Normal function of transplanted marrow cell lines from aged mice.

Transplantation experiments indicated that losses with age in erythrocyte production were not intrinsically timed within marrow cell lines. In most cases marrow cell lines from old donors functioned as well as those from young donors after transplantation into either W/W-v anemic or lethally irradiated normal recipients. After normal marrow cells had been serially transplanted into successive W/W-v mice 5 times, both old and young cell lines began to fail; the old cell lines had produced erythrocytes normally for 77 to 84 mo. Transplanted old and young control marrow cell lines, identified by T6 chromosomes, saved the lives of lethally irradiated recipients; the oldest cell lines functioned normally for 54 mo. The hypothesis is suggested that senescence of an organism is caused by intrinsically timed functional declines in only a few vital cell types. In transplantation experiments to identify these cell types, four criteria--function, identification, control, and health--should be met. The marrow transplantation experiments led to and illustrate the hypothesis and the four criteria.