During periods of immunosuppression, such as postallogeneic stem cell transplantation (SCT), patients are at significant risk for severe viral infections. Human adenovirus (HAdV) infection is a serious complication post-SCT, especially in children. Virus-specific T cells are essential for the clearance of HAdV, as antiviral chemotherapy has revealed limited success. We present feasibility data for a new treatment option using virus-specific donor T cells for adoptive transfer of immunity to patients with HAdV-infection/reactivation. Virus-specific donor T cells were isolated and infused into nine children with systemic HAdV infection after SCT. Isolation was based on gamma-interferon (IFN-gamma) secretion after short in vitro stimulation with viral antigen, resulting in a combination of CD4(+) and CD8(+) T cells. 1.2-50 x 10(3)/kg T cells were infused for adoptive transfer. Isolated cells showed high specificity and markedly reduced alloreactivity in vitro. Adoptive transfer of HAdV-specific immunity was successful in five of six evaluable patients, documented by a dose-independent and sustained in vivo expansion of HAdV-specific T cells, associated with a durable clearance/decrease of viral copies. T-cell infusion was well tolerated in all nine patients, except one case with graft-versus-host disease II of the skin. In conclusion, induction of a specific T-cell response through adoptive transfer was feasible and effective. When performed early in the course of infection, adoptive T-cell transfer may protect from HAdV-related complications.