BK virus specific humoral and cell mediated immunity in allogeneic bone marrow transplant (BMT) recipients

BKV specific humoral and cell mediated immunity was examined weekly in 19 allogeneic BMT recipients and correlated with the occurrence of BKV shedding. Responses to staphylococcal antigen (SPL) and tetanus toxoid (TET) were measured as specificity controls. Responses and virus shedding were assayed weekly for up to 15 weeks after BMT. Fourteen of 19 patients enrolled in this study were immunized with TET on the day of transplant. Significant rises in TET specific IgG were observed in TET immunized, but not in unimmunized, subjects. Similarly, TET specific lymphoproliferative responses were observed only in TET immunized subjects when they emerged from aplasia 3 to 4 weeks later. In contrast, all subjects had positive lymphoproliferative responses to SPL, an antigen derived from a ubiquitous agent. All subjects were assayed weekly for the presence of BKV in the urine as detected by ELISA. By 15 weeks, 11 (58%) of these patients shed detectable quantities of BKV antigen at least once. Subjects who excreted BKV (BKV +) maintained BKV specific IgG at pretransplant levels, whereas levels steadily declined in those who did not (BKV‐) (p < 0.001). Lymphoproliferative responses to BKV, TET, and SPL antigens were not significantly different across time or between excretion groups. The temporal relationship of BKV shedding and the expression of BKV specific immunity was investigated by examining average responses measured in 5‐week intervals surrounding positive and negative antigen detection assays. Both BKV specific IgG and BKV specific lymphoproliferative responses were higher (1.8 fold, p < 0.005 and 2.5 fold, p = 0.06, respectively) surrounding positive detection assays. These findings indicate a strong association between BKV excretion and the development of indicators of virus specific immunity following BMT.