Severe Combined Immunodeficiency (SCID)

This study is evaluating the safety and effectiveness of virus-specific cytotoxic T lymphocytes (vCTLs) for treating difficult-to-control viral infections caused by cytomegalovirus (CMV), adenovirus (ADV), Epstein-Barr virus (EBV), or BK virus in children, adolescents, and young adults with weakened immune systems. Eligible participants include recipients of hematopoietic stem cell transplantation, solid organ transplantation, and patients with primary immunodeficiency disorders. vCTLs are immune cells collected from a related donor and selected to recognize and fight specific viruses. The cells are manufactured using the CliniMACS® Cytokine Capture System and administered by intravenous infusion. Additional infusions may be given if viral infection persists. The study will assess the safety of vCTL therapy, including the risk of graft-versus-host disease (GVHD) and infusion-related reactions, as well as its ability to reduce viral infection, improve clinical outcomes, and support survival. Participants will be monitored for approximately 12 weeks after their final vCTL infusion. Participants will all receive vCTLs; there is no comparison group. Participants will: 1. Have donor-derived vCTLs manufactured for infusion using the CliniMACS Cytokine Capture System 2. Receive the vCTLs through an intravenous infusion 3. Be monitored for side effects and infusion reactions, viral levels through blood testing, clinical outcomes, including response to treatment, survival, and time without detectable virus