Decreased cloning of lymphocytes from elderly individuals.

Limiting-dilution cloning of human lymphocytes was used to study cloning and proliferation of lymphocytes in 10 young and 10 elderly individuals. The cloning efficiency for elderly individuals, 3.5%, was significantly lower than that for young individuals, 19.8%. Mixing experiments showed that this decrease was due to both a decrease in the frequency of the clone-forming cells and a decrease in the interacting ability of the lymphocytes. Lymphocytes from elderly individuals which did form clones, however, proliferated at the same rate as did those from young individuals.