Ultimately, the treatment of aging as a medical condition must include ways to either repair or replace damaged stem cell populations. This is a monumental task, given the sizable number of distinct types of stem cell in the body, but there is progress towards replacement via cell therapy in the case of a few of the better studied and characterized stem cell populations. Arguably the most advanced of this work is focused on replacement of hematopoietic stem cells, the stem cell population responsible for generating blood and immune cells. This is fortunate, as the decline of these stem cells has a profound detrimental effect on the immune system, and the age-related decline of immune function is an important contribution to the frailty of older individuals. Improving hematopoietic function in older individuals is one of the necessary steps that must be taken to reverse immunosenescence.

Transplantation of hematopoietic stem cells, in the form of bone marrow transplantation, has been an ongoing concern for decades, and there has consequently been a great deal of research into the biochemistry of these stem cells, as well as how to move towards therapies that deliver just hematopoietic stem cells rather than tissue. It is now possible to produce patient matched stem cells using reprogramming techniques, potentially eliminating many of the serious issues of rejection and autoimmunity that make hematopoietic stem cell transplant as presently practiced a procedure with significant risk. The major blocking challenge at the moment is how to ensure that enough of the transplanted cells engraft in the bone marrow niches and survive to produce a steady supply of blood and immune cells. This issue has yet to be robustly solved, despite a few promising demonstrations in animal models.

Hematopoietic Differentiation of Human Pluripotent Stem Cells: HOX and GATA Transcription Factors as Master Regulators