Bone marrow transplant

The immunosuppressive regimens used in bone marrow transplant (BMT) tend to be even more severe than those in solid organ transplant. Most BMT recipients are immunocompromised initially by their underlying disease that is further exacerbated by total body irradiation, lymphodepleting antibodies, steroids, and the anti-pro-liferative drugs associated with chemotherapy. Although the immunosuppressive protocol for allogeneic transplants is considerably more aggressive than autologous transplants, there is no apparent significant difference in the incidence of HHV-6 recurrence between these transplants nor sibling versus unrelated donor grafts in a pediatric population (Yoshikawa et al., 2002; Savolainen et al., 2005). HHV-6 reactivation is common in BMT transplant patients (Wang et al., 2002) and associated with skin rash and fever, the same symptoms often manifested at the time of primary infection in children. Idiotypic myelosuppression is characterized by delayed ne-utrophil and platelet engraftment and is highly associated with the reactivation of HHV-6 (Dobryski et al., 1993; Carrigan and Knox, 1994). Bethge et al. (1999) has reported two cases of BMT patients with HHV-6 PCR-positive spinal fluid who display neurological symptoms, including disorientation, sleepiness, and short-term memory loss and showed improvement following treatment with foscarnet. Appleton et al. (1995) conducted a study in BMT recipients to determine the potential role of HHV-6 in graft-versus-host disease (GVHD). They established a significant relationship between the detection of HHV-6 in biopsy tissue and the severity of GVHD suggesting a causal role for HHV-6 in exacerbation of GVHD rather than as a consequence of GVHD therapy.

However, despite the severity of immunosuppression in BMT patients, a number of researchers report that life-threatening complications with HHV-6 are rare (Cone et al., 1999; Savolainen et al., 2005). It is possible that the extended prophylactic use of ganciclovir for CMV in BMT recipients has had the unintended benefit of limiting HHV-6 disease in these patients.

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