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.