A 71-year-old woman became aware of a 25-mm mass in her right breast as identified by her previous doctor. Needle biopsy findings suggested malignant lymphoma, and she was referred to our hospital for further evaluation. She was diagnosed with diffuse large B-cell lymphoma (DLBCL) at our hospital. Positron emission tomography-computed tomography (PET-CT) revealed an elevated SUVmax (maximum standardized uptake value; 10.3), with the mass localized in the right breast, but magnetic resonance imaging findings revealed that the mass had shrunk to 10 mm. Needle biopsy was repeated in our hospital, and lymphoma cells were absent. Two months later, CT scan revealed complete disappearance of the mass, and, since then, the patient has been free of recurrence. Although there are reports of spontaneous remission of nonHodgkin’s lymphoma, it is rare in the case of high-grade B-cell lymphoma. The mechanism of spontaneous remission is unclear; however, advancing age, localized stage, activated B-cell (ABC) or nongerminal center B-cell (GCB) type, and a history of infection are the associated factors. The findings from this case suggest that DLBCL can be cured without therapeutic intervention; however, careful followup may be needed.

Follicular T-cell lymphoma (FTCL) is a rare disease, recently defined in the revised WHO classification Tumours of Haematopoietic and lymphoid tissues (4th edition). Although angioimmunoblastic T-cell lymphoma (AITL) and FTCL share similar T follicular helper (TFH) cell immunophenotypes and gene mutations, the clinical course of FTCL is not well characterized. Herein, we report the case of a 91-year-old woman with FTCL, who was successfully treated with corticosteroid. The patient, who had systemic lymphadenopathy and splenomegaly, was first diagnosed with necrotizing lymphadenitis. Re-biopsy was performed because of her persistent lymphadenopathy, which revealed FTCL. She was treated with corticosteroid because of her advanced age, poor performance, edema, and pleural effusion. After administering 100 mg prednisone, her condition improved and was discharged with prednisone tapering. Six-month positron emission tomography-computed tomography (PET-CT) scan showed complete metabolic remission. With a low dose of prednisone (6-10 mg), she remained disease-free for >3 years. Thus, these findings suggest that corticosteroid treatment is effective in some patients with peripheral T-cell lymphoma of TFH origin, including FTCL.

A 66-year-old man developed multiple erosions and pain in the lips and mouth, fever, and black stools. There was persistent bleeding from the lip erosions. When he was admitted to our hospital, his white blood cell count increased to 53,420/µl with 3% eosinophils, and hemoglobin decreased to 3.1 g/dl. Bone marrow biopsy revealed an elevated eosinophil level (24.0%) with markedly toxic granules. Gastrointestinal endoscopy revealed multiple ulcers and erosions in the pharynx, esophagus, stomach, and colon. Histopathological diagnosis indicated nonspecific inflammation with poor infiltration of eosinophils. Bone marrow FISH test was positive for 4q12 deletion (FIP1L1::PDGFRA), leading to the diagnosis of FIP1L1::PDGFRA-positive chronic eosinophilic leukemia. Following initiation of oral administration of imatinib 100 mg/day, the number of eosinophils decreased rapidly, and normalized 2 days after the start of imatinib. The mucosal lesions showed significant improvement and were diagnosed as leukemia-associated lesions. Based on the clinical course of our patient, multiple oral cavity and gastrointestinal ulcers could be the initial presentation in this leukemia.

A 78-year-old man with prostate squamous cell carcinoma recurrence in his pelvis was admitted to our hospital. Rectal obstruction led to creation of an artificial anus on the transverse colon. Then, docetaxel and radiation therapies were started. A week later, severe hematuria and melena occurred. Activated partial thromboplastin time (APTT) and prothrombin time (PT) were extremely prolonged. Cross-mixing test for APTT and PT revealed an inhibitor pattern, which was diagnosed as acquired factor V inhibitor. Fresh frozen plasma and vitamin K infusions were ineffective, but platelet transfusion successfully stopped the bleeding. Platelet factor V derived from megakaryocytes may affect local hemostasis. The patient received prednisolone (PSL), and the inhibitor disappeared on day 70 and was in remission. PSL could be stopped on day 100. Later, we demonstrated APTT and PT shortening of factor V deficient plasma by the supernatant of activated platelets with collagen.

