SCID refers to a group of genetic diseases which are characterized by lack of both humoral immunity (B-cell) and cell mediated immunity (T-cell) (Ochs, Smith, & Puck, 2007). This makes individuals unable to fight infections. The transplantation is done using bone marrow from a donor whose human lymphocyte antigen (HLA) matches with that of the patient (Ochs, Smith, & Puck, 2007). The bone marrow from the donor usually contains hematopoietic cells which are normal and these would serve to correct the genetic immune system defect in the baby.
Unseparated stem cells from the bone marrow are given to the patient intravenously and they find their way into the bone marrow where they will grow and differentiate into T and B lymphocytes which are normal and functional. This helps to reconstitute the immune system where the baby will get full immunological capacity following normalization of both the humoral immune response and cell mediated immune response and thus the baby will be able to fight infections (Ochs, Smith, & Puck, 2007).
Sometimes the procedure is not successful and reactions occur which can lead to death. One of these is graft rejection which can lead to graft versus host disease (GVHD) as happened with the baby. In this case, it is the donor’s bone marrow that rejected the baby’s tissues. This is because the absence of functional T-lymphocytes in the baby means that the baby has no capacity to reject the donor’s bone marrow (Ochs, Smith, & Puck, 2007).
The donor’s bone marrow stem cells in the baby’s body differentiated and matured to form fully functional T-lymphocytes which were histoincompatible with the baby’s tissues resulting in attack of the baby’s tissues by the T-lymphocytes as they recognized the tissues as foreign (Ochs, Smith, & Puck, 2007). Normally, the targeted organs includes the skin, the liver, and the gastrointestinal tract and this results in symptoms such as skin rashes, severe diarrhea, vomiting, abdominal cramps, jaundice, hepatomegaly, and sometimes encephalopathy (Ochs, Smith, & Puck, 2007). This can be fatal resulting in death as is seen with the baby.