Noboru Asada

Breakthrough Trichosporonosis in Patients with Hematologic Malignancies Receiving Micafungin

BACKGROUND Micafungin is a newly approved antifungal agent in the echinocandin class that is active against Candida species and Aspergillus species. However, this agent has limited activity against a number of fungi, including Trichosporon species. We describe 4 patients who developed disseminated trichosporonosis during the use of micafungin. No cases of trichosporonosis had been seen in the 2 years prior to January 2003, when micafungin became available in our hospital. METHODS We reviewed microbiological records of patients at Kameda General Hospital (Kamogawa City, Chiba, Japan) from 1 January 2002 to 31 July 2005, and identified 4 patients whose blood culture results were positive for Trichosporon species. RESULTS Since January 2003, four patients--3 with acute myelocytic leukemia and 1 with myelodysplastic syndrome--developed disseminated trichosporonosis while receiving treatment with micafungin with or without amphotericin B. The initial 2 isolates were identified as Trichosporon beigelii, and the later 2 isolates were identified as Trichosporon asahii. All 4 patients received micafungin, and 2 also received amphotericin B concomitantly. Minimal inhibitory concentrations of micafungin were >16 microg/mL for the 2 isolates available for susceptibility testing. One patient with hematologic recovery (neutrophils >500 cells/mm3) showed elimination of the fungus after receiving treatment with voriconazole. However, the 3 other patients without hematologic or immunological recovery died of disseminated infection. CONCLUSIONS The rarity of trichosporonosis in our hospital and its emergence after the introduction of micafungin therapy support the idea that micafungin may exert a significant, selective pressure toward resistant fungi, such as Trichosporon species. Therefore, care should be taken regarding the possibility of trichosporonosis in patients receiving micafungin with or without amphotericin B.

Use of Random Skin Biopsy for Diagnosis of Intravascular Large B-Cell Lymphoma

Intravascular lymphoma (IVL) is a rare type of extranodal lymphoma with an aggressive clinical course characterized by proliferation of large lymphoma cells within the lumina of the small vessels. Because of its varied clinical symptoms and the absence of lymphadenopathy, diagnosis of IVL is extremely difficult and requires histological confirmation. We report here 6 consecutive patients with IVL, admitted to Kameda General Hospital, Kamogawa-shi, Japan, from June 7, 2006, to February 28, 2007, whose IVL was diagnosed by random skin biopsy of healthy-appearing skin. Three patients presented with progressive neurological deterioration and 2 others with hypoxemia with interstitial infiltration on chest radiography. One patient presented with confusion and severe hypoxia without apparent interstitial infiltration. Two patients showed localized skin involvement. Irrespective of the presence of skin lesions, almost all skin biopsy specimens showed obliteration of small vessels of subcutaneous fat tissues by lymphoma cells, allowing a prompt diagnosis of IVL. Early institution of rituximab-based chemotherapy induced favorable responses in all patients treated. Because diagnosis based on tissue other than skin is usually difficult in patients with suspected IVL, random skin biopsy should be considered even in patients with no evident skin lesions.

Matrix-embedded osteocytes regulate mobilization of hematopoietic stem/progenitor cells.

The bone marrow (BM) niche comprises multiple cell types that regulate hematopoietic stem/progenitor cell (HSPC) migration out of the niche and into the circulation. Here, we demonstrate that osteocytes, the major cellular component of mature bone, are regulators of HSPC egress. Granulocyte colony-stimulating factor (G-CSF), used clinically to mobilize HSPCs, induces changes in the morphology and gene expression of the osteocytic network that precedes changes in osteoblasts. This rapid response is likely under control of the sympathetic nervous system, since osteocytes express the β2-adrenergic receptor and surgical sympathectomy prevents it. Mice with targeted ablation of osteocytes or a disrupted osteocyte network have comparable numbers of HSPCs in the BM but fail to mobilize HSPCs in response to G-CSF. Taken together, these results indicate that the BM/bone niche interface is critically controlled from inside of the bone matrix and establish an important physiological role for skeletal tissues in hematopoietic function.

Osteocytes Regulate Primary Lymphoid Organs and Fat Metabolism

Osteocytes act as mechanosensors to control local bone volume. However, their roles in the homeostasis of remote organs are largely unknown. We show that ablation of osteocytes in mice (osteocyte-less [OL] mice) leads to severe lymphopenia, due to lack of lymphoid-supporting stroma in both the bone marrow and thymus, and complete loss of white adipose tissues. These effects were reversed when osteocytes were replenished within the bone. In contrast, neither in vivo supply of T cell progenitors and humoral factors via shared circulation with a normal parabiotic partner nor ablation of specific hypothalamic nuclei rescued thymic atrophy and fat loss in OL mice. Furthermore, ablation of the hypothalamus in OL mice led to hepatic steatosis, which was rescued by parabiosis with normal mice. Our results define a role for osteocytes as critical regulators of lymphopoiesis and fat metabolism and suggest that bone acts as a central regulator of multiple organs.

Successful Treatment of Breakthrough Trichosporon asahii Fungemia with Voriconazole in a Patient with Acute Myeloid Leukemia

We describe a 55-year-old man with acute myelogenous leukemia who developed breakthrough Trichosporon asahii fungemia during 5 days of micafungin treatment. Although the patients clinical condition improved considerably after the start of voriconazole treatment, blood culture results remained positive for T. asahii for 3 days, and fever persisted for 7 days thereafter. The patient achieved complete hematological remission, and he received successful consolidation chemotherapy without developing Trichosporon infection with the prophylactic use of voriconazole therapy. This case report illustrates that voriconazole may be useful in the treatment of disseminated T. asahii infection in neutropenic patients.