A 34-year-old man with no medical history presented with fever 4 days after receiving the first dose of mRNA-1273 coronavirus disease 2019 (COVID-19) vaccine. He had no prior clinical evidence of severe acute respiratory syndrome coronavirus 2 infection and was negative for serial polymerase chain reaction testing. Ten days after vaccination, he was referred to our hospital because of no response to antibiotics and the emergence of neutropenia, thrombocytopenia, and liver dysfunction. Blood tests also showed elevated serum ferritin and plasma soluble interleukin-2 receptors. Serological and PCR testing excluded active infections of cytomegalovirus, Epstein-Barr virus, and hepatitis viruses. Blood culture yielded no growth. Computed tomography revealed mild hepatosplenomegaly and porta hepatis lymphadenopathy but no focus on infection. Bone marrow aspiration demonstrated hemophagocytosis but no infiltrating lymphoma cells. Immediately, 2-mg/kg intravenous methylprednisolone was commenced based on the presumptive diagnosis of hemophagocytic lymphohistiocytosis (HLH), leading to the rapid and durable improvement of his symptoms and laboratory data. Later, without other causes triggering hemophagocytosis, and with the close link between vaccination and disease onset, the final diagnosis of vaccination-induced secondary HLH was made. HLH after COVID-19 vaccination, though extremely rare, can occur regardless of the vaccine type. Therefore, clinicians should recognize and deal with this occasionally fatal adverse event.

We report a case of early asymptomatic acute promyelocytic leukemia (APL) with leukopenia as the only hematologic abnormality. A 55-year-old woman was referred to our hospital with leukopenia (white blood cell [WBC] count of 1,500/µl with 36% neutrophils), which was incidentally determined during an annual medical checkup. Two months before the presentation, her WBC was 3,400/µl with 60% neutrophils. A WBC count was 1,200/µl with 40% neutrophils. Immature myeloid cells were not observed. Her hemoglobin level and platelet count were normal. Moreover, no clinical or laboratory evidence was suggestive of disseminated intravascular coagulation or infection. The peripheral blood WT1 mRNA level was increased to 26,000 copies/µg RNA. The bone marrow aspirate smear revealed 40% myeloperoxidase-positive promyelocytes with occasional Auer rods and faggots; however, circulating leukemia cells were not revealed by cell morphology or flow cytometry analysis. Quantitative reverse-transcription polymerase chain reaction analysis revealed WT1 and PML-RARA fusion transcripts in both the peripheral blood and bone marrow samples. Thus, the determination of peripheral blood WT1 expression may be sufficiently sensitive for detecting a small number of circulating APL cells.

A 76-year-old woman with leukocytosis and thrombocytopenia was admitted to our hospital. A bone marrow examination showed a composition of 82.0% blasts, i.e., positive for TdT, CD10, CD19, CD34, and HLA-DR and negative for cyCD3, CD13, CD33, MPO, and cyµ. The reverse transcription-polymerase chain reaction analysis revealed a minor BCR-ABL1 fusion gene, leading to a diagnosis of acute lymphocytic leukemia (ALL) with a BCR-ABL1 fusion gene. G-band assay was negative for Philadelphia (Ph) chromosome and also revealed add (21) (q22. 1) and del (20) (q11. 2q13.3). Fluorescence in situ hybridization (FISH) assaying revealed a positive BCR-ABL1 fusion signal. Thus, this patient was diagnosed as Ph chromosome-negative and BCR-ABL1-positive fusion gene ALL, which suggested the presence of ALL with the “masked” Ph chromosome found in approximately 1% of chronic myeloid leukemia. Therefore, the FISH analysis may complement cytogenetic analysis when cytogenetic and molecular genetic findings are contradictory in ALL.

COVID-19 often contributes to thrombus formation in microvessels, resulting in damaged vital organs. In this study, we report a case of COVID-19 associated with acquired thrombotic thrombocytopenic purpura (TTP). A 44-year-old man with a history of systemic lupus erythematosus presented with COVID-19 and concomitant hemolytic anemia and a marked thrombocytopenia. The patient was diagnosed with acquired TTP because ADAMTS13 inhibitor was detected and ADAMTS13 activity below the sensitivity level. The patient developed agitated neuropsychiatric symptoms, such as aphasia, disorientation, and delirium, which improved after a plasma exchange, prednisolone, and rituximab administration. Only a few reports have revealed COVID-19 with TTP, and this is the first case in Japan. Although acquired TTP rarely develops, it is an important complication of COVID-19, and thus, it should be promptly diagnosed and treated as soon as possible.

A 75-year-old woman who was treated with methotrexate (MTX) for rheumatoid arthritis was admitted to our hospital because of fever and loss of appetite. Physical examination revealed exanthems in the upper limbs and systemic lymphadenopathy. Her blood test showed elevated levels of serum lactate dehydrogenase (LDH) and soluble interleukin-2 receptor (sIL-2R). Lymph node biopsy indicated atrophic follicles, interfollicular hyperplasia, and infiltration of macrophages phagocytosing nuclear debris and T-lymphocytes. This suggested lymphadenitis associated with viral infection. Human herpesvirus 7 (HHV-7) DNA was detected in the lymphoid tissue using polymerase chain reaction. The patient was successfully treated with MTX discontinuation and short-term administration of dexamethasone. Her symptoms improved, and LDH and sIL-2R levels were normalized. Human herpesvirus reactivates in patients with immunodeficiency on MTX administration. To the best of our knowledge, this is a valuable case of lymphadenitis considered to have been caused by HHV-7.

