Viral specific T-cells (VSTs) are an innovative way to treat severe viral infections in immune-compromised patients. They have generally been free from severe side effects, but we report here a unique event in a child with severe combined immune deficiency (SCID) who underwent bone marrow transplantation with T-cell depletion. One month after infusion of the VSTs, the patient rejected their marrow. The only T-cells remaining in the patient were from the VST product, suggesting that the VSTs may have caused the rejection. Caution should be used when giving this therapy very early after transplant in patients with SCID undergoing T-cell depleted bone marrow transplantation.