HSC Transplants...young thymus helps

Osaka, Japan -

It is known that as humans grow up their thymus involutes, this is particularly noticable after puberty when various hormones cause en mass death and atrophy of thymic components. Now maybe its just me, but does it not seem odd that hematopoietic stem cell transplants which require the stem cell to differentiate into T cells, rely on the adult thymus? I mean, since the adult thymus is atrophied substantially, how in the world can one expect normal T cells to be developed after the hematopoietic stem cell transplant?

In a recent paper (Ryu et al. Transplantation of newborn thymus plus hematopoietic stem cells can rescue supralethally irradiated mice. Bone Marrow Transplant. 2008 Jan 7) the possibility of increasing efficacy of hematopoietic stem cell transplants by co-transplantation of a young thymus was assessed.

The investigators were trying to save the lives of supralethally irradiated mice. They noticed that the transplantation of early hematopoietic stem cells along with newborn thymus was effective, whereas other combinations (ie adult thymus) resulted in mortality. In the model of supralethal irradiation, the major cause of death is radiation induced damage to the small intestine. It was found that the thymic transplant allowed for proper T cell reconstituion which caused protection to the small intestine by virtue of IL-7 and KGF secretion.

Given the helpfulness of the young thymus in accelerating reconstitution, it may be interesting to use artificial thymus systems or components secreted by the thymus, such as thymosin to accelerate hematopoietic reconstitution after bone marrow transplants in adults.