The role of donor age in naive T-cell recovery following allogeneic hematopoietic stem cell transplantation: the younger the better.

The high incidence of opportunistic infections after unrelated bone marrow transplantation has been reported. Delayed lymphocyte recovery may be associated with opportunistic infections. Immune reconstitution is influenced by recipient age and graft-vs-host disease. However, the role of donor age is largely unknown. When the effect of donor age on lymphocyte reconstitution post-transplant was examined in the murine allogeneic hematopoietic stem cell transplantation, the recovery of CD4+ naive T-cells in early post-transplant period was correlated inversely with donor age. Clinically, recipient mice transplanted from younger donors showed significantly higher survival rate and mitogenic responses than adult donors. Since CD4+ naive T-cells are mainly involved in primary immune responses to newly encountered antigens and play an important role in host defense, faster recovery of CD4+ naive T-cells in younger donors may contribute to the reduced mortality in early post-transplant period. Therefore, it is better to choose a younger donor if sufficient cell dose is available. In this review, age-related changes in hematopoiesis and lymphopoiesis as well as thymus-dependent and thymus-independent pathways following allogeneic hematopoietic stem cell transplantation are discussed.