Bone Marrow Transplantation in Severe Combined Immunodeficiency (SCID) and Primary Immunodeficiencies: Current Approaches and Future Directions

Abstract Severe Combined Immunodeficiency (SCID) represents a group of rare, genetically heterogeneous disorders characterized by profound defects in cellular and humoral immunity. Bone marrow transplantation (BMT), also referred to as hematopoietic stem cell transplantation (HSCT), remains the cornerstone of curative therapy for SCID and several other primary immunodeficiencies (PIDs). This paper discusses the immunopathology of SCID, the clinical utility of BMT, donor selection strategies, outcomes based on conditioning regimens, and emerging gene-editing therapies. Despite high success rates in early-diagnosed infants, challenges remain in graft-versus-host disease (GVHD), delayed immune reconstitution, and access disparities. Future research continues to explore gene therapy, improved conditioning regimens, and expanded newborn screening.