Delayed immune reconstitution is 1 of the major contributions to the morbidity and mortality after haploidentical transplantation. Patients with a slow recovery of the innate and especially of the adaptive immune system are at high risk for severe and often lethal infections. The reason for delayed immune reconstitution after haploidentical transplantation include the T cell depletion (TCD) of the graft, the thymic dysfunction induced by pretransplant chemotherapies and by the conditioning regimens, and the occurrence of graft-versus-host disease (GVHD) and its treatment. The detailed analysis, understanding, and manipulation of the reconstitution of the cellular immune system will be of utmost importance to overcome the posttransplant immunodefcient status, and should result in a reduced risk of severe and overwhelming infections and hopefully also to a reduced risk of relapse through better immunological control of residual malignant cells.
