The thymus: Its influence on recognition of “self major histocompatibility antigens” by T cells and consequences for reconstitution of immunodeficiency

Fetal tissue transplantation, bone marrow transplantation and prospective gene therapy in severe immunodeficiencies and enzyme deficiencies

The successful development of fetal tissue transplantation has resulted in therapeutical solutions for patients with a variety of diseases. Fetal liver transplants as well as bone marrow transplants, can completely cure patients with severe combined immunodeficiency disease. These transplants can also be applied to treat other types of immunodeficiency, hemopathies, and inborn errors of metabolism, in association with immunosuppressive therapy. Despite complete HLA incompatibility between transplanted stem cells and host cells, functional activities of donor-derived T-lymphocytes are not restricted. In severe forms of Di George syndrome, immunological reconstitution can be obtained by fetal thymus transplantation. It is expected that, in the near future, pure stem cell transplants and gene transplants will develop and will provide remarkable solutions for the therapy of a large number of diseases.

Immunodeficiency diseases and expression of HLA antigens

The role of HLA antigens in lymphocyte differentiation is strongly suggested by the existence of a recently identified immunodeficiency associated with, and probably resulting from, the lack of expression of HLA-A, B, and C antigens as well as beta2 microglobulin on various cells of hematopoietic origin. This "bare lymphocyte syndrome" has been described in a family where the transmission appeared to be autosomal recessive, and the responsible gene was not borne by the sixth chromosome. Another infant with a severe combined immunodeficiency disease has been treated with fetal liver and thymus transplants (FLTT). A persisting chimerism has been documented: T cells derived from the donor and B cells from the host. Despite complete HLA-A, B, and DR mismatch, T and B cells did cooperate resulting in significant antibody production, and defense against viral infection has been normal. Such an observation may suggest that "allogeneic restriction" of T-cell effector functions can be circumvented.