Explain why it is necessary to match at least some of the HLA allotypes between donor and recipient in a bone marrow transplant given to remedy SCID

Question

What will be an ideal response?

Answer 1

After the bone marrow transplant, the patient's entire immune system, including T cells and dendritic cells, will become reconstituted from hematopoietic stem cells in the donor bone marrow. Donor-derived T cells developing in the recipient's thymus will, however, be positively selected on the recipient's HLA molecules, and will only recognize antigen in that context. If the donor and recipient do not share any HLA molecules, these T cells will not be able to recognize antigen presented by the donor-derived dendritic cells or macrophages and will not be activated in response to pathogens. Because T-cell activation is central to all adaptive immune responses, the recipient will remain severely immunodeficient and unable to make adaptive immune responses to pathogens. In addition, HLA matching reduces the severity of graft-versus-host disease (GVHD), in which mature T cells in the donor graft respond to the allogeneic MHC class I and II molecules of the recipient and attack host tissue.