An HLA-matched singling is the ideal donor for allogeneic hematopoietic stem cell transplantation (HSCT), but such a donor is available for less than 30% of patients who require allogeneic HSCT. Therefore, HLA-matched unrelated HSCT, HLAmismatched related HSCT, and unrelated cord blood transplantation have been investigated. One-antigen mismatched related HSCT can be performed without T-cell depletion, but the outcome has been somewhat inferior to HSCT from an HLA-matched sibling or HSCT from an HLA-allele-matched unrelated donor. The use of in vivo T-cell depletion may improve its outcome. Two- or three-antigen mismatched related HSCT without ex vivo T-cell depletion has been investigated in Japan using a variety of strategies including in vivo T-cell depletion using anti-thymocyte globulin or alemtuzumab, and its safety has become close to that of HLA-matched HSCT. However, the appropriate choice of these strategies as well as the difference in HSCT outcome with cord blood transplantation has not been clarified.
Human herpesvirus (HHV)-6 reactivation is common (30-50%) after allogeneic hematopoietic cell transplantation (allo-HCT), and is linked to various clinical manifestations. HHV-6 has been recognized as an important pathogen that can cause encephalitis after allo-HCT. HHV-6 encephalitis typically develops around 2-6 weeks after allo-HCT, and is characterized by short-term memory loss, loss of consciousness, and seizures. Magnetic resonance imaging typically shows bilateral signal abnormalities in the limbic system. Umbilical cord blood transplantation is associated with increased risk of HHV-6 encephalitis. While antiviral therapy using ganciclovir or foscarnet is recommended as a first-line therapy for HHV-6 encephalitis, mortality rates attributable to this pathology remain high. Even among survivors, many patients display cognitive sequelae. Establishment of optimal strategies is urgently needed to prevent HHV-6 encephalitis. Besides encephalitis, associations between HHV-6 and various important post-transplant complications have been reported, including pneumonitis, gastroenterocolitis, hepatitis, bone marrow suppression/graft failure, graft-versus-host disease, and cytomegalovirus infection. Further investigations are needed to determine the roles of HHV-6 in these manifestations.
A 50-year-old woman was diagnosed as having multiple myeloma (MM) (IgM- κ type, urinary Bence-Jones Protein positive). She received bortezomib plus dexamethasone chemotherapy and achieved partial response. After autologous peripheral blood stem cells were collected, she underwent autologous peripheral blood stem cell transplantation by conditioning with high-dose melphalan chemotherapy. On the 10th day, her consciousness level worsened with the renal failure. Since she was administered acyclovir (ACV) for herpes simplex virus (HSV) prophylaxis, we suspected her consciousness disturbance to be ACV encephalopathy. ACV was discontinued and she underwent hemodialysis, resulting in improved consciousness and renal function. The diagnosis of ACV encephalopathy was based on very high ACV concentrations in the serum and cerebrospinal fluid when her consciousness level worsened. As hematopoietic stem cell transplantation is accompanied by severe immunodeficiency, ACV for HSV prophylaxis is required. The possibility of ACV encephalopathy should be considered in patients following stem cell transplantation who develop acute encephalopathy, especially in the cases of MM patients, who are prone to develop renal dysfunction.