The effect of sequential multiple grafting of syngeneic newborn thymus on the immune functions and life expectancy of aging mice.

Enhancement of the immune functions and extension of the mean life expectancy were successfully performed in aging mice by sequential multiple grafting of syngeneic newborn thymus. In the first experiment, 2-month-old female C57BL/6 mice were grafted with either syngeneic newborn thymus or newborn spleen every 2 months, 5 or 6 times. A significant enhancement of T cell dependent immune functions were observed in the group sequentially grafted with newborn thymus, in comparison to that grafted with multiple sequential newborn spleen or with a single newborn thymus and that without a graft. In the second experiment, the same sequential grafting protocol was performed in middle aged mice at monthly interval for 4-5 consecutive months and the immune functions and survival rate were compared between the experimental and control groups. The immune functions were only partially rejuvenated, but an extension of the mean remaining life expectancy was observed in the experimental group (312 +/- 38 days) as compared with control (214 +/- 42 days), although maximal life-span was the same in both groups (1100 days).