Immune reconstitution: an important component of a successful allogeneic transplantation

The recipients of allogeneic haematopoietic stem cell transplants are characterised by an immunodeficiency of varying severity and duration. Their immunocompromised state is due in part to: (1) an impaired recapitulation of lymphoid ontogeny, (2) a lack of sustained transfer of donor immunity, (3) the effects of graft versus host disease and its therapy, and (4) a reduction in thymic function. Recipients can have delays in the production of naive T lymphocytes following transplantation which result in defects in the production of new antigen specific T lymphocytes and an inability to produce antibodies, especially to carbohydrate antigens. T-cell proliferation as well as immunoglobulin production remains impaired usually until the second half of the first year post-transplant. Other factors that can influence immunological reconstitution include the donor–recipient relationship (histocompatible or matched unrelated donor), intervening infections and recipient age, among others.