People Who Live Past 110 Carry Unusually High Levels of Killer Immune Cells

People who live to age 110 or older, known as supercentenarians, carry unusually high levels of a specialized immune cell called CD4 cytotoxic T lymphocytes (CD4 CTLs), according to a study published Aug. 19 in the Cell Press journal Cell Reports. These cells have previously been shown to kill tumor cells in certain cancers and can rapidly multiply through a process called clonal expansion to help the body respond to infection.

Researchers led by Kosuke Hashimoto, an associate professor at the University of Osaka in Japan, examined blood samples from 28 adults divided into three age groups: 70-99, 100-109, and 110 and older. The median proportion of CD4 CTLs rose steadily across the groups, from 4% in the youngest group to 9.6% among those aged 100 to 109 and 17.6% among those 110 and older, suggesting the expansion of these cells may begin around age 100. The pattern was not limited to centenarians, however — one participant younger than 100 had the highest proportion of CD4 CTLs observed in the study.

Analyzing the participants' T cell receptors, the researchers found that clonal expansion plays a major role in the cells' abundance: the largest individual clone represented an average of 33.3% of all CD4 CTLs, and in one centenarian, a single clone made up 53.8%. When the researchers compared these receptor sequences with a public database, nearly three dozen matches came from people diagnosed with lung, breast or liver cancer, though none of the centenarians or supercentenarians in the study had been diagnosed with those cancers.

"Immune aging is not simply a process of decline," Hashimoto said. "The selective expansion of certain T cells suggests that, even in extreme old age, the immune system may continue to adapt to age-related challenges." The findings do not establish that high CD4 CTL levels protect against cancer or directly help people live longer; the study examined only T cells circulating in the blood, and researchers do not yet know what these cells are doing elsewhere in the body.