatory signals are required for complete T cell activation. Therefore blocking strategies of costimulatory signals, CD28/B7, CD40/CD40L, et al., have been evaluated as targets of therapeutic intervention for GVHD after allo-SCT. It is very important to consider the way to induce a graft-versus-leukemia (tumor) effect without GVHD for successful clinical allo-SCT.

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The presence of multilineage hematopoietic stem cells in liver allograft produces a complex bidirectional cell communication in liver transplantation. Although direct contribution of HLA is low and a reduction of immunosuppression is easy after liver transplantation, a contribution of humoral immunity is also strongly suggested. Various factors are involved in the pathogenesis of liver allograft rejection, and many factors remain to be clarified in the pathogenesis of refractory and/or chronic rejection. Apart from one-way HLA matching, the factors contributing to the pathogenesis of fatal GVHD, the risk of which is unnegligible especially in living related liver transplantation, are largely unknown. There exists a wide window between HVG and GVHD in bidirectional cell traffics in liver transplantation, which should play important roles in the acquisition of immune tolerance.

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Because of the recent advances in the technology of organ/hematopoietic stem cell transplantation, opportunistic virus infections have become problematic. The management of cytomegalovirus, Epstein-Barr virus, varicella-zoster virus, and herpes simplex virus are very important because these viruses latently infect hosts and reactivate during immunosuppression. Since these viruses are detectable from healthy individuals, a quantitative analysis is necessary for the diagnosis of reactivation. Real-time quantitative PCR is a fast, convenient, reproducible method for monitoring viral loads. The assay has been shown to be useful for the management of virus infections in immunocompromised hosts. The other recent advance in the management of viral infections is monitoring virus-specific immunity by using a combination of intracellular interferon-γ detection and flow cytometry. With this method, the frequency of virus-specific CD8⁺ T cells can be rapidly determined.

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A 15-year-old boy had Burkitt lymphoma complicated by portal vein thrombosis (PVT) after unrelated-donor bone marrow transplantation (u-BMT). He presented with right cervical tumor, and pathological examination revealed Burkitt lymphoma. Although he was initially treated with irradiation and chemotherapy, his disease relapsed about 9 months after starting treatment. He received u-BMT after conditioning with total body irradiation, etoposide, and ifosfamide. On day 24, fibrinogen degradation products (FDP) and D-dimer in plasma were increased, so ultrasound examination was performed to screen for thrombus. A high-echogenic region was detected in the portal vein, and PVT was diagnosed by computed tomography (CT). At that time, plasma protein C and antithrombin III were not decreased, and thrombomodulin was slightly increased. He was treated with urokinase and heparin, and CT on day 55 showed no thrombus in the portal vein. The complication of PVT after stem cell transplantation (SCT) is rare, and an ultrasound examination is useful for diagnosing PVT. We speculate that the cause of PVT may be the existence of a hypercoagulable state and endothelial damage after SCT.

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We report here a case of paroxysmal nocturnal hemoglobinuria (PNH) that was thought to have developed at the age of 7. At his initial presentation, the patient showed only mild thrombocytopenia with no signs of hemolysis and was diagnosed as having idiopathic thrombocytopenic purpura. During the follow up, he showed pancytopenia, and his serum level of LDH started to increase at the age of 13. Both sugar water and Ham tests disclosed negative results. At the age of 15, macrohematuria became positive for the first time on an infection. He was finally diagnosed as having PNH based on the low expression of CD55 and CD59 on the surface membranes of his blood cells, determined by flow cytometry. Pediatric cases of PNH tend to lack evidence of hemolysis at their initial presentation, which makes it difficult to reach an accurate diagnosis of PNH. The membrane expressions of CD55 and CD59 should be examined at an early phase of the disease, when hemolysis or pancytopenia of unknown origin was seen.

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We report the case of a one-year-old boy with mediastinal non-Hodgkin lymphoma (NHL), whose serum neuron specific enolase (NSE) level was markedly elevated at his first clinic visit. His chest X-ray and chest CT findings showed a large mediastinal mass and his serum NSE level was elevated to 110 ng/ml on admission. He was diagnosed as having NHL (diffuse, lymphoblastic, T-cell type) by needle biopsy and categorized as stage III according to Murphy's classification. Immunohistochemical studies on NSE using polyclonal anti-NSE antibody showed positive staining of tumor tissue. He was treated with chemotherapy using CCLSG NHL 960 protocol and was successfully put into remission. We consider that serum NSE levels might serve as a useful tumor marker on NHL patients whose initial serum NSE levels are elevated. Further studies might be needed to prove our hypothesis.

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