Role for vitamin D receptor in the neuronal control of the hematopoietic stem cell niche

Hematopoietic stem/progenitor cells (HSPCs) are released from the bone marrow to the circulation by the cytokine, granulocyte colony-stimulating factor, via sympathetic nervous system (SNS)-mediated osteoblast suppression. Because the orientation of HSPCs in their osteoblastic niche is reported to be guided by [Ca(2+)], we speculated on a cooperation between the calcium-regulating hormones and SNS in the regulation of HSPC trafficking. Here, we present the severe impairment of granulocyte colony-stimulating factor-induced osteoblast suppression and subsequent HSPC mobilization in vitamin D receptor (VDR)-deficient mice. In osteoblasts, functional VDR possessing, at least in part, a transcriptional activity, was specifically induced by β2-adrenergic receptor (AR) agonists. While β2-AR agonists transiently increased mRNA expression of Vdr and its downstream gene, Rankl, 1α,25-dihydroxyvitamin-D(3) sustained the β2-AR-induced Rankl expression at high level by stabilizing VDR protein. These data suggest that VDR is essential for durable β2-AR signaling in the stem cell niche. Our study demonstrates not only a novel function of VDR as a critical modulator of HSPC trafficking, but also the presence of a SNS-mediated, bone-remodeling mechanism through VDR. VDR contributes to brain-bone-blood integration in an unanticipated way distinct from other classical calcium-regulating hormones.

A clinicopathological study of 13 cases of intravascular lymphoma: experience in a single institution over a 9-yr period.

Intravascular lymphoma (IVL) is a rare type of extranodal lymphoma in which the lymphoma cells proliferate exclusively in lumina of small vessels. Here, we report a clinicopathological study of 13 cases IVL diagnosed at our institution between March 1999 and July 2007, and evaluated the clinical characteristics, usefulness of random skin biopsy and response to chemotherapy containing rituximab. Three of 13 patients were diagnosed at autopsy. The most common clinical features were unexplained fever, neurological deterioration, respiratory failure, and poor performance status. Thrombocytopenia, high serum lactate dehydrogenase and soluble interleukin2 receptor levels were the most common laboratory abnormalities. Adrenal tumor was detected in four cases and pituitary involvement was seen in all three autopsied cases and in two surviving patient by brain magnetic resonance imaging. Bone marrow invasion was seen in all 13 cases by bone marrow smear, and it was subtle in trephine biopsy. Immunohistochemical analyses revealed that CD5 was positive in one‐third of the cases. Most of the cases were positive for MUM1/IRF, Bcl‐2 and negative for CD10 and BCL‐6 indicating the postgerminal center cell origin of this peculiar type of lymphoma. On random skin biopsy, the most recent seven patients were diagnosed promptly and chemotherapy containing rituximab was successfully administered. Patients with IVL exhibit the characteristic clinical and immunophenotypic features cited above and the use of random skin biopsy facilitates prompt diagnosis. Early commencement of chemotherapy containing rituximab appears promising for this peculiar lymphoma. As the recent seven patients were diagnosed by random skin biopsy over the past 13 months, the incidence of IVL is thought to be much higher than generally accepted.

Regulation of hematopoiesis in endosteal microenvironments

After birth, the hematopoietic system develops along with bone formation in mammals. Osteolineage cells are derived from mesenchymal progenitor cells, and differentiate into several types of bone-forming cells. Of the various types of cell constituents in bone marrow, osteolineage cells have been shown to play important roles in hematopoiesis. Early studies have identified osteoblasts as a hematopoietic stem cell niche component. Since that time, the role of endosteal microenvironment as a critical regulator of hematopoietic stem/progenitor cell (HSC/HPC) behavior has been appreciated particularly under stress conditions, such as cytokine-induced HSC/HPC mobilization, homing/engraftment after bone marrow transplantation, and disease models of leukemia/myelodysplasia. Recent studies revealed that the most differentiated osteolineage cells, i.e., osteocytes, play important roles in the regulation of hematopoiesis. In this review, we provide an overview of recent advances in knowledge of regulatory hematopoietic mechanisms in the endosteal area.

Complexity of bone marrow hematopoietic stem cell niche

Hematopoietic stem cells (HSCs) that produce a variety of hematopoietic lineage cells throughout the life reside in specialized microenvironment called “niche” in the bone marrow (BM) where they are tightly regulated. With the recent advances in experimental technologies enabling the selective deletion of molecules, various types of cells in the BM have been proposed to contribute to HSC niche activity. Among these are stromal cells closely associated with the vasculature. In this review, we provide an overview of recent advances in HSC niche research, and focus on the studies describing the functional roles of perivascular cells for HSC maintenance and mobilization. Not only for physiologic state, we also discuss the recent evidences suggesting the importance of microenvironment for emergence of malignant hematopoietic diseases.

The hematopoietic stem cell niche: From embryo to adult

ABSTRACT Hematopoietic stem cells (HSCs) develop in discrete anatomical niches, migrating during embryogenesis from the aorta-gonad-mesonephros (AGM) region to the fetal liver, and finally to the bone marrow, where most HSCs reside throughout adult life. These niches provide supportive microenvironments that specify, expand and maintain HSCs. Understanding the constituents and molecular regulation of HSC niches is of considerable importance as it could shed new light on the mechanistic principles of HSC emergence and maintenance, and provide novel strategies for regenerative medicine. However, controversy exists concerning the cellular complexity of the bone marrow niche, and our understanding of the different HSC niches during development remains limited. In this Review, we summarize and discuss what is known about the heterogeneity of the HSC niches at distinct stages of their ontogeny, from the embryo to the adult bone marrow, drawing predominantly on data from mouse studies. Summary: This Review gives an overview of what is known regarding niche heterogeneity at distinct stages of HSC ontogeny, from embryonic life to the adult bone marrow.