The CRISPR/Cas9 system was initially discovered as a means of acquired immune response in bacterial species and has been developed and applied to genome editing technology in mammalian cells. This system consists of three key components: crRNA, tracrRNA, and Cas9 protein. Once Cas9 is drawn to the target sequence, it creates DNA double-strand breaks, which then undergo repair via nonhomologous end joining or homology-directed repair. Thus, the CRISPR/Cas9 system enables us to knock out the gene of interest and insert the desired sequences for downstream analyses and clinical applications. Because of the simplicity of CRISPR/Cas9 technology, it has been widely adopted. For effective genome editing, several factors such as off-target effect and CRISPR/Cas9 delivery methods should be considered. Beyond gene knockout and nucleotide substitutions, CRISPR/Cas9 has been applied for various purposes, including more flexible nucleotide substitutions, transcriptional regulation, epigenetic modification, chromatin-chromatin interaction, and live-cell imaging using the nuclease domain deactivated mutant Cas9s, nCas9 and dCas9. This chapter discusses the expanding CRISPR/Cas9 technology—from basics to applications.

The impact of gene-editing technology has rapidly expanded into developmental engineering. Using this technology, gene targeting in mice can be performed within 2-3 months, which is a much shorter timespan than that required while using embryonic stem cell-based conventional methods, which require nearly two years. In addition, genome-editing technology omits several skillful laborious steps. This review describes the prominent merits of gene targeting using this recently established and still ongoing technology in the field of hematology. In addition, the experience of the authors is reviewed to identify and characterize genes involved in the loss of the long arm of chromosome 7 in myeloid malignancies and highlight the significance of establishing the mouse model of human diseases.

Genome editing has been attracting increasing attention as a new treatment for several refractory diseases since the CRISPR-Cas discovery has facilitated easy modification of target chromosomal DNA. The concept of treating refractory diseases by genome editing has been achieved in various animal models, and genome editing has been applied to human clinical trials for β-thalassemia, sickle cell disease, mucopolysaccharidosis, transthyretin amyloidosis, HIV infection, and CAR-T therapy. The genome editing technology targets the germline in industrial applications in animals and plants and is directed at the chromosomal DNA of the somatic cells in human therapeutic applications. Genome editing therapy for germline cells is currently forbidden due to ethical and safety concerns. Concerns regarding genome editing technology include safety (off-target effects) as well as technical aspects (low homologous recombination). Various technological innovations for genome editing are expected to expand its clinical application to various diseases in the future.

Therapeutic outcome in childhood acute lymphocytic leukemia has been dramatically improved by recent developments in treatment. However, disease relapse is still observed in approximately 10-15% of the patients. Moreover, adverse effects associated with intensified chemotherapy and hematopoietic stem cell transplantation remain important clinical issues for some survivors. Personalized medicine is valuable, under these circumstances, to reduce adverse effects and further improve the therapeutic outcome. Thus, identifying pharmacogenomic backgrounds associated with individual variation in drug sensitivity of leukemia cells and chemotherapy-induced adverse effects is important for precision medicine development. Recent advances in genome-editing technologies, such as CRISPR/Cas9 system, enable direct confirmation of associations between drug sensitivities and genetic backgrounds, such as polymorphisms and mutations, in the intrinsic genes of leukemia cells. Consequently, genome-editing systems are an ideal tool to develop in vitro and in vivo experimental models of drug sensitivity or resistance. The usefulness of the CRISPR/Cas9 system for the validation of pharmacogenomics in the selection of chemotherapeutic agents for acute lymphocytic leukemia has been discussed with specific examples in this review.

Recent advances in comprehensive genome analysis have contributed to the discovery of several leukemia-related genes; however, the role of mutated genes in the pathogenesis of leukemia remains unknown. Clustered regularly interspaced short palindromic repeats-associated nuclease 9 (CRISPR-Cas9) technology is a powerful tool for genome-wide editing in both coding and noncoding regions. CRISPR screening has enabled high-throughput validation of gene function in diverse tumor processes, including tumor growth and survival, synthetic lethal interactions, therapeutic resistance, and response to immunotherapy, and is actively used in leukemia research. Herein, we discuss recent advances in CRISPR screening in cancer research, focusing on leukemia, and outline application strategies and prospects for CRISPR screening.