Cytomegalovirus (CMV) reactivation is a potential complication following allogeneic stem cell transplantation. Resistance and intolerance to the antiviral drugs used to treat the infection are common. In this video, physician-scientist Guenther Koehne, of Memorial Sloan Kettering’s Adult Bone Marrow Transplant Service and Medical Director of the Cytotherapy Laboratory, explains a therapy developed at the institution that successfully uses sensitized T cells to treat resistant CMV infection in adult recipients of allogeneic stem cell transplants. In this approach, the T cells are provided by the patient's stem cell donor and are stimulated with fragments of a CMV protein called CMV pp65. These T cells are processed in the laboratory and sensitized to specifically recognize and attack the CMV virus. Dr. Koehne and colleagues have shown that patients with resistant CMV infection who received these modified T cells were able to clear the infection in two to eight weeks. The treatment with donor-derived, CMV-specific T cells presents a promising new immunotherapeutic approach for this complication of allogeneic stem cell transplantation.