Human herpesvirus-6 encephalopathy after hematopoietic stem cell transplantation and class I human leukocyte antigen

Human herpesvirus-6 (HHV-6) encephalopathy is a serious complication of allogeneic hematopoietic stem cell transplantation (allo-HSCT). Although reactivation of HHV-6 is often observed after allo-HSCT, encephalopathy only affects a few patients with HHV-6 reactivation. Human leukocyte antigen (HLA) class I is expressed by most somatic cells, and a relationship between some class I alleles and neurological diseases has been reported. The HHV-6 load at two, three, and four weeks after allo-HSCT was examined. HHV-6 encephalopathy was diagnosed from symptoms, results of cerebrospinal fluid examination, and magnetic resonance imaging findings. The relation between HHV-6 reactivation or encephalopathy and the HLA class I status of the recipients was investigated. In 130 patients, 147 allo-HSCT transplantation procedures were carried out. HHV-6 reactivation and encephalopathy occurred in 56 and nine procedures, respectively. HLA mismatch (p = 0.008) and unrelated donor (p = 0.001) were associated with HHV-6 reactivation, but not with HHV-6 encephalopathy. HHV-6 encephalopathy was more frequent in patients with HLA-B*40:06 (p = 0.027). In addition, HLA-A*26:01 and HLA-B*40:06 were found to be associated with each other (p = 0.089), while HLA-B*40:06 and HLA-C*08:01 showed a significant association (p < 0.001). The HLA class I alleles of recipients may be associated with the occurrence of HHV-6 encephalopathy after allo-HSCT.